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Platnica SV-JME 12-2010_2.ai 1 30.11.2010 17:46:38Platnica SV-JME 12-2010_2.ai 1 30.11.2010 17:46:38

Strojniški vestnik – Journal of Mechanical Engineering (SV-JME)

© 2010 Strojniški vestnik - Journal of Mechanical Engineering. All rights reserved. SV-JME is indexed / abstracted in: SCI-Expanded, Compendex, Inspec, ProQuest-CSA, SCOPUS, TEMA. The list of the remaining bases, in which SV-JME is indexed, is available on the website. The journal is subsidized by Slovenian Book Agency.

Strojniški vestnik - Journal of Mechanical Engineering is also available on http://www.sv-jme.eu, where you access also to papers’ supplements, such as simulations, etc.

Editor in ChiefVincenc ButalaUniversity of Ljubljana Faculty of Mechanical Engineering, Slovenia

Co-EditorBorut BuchmeisterUniversity of MariborFaculty of Mechanical Engineering, Slovenia

Technical EditorPika ŠkrabaUniversity of Ljubljana Faculty of Mechanical Engineering, Slovenia

Editorial OfficeUniversity of Ljubljana (UL)Faculty of Mechanical EngineeringSV-JMEAškerčeva 6, SI-1000 Ljubljana, SloveniaPhone: 386-(0)1-4771 137Fax: 386-(0)1-2518 567E-mail: [email protected]://www.sv-jme.eu

Founders and PublishersUniversity of Ljubljana (UL)Faculty of Mechanical Engineering, Slovenia

University of Maribor (UM)Faculty of Mechanical Engineering, Slovenia

Association of Mechanical Engineers of Slovenia

Chamber of Commerce and Industry of SloveniaMetal Processing Industry Association

President of Publishing CouncilJože DuhovnikUL, Faculty of Mechanical Engineering, Slovenia

International Editorial BoardKoshi Adachi, Graduate School of Engineering,Tohoku University, JapanBikramjit Basu, Indian Institute of Technology, Kanpur, IndiaAnton Bergant, Litostroj Power, Slovenia Franci Čuš, UM, Faculty of Mech. Engineering, SloveniaNarendra B. Dahotre, University of Tennessee, Knoxville, USAMatija Fajdiga, UL, Faculty of Mech. Engineering, SloveniaImre Felde, Bay Zoltan Inst. for Mater. Sci. and Techn., HungaryJože Flašker, UM, Faculty of Mech. Engineering, SloveniaBernard Franković, Faculty of Engineering Rijeka, CroatiaJanez Grum, UL, Faculty of Mech. Engineering, SloveniaImre Horvath, Delft University of Technology, NetherlandsJulius Kaplunov, Brunel University, West London, UKMilan Kljajin, J.J. Strossmayer University of Osijek, CroatiaJanez Kopač, UL, Faculty of Mech. Engineering, SloveniaFranc Kosel, UL, Faculty of Mech. Engineering, SloveniaThomas Lübben, University of Bremen, GermanyJanez Možina, UL, Faculty of Mech. Engineering, SloveniaMiroslav Plančak, University of Novi Sad, SerbiaBrian Prasad, California Institute of Technology, Pasadena, USABernd Sauer, University of Kaiserlautern, GermanyBrane Širok, UL, Faculty of Mech. Engineering, SloveniaLeopold Škerget, UM, Faculty of Mech. Engineering, SloveniaGeorge E. Totten, Portland State University, USANikos C. Tsourveloudis, Technical University of Crete, GreeceToma Udiljak, University of Zagreb, CroatiaArkady Voloshin, Lehigh University, Bethlehem, USA

PrintLITTERA PICTA d.o.o., Barletova 4, 1215 Medvode, Slovenia

General informationStrojniški vestnik – The Journal of Mechanical Engineering is published in 11 issues per year (July and August is a double issue). Institutional prices include print & online access: institutional subscription price €100,00, general public subscription €25,00, student subscription €10,00, foreign subscription €100,00 per year. The price of a single issue is €5,00. Prices are exclusive of tax. Delivery is included in the price. The recipient is responsible for paying any import duties or taxes. Legal title passes to the customer on dispatch by our distributor. Single issues from current and recent volumes are available at the current single-issue price.To order the journal, please complete the form on our website. For submissions, subscriptions and all other information please visit: http://en.sv-jme.eu/ You can advertise on the inner and outer side of the back cover of the magazine.We would like to thank the reviewers who have taken part in the peer-review process.

Cover: Integrated measurement system: co-ordinate measuring machine and laser interferometer for precise geometry measurement and calibration & Precise measurement of sphere diameter with a universal measurement machine (left below).

Image courtesy: Laboratory for Production Measurement, Faculty of Mechanical Engineering, University of Maribor

ISSN 0039-2480

Aim and ScopeThe international journal publishes original and (mini)review articles covering the concepts of materials science, mechanics, kinematics, thermodynamics, energy and environment, mechatronics and robotics, fluid mechanics, tribology, cybernetics, industrial engineering and structural analysis. The journal follows new trends and progress proven practice in the mechanical engineering and also in the closely related sciences as are electrical, civil and process engineering, medicine, microbiology, ecology, agriculture, transport systems, aviation, and others, thus creating a unique forum for interdisciplinary or multidisciplinary dialogue.The international conferences selected papers are welcome for publishing as a special issue of SV-JME with invited co-editor(s).

no. 12year 2010

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Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12 Contents

Contents

Strojniški vestnik - Journal of Mechanical Engineering volume 56, (2010), number 12

Ljubljana, December 2010 ISSN 0039-2480

Published monthly

Editorial 789 Papers Tomaž Katrašnik: Fuel Economy of Hybrid Electric Heavy-Duty Vehicles 791Iztok Palčič, Borut Buchmeister, Andrej Polajnar: Analysis of Innovation Concepts in

Slovenian Manufacturing Companies 803Oğuz Yunus Sarıbıyık, Mustafa Özcanlı, Hasan Serin, Selahattin Serin, Kadir Aydın:

Biodiesel Production from Ricinus Communis Oil and Its Blends with Soybean Biodiesel 811

Antun Galović, Nenad Ferdelji, Saša Mudrinić: Entropy Generation and Exergy Efficiency in Adiabatic Mixing of Nitrogen and Oxygen Streams of Different Temperatures and Environmental Pressures 817

Dominik Kobold, Tomaž Pepelnjak, Gašper Gantar, Karl Kuzman: Analysis of Deformation Characteristics of Magnesium AZ80 Wrought Alloy under Hot Conditions 823

Janez Kušar, Tomaž Berlec, Ferdinand Žefran, Marko Starbek: Reduction of Machine Setup Time 833

Dragi Stamenković, Katarina Maksimović, Vera Nikolić-Stanojević, Stevan Maksimović, Slobodan Stupar, Ivana Vasović: Fatigue Life Estimation of Notched Structural Components 846

Instructions for Authors 853

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 789-790

789

Editorial

Anniversary: 55 Years of Strojniški vestnik – Journal of Mechanical Engineering

In the years 1954/55, an idea has emerged

in Slovenia to start publishing technical thought in the printed form of a journal, aiming to fill a substantial gap in the field of mechanical engineering among the technical periodicals of that time. Let us quote the editorial to the first issue of Strojniški vestnik, published in March 1955: »There is no doubt that the field of work of mechanical engineers and technicians belongs among the most versatile professions in the technical field«. Even during the time when the first issue of SV-JME was published, the lack of professional workforce was evident in a distinctly rapid industrial development. And what was expected of a mechanical engineer, who was supposed to be the most versatile of them all? It was proven day by day in the practice that the mechanical engineer must be that crucial member of each company, who is before anyone else promoting the implementation of modern technical methods for building machines and equipment, at the same time not ignoring even the simplest means to achieve productional and economical success, and endeavouring for the expansion of technical education as well as research. SV-JME has played a great role in this, as the technical culture of a nation ensures its competitiveness in the global developmental cycle.

Born on the Slovenian soil, the arrival of SV has filled a substantial gap in the professional (scientific) literature, considering it was the first autonomous publication in the field of mechanical engineering for engineers and technicians of the former country. Although its reach was limited to its homeland, the journal had to take into account from the very beginning the modest possibilities of a small, but intelligent and technically-oriented nation. The progress and the broad-mindedness of the very first issue of SV is shown by the fact that the content, written in Slovenian technical language, was also provided by the title and a short summary of each individual article in the Serbo-Croat, German, French and English language.

Although the first issue of SV-JME is now 55 years old, it is no less of a legend. Not only

was it the first issue, it also presented one of the high points of Slovenian science of mechanical engineering. In his article titled “Energy Value and Accounting”, Prof. Zoran Rant, one of the greatest Slovenian scientists in the field of thermodynamics, coined the term exergy. Among other things, he wrote: “The maximum work obtainable from a given quantity of energy is by all means a very important and remarkable property that deserves its own name. The word “energy” is derived from two Greek words: έν = inside and έργоν = work; meaning the “work” hidden “inside” a system. The name for the work obtainable “from” (in Greek: έχ or έξ) this system can therefore be composed as “e x e r g y”. The maximum work obtainable from energy shall be referred to as exergy E. Every energy contains a given exergy. Exergy is the part of energy having value. Energy without exergy is valueless.” The article is cited in numerous contemporary publications, and the first issue of SV-JME with this article was presented to many renowned institutions and professional associations all over the world, such as ASHRAE (The American Society of Heating, Refrigerating and Air-Conditioning Engineers).

Even today, the realisations from 55 years ago are not fully taken into consideration in energy accounting. The author of the article has presented a clear message: “The existing method for energy billing in combined plants on the basis of used enthalpies is fundamentally wrong. It has to be replaced with billing on the basis of used exergies, which is the only proper way. Consequentially, the price of electrical power will increase and the price of heat will fall, both in accordance with the value of these two energies.”

Upon the occasion of a double anniversary – 55 years of SV-JME and 50 years of independence of the Faculty of Mechanical Engineering at the University of Ljubljana – a book titled “The History of Mechanical Engineering and Technical Culture in Slovenia” was published, where I outlined what I believe are the key milestones of SV-JME as a history of technical thought in the co-existence of scientific spirit.


790

Fig. 1: Trend of citations (as of 22.11.2010) SV-JME was influential and of high

quality from the very beginning. Its path was marked by many changes. At the end of the 20th century, it was renamed to Strojniški vestnik – Journal of Mechanical Engineering (SV-JME) and it has earned the impact factor. The new editorial policy during the last years proves its success and proper orientation: SV-JME has become an important international journal in the field of mechanical engineering and its quality trend and publicity has experienced a modest growth during the last three years. According to the classification of Journal Citation Reports for 2009, the impact factor is 0.533, while the Web of Science also displays a trend of international influence (Fig. 1).

The success and quality of a journal is also a reflection of the excellence of its reviewers, so we are publishing a list of reviewers who participated with article reviews in 2010 in the first number of 57th volume and on the journal’s web site. We are grateful to each and every one of them for their cooperation and for their efforts. The editorial board of SV-JME would like to invite scientists and other distinguished top experts from all over the world to let us know if they are willing to do review work. We also ask you to submit to publication articles with possible breakthrough value, comparable to the article published in the first issue of SV-JME.

Allow me to conclude with a thought from Prof. Bojan Kraut, the first editor of SV-JME. In the editorial to the first issue, he wrote: “The magazine is emerging in a time that may not be favourable for such enterprises in some aspects. However, its tasks are well worth the effort. It shall serve anyone involved with mechanical engineering, and especially mechanical engineers and technicians, as a means to widen and deepen their knowledge in this profession and provide support in professional work.” Let me add: researching is like swimming against the current, when pausing for a moment one is carried back the next. SV-JME goes forward!

I wish you happy holidays and a lot of success in 2011!

Vincenc Butala

Fig. 2: Celebration upon the 55th anniversary of SV-JME

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 791-802 Paper received: 04.03.2010 UDC 629.4.038:621.182.3 Paper accepted: 31.08.2010

*Corr. Author's Address: University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva 6, SI-1000 Ljubljana, Slovenia, [email protected]

791

Fuel Economy of Hybrid Electric Heavy-Duty Vehicles

Tomaž Katrašnik* University of Ljubljana, Faculty of Mechanical Engineering, Slovenia

Fuel economy of parallel and series hybrid-electric heavy-duty vehicles was analyzed by a

combined analytical and simulation approach. The combined approach enables an evaluation of energy flows and energy losses on different energy paths and provides their impact on the fuel economy. The paper quantifies influences of different hybrid-electric vehicle (HEV) topologies, power ratios and characteristics of the components, and applied control strategies on the fuel economy of HEVs. Moreover, the impact of powertrain hybridization on the fuel economy is also analyzed for vehicles carrying different loads operating according to different drive cycles. It is discernable from the results that all of the above parameters significantly influence fuel economy of HEVs. Based on the innovative combined approach the paper reveals and analyzes mechanisms that lead to an optimized fuel economy of hybrid-electric heavy-duty vehicles. Valuable and generally valid guidelines for improving the fuel economy of HEVs are also given. ©2010 Journal of Mechanical Engineering. All rights reserved. Keywords: hybrid electric vehicles, fuel economy, simulation, analytical analysis

0 INTRODUCTION Improvement of the fuel economy is one

of the most important issues when developing new vehicle technologies. Among alternative powertrains being investigated, the HEVs consisting of an internal combustion engine (ICE) and an electric machine (EM) are considered to have the best potential in short to mid term future owing to their use of smaller battery pack and their similarities with conventional vehicles [1] and [2]. Hybrid electric heavy-duty vehicles have already proven to have a higher energy conversion efficiency compared to conventional internal combustion engine (ICE) powered vehicles on urban delivery and collection routes, and on bus routes. Although potential fuel economy improvements are much smaller, the introduction of hybrid electric heavy-duty vehicles for extra urban cycles seems promising.

Compared to conventional internal combustion engine vehicles (ICEVs), HEVs incorporate more electrical components featuring many available patterns of combining the power flows to meet load requirements of the vehicle. Dynamic interactions among various components and the multidisciplinary nature lead to complex energy flow patterns among various vehicle components and systems. Modeling and simulation are therefore indispensable for concept

evaluation, prototyping, and analysis of HEVs as discussed in [3].

To optimize energy conversion efficiency for particular operating conditions, i.e. drive cycles, it is necessary to have profound knowledge of the influences of the hybrid powertrain topology and of the energy flows through their constituting components on the energy conversion efficiency of the particular HEV. The focus of the paper is, therefore, to analyze influences of the powertrain topology, power ratios and characteristics of the components, drive cycles, control strategies and vehicle loads on the energy conversion efficiency of heavy-duty HEVs applying Li-Ion batteries. The paper reveals and quantifies mechanisms that lead to improved fuel economy of HEVs, and provides guidelines for optimizing fuel economy of HEVs. Energy conversion efficiency of HEVs and ICEVs is analyzed by a combined simulation [4] and analytical [3] approach that enables an analysis of energy flows and energy losses on different energy paths within the powertrain and an evaluation of their influences on the energy consumption of the powertrain.

1 ANALYTICAL FRAMEWORK

Analytical framework was fully derived in

[3], therefore only brief resume of equations needed for the presented analysis will be given.


Katrašnik, T. 792

Fig. 1. Parallel (a), series HEV topology (b) and ICEV topology with indicated energy paths (c)

The analytical framework considers all energy sources and energy sinks as well as all energy converters including their efficiencies. It thus enables an analysis of energy conversion phenomena considering complex interactions among various components and different control strategies. The advantage of this approach stems from the fact that it considers the complete HEV and therefore enables a direct and insightful evaluation of changes of HEV characteristics and operating conditions on the energy conversion efficiency of the HEV. Input data for the analytical analysis were obtained from the numerical simulations.

It is necessary to divide the HEV, i.e. system, into elements, i.e. subsystems, to investigate energy flows and energy losses and to optimize energy conversion efficiency of the HEV. The elements of the investigated parallel and series HEV topologies, and of the ICEV topology are shown in Fig. 1. A brief introduction of different HEV topologies is given in [3], whereas detailed information could be found in the literature, e.g. [5] and [6]. Energy is added through the fuel tank (F) denoted as “energy sources”. Energy is extracted through the load (L) and the brakes (BR), denoted as “energy sinks”. All other elements are denoted as “energy converters”. There exist unidirectional and bidirectional energy paths in the hybrid electric vehicle as indicated by the arrows in Fig. 1. It is assumed that energy can not be accumulated in the links.

Analysis of the fuel consumption is commonly performed for a specific test cycle. Therefore, all energy flows between the elements are integral values over the whole test cycle (tc). It is assumed that all losses that occur in the links between elements are included in the losses of the elements. The energy flow between arbitrary elements A and B is denoted WA-B and considers only the energy flow from A to B, whereas the energy flow from B to A is considered by WB-A. Efficiencies of the elements without energy accumulation capability with two bidirectional energy links are defined as the ratio between downstream and upstream energy flow. The efficiency index of such elements firstly indicates the element, and secondly, the direction of the energy flow, i.e. PR - propulsion and BR - braking. It is more complex to define efficiencies of the elements with more than two bidirectional energy links, i.e. TC and P, and elements with energy accumulation capability, i.e. ES; Fig. 1. Energy losses of these elements are split into inlet and outlet losses to make a clear derivation of equations possible. In order to perform this analysis, a point inside the element that represents the origin for evaluating the energy balance is defined; more details are given in [3]. The efficiency index of such elements thus indicates firstly, the element, secondly, losses associated with inflow or outflow of the energy, i.e. in or out, and thirdly, the energy path. Energy flow to the element with more than two links could be split into energy flow to two or more subsequent elements; for example energy flow ICE-TC1 in


Fuel Economy of Hybrid Electric Heavy-Duty Vehicles 793

parallel HEV (Fig. 1) could be split into energy flow ICE-TC1-TR (vehicle propulsion) and to energy flow ICE-TC1-EM1 (charging the EM by the ICE). These energy flows are denoted W'ICE-TC1,TR for the energy path ICE-TC1-TR and W'ICE-TC1,TR for the energy path ICE-TC1-EM1. It follows that W'ICE-TC1,TR=WICE-TC2-W'ICE-TC1,EM1, where »’« indicates that this is only a portion of the energy flow denoted by the first index directed to the element referred to by the second index.

Energy content of the electric storage devices at the end of the test cycle was equal to the energy content of the electric storage devices at the beginning of the test cycle (denoted non-depleting ES management), and plug-in option was not considered to enable a clear and demonstrative comparison of the fuel economy. A multiplication factor, i.e. F, defined as a ratio of the propulsion work over the test cycle for arbitrary vehicle topology to the propulsion work over the test cycle for ICEV is introduced. Therefore F=1 for ICEVs, whereas generally F≠1 for HEVs due to difference in vehicle parameters (vehicle mass, drag coefficient). Introduction of

multiplication factors enables comparison of the energy consumptions of different vehicle topologies, since it makes possible scaling of the propulsion work over the test cycle (Wtc,PR) of different HEV topologies to Wtc,PR of the ICEV, i.e. [Wtc,PR]P=FP[Wtc,PR]I and [Wtc,PR]S=FS[Wtc,PR]I. Index I denotes internal combustion engine vehicle, index S denotes the parallel HEV and index S denotes series HEV.

ICEVs are the most widespread type of vehicles and therefore they often represent the basis for the evaluation of the energy consumption of other vehicle topologies. The ratio of the fuel consumptions of parallel HEV and ICEV topology was derived in [3] where mf,tc is the mass of fuel consumed over the test cycle, efficiency, QLHV lower heating value of the fuel, indexes G and M denote operation of the EM in the generator and in the motor mode respectively, and other indexes denote elements in Fig. 1 according to the rules addressed above.

Similarly, fuel consumption ratio for series HEV and ICEV topology reads [3] in Eq. (2).

, , , ,

, , 1, , 1 1, , 1 , ,

, ,

, , , ,

1,

1

'

f tc ICE eff TR PR W PRP I

f tc ICE eff TC in ICE TC TC out TC TR TR PR W PRI P REFW

P P TR ICE TR PR W PRTcPrR If tc LHV ICE eff TR PR W PR I

TR TC ICE

m

m

F F Wm Q

W

1, , 1 1, , 1 1, , 1 1, , 1 , ,

, , 1, , ,

, , 1, , 1 1, , 1

, , , ,

'

TC in TR TC TC out TC ICE TC in ICE TC TC out TC TR TR PR W PR P MIce

tc BR BR W BR TR TC ICE W BR TR BR PW BR TR BR TC in TR TC TC out TC

f tc LHV ICE eff TR PR W PR I

W W W

m Q

1 1, , , 1

, , , , , , , , , , 1 1, 1, , 1 1 1, , 1 , ,

1, 1

1, , 1

, , , ,

'

EM EM G P in EM P

P out P ES ES in P ES ES out ES P P in ES P P out P EM EM M TC in EM TC TC out TC TR TR PR W PR P RB

ICE TC EM PTC in ICE TC


W

m Q

1, , 1 1 1, , , 1 , ,

, , , , , , , , 1 1, 1, , 1 1 1, , 1 , ,

1

.

TC out TC EM EM G P in EM P P out P ES

ES in P ES ES out ES P P in ES P P out P EM EM M TC in EM TC TC out TC TR TR PR W PRP CEsIce

(1)


Katrašnik, T. 794

, , , ,

, , 2, , 2 2, , 2 2 2, , , 2 , , 1 1, , ,

, ,

Pr, ,

f tc ICE eff TR PR W PRS I

f tc ICE eff TC in ICE TC TC out TC EM EM G P in EM P P out P EM EM M TR PR W PRI S REFW

S TR ICE TR PR W PR IS Tc R

f tc LHV ICE eff

m

m

F WF

m Q

, ,

, ,

, , 1, , , 1 , , , , , ,

, , , ,

, , , , 1 1, , ,

TR PR W PR I MIce

tc BR BR W BR SW BR TR BR EM G P in EM P P out P ES ES in P ES ES out ES P


P in ES P P out P EM EM M TR PR W PR S RB

W W

m Q

W

2 ,

, , 2 , , , , , , , ,

, , , ,

, , 1 1, , ,

'1

.

EM P ES SP in EM P P out P ES ES in P ES ES out ES P P in ES P


P out P EM EM M TR PR W PR S CEsIce

m Q

(2)

It can be concluded from Eqs. (1) and (2)

that both HEVs utilize fuel energy more efficiently than ICEV if

1

,

, Itcf

HEVtcf

m

m , (3)

whereas right-hand-side (rhs) of both equations reveals and quantifies the mechanisms that could lead to this goal; index HEV represents P or S. In Eqs. (1) and (2), REFW (Ratio of Efficiencies of the energy conversion chains from Fuel tank to Wheels) term represents the ratio of efficiencies of the energy conversion chains from the fuel tank (F) to wheels (W) of the ICEV topology and the particular HEV topology. The nominator and the denominator of REFW term thus include efficiencies of all converter elements in the energy conversion chain from F to W for the particular vehicle topology (Fig. 1). REFW term is multiplied by the sum of the terms: TcPrR (Test cycle Propulsion work Ratio), MIce (Motoring Internal combustion engine), RB (Regenerative Braking) and CEsIce (Charging Electric storage devices by the Internal combustion engine). TcPrR term is equal to the multiplication factor of the test cycle, FP or FS, that is generally larger than unity due to a larger vehicle mass of the HEVs as discussed above. This term thus, tends to decrease the energy conversion efficiency of both HEV topologies. MIce term considers the difference of energies delivered to the ICE of observed vehicle topologies by the external torque. Motoring of the

ICE by external torque rather than by fuel addition clearly reduces the fuel consumption of the ICEV. Series HEV topology does not enable motoring of the ICE by the external torque originating from the vehicle inertia, since ICE is not mechanically coupled to the wheels as it is discernable from Fig. 1. MIce thus clearly increases the ratio [mf,tc]S/[mf,tc]I in Eq. (2). In parallel HEV, MIce term generally increases the ratio [mf,tc]S/[mf,tc]I , Eq. (1), since parallel HEVs incorporate downsized ICEs featuring smaller energy consumption capability. It should be noted that energy consumed by the ICE in the ICEV could be used for regenerative braking in both HEV topologies. Additionally, control strategies of the parallel HEV attempt to avoid the operation of the ICE at low loads and correspondingly at low efficiency of the ICE, thereby reducing the amount of the energy consumed by the ICE through motoring by external torque. For HEVs, negative effects due to the MIce term are therefore generally overcompensated by positive effects due to regenerative braking (RB), higher ICE,eff, and lower losses due to charging ES by the ICE (CEsIce). RB term considers regenerative braking, which is one of the major mechanisms for increasing energy conversion efficiency of both HEV topologies. It is obvious that increase in the energy conversion efficiency is proportional to the amount of the energy available for regenerative braking.

SBRWBRBRtc WW ,, of

the series HEV is generally larger than



PBRTRBRWICETCTRBRWBRBRtc WWW ,,,1,, ' of

the parallel HEV, since EM1 in the series HEV needs to be sized for a maximum power output of the HEV and thus enables recuperation of larger amount of the energy through regenerative braking. CEsIce accounts for the losses due to charging the ES by the energy produced by the ICE. It therefore obviously decreases energy conversion efficiency of both HEV topologies.

Additionally, analytical framework for comparing conventional ICEV and ICEV featuring stop/start strategy (denoted I,SS) is given in [3]:

, , , ,,

, , , , ,

,

, , , ,

, , ,

, , ,

1

f tc ICE eff TR PR W PRI SS I

f tc ICE eff TR PR W PRI I SS REFW

I SS TcPrRf tc LHV ICE eff TR PR W PR I

I SS TR ICE TR PR W PR I

TR ICE TR PR W PR I SS MIce

m

m

Fm Q

F W

W

.

(4)

Generally mass of the vehicle does not change significantly with the introduction of the stop/start strategy, therefore, TcPrR→1. If an additionally equal driver model is applied, then MIce→0. Therefore, introduction of the stop/start strategy influences REFW term through ICE,eff and increases energy conversion efficiency of ICEV featuring stop/start strategy. RB and CEsIce terms are not considered in Eq. (4), since these mechanisms are not inherent to either of the vehicle topologies compared in Eq. (4).

2 SIMULATION MODEL

A forward-facing model was applied for

modeling of ICEV and both HEV topologies. Simulation models for ICE powertrain and both hybrid powertrains were described in detail in [7] and [8], whereas an extended simulation model incorporating sub-models of additional components required for modeling vehicle dynamics and corresponding control strategies

was proposed in [4]. Therefore, the models are only briefly summarized subsequently.

Analyses were performed for a MAN 8.225 LC truck equipped with a six gear S6-850 gearbox representing a baseline ICEV. Vehicle mass amounts to 3485 kg, whereas maximum gross mass equals 7490 kg. Simulations were performed for a fully loaded vehicle, for a vehicle carrying no load and for vehicle carrying half of the maximum payload to expose influences of the vehicle mass on the energy conversion efficiency. When modeling HEVs, mass increase due to additional batteries, electric machines and other electric accessories is considered, as well as mass decrease due to downsizing ICE in both HEV topologies, and omission of the gear box in the series HEV. Masses of HEVs are thus larger than masses of the ICEV, however this approach enables a comparison of the energy consumption for equal payloads.

The MAN D0826 LOH 15 turbocharged diesel engine (max. torque 862 Nm at 1400 rpm, max. power 158 kW at 2400 rpm) is applied as the baseline internal combustion engine. The ICEs with RV = Vdownsized / Vbaseline equal to 0.8 and 0.5 were analyzed with the parallel HEV, and the ICE with RV = 0.5 was analyzed with the series HEV; V is swept volume of the ICE.

The ENAX Li-Ion High Power 3.8 V, 2 Ah cell is applied as the module of the Li-Ion storage system. A prototype electric motor-generator presented in [7] was applied in the parallel hybrid powertrain and as an electric motor in the series one. Characteristics of the STAMFORD UCM 274F (max. input power 94.6 kW, max. efficiency 93%) were used to simulate an electric generator in the series hybrid powertrain.

Components of the analyzed HEVs were sized according to the following constraint max,,max,,

,,bICEbICE MnbICEMnEMhICE MMM for the

parallel HEV, and

max,,max,,,

bICEbICE MnbICEMnEM MM for the series

one, M is torque and max,,bICEMn represents engine

speed that corresponds to the maximum torque of the baseline ICE engine.


Katrašnik, T. 796

Fig. 2. Velocity profile of: a) ECE_EUDC_LOW, b) BUSRTE, and c) UDDSHDV cycles

Energy losses and thus efficiency of the

tire are evaluated by the rolling resistance momentum model of the tire that was modeled according to model proposed in [9]. In the proposed analysis both HEV topologies do not incorporate torque couplers (TC). In the series HEV, ICE is directly mechanically connected to the EM2, whereas in parallel HEV, EM1 operates in the same speed range as ICE and it could therefore be directly mechanically coupled to the shaft.

Two control strategies were applied to ICEVs: 1) normal operation of the ICEV, and 2) ICEV with stop/start control strategy (denoted SS).

All parallel HEVs apply SS control strategy. Additionally, two different regimes of vehicle propulsion during drive-away and at low powertrain loads were analyzed: 1) ICE solely provides the torque for vehicle propulsion up to maximum torque output of the ICE, and 2) EM solely provides the torque up to a specified limit and afterwards ICE solely provides the torque for vehicle propulsion up to the maximum torque output of the ICE. The latter control strategy is denoted as EM_START. This control strategy avoids operation of the ICE in the inefficient regions [4] and [10]. The control strategy of the parallel HEV allows for: 1) drive-away and vehicle propulsion by EM at low powertrain loads if EM_START operating regime is enabled, 2) ICE and EM deliver power in parallel if ICE is not able to provide a required power output, 3) replenishing the batteries by operating the ICE at a higher torque output, 4) regenerative braking, 5) simultaneous operation of the ICE and the EM in order to prevent charging of the batteries above the specified limit, and 6) normal operation of the ICE.

The ICEs of the series HEVs were operated according to the optimum engine

operation line (OEOL) [6]. In the presented analysis the power output of the ICE operating according to OEOL was based on the battery state-of-charge (SOC), i.e. fuel rack (FR)SOC, and engine speed (n)FR as presented in Ref. [4]. Corresponding to the OEOL two control strategies were applied to series HEVs [4]: 1) ICE is turned on and off according to the SOC (denoted CS_S_SOC), and 2) ICE is turned on and off according to the characteristics of the test cycle, i.e. ICE is turned on during the vehicle propulsion period and it is turned off during vehicle stops and during regenerative braking (denoted CS_S_tc). These two control strategies were introduced to analyze influences of the energy flow W'EM2-P,ES Eq. (2), i.e. charging the ES by the ICE, on the energy conversion efficiency of the series HEV. CS_S_tc ensures a smaller energy flow through the ES, however it also decreases maximum sustained power.

3 TEST CYCLES

Three different test cycles were analyzed

to investigate the influences of the test cycle characteristics on energy conversion efficiency of different HEV topologies and configurations [11]: ECE+EUDC (NEDC) for low-powered vehicles (ECE_EUDC_LOW), Fig. 2a), 2.65 km bus route with 28 stops (BUSRTE), Fig. 2b, and Urban Dynamometer Driving Schedule for Heavy-Duty Vehicles (UDDSHDV) Fig. 2c. By comparing ECE_EUDC_LOW and BUSRTE cycle it can be observed that the latter features a significantly lower average velocity, frequent decelerations to stand-still and longer vehicle stop period. The average velocity of the ECE_EUDC_LOW is similar to that of the UDDSHDV, however UDDSHDV cycle features more frequent and more severe accelerations.



4 RESULTS The results for three vehicle topologies

giving eight different configurations carrying different loads and driven according to three different test cycles are shown in this section. Only the results of powertrain configurations that are able to comply with non-depleting ES management strategy are shown in order to enable credible comparison of energy conversion efficiencies.

The relative change in the fuel consumption, mf,X could also be written as the sum of the products of the REFW term with terms TcPrR, MIce, RB and CEsIce, where a particular term reveals the influence of a particular mechanism on the mf,X. It follows:

,

,

,

**

* *

1

1

,

f tc Xf X

f tc I

MIceTcPrR

RB CEsIce

mm

m

REFW TcPrR REFW MIce

REFW RB REFW CEsIce

(5)

where X represents P or S or I,SS. Terms larger than 0 indicate an increase in the mf,X, and terms smaller that 0 indicate a decrease in the mf,X. Additionally, the vehicle mass ratio

1,

,,

IV

XVXV m

mm (6)

is introduced to reflect change in the vehicle mass relative to the mass of the ICEV. In the subsequent text indexes are not written with the parameters introduced in Eqs. (5) and (6), since it is discernable from the accompanying text and figures which topology and configuration is analyzed.

The following notation is adopted in this section: ICEV – internal combustion engine vehicle, ICEV_SS – internal combustion engine vehicle with stop/start (SS) strategy, PHEV_Rv = 0.8_EM = 0 – parallel HEV incorporating ICE with RV = 0.8 without EM_START strategy, PHEV_Rv = 0.8_EM = 1 –parallel HEV incorporating ICE with RV = 0.8 with EM_START strategy, PHEV_Rv = 0.5_EM = 0 – parallel HEV incorporating ICE with RV = 0.5 without

EM_START strategy, PHEV_Rv = 0.5_EM = 1 – parallel HEV incorporating ICE with Rv = 0.5 with EM_START strategy, SHEV_SOC – series HEV with CS_S_SOC strategy, and SHEV_tc – series HEV with CS_S_tc strategy.

4.1 ECE_NEDC_LOW Cycle

Figs. 3a to 3c shows parameters of fully

loaded vehicles driven according to the ECE_NEDC_LOW cycle: a) relative change in fuel consumption (mf), effective efficiency of the ICE (ICE,eff), and mV introduced in Eq. (6), b) TcPrR*, MIce*, RB* and CEsIce*, parameters introduced in Eq. (5), and c) energy needed for vehicle propulsion (Wtc,PR), energy needed for braking the vehicle (integral over negative values of the test cycle power trace - Wtc,PR) and energy consumed by the brakes (WBR), whereas in Figs. 3d to 3f the same parameters are shown for an empty vehicle. PHEV_Rv = 0.5_EM = 1 was not able to comply with non-depleting ES management when fully loaded, since ICE could not provide enough energy to replenish the ES in the period when it was turned on. These results are therefore not shown in Figs. 3a to c.

It is discernable from the results that different topologies and configurations significantly influence fuel economy of HEVs (mf – Figs. 3a and d). It can also be observed that HEVs featuring the highest ICE,eff and recuperating the largest amount of energy by regenerative braking (indicated by RB* and by the difference between Wtc,BR and WBR) do not necessarily feature the highest fuel economy. It is therefore necessary to analyze particular terms of Eq. (5) to explain the influence of the energy conversion phenomena along different energy paths on the fuel consumptions of particular vehicle topology.

It is discernable from Figs. 3c and f that vehicle mass of parallel HEVs increases with an increasing hybridization factor and that series HEVs feature larger vehicle mass due to an application of two electric machines and due to a larger number of battery modules. mv values differ for fully loaded and empty HEVs, since additional mass due to powertrain hybridization is constant and mV,I Eq. (6) changes with the vehicle load. Wtc,PR and Wtc,BR (Figs. 3c and f) increase corresponding to the vehicle mass.


Katrašnik, T. 798

Fig. 3. ECE_NEDC_LOW cycle: a) mf , ICE,eff and mV b) TcPrR*, Mice*, RB* and CEsIce* and c) Wtc,PR, Wtc,BR and WBR for fully loaded vehicle, and

d) to f) the same parameters for an empty vehicle

It can be observed from Figs. 3a and d that fuel economy improvement of ICEV_SS and all HEVs over ICEV is slightly larger for the empty vehicle compared to the fully loaded vehicle

However, by analyzing particular terms of Eq. (5) it can be concluded that the contribution of different mechanisms to the relative change in the fuel consumption (mf) is significantly influenced by the vehicle load. It is discernable that lower vehicle mass results in lower values of Wtc,PR and Wtc,BR, which is quite obvious (Figs. 3c

and f). However, the ratio between Wtc,BR and Wtc,PR also decreases for the empty vehicle, since relatively more energy is consumed to overcome the aerodynamic drag. The ratio between Wtc,BR and Wtc,PR significantly influences relative amount of the energy available for regenerative braking and thus the term RB*. Therefore, regenerative braking posses a smaller potential to improve the fuel economy of lighter vehicles. It is discernable from Figs. 3a and d that ICE,eff of the ICEV is lower for the empty vehicle compared to the fully



loaded one, which is also quite obvious since lower torque is needed to drive an empty vehicle according to a specified velocity trace resulting in lower ICE,eff. Therefore, a relative improvement in ICE,eff of ICEV_SS and all HEVs over ICEV is more pronounced for the empty vehicle. This phenomenon mainly influences lower values of TcPrR* for the empty vehicle.

It is discernable from Figs. 3a and d that stop/start strategy increases ICE,eff and therefore improves the fuel economy of the fully loaded and empty ICEV_SS, since other vehicle parameters are equal for ICEV_SS and ICEV.

Fig. 3 shows that fully loaded and empty PHEV_Rv = 0.8_EM = 0 and PHEV_Rv = 0.8_EM = 1 feature improved fuel economy (mf) over ICEV and over ICEV_SS. It can also be seen that the difference in mf of PHEV_Rv = 0.8_EM = 1 and PHEV_Rv = 0.8_EM = 0 is much smaller than difference in ICE,eff . The operation according to the EM_START (PHEV_Rv = 0.8_EM = 1) strategy avoids inefficient engine operating conditions and thus results in higher ICE,eff. However, the operation according to the EM_START strategy also implies higher electric energy consumption by the EM, and thus ES are also charged by the ICE (CEsIce*>0), since regenerative braking alone does not provide enough electric energy to operate the HEV according to the non-depleting ES management strategy. Moreover, these facts result also in MIce*>0, since ICE is less frequently motored by external torque due to an operation at a higher torque output to replenish the batteries. PHEV_Rv = 0.8_EM = 0 thus features an improved fuel economy over ICEV_SS mainly due to regenerative braking (RB*<0). PHEV_Rv = 0.8_EM = 1 features improved fuel economy over ICEV_SS due to higher ICE,eff, whereas all other mechanisms, i.e. TcPrR+MIce+RB+CEsIce>1 in Eq. (1), deteriorate its fuel economy.

It is discernable from Fig. 3 that a fully loaded and empty PHEV_Rv = 0.5_EM = 0 features the highest fuel economy for the ECE_NEDC_LOW cycle. PHEV_Rv = 0.5_EM = 0 consumes less fuel than PHEV_Rv = 0.8_EM = 0 due to higher ICE,eff and due to a larger amount of the energy recuperated by regenerative braking. The first improvement arises from the application of the

downsized ICE featuring higher ICE,eff, whereas the latter improvement arises from the application of a more powerful EM that is capable of recuperating more energy by regenerative braking. PHEV_Rv = 0.5_EM = 0 consumes less fuel than PHEV_Rv = 0.8_EM = 1 mainly due to lower losses associated with charging the ES by the ICE (CEsIce*) and due to a larger amount of the energy recuperated by regenerative braking (RB*). It can be observed that empty PHEV_Rv = 0.5_EM = 1 vehicle consumes more fuel than empty PHEV_Rv = 0.5_EM = 0 vehicle, since improvement in ICE,eff is smaller than losses associated with charging the ES by the ICE.

EM_START strategy thus improves fuel economy of the parallel HEV with RV = 0.8 and deteriorates fuel economy of the parallel HEV with RV = 0.5. It can generally be concluded that EM_START strategy leads to improved fuel economy if improvement in ICE,eff overcompensates negative influences of charging the ES by the ICE (CEsIce*) and smaller energy consumption of the energy by motoring the ICE by external torque (MIce*).

It is instructive to compare values of the *CEsIce terms for PHEV_Rv = 0.8_EM = 1 and

PHEV_Rv = 0.5_EM = 0 for both vehicle loads. CEsIce* of the empty PHEV_Rv = 0.8_EM = 1 vehicle is larger than CEsIce* of a fully loaded PHEV_Rv = 0.8_EM = 1 vehicle, since RB* term is smaller indicating that relatively less energy is recuperated by regenerative braking and thus, more energy from ICE is needed to charge the ES thereby enabling an operation according to the EM_START strategy. Opposite, CEsIce* for the empty PHEV_Rv = 0.5_EM = 0 vehicle is smaller than CEsIce* for the fully loaded PHEV_Rv = 0.5_EM = 0 vehicle, since lower torque is needed to drive an empty vehicle according to a specified velocity trace and thus EM power assist is smaller.

Fuel consumption of all series HEVs exceed that of the ICEV despite the highest value of ICE,eff and the largest amount of the energy recuperated by regenerative braking (difference between Wtc,BR and WBR). This is the consequence of a lower efficiency of the energy conversion chain from F to W and to a lesser extent, a consequence of larger vehicle mass. Both effects result in TcPrR*>0. Increase in ICE,eff of the series HEVs is thus not high enough to overcompensate drawbacks of the longer energy


Katrašnik, T. 800

conversion chain incorporating EM2, P and EM1 (REFW term in Eq. (2)). Despite the largest amount of the energy recuperated by regenerative braking, TcPrR+MIce+RB+CEsIce>1 (eq. (2)) due to larger vehicle mass (mV) that results in a higher Wtc,PR value, due to losses associated with charging the ES by the ICE (CEsIce*), and due to MIce*>0 (since series HEVs do not incorporate the mechanism of energy consumption by the ICE). Larger vehicle mass of the series HEVs is mainly related to a larger number of battery stacks being required due to higher charging currents. 4.2 Influence of the Vehicle Load and of the Drive Cycle Characteristics on the Fuel Economy

Fig. 4 shows mf for different relative

loads (0 – empty vehicle, 1 – fully loaded vehicle) operating according to the a) ECE_NEDC_LOW, b) BUSRTE and c) UDDSHDV cycle. It is discernable from the results that drive cycle influences fuel economy improvement of HEVs more significantly than vehicle load.

From Fig. 4a it can be concluded that mf of the ICEV_SS decreases with increasing vehicle load, since a relative amount of the fuel consumed during idling also decreases with an increased vehicle load. It can be seen that mf curve of the PHEV_Rv = 0.8_EM = 0 features a negative slope, since positive effect due to a relatively larger amount of the energy available for regenerative braking at high vehicle loads overcompensate negative effects due to smaller improvement in ICE,eff as discernable in Fig. 3. On the other hand, mf curves of the PHEV_Rv = 0.8_EM = 1 and PHEV_Rv = 0.5_EM = 0 feature a positive slope, since positive effects due to a relatively larger amount of the energy available for regenerative braking at high vehicle loads are smaller than negative influences due to a smaller improvement in ICE,eff and due to charging the ES by the ICE (Fig. 3). mf curves of series HEVs are mainly characterized by the trade-off between an improvement in ICE,eff and thus, an improvement in the energy conversion efficiency from F to W, and regenerative braking (RB*- Fig. 3).

Fig. 4. mf for different vehicle loads: a)

ECE_NEDC_LOW, b) BUSRTE, c) UDDSHDV cycle

It can be seen from Fig. 4b that fuel

economy improvement (mf) of ICEV_SS and HEVs over ICEV is much larger for the BUSRTE cycle. This is mainly the consequence of a lower average load of the BUSRTE cycle originating from low average velocity and long vehicle stop periods (Fig. 2). ICEV thus features very low ICE,eff, a large amount of the energy consumed during idling and a relatively large amount of the energy consumed by the brakes and thus



dissipated to heat. It can be seen that all curves feature a positive slope, which is mainly the consequence of very low ICE,eff of the empty ICEV enabling significant fuel economy improvements at low vehicle loads. The stop/start strategy enables large fuel economy improvement through increased ICE,eff, whereas mf decreases with an increasing vehicle load since a relative amount of the fuel consumed during idling decreases. Moreover, regenerative braking posses significant potential for improving fuel economy due to frequent decelerations. Therefore, optimum fuel economy is shifted to the PHEV_Rv = 0.5_EM = 1 that features very high ICE,eff and recuperates large amount of the energy by regenerative braking. EM_START strategy thus enables a significant increase in the energy conversion efficiency since energy consumed by the EM is mainly gained by regenerative braking.

By analyzing the results of the UDDSHDV cycle (Fig. 4c) it can be concluded that relative changes in fuel consumption are similar to those of the ECE_NEDC_LOW cycle, which is related to the similar average velocity. However, the average load of the UDDSHDV cycle is larger than the average load of the ECE_NEDC_LOW cycle due to more frequent and more severe accelerations (Fig. 2). Optimum fuel economy therefore moves to parallel HEVs incorporating ICEs with larger swept volume (larger RV). This is mainly the consequence of more severe accelerations, which imply a higher energy flow through the EM for PHEV_Rv = 0.5_EM = 0 and thus increased losses due to charging the ES by the ICE. This case exposes that frequent operation at high powertrain loads favor powertrains applying ICEs with larger swept volume since losses due to charging the ES by the ICE become substantial if it is not possible to gain the majority of the electric energy by regenerative braking.

5 CONCLUSIONS

Fuel economy of different HEVs and

ICEVs was analyzed by simulation and analytical analysis. A combined approach clearly interprets influences of different test cycles, HEV topologies, configurations, vehicle loads and control strategies on the energy consumption of the HEVs and on the energy flows on different energy paths. It, therefore, proves to be an

efficient tool for optimizing HEVs based on their target application. It has been shown that HEVs make a significant fuel economy improvement for the test cycles where ICEVs feature low effective efficiency of the ICE and for test cycles enabling significant recuperation of the energy by regenerative braking possible. It is discernable that drive cycle characteristics influence potential improvement in the fuel economy of HEVs over ICEVs more significantly than vehicle load. It has been shown that HEVs featuring the highest effective efficiency of the ICE and the largest amount of the energy recuperated by regenerative braking do not necessary feature the best fuel economy, since losses due to electric energy production, storage and consumption, and, in particular cases, losses due to increased vehicle mass significantly influence the fuel economy of HEVs. It is discernable from the results that test cycles featuring increased average power and decreased possibility of recuperating energy by regenerative braking clearly favor the parallel HEV topology over the series HEV topology. It has also been shown that increased average power of the test cycle shifts optimum fuel economy towards parallel hybrid powertrains applying ICEs with larger swept volume. It is discernable from the results that drive-away and vehicle propulsion by the EM at low powertrain loads is always desirable for parallel HEVs if electric energy consumed by the EM could be recuperated by regenerative braking and not by operating the ICE at higher output. Otherwise, a detailed analysis revealing influences of different mechanisms on the fuel economy is necessary to justify this operation mode.

6 NOMENCLATURE

F multiplication factor of the test cycle [-] M torque [Nm] m mass [kg] n engine speed [rpm] QLHV lower fuel heating value [J/kg] RV=Vdownsized/Vbaseline swept volume ratio [-] t time [s] V swept volume of the internal combustion

engine [m3] velocity [m/s] W energy [J] efficiency [-]


Katrašnik, T. 802

Subscripts: b baseline BR brakes, braking eff effective EM electric machine ES electric storage F fuel tank f fuel G electric machine operating in the generator

mode ICE internal combustion engine M electric machine operating in the motor

mode max maximum P power converter, parallel PR propulsion S series TC torque coupling tc test cycle TR transmission W wheel Abbreviations: FR fuel rack position HEV hybrid electric vehicle ICE internal combustion engine ICEV vehicle driven by an internal

combustion engine ICEV_SS vehicle driven by an internal

combustion engine featuring start/stop functionality

OEOL optimum engine operation line PHEV parallel hybrid electric vehicle rhs right hand side of the equation SOC state of charge SHEV series hybrid electric vehicle

7 REFERENCES

[1] Lukic, S.M., Emadi, A. (2004). Effect of

drivetrain hybridization on fuel economy and dynamic performance of parallel hybrid electric vehicles. IEEE transactions on vehicular technology, vol. 53, no. 2, p. 385-389.

[2] Lee, H., Kim, H. (2005). Improvement in fuel economy for a parallel hybrid electric vehicle by continuously variable transmission ratio control. Proc. Instn. Mech. Engrs., Part D, J. of Automotive Engineering, vol. 219, p. 43-51.

[3] Katrašnik, T. (2009). Analytical framework for analyzing the energy conversion efficiency of different hybrid electric vehicle topologies. Energy Convers. Manage., vol. 50, p. 1924-1938.

[4] Banjac, T., Trenc, F., Katrašnik, T. (2009). Energy conversion efficiency of hybrid electric heavy-duty vehicles operating according to diverse drive cycles. Energy Convers. Manage., vol. 50, p. 2865-2878.

[5] Chan, C.C. (2007). The state of the art of electric, hybrid, and fuel cell vehicles, Proceedings of the IEEE, vol. 95, no. 4, p. 704-718.

[6] Chau, K.T., Wong, Y.S. (2002). Overview of power management in hybrid electric vehicles. Energy convers. manage., vol. 43, p. 1953-1968.

[7] Katrašnik, T. (2007). Hybridization of powertrain and downsizing of IC engine - a way to reduce fuel consumption and pollutant emissions - Part 1. Energy Convers. Manage., vol. 48, no. 5, p. 1411-1423.

[8] Katrašnik, T., Trenc, F., Rodman Oprešnik, S. (2007). Analysis of the energy conversion efficiency in parallel and series hybrid powertrains. IEEE transactions on vehicular technology, vol. 56, no. 6/2, p. 3649-3659.

[9] Pacejka, H.B. (2006). Tire and vechicle dynamics, 2nd ed. SAE International, Warrendale, PA.

[10] Wu, B., Lin, C.C., Filipi, Z., Peng, H., Assanis, D. (2004). Optimal power management for hydraulic hybrid delivery truck. Vehicle System Dynamics, vol. 42, no. 1-2, p. 23-40.

[11] National Renewable Energy Laboratory. ADVISOR Documentation.

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 803-810 Paper received: 13.04.2010 UDC 658.5:001.895 Paper accepted: 01.10.2010

* Corr. Author's Address: University of Maribor, Faculty of Mechanical Engineering, Smetanova ulica 17, SI-2000 Maribor, Slovenia, [email protected] 803

Analysis of Innovation Concepts in Slovenian Manufacturing Companies

Iztok Palčič* – Borut Buchmeister – Andrej Polajnar

University of Maribor, Faculty of Mechanical Engineering, Slovenia

Competitive advantages of manufacturing companies are not only generated by R&D based product innovations, but also by technical and non-technical process innovations aiming to modernise manufacturing processes. This paper presents the use of selected innovation concepts in Slovenian manufacturing companies. Later we analyse the relationship of the use of selected technical and organisational innovation concepts and companies’ performance indicators. The results show that R&D expenses and innovation concepts are not always correlated and that there is a difference in utilising innovation concepts between low, medium and high-tech industries. The data were obtained with The European Manufacturing Survey (EMS) that was conducted in 2009 within nine European countries. For the purpose of this paper the data of Slovenian manufacturing companies have been used. ©2010 Journal of Mechanical Engineering. All rights reserved. Keywords: innovation, technical innovation, organisational innovation, company performance

0 INTRODUCTION

Innovation, which is mostly linked to R&D of products [1], remains one of the leading issues in current science. There are many studies on innovation revealing that increased R&D activities lead to innovative products, which enable companies to achieve competitive advantages and to gain market shares [2]. For present purposes, we adopted Nohria and Gulati’s definition of innovation as “any policy, structure, method, or process, product or market opportunity that the manager of the innovating unit perceived to be new” [3].

Referring to many innovation researchers [4] to [6], innovation can be considered a complex phenomenon including technical (e.g., new products, new production methods) and non-technical aspects (e.g., new markets, new forms of organization) as well as product innovations (e.g., new products or services) and process innovations (e.g., new production methods or new forms of organization). Based on these considerations, there are four different types of innovations: technical product innovations, non-technical service innovations, technical process innovations, and non-technical process innovations, which are understood to be organizational innovations [7].

Technical innovations are defined as those that occur in the operating component and affect the technical system of an organisation. The

technical system consists of the equipment and methods of operations used to transform raw materials or information into product and services [8]. A technical innovation, therefore, can be an adoption of a new idea pertaining to a new product or a new service, or the introduction of new elements in an organisation’s production process or service operations [9] to [13].

The first three groups of innovation (technical product innovations, non-technical service innovations, technical process innovations) have been the subject of many studies. On the other hand, there have been little conceptual and methodological contributions to monitoring of organisational innovation so far [1].

This paper deals with analysis of technical and organisational innovation concepts in Slovenian manufacturing companies. We will present the use of selected innovation concepts in Slovenian manufacturing companies and their change in the last decade. Innovation in manufacturing companies is always related with the amount of money companies spend for R&D activities, so we will examine how the use of selected innovation concepts is related to R&D expenses. On the other hand, we will find out if the level of using technical innovation concept is interrelated with the use of level of organisational innovation concepts. Finally, we will form two groups of manufacturing companies based on the OECD classification for low, medium and high


Palčič, I. – Buchmeister, B. – Polajnar, A. 804

tech industries. The research question is the level of use of selected innovation concepts and the main reasons for implementing the innovation concept in question.

1 DESCRIPTION OF SELECTED

INNOVATION CONCEPTS First, two technical innovation concepts

that are widely used in manufacturing companies around Europe, and were of great interest for our research are presented. CAD/CAM software provides the interface between the human user and the CNC machine. These machines are programmed with the required tool trajectory using a special command set called G-codes. These G-codes are a de facto standard in the CNC machine industry. G-code programs can be written manually for simple parts. However, in most cases CAM software is used to produce G-code programs directly from CAD models. A CAM package typically produces a G-code program in two stages. First, tool paths consisting of generic cutter locations (CLDATA) are generated. The CLDATA consists of a list of tool positions in the workpiece coordinate system. The cutter locations must then be converted into G-code programs using a post-processor specific to the NC machines that will produce the part. CAD/CAM process has four phases. First of all, the product should be designed taking into consideration its applications. After designing the product, assembly drawings and parts drawings of the product have to be made. These drawings are used for the reference purposes and more importantly for manufacturing the product on production shop floor. The drawings are also made by using CAD software. The production planning and scheduling of the designed product can be carried out by computers, which helps managing the manufacturing resources properly. The latter is the CAM part of the product cycle, while the last phase is manufacturing the product, where nowadays the use of CNC machines has become quite widespread. In CNC machines, the programming instructions for the manufacturing of the product that has been designed using the CAD software, are fed. The program gives appropriate instructions to the machine control to carry out the manufacturing of the product.

Automated handling devices can be used to handle the material flow of work-pieces or

tools from one spot to another, carrying the right volume of parts with the accurate orientation at the proper time to the exact position. Non-automated, manual handling devices are called manipulators and are not an integral part of our definition. Industrial robots (IR) are a specific class of automated handling devices. An industrial robot is officially defined by ISO 8373:1994 as an automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes. Typical applications of industrial robots include welding, painting, ironing, assembly, pick and place, palletizing, product inspection, and testing. In this paper, the term industrial robots or IR, always implicitly including automated handling devices in our understanding is used.

The origin of industrial robots can be found in reactor technology, where automated instead of manual handling devices have been used at an early stage within radioactive rooms. First industrial applications of IR in Europe have taken place in the early 1970s. From the mid 1980s to 2000 the adoption rate of industrial robots rose from about 3% to about 22%, still representing only a minority of industrial companies in Europe [14].

As mentioned above, organisational innovation concepts did not receive as much attention in the literature as other concepts. Existing literature on organisational innovation is diverse and scattered. There is no consensus on a definition of the term “organisational innovation”, which remains ambiguous [15]. [16] defines it as the use of new managerial and working concepts and practices. When speaking about organisational innovation, Damanpour and Evan [5] consider them to be responses to environmental change or means of bringing change to an organisation. Organisations can cope with environmental changes and uncertainties not only by applying new technologies, but also by successfully integrating technical or administrative changes into their organisational structure thereby improving the level of achievement of their goals [17]. Innovations at the organisational level may involve implementation of a new technical idea or a new administrative idea. The adoption of a new idea in an organisation, regardless of the time of its adoption in the related organisation population, is expected to result in an organisational change that


Analysis of Innovation Concepts in Slovenian Manufacturing Companies 805

might affect the performance of that organisation. Therefore, an idea is considered new in relation to the adopting organisation, not in relation to its organisational population [16].

Armbruster et al. [7] prepared a classification of organisational innovation. There are several ways of differentiating organisational innovation. The first possibility is into structural organisational innovations and procedural organisational innovations. Structural organisational innovations influence, change and improve responsibilities, accountability, command lines and information flows as well as the number of hierarchical levels, the divisional structure of functions (R&D, production, human resources, financing, etc.), or the separation between line and support functions. Procedural organisational innovations affect a company’s processes and operations. Thus, these innovations change or implement new procedures and processes within the company, such as simultaneous engineering or zero buffer rules. Organisational innovation can be further differentiated along an intra-organisational and inter-organisational dimension. While intra-organisational innovations occur within an organisation or a company, inter-organisational innovations include new organisational structures

or procedures beyond a company’s boundaries. These comprise new organisational structures in an organisation’s environment, such as R&D cooperation with customers, just-in-time processes with suppliers or customers, supply chain management practices with suppliers or customer quality audits. Intra-organisational innovations may concern particular departments or functions or may affect the overall structure and strategy of the company as a whole. Examples of intra-organisational innovations include the implementation of teamwork, quality circles, continuous improvement processes, certification of a company under ISO 9000, simultaneous (concurrent) engineering, zero-buffer principles, environmental audits and cross-functional teams [7].

Lean production comprises an integrated variety of new organizational concepts such as teamwork, job enrichment and enlargement, decentralization of planning, operating and controlling functions, manufacturing cells, quality circles, continuous improvements (kanban), simultaneous engineering and just-in-time delivery, which was found to be the main cause of the superiority of the Japanese car industry at this time [18] to [23].

Fig. 1. An item-oriented typology of organisational innovations [7]

Cross-functional teams Decentralisation of planning, operating and

controlling functions Manufacturing cells or segments Reduction of hierarchical levels, etc.

Intra-organisational

Teamwork in production Job enrichment / job enlargement Simultaneous engineering / concurrent

engineering Continuous improvement process / Kaizen Quality circles Quality audits / certification (ISO) Environmental audits (ISO) Zero-buffer principles (KANBAN) Preventive maintenance, etc.

Cooperation / networks / alliances (R&D, production, service, sales),

Make or buy / outsourcing Offshoring / relocation, etc.

Inter-organisational

“Just-in-time” (to

customers, with suppliers) Single / dual sourcing Supply chain management Customer quality audits,

etc.

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ion

Focus of organisational innovation



One of the organisational innovation concepts that we will look into is a teamwork in production. Since the 1990s teamwork has been intensely discussed as an important element of a lean factory. It is argued that, contrary to the tayloristic way of production, the implementation of teamwork into the production process increases product and process flexibility along with productivity [18]. Teamworkers have a high variety of skills allowing for job rotation within the team, so that they can fill in for one another. The enlargement of skills and responsibilities as well as the cooperation with other workers is supposed to have a positive impact on workers’ job satisfaction and task commitment, which in turn positively supports the team's productivity [14].

The other interesting concept is zero buffer principle or “kanban”; a concept related to lean and just-in-time (JIT) production. Kanban is a signalling system to trigger action. As its name suggests, kanban historically uses cards to signal the need for an item. Kanban became an effective tool to support the running of the production system as a whole. In addition, it proved to be an excellent way for promoting improvements because reducing the number of kanban in circulation highlighted problem areas. We focused on inventory management. Kanban is used as a demand signal which immediately propagates through the supply chain. This can be used to ensure that intermediate stocks held in the supply chain are better managed, and usually smaller.

2 RESEARCH METHODOLOGY

Presented data on technical and organisational issues is the result of European Manufacturing Survey (EMS). EMS was first conducted in 2003/2004 as a pilot survey in nine European countries: Austria, Croatia, France, Germany, Great Britain, Italy, Slovenia, Switzerland and Turkey. In total, 2249 companies answered questions concerning manufacturing strategies, the application of innovative organisational and technological concepts in production and questions of personnel deployment and qualification. In addition, data on performance indicators such as productivity, flexibility, quality and returns was collected. The responding companies present a cross-section of

the main manufacturing industries, such as producers of rubber and plastics, producers of metal works, mechanical engineering, electrical engineering and textile. In the year 2006 a new survey was conducted in some other European countries when Greece, Netherlands and Spain joined the project. The third round was performed in 2009 and 2010. We received around 4000 responses from European manufacturing companies. The Slovenian sample consists of 67 responses with a 10.1% response rate.

Descriptive statistics is used to depict the state of the use of organisational and technical innovation concepts in Slovenian manufacturing companies. Later we use several correlation coefficients and statistical tests to analyse the relationship between the level of using selected innovation concepts and companies’ performance indicators.

3 THE USE OF INNOVATION CONCEPTS

First, the level of use of specific technical

and organisational innovation concepts in Slovenian manufacturing companies is presented. Our research included 13 technical innovation concepts and 15 organisational innovation concepts. We asked companies if they use specific innovation concepts. The first results depict the percentage of manufacturing companies that use specific innovation concepts.

Fig. 2. The use of technical innovation in percentage of companies

Fig. 2 presents six technical innovation

concepts that are most widely used in Slovenian manufacturing companies. It can be seen that the most widely used concept is classical integration of CAD-CAM technologies. Industrial robots are used in more than half of manufacturing companies. Other relatively widely used concepts



are process integrated quality control (PIQC), digital exchange of operation scheduling data with supply chain management systems of suppliers/customers (SCM), Manufacturing Execution System as an integration of PPS/ERP with production data logging (MES) and virtual reality and/or simulation in product development and/or manufacturing (VR).

Fig. 3. The use of organisational innovation in percentage of companies

Fig. 3 presents the use of six most used

organisational innovation concepts in Slovenian manufacturing companies. Teamwork in production and ISO 9000 quality management systems are the two most widely used concepts. Other concepts are used in approximately half of manufacturing companies. We were also interested in the zero buffer principle. The research has showed that these concepts are used by every fourth manufacturing company.

EMS 2009 is the third survey conducted in the last decade. Through the years we have observed the level of use of specific innovation concepts and its changes. We have selected two technical (CAD-CAM integration and industrial robots) and two organisational (zero buffer principle and teamwork in production) innovation concepts. It can be see that the use of both technical innovation concepts has been rising through the years. In 2003 only half of manufacturing companies used CAD-CAM integration. In little over five years this number has risen to an extent that three out of four companies now use this concept. The change is even bigger with industrial robots. The percentage of companies that use industrial robots and handling systems in manufacturing and assembly has doubled from 2003. This clearly proves that Slovenian manufacturing companies heavily invested in manufacturing equipment and

technology in the last decade. Teamwork in production has been at a high level throughout the years. A little more interesting is the use of zero buffer principles, whether it is kanban or the JIT principle. The use of these concepts reached its peak in 2006, where a third of companies used one of these concepts. However, in the last three years the level dropped down to one fourth of companies. This could mean different things. Slovenian manufacturing companies are not aware of the problems associated with inventory management and they do not pay enough attention to process reengineering issues within their companies or in the whole supply chain. Another explanation could be that as the majority of Slovenian manufacturing companies are suppliers to different industries they cannot afford to have problems with supplying their goods. This fact forces them to keep inventory level higher with no possibility to reduce it to a minimum (zero) level.

Fig. 4. The use of innovation concepts from 2003 until 2009 in Slovenian manufacturing companies

in percentage of companies

4 ANALYSIS AND DISCUSSION OF INNOVATION CONCEPTS

As mentioned above, the innovation

activity is related to the amount of money companies spend on R&D activities. We measured R&D expenses as a share of companies' annual turnover. Based on previous research, we assumed that the number of technical and organisational innovation concepts used, is directly correlated with the amount of R&D expenses. Therefore, we calculated correlation coefficients for two situations. First, we wanted to establish if the total number of technical innovation used is related with the amount of



R&D expenses. We used the Pearson’s correlation coefficient calculation. From 67 responses we included 60 with a complete data on innovation concepts used and amount of R&D expenses. Table 1 presents the results. Table 1. Correlation between technical innovation and R&D expenses

R&D expenses Number of technical innovation

Pearson Correlation *.280 Sig. (2-tailed) .030 N 60

*. Correlation is significant at the 0.05 level (2-tailed).

As predicted, there is a positive correlation

between the number of technical innovation concepts used and R&D expenses, but it is slightly lower than expected. Nevertheless, it can be assumed that R&D expenses are associated with investment in equipment and R&D activities in companies and higher the R&D expenses are more technical innovation concepts are implemented.

Similarly, we assumed that the number of organisational innovation concepts is also positively correlated with R&D expenses. Again, 60 companies were included in the test with the following results: Table 2. Correlation between organisational innovation and R&D expenses

R&D expenses Number of organisati. innovation

Pearson Correlation .110 Sig. (2-tailed) .404 N 60

It can be seen that there is no correlation

between the number of organisational concepts used and R&D expenses. The significance value is over 0.05 (0.404), which means there is no significant relationship between the number of organisational concepts used and R&D expenses. The results prove that implementation of organisational innovation concepts does not necessarily influence the amount of R&D expenses in the company. It seems that organisational concepts cost a lot less than investments in technical innovation or they are not directly seen as innovation drivers. Furthermore, we found that many companies that do not spend any money on R&D activities or they spend a very small percentage of total turnover still implement a high number of organisational innovation concepts.

We performed another test to find out how the number of technical innovation concepts is related to the number of organisational innovation concepts. Based on previous two correlations we allowed positive and negative correlation for this test. The results are in Table 3. Table 3. Correlation between technical innovation and organisational innovation

No. of org. in. Number of technical innovation

Pearson Correlation **.541 Sig. (2-tailed) .000 N 60

**. Correlation is significant at the 0.01 level (2-tailed).

It can be seen that there is a quite

significant positive relationship between the number of technical and organisational concepts used (significance value is under 0.01). It can be concluded that the use of technical innovation concepts usually requires the use of organisational innovation concepts in order to utilise them at a higher level.

OECD classifies manufacturing industries into four categories: low-tech, medium-low-tech, medium-high-tech and high-tech. We split our sample into two groups, one being low and medium-low tech industries (LMT, including NACE-2003 17 to 19, 25 and 28) and medium-high and high-tech industries (MHT, including NACE-2003 29 to 32, 34 and 35). We wished to find out if these two groups differ in the use of specific innovation concepts. Table 4 presents the percentage of the use of selected technical innovation concepts. Table 4. The use of technical innovation concepts in LMT and MHT industries

CAD robots PIQC SCM MES VR LMT 62 41 41 49 26 26 MHT 82 68 50 32 39 36

It can be observed that the use of technical

innovation concepts is higher in MHT industries. Obviously, they spend more money for R&D activities (2.86% of annual turnover in MHT and 2.21 in LMT) and these expenses, as already proven, are positively related to the use of these concepts. One of the exceptions is a digital exchange of operation scheduling data with supply chain management systems of suppliers/customers (SCM) that is widely used in LMT companies. It seems that these companies



are mostly suppliers and are tightly connected to their buyers and heavily depend on their schedules. It should also be pointed out that the use of new material is three times higher in MHT than in LMT companies.

Table 5 present results for the use of organisational innovation concepts in LMT and MHT industries. Table 5. The use of organisational innovation concepts in LMT and MHT industries team

work cross teams

custom. cells

ISO 9000

flex. hours

inter-views

LMT 82 51 46 72 59 46 MHT 86 61 71 68 61 50

The results show that organisational

innovation concepts are more equally represented in both industries. A big exception is the use of customer or product-focussed lines/cells in the factory (instead of task-/operation-structured shop floor). It is clear that MHT companies are more customer-oriented than LMT ones. Zero buffer principles and total costs of ownership (assessment of investment and activities reflecting all costs of their entire product life cycle) as well as financial participation by employees eligible for all employee groups (e.g. profit sharing schemes, share (options) plans, etc.) are substantially higher in MHT companies.

Finally, we asked companies about the level of use of specific innovation concepts. In other words, we were enquiring about the extent of use potential as an actual utilisation compared to the most reasonable potential utilisation in your factory: “low” for an initial attempt to utilise, “medium” for partly utilised and “high” for extensive utilisation. At the same time, we asked about the main aim of innovation concept utilisation: an increase in quality (precision), increase in productivity, increase in flexibility or product innovation. For this purpose, we selected two most widely popular concepts: CAD-CAM integration and teamwork in production. Table 6 presents the results for companies in LMT and MHT industries. Values for utilisation level are 1, 2 and 3 (high utilisation), the table presents the average value of utilisation level. Other values present the percentage of companies that use CAD-CAM or teamwork for specific aim of innovation concept utilisation.

The utilisation level of both innovation concepts is very similar in both industries and it is

very high. The companies that implemented them state that they are exploiting their potential fully. It is more interesting to observe the aim of utilisation. MTH companies implemented both concepts to improve quality and to increase flexibility, where LMT companies use them mainly to increase productivity (with the aim of decreasing production costs). The product innovation aim has quite lower values, which could again draw us to a conclusion that many innovation concepts are not really innovation-oriented.

Table 6. The use of CAD-CAM and teamwork in LMT and MHT industries CAD-CAM

utilis. level

quality productivity

flexi-bility

prod. innova.

LMT 2.58 58 50 21 25 MHT 2.70 65 39 35 17 weam work

utilis. level

quality productivity

flexi-bility

prod. innova.

LMT 2.44 38 69 31 19 MHT 2.26 48 65 35 22

5 CONCLUSION

This paper deals with several issues, concerned with innovation patterns in Slovenian manufacturing companies. Its primary aim was to depict the state-of-the art of technical and organisational innovation concepts used. It has proved that the scope and the level of innovation concepts utilisation are not always correlated with R&D expenses. On the other hand, the use of one type of innovation concepts in most cases requires the utilisation of the other type as well. The paper has also showed that there is a difference in innovation concepts utilisation regarding the industry type based on distinction into low-, medium- and high-tech industries and provides new directions for future research.

6 REFERENCES

[1] Bikfalvi, A. (2007). Innovation, Entrepreneurship and outsourcing: essays on the use of knowledge in business environments, doctoral dissertation. University of Gerona, Gerona.

[2] Freeman, C., Soete, L. (1997). The Economics of Industrial Innovation. Pinter Publisher, London.



[3] Nohria, N., Gulati, R. (1996). Is slack good or bad for innovation. Academy of Management Journal, vol. 39, p. 1245-1264.

[4] Anderson, N., King, N. (1993). Innovation in organizations. International Review of Industrial and Organizational Psychology, vol. 8, p. 1-34.

[5] Damanpour, F., Evan, W. M. (1984). Organizational innovation and performance: the problem of “Organizational Lag”. Administrative Science Quarterly, vol. 29, p. 392-409.

[6] Totterdell, P., Leach, D., Birdi, K., Clegg, C., Wall, T. (2002). An investigation of the contents and consequences of major organizational innovations. International Journal of Innovation Management, vol. 6, no. 4, p. 343-368.

[7] Armbruster, H., Bikfalvi, A., Kinkel, S., Lay, G. (2008). Organizational innovation: The challenge of measuring non-technical innovation in large-scale surveys. Technovation, vol. 28, no. 10, p. 644-657.

[8] Cummings, T. G. (1978). Self-regulating work groups: a socio-technical Systems Approach. Academy of Management Review, vol. 3, p. 625-634.

[9] Damanpour, F., Szabat, K. A., Evan, W. M. (1989). The relationship between types of innovation and organizational performance. Journal of Management Studies, vol. 26, no. 6, p. 587-601.

[10] Kušar, J., Bradeško, L., Duhovnik, J., Starbek, M. (2008). Project management of product development. Strojniški vestnik - Journal of Mechanical Engineering, vol. 54, no. 9, p. 588-606.

[11] Kostanjevec, T., Polajnar, A., Sarjaš, A. (2008). Product development through multi-criteria analysis. Strojniški vestnik - Journal of Mechanical Engineering, vol. 54, no. 11, p. 739-750.

[12] Novak, M., Dolšak, B. (2008). Intelligent FEA-based Design Improvement. Engineering Applications of Artificial Intelligence, vol. 21, no. 8, p. 1239-1254.

[13] Palčič, I., Lalić, B. (2009). Analytical Hierarchy Process as a Tool for Selecting and Evaluating Projects. International Journal of Simulation Modelling, vol. 8, no. 1, p. 16-26.

[14] Armbruster, H., Kinkel, S. Lay, G., Maloca, S. (2007). Techno-organisational innovation in the European manufacturing industry do European countries differ regarding the diffusion of technical and non-technical innovations in manufacturing companies? EUROMA 2007 Conference Proceedings.

[15] Lam, A. (2005). Organizational innovation. Fagerberg, J., Mowery, D. C., Nelson, R. R. (Eds.), The Oxford Handbook of Innovation. Oxford Press, Oxford.

[16] Damanpour, F. (1987). The adoption of technological, administrative and ancillary innovations: impact of organizational factors. Journal of Management, vol. 13, no. 4, p. 675-688.

[17] Rosner, M. M. (1968). Economic determinants of organisational innovation. Administrative Science Quarterly, vol. 12, p. 614-625.

[18] Womack, J. P., Jones, D. T., Roos, D. (1990). The machine that changes the world, New York.

[19] Maksimović, R., Lalić, B. (2008). Flexibility and complexity of effective enterprises. Strojniški vestnik - Journal of Mechanical Engineering, vol. 54, no. 11, p. 768-782.

[20] Plečko, A., Vujica-Herzog, N., Polajnar, A. (2009). An application of six sigma in manufacturing company. Advances in Production Engineering and Management, November 2009, vol. 4, no. 4, p. 243-254.

[21] Kehris, E. (2009). Web Based Simulation of Manufacturing Systems. International Journal of Simulation Modelling, vol. 8, no. 2, p. 102-113.

[22] Ficko, M., Brezovnik, S., Klancnik, S., Balic, J., Brezocnik; M., Pahole, I. (2010). Intelligent design of an unconstrained layout for a flexible manufacturing system. Neurocomputing, vol. 73, p. 639-647.

[23] Vujica-Herzog, N., Tonchia, S., Polajnar, A. (2009). Linkages between manufacturing strategy, benchmarking, performance measurement and business process reengineering. Computers & Industrial Engineering. October 2009, vol. 57, no. 3, p. 963-975.

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 811-816 Paper received: 29.04.2009 UDC 662.756.3 Paper accepted: 02.09.2010

*Corr. Author's Address: Çukurova University, Department of Mechanical Engineering, 01330, Adana, Turkey, [email protected] 811

Biodiesel Production from Ricinus Communis Oil and Its Blends with Soybean Biodiesel

Oğuz Yunus Sarıbıyık1 - Mustafa Özcanlı2 - Hasan Serin2 - Selahattin Serin1 - Kadir Aydın2,*

1Çukurova University, Department of Chemistry, Turkey 2Çukurova University, Department of Mechanical Engineering, Turkey

In this study, local vegetable oil named as Ricinus Communis (RC) is used as the raw material for

the production of biodiesel. In order to obtain RC oil, Soxhalet Extraction apparatus was used. This paper deals with the transesterification of Ricinus Communis oil with methanol to produce biodiesel. Moreover, this study analysis the fuel properties of RC biodiesel and soybean biodiesel blends. Various properties of the RC biodiesel, Soybean biodiesel and their blends such as the cold filter plugging point (CFPP), cetane number, flash point, kinematic viscosity and density were determined. Test results were compared well with European biodiesel standards EN 14214. Analysis showed that the cetane number and the cold flow behavior of the RC biodiesel and soybean biodiesel blends were improved due to the high cetane number (80) and the low cold filter plugging point (-35 oC) of RC biodiesel. © 2010 Journal of Mechanical Engineering. All rights reserved. Keywords: Ricinus Communis, biodiesel, transesterification, biodiesel properties, cetane number, CFPP

0 INTRODUCTION

Biodiesel is an alternative fuel for diesel engines that is produced by chemically reacting vegetable oil or animal fat with alcohol and the catalyst. Biodiesel is miscible in diesel fuel, and can be easily blended with diesel fuel with minor or no modifications to the engine and fuel system. According to EU guidelines the consumption of bio-fuels for road transportation should represent 20% of the total fuel consumption by 2020 and the use of bio-fuels will be stimulated by environmental aspects [1]. For these reasons, biodiesel has become a popular topic in energy sources.

The most common way to produce biodiesel is the transesterification method, which refers to a catalyzed chemical reaction involving vegetable oil and alcohol to yield fatty acid alkyl esters (i.e., biodiesel) and glycerol [2]. The reaction requires a catalyst, usually a strong base, such as sodium and potassium hydroxide or sodium methylate. A catalyst is usually used to improve the reaction rate and the yield. Since the reaction is reversible, excess alcohol is used to shift the equilibrium to the product side. Especially methanol is used as alcohol because of its low cost and its physical and chemical advantages. Methanol can quickly react with vegetable oil and NaOH can easily dissolve in it.

To complete a transesterification reaction stoichiometrically, a 3:1 molar ratio of alcohol to triglycerides is necessary. In practice, the ratio needs to be higher to drive the equilibrium to a maximum ester yield [3].

The transesterification conditions and biodiesel properties of RC oil were studied [4]. It has been concluded that the blends of RC biodiesel and diesel fuel up to approximately 40% of RC biodiesel meet most of the specifications of EN590. An optimization of transesterification of RC oil using central composite rotational design (CCRD) and response surface modeling method (RSM) has been reported by authors [5]. On the other hand, technical process and production cost of biodiesel plants from castor bean oil through a transesterification reaction using ethanol was studied [6]. It has been concluded that the castor bean oil is more expensive than the conventional ones used to produce biodiesel.

RC is cultivated for the seeds which yield fast-drying, non-yellowing oil, used mainly in industry and medicine. RC oil is critical to many industrial applications because of its unique ability to withstand high and low temperatures [7]. It is used in coating fabrics and other protective coverings, in the manufacture of high-grade lubricants, transparent typewriter and printing inks, in textile dyeing (when converted into sulfonated Castor Oil or Turkey-Red Oil, for


Sarıbıyık, O.Y. – Özcanlı, M. – Serin, H. – Serin, S. – Aydın, K. 812

dyeing cotton fabrics with alizarine), in leather preservation. Hydrogenated oil is utilized in the manufacture of waxes, polishes, carbon paper, candles and crayons. 'Blown Oil' is used for grinding lacquer paste colors, while when it is hydrogenated and sulfonated it can be used for preparation of ointments. Castor Oil Pomace, the residue after crushing, is used as a high-nitrogen fertilizer.

Previous studies on castor oil suggest that its uniquely high level of the hydroxy fatty acid ricinoleic acid may impart increased lubricity to the oil and its derivatives as compared to other vegetable oils [8].

1 MATERIAL AND METHODS

1.1 Materials and Apparatus

Ricinus Communis (Castorbean) seeds used in this study were supplied from Turkish vegetable sources. RC oil was produced by using Soxhalet Extraction method. Nearly 35 to 37% oil content was extracted from RC seeds. The chemicals which were used during the experiments were purchased from Merck and methanol was purified prior to use. Table 1 shows the technical specifications of chemicals. Diesel fuel with respect to EN 590 standards was purchased and used during the experimental studies.

Table 1. Specifications of chemicals

Chemicals Density [kg/m3]

Purity [%]

Methanol 790 99.5 Sodium Hydroxide Pellet - >99 Acetic Acid 1049 >98

Instruments used for analyzing the

product; Zeltex ZX 440 NIR petroleum analyzer with an accuracy of ±0.5 for determining cetane number; ISL CPP 97-2 with an accuracy of ±0.5 oC for pour point and cold filter plugging point; Koehler Saybolt viscosity test for determining the viscosity; Kyoto electronics DA-130 for density measurement and Tanaka flash point control unit FC-7 for flash point determination. Fatty acid methyl ester content in the esterified oil was determined by Gas Chromatograph (GC equipped with a FID detector, capillary SP TM 2380 column (60 m x 0.25 mm x 0.2 m) Shimadzu GC-

14A) and GC/MS, Thermo-Finnigan TR5 MS gas chromatograph connected to a TR-5 capillary column (60 m x 0.25 mm ID x 0.25 UM film). 1.2 Production and Purification Methods 1.2.1 Oil Production from Ricinus Communis seeds

Oil was extracted from RC seeds using Soxhlet extraction apparatus (1000 ml) and hexane was used as solvent. The dried Ricunus Communis seeds (4 x 36 g) were placed into a cellulose paper cone and extracted with 600 ml hexane for 5 h. The solvent was removed via a rotary vacuum distillation at 40 oC. The residue was filtered. Finally, the RC oil was stored at 20 oC [10]. 1.2.2 Reaction Conditions and Equipment

A glass pilot reactor with a 1000 ml volume was used for atransesterification reaction. It is equipped with mechanical stirrer, cascade heater system, contact thermometer and condenser with a guard tube to prevent moisture entering into the system. 400 g of neutral Ricinus Communis oil (crude grade) was added to the reactor and heated up to 60 oC with stirring. After sodium methoxide addition (80 ml methanol and 4 g NaOH), stirring condition (600 rpm) and the reaction were continued for two hours at constant temperature. 1.2.3 Purification of the Produced Biodiesel

All the products of the transesterification reaction in this study were allowed to settle overnight so as to enhance separation. Two distinct liquid phases were formed during separation in such a manner that the crude ester phase presented at the top and the glycerol phase at the bottom. The glycerol phase was removed and the methyl esters layer was then washed with warm diluted acetic acid at 60 oC repeatedly until the residual became clear. The excess methanol and water in the ester phase were then removed by heating the product to 110 oC [9] to [11].

The primary purpose of the biodiesel washing step is to remove any soaps formed during the transesterification reaction. In addition, the warm diluted water with acetic acid provides neutralization of the remaining catalyst and removes product salts.



CH2

CH

CH2

OCOR1

OCOR2

OCOR3

3CH3OH

CH2

HC

CH2

OH

OH

OH

R1COOCH3

R2COOCH3

R3COOCH3

Trigliseride Methanol Glycerol Methyl esters

Catalyst

Fig. 1. General equation for the transesterification of triglycerides

The use of warm water prevents

precipitation of saturated fatty acid esters and retards the formation of emulsions with the use of a gentle washing action. Slightly acidic water eliminates calcium and magnesium contamination and neutralizes remaining base catalysts. Gentle washing prevents the formation of emulsions and results in a rapid and complete phase separation [12].

2 RESULTS AND DISCUSSION

The fatty acid composition of RC oil

determined by GC/MS is shown in Table 2. The methyl ester content of the reaction mixture was quantified using a sample (150 ml) which was taken from the reaction mixture at specified periods. The conversion ratio of triglyceride to methyl ester was analyzed by GC using an FID in both ASTM D 6751 and EN 14214 for soybean oil and RC oil. The result of transesterification

reaction showed that all conversion values were in agreement with EN 14214. Table 3 shows the fatty acid methyl ester properties of the biodiesel produced from RC oil.

Biodiesel produced from RC oil was found to be much more viscous than other, more commonly tested, vegetable oil fuels (Table 4). Viscosity is one of the main drawbacks in the sense that its value is high, which means that it must be preheated in the fuel tank or blended with straight diesel during the cold winter periods [13]. According to the results, it has been determined that pure RC biodiesel usage can cause problems in the injection system because of its high viscosity. In order to solve the viscosity problem it can be suggested that RC biodiesel may use a mixture of others either diesel or biodiesels. Therefore, blending with Diesel fuel or other biodiesels may be the best solution for RC biodiesel usage in compression ignition engines.

Table 2. Fatty acids contents of RC Fatty acids Chemical formula % Palmitic acid CH3(CH2)14COOH 1.71 Linoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH 7.41 Oleic acid CH3(CH2)7CH=CH(CH2)7COOH 6.40 Stearic acid CH3(CH2)16COOH 2.04 Ricinoleic acid CH3(CH2)5CH(OH)CH2CH=CH(CH2)7COOH 82.44

Table 3. Analysis data of the RC biodiesel

Properties Units RC

biodiesel EU biodiesel EN 14214 values Test methods

% FAME - 98 96.5 prEN 14103 Kinematic viscosity at 40 oC mm2/s 11.5 3.5 – 5.0 EN ISO 3104 Density at 15 oC kg/m3 920 860 – 900 EN ISO 12185 Flash point oC >130 >120 EN ISO 3679 Cetane number - 80 >51 EN ISO 5165 Cold filter plugging point oC -35 Summer < 0, Winter < -15 EN 116 Pour point oC -30 Summer < 4.0, Winter < -1.0 ISO 3016



Although the viscosity and the density of RC biodiesel were noted to be greater than that of diesel fuel, the cetane number was found in the range of EN 14214. Cetane number is known as a measurement of the combustion quality of diesel fuel. It has been observed that Ricinus Communis biodiesel has a higher cetane number, which causes shorter ignition delays, and thus, higher efficiency in engine.

In addition, the high flash point (more than 120 oC) makes the RC biodiesel in compliance with EN 14214.

Biodiesel derived from RC oil has a lower cold filter plugging point (CFPP) than other biodiesels.

The comparison of RC biodiesel with various vegetable oil esters is shown in Table 4 [14].

2.1. Low Temperature Property Study

The behavior of fuels under low

temperature is an important quality measure. In order to assess biodiesel fuel performance in cold-temperature, various parameters have been

suggested, including pour point (PP) and cold-filter plugging point (CFPP) [15].

The blends of RC and soybean biodiesel samples were therefore examined for their low temperature properties to study the effect of RC biodiesel on soybean biodiesel PP and CFPP. The results shown in Table 5 reveal that the higher RC biodiesel amount in blends gives the decreased PP and CFPP values of RC biodiesel-Soybean biodiesel blends.

2.2 Cetane Number Study

One of the major problems associated with

the use of biodiesel, especially the one produced from soybean oil, is its low cetane number [16]. However, RC biodiesel has a higher cetane number, comparable to conventional biodiesels.

Cetane number and cold flow properties were determined in selected blends of RC biodiesel and soybean biodiesel. As shown in Table 5, the blending of 5% RC biodiesel to soybean biodiesel increased the cetane number of Soybean biodiesel from 45 to 48.

Table 4. Comparison of RC biodiesel with various biodiesels

Biodiesel produced from

Kinematic viscosity at

40 oC [mm2/s] EN ISO 3104

Cetane number EN ISO

5165

Pour point [oC]

ISO 3016

Cold filter plugging point [oC] EN 116

Flash point [oC]

EN ISO 3679

Density [kg/l]

EN ISO 12185

Peanut oil 4.9 54 5 - 176 0.883 Soybean oil 4.5 45 1 -4 178 0.885 Babassu oil 3.6 63 4 - 127 0.875 Palm oil 5.7 62 13 11 164 0.880 Sunflower oil 4.6 49 1 -2 183 0.860 Ricinus Communis oil

11.5 80 -30 -35 >130 0.920

Diesel EN 590 3.06 50 - -16 76 0.855

Table 5. Comparison of properties of RC biodiesel, soybean biodiesel properties and their blends

Biodiesel Kinematic

viscosity at 40 oC [mm2/s]

Cetane number

Cold filter plugging [oC]

Pour Point [oC]

Density [kg/m3]

Soybean 4.2 45 -4 1 884 Ricinus Communis (RC) 11.5 80 -35 -30 920 5% RC + 95% Soybean 4.5 48 -5 -2 887 10% RC + 90% Soybean 4.9 51 -7 -3 888 20% RC + 80% Soybean 5.6 56 -10 -6 891 50% RC + 50% Soybean 7.8 63 -20 -15 902



10% RC biodiesel and 90% soybean biodiesel, and 20% RC biodiesel and 80% soybean biodiesel blends were tested for cetane number and the results found were 51 and 56 respectively. Thus, the blending of RC biodiesel in soybean biodiesel increased the cetane numbers of the blends.

3 CONCLUSIONS

This study presents biodiesel production

from RC oil and its determined biodiesel properties. It has been observed that while cetane number, flash point, cold filter plugging point and the pour point values of RC biodiesel were found in compliance with EN 14214, the viscosity and the density values were determined to be out of range. On the other hand, as soybean biodiesel has a low cetane number and high low temperature properties, the effect of RC biodiesel addition to soybean biodiesel was investigated. The conclusions of this study are summarized as follows: 1. RC oil can be used as a biodiesel raw

material with its high oil content and its non-edible characteristics.

2. Cetane numbers of blends were increased with increased RC biodiesel contents. For this reason, RC biodiesel can be used as a cetane additive to improve cetane number of different biodiesel fuels.

3. The pour point and CFPP values were found to decrease with the increased RC biodiesel. From this point of view, RC biodiesel can be a very effective cold flow additive.

4. It can be said that pure RC biodiesel usage can cause problems in injection systems because of its high viscosity.

4 REFERENCES

[1] Hribernik, A., Kegl, B. (2007). The influence

of biodiesel on the combustion and emission characteristics of a diesel engine. Strojniški vestnik – Journal of Mechanical Engineering, vol. 53, no. 10, p. 683-695.

[2] Zhang, Y., Dube, M.A., McLean, D.D., Kates, M. (2003). Biodiesel production from waste cooking oil: 1. Process design and technological assessment. Bioresource Technology, vol. 90, p. 1-16.

[3] Fangrui, M., Milford, A.H. (1999). Biodiesel Production: A review. Bioresource Technology, vol. 70, p. 1-15.

[4] Canoira, L., Galean, J.G., Alcantara, R., Lapuerta, M., Contreras, R.Y. (2010). Fatty acid methyl esters (FAMEs) from castor oil: Production process assessment and synergistic effects in its properties. Renewable Energy, vol. 35, p. 208-217.

[5] Cavalcante, K.S.B., Penha, M.N.C., Mendonça, K.K.M., Louzeiro, H.C., Vasconcelos, A.C.S., Maciel, A.P., Souza, A.G., Silva, F.C. (2010). Optimization of transesterification of castor oil with ethanol using a central composite rotatable design (CCRD). Fuel, vol. 89, p. 1172-1176.

[6] Santana, G.C.S., Martins, P.F., Silva, N.L., Batistella, C.B., Filho, R.M., Maciel, M.R.W. (2010). Simulation and cost estimate for biodiesel production using castor oil. Chemical Engineering Research and Design, vol. 88, p. 626-632.

[7] Comar, V., Tilley, D., Felix, E., Turdera, M., Neto, M.C. (2004). Comparative emergy evaluation of castorbean (Ricinus Communis) production systems in Brazil and the U.S. Proceedings of IV Biennial International Workshop “Advances in Energy Studies, p. 227-237.

[8] Goodrum, J.W., Geller, D.P. (2005). Influence of fatty acid methyl esters from hydroxylated vegetable oils on diesel fuel lubricity. Bioresource Technology, vol. 96, p. 851-855.

[9] Puhana, S., Vedaramana, N., Rama, B.V.B., Sankarnarayananb, G., Jeychandranb, K. (2005). Mahua oil (Madhuca Indica seed oil) methyl ester as biodiesel-preparation and emission characterstics. Biomass and Bioenergy, vol. 28, p. 87-93.

[10] Saloua, F., Saber, C., Hedi, Z. (2010). Methyl ester of [Maclura pomifera (Rafin.) Schneider] seed oil: Biodiesel production and characterization. Bioresource Technology, vol. 101, p. 3091-3096.

[11] Kafuku, G., Mbarawa, M. (2010). Biodiesel production from Croton megalocarpus oil and its process optimization. Fuel, vol. 89, p. 2556-2560.

[12] Van Gerpen, J., Shanks, B., Pruszko, R., Clements, D., Knothe, G. (2004). Biodiesel Production Technology. National Renewable Energy Laboratory, Colorado.



[13] McGuiness, P. (2008). Fuelling the car of the future. Strojniški vestnik - Journal of Mechanical Engineering, vol. 54, no. 5, p. 356-363.

[14] Barnwal, B.K., Sharma, M.P. (2005). Prospects of biodiesel production from vegetable oils in India. Renewable and Sustainable Energy Reviews, vol. 9, p. 363-378.

[15] Voća, N., Krička, T., Janušić, V., Jukić, Z., Matin, A., Kiš, D. (2008). Fuel properties of biodiesel produced from different raw materials in Croatia. Strojniški vestnik - Journal of Mechanical Engineering, vol. 54, no. 3, p. 232-244.

[16] Ramadhas, A.S., Jayaraj, S., Muraleedharan, C. (2004). Use of vegetable oils as I.C. engine fuels-A review. Renewable Energy, vol. 29, p. 727-742.

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 817-822 Paper received: 08.05.2008 UDC 536.75:536.711 Paper accepted: 30.09.2010

*Corr. Author's Address: University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Ivana Lučića 5, 10000 Zagreb, Croatia, [email protected] 817

Entropy Generation and Exergy Efficiency in Adiabatic Mixing of Nitrogen and Oxygen Streams of Different

Temperatures and Environmental Pressures

Antun Galović* - Nenad Ferdelji - Saša Mudrinić 1 University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Croatia

The paper presents a non-dimensional model of entropy generation and exergy efficiency in the

adiabatic mixing of a nitrogen stream and oxygen stream with different temperatures and environmental pressure. The resulting mixture has the same, i.e. environmental, pressure. Non-dimensional variables in the model represent the ratio of thermodynamic stream temperatures u, the ratio between the thermodynamic temperature of one stream and the environmental temperature u1, and the mole fraction y1 of one of the streams. The model comprises irreversibility due to different temperatures of streams because of the mixing of different gases, while exergies of streams also comprise their mole fractions in the ambient air (atmosphere). In this respect, the model takes the standard values of mole fractions of oxygen and nitrogen of yO2 = 0.21 and yN2 = 0.79. The values of stream mole fractions at which maximum values of entropy generation and minimum values of exergy efficiencies occur are given. Calculation results are given in respective diagrams. © 2010 Journal of Mechanical Engineering. All rights reserved. Keywords: analytic model, entropy generation, exergy efficiency, mixing of nitrogen and oxygen streams

0 INTRODUCTION Adiabatic mixing of ideal gas streams

often occurs in thermal engineering. Usually, it is required for obtaining a particular temperature of the stream at the mixing chamber inlet. For given conditions of inlet streams, the mass flow ratio of streams, gives the required temperature at the outlet of the mixing chamber. Such processes belong to a group of characteristic irreversible processes in which the irreversibility is caused by two factors: a change in stream temperatures and the mixing of different ideal gases. Both of these factors, and consequently the total irreversibility and the exergy efficiency, are directly affected by mole fractions of particular streams in the mixture. As expressions for exergy streams in this paper also contain their partial pressures (or concentrations) in the environment, the analytic model also gives expressions for the streams of two-atom gases, i.e. of oxygen and nitrogen, whose mole fractions in the surrounding air (atmosphere) are known. These gases have the same isentropic exponent of = 1.4 [1].

1 ANALYTIC MODEL

1.1 Non-Dimensional Representation of Entropy Generation

In the observed case, two streams of gases

enter the isolated system, relevant for the entropy increase; therefore, according to [2], the entropy increase of the isolated system is expressed by the Eq. (1):

'

m 1n1 m mis.syst

1

'm 2

n2 m m2

ln ln

ln ln .

p

p

T pS q C R

T p

T pq C R

T p

(1)

One can easily obtain the temperature Tm at the outlet of the adiabatic mixing chamber from the First Law of thermodynamics:

2211m TyTyT . (2)

Using known Eqs., according to [2]:

;1-m

m R

C p ;n

n1

'

11 q

q

p

py y2 = 1 - y1


Galović, A. - Ferdelji, N. - Mudrinić, S. 818

and introducing the non-dimensional ratio of the temperatures of inlet streams,

1

2

T

Tu . (3)

Eq. (1) can be easily transformed into a non-dimensional form of:

is.syst1 1 1 1

n m

11

1 ln 1 ln

y 1ln ln .

1

Sy y y y

q R

u uy u

u

(4)

In Eq. (4), the first two members on the right side of the equation represent the entropy increase caused by the mixing of two different gases, while the last addend represents the entropy increase caused by different inlet temperatures of gases. The value of isentropic exponent κ is 5/3, 7/5 and 4/3 for one-atom, two-atom and three-atom gases, respectively [1]. From the same Eq., a physically justified fact that for y1 = 0.0 and y1 = 1.0, the value of entropy increase of the isolated system is equal to 0 can easily be obtained. If u = 1.0 is inserted into Eq. (4), then only the first two members remain, representing only the entropy increase caused by the mixing of two streams of different ideal gases. A detailed analysis of such a case can be found in [3]. If Eq. (4) is represented as a function of the mole fraction y1, for given values of u and κ, a diagram given in Fig. 1 is obtained.

The diagram shows that each curve, with its respective u, has its maximum for a physically justified local extreme and that each parametric curve u has a determined mole fraction y1stat (abscissa of a stationary point), which follows from a necessary condition for the existence of the function extreme (4). From this condition, the following equation is derived:

1stat1stat

1stat

1stat

1-1 ln

1 ln 1 0.1

yy u u

y

y u u u u

(5)

m

n

is.s

yst

RqS

y1

= 1.4

Fig. 1. Quantitative representation of non-

dimensional entropy generation depending on the mole fraction y1, temperature ratio u in the

adiabatic mixing of two streams of two different two-atom gases, = 1.4

It is obvious that the required value y1stat

from Eq. (5) cannot be expressed explicitly; therefore, Newton’s method [4] is used to solve the above equation. Table 1 gives the results of a numerical estimation of y1stat together with the respective maximum entropy increases, for κ = 1.4 and for specified values of u.

From Table 1, it can be observed that y1stat increases with an increase in u. If u = 1.0, then the entropy increase is caused only by the mixing of two different gas streams. In that case the value of y1stat = 0.5 with the respective entropy increase of 0.693 follows explicitly from Eq. 5 since the addend from this Eq. is dropped. If the mixing of two streams of the same gases, the same pressure and different temperatures is concerned, then y1stat can also be directly (explicitly) expressed from Eq. 5 since the first addend from the above Eq. is dropped.

uu

uuuy

ln1

ln1stat1

. (6)

If the values of y1stat obtained from Eqs. (5) and (6) are shown in a diagram, the result is a quantitative representation given in Fig. 2.

Table 1. Values of mole fraction y1stat and respective entropy increases depending on the value u u 0.1 0.25 0.50 0.75 1.0 2.0 3.0 4.0 5.0 y1stat 0.36 0.432 0.483 0.498 0.50 0.517 0.545 0.569 0.587 Sis.syst/(qnRm) 2.808 1.497 0.900 0.729 0.693 0.900 1.204 1.497 1.765


Entropy Generation and Exergy Efficiency in Adiabatic Mixing of Nitrogen and Oxygen Streams of Different Temperatures and Environmental Pressures 819

y 1st

at

u

Fig. 2. Effect of the mixing of two streams of different ideal gases on the displacement of y1stat

depending on the temperature ratio u The diagram shows the effect of the

mixing of two different ideal gases on the displacement of y1stat at which maximum entropy increases occur. For u < 1.0, the mixing of different ideal gases displaces the stationary point to higher values, while for u > 1.0 the displacement is in the direction of lower values. For u = 1.0, y1stat = 0.5 and at that point, the function under consideration has the inflection point with the horizontal tangent.

2 EXERGY EFFICIENCY AND AN

ANALYSIS OF THE MIXING PROCESS Exergy destruction of the observed process

can be adequately described by means of the so-called exergy efficiency, which can, according to [5], be defined in the following way:

21

is.systenv

ex 1EE

ST

, (7)

where 1E and 2E represent the exergies of

streams of oxygen and of nitrogen at the mixing chamber inlet, which can be determined, according to [6], by the following Eq.:

11 n1 m 1 env env m m

env 1

1ln lnp p

env

TE q C T T T C R

T y

,

(8)

env

p yR

T

TCTTTCqE

2

m

env

2mpenvenv2mn12

1lnln

. (9)

The mole fraction of oxygen in the air (atmosphere) is yO2 = y1env = 0.21, and of nitrogen yN2 = y2env = 0.79, so that these members in the above Eqs. give an additional contribution to the exergy value of the streams with respect to their concentration in the environment.

By using Eqs. (1) to (3) and Eqs. (7) and (8), it is possible to transform Eq. (7) into the following form:

nvnv yu

u

uuuu

yuuuuy

yu

uuy

y

yuyu

e2

1

1

11

e1

111

11

1

111

ex1

ln1

ln1

ln1

ln1

1ln11

ln-1

ln1

ln

1

,

(10)

where

1

ok1 T

Tu . (11)

It can be easily proved that from Eq. (11) it follows that the value of exergy efficiency is equal to one for y1 = 0.0 and for y1 = 1.0 since in these cases, either stream 2 or stream 1 is involved. Consequently, there is no mixing process and as a result no exergy destruction.

The results of exergy efficiency calculation for u1 = 0.5, 1.0 and 2.0, depending on the mole fraction and parametric values of u = 0.5; 1.0; 2.0; 3.0; 4.0 and 5.0, are shown in diagrams in Figs. 3 to 8.

ex

y1

u1 = 1.0

Fig. 3. Dependence of exergy efficiency on the mole fraction y1 and the temperature ratio u for

u1 =1.0 The diagram shows that each parametric

value of u has the minimum value εmin for the unambiguously determined mole fraction y1 = y1stat. It can be noted that while the value of u is increasing towards one, the value of εmin



decreases, and the values of respective y1 = y1stat also decrease. For u > 1.0, the values of εmin increase with an increase in u, as well as the values of y1 = y1stat, i.e. stationary points move to the right. The values of y1stat follow from the necessary condition of the existence of an extreme in Eq. (10). The equation which follows from this condition has to be solved numerically. In this case, Newton’s method is applied again and the calculation results are shown in the diagram in Fig. 4. For the limit values of y1 = 0.0 and y1 = 1.0, regardless of all parametric values of u, the values of exergy efficiency are equal to one.

miny1stat

u1 = 1.0

u

Fig. 4. Value of mole fractions y1stat and respective minimum exergy efficiencies ex min depending on

the values of u for u1 =1.0 The diagram shows that the value of the

function y1stat decreases at first and reaches the minimum for u = u1 = 1.0, and then increases continuously. But the curve representing the function εex min shows two local extremes, a maximum and a minimum. The maximum occurs close to u = 0.5, and the minimum occurs for u = 1.0, where the minimum absolute value of exergy destruction is also obtained. For u > 1.0, the function εex min rises continuously.

If Eq. (10) is quantified for u1 = 0.5, with the same parametric values of u as in the previous case, the results shown in the diagram in Fig. 5 are obtained.

The diagram shows that in this case the mole fraction y1stat moves to the area of higher values with respect to the previous case. The

values of y1stat with the respective εexmin, also obtained by a numerical solution of the condition of extreme in Eq. (10), are shown in the diagram in Fig. 6.

ex

y1

u1 = 0.5

Fig. 5. Exergy efficiency depending on the mole

fraction y1 and the temperature ratio u for u1 = 0.5

y1statmin

u1 = 0.5

u Fig. 6. Values of mole fractions y1stat and

respective minimum exergy efficiencies ex min depending on the value of u for u1 = 0.5

The diagram shows that the function y1stat

has a minimum for y1stat. The function of respective u = u1 = 0.5 also shows a minimum value in the absolute sense for u = u1 = 0.5. After that, the function rises steeply and after u > 1.5 it reaches almost a constant value, which is only slightly sensible to the values 1.5 < u < 5.0. A more detailed analysis shows that for u = 3.5, the


Entropy Generation and Exergy Efficiency in Adiabatic Mixing of Nitrogen and Oxygen Streams of Different Temperatures and Environmental Pressures 821

function εe min shows a maximum value of εex min = 0.79726, while εex min (u = 5.0) = 0.7942, which provides a numerical confirmation of the previous statement.

Figs. 8 and 9 give a graphical representation of the function analysis (10) for u1 = 2.0.

ex

y1

u1 = 2.0

Fig. 7. Exergy efficiency depending on the mole fraction y1, and temperature ratio u for u1 =2.0

miny1stat

u1 = 2.0

u

Fig. 8. Values of mole fractions y1stat and respective minimum exergy efficiencies min

depending on the value of u for u1 =2.0 Fig. 7 shows that in the case of a minimum

value of εex min, lower values of mole fractions y1stat are obtained with respect to the case in which u1 = 1.0. In addition, it can be concluded

that these values of local extremes are situated in a significantly large area of mole fractions y1stat, with respect to the previous two cases. This is explicitly shown in the diagram in Fig. 8.

The diagram shows that in this case again the function y1stat has a local extreme (minimum) for u = u1 = 2.0, while the maximum of y1stat = 0.52 = const. is obtained for a relatively wide range of u, i.e. 0.1 < u < 0.3. After that, y1stat falls to the absolute minimum of y1stat (u = 2.0) = 0.18, and it continuously rises to y1stat (u = 5.0) = 0.26197. The function ex min shows a local extreme (maximum) for u = 0.6 (ex min(u = 0.6) = 0.63753). After that, the function ex min falls, but it does not reach its minimum for u = 2.0 but for u = 2.3, where the value of the minimum equals 0.06783. Logically, having reached its minimum, the function ex min rises continuously and reaches the value of ex min(u = 5.0) = 0.2697 at the end of the examined interval.

3 CONCLUSION

The non-dimensional analytic model for

the calculation of the isolated system entropy increase presented in this paper can generate not only the expressions related to the mixing of two two-atom gases, but also the ones related to the mixing of two streams having the same isentropic exponent . Here, the model enables the quantification of the effects of all relevant variables, i.e. of the ratio of stream temperatures, mole fractions and isentropic exponent, on the entropy increase. It has been shown that for every ratio of inlet stream temperatures there is a mole fraction of one of the streams, the so-called “stationary” mole fraction y1stat, for which a maximum entropy increase is obtained, as shown in the diagram in Fig. 1. The effect of the ratio of inlet stream temperatures u on the value of y1stat has been quantified, and the calculation results have shown that the value of y1stat increases with an increase in the ratio u.

Secondly, it has been established that the mixing of two streams of different ideal gases moves y1stat towards higher values for the values of 0 < u < 0.5, in comparison with the mixing of two streams of the same ideal gases. For 0.5 < u < 1, the situation is reversed. As expected, for u = 1.0, the same value of y1stat = 0.5 (Fig. 2) is obtained.



On the other hand, it has been shown by the model that the exergy efficiency and exergy destruction are affected not only by the factors listed above, but also by the environmental temperature, which has been introduced into the algorithm by the temperature ratio u1, together with the mole fraction (concentration) of stream gases in the environment (atmosphere). This is the reason why the streams of oxygen and nitrogen, whose mole fractions in the environment (atmosphere) are known (fixed), have been analysed. A quantitative analysis carried out for particular given values of relevant variables shows that for every ratio of inlet temperatures there is a stream mole fraction for which a minimum value of exergy efficiency or a maximum value of exergy destruction is obtained. Figs. 3, 5 and 7 show a quantitative effect of relevant variables on the value of exergy efficiency ex min. If these minimum values for a given u1 are shown as depending on u, then the minimum value of ex min, also in its absolute value, occurs for y1stat(u u1). This means that the highest rate of exergy destruction is generated by processes in which the mole fraction amounts to y1 = u = u1, as shown quantitatively by Figs. 4, 6 and 8. Also, from these diagrams one can quantitatively determine the effect of the values of u, for a given u1, on the value of ex min.

4 NOTATIONS

Cmp molar heat capacity p = const [J/(kmol K)]

exE exergy [W]

ex exergy efficiency isentropic exponent qn quantity flow [kmol/s] p pressure [Pa] p' partial pressure [Pa] Rm universal (molar) gas constant [J/(kmol K)]

S entropy flow [W/K]

T thermodynamic temperature [K] u ratio of thermodynamic temperatures of

inlet streams u1 ratio of thermodynamic stream temperature

and the environment y stream mole fraction in the mixture

Indices is.syst isolated system m condition of the stream at the mixing

chamber outlet min minimum env environmental stat stationary (in relation to the function

local extreme) 1 stream 1 at the mixing chamber inlet

(stream of oxygen) 2 stream 2 at the mixing chamber inlet

(stream of nitrogen)

5 REFERENCES

[1] Stephan, K., Mayinger, F. (1998). Thermodynamik, Band 1: Einstoffsysteme, Grundlagen und technische Anwendungen, 15. Auflage. Springer Verlag, Berlin.

[2] Bošnjaković, F., Knoche, K.F. (1988). Technische Thermodynamik, Teil I, 7., vollstaendig neubearbeitete und erweiterte Auflage. Steinkopf Verlag, Darmstadt.

[3] Bejan, A. (1996). Entropy generation minimization. CRC Press, New York.

[4] Kreyszig, E. (1993). Advanced engineering mathematics, 7. ed. John Wiley & Sons, Inc., New York.

[5] Moran, M.J. (1999). Engineering thermodynamics. CRC Press LLC, Ohio.

[6] Fratzscher, W., Brodjanskij, V.M., Michalek, K. (1986). Exergy, Theirie und Anwendung. VEB Verlag, Leipzig.

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 823-832 Paper received: 02.07.2010 UDC 621.73:669.721.5 Paper accepted: 26.10.2010

*Corr. Author's Address: TECOS Slovenian Tool and Die Development Centre, Kidričeva 25, 3000 Celje, Slovenia, [email protected] 823

Analysis of Deformation Characteristics of Magnesium AZ80 Wrought Alloy under Hot Conditions

Dominik Kobold1,* - Tomaž Pepelnjak2 - Gašper Gantar1 - Karl Kuzman2

1 TECOS Slovenian Tool and Die Development Centre, Slovenia 2 University of Ljubljana, Faculty of Mechanical Engineering, Slovenia

Light-weight and environmentally friendly materials with good mechanical properties are much

appreciated in various modern applications. Weight reduction can improve the performance of many components while reducing the fuel consumption of vehicles.

Magnesium is one of the most popular weight-reducing materials because of its low density, good mechanical properties, large natural reserves and good machining properties. The strength, stiffness and favourable metallographic structure of products can be improved by a forging process in which components are shaped from feedstock slugs by applying compressive force through various forging dies. However, widespread usage of forging technology in industrial practice is very rare in comparison to casting, due to the specific deformation characteristics of magnesium having a hexagonal close packed basal crystal structure.

This paper deals with the determination of the influence of the most important process parameters on the deformation process of magnesium alloys. On the basis of extensive experimental study, anisotropic flow and the impact of the most important input process factors on the plastic deformation of AZ80 wrought alloy are considered. The results presented in this paper are directly related to industrial practice and have significant potential as a case study for the further development of FEM models capable of predicting anisotropic material flow during applied plastic deformation. The studies presented in the paper also make possible defining recommended technological parameters of the forging process. ©2010 Journal of Mechanical Engineering. All rights reserved. Keywords: magnesium forging, anisotropy, plastic deformation, flow curves, AZ80, wrought magnesium alloys

0 INTRODUCTION In recent years, light-weight design has

become even more important due to several benefits relating to improvements of the performances of many applications. Low density, good mechanical properties, recycling possibilities and (not the least) competitive price play important roles in the selection of the product’s material.

Since magnesium alloys are the lightest engineering metallic materials having good mechanical properties comparable to aluminium alloys [1], vast potential for use has been found in many different engineering applications in which weight is extremely important. However, in order to meet commitments to reduce the fuel consumption of vehicles, widespread usage of magnesium components in automotive industry is expected in the short-term future [1] and [2].

Nowadays, high-pressure die casting of magnesium alloys is mostly in use due to its high

productivity and the possibility of producing complex net-shape products. However, due to the high cost of casting machines and dies, only the production of large series is reasonable. Due to low mechanical properties and material porosity of casted products, (hot) forging can be a more appropriate technique for producing of structural magnesium components. Specifically, hot forging has been regarded as one of the main processing techniques enabling net-shape production and the possibility of obtaining high deformation combined with very good mechanical properties of products [3].

Despite the benefits, the forging of magnesium alloys is rarely in use in industrial practice due to specific deformation characteristics as well as a lack of know-how and practical experience related to deformation behaviour in applied plastic deformation.

However, proper design of the robust forming process needs consideration of many initial process parameters (material, machines


Kobold, D. – Pepelnjak, T. – Gantar, G. – Kuzman, K. 824

types and settings, CAD models, tools, initial temperatures, ram speeds etc.) to provide tailored and cost-efficient technologies for the production of components.

This paper deals with a study for the determination of the influence of various process parameters on the deformation process and anisotropic flow during compression loading conditions. The studies presented in the paper also make possible defining recommended process parameters of the forging process and also have significant potential for industrial use.

1 BACKGROUND

It is generally known that magnesium has

a hexagonal close packed (h. c. p.) basal crystal lattice with a significant effect on plastic deformation. For h. c. p., it is typical that plastic deformation applied in a conventional way at room temperature is not possible, because only slips of basal crystal planes (0001) are available [4]. At temperatures above 230 C [5], formations of additional prismatic and pyramidal gliding planes as well as a twining mechanism enable sufficient plastic deformation [4] to [6]. Moreover, the formation of gliding mechanisms depends on both on loading direction and on loading type (compression or tension, respectively), and causes anisotropic properties and asymmetry of yielding criterion as well [4].

Further, plastic deformation of magnesium as cast feedstock alloys is not possible due to too big crystal grains, with diameters from 200 to 400 m, usually formed during solidification and secondly, large material porosity [1]. Generally, during preparation of wrought feedstock alloys, a pre-deformation process (e.g. pre-extrusions) is essential for reducing grain sizes; however, it further affects anisotropic behaviour and material flow because texture with strong grain orientation is formed.

Metallographic analyses of AZ80 wrought alloy in T5 condition (artificial ageing at 170 to 180 C, 12 to 24 hours) show large differences in microstructure regarding to the cross section of the extruded bar. In cross sections parallel to the extrusion axis (Fig. 1a), strong grain orientation with fibre segregation of the participation phase Mg17Al12 between grain boundaries is observed. Energy-dispersive X-ray spectroscopy (EDX) was used for detection precipitation phase Mg17Al12

[2] and [7]. The Mg17Al12 phase strengthens the alloy and subsequently has significant influence on plastic deformation behaviour [2]. The metallographic structure in cross sections perpendicular to extrusion axis (Fig. 1b) is much more uniformly distributed across whole section without any fibre orientations as is observed in the longitudinal cross section [7]. It should be noted that the same alloy in the same state was used in further experimental investigations represented below in the paper.

a)

b)

Fig. 1. AZ80 crystal metallographic structure a) longitudinal cross-section b) transverse cross-

section [7] Many authors deal with the problem of

texture changes during the deformation process and determination of anisotropic characteristics of magnesium sheets or single crystals [4] to [6], but in fact, there is a major lack of studies dedicated to the consideration of the influence of process parameters on material flow in bulk forming of polycrystalline materials also having practical contributions that would make possible proper die cavities and slug design, as well as enabling the establishment of proper process parameters with the ultimate goal of ensuring the production of faultless parts with high repeatability.

20m

Mg17Al12

Mg17Al12

20m


Analysis of Deformation Characteristics of Magnesium AZ80 Wrought Alloy under Hot Conditions 825

2 EXPEREMENTAL PROCEDURES As mentioned before, the AZ80 feedstock

alloy in a T5 condition was investigated and studied for determination of anisotropic material flow and influence of process parameters on plastic deformation.

The basic characteristics of studied AZ80 feedstock alloy are represented in Table 1, where chemical composition is given, and in Table 2, where mechanical properties at room temperature are listed.

Table 1. Chemical composition of AZ80 commercial alloy [1]

Mark Chemical composition [%]

Al Zn Mn AZ80 7.8 – 9.2 0.2 – 0.8 0.12 – 0.5

Table 2: Mechanical properties of AZ80 commercial alloy in T5 condition [1] Hardness

[HB] Strength [N/mm2] Elongation

[%] Rp0.2 Rm 69 180 – 215 290 – 315 5 – 8

2.1 Tests for Determination Anisotropic Material Flow

In order to make possible analyses of interactions between different process parameters, a statistical approach for the experiment design (DOE) has been used. A general full factorial DOE was chosen. It required minimally two replicates at unchanged process parameters, making possible analyses of standard errors due to deviations from average [8].

Process parameters were selected in accordance with the wide range of process parameters required in forging practice.

The AZ80 feedstock alloy used in this study was in the shape of a pre-extruded bar with 28 mm in diameter. An extruded bar is a good example of material having orthotropic mechanical characteristics which can be described by an assigned Cartesian orthogonal coordinate system. In our case, the x axis is designated along extrusion direction, while the other two axes perpendicular to the extrusion axis are denoted by y and z. These two axes denote directions with equal material properties and are therefore equivalent.

To consider different loading directions and eventual differences in material flow in each direction, cylindrical work-pieces (diameter of 16 mm and length of 20 mm) were machined from pre-extruded bar in longitudinal, transverse and in direction of 45° regarding the extrusion axis as shown in Fig. 2. The first process parameter (work-pieces orientation) has three levels in DOE. The choice of the simple shape of a cylindrical work-piece enables equivalent material flow in unrestricted directions during experiments and enables simple and effective comparison of the shapes after compression.

Fig. 2. Orientation of test work-pieces The second process parameter was work-

piece placement before compression. Two different placements were chosen: upright and radial as is shown in Fig. 3. Upright placement actually represents upsetting giving a simple deformation state while at radial compression or the so-called “cigar test”, a much more complex deformation state is achieved. At upsetting work-pieces were upset from height of 20 to 6.7 mm, while at radial compression work-pieces were compressed from the initial diameter of 16 mm to final thickness of 4 mm.

Fig. 3. Testing tool with inserted work-piece a) upright and b) radial placement

The third process parameter taken into

account was initial work-piece temperature influencing deformability (forgeability) the most. It was selected and tested in three levels: 300 C,

Extrusion direction

Longitudinal direction

Schematic orientation of h. c. p grains

Transverse direction

45°



which is below the recommended temperature for plastic deformation of AZ80 alloy, 350 C as the recommended temperature derived from literature [2] and 400 C, which is above the recommended temperature.

The forth process parameter taken into account was ram speed (vr). To consider the influence of ram speed on deformation behaviour and material flow, two different velocities were chosen. The first at vr = 5 mm/s corresponded to slow and the second at vr = 20 mm/s to fast deformation.

Nevertheless, the ram speeds of forging hammers or screw presses are usually much faster, but due to characteristics of the hydraulic press used in experimental study, attaining faster ram speeds was limited.

Considering the interactions between work-pieces orientation on three levels, work-pieces placement on two levels, initial work-pieces temperature on three levels and ram speed on two levels according to the general factorial experiment design with three replicates at unchanged conditions required 108 experiments to be carried out. In Table 3, the main process parameters of the experimental process are listed, and the maximal logarithmic deformations and main strain rates are also calculated.

Table 3. Experimental process conditions

Material AZ80 T5

Work-piece dimension

diameter: 0,02016 mm

height: 0,02020 mm

Work-pieces orientation

longitudinal; transverse; 45°

Work-piece placement

upright; radial

Initial work-pieces temperatures

300 C; 350 C; 400 C

Ram speeds (vr)

5 mm/s; 20mm/s

Maximal log. deformation

upright: 1.09 radial: 1.37

Mean strain rates ( )

5 mm/s 20 mm/s upright 0.4 s-1 1.6 s-1 radial 0.57 s-1 2.3 s-1

Replicates 3 at unchanged conditions The design of a special small testing tool

consisting of upper and lower die each having

outer dimensions of 95 × 95 × 27 mm. The die’s surfaces were also fine polished to Ra(max) = 0.05 m. For each experiment testing tool with inserted work-piece (see Fig. 3) was put into the resistance-heated oven with an electro-controlled temperature field inside in order to enable isothermal testing. Typically, the testing tool together with the work-piece stayed inside the oven for 15 minutes. Before compression, the temperature of both dies and work-piece was checked using an electronic high-speed thermocouple to assure precise forging temperatures.

Constant temperature of testing tool during compression was also assured by using fireproof clay-block insulation between the lower die and press table, as shown in Fig. 4.

To reduce the friction between the die’s and the work-piece’s contact surfaces, an oil-based carbon lubricant emulsion (Thermex R7-271-03) was used.

Ram movement distance was measured with an inductive sensor mounted on the press while ram speed was controlled with an additional variable-flow restrictor valve. Data entry was automatic, carried out by a special-purpose computer program designed for real time measuring.

Fig. 4. Hydraulic press used for testing The measured parameters on output were

force-movement diagrams and shapes of compressed (forged) work-pieces. Force was measured continuously during the deformation by using a high precision 500 kN load sensor (type C450T) mounted between the hydraulic press ram



and testing tool. The shapes of the compressed work-pieces were measured with a 3D-optical digitalisation system (ATOS II). For measuring, two 35 mm camera lens and one 23 mm projector lens were used. Number of measuring points per individual scan was 1,300,000, achieved with camera resolution of 1280 × 1024 pixels. The achieved measuring accuracy was within 0.015 mm [9].

3 ANALYSES OF RESULTS

3.1 Mechanical Properties of Magnesium AZ80 Alloy

In order to better understand deformation

behaviour, mechanical properties corresponding to various deformation conditions were also analysed with upsetting tests in previous experiments. Flow curves (true stress-strain curves) were obtained as functions of temperatures T, loading directions and strain rates according to equivalent strains for exactly the same batch of feedstock material and in the same loading directions as is illustrated in Fig. 2 [10].

Cylindrical test specimens for determination flow curves had 10 mm in diameter and 15 mm in length. The temperature range taken into account was from 250 to 400 C where the AZ80 alloy shows good formability with temperature increments of 50 C and strain rates region from 0.01 to 10 s-1 with one decade

increment, respectively [10]. Flow curves determined at various process

parameters are presented in Fig. 5. From these charts, the vast dependencies of flow curves on process parameters and loading direction can be observed.

With the deformation of magnesium alloys, specifically AZ80, stress peak as a consequence of deformation hardening following by strong softening is apparent. At high strain rates above = 1 s-1 stress peak is achieved at

equivalent strain of 0.2, while at lower strain rates, the stress peak is achieved at a strain range from 0.05 to 0.1 depending on temperature and loading direction. After deformation hardening, strong deformation softening follows to strain of 0.6 at high strain rates or to 0.4 at slow stain rates.

The reasons for such behaviour are probably in the formation of new gliding planes and twining and, additionally, in dynamic recrystalisation, normally taking place at very slow strain rates [5].

Fig. 5a presents flow curves as a function of loading direction at constant temperature of 350 C and strain rates of = 10 and 0.1 s-1.

Particularly in the area where deformation hardening and softening occur (to equivalent strain of 0.4) especially at strain rate of =

10 s-1, major differences in flow curves regarding the loading direction are observed. The stress peaks are the highest in the longitudinal loading direction, followed by the transverse and direction of 45°. Such behaviour is a result of crystal grains orientation influencing the possibility of formation gliding planes and twining mechanisms in h. c. p. polycrystalline materials.

Furthermore, differences between flow curves as a function of strain rates at a constant temperature are also large (Fig. 5b). With increasing of strain rates, the so-called deformation hardening/softening phenomena is significant since the higher the strain rate is, the bigger the yielding stress peak is observed.

In that point of view, the identified behaviour shows very unfavourable properties with significant risk for cracking at conditions in which very high strain rates are applied, which certainly happens at forming (forging) operations.

Furthermore, temperature play major role in the deformation process of magnesium alloys since sufficient plastic deformation is enabled only at elevated temperatures. Fig. 5c presents flow curves in the longitudinal loading direction as a function of temperature. With increased temperatures, yielding stresses are decreasing and (more importantly) stress peak is significant decreased as well. Nevertheless, plastic deformation at too high temperatures is not recommended due to the risk of hot cracking, as explained later.

Since mechanical properties have significant influence on plastic deformation, the represented flow curves show very clearly that the process window for forming of magnesium alloys is extremely narrow with only small allowed deviations from optimal process parameters.



Fig. 5. Flow curves determined at various process parameters [10]

3.2 Upsetting Tests

Quite large differences between the shapes of the footprints have been observed at different process parameters (see Fig. 6). Cross-sections of work-pieces oriented in the 45° and transverse become elliptical as a consequence of anisotropic flow. Specifically, as is evident from flow curves, material flow is easier in the direction in which yielding stresses are lower rather than in the direction in which resistance against material flow is higher (greater yielding stresses).

Fig. 6. Footprints of upset work-pieces

From analyses of the footprints’ shapes, it can be assumed that formation of an elliptical shape is mainly affected by work-piece orientation, less so by initial work-piece

temperature, while ram speed has almost negligible influence.

There are well-established concepts for describing plastic anisotropy in sheet metals; however, in the field of bulk metal, there is a difference compared to sheet metal particular for materials having rotational symmetry (cylindrical orthotropy) as the extruded bars of AZ80 feedstock alloy studied in the present work have. The rotational symmetry is caused by crystallographic fibre texture along the extruded direction [11]. Below is a proposed mathematical evaluation of anisotropic flow at upsetting, based on the analogy of description anisotropy in sheet metals [12]. From the measurement of the principal axes of the ellipse, a mathematical function for evaluation of anisotropic material flow was proposed by introducing an axial anisotropy factor Rz. Factor Rz can be obtained by Eq. (1) [13]

zz

x

R

, (1)

where z and x are the natural strains vertical and parallel to the extrusion axis and are obtained as following:

2 1

0 0

ln and lnz x

D D

D D

,

(2)



where D1 and D2 are the axis of ellipse in two different directions (see Fig. 7) and D0 is an initial diameter of cylindrical work-piece [13].

Fig. 7. Definition of D1 and D2 after upsetting Unfortunately, as a consequence of friction

between the work-piece and the die’s contact surfaces, and especially due to inhomogeneous plastic deformation as a result of material anisotropic characteristics, the circumferential face of work-piece during upsetting is embossed, as shown on Fig. 8. To compensate for this, equivalent diameters D1 and D2 were calculated using Eq. (3). The equivalent diameter represents a measure between gravity centres of the cross section arcs of a work-piece (Fig. 8).

1,2

2 '' '

3

D DD

(3)

Fig. 8. Definition of D1 and D2 after upsetting Statistical analysis of the impact of the

studied process parameters on Rz is shown in Fig. 9 for a ram speed of 5 mm/s and in Fig. 10 for a ram speed of 20 mm/s. Box, triangle and deltoid on Figs. 9, 10, 14 and 15 represent arithmetic mean values of three measurements (Rz or L1 and L2) at a temperature of 300 °C, 350 °C and 400 °C respectively. Individual measured values are represented with coloured circles according to the legend below particular figure.

The analysed results show that ram speed does not have any influence on anisotropic flow described by factor Rz, while initial work-piece temperature and work-piece orientation (loading direction) have significant impact.

In the work-pieces oriented longitudinal, the value of factor Rz about 1 means that anisotropic flow is not present irrespective of the initial work-piece temperature and ram speed.

In the work-pieces oriented in the 45° anisotropic flow is present but smaller than in the work-pieces oriented transverse. At 300 C ratio Rz = 1.52 predicts an elliptical shape of the upset work-pieces, but with increasing of initial work-piece temperature significant decreasing of elliptical shape is observed.

In the work-pieces oriented transverse, ratio Rz shows significant presence of anisotropic flow with dependence on initial work-piece temperature as well. Factor Rz is decreasing with increasing of the initial work-piece temperature, from value of Rz = 2.6 at 300 C, following by Rz = 1.9 at 350 C to Rz = 1.6 at 400 C at both ram speeds. In this respect, decreasing of the elliptical shape is also noticed.

Fig. 9. Rz ratio at ram speed of 5 mm/s

Fig. 10. Rz ratio at ram speed of 20 mm/s Within the studied range of input process

parameters, mathematical formulations for the calculation of the statistically probable value of anisotropic factor Rz were proposed for work-



pieces oriented transverse Rz90 Eq. (4) and in the 45° Rz45 Eq. (5), respectively.

3 390

5

5,24969+3,59852 10 9,22595 10 +

+1,07448 10 .

z r

r

R v T

v T

(4)

4 345

5

2,57547+1,63637 10 3,95686 10

1,07448 10 .

z r

r

R v T

v T

(5)

Predicted R-squared (R2) factor is used in regression analysis to indicate how well the proposed mathematical model (equations 4 and 5) predicts responses and fits experimental data. Predicted R-squared factor is 0.9577 for both equations which indicates very accurate regression of obtained equations 4 and 5. Obtained equations are also appropriate for mathematical formulation of the Rz factor within the studied range of input process parameters.

In upsetting, so-called hot cracks at initial work-piece temperatures of 400 C were also observed. Cracks appeared in longitudinal work-pieces upset through both ram speeds of 5 and 20 mm/s while in the work-pieces oriented in 45° cracks appeared only at ram speed of 20 mm/s as shown in Fig. 11. Specifically, the reduced viscosity of material and exceeded melting point of precipitation phase Mg17Al12 (427 C) [2] as well as anisotropy of the structure, especially deposition of Mg17Al12 are the main reasons for hot cracking. The risk for hot cracking is even more expressive at higher ram speeds because a greater rise in temperature occurs due to plastic deformation.

Fig. 11. Cracks at upsetting

3.3 Radial Compression Tests

To determining material flow in more complex deformation circumstances, e.g. where work-pieces are compressed in radial directions, radial compression tests (“cigar tests”) were performed, as is a common practice in forging shops. Understanding material flow in conditions where loading force acts in a radial direction perpendicular to extrusion axis is crucial for the filling of die cavities and indirectly affects dies’

cavities and slugs’ design. Moreover, such a deformation state could be a good case study for verifying the precision of FEM codes.

Footprints of radial compression are shown in Fig. 12. Differences in the shapes of footprints show the presence of anisotropic flow.

Fig. 12. Footprints at radial compression

Material flow was observed by measuring

extension in the direction of work-piece flat planes L1 and work-piece radii direction L2 as shown on Fig. 13. The procedure for calculation of equivalent values L1 and L2 due to embossment of outer surfaces of radial compressed work-piece was the same as was used for determination diameters D1 and D2 at upsetting.

Fig. 13. Measurement of extension L1 and L2 at radial compression

Analyses of extension of L1 and L2 are

illustrated in Figs. 14 and 15. Work-pieces oriented longitudinal show more pronounced extension in radial direction L2 as in the direction of flat planes L1. Dimension L2 is increasing even more with the increasing of initial work-piece temperature or ram speed, while L1 is decreasing. In this case, the situation is opposite as with upsetting of work-pieces oriented transverse where anisotropic flow was decreasing with the increasing of initial work-piece temperature.

With the radial compression of work-pieces oriented in the 45°, material flow is quite similar to work-pieces oriented transverse, except that it is slightly more oriented in the direction of 45° regarding the main extrusion axis causing the



oblique final shape (observed from the top perspective). That could be explained by easier formation of gliding planes perpendicular to long-fibre grains as a result of extrusion. It should be also said that measures of L1 and L2 do not fully consider anisotropic flow, but is clear in any case that the shapes of radial compressed work-pieces oriented in the 45 are similar to those oriented transverse.

Fig. 14. Statistical analyses of dimension L1 for ram speed of 5 mm/s and ram speed of 20 mm/s

Fig. 15. Statistical analyses of dimension L2 for ram speed of 5 mm/s and ram speed of 20 mm/s

At radial compression of work-pieces oriented transverse at 300 C, material flows more uniformly in both directions L1 and L2. However, with increasing of initial work-piece temperature, material flow becomes more superior in the direction of work-piece radial surface L2.

Deformation behaviour in the radial compression also provided crack formation, but not to the extent to that happened in upsetting. Only in work-pieces oriented in the 45° did cracks appear in work-piece radial surfaces, as shown on Fig. 16.

Fig. 16. Cracking at radial compression

4 THE MOST IMPORTANT CONCLUSIONS

The performed analyses give some very important explanations of plastic deformation behaviour of magnesium wrought alloy AZ80.

The basic influence on material flow, the formation of an elliptical shape at upsetting or differences in material flow in radial compression, during deformation have strong grain orientation as a result of pre-extrusion process. From analysed results, it is clear that formation of gliding planes is easier perpendicular to long grains rather than in longitudinal direction parallel to long grains.

In terms of the most important contributions to industrial practice, the following findings can be highlighted: Ram speed between 5 and 20 mm/s does not

have remarkable influence on anisotropic flow regardless of the work-piece placement or work-piece orientation (loading direction).

The most optimal initial work-piece temperature for isothermal forging on hydraulic press is 350 C; however, lower initial work-piece temperatures would be recommended for forging on screw presses or hammers, because larger rises in temperature at relatively high strain rates are expected. As has also been experimentally detected, at an initial work-piece temperature of 400 C hot cracks already appeared at quite slow strain rates.



The hydraulic press machine was recognised as highly recommended for the forging of magnesium wrought alloys since slow strain rates suitable for the forging of magnesium alloys could be achieved with ram speed control.

The present study represents some new insights into magnesium forging technology with significant potential for practical use and further investigation. The main goal for further investigation should be focused on reliable numerical simulations of bulk forming of magnesium alloys.

For complete consideration of magnesium deformation characteristic with numerical simulations, attention should be paid on development of finite element models capable to predict and calculate texture changes of h. c. p. polycrystalline materials.

Further efforts should be made on the field of testing procedures for determination of anisotropic variables for any type of anisotropic yielding law.

The final stage results of present study could be used as a case study for testing the capabilities and accuracy of numerical simulations of anisotropic material flow.

5 ACKNOWLEDGEMENTS

The represented research work is a part of

a Collective Research Project MagForge – Magnesium Forged Components for Structural Lightweight Transport Applications with Contract no.: COLL-CT-2006-030208 founded by EC as a 6FP project.

6 REFERENCES

[1] Kurz, G., Sillekens, W.H., Swiostek, J.,

Letzig, D. (2007). Alloy development and processing for the European project MagForge. Proceedings of the 15th Magnesium Automotive and User Seminar, p. 27-28.

[2] Kurz, G., Clauw, B., Sillekens, W.H., Letzig, D. (2009). Die Forging of the Alloys AZ80 and ZK60. TMS – Magnesium Technology, p. 197-202.

[3] Kocańda, A., Czyżewski, P. (2008). Experimental and numerical analysis of side forces in a forging die. Strojniški vestnik – Journal of Mechanical Engineering, vol. 54, no. 4, p. 274-279.

[4] Cazacu, O., Plunkett, B., Barlat, F. (2006). Orthotropic yield criterion for hexagonal closed packed metals. International Journal of Plasticity, vol. 22, p.1171-1194.

[5] Lass, J.F., Bach, F.W., Schaper, M. (2005). Adapted Extrusion Technology for Magnesium Alloys. TMS – Magnesium Technology, p. 15-17.

[6] Graff, S., Brocks, W., Steglich, D. (2007). Yielding of magnesium: From single crystal to polycrystalline aggregates. International Journal of Plasticity, vol. 23, p. 1957-1978.

[7] Kurz, G., Leitzig, D. Delivery presentation – Progress on WP1 material development, from http://www.magforge.eu, accessed on 2007-06-26.

[8] Montgomery, D.C. (2001). Design and Analysis of Experiments, 5th Edition. John Wiley & Sons, New York. p. 363–387.

[9] ATOS User Information. ATOS II/II Small Object Hardware, from http://www.gom.com, accessed on 2008-01-31.

[10] Kobold, D., Pepelnjak, T., Gantar, G., Kuzman, K. (2009). Analyses of material properties of magnesium alloys on warm forging processes. Proceedings of the 8th International Conference on Magnesium Alloys and their Applications, p. 113-119.

[11] Lekhnitskii, S.G. (1989). Theory of Elasticity of an Anisotropic Body. Moscow – MIR Publishers. p. 15-78, (English translation of supplemented Russian edition from year 1977).

[12] Aleksandrović, S., Stefanović, M., Adamović, D., Lazić, V. (2009). Variation of normal anisotropy ratio "r" during plastic forming. Strojniški vestnik – Journal of Mechanical Engineering, vol. 55, no. 6, p. 392-399.

[13] Banabic, D., Bunge, H.J., Pohlandt, K., Tekkaya, A.E. (2000). Formability of Metallic Materials: Plastic Anisotropy, Formability Testing, Forming Limits. Springer Verlag. p. 86-107.

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 833-845 Paper received: 22.04.2010 UDC 658.512.4:658.512.62 Paper accepted: 26.05.2010

*Corr. Author's Address: Faculty of Mechanical Engineering, Aškerčeva 6, Ljubljana SI-1000, Slovenia, [email protected]

833

Reduction of Machine Setup Time

Janez Kušar* - Tomaž Berlec - Ferdinand Žefran - Marko Starbek University of Ljubljana, Faculty of Mechanical Engineering, Slovenia

Customers today require smaller series of products. In manufacturing companies, this increases

machine setup time, which is a waste. This paper presents a procedure for organizing and implementing a reduction of machine setup

time. It is based on teamwork and uses the SMED method, which allows a gradual reduction of machine setup time to less than 10 minutes, and a continuous improvement system.

The paper also presents the results of the organization and execution of a SMED workshop for the reduction of setup times in a jet machine, as well as first suggestions for improvements that should significantly reduce machine setup time. ©2010 Journal of Mechanical Engineering. All rights reserved. Keywords: machine setup time, SMED workshop, continuous improvement, teamwork, microelements

0 INTRODUCTION

In the 1950s, Taiichi Ohno, the legendary president of Toyota, was very unhappy because his company produced cars for stock. The cars were driven from the manufacturing hall to a parking lot, where they waited for customers. T. Ohno considered that this waiting of cars for customers was a waste that should be eliminated, or at least reduced. He found that the waste was caused by manufacturing components and final products (cars) in excessively large series.

The equation for calculating the time required for manufacturing a series of parts and the assembly of components is:

t = ts + m · t1 (1)

where: t time required for manufacturing parts and

assembling components [Nh/series] ts machine setup time or assembly workplace

setup time [Nh/series] m number of units within a series

[pieces/series] t1 manufacturing/assembly time per unit

[Nh/piece]. Analysis of this equation led Ohno to the

conclusion that the company could make a transition from large series manufacturing to small series only if they could substantially reduce the setup times of machines and assembly workplaces.

The task of finding a suitable method for reducing setup time was given to Shigeo Shingo, who is the author of the rapid machine setup method, also known as SMED (single minute exchange of dies) [1].

The SMED method is one of the lean manufacturing methods or tools [1], which allow successful competition in domestic and foreign markets (Fig. 1).

Van Goubergen says [2] that it is very

important to reduce machine setup time during the implementation of lean manufacturing because this time has a significant impact on manufacturing costs due to decreasing sizes of series orders.

Van Goubergen justifies the reduction of machine setup time by [2]:

SMOOTHING OF PRODUCTION

STANDARDIZED WORK

KAIZEN

OPERATIONAL STABILITY

Pull system KANBAN 5S 5WSolution of the problem based on the cause

Cycle timeCELL

PRODUCTIONVSM ANDON

Stopping the manufacturing

Current manufacturing

SMED TPMPOKA YOKE

Detection of errors

JIT: TOOLS: STOPPING THE PRODUCTION

PROCESS:

LEAN MANUFACTURING METHODS

Fig. 1. Lean manufacturing methods and tools


Kušar, J. – Berlec, T. – Žefran, F. – Starbek, M. 834

greater flexibility of the company (the company can offer customers more products and their variants in smaller series ),

higher throughput through company bottlenecks (reduced setup times of bottleneck machines ensure higher throughput),

increased efficiency of the company (by reducing machine setup time, the efficiency of these machines increases, which increases company income).

The quality of machine setup is defined by three parameters [2]: the method used for machine setup (how), organization of work needed for machine

setup (who, what, when), technical aspects of tools and devices, as presented in Fig. 2.

Fig. 2. Elements of machine setup Rapid and efficient machine setup requires

optimal values of all three elements of machine setup, supported by the motivation of the personnel that carry out machine setup.

Quality and machine setup time also depend on machine design.

A company can select one of three options [3] to [ 5]: design of a new machine that will ensure

minimum setup time - large investment, improvement of an existing machine and the

use of the SMED method to achieve a setup time of 3 minutes,

use of the SMED method to achieve a setup time of less than 10 minutes.

Fig. 3 shows the relations between machine setup time and costs with these three strategies [3].

It can be seen from Fig. 3 that a reduction of machine setup time using the SMED method is cheap, but has only limited effects. The design of a new machine is expensive, but the new setup time will be very short. Taking into account both costs and setup time, it is most efficient for the company to select the SMED method and to make improvements to the machines.

Cos

ts

desig

n of

a n

ew m

achin

e

Fig. 3. Dependency between machine setup time and costs

1 ORGANIZATION AND EXECUTION OF

SMED WORKSHOP The goal of a SMED workshop is to

reduce machine setup time and thus increase machine availability.

Experience in using the SMED method has shown that teamwork is essential for its successful implementation. When selecting team members to participate in the organization and execution of a SMED workshop, it is necessary to ensure that all nine team roles defined by Dr. Belbin are occupied [6].

A review of the literature [3], [7] and [8] and our experience obtained in introducing the SMED method in companies have led us to the creation of a procedure for the organization and execution of a SMED workshop for the reduction of machine setup time (Fig. 4).


Reduction of Machine Setup Time 835

Wor

k of

man

ufac

turin

g m

anag

emen

tT

eam

wor

k

Fig. 4. Procedure for the organization and execution of a SMED workshop

Step 1: SELECTION OF THE MACHINE Manufacturing management selects the

machine for reduction of setup time by taking into account the pre-defined criteria (e.g., the longest machine setup time, frequency of setup, bottleneck machines).

Selection is made on the basis of ABC analysis [9].

Step 2: DEFINITION OF TARGET

SETUP TIME The definition of the target value for

reduced setup time is very important, since it directly influences the motivation of team members who will carry out the SMED method.

Manufacturing management usually specifies that the team should reduce the setup

time by 50% during the first SMED workshop (Fig. 5).

Fig. 5. Target setup time



It is difficult to improve this result in each consecutive SMED workshop, except when a new team member appears with revolutionary (and not too expensive) ideas [10] and [11].

Step 3: SELECTION OF TEAM

MEMBERS Team members that will participate in the

execution of a SMED workshop are selected by the manufacturing management. The team should include representatives from manufacturing planning and management departments, workers who are responsible for machine setup and processing of orders, and maintenance personnel.

After carrying out the Belbin test of team roles [12] the manufacturing management appoints: a TEAM LEADER, responsible for leading

the team, organization and documentation of team sessions and for achieving agreement within the team,

a TEAM MODERATOR, who is the SMED method expert and who will lead the team from step 4 to step 7 of the SMED workshop,

other team members: o a setup operator, who will carry out the

machine setup as it has been done up to that point,

o a protocol writer, who will take notes on machine setup elements,

o a time recorder operator, who will record the time required for machine setup elements,

o a photographer, who will take photos of details of machine setup elements,

o a cameraman, who will use a video camera to film the execution of all machine setup

elements, o a team member to draw a diagram of the

path made by the setup operator. Manufacturing management informs the

selected team members and their heads about the date of the SMED workshop. They confirm their approval by signing the "SMED workshop order" form (Table 1).

Step 4: DOCUMENTING ELEMENTS

AND MICROELEMENTS OF MACHINE SETUP USING THE EXISTING PROCEDURE

The existing machine setup procedure is carried out and documented. The actual sequence and execution time of machine setup elements/microelements are defined.

The following tools are available for documenting the elements and microelements of machine setup: notebook of machine setup elements, monitoring paper, list of paths made by the machine setup

operator, photos of machine setup details, video film of the entire machine setup

process. A notebook with the elements and

microelements of the machine setup is the simplest tool for documenting the sequence and timing of setup elements/microelements. The protocol writer enters the elements and microelements of the machine setup in the notebook.

The data are entered in the exact sequence of the setup, with the exact times noted, as reported by the time recorder operator.

Table 1. SMED workshop order

SMED workshop order

Ordered by: Workshop name Workshop date from to Workshop goals Management: Signature: Team members: Department: Signature:

: : : : : Date of meeting: ………………………

Date of workshop presentation …….……….

Manufacturing manager: ……………………….



The monitoring paper is a form on which the protocol writer enters the following data: sequential numbers of machine setup elements

and microelements, short description of machine setup elements

and microelements, cumulative times of machine setup elements

and microelements, individual times of machine setup elements

and microelements, histogram of individual times of machine

setup elements and microelements. The purpose of the list of paths made by

the setup operator is to visualize unnecessary movements of the operator during setup. The basis for the list of paths is a drawing of the workplace. The movements of the setup operator are drawn onto it with a continuous line.

During thr subsequent analysis of the elements and microelements of the machine setup and on the basis of the list of actual paths made by the setup operator, the team can establish necessary paths and eliminate unnecessary ones.

Photos of details of machine setup elements and microelements are taken with a high-definition digital camera with zoom. The photographer should be careful not to be in the way of the setup operator.

A video camera is the most effective tool for recording the machine setup. For this purpose, a camera with a hard disk capacity of at least 120 GB and a battery for at least 50 hours of filming is required. Filming starts at the beginning of the execution of the first machine setup element/microelement and ends with the completion of the last element (without interruption). SMED team members can view the machine setup video several times and analyze it thoroughly.

Step 5: TRANSFORMATION OF

MACHINE SETUP ELEMENTS AND MICROELEMENTS INTO A VISUAL FORM

The data obtained on the machine setup elements and microelements are copied from the notebook to stickers that can be affixed to a panel during the next step.

Step 6: ANALYSIS OF MACHINE

SETUP ELEMENTS AND MICROELEMENTS Analysis of machine setup elements and

microelements is carried out by the team in a

room with a large panel, which allows the affixing of stickers, and chairs placed around in a semicircle.

Analysis is carried out in a sequence of phases as presented in Fig. 6.

PHASE 0

Analysis of the current

situation

PHASE 2

Transformation of internal

microelements into external

ones

PHASE 1

Separation of internal and

external microelements

PHASE 3

Improvement of internal and

external microelements

- external elements (machine operates)

- internal elements (machine does not operate)

Fig. 6. Analysis phases of setup elements and microelements

Phase 0: Analysis of the current situation Before the meeting, the team moderator

brings into the meeting room all stickers of machine setup elements and microelements, with their duration times, labeled as X or E. An X label on the microelement sticker indicates that another microelement follows this one, while an E label denotes that this is the last microelement.

At the beginning of the session, the moderator projects onto the panel the analytical card for entering the current situation of machine setup. By affixing stickers onto the panel (with the agreement of the team members) the current situation of machine setup is obtained.

Phase 1: Separation of internal and

external microelements The moderator presents every

microelement of a particular element in the current machine setup and the team members must decide whether the microelement is: internal (it can be carried out only during

machine shutdown) or external (it can be carried out during machine

operation).



The moderator marks the stickers of internal microelements with red and those of external microelements with yellow.

Phase 2: Transformation of internal

microelements into external ones The moderator (with the cooperation of the

team) moves the yellow stickers either to column 1 (starting activities) or to column 5 (completion activities).

Phase 3: Improvement of internal and

external microelements By carrying out several creativity

workshops [12] the team obtains suggestions for improvements of internal and external microelements.

The moderator enters all improvements of machine setup microelements into the lower part of the analytical card ("improvements" field).

Phase 4: Standardization of machine setup

microelements In this phase, standardization of internal

and external microelements is carried out, and a continuous improvement principle is put into effect.

Training is organized for setup operators, machine operators and maintenance workers. Machine setup according to the improved procedure is carried out at least three times during this training.

Step 7: IMMEDIATE REPETITION OF

THE ANALYSIS OF ELEMENTS AND MICROELEMENTS

If the target setup time defined in step 2 has not been achieved, the team immediately repeats the analysis of machine setup microelements.

Step 8: REPETITION OF THE SMED

WORKSHOP Reduction of machine setup time is a

never-ending process, so it is necessary to repeat the SMED workshop every six months and in this way get closer to the set goal of "achieving a machine setup time shorter than 10 minutes".

2 CASE STUDY OF JET-MACHINE SETUP TIME REDUCTION

The manufacturing management decided

that the company would test the SMED workshop in order to reduce machine setup time.

Step 1: SELECTION OF THE MACHINE The manufacturing management used the

following criteria during machine selection: machine setup times in the last three months, number of machine setups in the last three

months. Using a weighted-scoring method, the

manufacturing management decided that a reduction of setup time would be tested on a KM 800 – CNC Injection Molding Machine, Crauss-Maffei (Fig. 7).

Fig. 7. KM 800-CNC injection molding machine Step 2: DEFINITION OF TARGET

SETUP TIME The time recorder operator measured the

time required for machine setup: 119.97 minutes. The manufacturing management decided

that the target reduced setup time would be 60 minutes, i.e., 50% of the current value.

Step 3: SELECTION OF TEAM

MEMBERS The manufacturing management selected

an 8-member team for the SMED workshop: a team leader from the operation logistics

department, a team moderator from the technology

department, team members, a setup operator from the manufacturing

department, a protocol writer from the planning

department,



Table 2. Monitoring paper - standard machine setup procedure

MONITORING PAPER

Element number

DESCRIPTION OF THE ELEMENT

Cumulative time

Individual time [sec]

HISTOGRAM OF INDIVIDUAL TIMES [sec]

hour minsec 10 20 30 40 50 60 70 80 90 100

1 Machine shutdown 0 00 31 31 2 Setup of the manipulat. 0 01 12 41 3 Walk to the office 0 01 26 14

4 Searching for documentation

0 01 35 9

5 Walk to the machine 0 01 50 15

: : : : : : : : : : : : : : : : : :

55 Confirmation of first samples

1 59 04 80

a time recorder operator from the

manufacturing department, a photographer from the manufacturing

department, a cameraman from the supply department, a drawer of paths made by the setup operator

from the process control department. The manufacturing management sent the

"SMED-workshop order" form to departmental heads and team members for them to confirm their agreement with participation in the workshop.

Step 4: DOCUMENTING ELEMENTS

AND MICROELEMENTS OF JET-MACHINE SETUP (existing procedure)

During the actual machine setup, the protocol writer entered the sequence of elements and microelements of machine setup into his notebook. He also noted exact setup times, reported by the time recorder operator.

After recording the machine setup elements, the protocol writer entered the data on the monitoring paper (Table 2).

The drawer of the paths made by the setup operator made a drawing of the operator's movements. The results are presented in Fig. 8.

It is obvious that the setup operator is disorganized and that he often leaves his workplace and walks around unnecessarily.

During machine setup, photos of the microelement details were taken with a Sony Cybershot DSC-H98MP camera. The whole

machine setup was filmed with a Sony HDR-XR200 video camera equipped with a high-capacity battery and high-capacity film memory.

Step 5: TRANSFORMATION OF JET-

MACHINE SETUP ELEMENTS AND MICROELEMENTS INTO A VISUAL FORM

The data obtained on the jet-machine setup elements and microelements were copied from the notebook to stickers to be affixed to a panel during the next step. The stickers were labeled as X - if there was another microelement after the current one, E - if the current microelement was the last one.

Step 6: ANALYSIS OF JET-MACHINE

SETUP ELEMENTS AND MICROELEMENTS Phase 0: Analysis of the current situation

of jet-machine setup At the beginning of the session, the

moderator projected the analytical card for entering the current situation onto the panel. By affixing stickers to the panel (in agreement with other team members) the current situation of jet-machine setup was obtained (Table 3).

Phase 1: Separation of internal and

external setup microelements The moderator presented each

microelement of the current machine setup and the team decided whether the microelement was internal or external.



Table 3. Analytical card of the current situation of jet-machine setup ANALYTICAL CARD – CURRENT SITUATION

Machine setup element

EXTERNAL ELEMENTS INTERNAL ELEMENTS EXTERNAL

ELEMENTSTOTAL TIME

[min]

Element duration [min]

1. Starting activities

2. Tool dismantling procedure

3. Tool mounting procedure

4. Start of the machine

5. Completion activities

0 19.30 93.97 6.70 0

MICROELE-MENTS

Machine shutdown31 sec X

Fixing the crane clamps69 sec X

Test of the jet operation117 sec X

Manipulator setup41 sec X

Insertion of a new tool29 sec X

Synchronization of jet-machine166 sec X

Walk to the office14 sec X

Centering the tool position164 sec X

Confirmation of the first samples81 sec E

Lifting the previous tool from the machine89 sec E

Entering the data into the documentation385 sec X

Tool heating3811 sec X

Spraying the cylinder72 sec E

Table 4. Analytical card for separation of internal and external microelements

ANALYTICAL CARD – separation of elements



ELEMENTSTOTAL TIME

[min]







0 19.30 93.97 6.70 0 119.97

MICROELE-MENTS











Entering the data into the documentation385 sec X



DURATION OF INTERNAL ELEMENTS

[min]

DURATION OF EXTERNAL ELEMENTS

[min]

0.00 12.40 24.67 6.70 0.00 43.77

0.00 6.90 69.30 0.00 0.00 76.20



MA

CH

INE

1

MA

CH

INE

2

MA

CH

INE

3

Mat

eria

l cab

inet

Pas

sage

to

the

hall

110

to 4

0 m

Machine 1: jet-machine Machine 2: tempering device Machine 3: place of control

Fig. 8. List of paths made by the setup

operator - standard machine setup procedure The moderator marked the stickers of

internal microelements with red and those of external microelements w ith green (Table 4).

The team members found that it would be possible to carry out 76.2 minutes (out of the total 119.97 minutes) of setup during the jet-machine operation—this is the duration of the external microelements of machine setup.

Phase 2: Transformation of internal

microelements into external ones The moderator moved (in agreement with

team members) the green stickers (external microelements) either to column 1 (starting activities) or to column 5 (completion activities) (Table 5).

Phase 3: Improvements of internal and

external microelements After the separation of internal and

external microelements of machine setup, the team made some suggestions for improvements of internal and external microelements.

The results of the creativity workshop are presented in Table 6.

Table 5. Analytical card of transformation of internal into external microelements of jet-machine setup

ANALYTICAL CARD – conversion of microelements



ELEMENTSTOTAL TIME

[min]







MICROELE-MENTS












0.00 12.40 24.67 6.70 0.00 43.77

73.00 0.00 0.00 0.00 3.20 76.20

73.0 12.4 24.67 6.7 3.2 119.97

Entering the data into the documentation385/2=192 sec X

Entering the data into the documentation385/2=192 sec X


DURATION OF INTERNAL ELEMENTS

[min]

DURATION OF EXTERNAL ELEMENTS

[min]



Table 6. Analytical card of improvements to internal and external microelements of jet-machine setup

The results of the first SMED workshop

were: a reduction of internal microelements of

machine setup time from 119.97 minutes to 43.77 minutes (a reduction of 63.5%),

a reduction of the total machine setup time of 6.16 minutes.

The largest reduction of machine setup

time was achieved by moving the microelement "Tool heating" from being an internal element "3. Tool mounting" to an external element "1. Starting activities" with an anticipated time of 64 minutes.

Pre-heating of the tool at the pre-heating station (Fig. 9) allows the tool to be heated to the



operating temperature before mounting. Thus, heating in the machine is not necessary.

Fig. 9. Pre-heating station The team calculated the time required for

the return of investment in the pre-heating station:

NtC

At I

I

60

, (2)

where: tI time for return of investment [weeks] AI invested amount [€] C cost of machine downtime per hour [€] t saved time due to tool

pre-heating [min/changeover] N number of tool changeovers per

week [changeovers/week].

The pre-heating station costs about € 9000. It is estimated that the tool is changed 12 times per week. The cost of jet-machine waiting-time is 54 €/h. The time saved due to tool pre-heating is 63.5 min/changeover. The return of investment in the pre-heating station is:

13.11263.554

609000t

weeks.

MA

CH

INE

1

MA

CH

INE

2

MA

CH

INE

3

Mat

eria

l cab

inet

Pas

sage

to

the

hall

110

to 4

0 m

Fig. 10. List of new paths for the setup operator The team organized a creativity workshop

in order to eliminate unnecessary paths for the setup operator. The results of the creativity workshop are presented in Fig. 10.

Table 7. Operating instructions for jet-machine setup

Machine KM 800 OPERATING INSTRUCTIONS

No. MICROELEMENTS Pay attention to: Figure:

1 Read operating instructions 2 Check if the new tool is ready : : :

15 Setup of new tool handle 16 Machine shutdown 17 Program loading

: : : 42 Control of products Control dept. participates 43 Packing of personal tools 44 Packing of vacuum cleaner

: : : 47 Packing of documentation



Phase 4: Standardization of microelements The team also carried out a standardization

of internal and external microelements and entered the results on the form "Operating instructions for jet-machine setup" (Table 7).

The new operating instructions had to be tested, so the day after the first SMED workshop the setup operator carried out machine setup according to the new operating instructions and completed internal microelements within 39 minutes, which is an additional improvement of 4.77 minutes.

Step 7: REPEATED ANALYSIS OF

MICROELEMENTS The target setup time defined in step 2 was

not achieved, so the team decided to repeat the analysis of machine setup microelements.

Before the second SMED workshop, the team leader organized a creativity workshop in order to obtain suggestions for improvements, the realization of which would additionally reduce setup time.

The creativity workshop indicated that setup time could be significantly reduced if the following improvements were made: introduction of fast hydraulic chuck-and-

center system for tool fixing, introduction of fast hydraulic multi-joints.

3 CONCLUSION

The manufacturing management decided

that the KM 800 jet-machine setup time should be reduced. They selected team members to carry out a SMED workshop with the goal of reducing the setup time. The target value was a reduction of 50%.

The team first documented the elements of the existing jet-machine setup, recorded microelement setup times, drew the path made by the setup operator, took photos of setup details and filmed the whole setup procedure with a video camera.

An analysis of setup microelements was then made, which indicated that some internal microelements could be transformed into external ones.

The team leader organized a creativity workshop, the goal of which was to make improvements to internal and external microelements. The creativity workshop yielded

two suggestions for improvements that should significantly reduce the setup time.

The SMED workshop on the reduction of jet-machine setup time will be repeated until the goal has been achieved: a setup time shorter than 10 minutes [14].

4 REFERENCES

[1] Shingo, S. (1985). A Revolution in

manufacturing: The SMED system. Productivity Press, Portland, Oregon.

[2] Van Goubergen, D., Van Landeghem, H. (2002). Rules for integrating fast changeover capabilities into new equipment design. Robotics and Computer Integrated Manufacturing, vol. 18, p. 205-214.

[3] Mileham, A. R., Culley, S. J., Owen, G. W., McIntosh, R. I. (1999). Rapid changeover – a pre-requisite for responsive manufacture. International Journal of Operations& Production Management, vol. 19, no. 8, p. 785-796.

[4] Cakmakci, M. (2009). Process improvement: performance analysis of the setup time reduction - SMED in automotive industry. Internation Journal of Advanced Manufacturing Technology, vol. 41, p. 168-179.

[5] Sekine, K., Arai, K. (1992). KAIZEN for quick changeover – going beyond SMED. Productivity Press, Portland, Oregon.

[6] Belbin, R. M. (2003). Team roles at work. Elsevier, Amsterdam.

[7] Menzel, F. (2009). Produktionsoptimierung mit KVP. mi-Fachverlag, München.

[8] Steven, B. (2006). Total preventive maintenance. McGraw Hill, New York.

[9] Starbek, M., Petrišič, J., Kušar, J. (2000). Extended ABC analysis. Strojarstvo, vol. 42, no. 3-4, p. 103-108.

[10] Fulder, T., Palčič, I., Polajnar, A., Pižmoht, P. (2005). The process of manufacturing-capability development in industrial cluster - A case study of the automotive cluster of Slovenia, Strojniški vestnik – Journal of Mechanical Engineering, vol. 51, no. 12, p. 771-785.

[11] Anišić, Z., Krsmanović, C. (2008). Assembly initiated production as a prerequisite for mass customization and effective manufacturing. Strojniški vestnik –



Journal of Mechanical Engineering, vol. 54, no. 9, p. 607-618.

[12] INTERPLACE (2008). User's manual, Belbin Associates.

[13] Scherer, J. (2007). Kreativitätstechniken. Gabal Verlag, Offenbach.

[14] Kušar, J., Berlec, T., Duhovnik, J., Grum, J., Starbek, M. (2005). Finding and exploiting the hidden logistic potentials in a company. Strojniški vestnik – Journal of Mechanical Engineering, vol. 51, no. 6, p. 304-329.

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, 846-852 Paper received: 01.03.2010 UDC 629.7:620.178.3 Paper accepted: 19.05.2010

* Corr. Author's Address: Termoelektro d.o.o., Uralska 9, 11000 Belgrade, Serbia, [email protected]

846

Fatigue Life Estimation of Notched Structural Components

Dragi Stamenković1,* - Katarina Maksimović2 – Vera Nikolić-Stanojević3 – Stevan Maksimović4 – Slobodan Stupar5 – Ivana Vasović6

1Termoelektro d.o.o., Serbia 2City of Belgrade - City Government, Secretariat for Communal and Housing Affairs Office

of Water Management, Serbia 3The State University of Novi Pazar, Serbia

4Military Technical Institute, Serbia 5Faculty of Mechanical Engineering, Serbia

6Gosa Institute, Serbia

This work considers the analytical/numerical methods and procedures for obtaining the stress intensity factors and for predicting the fatigue crack growth life of notched structural components. Many efforts have been made during the past two decades to evaluate the stress intensity factor for corner cracks and for through cracks emanating from fastener holes. A variety of methods have been used to estimate the stress intensity factor (SIF), values, such as approximate analytical methods, finite element method (FEM), finite element alternating, weight function, photo elasticity and fatigue tests. In this paper the analytic/numerical methods and procedures were used to obtain SIF, and predict the fatigue crack growth life for cracks at attachment lugs. Single through crack in the attachment lug analysis is considered. For this purpose analytic expressions are evaluated for SIF of cracked lug structures. For validation of the analytic stress intensity factors of cracked lugs, FEM with singular finite elements is used. Good agreement between computation and experimental results for fatigue life of aircraft cracked lugs was obtained. To determine crack trajectory of cracked structural components under mixed modes,, conventional singular finite elements and X-FEM are used. ©2010 Journal of Mechanical Engineering. All rights reserved. Keywords: Notched structural components, lugs, analytic stress intensity factor of lugs, finite elements, X-FEM, fatigue life estimation

0 INTRODUCTION

Surface and through-thickness cracks frequently initiate and grow at notches, holes in structural components. Such cracks are present during a large percentage of the useful life of these components. Hence, understanding the severity of cracks is important in the development of life prediction methodologies [1]. Current methodologies use the stress intensity factor (SIF) to quantify the severity of cracks and the development of SIF solutions for notched structural components using analytical, numerical and semi-analytical methods has continued for the last three decades.

The adoption of the damage tolerance design concept [2] and [3] along with an increased demand for accurate residual structure and notched component life predictions have provided a growing demand for the study of fatigue crack growth in aircraft mechanical components. The damage tolerance approach assumes that the structure contains an initial

crack or defect that will grow under service usage. The crack propagation is investigated to ensure that the time for crack growth to a critical size takes much longer than the required service life of notched structural components. For damage tolerance program to be effective it is essential that fracture data can be evaluated in a quantitative manner. Since the establishment of this requirement not only the understanding of fracture mechanics has greatly improved, but also a variety of numerical tools have become available to the analyst. These tools include Computer Aided Design (CAD), Finite Element Modelling (FEM) and Computation Fluid Dynamics (CFD). Fracture mechanics software provides the engineering community with this capability.

Computer codes can be used to predict fatigue crack growth and residual strength in aircraft structures.

They can also be useful to determine in-service inspection intervals, time-to-onset of widespread fatigue damage and to design and certify structural repairs. Used in conjunction with

Strojniški vestnik – Journal of Mechanical Engineering 56(2010)12, 846-852

Fatigue Life Estimation of Notched Structural Components 847

damage tolerance programs fracture analysis codes can play an important role in extending the life of “high-time” aircraft. Traditional applications of fracture mechanics have been concerned on cracks growing under an opening or mode I mechanism. However, many service failures occur from cracks subjected to mixed mode loadings. A characteristic of mixed mode fatigue cracks is that they usually propagate in a non-self similar manner. Therefore, under mixed mode loading conditions, not only the fatigue crack growth rate is of importance, but also the crack growth direction. Several criteria have been proposed regarding the crack growth direction under mixed mode loadings. In this work, maximum strain energy density criterion [4] and [5] is used. This S-criterion allows stable and unstable crack growth in mixed mode. The application of this criterion can be found from the works by several authors [6] and [7]. The aim of this work is to investigate the strength behaviour of an important aircraft notched structural elements such as cracked lugs and riveted skin.

1 NUMERICAL SIMULATION OF CRACK GROWTH

Numerical simulations of crack growth

provide a powerful predictive tool to be used during the design phase as well as for evaluating the behaviour of the existing crack. These simulations can be used to compliment experimental results and allow engineers to economically evaluate a large number of damage scenarios. Numerical methods are the most efficient way to simulate fatigue crack growth because crack growth is an incremental process where stress intensity factors (SIF) values are needed at each increment as input to crack growth equations.

In order to simulate mixed-mode crack growth an incremental type analysis is used, where knowledge of both the direction and size of the crack increment extension are necessary.

For each increment of crack extension, a stress analysis is performed using the quarter-point singular elements (Q-E) [8] and SIF are evaluated. The incremental direction and size along the crack front for the next extension are determined by fracture mechanics criteria involving SIF as the prime parameters. The

crack front is re-meshed and the next stress analysis is carried out for the new configuration.

2 STRESS INTENSITY FACTOR

SOLUTIONS OF CRACKED LUGS

In general geometry of notched structural components and loading it is too complex for the stress intensity factor (SIF) to be solved analytically. The SIF calculation is further complicated because it is a function of the position along the crack front, crack size and shape, type loading and geometry of the structure. In this work analytic [3] and FEM [2] and [17] were used to perform linear fracture mechanics analysis of the pin-lug assembly. Analytic results are obtained using relations derived in this paper. Good agreement between the finite element and analytic results is obtained. This is very important because analytic derived expressions can be used as a useful approach in crack growth analyses. Lugs are essential components of an aircraft for which proof of damage tolerance has to be undertaken.

Fig.1. Geometry and loading of lugs Since the literature does not contain the

stress intensity solution for lugs which are required for proof of damage tolerance, the problems posed in the following investigation are: selection of a suitable method of determining other SIF, determination of SIF as a function of crack length for various form of lug and setting up a complete formula for calculation of the SIF for lug, allowing essential parameters. The stress intensity factors are the key parameters to estimate the characteristic of the cracked structure. Based on the stress intensity factors, fatigue crack growth and structural life predictions have been investigated. The lug


Stamenković, D. – Maksimović, K. – Nikolić-Stanojević, V. – Maksimović, S. – Stupar, S. – Vasović, I. 848

dimensions are defined in Fig. 1. To obtain the stress intensity factor for

the lugs it is possible to start with a general expression for the SIF in the next form:

aYK SUM , (1)

where Y is the correction function, a is the crack length. This function is essential in determining the stress intensity factor. Primary, this function depends on stress concentration factor, kt, and geometric ratio a/b. The correction function is defined using experimental and numerical investigations. This function can be defined in the next form [9] and [10]:

The stress concentration factor kt is very important in calculation of correction function, Eq. (2). In this investigation a contact finite element stress analysis was used to analyse the load transfer between the pin and lug.

3 CRACK GROWTH ANALYSES OF DAMAGED STRUCTURAL ELEMENTS

UNDER MIXED MODES

To determine crack growth trajectory for structural components under mixed modes here conventional singular finite elements and X-FEM are used. The finite element method is widely used in industrial design applications and many different software packages based on FEM techniques have been developed. It has proved to be very well suited for the study of

crack initiation and crack growth [1]. Over the past few decades, several approaches have been proposed to model crack problems: method based on quarter-point finite element [8]. To avoid the re-meshing step in crack modelling, drives techniques were proposed: the incorporation of a discontinuous mode on the element level [11], a moving mesh technique [4], and an enrichment technique based on a partition-of unity X-FEM. The essential idea in the extended finite element method is to add discontinuous enrichment functions to the finite element approximation using the partition of unity. An overview of the developments of the X-FEM method has been given by Rashid [12].

Several criteria have been proposed to describe the direction of crack propagation for mixed mode crack growth. Only the minimum strain energy density criterion [4] and [5] is discussed in this work. The strain energy density criterion is based on the postulate that the direction of crack propagation at any point along the crack front toward the region where the strain energy density factor is minimum. The strain energy density factor, S, is given as:

23312

211)( IIIIIII KaKKaKaS , (9)

where the factors aij are functions of the angle , and are defined as:

)cos)(cos1(16

111

k

Ga ,

)1(cos2sin16

112 k

Ga

,

)1cos3)(cos1()cos1)(1(16

122

k

ga ,

(10)

where G is the shear modulus and k is a constant depending upon stress state, and is defined as: k = (3-)/(1+) for plane stress. The direction of crack of crack growth is determined by minimizing this equation with respect to the angle theta ( ). In mathematical form, the strain energy density criterion can be stated as:

4 2 2 3

2 2 2

2(1 ) tan 2 (1 ) 2 10 tan2 2

24 tan 2 (1 ) 6 14 tan2 2

2(3 ) 0 ,

k k

k

k

(11)

Qz

b

aA

AkY t

SUM

12.1 ,(2)

barez , (3)

2

2

w Rb

,

(4)

22 2

3.22 10.39 7.67R R

rw w

,

(5)

3

3

10

10

aU

bQab

,

(6)

22 2

0.72 0.52 0.23R R

UH H

.

(7)



2

2

2( 1) sin 8 sin 2 ( 1)(1 )

cos 2( 3) cos 2 0 ,

k k

(12)

where III KK . Once S is established, crack

initiation will take place in a radial direction r, from the crack tip, along which the strain energy density is minimum.

The main advantage of this criterion is its ease and simplicity, and its ability to handle various combined loading situations. The crack growth direction angle in the local coordinate plane perpendicular to the crack front can then be determined for each point along the crack front. In this work, the crack inclination angle is taken into account in the calculations by means of the values of the SIF, KI and KII, because their values are a function of the orientation of the crack plane.

4 NUMERICAL EXAMPLES

In order to demonstrate the accuracy and efficiency of the methodology discussed in the preceding sections, two crack growth applications are described. The first applications describe crack growth in aircraft wing lug and the second illustrates the use of the finite element methodology to simulate crack trajectory under mixed-mode.

4.1 Fatigue Crack Growth in an Aircraft Wing Lug

This example describes the analytical and numerical methods for obtaining the stress intensity factors and for predicting the fatigue crack growth life for cracks at attachment lugs. Straight-shank male lug is considered in the analysis, Fig. 2. Three different head heights of lug are considered in the analysis. The straight attachment lugs are subjected to axial pin loading only. Material properties of lugs are (Al 7075 T7351) [10]: Rm = 432 MPa Ultimate tensile strength, RP0,2 = 334 MPa, CF= 3.10-7, nF

= 2.39, mMPaKIC 36.70 .

The stress intensity factors of cracked lugs are calculated under stress level: g = max

= 98.1 MPa, or corresponding axial force, Fmax = g·(w-2R)·t = 63716 N. In the present work finite element analysis of cracked lug is

modelled with special singular quarter-point six-node finite elements around crack tip, Fig. 3. The load of the model, i.e. a concentrated force, Fmax, was applied at the centre of the pin and reacted at the other and of the lug. Spring elements were used to connect the pin and lug at each pair of nodes with identical nodal coordinates all around the periphery. The area of contact was determined iteratively by assigning a very high stiffness to spring elements which were in compression and very low stiffness (essentially zero) to spring elements which were in tension. The stress intensity factors of lugs, analytic and finite elements, for through-the-thickness cracks are shown in Table 2. Analytic results are obtained using relations from previous sections, Eq. (1).

Table 1. Geometric parameters of lugs [10]

Lug No.

Dimensions [mm] 2R W H L t

2 6 7

40 40 40

83.3 83.3 83.3

44.4 57.1 33.3

160 160 160

15 15 15

Table 2. Comparisons analytic and FE results for SIF, KI

Lug No.

a [mm]

MKEIK max

[daN/mm2]

.max

ANALIK

[daN/mm2] 2 5.00 68.78 65.62 6 5.33 68.12 70.24 7 4.16 94.72 93.64

Fig. 4 shows a comparison between the

experimentally determined crack propagation curves and the load cycles calculates, and Walker law [11] for several crack lengths. Experimental results of crack growth behaviour of lugs were carried out on the servo-hydraulic MTS system. A detailed description of experimental fatigue behaviour of cracked lugs is described in reference [3]. A relatively close agreement between the test and the presented computation results is obtained. The analytic computation methods presented in this work can be a reliable method for damage tolerance analyses of notched structural components such as lugs-type joints. 4.2 Crack Growth from Riveted Holes

In this section, the modelling of crack

propagation in a plate (Al 2024 T351) with cracks



emanating from one hole subjected to a far-field tension is considered, σ Fig. 5. In the initial configuration the left crack has 2.54 mm and is oriented at angle 33.6 to the left hole. The change in crack length for each iteration is taken to be a constant, a = 2.54 mm, and the cracks are grown in eight steps. In this analysis the strain energy density criterion (S-criterion) is used to determine the crack trajectory or angle of crack propagation.

Fig. 2. Geometry of cracked lug 2

Fig. 3. Finite element model of cracked lug with stress distribution

In this work, the crack inclination angle

is taken into account in the calculations by means of the values of the SIF, KI and KII, because their values are a function of the orientation of the crack plane. These parameters

were calculated numerically with the finite element method.

Fig. 4. Crack propagation at lug –Comparisons analytic results with tests (H = 44.4 mm)

Fig. 5. Geometry and load of the riveted crack problem

Fig. 6. The crack trajectory using Q-P elements and S-criterion



Figure 6 shows the stress contour and crack trajectory for the last configuration. In this crack growth analysis quarter-point (Q-P) singular finite elements are used with S-criterion. These results are compared with an extended finite element method (X-FEM) [13] and [14], Table 3 and Fig. 7.

The predicted crack trajectories using Q-P singular finite elements and X-FEM method are nearly identical. The extended finite element method allows for the modelling of arbitrary geometric features independently of the finite element mesh. This method allows the modelling of crack growth without re-meshing.

Fig. 7 shows good agreement between conventional QP singular finite elements and X-FEM in determining crack growth trajectory.

5 CONCLUSIONS

The finite element method is a robust and efficient technology that can be used to investigate the impact crack on the performance of notched structural components.

Table 3. Position for left crack tip

X-FEM [13] Presented Q-P

singular FE solutions XC [mm] YC [mm] XC [mm] YC [mm]54.458 64.618 54.458 64.618 57.404 64.465 56.987 64.389 60.350 64.287 59.525 64.287 63.322 64.287 62.065 64.259 66.294 64.364 64.605 64.247 69.266 64.338 67.145 64.247 72.136 64.262 69.685 64.270 74.168 63.754 72.227 64.315

The aim of this work is to investigate the

strength behaviour of the notched structural elements such as the aircraft cracked lugs. In the fatigue crack growth and fracture analysis of lugs, accurate calculation of SIF is essential. Analytic expression for stress intensity factor of cracked lug is derived using the correction function and FEM. The contact finite element analyses for the true distribution of pin contact pressure are used for determining stress concentration factors used in the correction function. Good agreement between the derived

analytic SIF of cracked lug with finite elements is obtained.

Fig. 7. Comparison of crack trajectory using present QP singular FE and X-FEM

Two applications were discussed in this

work in order to demonstrate the effectiveness of finite element based on computer codes in evaluating the impact of fatigue crack growth on structural components. Firstly, the predicted crack trajectory is calculated using quarter-point singular finite elements. The applications described a fatigue crack growths analysis of lugs with complex geometry and loading. Good agreements between present computation results with experiments have been obtained. Secondly, the predicted crack trajectory under mixed modes is determined using quarter-point singular finite elements together with the strain energy density criteria. The predicted crack growth trajectory under mixed modes in a plate with cracks emanating from one hole subjected to a far-field tension was nearly identical to the trajectories predicted with X-FEM.

6 ACKNOWLEDGMENTS

The authors wish to thank the

management of MTI in Belgrade for providing the encouragement and infrastructure to carry out this work. We would like to thank colleagues for all their valuable suggestions regarding this work.

7 REFERENCES

[1] Maksimović, S. (2005). Fatigue life analysis of

aircraft structural components. Scientific Technical Review, vol. LV, no. 1, p. 15-22.

[2] MIL-A-83444, Airplane Damage Tolerance Requirements.



[3] Maksimović, K. (2003). Strength analysis of structural components with respect to damage tolerance damages under dynamic loads, Master Thesis, Faculty of Mechanical Engineering, University of Kragujevac, Kragujevac.

[4] Sih, G.C. (1991). Mechanics of fracture initiation and propagation, Kluwer, Dordrecht.

[5] Sih, G.C. (1974). Strain density factor applied to mixed mode crack problems. Int. J. Fract., vol. 10, p. 305-321.

[6] Gdoutos, E.E. (1990). Fracture mechanics criteria and applications, Kluwer, Dordrecht.

[7] Jeong, D.Z. (2004). Mixed mode fatigue crack growth in test coupons made from 2024-T3 aluminium. Theoretical and Appl. Frac. Mech., vo. 42, p. 35-42.

[8] Barsoum, R.S. (1977). Triangular quarter-point elements as elastic and perfectly plastic crack tip elements, Int. J. Numer. Meth. Eng., vol. 11, p. 85-98.

[9] Maksimović, K. (2002). Estimation of residual strength for aircraft structural elements. J. Technical Diagnostics, no. 3, p. 54-57.

[10] Geier, W. (1980). Strength behaviour of fatigue cracked lugs, Royal Aircraft Establishment, LT 20057.

[11] Walker, K. (1970). The effect of stress ratio during crack propagation and fatigue for 2024 T3 Aluminium, in “Effects of environment and complex loading history on fatigue life”, ASTM STP 462,

American Society for Testing and Materials, Philadelphia PA, pp. 1-14.

[12] Rashid, M. (1998). The arbitrary local mesh refinement method: an alternative to re-meshing for crack propagation analysis. Comput Meth Appl Mech Eng, vol. 154, p. 133-50.

[13] Jovičić, G., Živković, M., Jovičić, N. (2009). Numerical simulation of crack modelling using extended finite element method, Strojniški vestnik- Journal of Mechanical Engineering, vol. 55, no. 9, p. 549-554.

[14] Jovičić, G, Živković, M, Maksimović, K, Djordjević, N. (2008). The crack growth analysis on the real structure using the X-FEM and EFG methods, Scientific Technical Review, vol. LVIII, no. 2, p. 21-26.

[15] Maksimović, K, Nikolić-Stanojević, V, Maksimović, S. (2004). Efficient computation method in fatigue life estimation of damaged structural components. Series Mechanics, Automatic Control and Robotics, vol. 4, no. 16, p. 101-114.

[16] Oliver, J. (1995). Continuum modelling of strong discontinuities in solid mechanics using damage models. Comput Mech, vol. 17, p. 49-61.

[17] Stamenković, D. (2006). Determination of fracture mechanics parameters using FEM and J-integral approach, Finite element simulation of the high risk constructions. Special Session within 2nd WSEAS International Conference on Applied and Theoretical Mechanics (MECHANICS '06), Mijuca, D., Maksimovic, S. (eds.), p. 252-257, Venice.

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Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12 Vsebina

Vsebina

Strojniški vestnik - Journal of Mechanical Engineering letnik 56, (2010), številka 12 Ljubljana, december 2010

ISSN 0039-2480

Izhaja mesečno

Uvodnik SI 169 Povzetki člankov Tomaž Katrašnik: Gospodarnost hibridnih električnih težkih vozil SI 171 Iztok Palčič, Borut Buchmeister, Andrej Polajnar: Analiza inovacijskih konceptov v

slovenskih proizvodnih podjetjih SI 172 Oğuz Yunus Sarıbıyık, Mustafa Özcanlı, Hasan Serin, Selahattin Serin, Kadir Aydın:

Proizvodnja biodizla iz olja kloščevca in njegove zmesi z biodizlom iz soje SI 173 Antun Galović, Nenad Ferdelji, Saša Mudrinić: Ustvarjanje entropije in eksergijska

učinkovitost pri adiabatnem mešanju tokov dušika in kisika pri različnih temperaturah in tlakih okolice SI 174

Dominik Kobold, Tomaž Pepelnjak, Gašper Gantar, Karl Kuzman: Analiza preoblikovalnih lastnosti gnetne magnezijeve zlitine AZ80 v vročem stanju SI 175

Janez Kušar, Tomaž Berlec, Ferdinand Žefran, Marko Starbek: Krajšanje časov priprave strojev SI 176

Dragi Stamenković, Katarina Maksimović, Vera Nikolić-Stanojević, Stevan Maksimović, Slobodan Stupar, Ivana Vasović: Ocenjevanje utrujenostne trajnostne dobe zarezanih konstrukcijskih komponent SI 177

Navodila avtorjem SI 179 Osebne vesti Doktorati, magisteriji, specializacija in diplome SI 181

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 169-170

SI 169

Uvodnik

Jubilej:

Strojniški vestnik – Journal of Mechanical Engineering 55 let

V letih 1954/55 je v Sloveniji zrasla ideja

za izdajanje tehniške besede v tiskani obliki, z revijo, ki bo med periodičnimi publikacijami različnih panog tehnike izpopolnila občutnejšo vrzel na področju strojništva. »Področja dela strojnih inženirjev in tehnikov so prav gotovo med najbolj raznolikimi na področju tehnike« je zapisano v uvodniku prve številke Strojniškega vestnika (SV), ki je izšla marca 1955. Tudi v času izdaje prve številke SV je bilo pomanjkanje strokovnih kadrov očitno za izrazito hiter razvoj industrije. In kaj se je pričakovalo od strojnega inženirja, ki mora biti med vsemi najbolj vsestranski? Praksa je dan za dnem kazala, da mora prav strojni inženir predstavljati tisti člen v vsakem podjetju, ki pred vsemi drugimi teži za uvedbo sodobnih tehničnih metod za gradnjo strojev in naprav, pri tem pa ne sme zanemarjati niti uporabe najpreprostejših sredstev za dosego proizvodnih in ekonomskih uspehov, pri čemer se mora prizadevati za širjenje tehnične izobrazbe, kakor tudi za raziskovanje. In tu je SV pripomogel v veliki meri, saj tehniška kultura zagotavlja primerljivost posameznemu narodu v svetovnem razvojnem ciklu.

Porojen na slovenskih tleh je SV ob začetku izhajanja izpolnil občutno vrzel v strokovni (znanstveni) literaturi, saj je bil prvo samostojno strojniško glasilo za inženirje in tehnike v takratni državi. Vendar, namenjen predvsem ožji domovini, je moral že vse od začetka upoštevati skromne možnosti majhnega a inteligentnega, tudi v tehniko usmerjenega naroda. Naprednost in širino že prve številke SV izkazuje tudi dejstvo, da je v slovenskem tehničnem jeziku napisana vsebina, bila z naslovom in kratkim povzetkom posameznega članka, podana v srbsko-hrvaškem, nemškem, francoskem in angleškem jeziku.

Navzlic 55 letniku, je še vedno prva številka prvega letnika SV legendarna. Pa ne samo zato, ker je bila prva, temveč tudi zato, ker je v njej objavljen eden od vrhuncev slovenske strojniške znanosti. S člankom »Vrednost in

obračunavanje energije« je eden največjih slovenskih znanstvenikov na področju termodinamike prof. Zoran Rant, kot prvi na svetu uvedel pojem eksergije. Med drugim je zapisal: »Maksimalno delo, ki ga lahko dobimo iz neke energije, je prav gotovo zelo važna in imenitna veličina in zasluži svoje posebno ime. Beseda »energija« je izvedena iz dveh grških besed: έν = v in έργоν = delo; pomeni torej »delo«, ki tiči »v« nekem sistemu. Delo, ki ga lahko dobimo »iz« (grško έχ ali έξ) tega sistema, je potemtakem »e k s e r g i j a«. Maksimalno delo, ki ga lahko dobimo iz energije, bomo imenovali eksergijo E. Vsaki energiji pripada določena eksergija. Eksergija je tisti del energije, ki ima vrednost. Energija brez eksergije je brez vrednosti.« Članek je tudi dandanes citiran v številnih objavah, prva številka SV s tem člankom pa podarjena številnim uglednim svetovnim institucijam in strokovnim združenjem, kot na primer ASHRAE (Ameriško društvo inženirjev ogrevanja, hlajenja in klimatizacije).

Spoznanja izpred 55 let pa še danes ne upoštevamo v celoti pri obračunavanju energije, kar je avtor članka že takrat opozoril z navedbo: »Dosedanji način obračunavanja energij v kombiniranih obratih na porabljenih entalpij je načeloma nepravilen. Namesto njega se mora uvesti obračunavanje na podlagi porabljenih eksergij, ki je edino pravilno. Posledica tega bo zvišanje cene elektroenergije in znižanje cene kurilne energije, kar pa je tudi v skladu z vrednostjo teh dveh energij.«

Ob letošnjem dvojnem jubileju: 55 letnici SV-JME in 50 letnici samostojnosti Fakultete za strojništvo Univerze v Ljubljani je bila izdana knjiga »Zgodovina strojništva in tehniške kulture na Slovenskem« v kateri sem orisal, po moji oceni, ključne mejnike SV-JME, kot zgodovino tehniške besede v sožitju znanstvenega duha.

SV je bil vpliven in kakovosten od samega začetka. Prehodil je pot z različnimi spremembami, koncem 20. stoletja se je preimenoval v Strojniški vestnik – Journal of


SI 170

Mechanical Engineering (SV-JME), ter si pridobil faktor vpliva. Nova uredniška usmeritev v zadnjih letih dokazuje uspešnost in pravilno usmerjenost, saj je SV-JME postal pomembna mednarodna revija na področju strojništva, katere kakovostni trend in odmevnost zmerno hitro narašča v zadnjih treh letih. Po razvrstitvi v Journal Citation Reports za leto 2009 SV-JME dosega faktor vpliva 0,533, iz Web of Science pa je tudi razviden trend mednarodnega vpliva (Fig. 1).

Sl. 1: Trend rasti števila citatov (na dan 22.11.2010)

Ker je uspešnost in kakovost revije tudi odsev vrhunskosti recenzentov, bomo v prvi številki letnika 57 ter na spletni strani revije objavili seznam recenzentov, ki so sodelovali pri čistih recenzijah člankov v letu 2010. Vsakemu recenzentu posebej smo hvaležni za sodelovanje in za porabljeni čas. Uredništvo SV-JME vabi znanstvenike in druge vrhunske ter eminentne strokovnjake iz vsepovsod, da nam sporočite voljnost za opravljanje recenzijskega dela, kakor tudi, da uredništvu pošljete za objavo članke, katerih odmev naj bi bil podoben članku objavljenem v prvi številki SV.

Naj sklenem z mislijo prvega urednika SV prof. Bojana Krauta, ko je v uvodniku prve številke zapisal: »Revija se pojavlja v času, ko za take podvige v nekaterih pogledih ni ugoden. Njene naloge pa so vredne truda. Vsem, ki imajo opravka s strojništvom, posebej pa še strojnim inženirjem in tehnikom, naj služi za širjenje in poglabljanje znanja v tej stroki in daje pomoč pri strokovnem delu«. Ob tem pa dodajam: Raziskovati je, kakor proti toku plavati, za hip se ustaviš in že te odnese nazaj. SV-JME gre naprej!

Želim Vam vesele praznike

in obilo uspehov v letu 2011!

Vincenc Butala

Sl. 2. Proslava ob 55 letnici SV-JME

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 171 Prejeto: 04.03.2010 UDK 629.4.038:621.182.3 Sprejeto: 31.08.2010

*Naslov avtorja za dopisovanje: Univerza v Ljubljani, Fakulteta za strojništvo, Aškerčeva 6, SI-1000 Ljubljana, Slovenija, e-mail: [email protected]

SI 171

Gospodarnost hibridnih električnih težkih vozil

Tomaž Katrašnik Univerza v Ljubljani, Fakulteta za strojništvo, Ljubljana, Slovenija

Gospodarnost zaporednih in vzporednih hibridnih električnih težkih vozil je analizirana z

analitičnim in simulacijskim pristopom. Kombiniran pristop omogoča izračun energijskih tokov in energijskih izgub na različnih energijskih poteh in ovrednoti njihov vpliv na porabo goriva. Članek poda vpliv različnih topologij hibridnih električnih vozil (HEV), razmerij moči in značilnostmi gradnikov pogonskih agregatov ter uporabljenih krmilnih strategij na porabo goriva HEV. Analiziran je tudi vpliv hibridizacije pogonskega sistema na porabo goriva vozil, ki prevažajo različna bremena in vozijo v skladu z različnimi voznimi cikli. Iz rezultatov je razvidno, da navedeni parametri pomembno vplivajo na porabo goriva HEV. Inovativen kombinirani pristop omogoča identifikacijo in analizo mehaniznov, ki vodijo k zmanjšani porabi goriva hibridnih električnih težkih vozil. V zaključku so podane tudi splošno veljavne smernice za zmanjšanje porabe goriva HEV. ©2010 Strojniški vestnik. Vse pravice pridržane. Ključne besede: hibridna električna vozila, poraba goriva, simulacija, analitična analiza

Sl. 3. ECE_NEDC_LOW cikel: a) fm ,

effICE , in Vm b) *TcPrR , *MIce , *RB in *CEsIce , in c)

PRtcW ,,

BRtcW , in

BRW za polno obteženo vozilo, ter d) do f) enaki parametri za neobteženo vozilo

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 172 Prejeto: 13.04.2010 UDK 658.5:001.895 Sprejeto: 01.10.2010

* Naslov avtorja za dopisovanje: Univerza v Mariboru, Fakulteta za strojništvo, Smetanova ulica 17, SI-2000Maribor, Slovenija, [email protected]

SI 172

Analiza inovacijskih konceptov v slovenskih proizvodnih podjetjih

Iztok Palčič* – Borut Buchmeister – Andrej Polajnar

Univerza v Mariboru, Fakulteta za strojništvo, Slovenija

Konkurenčne prednosti evropskih podjetij ne izhajajo zgolj iz inovacij izdelkov, temelječih na raziskovalno-razvojnem delu, ampak tudi iz tehniških in netehniških (organizacijskih) inovacij, s katerimi želimo posodobiti proizvodne procese. Prispevek predstavlja rabo izbranih inovacijskih konceptov v slovenskih proizvodnih podjetjih. V njem smo analizirali odnos med tehniškimi in organizacijskimi inovacijskimi koncepti ter izbranimi kazalniki poslovanja podjetij. Rezultati nakazujejo, da izdatki za raziskovalno-razvojno dejavnost in inovacijski koncepti niso zmeraj v korelaciji ter da obstajajo razlike pri implementaciji inovacijskih konceptov med nizko-, srednje- in visokotehnološkimi podjetji. Podatke za analizo smo pridobili s pomočjo ankete o proizvodni dejavnosti v Evropi v letu 2009, ki smo jo izvedli v 9-ih državah. Za prispevek smo uporabili podatke, ki so jih posredovala slovenska proizvodna podjetja. ©2010 Strojniški vestnik. Vse pravice pridržane. Ključne besede: inovacije, tehniške inovacije, organizacijske inovacije, kazalniki poslovanja podjetij

Sl. 1. Tipologija organizacijskih inovacij [7]

.

Medfunkcionalni timi Decentralizacija načrtovanja, izvedbenih

aktivnosti in kontrolne funkcije Proizvodne celice ali segmenti Zmanjšanje števila hierarhičnih ravni itn.

Znotraj organizacije

Timsko delo v proizvodnji Obogatitev dela, povečanje obsega dela Sočasni inženiring Procesi nenehnih izboljšav / Kaizen Krogi kakovosti Presoja kakovosti / certificiranje Okoljske presoje KANBAN (principi »brez zalog«) Preventivno vzdrževanje itn.

Sodelovalne mreže ali zavezništva (R&R, proizvodnja, prodaja …)

Odločitev »kupi-naredi«, outsourcing

Selitev proizvodnje itn.

Zunaj organizacije

»Just-in-time« (s kupci in z dobavitelji)

Menedžment dobavnih verig Presoja kakovosti s strani kupcev

itn.

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Težišče organizacijske inovacije

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 173 Prejeto: 29.04.2009 UDK 662.756.3 Sprejeto: 02.09.2010

*Naslov avtorja za dopisovanje: Univerza Çukurova, Oddelek za strojništvo, 01330, Adana, Turčija, [email protected]

SI 173

Proizvodnja biodizla iz olja kloščevca in njegove zmesi z biodizlom iz soje

Oğuz Yunus Sarıbıyık1 - Mustafa Özcanlı2 - Hasan Serin2 - Selahattin Serin1 - Kadir Aydın2,*

1Univerza Çukurova, Oddelek za kemijo, Turčija 2Univerza Çukurova, Oddelek za strojništvo, Turčija

V študiji je bilo olje kloščevca (Ricinus Communis – RC) uporabljeno kot surovina za proizvodnjo

biodizla. Za pridobivanje olja RC je bil uporabljen ekstrakcijski aparat soxhlet. Članek obravnava transesterifikacijo olja kloščevca z metanolom za proizvodnjo biodizla. Študija analizira tudi gorivne lastnosti zmesi biodizla RC in biodizla iz soje. Določene so bile različne lastnosti biodizla iz RC, biodizla iz soje in njunih zmesi, kot so filtrirnost (CFPP), cetansko število, plamenišče, kinematična viskoznost in gostota. Podana je primerjava rezultatov preizkusa z evropskimi standardi za biodizel EN 14214. Analiza je pokazala, da se je cetansko število in obnašanje v hladnem zmesi biodizla RC in biodizla iz soje izboljšalo zaradi visokega cetanskega števila (80) in nizke filtrirnosti (-35 °C) biodizla RC. © 2010 Strojniški vestnik. Vse pravice pridržane. Ključne besede: Ricinus Communis, biodizel, transesterifikacija, lastnosti biodizla, cetansko število, CFPP

CH2

CH

CH2

OCOR1

OCOR2

OCOR3

3CH3OH

CH2

HC

CH2

OH

OH

OH

R1COOCH3

R2COOCH3

R3COOCH3

Cata lyst

trigliceridi metanol glicerol metilni ester

Sl. 1: Enačba za transesterifikacijo trigliceridov

katalizator

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 174 Prejeto: 08.05.2008 UDK 536.75:536.711 Sprejto: 30.09.2010

*Naslov avtorja za dopisovanje: Univerza v Zagrebu, Fakulteta za strojništvo in ladjedelništvo, Ivana Lučića 5, 10000 Zagreb, Hrvaška, [email protected] SI 174

Ustvarjanje entropije in eksergijska učinkovitost pri adiabatnem mešanju tokov dušika in kisika pri različnih

temperaturah in tlakih okolice

Antun Galović* - Nenad Ferdelji - Saša Mudrinić Univerza v Zagrebu, Fakulteta za strojništvo in ladjedelništvo, Hrvaška

V članku je predstavljen brezdimenzijski model povečevanja entropije in eksergijske učinkovitosti pri adiabatnem mešanju tokov dušika in kisika pri različnih temperaturah in tlakih okolice. Nastala mešanica ima tlak okolice. Brezdimenzijske spremenljivke v modelu predstavljajo razmerje med termodinamičnimi temperaturami tokov u, razmerje med termodinamično temperaturo enega toka in temperaturo okolice u1 ter molski delež y1 enega od tokov. Model upošteva nepovračljivost zaradi različnih temperatur tokov pri mešanju različnih plinov, eksergija tokov pa upošteva tudi njihove molske deleže v okolišnjem zraku (atmosferi). Model pri tem upošteva standardne vrednosti molskih deležev kisika in dušika yO2 = 0,21 in yN2 = 0,79. Podane so tudi vrednosti molskih deležev tokov, pri katerih se ustvari največ entropije in je vrednost eksergijske učinkovitosti najmanjša. Rezultati izračunov so prikazani v diagramih. © 2010 Strojniški vestnik. Vse pravice pridržane. Ključne besede: analitični model, ustvarjanje entropije, eksergijska učinkovitost, mešanje tokov dušika in kisika

m

n

is.s

yst

RqS

y1

= 1.4

Sl. 1. Količinski prikaz brezdimenzijskega modela povečevanja entropije v odvisnosti od molskega deleža y1, temperaturnega razmerja u pri adiabatnem mešanju tokov dveh različnih dvoatomskih plinov, = 1.4

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 175 Prejeto: 02.07.2010 UDK 621.73:669.721.5 Sprejeto: 26.10.2010

*Naslov avtorja za dopisovanje: TECOS Razvojni center orodjarstva Slovenije, Kidričeva 25, 3000 Celje, Slovenija, [email protected] SI 175

Analiza preoblikovalnih lastnosti gnetne magnezijeve zlitine AZ80 v vročem stanju

Dominik Kobold1,* - Tomaž Pepelnjak2 - Gašper Gantar1 - Karl Kuzman2

1 TECOS Razvojni center orodjarstva Slovenije, Slovenija 2 Univerza v Ljubljani, Fakulteta za strojništvo, Slovenija

Lahki in okolju prijazni materiali z dobrimi mehanskimi lastnostmi se vedno bolj pogosto

uveljavljajo kot konstrukcijski materiali v številnih sodobnih aplikacijah. Zmanjševanje mase lahko namreč bistveno pripomore k izboljšanju karakteristik številnih proizvodov in omogoča zmanjšanje porabe goriva pri prevoznih sredstvih.

Magnezij je eden izmed najbolj cenjenih lahkih konstrukcijskih materialov, saj ima zelo majhno gostoto, izredno dobre mehanske in odrezovalne lastnosti, v naravi pa obstajajo neusahljive zaloge surovega materiala. S procesom kovanja, kjer se iz oblikovno enostavnih surovcev z delovanjem kompresijskih sil povzročenih preko utopov raznolikih gravur oblikujejo končni proizvodi, se lahko še dodatno izboljšata trdnost in metalografska struktura proizvodov. Kljub možnosti izboljšanja mehanskih lastnosti, pa je proces kovanja magnezijevih zlitin v primerjavi z litjem zelo redko uporabljen. Razlogi za to se skrivajo v specifičnih preoblikovalnih lastnostih, ki so predvsem posledica osnovne heksagonalne gosto zložene kristalne rešetke magnezija.

V članku so predstavljene študije vpliva najpomembnejših procesnih parametrov na plastično preoblikovanje magnezijevih zlitin. Na podlagi intenzivne eksperimentalne študije je pojasnjen anizotropni tok materiala in vpliv bistvenih vhodnih parametrov na plastično preoblikovanje gnetne magnezije zlitine AZ80. Rezultati študije se neposredno dotikajo industrijskega okolja in se lahko tudi uporabijo za kalibracijo in postavitev MKE modelov, kjer bi se upoštevali anizotropni zakoni tečenja materiala. Predstavljene študije v članku omogočajo tudi določitev primernih tehnoloških parametrov za proces kovanja gnetnih magnezijevih zlitin. ©2010 Strojniški vestnik. Vse pravice pridržane. Ključne besede: kovanje magnezija, anizotropija, plastična deformacija, krivulje plastičnosti, AZ80, gnetne magnezijeve zlitine

a) b)

Sl. 1. Metalografska struktura zlitine AZ80 a) vzdolžni presek b) prečni presek [7]

Mg17Al12 Mg17Al12

20m 20m

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 176 Prejeto: 22.04.2010 UDK 658.512.4:658.512.62 Sprejeto: 26.05.2010

*Naslov avtorja za dopisovanje: Univerza v Ljubljani, Fakulteta za strojništvo, Aškerčeva 6, SI-1000 Ljubljana, Slovenija, [email protected] SI 176

Krajšanje časov priprave strojev

Janez Kušar* - Tomaž Berlec - Ferdinand Žefran - Marko Starbek Univerza v Ljubljani, Fakulteta za strojništvo, Slovenija

Danes se podjetja srečujejo z zahtevami kupcev po vse manjših serijah izdelkov, to pa povzroča

vse pogostejšo pripravo strojev, ki pa predstavlja zapravljanje. Predstavljen je postopek organizacije in izvedbe krajšanja časov priprave strojev, ki temelji na

timskem delu in uporabi tako metode SMED, ki omogoča postopno krajšanje časov priprave strojev pod 10 min, kot tudi sistema stalnih izboljšav.

V članku so prikazani rezultati organizacije in izvedbe SMED-delavnice krajšanja časov priprave stroja za brizganje ter predstavljeni prvi predlogi izboljšav, ki naj bi bistveno vplivali na skrajšanje časov priprave stroja. ©2010 Strojniški vestnik. Vse pravice pridržane. Ključne besede: čas priprave strojev, SMED-delavnica, stalne izboljšave, timsko delo, mikroelementi

1. korak:IZBOR STROJA

2. korak:DOLOČITEV CILJA KRAJŠANJA ČASOV PRIPRAVE IZBRANEGA

STROJA

3. korak:DOLOČITEV ČLANOV TIMA

4. korak:DOKUMENTIRANJE

ELEMENTOV PRIPRAVE STROJA – po veljavnem postopku

5. korak:PREOBLIKOVANJE

ELEMENTOV PRIPRAVE STROJA – v vizualno obliko

6. korak:IZVEDBA ANALIZE MIKROELEMENTOV

PRIPRAVE STROJA:

FAZA 0 – Analiza obstoječega stanja

FAZA 1 – Ločevanje notranjih in zunanjih mikroelementov priprave strojev

FAZA 2 – Pretvorba notranjih v zunanje mikroelemente priprave strojev

FAZA 3 – Izboljšanje notranjih in zunanjih mikroelementov priprave strojev

FAZA 4 – Standardizacija mikroelementov priprave strojev

Ali je CILJ dosežen?

7. korak:Takojšnja ponovitev izvedbe

analize mikroelementov priprave strojev

8. korak:Čez ŠEST MESECEV ponovitev

organizacije in izvedbe SMED-delavnice

SMED-delavnica

Da

Ne

Sl. 4: Postopek organizacije in izvedbe SMED-delavnice

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 177 Prejeto: 01.03.2010 UDK 629.7:620.178.3 Sprejeto: 19.05.2010

*Naslov avtorja za dopisovanje: Termoelektro d.o.o., Uralska 9, 11000 Beograd, Srbija, [email protected]

SI 177

Ocenjevanje utrujenostne trajnostne dobe zarezanih konstrukcijskih komponent

Dragi Stamenković1,* - Katarina Maksimović2 – Vera Nikolić-Stanojević3 – Stevan Maksimović4 -

Slobodan Stupar5 – Ivana Vasović6

1Termoelektro d.o.o., Srbija 2Mesto Beograd – mestna uprava, sekretariat za komunalne in stanovanjske zadeve, uprava za vode,

Srbija 3Državna univerza v Novem Pazarju, Srbija

3Vojno-tehnični institut, Srbija, 5Fakulteta za strojništvo, Srbija

6Inštitut Gosa, Srbija

V prispevku so obravnavane analitične in numerične metode in postopki za pridobivanje faktorjev intenzitete napetosti in napovedovanje rasti utrujenostnih razpok pri razpokanih ali zarezanih konstrukcijskih komponentah. V zadnjih dveh desetletjih je bilo veliko truda posvečenega vrednotenju faktorja intenzitete napetosti za vogalne razpoke in za razpoke po celotni debelini, ki izhajajo iz lukenj za pritrdilne elemente. Za ocenjevanje faktorja intenzitete napetosti (SIF) so bile uporabljene različne metode, od analitičnih metod s približki, metode končnih elementov (FEM), metode končnih elementov z alternacijo, utežne funkcije in fotoelastičnosti do preizkusov utrujanja. V tem prispevku so bile za določanje SIF ter za napovedovanje rasti utrujenostnih razpok v pritrdilnih ušesih uporabljene analitične oz. numerične metode in postopki. Predstavljena je analiza ene skoznje razpoke v pritrdilnem ušesu. Za ta namen so bili uporabljeni analitični nastavki za SIF na razpokanih ušesih. Za validacijo analitičnih faktorjev intenzitete napetosti pri razpokanih ušesih je bila uporabljena metoda FEM s singularnimi končnimi elementi. Ugotovljeno je bilo dobro ujemanje med rezultati izračunov in eksperimentov za utrujenostno trajnostno dobo razpokanih ušes pri letalih. Za določanje trajektorije razpok na razpokanih konstrukcijskih komponentah v mešanih načinih je bila uporabljena običajna metoda singularnih končnih elementov in X-FEM. ©2010 Strojniški vestnik. Vse pravice pridržane. Ključne besede: zarezane konstrukcijske komponente, ušesa, analitični faktorji intenzitete napetosti za ušesa, končni elementi, X-FEM, ocenjevanje utrujenostne trajnostne dobe

Sl.1. Geometrija in pritrdilna ušesa

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 179-180 Navodila avtorjem

SI 179

Navodila avtorjem

Navodila so v celoti na voljo v rubriki "Informacija za avtorje" na spletni strani revije: http://en.sv-jme.eu/ Članke pošljite na naslov: Univerza v Ljubljani Fakulteta za strojništvo SV-JME Aškerčeva 6, 1000 Ljubljana, Slovenija Tel.: 00386 1 4771 137 Faks: 00386 1 2518 567 E-mail: [email protected] [email protected] Članki morajo biti napisani v angleškem jeziku. Strani morajo biti zaporedno označene. Prispevki so lahko dolgi največ 10 strani. Daljši članki so lahko v objavo sprejeti iz posebnih razlogov, katere morate navesti v spremnem dopisu. Kratki članki naj ne bodo daljši od štirih strani. V spremnem dopisu navedite podatke o predhodnem ali hkratnem predlaganju članka v objavo drugje. Prosimo, da članku določite tudi tipologijo – opredelite ga lahko kot izvirni, pregledni ali kratki članek. Navedite vse potrebne kontaktne podatke (poštni naslov in email) in predlagajte vsaj dva potencialna recenzenta. Navedete lahko tudi razloge, zaradi katerih ne želite, da bi določen recenzent recenziral vaš članek.

OBLIKA ČLANKA

Članek naj bo napisan v naslednji obliki:

- Naslov, ki primerno opisuje vsebino članka. - Povzetek, ki naj bo skrajšana oblika članka in

naj ne presega 250 besed. Povzetek mora vsebovati osnove, jedro in cilje raziskave, uporabljeno metodologijo dela, povzetek rezultatov in osnovne sklepe.

- Uvod, v katerem naj bo pregled novejšega stanja in zadostne informacije za razumevanje ter pregled rezultatov dela, predstavljenih v članku.

- Teorija. - Eksperimentalni del, ki naj vsebuje podatke o

postavitvi preskusa in metode, uporabljene pri pridobitvi rezultatov.

- Rezultati, ki naj bodo jasno prikazani, po potrebi v obliki slik in preglednic.

- Razprava, v kateri naj bodo prikazane povezave in posplošitve, uporabljene za pridobitev rezultatov. Prikazana naj bo tudi pomembnost

rezultatov in primerjava s poprej objavljenimi deli. (Zaradi narave posameznih raziskav so lahko rezultati in razprava, za jasnost in preprostejše bralčevo razumevanje, združeni v eno poglavje.)

- Sklepi, v katerih naj bo prikazan en ali več sklepov, ki izhajajo iz rezultatov in razprave.

- Literatura, ki mora biti v besedilu oštevilčena zaporedno in označena z oglatimi oklepaji [1] ter na koncu članka zbrana v seznamu literature.

Enote - uporabljajte standardne SI simbole in okrajšave. Simboli za fizične veličine naj bodo v ležečem tisku (npr. v, T, n itd.). Simboli za enote, ki vsebujejo črke, naj bodo v navadnem tisku (npr. ms-1, K, min, mm itd.) Okrajšave naj bodo, ko se prvič pojavijo v besedilu, izpisane v celoti, npr. časovno spremenljiva geometrija (ČSG).

Pomen simbolov in pripadajočih enot mora biti vedno razložen ali naveden v posebni tabeli na koncu članka pred referencami. Slike morajo biti zaporedno oštevilčene in označene, v besedilu in podnaslovu, kot sl. 1, sl. 2 itn. Posnete naj bodo v ločljivosti, primerni za tisk, v kateremkoli od razširjenih formatov, npr. BMP, JPG, GIF. Diagrami in risbe morajo biti pripravljeni v vektorskem formatu, npr. CDR, AI.

Vse slike morajo biti pripravljene v črno-beli tehniki, brez obrob okoli slik in na beli podlagi. Ločeno pošljite vse slike v izvirni obliki Pri označevanju osi v diagramih, kadar je le mogoče, uporabite označbe veličin (npr. t, v, m itn.). V diagramih z več krivuljami, mora biti vsaka krivulja označena. Pomen oznake mora biti pojasnjen v podnapisu slike. Tabele naj imajo svoj naslov in naj bodo zaporedno oštevilčene in tudi v besedilu poimenovane kot Tabela 1, Tabela 2 itd.. Poleg fizikalne veličine, npr t (v ležečem tisku), mora biti v oglatih oklepajih navedena tudi enota. V tabelah naj se ne podvajajo podatki, ki se nahajajo v besedilu. Potrditev sodelovanja ali pomoči pri pripravi članka je lahko navedena pred referencami. Navedite vir finančne podpore za raziskavo. REFERENCE Seznam referenc MORA biti vključen v članek, oblikovan pa mora biti v skladu s sledečimi navodili. Navedene reference morajo biti citirane v besedilu. Vsaka navedena referenca je v besedilu oštevilčena s številko v oglatem oklepaju (npr. [3]


SI 180

ali [2] do [6] za več referenc). Sklicevanje na avtorja ni potrebno. Reference morajo biti oštevilčene in razvrščene glede na to, kdaj se prvič pojavijo v članku in ne po abecednem vrstnem redu. Reference morajo biti popolne in točne. Navajamo primere: Članki iz revij: Priimek 1, začetnica imena, priimek 2, začetnica imena (leto). Naslov. Ime revije, letnik, številka, strani. [1] Zadnik, Ž., Karakašič, M., Kljajin, M.,

Duhovnik, J. (2009). Function and Functionality in the Conceptual Design Process. Strojniški vestnik – Journal of Mechanical Engineering, vol. 55, no. 7-8, p. 455-471.

Ime revije ne sme biti okrajšano. Ime revije je zapisano v ležečem tisku. Knjige: Priimek 1, začetnica imena, priimek 2, začetnica imena (leto). Naslov. Izdajatelj, kraj izdaje [2] Groover, M. P. (2007). Fundamentals of

Modern Manufacturing. John Wiley & Sons, Hoboken.

Ime revije je zapisano v ležečem tisku. Poglavja iz knjig: Priimek 1, začetnica imena, priimek 2, začetnica imena (leto). Naslov poglavja. Urednik(i) knjige, naslov knjige. Izdajatelj, kraj izdaje, strani. [3] Carbone, G., Ceccarelli, M. (2005). Legged

robotic systems. Kordić, V., Lazinica, A., Merdan, M. (Editors), Cutting Edge Robotics. Pro literatur Verlag, Mammendorf, p. 553-576.

Članki s konferenc: Priimek 1, začetnica imena, priimek 2, začetnica imena (leto). Naslov. Naziv konference, strani. [4] Štefanić, N., Martinčević-Mikić, S.,

Tošanović, N. (2009). Applied Lean System in Process Industry. MOTSP 2009 Conference Proceedings, p. 422-427.

Standardi: Standard (leto). Naslov. Ustanova. Kraj.

[5] ISO/DIS 16000-6.2:2002. Indoor Air – Part 6: Determination of Volatile Organic Compounds in Indoor and Chamber Air by Active Sampling on TENAX TA Sorbent, Thermal Desorption and Gas Chromatography using MSD/FID. International Organization for Standardization. Geneva.

Spletne strani: Priimek, Začetnice imena podjetja. Naslov, z naslova http://naslov, datum dostopa.

Rockwell Automation. Arena, from http://www.arenasimulation.com, accessed on 2009-09-27.

AVTORSKE PRAVICE

Avtorji v uredništvo predložijo članek ob predpostavki, da članek prej ni bil nikjer objavljen, ni v postopku sprejema v objavo drugje in je bil prebran in potrjen s strani vseh avtorjev. Predložitev članka pomeni, da se avtorji avtomatično strinjajo s prenosom avtorskih pravic SV-JME, ko je članek sprejet v objavo. Vsem sprejetim člankom mora biti priloženo soglasje za prenos avtorskih pravic, katerega avtorji pošljejo uredniku. Članek mora biti izvirno delo avtorjev in brez pisnega dovoljenja izdajatelja ne sme biti v katerem koli jeziku objavljeno drugje.

Avtorju bo v potrditev poslana zadnja verzija članka. Morebitni popravki morajo biti minimalni in poslani v kratkem času. Zato je pomembno, da so članki že ob predložitvi napisani natančno.

Avtorji lahko stanje svojih sprejetih člankov spremljajo na http://en.sv-jme.eu/.

PLAČILO OBJAVE Avtorji vseh sprejetih prispevkov morajo za

objavo plačati prispevek v višini 180,00 EUR (za članek dolžine do 6 strani) ali 220,00 EUR (za članek dolžine do 10 strani) ter 20,00 EUR za vsako dodatno stran. Dodatni strošek za barvni tisk znaša 90,00 EUR na stran.

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)12, SI 181-184 Osebne vesti

Osebne vesti SI 181

Doktorati, magisterij in diplome

DOKTORAT

Na Fakulteti za strojništvo Univerze v Ljubljani so z uspehom obranili svojo doktorsko disertacijo:

dne 10. novembra 2010 Aljaž OSTERMAN z naslovom: »Termografija termičnih učinkov pri ultrazvočno vzbujevani kavitaciji« (mentor: prof. dr. Brane Širok, somentor: doc. dr. Matevž Dular);

Prisotnost pojava kavitacije je zaradi močnih negativnih, pa tudi pozitivnih učinkov v mnogih primerih ključnega pomena. Pri obravnavi kavitacijskih učinkov, med katere sodijo tudi termični, pa so slednji večinoma zanemarjeni, saj se kavitacija navadno obravnava kot izotermni proces. Takšna obravnava pa na lokalnem nivoju ni primerna, saj tam to ne drži. Pričujoče doktorsko delo se ukvarja z ultrazvočno vzbujevano kavitacijo v vodi, pri kateri so bili izmerjeni temperaturni učinki kavitacije, poleg tega pa je bila uporabljena vizualizacija za spremljanje kavitacijskih mehurčkov. Za merjenje temperaturnih učinkov je bila vpeljana metoda termografije, ki predstavlja novo eksperimentalno metodo na področju kavitacije. Z njo so bili uspešno izmerjeni temperaturni učinki kavitacije, ki so se na časovno spremenljivih temperaturnih poljih odražali v obliki lokalnih ohladitev. Poleg tega so bila na osnovi rezultatov termografije in vizualizacije določena časovno odvisna hitrostna polja v kavitirajoči vodi. V doktorskem delu je tudi opisana povezava med temperaturnimi učinki in lokalnim pojavljanjem kavitacijskih mehurčkov, kar prav tako do sedaj še ni bilo izvedeno. Opis eksperimentalnega dela in rezultatov je dopolnjen z numerično simulacijo kavitacijskega mehurčka v ultrazvočnem polju, ki z rezultati smiselno nadgrajuje eksperimentalno analizo. Pri tem je bilo na podlagi simulacije gibanja stene generirano ustrezno ultrazvočno polje, nadaljnja simulacija pa je potrdila nesferični kolaps mehurčka ob steni. Z numerično simulacijo je bil tudi predstavljen pojav radialnega toka ob steni kot posledica kolapsa mehurčka. S pojavom tega toka se numerična simulacija še dodatno povezuje z eksperimentom. Skupni rezultati, predstavljeni v doktorskem delu, tako predstavljajo napredek v poznavanju samega pojava kavitacije. To bi lahko v prihodnosti

vodilo k optimiranju procesov, kjer nastopa kavitacija, oziroma k izboljšanju strojev in njihovih delov, pri katerih prihaja do kavitacije;

dne 12. novembra 2010 Simon OMAN z naslovom: »Model napovedovanja dobe trajanja zračnega vzmetenja na osnovi pospešenih preizkušanj« (mentor: prof. dr. Marko Nagode, somentor: prof. dr. Matija Fajdiga);

V doktorski nalogi je postavljena metodologija s katero je mogoče že v zgodnji fazi razvoja oceniti dobo trajanja zračne vzmeti. Metodologija prav tako omogoča pretvorbo poljubnega obremenitvenega kolektiva v obremenitveni kolektiv s konstantno amplitudo obremenjevanja, pri čemer se poškodbi, ki nastaneta po enem in drugem obremenitvenem kolektivu med seboj bistveno ne razlikujeta.

Za izračun poškodbe je uporabljen klasičen napetostni pristop z upoštevanjem elementarne Palmgren-Miner-jeve hipoteze o linearni akumulaciji poškodbe. Določitev napetosti na mehu zračne vzmeti, kjer se poškodbo računa, je izvedena z uporabo MKE-analize in nadaljnje transformacije več-osnega v eno-osno napetostno stanje s pomočjo metode kritičnih ravnin. S-N krivulja je za kritično točko določena z združitvijo eksperimentalnih rezultatov (število ciklov do nastanka kritične poškodbe) in rezultatov metode kritičnih ravnin (napetosti). Eksperimentalni rezultati za posamezne pogoje obremenjevanja so pridobljeni z izvedbo pospešenih preskušanj s konstantno amplitudo obremenitve;

dne 19. novembra 2010 Boštjan PERDAN z naslovom: »Laserski sistemi za merjenje oblike jermenov v industrijskem okolju« (mentor: prof. dr. Janez Diaci);

Delo obravnava uporabo laserskih sistemov za merjene oblike jermenov v industrijskem okolju s poudarkom na razvoju metod za avtomatsko vrednotenje izmerkov. V uvodnem delu je predstavljena problematika nadzora kakovosti jermenov s poudarkom na merjenju oblike. Obravnavamo dve metodi. Metoda vrednotenja profilov je osnovana na prilagajanju krivulj izmerjenim točkam, omogoča izračun geometrijskih dimenzij in je primerna v primeru manjših odstopanj. Metoda vrednotenja površin bazira na uporabi karte odstopkov, ki prikazuje odstopanja med izmerjeno in referenčno


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površino. Primerna je za odkrivanje napak oblike in jih tudi klasificira. Obe razviti metodi je možno uporabiti za razvoj algoritma za vrednotenje jermenov v proizvodnem procesu;

dne 26. novembra 2010 Andrej ŽEROVNIK z naslovom: »Fenomen tečenja v konstitutivnih modelih ciklične plastifikacije« (mentor: prof. dr. Ivan Prebil, doc. dr. Robert Kunc);

Nekateri materiali izkazujejo ob prvem prehodu iz elastičnega v elasto-plastično področje fenomen tečenja, ki vpliva na napetostno-deformacijski odziv konstrukcijskih elementov, podvrženih ciklični plastifikaciji. Na podlagi ugotovitev eksperimentalnega opazovanja vpliva fenomena tečenja na ciklično plastifikacijo materiala je zapisan konstitutivni model ciklične plastifikacije, v katerem je predstavljen tudi popis fenomena tečenja. Predstavljeni konstitutivni model je za potrebe popisa malocikličnega napetostno-deformacijskega stanja konstrukcijskih elementov in prikaza doprinosa popisa fenomena tečenja v konstitutivnih modelih ciklične plastifikacije vključen v kodo končnega elementa. Na osnovi eksperimentalnih rezultatov enoosnih eksperimentov so določeni parametri materiala, podan je tudi protokol njihove določitve. Predstavljeni konstitutivni model je verificiran na podlagi primerjave rezultatov eksperimentalnih preizkusov in numeričnih simulacij enoosnih preizkusov in ciklične plastifikacije konzolnega nosilca. V sklopu verifikacije je prikazan tudi doprinos upoštevanja fenomena tečenja v konstitutivnih modelih ciklične plastifikacije.

MAGISTRSKA DELA

Na Fakulteti za strojništvo Univerze v Mariboru sta z uspehom zagovarjala svoje magistrsko delo:

dne 19. novembra 2010 Vladan MLADENOVIĆ z naslovom: »Razvoj, izdelava in upravljanje z visoko zahtevnimi izdelki nove generacije motorjev v avtomobilski industriji« (mentor: prof. dr. Andrej Polajnar);

dne 19. novembra 2010 Dejan DREN z naslovom: »Upravljanje zanesljivosti hladilnih aparatov« (mentor: prof. dr. Andrej Polajnar).

SPECIALISTIČNO DELO Na Fakulteti za strojništvo Univerze v

Mariboru sta z uspehom zagovarjala svoje specialistično delo:

dne 5. novembra 2010 Darko SKERBIŠ z naslovom: »Obdelava orodja za ekstruzijo aluminija večjega formata« (mentor: prof. dr. Franci Čuš);

dne 18. novembra 2010 Adrijan PLEVNIK z naslovom: »Optimizacija izdelave pedalnega sklopa« (mentor: prof. dr. Andrej Polajnar).

DIPLOMIRALI SO Na Fakulteti za strojništvo Univerze v

Ljubljani so pridobili naziv univerzitetni diplomirani inženir strojništva:

dne 2. novembra 2010: Jernej BASLE z naslovom: »Ugotavljanje

natančnosti obdelovalnih strojev« (mentor: prof. dr. Janez Kopač, somentor: doc. dr. Peter Krajnik);

Jože BOVHA z naslovom: »Brezžični uporabniški vmesnik SCARA robota LAKOS« (mentor: izr. prof. dr. Peter Butala);

Luka REDNAK z naslovom: »Optimiranje kogeneracijskega postrojenja za sežiganje komunalnih odpadkov« (mentor: prof. dr. Janez Oman);

Jan ŽILIĆ z naslovom: »Vzdrževanje luških dvigal« (mentor: doc. dr. Jožef Pezdirnik);

dne 3. novembra 2010: Anže KALAN z naslovom: »Maček

laboratorijskega stebrnega žerjava« (mentor: doc. dr. Boris Jerman);

Gorazd KRESE z naslovom: »Vpliv latentnih obremenitev na rabo električne energije za hlajenje stavb« (mentor: prof. dr. Vincenc Butala, somentor: doc. dr. Matjaž Prek);

Gregor OGRADI z naslovom: »Vpliv števila udarnih obremenitev na dinamične karakteristike elastomerno-termoplastičnih kompozitov« (mentor: prof. dr. Igor Emri);

Matija TRDAN z naslovom: »Transportni sistem za sušenje in manipuliranje z lesnimi sekanci« (mentor: doc. dr. Boris Jerman);

dne 30. novembra 2010: Luka ČERNIGOJ z naslovom:

»Parametrična analiza elementov toplotne črpalke


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za sanitarno vodo« (mentor: prof. dr. Alojz Poredoš);

Marko OŽBOLT z naslovom: »Elektrokalorično hlajenje« (mentor: prof. dr. Alojz Poredoš, somentor: doc. dr. Andrej Kitanovski);

Gregor SABLIČ z naslovom: »Plazemski sežig medicinskih odpadkov« (mentor: prof. dr. Iztok Golobič);

Rok ŽGAJNAR z naslovom: »Razvoj hidravlične stiskalnice za ravnanje izolacijskih blokov« (mentor: prof. dr. Marko Nagode, somentor: doc. dr. Jožef Pezdirnik).

*

Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv univerzitetni diplomirani inženir strojništva:

dne 4. novembra 2010: Darjan SAVIĆ z naslovom: »Okoljsko

ekonomska analiza uporabe biopolimernih materialov namesto plastike« (mentor: prof. dr. Niko Samec, somentor: prof. dr. Jožica Knez Riedl);

dne 23. novembra 2010: Janez GOTLIH z naslovom: »Prehod iz

meritev na simulacijski 3D in 1D model zgorevanja za dizelski DI motor« (mentor: prof. dr. Leopold Škerget, somentor: prof. dr. Niko Samec);

dne 25. novembra 2010: Bojan GOLUH z naslovom: »Retro-

commissioning poslovnega objekta« (mentor: prof. dr. Andrej Polajnar, somentor: doc. dr. Iztok Palčič);

Robert KELAVIĆ z naslovom: »Razvoj in načrtovanje proizvodnje osi za večnamensko uporabo« (mentor: prof. dr. Andrej Polajnar, somentor: doc. dr. Marjan Leber);

Denis MATJAŠIČ z naslovom: »Konstrukcija zložljivih tračnih transporterjev mobilne separacije« (mentor: prof. dr. Iztok Potrč, somentor: doc. dr. Tone Lerher);

Aleksander PLASKAN z naslovom: »Numerični preračun orodja za globoki vlek čelne plošče štedilnika« (mentor: prof. dr. Zoran Ren, somentor: izr. prof. dr. Ivan Pahole).

*

Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv diplomirani inženir strojništva:

dne 10. novembra 2010: Rok PERKO z naslovom: »Možnosti

uporabe avtonomnega navigacijsko informacijskega sistema za izvajanje nalog v letalski policijski enoti« (mentor: pred. mag. Primož Škufca, somentor: doc. dr. Tadej Kosel);

Nejc TRAVNER z naslovom: »Analiza ustreznosti helikopterjev Agusta A109 Power in Eurocopter EC135 za opravljanje nadzora državne meje Republike Slovenije« (mentor: pred. mag. Primož Škufca, somentor: doc. dr. Tadej Kosel);

Branko ZORKO z naslovom: »Energetska sanacija tradicionalne Ptujsko Podravske stavbe« (mentor: doc. dr. Andrej Bombač, somentor: prof. dr. Vincenc Butala);

dne 11. novembra 2010: Dejan BREMEC z naslovom: »Cenovna

primerjava izdelave nosilne plošče z različnima tehnologijama« (mentor: prof. dr. Mihael Junkar, doc. dr. Henri Orbanić);

Boris MAKARIĆ z naslovom: »Tipizacija enonosilčnih mostnih žerjavov z visečim mačkom« (mentor: izr. prof. dr. Janez Kramar);

Gregor SILJAN z naslovom: »Analiza postopka nenatančnega pristanka pri dodatni namestitvi radionavigacijskega sredstva v neposredni bližini pristajalne steze« (mentor: pred. Miha Šorn, somentor: doc. dr. Tadej Kosel);

dne 12. novembra 2010: Uroš BAN z naslovom: »Razvoj naprave

za brušenej kardanskih križev« (mentor: prof. dr. Marko Nagode);

Jurij FERFOLJA z naslovom: »Vpliv procesnih parametrov na strukturo in termične lastnosti ekstrudiranega LDPE« (mentor: prof. dr. Igor Emri);

Nejc GROBIŠA z naslovom: »Spajanje bakrenih kablov s pokositrenim priključkom« (mentor: doc. dr. Damjan Klobčar);

Miha JANČAR z naslovom: »Enostransko uporovno točkovno varjenje nerjavnih jekel« (mentor: prof. dr. Janez Tušek);

Gregor KROPOVŠEK z naslovom: »Obdelava orodnih snemalnih plošč« (mentor: prof. dr. Janez Kopač, somentor: doc. dr. Peter Krajnik).

*


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Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv diplomirani inženir strojništva:

dne 12. novembra 2010: Jakob ŽILJCOV z naslovom: »Primerjava

metod za merjenje notranjih premerov« (mentor: izr. prof. dr. Bojan Ačko);

dne 19. novembra 2010: Jožef DVORJAK z naslovom: »Določitev

optimalnih posebnih postopkov za razrez materialov« (mentor: prof. dr. Franci Čuš);

dne 25. novembra 2010: Damir BANFI z naslovom: »Koncipiranje

in snovanje naprave za samopostrežno prodajo sveč« (mentor: izr. prof. dr. Stanislav Pehan, somentor: doc. dr. Janez Kramberger);

Gregor BRCE z naslovom: »Računalniško podprto konstruiranje sprožilnega mehanizma za

nadometni kotliček« (mentor: izr. prof. dr. Bojan Dolšak, somentorica: viš. pred. dr. Marina Novak);

Matevž KAUČIČ z naslovom: »Rekonstrukcija etiketirnega stroja« (mentor: prof. dr. Iztok Potrč);

Gorazd KOPAČ z naslovom: »Delovanje in vzdrževanje tlačno livarskega stroja Bühler« (mentor: doc. dr. Darko Lovrec);

Vladimir KOPIĆ z naslovom: »Zasnova progresivnega preoblikovalnega orodja za preoblikovanje pločevine iz AlMg3« (mentor: izr. prof. dr. Ivan Pahole, somentor: doc. dr. Mirko Ficko);

Ervin ŠTRUMPFL z naslovom: »Postopek prvega zagona hidravličnega sistema« (mentor: doc. dr. Darko Lovrec, somentor: doc. dr. Samo Ulaga).

Strojniški vestnik – Journal of Mechanical Engineering (SV-JME)

© 2010 Strojniški vestnik - Journal of Mechanical Engineering. All rights reserved. SV-JME is indexed / abstracted in: SCI-Expanded, Compendex, Inspec, ProQuest-CSA, SCOPUS, TEMA. The list of the remaining bases, in which SV-JME is indexed, is available on the website. The journal is subsidized by Slovenian Book Agency.

Strojniški vestnik - Journal of Mechanical Engineering is also available on http://www.sv-jme.eu, where you access also to papers’ supplements, such as simulations, etc.

Editor in ChiefVincenc ButalaUniversity of Ljubljana Faculty of Mechanical Engineering, Slovenia

Co-EditorBorut BuchmeisterUniversity of MariborFaculty of Mechanical Engineering, Slovenia

Technical EditorPika ŠkrabaUniversity of Ljubljana Faculty of Mechanical Engineering, Slovenia

Editorial OfficeUniversity of Ljubljana (UL)Faculty of Mechanical EngineeringSV-JMEAškerčeva 6, SI-1000 Ljubljana, SloveniaPhone: 386-(0)1-4771 137Fax: 386-(0)1-2518 567E-mail: [email protected]://www.sv-jme.eu

Founders and PublishersUniversity of Ljubljana (UL)Faculty of Mechanical Engineering, Slovenia

University of Maribor (UM)Faculty of Mechanical Engineering, Slovenia

Association of Mechanical Engineers of Slovenia

Chamber of Commerce and Industry of SloveniaMetal Processing Industry Association

President of Publishing CouncilJože DuhovnikUL, Faculty of Mechanical Engineering, Slovenia

International Editorial BoardKoshi Adachi, Graduate School of Engineering,Tohoku University, JapanBikramjit Basu, Indian Institute of Technology, Kanpur, IndiaAnton Bergant, Litostroj Power, Slovenia Franci Čuš, UM, Faculty of Mech. Engineering, SloveniaNarendra B. Dahotre, University of Tennessee, Knoxville, USAMatija Fajdiga, UL, Faculty of Mech. Engineering, SloveniaImre Felde, Bay Zoltan Inst. for Mater. Sci. and Techn., HungaryJože Flašker, UM, Faculty of Mech. Engineering, SloveniaBernard Franković, Faculty of Engineering Rijeka, CroatiaJanez Grum, UL, Faculty of Mech. Engineering, SloveniaImre Horvath, Delft University of Technology, NetherlandsJulius Kaplunov, Brunel University, West London, UKMilan Kljajin, J.J. Strossmayer University of Osijek, CroatiaJanez Kopač, UL, Faculty of Mech. Engineering, SloveniaFranc Kosel, UL, Faculty of Mech. Engineering, SloveniaThomas Lübben, University of Bremen, GermanyJanez Možina, UL, Faculty of Mech. Engineering, SloveniaMiroslav Plančak, University of Novi Sad, SerbiaBrian Prasad, California Institute of Technology, Pasadena, USABernd Sauer, University of Kaiserlautern, GermanyBrane Širok, UL, Faculty of Mech. Engineering, SloveniaLeopold Škerget, UM, Faculty of Mech. Engineering, SloveniaGeorge E. Totten, Portland State University, USANikos C. Tsourveloudis, Technical University of Crete, GreeceToma Udiljak, University of Zagreb, CroatiaArkady Voloshin, Lehigh University, Bethlehem, USA

PrintLITTERA PICTA d.o.o., Barletova 4, 1215 Medvode, Slovenia

General informationStrojniški vestnik – The Journal of Mechanical Engineering is published in 11 issues per year (July and August is a double issue). Institutional prices include print & online access: institutional subscription price €100,00, general public subscription €25,00, student subscription €10,00, foreign subscription €100,00 per year. The price of a single issue is €5,00. Prices are exclusive of tax. Delivery is included in the price. The recipient is responsible for paying any import duties or taxes. Legal title passes to the customer on dispatch by our distributor. Single issues from current and recent volumes are available at the current single-issue price.To order the journal, please complete the form on our website. For submissions, subscriptions and all other information please visit: http://en.sv-jme.eu/ You can advertise on the inner and outer side of the back cover of the magazine.We would like to thank the reviewers who have taken part in the peer-review process.

Cover: Integrated measurement system: co-ordinate measuring machine and laser interferometer for precise geometry measurement and calibration & Precise measurement of sphere diameter with a universal measurement machine (left below).

Image courtesy: Laboratory for Production Measurement, Faculty of Mechanical Engineering, University of Maribor

ISSN 0039-2480

Aim and ScopeThe international journal publishes original and (mini)review articles covering the concepts of materials science, mechanics, kinematics, thermodynamics, energy and environment, mechatronics and robotics, fluid mechanics, tribology, cybernetics, industrial engineering and structural analysis. The journal follows new trends and progress proven practice in the mechanical engineering and also in the closely related sciences as are electrical, civil and process engineering, medicine, microbiology, ecology, agriculture, transport systems, aviation, and others, thus creating a unique forum for interdisciplinary or multidisciplinary dialogue.The international conferences selected papers are welcome for publishing as a special issue of SV-JME with invited co-editor(s).

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Strojniški vestnik / december 2010