investigation of laser cutting parameters on surface quality...

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


x

3.3.1.4 Electric properties of


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


power (A) and focus length (D) 71


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


cutting speed(B) and pressure (C) 80


cutting speed(B) and focus

length (D) 81



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


power (A) and focus length (D) 89


cutting speed(B) 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


workpiece 8

112


workpiece 12

113


workpiece 16

114


workpiece 20

115

C1 Dross for machining condition workpiece 1 to

workpiece 4

116


workpiece 8

117


workpiece 12

118


workpiece 16

119


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.

investigation of laser cutting parameters on surface quality...

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