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OPTIMIZATION OF PARAMETERS OF LASER NON-LINEAR
INCLINED CUTTING ON STAINLESS STEEL METAL
ABBAS ALLAWI ABBAS
A project submitted in partial fulfillment of the requirements for the award of the Master
of Mechanical Engineering
Faculty of mechanical and manufacturing Engineering
Universiti Tun Hussein Onn Malaysia
JUN 2014
v
ABSTRACT
The aim of this research is to develop a laser cutting process model that can predict the
relationship between the process input parameters and resultant surface roughness; kerf
width characteristics. The research conduct is based on the Design of Experiment (DOE)
analysis. Response Surface Methodology (RSM) is used in this research, it is one of the
most practical and most effective techniques to develop a process model. Even though
RSM has been used for the optimisation of the laser process, published RSM modelling
work on the application of laser cutting process on cutting material is lacking. This
research investigates laser cutting stainless steel to be best the circumstances laser
cutting using RSM process. The input parameters evaluated are gas pressure, power
supply and cutting speed, the output responses being kerf width, surface roughness. The
laser cutting process is one of the widely used techniques to cut thickness material for
various applications such as fiber, steel wood fabrication. In the area of laser cutting
material,it can be improved drastically with the application of hard cutting. The
application of cut on stainless steel for various machining techniques, such as bevel
linear and bevel non-linear cutting, requires different cut characteristics, these being
highly dependent on the process parameters under which they were formed. To
efficiently optimize and customize the kerf width and surface roughness characteristics,
a machine laser cutting process model using RSM methodology was proposed.
vi
ABSTRAK
Matlamat penyelidikan ini adalah untuk membangunkan satu model proses pemotongan
laser yang boleh meramalkan hubungan antara proses penginputan parameter dan
kekasaran permukaan yang terhasil; ciri-ciri lebar alur gergaji. Penyelidikan yang
dijalankan adalah berdasarkan Rekabentuk Eksperimen (JAS) analisis. Respons
Permukaan Metodologi (RSM) digunakan dalam penyelidikan ini dan ia adalah salah
satu teknik yang paling praktikal serta paling berkesan untuk membangunkan satu model
proses. Walaupun RSM telah digunakan untuk pengoptimuman proses laser tersebut,
terbitan kerja pemodelan RSM atas aplikasi proses pemotongan laser atas pemotong
bahan adalah kurang. Kajian ini dijalankan pula bagi mengetahui laser memotong keluli
tahan karat menjadi kaedah terbaik untuk pemotongan laser menggunakan proses
RSM.Penginputan parameter yang dinilai adalah tekanan gas, bekalan kuasa dan
kelajuan pemotongan, sambutan keluaran menjadi lebar alur gergaji, kekasaran
permukaan. Proses pemotongan laser adalah salah satu teknik yang digunakan secara
meluas untuk memotong bahan yang tebal untuk pelbagai aplikasi, seperti serat, keluli
kayu fabrikasi. Dalam bidang laser pemotongan bahan, ia boleh diperbaiki secara drastik
dengan aplikasi pemotongan keras. Aplikasi pemotongan pada keluli tahan karat untuk
pelbagai teknik pemesinan, seperti serong selari dan serong memotong bukan selari, ini
memerlukan ciri-ciri pemotongan yang berbeza justeru ini menjadi sangat bergantung
kepada proses parameter di mana mereka telah dibentuk.Bagi mengoptimumkan dan
menyesuaikan lebar alur gergaji dan permukaan ciri-ciri kekasaran dengan kecekapan,
mesin proses pemotongan laser model menggunakan kaedah RSM telah dicadangkan.
vii
CONTENTS
TITLE…….... ................................................................................................................... i
DECLARATION….…………………………………………………………………….ii
DEDICATION.................................................................................................................iii
ACKNOWLEDGEMEN..……………….......................................................................iv
ABSTRACT…………………………………….……………………………………….v
ABSTRAK……………………………………………………………………………...vi
CONTENTS………………...………………………………………………………….vii
LIST OF TABLES……………………………………………………………………..xi
LIST OF FIGURES…………………………………………………………………..xiii
LIST OF SYMBOLS AND ABBREVIATION............................................................xv
LIST OF APPENDICES..............................................................................................xvi
CHAPTER 1: INTRODUCTION .................................................................................. 1
1.1 Introduction.. .......................................................................................................... 1
1.1.1 Laser .............................................................................................................. 1
1.1.2 Lasers Parameters ......................................................................................... 3
1.1.3 Laser Cut Quality Characteristics ................................................................. 4
1.2 Problem Statement ................................................................................................. 4
1.3 Research Objectives ............................................................................................... 5
1.4 Research Scope ...................................................................................................... 5
CHAPTER 2: LITERATURE REVIEW ..................................................................... 6
viii
2.1 Introduction ............................................................................................................ 6
2.2 History of Laser…………………………………………………………………..7
2.3 Materials of Laser Cutting………………………………………………………..8
2.4 Laser principal……………………………………………………………………9
2.5 Basic components and work principle…………………………………………..10
2.6 Metal Cutting Process .......................................................................................... 11
2.7 Types of Laser Cutting…………………………………………………………..13
2.8 Laser Types……………………………………………………………………...13
2.8.1 CO2 Laser .................................................................................................. 14
2.8.2 Nd: YAG Laser .......................................................................................... 15
2.8.3 Fibre Laser ................................................................................................. 17
2.9 Laser Gas Assistance………………………………………….………………...18
2.9.1 Oxygen as Assist Gas .................................................................................. 18
2.9.2 Nitrogen as Assist Gas ................................................................................ 19
2.10 Laser Cut Quality ................................................................................................. 20
2.10.1 Laser Cutting Typical Imperfection .......................................................... 23
2.11 Optimization of Cutting Process Parameters ....................................................... 24
2.11.1 Fuzzy Logic ............................................................................................... 25
2.11.2 Genetic Algorithm ..................................................................................... 25
2.11.3 Taguchi Technique .................................................................................... 25
2.11.4 Artificial Neural Network (ANN) ............................................................. 26
2.11.5 Response Surface Methodology (RSM).................................................... 27
2.12 Related Work ....................................................................................................... 28
2.13 The Research Work .............................................................................................. 29
CHAPTER3: RESEARCH METHODOLOGY…………………………………….30
3.1 Introduction .......................................................................................................... 30
3.2 Laser Cutting ........................................................................................................ 30
3.2.1 Advantages of Laser Cutting………………………………………….....33
3.2.2 Disadvantages of Laser Cutting………………………………………….35
ix
3.3 Initial Design…………………………………………………………………….35
3.4 Methodology…………………………………………………………………….36
3.5 Work Material…………………………………………………………………...37
3.6 Cutting Parameters………………………………………………………………37
3.7 Cutting Machine…………………………………………………………………41
3.8 Analytical Tool…………………………………………………………………..43
3.8.1 Minitab 16 ................................................................................................. 43
3.8.2 RSM .......................................................................................................... 43
CHAPTER4: RESULTS & DISCUSSON…………………………………………...46
4.1 Introduction...……………………………………………………………………46
4.2 Optimization of the Cut Kerf Width and Roughness……………………………46
4.3 RSM Modeling of Kerf With Respect to Laser Cutting Process Parameters…...47
4.4 Response Surface Regression: Kerf Vs Pressure, Power, Speed………………..49
4.5 Discussion Interpreting the Results……………………………………………...52
4.6 Interpreting the Results………………………………………………………….54
4.7 Response Optimization of Kerf Width…………………………………………..54
4.8 Discuss Interpreting the Results Optimization Plot……………………………..55
4.9 Interpreting the Results………………………………………………………….56
4.10 Response Surface Regression: Roughness Vs Pressure, Power, Speed………....57
4.11 Interpreting the Results and Discussion…………………………………………62
4.12 Response Optimization of Roughness………………………………………..….65
4.13 Response Optimization of Kerf Width and Surface Roughness………………...67
CHAPTER5: CONCLUSION………………………………………………………...67
5.1 Conclusion……………………………………………………………………….69
5.2 New Contributions to Body Knowledge………………………………………...71
5.3 Future Work……………………………………………………………………...71
x
REFRENCES……………………………………………………………………….....73
APPENDICES………………………………………………………………………....79
xi
LIST OF TABLES
TABLE
2.1
TITLE
Materials for Laser Cutting
PAGE
8
2.2 Laser Types and Applications 14
3.1 Parameters Levels 38
3.2 Parameters Values during the Central Composite Design. 39
3.3
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
Experimental Layout for Response
The Measuring Values of Kerf Width and Average of These
Values
Estimated Regression Coefficients for Kerf
Analysis of Variance of Kerf Width
Estimated Regression Coefficients for Kerf Using Data in
Uncoded Units
Estimated Regression Coef for All the Terms
Predicted Responses for New Design Points Using Model
for Kerf
Parameters Response Optimization
Starting Points
Global Solution for Kerf Width
Predicted Response
The Measuring Values of Surface Roughness and Average
of These Values
Experimental Runs and Results of Surface Roughness(Non-
Linear inclined cutting)
40
48
49
50
50
51
51
54
55
55
55
57
58
xii
4.13
4.14
4.15
4.16
4.17
4.18
4.19
4.20
4.21
4.22
4.23
4.24
4.25
Experimental Runs and Results of Kerf Width and Surface
Roughness
Estimated Regression Coef for Roughness
Analysis of Variance for Roughness
Estimated Regression Coef for Roughness Using Data in
Uncoded Units
Responses for New Design Points Using Model for
Residual
Predicted Responses for New Design Points Using Model
for Roughness
Surface Roughness Optimization
Starting Points
Global Solution for Surface Roughness
Predicted Responses
Kerf Width and Surface Roughness Optimization
Global Solution
Predicted Response of Kerf Width and Surface Roughness
59
59
60
60
61
61
65
65
66
66
67
67
67
xiii
LIST OF FIGURES
FIGURE
TITLE PAGE
1.1
1.2
2.1
2.2
2.3
Applications Spectrum of Laser
Laser Parameters
Illustration of Laser Working
Coherent electromagnetic waves have identical frequency, and are
aligned in phase
Basic Components of Laser
2
3
9
10
11
2.4 N2, O2 laser 15
2. 5
2.6
Nd: YAG laser
JK300HPS Pulsed Nd:YAG Laser Machine and STRONG-
7090DS CNC Machine
16
16
2. 7
2.8
Fiber lasers
Laser Beam Melting the Material as the Assist Gas Forces Out the
Molten Mass
17
20
2. 9 Schematic Mechanism of Striations Formation during Laser
Cutting
23
2.10
3.1
Formation of Dross: a) Formation of a Droplet, b) Growing, c)
Merging of the Droplet with Previous Molten Material
Basic Principle of Laser Cutting
24
31
3.2 Research Methodology Flow Chart 36
3. 3 RSM Central Composite Design for 3 factors at two levels 38
3.4
3.5
Laser Cutting Machine (LVD) model 2512
Workpiece before the cutting
41
42
xiv
3.6
3.7
Workpiece after the cutting
The workpiece base at an angle 22°
42
43
3.8
3.9
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
5.1
Overall approach of Laser process Non-Linear inclined Cutting
study
Minitab Software Window
The Resultant Cut Kerf by Using Laser Cutting Machine
Measuring of Kerf Width at Three Areas (X1, X2 and X3)
Residual Plots of Kerf Width
Contour Plot of Kerf Width Vs, Power, Speed
Surface Plot of Kerf Width
Optimization Plot of Kerf Width
Graph Window output of Kerf
Measuring Surface Roughness of Cutting Edge at Three Areas (X1,
X2 and X3 ) for one Sample
Residual Plots of Roughness
Contour Plot of Roughness Vs, Power, Speed
Surface plot of Roughness
Graph Window output of Roughness
Optimization Plot of Surface Roughness
Optimization Responses of Kerf and Roughness
Laser Cutting Process as Applied to the Cutting Kerf Width and
Surface Roughness
45
45
47
48
52
53
54
55
56
58
62
63
64
65
66
67
69
xv
LIST OF SYMBOLS AND ABBREVIATION
ANNs - Artificial Neural Networks
ANOVA - Analysis Of Variance
CCD - Central Composite Design
CW - Continuous Wave
CO2 - Carbon dioxide
DC - Direct Current
I, V, Y - Types of bevel
K/W - kerf width
K = 1 - For an ideal Gaussian beam and
K < 1 - For real laser radiation.
LBC - Laser Beam Cutting
MRA - Multiple Regression Analysis Model
N2 - Nitrogen
Nd:YAG and Yt:YAG - Yttrium-Aluminum-Garnet (Crystal) Enriched with
Neodymium
O2 - Oxygen
OP - Optical Microscopy
Psi - Pounds per square inch
RF - Radio frequency
RSM - Response Surface Methodology
SEM - Scanning Electrical Microscopy
XRD - X-Ray Diffraction
xvi
LIST OF APPENDICES
FIGURE
TITLE PAGE
A
B
C
D
E
F
Measuring for Laser Process Kerf Width Non-Linear Incline
Cutting
Measuring for Laser Process Surface Roughness Non-Linear
Incline Cutting
Experimental for Laser Process Kerf Width and Surface Roughness
Non-Linear Incline Cutting
Inspection Devices of Kerf Width and Surface Roughness
Analysis Results
Gantt Chart
79
85
90
94
95
101
1
CHAPTER 1
INTRODUCTION
1.1 Introduction
This chapter describes the research background, problem statement, objectives and
scope of the research.
1.1.1 Laser
Laser (Light Amplification by Stimulated Emission of Radiation) is basically a cohesive,
convergent and monochromatic electromagnetic radiation beam. Its wavelength ranges
from ultra-violet to infrared. It can provide very low to very high power with a precise
spot to any substrate type through any medium. Laser is differed from other
electromagnetic radiation especially in terms of its cohesion, spectral purity and its
straight line propagation. Therefore, it plays an important role in different industries, and
used in many applications such as communication, military, medical and others. It is
used in wide applications due to several properties such as spatial and temporal
coherence, low divergence, high continuous or pulsed power density and mono -
chromaticity (Majumdar & Manna, 2003). One of its main applications is its ability to
act as a heat source known as Laser Materials Processing (LMP). This feature helps to
utilize it in forming, joining, machining, manufacturing, coating, deposition and surface
engineering. Due to the advantages of laser over the traditional cutting processes, it is
2
commonly used in machining various types of materials, especially very hard materials
in many industrial applications. The fundamental advantages of laser cutting are: no
vibration because it is a non- contact process and a low heat input that leads to less
distortion and its ability to be controlled numerically.
The parameters of laser cutting process play a main role on the cutting edge quality
features. The commercially available lasers for material processing are (Eltawahni et al.,
2010):
Solid state crystal or glass laser – Nd:YAG, Ruby
Semiconductor laser – AlGaAs, GaAsSb and GaAlSb lasers
Dye or liquid laser solutions of dyes in water/alcohol and other solvents
Neutral or atomic gas lasers – He–Ne laser, Cu or Au vapor laser
Ionized gas lasers or ion lasers – argon. ArC / and krypton .KrC / ion lasers
Molecular gas lasers – CO2 or CO laser
Excimer laser – XeCl, KrF, etc
Fiber laser-ytterbium
But, there are main obstacles that limit the laser extensive use in applications of routine
material processing such as a beam size limitation, high cost of installation and
replacement, additional and costly accessories, and need for skilled workers (Majumdar
& Manna, 2003).
Figure1.1: Application spectrum of lasers (Majumdar & Manna 2003).
3
1.1.2 Laser Parameters
The laser cutting process quality and the response in terms of cut edge quality is
controlled by a number of parameters linked to the laser system, used material, and the
cutting process. The laser system parameters are summarized in figure 2 below.
Figure1. 2: Laser Parameters (Wandera, 2010)
Researchers studied the impact of different laser parameters on cut edge quality, kerf
dimensions, roughness and surface finish. Karet.al studied the process parameters
impacts, such as laser power, spot size and dimensions, and cutting speed on the
resulting kerf size. Yilbas (2008) studied the effect of laser power and oxygen gas
pressure on the kerf width variation. Ghany and Newishy (2005) indicated a positive
relationship between laser cutting quality and the laser power, pulse frequency, cutting
speed and focus position.
LASER CUTTING PARAMETERS
Processing Parameters
- Used laser power
- Cutting speed
- Focal length
- Focal point position
- Type and process of
assist gas
- Nozzle diameter
- Nozzle stand-off
distance
Workpiece
parameters
- Material
Type
- Thickness
Laser system parameters
- Maximum output laser
power
- Beam quality
- Wavelength
Parameters adjusted by
operator
Parameters not adjusted
by operator
4
1.1.3 Laser cut quality characteristics
The laser cut edge characteristics, which can be used to measure the laser cut quality
include: the cut kerf width, dross attachment on the lower cut edge, cut edge squareness
deviation (perpendicularity), cut edge surface roughness, and boundary layer separation
point.
1.2 Problem Statement
The common metal machining is performed by using a laser machine with a vertical
cutting head. The literature did not mention and explain the impact of the nonlinear
inclined cutting process parameters on the surface quality, and it did not compare this
effect with the linear cutting.
The nonlinear inclined cutting is very important in assembling parts or
appliances or in welding pieces together as some of the parts and design must have
inclined surfaces for ease of their linking and assembling. Therefore, an inclined cutting
laser machine should be available, but this machine may not be available because it is
expensive. For this reason, the available vertical cutting machine will be used to address
this problem, where the incline degree of the work piece will be controlled (usually at an
angle of 22˚) under the vertical head to get the inclined cutting. After that the impact of
inclined cutting process parameters will be examined on surface quality. This project is
focused of an alternative process of the Acetylene oxygen cutting material in the CNC
machine. It also focused on their defects on the metal surface, the changing
characteristics at a mechanical level, the safety of the surface, the transactions thermal
and many more. Therefore, the presence of the CNC laser machine using nitrogen gas
best for the safety of the surface, the characteristics of the mechanical and others through
the literature review of cutting mild steel, stainless steel and etc.
5
1.3 Research Objectives
The main objective of this research is to conduct a comprehensive study on the
processing parameters effect during an inclined laser cutting of thin sheet stainless steel.
The effect of processing parameters is evaluated in terms of the surface’s finish and
flatness. The research aims to achieve the following objectives:
1. To investigate the laser material processing in inclined cutting.
2. To establish significant design parameters for a high quality of cut.
3. To model the optimal laser processing of a non-linear inclined cutting.
1.4 Research Scope
The aim of this research is to identify the parameters in the inclined laser cutting process
that play a major role in producing very low roughness cuts and surface finish, which
improve the end product quality. The laser nitrogen assistance will be used for the non-
linear inclined cutting process of a thin sheet of stainless steel of 4 mm thickness.
The Response Surface Methodology (RSM) will be applied to construct a
mathematical relationship between the laser cutting process parameters, power supply,
cutting speed and gas pressure, and between the quality of the responses, namely the
quality of cut edge and, and the surface roughness during an inclined cutting process.
The potential impact of each laser cutting parameter on the responses will be defined by
the verified mathematical models to identify the optimal cutting conditions that lead to
the highest quality.
6
CHAPTER 2
LITERATURE REVIEW
This chapter provides an overview of the laser and laser-cutting machine. The principles
of the laser beam generation and the technology involved in the laser cutting machine is
presented. The previous studies conducted on lasers and laser-cutting machines were
reviewed and suggestions and recommendations from those studies were used in the
current study.
2.1 Introduction
The conventional machining use has been restricted because of the sophisticated shape
and unusual size of the work material, rigorous design need and the emergence of
advanced engineering materials. Thus, the need for nonconventional machining methods
becomes an urgent demand which lead to the emergence of Advanced Machining
Processes (AMPs). (Choudhury & Shirley, 2010).
Laser machining is one of the AMPs utilized to cut various types of materials
economically. Laser beam machining has a wide application because it gives a finer
finish to the end product as compared to conventional cutting methods. (Choudhury &
Shirley, 2010). Lasers are commonly used to cut or in machine for different types of
materials, especially difficult-to-cut materials, in many industrial applications, due to its
advantages over the conventional cutting processes. (Eltawahni et al., 2010). Compared
with other conventional mechanical processes, laser cutting removes little material,
7
involves highly localized heat input to the workpiece, minimizes distortion, and offers
no tool wear. Laser cutting is a thermal, non-contact, and highly automated process well
suited for various manufacturing industries where a variety of components in large
numbers are required to be machined with high dimensional accuracy and surface finish.
(Madic et al., 2012).
2.2 History of laser
The first gas laser was developed in 1961 by A. Javan, W. Bennet, and D. Harriott of
Bell Laboratories, using a mixture of helium and neon gases. At the same laboratories,
L. F Johnson and K. Nassau demonstrated the first neodymium laser, which has since
become one of the most reliable lasers available. This was followed in 1962 by the first
semiconductor laser, demonstrated by R. Hall at the General Electric Research
Laboratories. In 1963, C. K. N. Patel of Bell Laboratories discovered the infrared carbon
dioxide laser, which is one of the most efficient and powerful lasers available today.
Later that same year, E. Bell of Spectra Physics discovered the first ion laser, in mercury
vapor. In 1964 W. Bridges of Hughes Research Laboratories discovered the argon ion
laser, and in 1966 W. Silfvast, G.R. Fowles, and B. D. Hopkins produced the first blue
helium-cadmium metal vapor laser. During that same year, P. P. Sorokin and J. R.
Lankard of the IBM Research Laboratories developed the first liquid laser using an
organic dye dissolved in a solvent, thereby leading to the development of broadly
tunable lasers. Beside, W. Walter and co-workers at TRG reported the first copper vapor
laser. In 1961, Fox and Li described the existence of resonant transverse modes in a laser
cavity. That same year, Boyd and Gordon obtained solutions of the wave equation for
confocal resonator modes. Unstable resonators were 9 demonstrated in 1969 by Krupke
and Sooy and were described theoretically by Siegman. Q-switching was first obtained
by McClung and Hellwarth in 1962 and described later by Wagner and Lengyel. The
first mode-locking was obtained by Hargrove, Fork, and Pollack in l964. Since then,
many special cavity arrangements, feedback schemes, and other devices have been
developed to improve the control, operation, and reliability of lasers.
8
2.3 Materials for laser cutting
Laser can cut plastics, woods, rubbers, foams, papers, and thin metals as long as they do
not contain chlorine. Depending on the material, there is usually no limit to the thinnest
sheet that can be cut, and the thickest sheet that can be cut is typically 1" {24 mm}. Also
on the same list are some woods, various plastics including acrylic, ABS, Mylar, Delrin,
PETG, and styrene, as shown in table1 below.
Table 2.1 Materials for Laser Cutting.
Plastics ABS (acrylonitrile butadiene styrene)
Acrylic (also known as Plexiglas, Lucite, PMMA)
Delrin (POM, acetal) – for a supplier, try McMaster-Carr.
High density polyethylene (HDPE) – melts badly
Kapton tape (Polyimide)
Mylar (polyester)
Nylon – melts badly
PETG (polyethylene terephthalate glycol)
Polyethylene (PE) – melts badly
Polypropylene (PP) – melts somewhat
Styrene
Two-tone acrylic – top color different than core material, usually for custom
instrumentation panels, signs, and plaques.
Metals
materials
Such as aluminum alloys, alloy steel, brass, carbon steel, stainless steel, titanium
steel, and tool steel, Chrome, Coated metals, Cobalt, Copper, Gold, Platinum,
Silver, Tin , Zinc
Foam Depron foam – often used for RC planes.
EPM (Ethylene propylene rubber)
Gator foam – foam core gets burned and eaten away compared to the top and
bottom hard shell.
Other Cloths (leather, suede, felt, hemp, cotton)
Magnetic sheets
Papers (Such as paper, cardboard, and matte board)
Rubbers (only if they do not contain chlorine)
Teflon (PTFE, Polytetrafluoroethylene).
Woods (MDF, balsa, birch, poplar, red oak, cherry, holly, etc.)
9
2.4 Laser Principal
The principles of current lasers are the same as the first one developed. A laser beam is
generated in a glass tube with a mirror at each end. The laser gas is pumped into the
glass and circulated by a turbine. One of the mirrors is 100 percent reflective, and the
other is less than 100 percent reflective (usually seventy percent) as shown in Figure 2.1.
The laser gas can be a mixture of helium, carbon dioxide and nitrogen. This mixture of
laser gas is commonly known as a CO2 laser. There are several other lasing gas mixtures
available and in use, but only for high powered industrial lasers, the CO2 mixture is the
most common. An external energy source, such as the electrical power (most commonly
DC power) or radio frequency (RF generator) excites the atoms in the laser gasor radio
frequency (RF generator) that in turn, excites the atoms in the laser gas mixture. When
the atoms of the laser gas become excited, the stimulated gas atoms give off a photon of
17 lights. This photon excites other atoms of the laser gas giving off more photons. This
forms a chain reaction. There are many examples of artists and designers using the laser
cutting technology to produce innovative concepts, especially with the use of soft
bending - a process that slits cut into the profile to allow for bending by hand (Myers, et
al., 2010).
Figure 2.1 Illustration of Laser Working (Myers et al., 2010)
10
The photons generated move back and forth between the two mirrors in the glass tube
until a portion escapes through the partially reflective (less than hundred percent
reflective) mirror. The laser beam is focussed onto the workpiece to be cut. Matching the
focal length of the laser beam to the depth of the cut results in maximum productivity
and the best cut quality. The laser beam is “hourglass” shaped after passing through the
machine. The maximum power concentration in the beam is at its “waist” and cuts best
at that area. Focal length is measured from the lens to the centre of the focus waist.
Common industrial focal lengths are 5 inches for thin and sheet metals and 7.5 inches
for thicker material (Myers, 2010).
2.5 Basic component and working principle
Lasers work as a result of resonant effects. The output of a laser is a coherent
electromagnetic field. In a coherent beam of electromagnetic energy, all the waves have
the same frequency and phase, as shown in Figure 2.2 and Figure 2.3.
Figure 2.2: Coherent electromagnetic waves have identical frequency, and are aligned in
phase (Tezuka et al., 2005)
11
Figure 2.3: Basic Components of Laser (Tezuka et al., 2005)
In a basic laser, a chamber called a cavity is designed to internally reflect infrared (IR),
visible-light or ultraviolet (UV) waves so they reinforce each other. The cavity can
contain gases, liquids, or solids. The choice of cavity material determines the
wavelength of the output. At each end of the cavity, there is a mirror. One mirror is
totally reflective, allowing none of the energy to pass through; the other mirror is
partially reflective, allowing approximately 5 percent of the energy to pass through.
Energy is introduced into the cavity from an external source; this is called pumping.
As a result of pumping, an electromagnetic field appears inside the laser cavity at
the natural (resonant) frequency of the atoms of the material that fills the cavity. The
waves reflect back and forth between the mirrors. The length of the cavity is such that
the reflected and reflected wave fronts reinforce each other in phase at the natural
frequency of the cavity substance. Electromagnetic waves at this resonant frequency
emerge from the end of the cavity have the partially-reflective mirror. The output may
appear as a continuous beam, or as a series of brief, intense pulses (Tezuka et al., 2005).
2.6 Metal cutting process
Metals are one of the structural materials. Metals are strong, cheap and tough; they are
chemically reactive, heavy and have limitations on the maximum operating temperature
(Samant & Dahotre, 2009).
12
Metalworking is the process of working with metals to create individual parts,
assemblies, or large scale structures. It therefore includes a correspondingly wide range
of skills, processes, and tools. Cutting is a collection of processes wherein material is
brought to a specified geometry by removing excess material using various kinds of
tooling to leave a finished part that meets specifications. The net result of cutting is two
products, the waste or excess material, and the finished part. In cutting metals the waste
is chips and excess metal. These processes can be divided into chip producing cutting,
generally known as machining. Burning or cutting with an Oxy-fuel torch is a welding
process not machining. There are also miscellaneous specialty processes such as
chemical cutting. Using an Oxy-fuel cutting torch to separate a plate of steel into smaller
pieces is an example of burning. Chemical turning is an example of a specialty process
that removes excess material by the use of etching chemicals and masking chemicals
(Tulasiramarao et al., 2013).The emergence of advanced engineering materials, stringent
design requirements, intricate shape and unusual size of workpiece restrict the use of
conventional machining methods. Hence, it was an urgent need to develop some of the
nonconventional machining methods known as Advanced Machining Processes.
Nowadays many AMPs are being used in the industry such as; Electro Discharge
Machining (EDM), beam machining processes (Laser Beam Machining (LBM), electron
beam machining, ion beam machining and plasma beam machining), electrochemical
machining, chemical machining processes (chemical blanking, photochemical
machining), Ultrasonic Machining (USM), jet machining processes and others. (Dubey
& Yadava, (2008) & Samant & Dahotre, (2009)). For instance, stainless steel is an
important engineering material that is difficult to be cut by Oxy-fuel methods because of
the high melting point and low viscosity of the formed oxides. However, it is suitable to
be cut by laser (Ghany & Newish, 2005), which replaces the traditional cutting methods
in most industrial applications. Material cutting is done by the spot translation along the
desired cutting path. The most common method is the use of two axes machines, which
move the steel sheet underneath the laser beam. There are also machines capable of
interpolating up to five axes, simultaneously. These type of machines are designed for
cutting complex forms and their programming is much more complex than the 2D case
(Majumdar & Manna, 2003). The cut can be executed in two dimensions (2D), for
13
instance on metal sheets, or in three dimensions (3D) in the case of components that
need to be cut in width, length and height such as tubes (ICS-UNIDO 2008).
2.7 Types of Laser Cutting
i. Laser Fusion Cutting
In case of higher alloyed steels and aluminum, the typically cutting gas is nitrogen or
argon. This process depends only on the laser beam energy therefore; the needed laser
power is higher than the power of laser flame cutting. Laser fusion cutting gives oxygen-
free cut edges, which is especially important if welding is the next process step after
cutting (Macquarie University, n.d).
ii. Laser Flame Cutting
For particularly low-alloyed steels, oxygen is normally used as a cutting gas. The laser
flame cutting process, receives more energy from the material exothermic reaction,
which is heated above the ignition temperature. Therefore, the required laser power is
lower than for laser fusion cutting. Flame cutting has the ability to cut at high speeds for
thick plates such as mild steel, stainless steel (Macquarie University, n.d).
iii. Laser Sublimation Cutting
In this type of cutting, the material is molten by the laser energy until it slightly
evaporates. Due to the steam pressurizing, the remove of material is influenced by the
ejection from the open cut against the impact direction of the beam. This needs
considerably higher power densities and is simultaneously related to slower speeds than
the above cutting processes (Macquarie University, n.d).
2.8 Laser Types
Based on the laser type and wavelength desired, the laser medium is solid, liquid or
gaseous. Various laser types are commonly named according to the state or the physical
properties of the active medium. Therefore, there are crystal, glass or semiconductor,
solid state lasers, liquid lasers, and gas lasers. Table 2 shows commercial lasers and their
main areas of application (Majumdar & Manna, 2003).
14
Table 2.2: Laser Types and Applications (Majumdar & Manna, 2003).
Type Application
Ruby Metrology, medical applications, inorganic material processing
Nd-Glass Length and velocity measurement
Diode Semiconductor processing, biomedical applications, welding
He–Ne Light-pointers, length/velocity measurement, alignment devices
Carbon dioxide Material processing-cutting/joining, atomic fusion
Nd-YAG Material processing, joining, analytical technique
Argon ion Powerful light, medical applications
Dye Pollution detection, isotope separation
Copper Isotope separation
Excimer Medical application, material processing, coloring
The most widely used industrial lasers for the cutting of sheet metals are gaseous CO2,
solid state Nd:YAGand recently fibre. The gas laser CO2 and solid state Nd:YAGlaser
have low beam power, better efficiency and good beam quality (Choudhury & Shirley,
2010). The fibre gains too much interest and development recently. There has been
growing interest in recent years in the use of pulsed Nd:YAG lasers for precision cutting
of thin sheet metals because of its high intensity, low mean beam power, good focusing
characteristics, and narrow Heat Affected Zone (HAZ) (Dubey & Yadava, 2008).
2.8.1 CO2 Laser
CO2 laser is one of the most main lasers in the laser machining of material. It is an
electrically pumped gas laser that radiates at a wavelength of 10.6 mm. They are
commercially available, with high laser powers of 20kW and more. The system is
chosen due to a very compact laser with low investment and operating costs. The CO2
15
laser is usually more expensive than the Nd: YAG laser (Sivarao et al., (2012) Sharma &
Yadava, (2012)). CO2 laser systems are available with reasonably a good beam quality at
high output powers sufficient for thick-section metal cutting (Wandera, 2010). CO2 laser
is shown in figure 4. Kar et al. (1996) used a high power Chemical Oxygen–Iodine Laser
(COIL) to cut the thick‐section stainless steel.
Figure 2.4 N2, O2 laser (Sivarao et al., 2012)
2.8.2 Nd: YAG Laser
Nd:YAG laser consist of crystalline YAG with a chemical formula Y3Al5O12 as a host
material. YAG laser is an optically pumped solid state laser, working at a wavelength of
1.06 mm for which the matrix is highly transparent. Figure 2.5 shows the Nd:YAG laser
diagram (Sivarao et al., (2012) & Sharma & Yadava, (2012)) and figure 2.6 shows
Nd:YAG laser machine. Nd:YAG laser advantages includes its lower reflectivity of the
cut material, smaller kerf width, narrower heat affected zone, better cut edge profile,
smaller thermal load, the enhanced transmission through plasma, so it is preferred for
applications that need a narrow kerf width and a small HAZ width (Salem et al., 2008).
Moreover, the smaller thermal load of the Nd:YAG laser facilitates the brittle materials
machining without crack damage in the manufactured part. In general, Nd:YAG laser is
suitable for the processing of metals in general and reflective materials in particular
(Sharma & Yadava, 2012). Since Nd:YAG laser has many selection of waveforms, it
N2 O2
16
can be applied to various processes such as trimming, repairing, scribing, welding,
cutting, annealing, and soldering (Salem et al., 2008). However Nd: YAG lasers have
lower overall efficiency and lower beam quality resulting in lower focus ability
(Wandera, 2010).
Figure 2.5: Nd: YAG laser (Sivarao et al., 2012)
Figure 2.6: JK300HPS Pulsed Nd:YAG Laser Machine and STRONG- 7090DS CNC
Machine
17
2.8.3 Fibre Laser
Fibre laser systems are a comparatively new development. Due to their different
resonator set-up, the beam quality of fibre lasers are more advanced than that of
comparable Nd:YAG systems(Sivarao et al., 2012). The most important characteristic of
the beam generated by a fibre laser is its superior brightness with respect to other
sources of similar power (ICS-UNIDO, 2008).
This type of laser is the most recent development and is undergoing rapid growth. There
are many benefits of using fibre laser in materials processing applications such as: a
higher absorptivity by metals, lower sensitivity against laser-induced plasmas, and
flexible beam handling through narrow optical fibre (Wandera, 2010). Compared to
CO2-lasers, fibre lasers have relatively low operational costs and offer a very high
flexibility in production due to the beam delivery with process fibers (Kratky et al,
2008). Figure 2.7 shows the fibre laser diagram.
Figure 2.7: Fiber lasers (Sivarao et al., 2012).
18
2 .9 Laser Gas Assistance
The heating and cooling processes coupled with the laser jet affect the structure of
material, HAZ width and the surface hardness. Moreover, the number of processing
variables and their impact on the cutting quality controls the material’s behaviour during
laser cutting. This task is complex because material laser cutting is an exothermal
reaction, which is dependent on inter-related material properties, such as thermal
conductivity, melting point, effect of oxidation reactions, reflectivity, viscosity, density,
latent heat of transformation, specific heat capacity, phase transformation temperature
and its dimension. The assist gas is responsible for removing the molten metal from the
cut kerfs, and it protects laser optics from being damaged by the resulting ejected
spatters. In addition, the assist gas works as a cooler to the laser optics and helps to blow
away the plasma formed during the laser material interactions, which reduce the
absorption of the material to the laser energy (Salem et al., 2008). The most common
assist gases used are oxygen and nitrogen. They are selected based on the type of
material being cut, its thickness and the edge quality required.
2.9.1 Oxygen as assist gas
Oxygen assisted laser in materials cutting such as mild steel is a very successful
industrial method, which was developed and is under continuous development since its
invention in the sixties (Powell et al., 2011). The use of oxygen as assist gas drags the
melt away and then reacts with the molten material forming the oxide film, which blows
into the kerfs covering the molten metal beneath. This technique of cutting increases the
cutting speed. The use of oxygen as assist gas also simplifies the exothermic energy
utilization, which decreases viscosity and surface tension but increases the absorption of
laser beam. And then, drosses adhering to the cutting edge bottom would represent
oxides various forms that could be readily removed (Salem et al., 2008). But the cut
edge produced by oxygen assisted laser cutting always characterized by parallel
striations (Powell et al, 2011). Salem et al (2008) investigated the cutting parameters of
the CW ND: YAG laser such as the gas pressure, laser power, and scanning speed for
19
1.2 mm thick ultra-low carbon steel sheets. Results showed that good quality cuts can be
obtained in ultra-low carbon steel thin sheets, at laser scanning speed of 1100–
1500mm/min and at a minimum heat input of 337W under an assisting O2 gas pressure
of 5 bars. Higher laser power can lead to either strength or soften the HAZ surrounding
the cut kerfs (Salem et al., 2008).
2.9.2 Nitrogen as assist gas
Nitrogen is commonly known as a clean cut process. Nitrogen is used for the cutting of
stainless, aluminium and alloy steels and also showed improvement in cutting speeds
with higher power lasers on thinner gauge carbon steels. The nitrogen purity affects the
quality and cleanliness of the cut. Using Nitrogen can lead to (Nitrogen Applications,
2010):
• High Cutting Speeds
• High Quality Edge Cut (No Grinding)
• Absence of an Oxide Layer or Blackening
• Low Distortion and Dross Formation
• Very Narrow Kerf Width
Ghany and Newishy (2005) evaluated the optimum laser cutting parameters for 1.2mm
austenitic stainless steel sheets using pulsed and CW Nd:YAG laser beam and nitrogen
or oxygen as assistant gases, each one separately. The results showed that the laser
cutting quality depends mainly on the laser power, pulse frequency, cutting speed and
focus position (Ghany & Newish 2005).
Eltawahni et al. (2012) studied the effect of CO2 laser cutting process parameters
on edge quality and operating cost of austenitic stainless steel of 2mm thickness. The
results showed that the width of upper kerf increases with the increase of laser power,
nitrogen pressure and nozzle diameter, and it decreases with the increase of the cutting
speed and focal position. However, the cutting speed is the major factor affecting the
upper kerf.
20
Figure 2.8: Laser Beam Melting the Material as the Assist Gas Forces out the Molten
Mass (Sommer, 2009).
2.10 Laser Cut Quality
The laser cutting process performance is affected by many factors, where it is important
to identify the dominant factors that significantly affect the cut quality is important. The
quality of cut depends on the process parameters setting such as laser power, assist gas
type and pressure, sheet material thickness and its composition, cutting speed, and
operation mode (continuous wave or pulsed mode) (Dubey & Yadava, 2008). Gas
pressure and the shape of the nozzle have an effect on the roughness of the cut. The
consumption of cutting gas depends on gas pressure and diameter of the nozzle
(Radonjic et al., 2012). The cut section quality in the laser cutting of a metallic sheet can
be estimated by the surface roughness, the striations formation and the cut and break
area formation (Ahn & Byun, 2009).
Using the laser to cut sheet and plate metal is vastly implemented in the industry
nowadays. Steel and aluminium is one of the more metals that are usually subject to
Laser Cutting. Constant development in available output power and the laser systems
beam quality expands industrial laser applications of cutting process to cover various
21
pieces thickness (Wandera, 2010). The experimental researches achieved by different
researchers have been supported recently by mathematical models to understand the
variable processing parameters impact on laser cutting quality. In addition, establishing
such processing parameters also allows to process parameters optimization, such as
cutting speed, laser power, and assists gas pressure on the actual operating costs basis.
Sivarao & Ammar (2010) used RSM based on the mathematical model to predict surface
roughness in laser cutting of mild steel. Baskoro et al (2011) used Response Surface
Method (RSM) to select the parameter that has a less significant effect to the depth of
cut. Sharma and Yadava (2012) used the response surface methodology (RSM) to model
and optimize cut quality during the cutting process. Madic & Radovanovic (2012) used
artificial neural networks ANNs to develop a mathematical model to estimate the surface
roughness characteristics.
Generally, the width of laser cut or kerf, quality of the cut edges, surface quality
and the operating cost are affected by a number of parameters related to the laser system,
used material, and the cutting process. Kar et al. (1996) studied the process parameters
impacts, such as laser power, spot size and dimensions, and the cutting speed on the
resulting kerf size. Eltawahni et al. (2011) used CO2 laser cutting of (4, 6, 9 mm) of
Medium Density Fiberboard (MDF). The results showed that the surface roughness is
decreased when the focal point position and laser power were increased and the cutting
speed and gas pressure were reduced. Kurt et al (2009) investigated the effect of CO2
laser cutting of engineering plastics. They deduced that the laser power and cutting
speed must be regulated and optimized to obtain the desired dimensions and optimize
surface quality and roughness values.
Eltawahni et al (2010) studied the cutting process parameters, laser power,
cutting speed and focal point position and the quality of the cut (responses) namely:
upper kerf, lower kerf, ratio between upper kerf to lower kerf and surface roughness.
The study used CO2 laser cutting of ultra-high-performance polyethylene and aimed to
find out the optimal process setting at which the quality features are at their desired
values. They stated that all the investigated factors have a potential effect on the
responses with different levels (Eltawahni et al., 2010).
22
Choudhury and Shirley (2010) used CO2 laser to cut different polymeric
materials to investigate the effect of the main input laser cutting parameters (laser
power, cutting speed and compressed air pressure) on laser cutting quality. The results
showed that the dimension of HAZ for all polymers is directly proportional to the laser
power and inversely proportional to cutting speed and compressed air pressure.
Moreover, surface roughness is inversely proportional to laser power, cutting speed and
compressed air pressure. Ahn and Byun (2009) used high-power Nd:YAG laser to cut
Inconel 718 super-alloy sheet and studied the effect of cutting parameters such as laser
power, laser cutting speed and workpiece thickness, on the surface quality of a cut
section to get the optimal cutting condition. The results showed that the surface
roughness difference of the cut section is affected significantly by the cutting speed.
Stournara et al (2009) used a pulsed CO2 laser cutting system to investigate
experimentally the quality of laser cutting for the aluminum alloy AA5083. They
evaluated the effect of processing parameters, such as the laser power, the scanning
speed, the pulsing frequency and the gas pressure by statistical analysis (Taguchi
methodology) of the results. The quality of the work pieces is determined by the kerf
width, the cutting edge surface roughness and the size of the heat-affected zone. The
results showed that the laser power and cutting speed play the most important role on the
cutting quality, while the Kerf’s width and heat-affected zone are mostly affected by
laser power and cutting speed parameters.
Riveiro et al (2012) investigated the processing parameters effect during the CO2
pulse laser cutting of an Al–Cu alloy using a cutting head assisted by an off-axis
supersonic nozzle. The result showed that the pulsed mode reduces the maximum cutting
speed, and increases the possibility to obtain cuts with a lower width, average roughness,
dross, and with a minimum HAZ.
Sparkes et al (2008) used a high brightness fiber laser in a series of high
brightness trials on stainless steels of section thicknesses in the range of 6–10 mm. The
results showed that the cutting performance varied with changing gas pressure, focal
position, and nozzle diameter. They observed a poor cut edge quality in thick section
stainless steel caused by the difficulty in obtaining full melt ejection through the narrow
thick-section cut kerfs.
23
2.10.1 Laser cutting typical imperfection
The mechanisms that control the laser cutting process are not totally understood because
laser cutting is a complex thermal process. The laser cutting quality did not improve
perfectly in an industry, where many post-machining operations occur and lead to affect
the cutting quality. One of the important lasers cutting imperfections is striation
formation on the cut surfaces, which affects the surface roughness and geometry
precision of a laser cut product (Rajpurohit & Patel, 2012).
The schematic of striation formation mechanism by side burning is shown in
Figure 9. The other typical imperfection is dross formation generated on the cut edges.
This process is a consequence of the agglomeration of molten material, which flows
along the cut edge in its lower wedge (Riveiro et al., 2011). Figure 2.10 shows the
formation of dross.
Figure 2.9: Schematic mechanism of striations formation during laser cutting
(Rajpurohit & Patel, 2012)
24
Figure 2.10: (Formation of Dross, a), (Formation of a Droplet, b), (Growing, c) Merging
of the droplet with previous molten material (Riveiro et al., 2011).
2.11 Optimization of Cutting Process Parameters
In the cutting process, cutting parameters optimization is regarded as a vital tool for
improving the output quality of a product as well as reducing the overall production
time. An optimization technique provides an optimal or near optimal solution of
optimization problem, which can be implemented in the actual metal cutting process
(Deepak, 2012). There are different techniques of have been successfully applied in the
past for optimizing the various cutting process variables, such as:
73
REFERENCES
Ahn, D. G., &Byun, K. W. (2009). Influence of cutting parameters on surface
characteristics of cut section in cutting of Inconel 718 sheet using CW Nd: YAG
laser. Transactions of Nonferrous Metals Society of China, 19, s32-s39
Al-Wedyan H., Demirli K. and Bhat R. (2001).A technique for fuzzy logic modeling of
machining process, 20th NAFIPS international conference, 5, 3021–3026
Baskoro, A. S., Herwandi, K. G. S., Siswanta, A., &Kiswanto, G. (2011).Analysis of
Cutting Process of Materials Using Low Power Laser Diode and
CO2.International Journal of Mechanical & Mechatronics Engineering IJMME-
IJENS Vol: 11 No: 06
Çaydaş, U., &Hasçalık, A. (2008).Use of the grey relational analysis to determine
optimum laser cutting parameters with multi-performance characteristics. Optics
& Laser Technology, 40 (7), 987-994
Chaudhari P. S., Prof. Patel D. M., Dr. Juneja J. L. (2012).Artificial Intelligence apply
for prediction of Laser Cutting Process – A review. International Journal of
Engineering Research and Applications (IJERA). Vol. 2, Issue 4
Choudhury, I. A., & Shirley, S. (2010). Laser cutting of polymeric materials: An
experimental investigation. Optics & Laser Technology, 42 (3), 503-508
Choudhury, I. A., & Shirley, S. (2010). Laser cutting of polymeric materials: An
experimental investigation. Optics & Laser Technology, 42 (3), 503-508
Chowdhury K., Pratihar D.K. and Pal D.K. (2002). Multi-objective optimization in
turning—using GA algorithm, Journal of the Institute of Engineers (India), 82, 37–44
Cus F. and Balic J. (2003).Optimization of cutting process by GA approach, Robotics
and Computer Integrated Manufacturing, 19, 113–121
Deepak, S. S. K. (2012). Applications of Different Optimization Methods for Metal
Cutting Operation–A Review. Research Journal of Engineering Sciences . Vol.
1(3), 52-58
74
Dubey, A. K., &Yadava, V. (2008).Laser beam machining: a review. International
Journal of Machine Tools and Manufacture, 48 (6), 609-628
Dubey, A. K., &Yadava, V. (2008). Laser Beam Machining: A review. International
Journal of Machine Tools and Manufacture, 48 (6), 609-628. Elsevier
Eltawahni H. A. , A. G. Olabi, and K. Y. Benyounis, “Investigating the CO2 laser
cutting parameters of MDF wood composite material,” Optics & Laser
Technology, vol. 43, no. 3, pp. 648–659, Apr. 2011
Eltawahni H.A., Olabi A.G., Benyounis K.Y. (2010).Effect of Process Parameters and
Optimization of CO2 Laser Cutting of Ultra High-Performance Polyethylene.
Materials and Design 31 (2010) 4029–4038. Elsevier Ltd.
Eltawahni, H. A., Hagino, M., Benyounis, K. Y., Inoue, T., &Olabi, A. G. (2012).Effect
of CO2 laser cutting process parameters on edge quality and operating cost of
AISI316L. Optics & Laser Technology, 44 (4), 1068-1082
Ghany KA, Newish M. Cutting of1.2 mm thick austenitic stainless steel sheet using
pulsed and CWNd:YAG laser. Journal of Materials Processing Technology 2005;
168:438–47.
Gok, A., Gologlu, C., Demirci, H. I., & Kurt, M. (2012).Determination of Surface
Qualities on Inclined Surface Machining with Acoustic Sound
Pressure.Strojniškivestnik - Journal of Mechanical Engineering, 58 (10), 587-597
Grzesik W. and Brol S. (2003).Hybrid approach to surface roughness evaluation in
multistage machining processes, Journal of Materials Processing Technology,
134, 265– 272
Hashmi K., El Baradie M.A. and Ryan M. (1998).Fuzzy logic based intelligent selection
of machining parameter, Computers and Industrial Engineering, 35 (3–4), 571–574
I N G. Houston 267.
ICS-UNIDO (2008).Laser Technologies: a step forward for small and medium
enterprises.United Nations Industrial Development Organization and the
International Centre for Science and High Technology. Italy
Kar, A., Scott, J.E., Latham, W.P., 1996. Theoretical and experimental studies of thick-
section cutting with a chemical oxygen-iodine laser (COIL). J. Laser Appl. 8, 125–
133
75
Karatas, C., Keles, O., Uslan, I., &Usta, Y. (2006). Laser cutting of steel sheets:
Influence of workpiece thickness and beam waist position on kerf size and stria
formation. Journal of materials processing technology, 172 (1), 22-29
Kratky, A., Schuöcker, D., &Liedl, G. (2008, October).Processing with kW fibre lasers:
advantages and limits. In XVII International Symposium on Gas Flow and
Chemical Lasers and High Power Lasers (pp. 71311X-71311X). International
Society for Optics and Photonics
Krimpenis A. and Vosniakos G.C. (2002).Optimization of multiple tool NC rough
machining of a hemisphere as a genetic algorithm paradigm application,
International Journal of Advanced Manufacturing Technology, 20, 727– 734
Kumar Dubey, A., &Yadava, V. (2008).Multi-objective optimisation of laser beam
cutting process. Optics & Laser Technology, 40 (3), 562-570
Kurt M, Kaynak Y, Bagci E, Demirer H, Kurt M. Dimensional analyses and surface
quality of the laser cutting process for engineering plastics. International Journal
of Advanced Manufacturing Technology 2009;41 (3–4) 259–67
Lamiki A. et al (2005). CO2 laser cutting of advanced high strength steels (AHSS).
Applied Surface Science 242 (2005) 362–368
Lee Y.H., Yang B.H. and Moon K.S. (1999). An economic machining process model
using fuzzy non-linear programming and neural network, International Journal of
Production Research, 37 (4), 835–847
Madić, M., Radovanović, M., &Nedić, B. (2012).Correlation between Surface
Roughness Characteristics in CO2 Laser Cutting of Mild Steel. Tribology in
Industry vol. 34, No. 4
Madić, M., Radovanović, M., &Nedić, B. (2012).Correlation between Surface
Roughness Characteristics in CO2 Laser Cutting of Mild Steel. Tribology in
Industry vol. 34, No. 4
Madić, M., Radovanović, M., &Slatineanu, L. (2013).Surface Roughness Optimization
In Co2 Laser Cutting By Using Taguchi Method. U.P.B. Sci. Bull., Series D, Vol.
75, Iss. 1,
76
Madić, M., Radovanović, M., &Slatineanu, L. (2013).Surface Roughness Optimization
In Co2 Laser Cutting By Using Taguchi Method. U.P.B. Sci. Bull., Series D, Vol.
75, Iss. 1,
Majumdar, J. D., & Manna, I. (2003).Laser Processing of Materials.Sadhana, 28 (3-4),
495-562
Myers, R. H., Montgomey, D. C., and Anderson-Cook, C. M., 2010. Response Surface
Methodology: Process and Product Optimization Using Designed Experiments,
3rd ed. WILEY.
Nitrogen Applications (2010).Metal Fabrication: Laser Cutting. Generon IGS.
Phipon, R., &Pradhan, B. B.(2012). Control Parameters Optimization of Laser Beam
Machining Using Genetic Algorithm. International Journal of Computational
Engineering Research (ijceronline.com) Vol. 2 Issue. 5
Physics and Astronomy department (n.d).Laser Machining.Macquarie
University.Faculty of science. Sydney, Australia. Retrievef on April 2013
http://physics.mq.edu.au/files/file/Laser%20Machining.pdf
Powell, J., Al-Mashikhi, S. O., Kaplan, A. F. H., &Voisey, K. T. (2011).Fibre laser
cutting of thin section mild steel: An explanation of the ‘striation free’effect.
Optics and Lasers in Engineering, 49(8), 1069-1075
Radonjić, P. D. S., Save, S., Čačak, S., Kovač, P. D. P., & Sad, N.( 2012). Defining New
Processing Parameters In Laser Cutting.16th International Research/Expert
Conference. Dubai, UAE
Radovanovic, M., &Madic, C. (2011).Experimental investigations of CO2 laser cut
quality: a review. Nonconventional Technologies Review, 4, 35-42
Rajpurohit S. R., Prof. Patel D.M. (2012). Striation Mechanism In Laser Cutting : The
Review. International Journal of Engineering Research and Applications (IJERA).
Vol. 2, Issue 2
Riveiro, A., Quintero, F., Lusquiños, F., Comesaña, R., &Pou, J. (2011).Effects of
processing parameters on laser cutting of aluminium–copper alloys using off-axial
supersonic nozzles. Applied Surface Science, 257(12), 5393-5397
77
Riveiro, A., Quintero, F., Lusquiños, F., Comesaña, R., &Pou, J. (2011).Study of melt
flow dynamics and influence on quality for CO2 laser fusion cutting. Journal of
Physics D: Applied Physics, 44(13), 135501
Salem, H. G., Mansour, M. S., Badr, Y., & Abbas, W. A. (2008).CW Nd: YAG laser
cutting of ultra-low carbon steel thin sheets using O2 assist gas. Journal of
materials processing technology, 196(1), 64-72
Samant, A. N., &Dahotre, N. B. (2009).Laser machining of structural ceramics: a
review. Journal of the European Ceramic Society, 29(6), 969-993
Sathyanarayanan G., Lin I.J. and Chen M. (1992).Neural network modeling and multi
objective optimization of creep feed grinding of super alloys, International Journal
of Production Research, 30(10), 2421–2438
Schrader R.S. (2003). Optimization of cost and cycle time for multi-pass turning
operation using GA, genetic algorithm at the University of Illinois Fall 2002,
Report no 2003010, 205-2065
Shaji S. and Radhakrisnan V. (2003).Analysis of process parameters in surface grinding
with graphite as lubricant based on Taguchi method, Journal of Material
Processing Technology , 1–9
Sharma, A., &Yadava, V. (2012).Modelling and optimization of cut quality during
pulsed Nd: YAG laser cutting of thin Al-alloy sheet for straight profile. Optics &
Laser Technology, 44(1), 159-168
Sharma, A., &Yadava, V. (2012).Modelling and optimization of cut quality during
pulsed Nd: YAG laser cutting of thin Al-alloy sheet for straight profile. Optics &
Laser Technology, 44(1), 159-168
Singh S., Shan H.S. and Pradeep K. (2002).Parametric optimization of magnetic field
assisted abrasive flow machining by the Taguchi method, Quality and Reliability
Engineering International, 18, 273–283
Sivarao, S., Sivakumar, D. M., Yuhazri, Y., Tan, C., &Haeryip, S. (2012). An
Exploratory Study-Critical Laser Processing of Composite Materials. International
Journal of Engineering Research & Technology, 1(10), 1-8
78
Sivarao, T. J. S., &Ammar, S (2010).RSM Based Modeling for Surface Roughness
Prediction in Laser Machining. International Journal of Engineering &
Technology IJET-IJENS Vol: 10 No: 04
Sommer, C.(2009), Non-Traditional Machining Handbook, Advance Publishing,
Sparkes M., Gross M., Celotto S., Zhang T., and O’Neill W. Practical and theoretical
investigations into inert gas cutting of 304 stainless steel using a high brightness
fiber laser, Journal of Laser Applications, 2008, 20, pp. 59-67
Stournaras, A., Stavropoulos, P., Salonitis, K., &Chryssolouris, G. (2009).An
investigation of quality in CO< sub> 2</sub> laser cutting of aluminum. CIRP
Journal of Manufacturing Science and Technology, 2(1), 61-69
Syn, C. Z., Mokhtar, M., Feng, C. J., &Manurung, Y. H. (2011).Approach to prediction
of laser cutting quality by employing fuzzy expert system. Expert Systems with
Applications, 38(6), 7558-7568
Tezuka, S., Tokura, H., & Yoshikawa, M., 2005. Cutting Of Diamond Grit With YAG
Laser [pdf] Available at: <http://www.dtic.mil/cgi-
bin/GetTRDoc?AD=ADA206954> [Accessed 20 August 2013].
Tulasiramarao, B., Srinivas, K., Reddy, P. R., Raveendra, A., & Ravi, B. Effect of
Processing Parameters on Surface Finish of the Components Processed By CNC
Turning Machine. International Journal of Mechanical Engineering applications
Research – IJMEAR.Vol 04, Issue 01
University of Bradford.Response Surface Methodology.Book chapter. Retrieved
Wandera, C. (2010). Performance of high power fibre laser cutting of thick-section steel
and mediumsectionaluminium.PhD thesis. Lappeenranta University of
Technology, Finland
Yilbas, B. S. (2008). Laser cutting of thick sheet metals: Effects of cutting parameters on
kerf size variations. Journal of materials processing technology, 201(1), 285-290
Yilbas, B. S., Karatas, C., Uslan, I., Keles, O., Usta, Y., Yilbas, Z., &Ahsan, M. (2008).
Wedge cutting of mild steel by CO laser and cut-quality assessment in relation to
normal cutting. Optics and Lasers in Engineering, 46(10), 777-784
