investigation of laser cutting parameters on surface quality...
TRANSCRIPT
INVESTIGATION OF LASER CUTTING PARAMETERS ON SURFACE
QUALITY OF STAINLESS STEEL
AZMAN BIN ANUAR
A project report submitted in partial fullfilment of
the requirements for the award of the degree of Master of
Engineering (Mechanical – Advanced Manufacturing Technology)
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
MAY 2010
iii
To my beloved family father and mother , my wife - Norhasniza , my kids -
Muhammad Aqil Farihin and Nur Damia Harisa, and my siblings. Thank for all your
support .
iv
ACKNOWLEDGEMENT
First of all, I would like to thank Allah s.w.t for giving me strength and
guidance to complete this project. I would like to express my sincere thanks to my
supervisor Prof. Dr. Ashraf Hafiz Radwan and co-supervisor Dr.-Ing. Yupiter HP
Manurung for the constant guidance, invaluable knowledge, and constructive ideas in
leading us to accomplish this project
I would like to thank all staff in the Universiti Sains Malaysia especially to
Mr. Mohzani and Mr. Fahmi who have provided with assistance on various
occasions. Assistance given by my fellow postgraduate collegues Mr. Zaeime are
also acknowledged.
I am indebted to Majlis Amanah Rakyat (Mara) for grating me the
scholarship to pursue my study at the Universiti Teknologi Malaysia. Finally, I
would like to extend my heartful thank you to all my lecturers in the Department of
Manufacturing and Industrial Engineering of the Universiti Teknologi Malaysia,
friends and family members who have given me moral support during my studies.
v
ABSTRACT
In this thesis, the optimal CO2 laser cutting parameters on stainless steel AISI
304 with 2 mm in thickness were studied. The cut quality to achieve a uniform kerf
with minimum kerf width for circular cuts of stainless steel sheets depends on
appropriate selection of process parameters was investigated. The cutting parameters
considered include laser output power level, cutting speed, cutting gas pressure, and
focus length. The effect of the cutting parameters on the cut quality was further
investigated by monitoring the kerf width, roundness, and diameter accuracy. The
experiments were conducted by using the nitrogen gas assisted laser cutting, and the
factorial analysis is employed to formulate an empirical formula for optimum.
vi
ABSTRAK
Dalam tesis ini, mengkaji CO2 laser cutting parameter optimum pada
stainless steel AISI 304 dengan ketebalan 2 mm. Untuk permotongan yang berkualiti
mencapai garitan seragam dengan kerf width bagi kepingan stainless steel yang tepat
bergantung pada parameter proses. Parameter pemotongan dianggap meliputi tahap
keluaran kuasa laser, kelajuan potong, pemotongan tekanan gas, dan panjang fokus.
Pengaruh parameter pemotongan terhadap kualiti pemotongan itu berdasarkan
penyelidikan lebih lanjut oleh pemantauan kerf width, kebulatan, dan diameter.
Ekseperimen ini dijalankan dengan menggunakan laser cutting gas nitrogen dibantu
dan dianalisa dengan faktoran untuk merumuskan empirical formula menjadi
optimum.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xii
LIST OF FIGURES xv
LIST OF SYMBOLS AND ABBREVIATIONS xix
LIST OF APPENDICES xx
1 INTRODUCTION 1
1.1 Overview 1
1.2 Project statement 2
1.3 Objective 3
1.4 Scope 3
viii
2 LITERATURE REVIEW 4
2.1 Introduction 4
2.2 Laser cutting 5
2.2.1 Definition of laser cutting 5
2.2.2 Principle of laser cutting 6
2.2.3 Laser cutting approach 7
2.2.3.1 Evaporative laser cutting 8
2.2.3.2 Laser fusion cutting 9
2.2.3.3 Reactive or oxygen assisted
laser cutting 10
2.2.3.4 Controlled fracture technique 11
2.2.4 CO2 laser cutting 14
2.2.4.1 Fast axial flow CO2 laser cutting 15
2.2.4.2 Diffusion cooled (slab) CO2
laser cutting 16
2.2.4.3 Sealed off CO2 laser cutting 17
2.2.5 Gas assist on laser cutting 17
2.2.5.1 Oxygen 18
2.2.5.2 Nitrogen 19
2.3 Laser parameters 19
2.3.1 Beam parameter 20
2.3.1.1 Wave length 20
2.3.1.2 Power and intensity 22
2.3.1.3 Beam quality 23
2.3.1.4 Beam polarization 24
2.3.2 Process parameter 27
2.3.2.1 Continuous wave (cw) or
pulsed (p) laser power 27
2.3.2.2 Focal length of the lens 28
2.3.2.3 Focal position relative to
the material surface 29
2.3.2.4 Cutting speed 29
ix
2.3.2.5 Process gas and gas pressure 30
2.3.2.6 Nozzle diameter and
standoff distance 31
2.3.2.7 Nozzle alignment 33
2.4 Material 34
2.4.1 Stainless steel 35
2.5 Effect the cutting process 37
2.5.1 Kerf width 37
2.5.2 Diameter 39
2.5.3 Roundness 40
2.6 Review of previous studies 41
2.6.1 Wedge cutting of mild steel by CO2
laser and cut quality assessment in
relation to normal cutting 41
2.6.2 Experimental investigation into
CO2 laser cutting parameters 45
2.6.3 Investigation of optimum condition
in oxygen gas assisted laser cutting 48
3 METHODOLOGY 51
3.1 Introduction 51
3.2 Machine parameters 51
3.3 Response parameter 52
3.4 Material 52
3.3.1 Stainless steel (AISI 304) 53
3.3.1.1 Composition of stainless steel
(AISI 304) 53
3.3.1.2 Mechanical properties of
stainless steel (AISI 304) 53
3.3.1.3 Thermal properties of
stainless steel (AISI 304) 54
x
3.3.1.4 Electric properties of
stainless steel (AISI 304) 55
3.3.2 Sample of specimen 55
3.5 Machine and equipment 56
3.6 Analysis 59
3.6.1 Statistical analysis 59
3.6.2 Kerf width 60
3.6.3 Roundness error 60
3.6.4 Diameter accuracy 61
3.7 Experimental flowchart 61
4 RESULTS AND DISCUSSIONS
4.1 Introduction 62
4.2 Experimental results 62
4.2.1 Laser cutting of stainless steel 304 63
4.3 Experimental result for kerf width 66
4.3.1 Analysis of kerf width 66
4.3.1.1 Cutting speed (B) 69
4.3.1.2 Interaction graph between
power (A) and pressure (C) 70
4.3.1.3 Interaction graph between
power (A) and focus length (D) 71
4.3.1.4 Interaction graph between
pressure (C) and focus length (D) 72
4.3.1.5 Perturbation plot for kerf width in
laser cutting process 73
4.3.2 Empirical equations and graphical form for
kerf width model 74
4.4 Experimental result for roundness error 76
4.4.1 Analysis of roundness 76
4.4.1.1 Power (A) 79
xi
4.4.1.2 Interaction graph between
cutting speed(B) and pressure (C) 80
4.4.1.3 Interaction graph between
cutting speed(B) and focus
length (D) 81
4.4.1.4 Interaction graph between
pressure (C) and focus length (D) 82
4.4.1.5 Perturbation plot for roundness
in laser cutting process 83
4.4.2 Empirical equations and graphical form
for roundness model 84
4.5 Experimental result for diameter accuracy 86
4.5.1 Analysis of diameter 86
4.5.1.1 Interaction graph between
power (A) and focus length (D) 89
4.5.1.2 Interaction graph between
cutting speed(B) and focus
length (D) 90
4.5.1.3 Interaction graph between
pressure (C) and focus length (D) 90
4.5.1.4 Perturbation plot for diameter
in laser cutting process 91
4.5.2 Empirical equations and graphical form for
diameter model 92
4.6 Summary of significant factors in laser cutting
processs 92
4.7 Confirmation run 94
4.8 Discussions 96
4.8.1 Kerf width 96
4.8.2 Roundness error 98
4.8.3 Diameter accuracy 99
xii
5 CONCLUSIONS AND RECOMMEDATIONS 100
5.1 Conclusions 100
5.2 Recommendations 103
REFERENCES 104
Appendices A - C 109 - 120
xiii
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Various approaches of laser cutting 8
2.2 Laser cutting condition 43
2.3 Optimum experimental conditions for steel laser
cutting
50
2.4 Optimum experimental conditions for mild steel laser
cutting
50
3.1 Machining parameter 52
3.2 Composition of stainless steel (AISI 304) 53
3.3 Mechanical properties of stainless steel (AISI 304) 54
3.4 Thermal properties of stainless steel (AISI 304) 54
3.5 Electric properties of stainless steel (AISI 304) 55
4.1 Factors and levels for laser cutting of stainless steel
304
63
4.2 Experimental plan for laser cutting stainless steel 304 64
4.3 Experimental results for laser cutting stainless steel
304
65
4.4 ANOVA table for kerf width in laser cutting process 67
4.5 ANOVA table for roundness in laser cutting process 77
4.6 ANOVA table for diameter in laser cutting process 87
4.7 Summary of significant factors in laser cutting
experiments
94
xiv
4.8 Analysis of comfirmation run experiment for kerf
width
95
4.9 Analysis of comfirmation run experiment for
roundness
95
4.10 Analysis of comfirmation run experiment for diameter 95
xv
LIST OF FIGURES
FIGURE NO. TITLE
PAGE
2.1 Basic principle of laser cutting 6
2.2 General schematic of a laser-cutting process with a
coaxial gas jet to blow the molten material
7
2.3 A sketch of laser vaporization cutting 9
2.4 A sketch of laser fusion cutting 10
2.5 A sketch of laser oxygen cutting 11
2.6 Experimental setup for laser cutting using
controlled fracture technique
13
2.7 Mechanism of laser cutting by controlled fracture
for asymmetrical cutting
13
2.8 Model geometry for calculating temperature and
stress distribution during controlled fracture
cutting
14
2.9 Fast axial flow (FAF) laser with beam trajectory
planes oriented at 45° angle
16
2.10 Diffusion-cooled (slab) CO2
laser 17
2.11 Absorption phenomena of typical metals over a
range of different laser wavelengths
21
2.12 The relative absorption of energy for different
orientations of the cutting direction and direction
of polarization, whereby ψ is the angle between the
plane of polarization, p, and the cutting direction, c
25
xvi
2.13 Effects of polarization in cutting 26
2.14 Focusability of laser beams 28
2.15 Nozzle geometry – definitions 32
2.16 (a) The equilibrium set up when the gas jet and
laser beam are coaxial
(b) Nozzle-laser beam misalignment
33
2.17 (a) Variation of the kerf width with cutting speed
(b) Variation of the kerf width with laser output
power
(c) Variation of kerf width with energy coupling
factor
38
2.18 Perpendicularity tolerance of a straight laser cut 39
2.19 Sketch a diameter of a circle 40
2.20 Experimental setup for wedge and normal cutting
situations
43
2.21 Layout of neural network used the simulation 43
2.22 Schematic view of dross height and out of flatness 44
2.23 Experimental set-up 46
3.1 CO2 laser cutting 56
3.2 Profile projector 57
3.3 Roundness tester 57
3.4 Coordinate measurement machine 58
3.5 Design expert version 6.0.5 software 58
3.6 Flowchart outlining the analysis steps undertaken 59
3.7 A diagram of the measurement method of
roundness
60
3.8 Overall procedure for whole experimental work 61
4.1 Normal probability plots of residuals for kerf
width in laser cutting process
68
4.2 Residual vs predicted response for kerf width in
laser cutting process
68
xvii
4.3 Outlier T plot for kerf width in laser cutting
process
69
4.4 One factor plot for kerf width in laser cutting
process
70
4.5 Interaction between power and pressure on kerf
width(focus length = -2 mm and cutting speed =
850 mm/min)
71
4.6
Interaction between power and focus length on
kerf width(pressure = 11 bar and cutting speed =
850 mm/min)
72
4.7 Interaction between pressure and focus length on
kerf width(power =1000 watt and cutting speed =
850 mm/min)
73
4.8 Perturbation plot for kerf width in laser cutting
process
74
4.9 3D response surface for kerf width in laser cutting
process
75
4.10 Normal probability plots of residuals for roundness 78
4.11 Residual vs predicted response for roundness 78
4.12 Outlier T plot for roundness 79
4.13 One factor plot for Roundness in laser
cutting(cutting speed = 850 mm/min, pressure = 11
bar and focus length = -2 mm)
80
4.14 Interaction between cutting speed (B) and pressure
(C) on roundness(power =1000 watt and focus
length = -2 mm)
81
4.15 Interaction between cutting speed (B) and focus
length (D) on roundness(power =1000 watt and
pressure = 11 bar)
82
4.16 Interaction between pressure (C) and focus length
(D) on roundness(power =1000 watt and cutting
speed = 850 mm/min)
83
xviii
4.17 Perturbation plot for roundness in Laser Cutting
process
84
4.18 3D response surface for roundness in laser cutting
process
85
4.19 Normal probability plots of residuals for diameter 88
4.20 Residual vs predicted response for diameter 88
4.21 Outlier T plot for diameter in laser cutting process 88
4.22 Interaction between power (A) and focus length
(D) on diameter(cutting speed = 850 mm/min and
pressure = 11 bar)
89
4.23 Interaction between cutting speed (B) and focus
length (D) on diameter(power = 1000 watt and
pressure = 11 bar)
90
4.24 Interaction between pressure (C) and focus length
(D) on diameter(power = 1000 watt and cutting
speed = 850 mm/min)
91
4.25 Perturbation plot for diameter in laser cutting
process
92
4.26 3D response surface for diameter in laser cutting
process
93
4.27 Interaction between power and pressure on kerf
width (focus length= -1 mm and cutting speed =
850 mm/min)
97
4.28 Interaction between power and focus length on
kerf width(pressure=12 bar and cutting speed =
850 mm/min)
97
xix
LIST OF SYMBOLS AND ABBREVIATIONS
λ - wavelength
K - beam quality factor
M2
- times diffraction limit factor
D - beam diameter at the optic
df - focused beam diameter
z - depth of focus
f - focus length
F - focus length diveded by the beam diameter at the optic
do - beam waist diameter
- angle between the plane of polarization and cutting direction
P plane of polarization
cw continuous wave laser power
BPP Beam Parameter Product
CO2
carbon dioxide
DPSSLs diode pumped solid state lasers
HAZ heat affected zone
LPSSLs Lamp Pumped Solid State Lasers
Nd: YAG Neodymium –Yttrium Aluminium Garnet
TEM00
lowest order beam mode/ diffraction limit
Yb: YAG Ytterbium: Yttrium Aluminium Garnet
xx
LIST OF APPENDICES
APPENDIX NO. TITLE PAGE
A1 Flowchart outlining the steps undertaken in
statistical analysis
110
B1 Specimen after machining workpiece 1 to
workpiece 4
111
B2 Specimen after machining workpiece 5 to
workpiece 8
112
B3 Specimen after machining workpiece 9 to
workpiece 12
113
B4 Specimen after machining workpiece 13 to
workpiece 16
114
B5 Specimen after machining workpiece 17 to
workpiece 20
115
C1 Dross for machining condition workpiece 1 to
workpiece 4
116
C2 Dross for machining condition workpiece 5 to
workpiece 8
117
C3 Dross for machining condition workpiece 9 to
workpiece 12
118
C4 Dross for machining condition workpiece 13 to
workpiece 16
119
C5 Dross for machining condition workpiece 17 to
workpiece 20
120
CHAPTER 1
INTRODUCTION
1.1 Overview
Laser cutting is a two-dimensional machining process in which material
removal is obtained by focusing a highly intense laser beam on the workpiece. Laser
cutting finds wide application in industry. This is mainly due to the ability of lasers
to produce high quality cuts at reasonable production rates.[1]).
The production of lasers and laser systems for material processing has grown
continuously over the last few years because of its economic benefits, such as high
quality, high productivity, saving of the pre- and post-processing of the material, and
minimum waste of base material. The industrial applications of material processing
with laser machining systems are mainly laser cutting (39%), laser welding (20%),
laser labelling (16%), laser micromachining (8%), and laser drilling (4%) [2].
Industrial applied materials, which can be machined by a laser beam, include
steel, alloyed steel, aluminium, copper, ceramics, composite material, plastic, glass,
and wood. The CO2
laser and Nd:YAG laser (solid state laser) are the main lasers
used for industrial cutting applications. The CO2
laser is the most commonly used,
especially for cutting of thick sections, because of its better beam quality compared
2
with the Nd:YAG laser of a similar power level and the CO2
lasers are also available
in higher output powers than the Nd:YAG lasers.[3]
Stainless steel is used extensively in a number of everyday applications in the
home, industry, hospitals, food processing, farming, aerospace, construction,
chemical, electronics, and energy industries; the austenitic grade of stainless steel is
the most used by far. Cutting of stainless steel sheets is one of the primary
requirements in the fabrication of most of the components. Laser cutting offers
several advantages over conventional cutting methods such as plasma cutting.[3]
In the experimental part of this study, the cutting experiments covered cutting
of austenitic stainless steel (grades AISI 304) of sheet thickness of 2.0 mm using the
CO2
laser cutting. The cut qualities were analyzed by measuring the kerf width,
roundness and diameter.
The laser cutting parameters will be used for these experiments are power and
cutting speed, pressure and focus length Because the previous researchers, prove this
parameter affect to cutting quality of laser cutting.
1.2 Problem statement
Laser cutting finds wide application in industry. This is mainly due to the
ability of lasers to produce high quality cuts at reasonable production rates. However,
there are some problems with the process that require immediate attention, because
no standard laser cutting setting parameters to archive the good cutting quality on
stainless steel.
This material are common used in industry, home, hospitals, food processing,
farming, aerospace, construction, chemical, electronics, and energy industries but
3
difficult to setting the parameter with good cutting quality by CO2 Laser Cutting
Machine.
1.3 Objective
To investigate the effect of independent factor such as machine power,
cutting speed, pressure and focus length on cutting quality of stainless steel
sheet with 2mm thickness using CO2 laser cutting.
1.4 Scope
a) These experiments are conducted by using of machine CO2 laser cutting
model Trumatic L2530 plus 2.0 kw.
b) The investigated material is 2 mm thickness of stainless steel 304 sheet.
c) The laser cutting parameters will be used for these experiments are
machine power, cutting speed, pressure and focus length.
d) The responses to be study are kerf width, roundness error and diameter
accuracy.