FATIGUE ANALYSIS ON DIE INSERT OF CONNECTING ROD

IN CLOSED DIE FORGING PROCESS

By

MOHD AMRI BIN SULAIMAN

Project Paper submitted to Department of Mechanical and Manufacturing, Faculty of

Engineering, University of Putra Malaysia, in partially fulfilment of the requirements

for the Degree of Master in Manufacturing System Engineering.

May 2006

Abstract of the project to the Department of Mechanical and Manufacturing, Faculty of

Engineering, University of Putra Malaysia in partially fulfillment of the requirement for the

Degree of Master in Manufacturing System Engineering.

Abstract:

FATIGUE ANALYSIS ON DIE INSERT OF CONNECTING ROD IN

CLOSED DIE FORGING PROCESS

By

MOHD AMRI SULAIMAN

Supervisor: Prof. Dr. Abdel Magid Salem Hamouda

Faculty: Engineering

To meet the increasing demand for more accurate forged products with a higher added value

and of higher material yield, precision forging-related technology has been making

remarkable progress.

In this regard, research and development on CAD/CAM/CAE (computer-aided

design/computer-aided manufacturing/computer aided engineering) systems for practical use

have been vigorously promoted. CAD/CAM/CAE technology has already established itself

in the fields of designing and manufacturing sheet metal dies and is extensively used in the

aircraft and automobile industries. The CAD/CAM/CAE system developed and operated for

the hot forging of connecting rod.

In conventional hot forging of connecting rods, the material wasted to the flash accounts

approximately 20-40% of the original workpiece. In order to reduce the cost of forged

products, the forging must be performed in a closed cavity to obtain near-net or net shape

parts. In flash less forging, the volume distribution of the preform must be accurately

controlled to avoid overloading the dies and to fill the cavity. Additionally, the preform

must be simple enough to be mass-produced.

This work used the CAD/CAM/CAE system for fatigue analysis on die insert of connecting

rod in closed die forging process. The implementation of this study consists of five stages; i)

modelling part (connecting rod) using CAD software (Solidworks 2005), ii) preliminary die

insert design, iii) stress-strain simulation of die insert, iv) die insert fatigue analysis and

lifetime, and v) developed CNC code programming for die insert. In the first stage,

Solidworks 2005 software was used for modeling part (connecting rod). The second stage,

again CAD software (Solidworks 2005) was used to model the primary design of the die

insert based on the shape of the forged part. In third stage, simulated the die inserts of

connecting rod and analysed the maximum stress-strain applied on the die insert and the

requirement of load to perform the forging operation. Meanwhile in fourth stage,

determination fatigue analysis and lifetime on die insert was done by comparing the values

from S-N curve and maximum stress-strain value from FEA result. In the last stage,

Unigraphics software was used to develop CNC machining code or known GM code for

fabricating the die inserts.

11

Abstrak projek yang dikemukakan kepada Jabatan Mekanikal dan Pembuatan, Fakulti

Kejuruteraan, Universiti Putra Malaysia sebagai memenuhi sebahagian dari keperluan untuk

Ijazah Sarjana Kejuruteraan Sistem Pembuatan.

Abstrak:

ANALISIS KELEMAHAN TERHADAP SELITAN ACUAN ROD

PENYAMBUNG DALAM PROSES TEMPA ACUAN TERTUTUP

Oleh

MOHD AMRI SULAIMAN

Penyelia: Prof. Dr. Abdel Magid Salem Hamouda

Fakulti: Kejuruteraan

Bagi memenuhi peningkatan terhadap permintaan kepada barang tempa yang lebih jitu dan

berkualiti tinggi, proses teknologi berkaitan kejituan tempaan telah begitu menonjol.

Sehubungan dengan itu, pembangunan dan penyelidikan sistem CAD/CAM/CAE untuk

tujuan praktikal amat digalakkan. Teknologi CAD/CAM/CAE telah lama diwujudkan

terutamanya dalam rekabentuk dan pembuatan acuan kepingan logam dan ia digunakan

secara meluas di dalam indusri pembuatan kapal terbang dan kereta. Sistem

CAD/CAM/CAB ini juga telah dilaksanakan dan diguna pakai dalam pembikinan rod

penyambung.

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Di dalam proses penempaan panas rod penyambung secara normal, pembaziran bahan

logam sering berlaku kira-kira 20 - 40 peratus daripada bahan logam asal. Oleh itu, untuk

mengurangkan kos produk tempaan, proses tempaan mesti dilakukan pada acuan tertutup

untuk mendapatkan bentuk yang seakan hampir dari bentuk asal. Di dalam proses tempaan

kurang lebihan bahan, jumlah pengaliran logam mestilah dikawal dengan tepat bagi

mengelakkan lebihan bebanan kepada acuan. Secara ringkasnya, prabentuk hendaklah sesuai

untuk pengeluaran secara besar-besaran.

Kajian ini melibatkan penggunaan sistem CAD/CAM/CAE untuk menganalisis kelemahan

selitan acuan rod penyambung dalam proses tempa acuan tertutup. Perlaksanaan kajian ini

terdiri daripada lima peringkat; i) merekabentuk rod penyambung menggunakan program

CAD, (Solidworks 2005), ii) persediaan utama merekabentuk selitan acuan, iii) Simulasi

ketegangan selitan acuan, iv) menentukan jangka hayat dan analisis kelemahan selitan

acuan, dan v) membangunkan kod program CNC untuk selitan acuan. Pada peringkat

pertama, program Solidworks 2005 digunakan untuk merekabentuk rod penyambung. Pada

peringkat kedua, sekali lagi program Solidworks 2005 digunakan untuk merekabentuk

selitan acuan berdasarkan bentuk rod penyambung. Bagi peringkat ketiga pula, simulasi

selitan acuan rod penyambung dan analisis ketegangan maksimum terhadap selitan acuan

serta bebanan yang diperlukan untuk proses tempaan ini. Seterusnya peringkat ke empat,

menentukan jangka hayat dan analisis kekuatan-kelemahan selitan acuan dengan membuat

perbandingan nilai dari graf S-N dan keputusan dari ' finite element analisis' (FEA). Pada

peringkat terakhir pula, program Unigraphics digunakan untuk membangunkan kod

pemesinan CNC atau dikenali GM-code untuk fabrikasi selitan acuan.

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ACKNOWLEDGEMENT

First of all I would like to appreciate to the Kolej Universiti Teknikal Kebangsaan Malaysia,

KUTKM as an employer and gave approval to me for furthering my Master study. Also

thanks to the Jabatan Perkhidmatan Awam, JPA as sponsorship in this study.

Many industry person and academicians from various sources have contributed generously

to the completion of this case study. I greatly acknowledge my supervisor Prof. Dr. A.

Magid Hamouda, lecturer in the Department of Mechanical and Manufacturing Engineering

for his trust, sharing ideas and supportive effort all these while. I would also like to take this

opportunity to thank my examiner, Assoc. Prof. Dr. Wong Shaw Voon for his effort and

guidance in correcting this case study.

I would like to thanks my family, who always has been with me supporting me even in the

hardest of time, my dear friends whom have been very helpful and encouraging.

This case study is the combination of computer aided design (CAD) for modeling purpose,

computer of manufacturing (CAM) for G-code program and fabrication purpose and

computer aided engineering (CAE) for finite element analysis purpose. For this I would also

like to thank the individual stated below for their time to share information and ideas.

Mr. Amir Radzi

Engineer Researcher,

National CADCAM, Sirim Berhad.

Mr. Jefridi Mat Siman

Engineer Researcher,

Machinery and Tooling Technology Program, Sirim Berhad.

v

Mr. Goh Kok Ming

Production Engineer,

Metal Techs Sdn. Bhd,

Ayer Keroh, Melaka.

Mr. Jaafar Lazim

Senior Technician,

Faculty of Manufacturing,

Kolej Universiti Teknikal Kebangsaan Malaysia.

vi

APPROVAL

This project submitted to the Department of Mechanical and Manufacturing, Faculty of

Engineering, University of Putra Malaysia has been accepted as a partial fulfillment of the

requirements for the Degree of Master of Manufacturing System. The members of the

examinations committee are as below;

fA (;2 -·-~~------------------------Supervisor, PhD

Prof. Dr. A. Magid Hamouda

Department of Mechanical and Manufacturing,

Faculty of Engineering,

University of Putra Malaysia

Examiner, PhD

Assoc. Prof. Dr. Wong Shaw Voon

Department of Mechanical and Manufacturing,

Faculty of Engineering,

University of Putra Malaysia

vii

DECLARATION

I hereby declare that the project paper is based on my original work except for quotations

and citations that have been duly acknowledge. I also declare that it has not been previously

or concurrently submitted for any other degree of university or other institutions.

MOHD AMRI BIN SULAIMAN

viii

List of Contents

ABSTRACT

ABSTRAK

ACKNOWLEDGEMENTS

APPROVAL SHEETS

DECLARATION FORM

LIST OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

CHAPTER

1 INTRODUCTION

2

Forging for connecting rod

Objective

Scope of studies

Project organizations

LITERATURE REVIEW

Forging

Comparison forging with other processes

Why are forging so prevalent

Closed die forging

Requirements for closed die forging

Case Study Flashless Forged Connecting Rod

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Page

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Process details Closed-die forging 24

Process requirements 27

Open die forging 29

Hot forging 30

Die life service 30

Die service life based on plastic deformation 31

A brief history of the Finite Element Method 32

The history ofMSC.NASTRAN 33

The overview ofMSC.NASTRAN 35

Connecting Rod in the engine block 37

Basic steps in the finite element method 39

3 METHODOLOGY 40

Stage I: Modelling part using CAD software (Solidworks 2005) 41

Stage 2: Preliminary die insert design 42

Stage 3: Stress-strain simulation of die inserts 43

Stage 4: Die inserts fatigue analysis and lifetime 43

Stage 5: Developed CNC code for the die inserts 43

4 COMPUTER AIDED DESIGN-CAD: Modeling Die Insert 44

Computer Aided Design, (CAD) 44

Solidworks 2005 software for modelling 44

Die insert drawing and dimensions 46

Material properties for die insert 48

Connecting rod drawings, dimensions and material 50

Billet dimensions 52

x

5 COMPUTER AIDED ENGINEERING-CAE: Finite Element

Analysis on Die Inserts of Closed Die Forging 54

Computer Aided Engineering, (CAE) 54

MSC.NASTRAN software 55

Die Inserts analysis 56

Mesh Element 56

Pressure Load 57

Stress-Strain 58

Displacement on Die Inserts 59

Constraint Force on Die Inserts 59

S-N Curve for Carbon Steels (AISI 1055) 61

Fatigue Analysis of Die Inserts 62

Comparison values between Finite Element Analysis and S-N curve 63

6 COMPUTER AIDED MANUFACTURING-CAM: Die Insert of

Closed Die Forging

Computer Aided Manufacturing, (CAM)

Overview Unigraphics software

Tool Path

Cavity Mill

GM code

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7 RESULTS AND DISCUSSIONS

Determination Fatigue Analysis of Die Insert

Billet Dimensions

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8 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK

The Conclusions of Project 76

Project Contribution

System Limitations

Recommendations for Future Work

REFERENCES

APPENDICES

Appendix 1: In Part of CNC code for the Machining Operation

Required to Produce the Die Insert

Appendix 2: A diskette that contain Full CNC code for Die Insert

Fabrication

BIODATA OF AUTHORS

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List of Figures

Figure

1. Connecting rod

2. Closed die forging with and without flash

3. Closed die forging

4. Comparison between conventional forging and closed die forging

5. Closed die forged connecting rod

6. Stages in forging a connecting rod

7. A heated blank between 2 halves of a die

8. Compressive stroke squeezes the blank into the die

9. Part ejected using an ejector pin

10. Waste material (flash)

11. Connecting rod location in the engine block

12. Forging industry

13. Industrial - Closed Die Forging

14. Flowchart of the methodology

15. Connecting rod

16. Die insert

17. Cavity dimensions (in mm)

18. Cavity depth for Lower Die Insert (in mm)

19. Lower Die Insert dimensions (in mm)

20. Cavity depth for Upper Die Insert (in mm)

21. Upper Die Insert dimensions (in mm)

22. The Upper die insert and lower die insert at open position

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23. Product (connecting rod) dimensions (in mm)

24. Billet dimensions with offset 2% (in mm)

25. Mesh element on die insert

26. Pressure load applied on the cavity profile

27. Stress-strain

28. Displacement on the die insert (in mm)

29. Constraints force on die inserts

30. Constraints force on bottom die inserts

3 1. S-N curve for carbon steel ( AISI 105 5)

32. S-N curve show comparison between O"max and O"se

33. The Create Operation

34. Tool paths for first cavity milling

35. Cavity Mill part

36. Cavity Mill Parameters Setting

37. S-N curve show comparison between O"max and O"se

38. Stress-strain values (in N/m2) for carbon steel AISI 1055 die insert

39. The thickness of billet (in mm)

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List of Tables

Table

I. Comparison between forging and welding/fabrication

2. Comparison between forging and casting

3. Comparison between forging and powder metallurgy

4. Comparison between forging and reinforced plastic and composites

5. Comparison between forging and machined steel bar/plate

6. Advantages of forging compare to other process

7. Specifications of the Closed die forged connecting rod

8. AISI 1055

9. Composition of AISI I 055

I 0. Mechanical properties of AISI 1055

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1.1 Introduction

Chapter 1

Introduction

If the weight of a connecting rod (see Fig. 1) can be reduced while increasing its strength,

an automobile's fuel efficiency will be improved. Currently, steel connecting rods are used

in passenger cars. However, some manufacturers have attempted to use alternative lighter

materials. Recently, various composite materials based on aluminum have been considered,

but not yet successfully adopted, for automotive engines. The main reasons are that these

materials are not strong enough, or when strong enough, are too expensive.

Flash less forging offers the possibility of producing aluminum composite connecting rods

at competitive costs. The design of flash less forging processes is more complex than the

design of conventional closed die forging with flash. Therefore, in order to accelerate the

development of the manufacturing process as well as to reduce the development costs, a new

design method must be developed and applied. The finite element method (FEM) offers the

possibility to design the entire manufacturing process on a computer. This leads to a

reduction of the cost and time in process and tool design, tool manufacturing, and die try­

out. In addition, it is possible to modify the process conditions in the simulation to find the

best manufacturing conditions for a product.

1

Figure 1: Connecting rod

1.2 Forging for connecting rod;

In the forging of connecting rods, three main methods are employed. The first method

consists of making a rough pre-form from a non-porous billet and hitting it several times in

a press until the final shape is obtained (Figure 2a). This method results in 20-40% of the

material to be wasted as flash. A major advantage of the closed-die forging with flash is that

the volume of the pre-form can vary within a wider range than for flash less forging. This

makes it easier to continuously manufacture products with the same quality (3].

However, a trimming process is necessary to remove the existing flash . The second method

is net shape flash less forging (Figure 2b). During this process the pre-form is totally

enclosed in the die cavity so that no flash formation is allowed. There is no material waste

as in impression forging. However, tight volume control of the pre-form is necessary to

insure filling of the cavity and to avoid overloading the tooling. The third method, which is

widely used, is hot forging of powder metallurgy pre-forms. This method yields virtually no

material waste and produces near-net shape products. However, the metal powder is '

expensive compared to conventional materials.

2

In principle, forging operations are non-steady state processes, in which the deformation of

the material takes place under three-dimensional stress and strain conditions. The material

flow depends mainly on the following;

I. geometry of the cavity;

2. geometry of the flash opening;

3. initial and intermediate billet geometry;

4. percentage of flash;

5. heat transfer between the tooling and the billet;

Forging wi~h Flash

Lower Die

I

Flash less Forging

· Lower Punch

Start of Stroke

(a)

Forging with Flash

I I

I

Flashles~ For~111g

End of Stroke

(b)

Figure 2: Closed die forging with and without flash

Thus, the requirements to perform a successful flashless forging process are:

I. The volume of the initial pre-form and the volume of the cavity at the end of the ,

process must be the same.

2. There must be neither a local volume excess nor a shortage, which means that the

mass distribution and positioning of the pre-form must be very exact.

3. If there is a compensation space in the dies, the real cavity must be filled first.

3

1.3 Objective of the study

Currently most finite element codes that simulate billet-forming processes consider only

plane-strain or axisymmetric deformations. Since many industrial parts such as connecting

rods have very complex geometries, the metal flow is three-dimensional and cannot be

properly modeled with a two-dimensional approximation. This means that a three

dimensional simulation of the manufacturing process must be performed to get adequate

results.

For this study, it is focusing on simulation non-steady process using a finite element method

(MSC.NASTRAN) in order to better understanding of structural and fatigue analysis on the

closed die forging. The main product to study is connecting rod that most using in

automotive industry. Besides, the goals of the study are;

);;> To develop a finite element model of die insert for connecting rod in closed­

die forging process.

);;> To determine fatigue strength material analysis and cycle lifetime of die

insert.

);;> To developed the CNC code for the die insert using Unigraphics software.

4

1.4 Scope of study

There are many finite element analysis techniques on closed die forging, for the

development of this project, it only concentrated on fatigue strength material analysis of the

die insert design using the MSC.NASTRAN software. Meanwhile the Solidworks 2005 and

Unigraphic software will be used for modeling and CAM purpose. Currently there have

some stages of connecting rod manufacture such as blank, edging, blocking and finishing

but in this project, it only highlighted on the final stage (finishing).

1.5 Project organization

This project consists of eight chapters:

Chapter 1: Introduction of forging for connecting rod, objective and scope of this study.

Chapter 2: Reviews on the literature from journal, books and internet. The area covered

including types of forging, requirements of closed die forging, process detail of closed die

forging, material forged, die life service, history of finite element analysis, history of

NASTRAN software and basic steps in the finite element analysis.

Chapter 3: Describe methodology in this study to do the modeling, simulation, analysis and

developed CNC code.

Chapter 4: Modeling the connecting rod and die insert by using CAD software, Solidworks

2005.

5

Chapter 5: Finite Element Analysis on Die Inserts of Closed Die Forging, by using finite

element software, MSC.NASTRAN.

Chapter 6: Developed CNC machining program or known as GM code for die insert

fabrication purpose.

Chapter 7: Results on of the project and discussions.

Chapter 8: Conclusion of the project and recommendations for future works.

6

Chapter 2

Literature review

2.1 Forging

Forging is defined as the process in which metal is plastically deformed with application of

temperature and pressure. It is used to change not only the shape but also the properties of

the metal because it refines the grain size and therefore improves its structure [2]. Forging is

a cost-effective way to produce net-shape or near-net-shape components. Forged parts are

used in high performance, high strength and high reliability applications where tension,

stress, load and the human safety are critical considerations. They are also employed in a

wide range of demanding environments, including highly corrosive and extreme

temperatures and pressures.

Various parameters such as complexity of the part, friction between dies and workpiece,

type of press, die and workpiece temperature, material of workpiece governs the forging

process. Forging process is said to be successful if die cavity is completely filled and stress

in the workpiece is less than ultimate stress corresponding to the workpiece material, with

minimum force .

Forging is the controlled deformation of metal into a specific shape by compressive forces.

In year 8000 B.C. forging process are evolved from the manual art of simple blacksmithing.

Then a series of compressive hammer blows performs the shaping or forging of the part.

Now, modem forging uses machine driven impact hammers or processes, which deform the

workpiece by controlled pressure [1] .

7

The forging process is superior to casting in that the parts formed have denser

microstructures, more defined grains patterns, and less porosity, making such parts much

stronger than casting. All metals and alloys are forgeable, but each will have a forgeability

rating from high to low or poor.

The factors involved are the material's composition, crystal structure and mechanical

properties all considered within a temperature range. The wider the temperature range, the

higher the forgeability rating. Most forging is done on heated workpieces. Cold forging can

occur at room temperatures. The most forgeable materials are aluminum, copper, and

magnesium. Lower ratings are applied to the various steels, nickel, and titanium alloys. Hot

forging temperatures range from 93°C (200°F) to 1650°C (3000°F) for refractory metals [6].

2.2 Comparison forging with other processes

There are some processes in forming and shaping part such as forging, casting, welded or

fabrication, machined steel bar, powder metallurgy, reinforced plastics and composites. All

of these processes have their own characteristics, advantages and disadvantages. Here

comparison some characteristics such as strength of the part (grain oriented), cost effective,

material savings, design flexibility, simplified production, and part inspections, between

forging and other process are made. Below Table 1-6 have shown this comparison.

8