PRELIMINARY INVESTIGATION OF LASER JOINING

NOR FAZIELAH BINTI DARWIS

B051010177

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

2013

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

PRELIMINARY INVESTIGATION OF LASER JOINING

This report submitted in accordance with requirement of the Universiti Teknikal

Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Process Manufacturing) (Hons.)

by

NOR FAZIELAH BINTI DARWIS

B051010177

890820045368

FACULTY OF MANUFACTURING ENGINEERING

2013

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: Preliminary Investigation of Laser Joining

SESI PENGAJIAN: 2012/13 Semester 2 Saya NOR FAZIELAH BINTI DARWIS mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:

1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan

pertukaran antara institusi pengajian tinggi.

4. **Sila tandakan ( )

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia sebagaimana yang termaktub dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

Alamat Tetap:

No 4, Jalan Desa Baru 9,

Taman Desa Baru,

75350 Melaka

Tarikh: ________________________

Disahkan oleh:

Cop Rasmi: Tarikh: _______________________

** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai SULIT atau TERHAD.

28.JUN.2013

DECLARATION

I hereby, declared this report entitled “Preliminary Investigation of Laser Joining” is

the results of my own research except as cited n references.

Signature : ………………………………………….

Author’s Name : …………………………………………

Date : …………………………………………

NOR FAZIELAH BINTI DARWIS

28 JUN 2013

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a

partial fulfillment of the requirements for the degree of Bachelor of Manufacturing

Engineering (Process Manufacturing) with honor. The member of the supervisory is

as follow:

………………………………

(PM IR. DR. SIVARAO SUBRAMONIAN)

i

ABSTRAK

Kini, kimpalan laser adalah satu proses yang digunakan dalam industri.

Proses ini adalah salah satu teknologi yang canggih yang sangat diperlukan dalam

industri kerana pemprosesan masa yang singkat dan mata alat yang tidak bersentuhan

dengan bahan kerja. Tetapi, kelemahan proses ini memerlukan kos yang tinggi untuk

penyediaan mesin kimpalan laser yang baru. Hybridizing adalah jalan penyelesaian

yang mana laser mesin pemotong digunakan untuk melakukan proses kimpalan.

Hybridization adalah di mana dua set proses yang berbeza dilaksanakan di dalam

satu mesin yang sama. Kajian ini adalah untuk menyiasat potensi hybridizing

kimpalan laser CO2 ke mesin pemotong laser. Dari proses hybridizing, ia

menyediakan penyelesaian ekonomi dalam pemprosesan bahan. Siasatan dibuat

untuk mencari parameter proses yang optimum seperti kuasa laser, kelajuan

perjalanan, kekerapan. Kemudian, Rekabentuk Eksperimen (D.O.E) analisis adalah

berstruktur dan daripada proses eksperimen, keputusan diperoleh. Keputusan

menunjukkani kebolehkimpalan yang cemerlang dalam menyambungkan keluli

lembut ss400 dengan ketebalan 2.6mm.

ii

ABSTRACT

Nowadays, laser welding is a process that been used in the industry. This process is

one of the advance technologies that really need in the industry because of the short

time processing and non-contact tool with the workpiece. But, the disadvantage of

this process is required high cost in order to setup a new laser welding machine.

Hybridizing is a solution whereby laser cutting machine is used in order to do the

laser welding process. Hybridization is the process by which two different sets of

process are bred together in one machine. This study is to investigate the potential of

hybridizing laser welding onto CO2 laser cutting machine. From the hybridizing

process, it provides the economical solution in material processing. Investigation is

made in order to find the optimized process parameters that are laser power, travel

speed, frequency. Then, Design of Experiment (D.O.E) analysis is structured and

result is obtained from the experimental process. The results give an excellent

weldability in joining mild steel ss400 with the thickness of 2.6mm

iii

DEDICATION

To my beloved family.

iv

ACKNOWLEDGEMENT

With the name of Allah, I would like to thank god for giving me this opportunity to

complete this work. A special thanks to my supervisor, PM Ir. Dr. Sivarao for

guiding me during the planning and development of this report. His willingness to

give his time so generously has been very much appreciated. I would like to thank

my parents for their support and encouragement throughout my study. Finally, a

million thanks to my friends for helping and supporting me always.

v

TABLE OF CONTENT

Abstrak..…………………………………………………………………………………..i

Abstract…................................................................................................………………..ii

Dedication…………………………………………………………………….…………iii

Acknowledgement………………………………………………………………………iv

Table of Content…………………………………………………………..…….………..v

List of Tables…………………………………………………………………………..viii

List of Figures…………………………………………………………………….……..ix

List of Abbreviation, Symbols and Nomenclatures…………………………………….xii

CHAPTER 1 : INTRODUCTION………………………………………….………….1

1.1 Project Background……………………………………………………..………..1

1.2 Problem Statement……………….…………………………………………..…..2

1.3 Objectives…………………………………………………………………….…..2

1.4 Scope of Project…………………………………………………………………..2

1.5 Laser…………………………………………………………….…………….….3

1.5.1 Laser History………………………………………………………….….3

1.5.2 Types of Laser...……………………………………...……………….….5

1.5.2.1 Carbon Dioxide Laser

1.5.2.2 Nd:YAG Laser

1.5.3 Laser Cutting…………………………………………………………….7

1.5.3.1 Laser Cutting Process

1.5.4 Laser Welding………………………………………………….………10

1.5.4.1 Laser Welding Process

1.5.5 Types of Parameters……………………………………………………11

1.5.5.1 Non-controllable Parameters

1.5.5.2 Controllable Parameters

vi

1.6 Material…………………………………………………………………………19

1.6.1 Metal……………………………………………………………..……..19

1.6.1.1 Ferrous

1.6.1.2 Non-ferrous

1.7 Metal Joining Process…………………………….………………..….….……..22

1.7.1 Types of Metal Joining...…………………….………….…….….……..22

1.7.1.1 Conventional Joining

1.7.1.2 Fusion

1.7.2 Types of Joint……………………………………………………….…..27

1.7.2.1 Butt Joint

1.7.2.2 Corner Joint

1.7.2.3 T-Joint

1.7.2.4 Lap Joint

CHAPTER 2 : LITERATURE REVIEW……………..…………………...………..31

2.1 Laser Welding of Metallic Material…………………………………………….31

CHAPTER 3 : METHODOLOGY……………………………………………….…..36

3.1 Material Selection…………………………………………………………….…38

3.2 Investigation of Process Parameters…………………………………………….38

3.3 Design Parameters of Identification……………………………………………39

3.4 Design of Experiment……………………………………………………..……40

3.4.1 Design of Experiment (DOE) Matrix…………………………..………40

3.5 Experimental Work……………………………………………………….…….43

3.5.1 Material Design, Collection and Programming……..………………….44

3.5.2 Setup Machine and Load Material…..………………………………….47

3.5.3 Cutting Process……………………………………………………….…47

3.5.4 Welding Process………………………………………………………...48

3.5.5 Testing Setup……………………………………………………………52

3.5.5.1 Destructive Test

3.5.5.2 Visual Inspection

vii

3.6 Result and Analysis……..…………………………………….…….……….….59

3.7 Discussion/Conclusion………………………………………….…………..…..59

CHAPTER 4 : RESULT & DISCUSSION…………………………………………..60

4.1 Tensile Test……………………………………………………………………..60

4.2 Hardness Test…………………………………………………………………...65

4.3 Optical Result.…………………………………………………………………..69

4.4 Microstructure…………………………………………………………………..71

CHAPTER 5 : CONCLUSION & FUTURE WORK……………………………….74

5.1 Conclusion…………………………………………………………………...….74

5.2 Future Work………………………………………………………………….….75

REFERENCES………………………………………….……………………….….…76

APPENDICES……...…………………………………………………………………..79

Appendix A……………………………………………………………………………..79

viii

LIST OF TABLES

1.1 Cylindrical and conical nozzle……………………………………....……...…..15

1.2 Types of assisted gas used in Co2 Laser Cutting……….………………...……..16

3.1 Properties of low carbon steel………………………..…………………………38

3.2 DOE matrix that involves the selected five controllable parameters varied at

two levels..………………...………………….……………..…………………..42

3.3 Tensile specimen measurement………………………………..…….………….44

3.4 Basic specifications of the LVD Helius Hybrid 2531 Laser Cutting

Machine…………………………………………..………………………….….45

3.5 Constant parameter for welding..........................................................................49

3.6 DOE of full factorial…………………………………………………………….50

3.7 Parameter of mounting process…………………………………………………57

4.1 Tensile test result……………………..……………………………….….……..63

4.2 Observed Hardness Result……………………..…………………….………….66

4.3 Standard Deviation on different poser and same power….…….……………….67

4.4 Optical result on the experiment with different power………………………….70

ix

LIST OF FIGURES

1.1 Schematic view of laser beam cutting (O’Brien & Annette,2007)………….…7

1.2 Laser cutting descriptions (Yilbas, 2004)..........................................................9

1.3 The elements of an Nd:YAG Laser (O’Brien & Annette,2007)..……....….…10

1.4 Different types of nozzle design; From left: Standard nozzle, Laval

nozzle and Autonomous nozzle…………………….………………………….14

1.5 Focal position (Manual of Helius 2513 Laser Machine, 2000)………..…...…17

1.6 Stand-off distance………………...… ……………………………………….17

1.7 Classification scheme for the various ferrous alloy

(Callister and Rethwisch, 2011)……………………………………………….20

1.8 Oxyacetylene welding (a) overall process, (b) welding area.

(Tapany Udamphol, 2007)………………………………......…….…………..24

1.9 Simple diagram of the gas metal arc welding process

(Tapany Udamphol, 2007)……………………….………...……………..……25

1.10 Schematic illustrations of laser- beam welding (LBW) processes

(Messler Jr. 1993)………………………………………………………......…26

1.11 Friction stir welding (Tapany Udamphol, 2007)…….………………….....…27

1.12 Five basic types of weld joint designs (Tapany Udamphol, 2007).….……....27

1.13 Joint Configurations for Laser Beam Welds…………….……………..……..28

2.1 Welded area from SEM view (Lucien Reclaru et al.,2009)……...…………...31

2.2 Relations of laser power and weld depth (Hu Min Ying et al.,2001)..……….32

2.3 Bead appearance and metallurgical organization with variation in laser output

(Song C.Y et al.,2007)…………………………………………………………33

2.4 Comparison of (a) experimental and (b) finite-element simulation for laser

power of 250W and welding speed of 1500mm/min

(Buvanashekaran G. et al.,2008)……………………………………......…..…34

2.5 Schematic representation of the geometry (Renping Wang et al.,2010)...……35

x

3.1 Methodology that used in this project……………………….…….……….….37

3.2 Flow chart of experimental work………………………………………….…..43

3.3 Tensile specimen design………………………………….……………….…..44

3.4 Hardness specimen design and measurement……………………….…….…..45

3.5 Helius Hybrid 2513 Laser Cutting Machine………………………....….…….46

3.6 Illustration while running the cutting and welding process………….…….….48

3.7 Data display where the parameter was changed. (a) Travel speed.(b) power.

(c) Frequency………………………………………………………….…….....51

3.8 Sample of specimen after the cutting and welding process……………......….52

3.9 Universal Testing Machine…………………………………………….…..…..53

3.10 Rockwell Hardness Machine………………………………………….…….…54

3.11 Steel ball indenter…………………….……………………………….…….…55

3.12 Hardness test on three parts. (a) On the parent metal area. (b) On the HAZ area.

(c) On the welding area………………………………………………….…….55

3.13 Automatic mounting press machine………………….………….…….………56

3.14 Grinding and polishing machine………………………………………….……58

3.15 Optical Microscope (OM)………………………………………………...……58

4.1 Stress vs Frequency/Travel Speed……………………………………………..64

4.2 Elongation vs Experiment number ………………...………………………….64

4.3 Hardness at fusion zone….…………………………………………………….67

4.4 Indentation point for Rockwell Hardness test .………………………………..68

4.5 Hardness vs Indentation point….………………………..…………………….68

4.6 Microstructure of sample 22 with magnification 200x. (a) Parent metal (b) HAZ

(c) fusion zone..................................................................................................72

4.7 Microstructure of sample 22 with magnification 200x (a) interface parent metal

and fine grain HAZ (b) interface weld zone and coarse grain HAZ................73

xi

LIST OF ABBREVIATIONS, SYMBOLS, SPECIALIZED

NOMENCLATURE

% - percent

& - and

” - inch

< - less than

> - more than

± - plus minus

≈ - almost equal to

® - Right

3D - three dimensional

A - Absorption

angstroms - measure of length, 1 angstrom= 10E-10

m

ANOVA - Analysis Of Variance

ANSI - American National Standard Institute

cm - centimetre

CO2 - Carbon Dioxide Gas

CVL - Copper Vapour

Cw - clock wise

CW - Continuous Wave

D - Diameter

D.O.E - Design of Experiment

DC - Duty Cycle

DIN - Deutsche Industry Norm

E - Energy per Pulse

e.g. - example

EB - Electron Beam

EDM - Electro Discharge Machining

xii

etc. - Exedra/ and others

F - Frequency

F.D. - Focal Distance

FKP - Faculty of Manufacturing Engineering (Fakulti Kejuruteraan

Pembuatan)

GP - Gated Pulse

H2 - Hydrogen Gas

HAZ - Heat Affected Zone

He - Helium Gas

Hz - Hertz

in. - inch

IPTA - The Public Institution of Higher Learning (Institut Pengajian

Tinggi Awam)

ISO - International Organization for Standardization

J - Joule

K - Kelvin

k - kilo

kg - Kilogram

L - Length

LASER - Light Amplification by Stimulated Emission of Radiation

m - meter

mA - mili Ampere

MB - Mega Byte

Mil - 1 mil = 0.254 mm

mJ - mili Joule

mm - millimetre

MPa Mega Pascal

N Nominal value

N2 - Nitrogen Gas

NC - Numerical Control

Nd:YAG - Neodymium Yttrium Aluminium Garnet

xiii

Nm - Nanometer

No/Num - Number

o - Degree

ø - Diameter

O2 - Oxygen Gas

p - Pressure

P - Power

Pa - average power

Pp - peak power

ps - Pico second

PSM - Bachelors Degree Project (Projek Sarjana Muda)

R - Radius

R - Reflectivity

RF - radio-frequency

s - Seconds

SOD - Stand Off Distance

STD. Standard

T - Transmissivity

t - Thickness

TEA - Transversely Excited Atmosphere Pressure

UTeM - Malaysia Melaka Technical University (Universiti Teknikal

Malaysia Melaka)

UV - Ultraviolet

V - Volt

W - Watt

WJ - Water jet

λ - Wave length symbol

μm - micrometer

Σ - Total

τ - Pulse width symbol

1

1.1 Project Background

In this new era, in order to cut almost any material easily, laser machining is

widely known and most suitable for this kind of job. In a controlled manner, the

highly focused, high-density energy source and high-pressure gas are used to melt

and evaporate portions of the work piece. One of the lasers machining process which

is laser cutting could be referred as a material removal process accomplished by laser

material interaction. Laser is also being used in processing such as welding besides

machining that it being commonly used. Laser welding is a non-contact process and

involves localized heat treating of materials to modify the surface mechanical and

and tribological properties (Kalpakjian and Schmid, 2010).

The main goal of this study is to optimize the usage of the existing laser

cutting machine due to high investment cost needed to setup a laser machine. Laser

welding process will not be performed by laser welding machine in this study, but

will be performed by using laser cutting machine. The controllable process

parameters are quite same for any process in laser processing. The identifying

process in order to find the most suitable parameters to be applied in laser welding

process is the challenging part in conducting this study. The capability of laser

cutting machine to do laser welding just by varying some of process parameters will

be determined by this preliminary investigation. This experimentation work use a

laser cutting machine with rated power 3kW and carbon dioxide, CO₂ laser beam.

INTRODUCTION

CHAPTER 1

2

Visual inspection and destructive tests are used to evaluate the weldment. The

ability to weld the materials is expected to have from the laser cutting machine and at

least pass the minimum quality produced by laser welding machine.

1.2 Problem Statement

Hybrid machine is a machine that might give human more advantage

compared to traditional machine. For example may reduce time constraint and

economical purpose. High capital cost is required in order to setup a new laser

machine because any machine that involves laser is generally very expensive. There

is a high possibility that a laser cutting machine can do welding without changing

any part of the machine. However, several of the welding parameters may affect the

laser cutting machine. In order to identify which controllable process parameters that

have big impact in laser processing of metals, preliminary investigation is needed

and the values are set within the range of experimental values in order to observe the

weldability of laser cutting machine..

1.3 Objectives

The main objectives of this preliminary investigation are as followed:

i. To study the weldability of metal by using laser cutting machine.

ii. To analyse the quality and performance of the weldment.

1.4 Scope of Project

The main target of this project is to identify the best controllable process

parameters that have big impact in laser processing. A set of process variables is

developed and recommended in order to produce a high quality of weldment. There

are three chosen parameters which are laser power, travel speed, and frequency that

3

are varied within the range of experiment while other controllable parameters are

fixed. Helius 2513 hybrid series is the model of laser cutting machine to perform

welding process and was made in Belgium. Nitrogen that work as laser assisted gas

and carbon dioxide (CO₂) laser beam with rated power of 3kW are equipped in the

laser machine. The experimental on research work is conducted by butt welding on

mild steel ss400 material. Non-destructive and destructive test are being used to

examine the weldment.

1.5 Laser

Lasers are used as cutting tools due to high precision of operation and desirable end

product quality. In laser cutting process, an assisting gas jet is used. In the case of

inert gas assisted processing, assisting gas protects the surface from high temperature

oxidation reactions while high temperature exothermic reactions takes place when

oxygen is used as assisting gas. In laser gas assisted processing; proper selection of

laser and work piece parameters (cutting parameters) increases the laser cutting

efficiency and improves the end product quality. (Yilbas, 2004)

1.5.1 Laser History

According to Silfvast and William T. (2004), Charles Townes took the benefit of the

stimulated emission process in order to create a microwave amplifier, known as

maser. The device is use in the communication which is the device produced a

coherent beam of microwaves. First production of maser was produced in ammonia

vapour with the inversion between two energy levels that produced gain at a

wavelength of 1.25 cm. The maser produced the wavelengths that were comparable

to the dimensions of the device.

Townes and Schawlow published a paper on 1958 which concerning on the ideas

about extending the maser concept to optical frequencies. The concept was an optical

amplifier surrounded by an optical mirror resonant cavity to allow for growth of the

4

beam. In 1960, Theodore Maiman of Hughes Research Laboratories used ruby

crystal as the amplifier and a flashlamp in order to produce the first laser. A rod-

shaped ruby crystal surrounded by the helical flash lamp and coated the flattened

ends of the ruby rod with highly reflecting material to form the optical cavity. When

the flashlamp was fired, an intense red beam was observed to emerge from the end of

the rod.

A. Javan, W. Bennett, and D. Harriott of Bell Laboratories developed the first

gas laser by missing the helium and neon gases on 1961. Besides, L. F. Johnson and

K. Nassau demonstrated the first neodymium laser in the same laboratories which it

became one of the lasers available. Then, the first semiconductor laser was

demonstrated in 1962 by R. Hall at the General Electric Research Laboratories while

one of the most efficient and powerful lasers available today which is the infrared

carbon dioxide laser is discovered by C. K. N. Patel of Bell Laboratories in 1963. In

the same years, E. Bell of Spectra Physics found 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 ResearchLaboratories developed the first liquid laser by using

an organic dye, which was dissolved in a solvent, thereby leading to the category of

broadly tunable lasers.,W. Walter and co-workers at TRG reported the first copper

vapor laser at 1966 too (Silfvast and William T. 2004).

In 1970, R. Hodgson of IBM reported that the first vacuum ultraviolet laser

occured in independent molecular hydrogen by R. Waynant et al. of the Naval

Research Laboratories . On the other hand, J. J. Ewing and C. Brau of the Avco–

Everett Research Laboratory discovered the first of the well-known rare gas which

was halide excimer lasers found in xenon fluoride in 1975.In that same year, J. van

der Ziel and co-workers at Bell Laboratories, made the first quantum well laser

gallium in aarsenide semiconductor.

In 1976, the first free-electron laser amplifier operating in the infrared at the

CO2 laser wavelength demonstrated by J. M. J. Madey and co-workers at Stanford

University. Then, Walling and co-workers at Allied Chemical Corporation obtained

5

broadly tunable laser output, in 1979, from a solid-state laser material called

alexandrite. Besides, D. Matthews and a large number of co-workers at the Lawrence

Livermore Laboratories were successfully demonstrated the first soft–X-ray laser in a

highly ionized selenium plasma in 1985. While in 1986, the titanium sapphire laser

was discovered by P. Moulton. The first blue-green diode laser in ZnSe was

developed by M. Hasse and co-workers in 1991. Then, In 1994, the quantum cascade

laser was developed by F. Capasso and co-workers. S. Nakamura developed the first

blue diode laser in GaN-based materials in the year of 1996.

1.5.2 Types of Laser

In the industrial of cutting, welding, and other material processing

application, there are two types of laser that have been used. First, the 1.06 µm

wavelength Nd:YAG laser, which uses the neodymium (Nd) ion as the active

element. The second type of laser is the 10.6 µm wavelength CO2 laser, which uses

the CO2 molecule as the active element. For the excitation, some equipment might

be used, for example, electrically pumped, pulsed and continuous wave gas lasers

which use alternating current (ac), direct current (dc), or radio frequency (rf). Carbon

dioxide (CO2) lasers with beam power outputs of up to 12 kW also are in general

use. Laser that have power till 45kW is still in used for the industrial material

processing task even though it is no longer production. These lasers are capable to

make single pass weld with complete joint steel with the thickness of 16mm

maximum. Besides, it is also capable in cutting the material with the thickness

25mm. The laser beam is directed to the workpiece by flat optical elements, such as

mirrors, and then focusedonto a small spot, which creates high power density at the

weld joint or cut location using either reflective focusing elements or lenses.

Although the bulk laser power is important, it is predominantly the beam power

density, or the amount of power per unit area.

6

1.5.2.1 Carbon dioxide Laser

Nowadays, the most popular gas laser for material processing is the CO2 laser. The

C02 is mixed with the N2 while the He is in the different amount for the lasing

medium. However, it depends on the design of laser resonator, operating pressure,

and the operating mode either it is pulsed or continuous. Electric discharge excites

the CO2 molecules through the gas mixture. The wavelength that IS emitted by the

laser radiation is 10.6 µm. Normally, the range of conversion efficiencies is between

12 to 14%. For a long time, CO2lasers have been the highest CW power sources

available for laser materials processing (Olsen and FlemmingOve , 2009). For the

current commercial systems, the maximum power output is 20 Kw. One of the

disadvantages of CO2 lasers is associated with the long wavelength of the emitted

radiation. It causes most of the transparent material within the visible range of

electromagnetic spectrum such as glass is opaque for CO2 laser radiation. Thus, the

laser resonator need the transmission elements and manufactured the beam guidance

from special and expensive material such as Zink Selenide. Then, the beam

deflection and focusing must be realised by means of reflective optics. For example,

multilayer coated copper substrates. Another effect of the long wavelength is the

high reflectivity of metals, which is normally used in materials processing and the

radiation interaction with laser-induced plasma is increased.

1.5.2.2 Nd:YAG Laser

According to Olsen and Flemming Ove (2009), The Nd:YAG laser is still the most

prevalent solid-state laser in used. A Nd-doped YAG crystal serves as lasing medium

with an emitted wavelength of 1.06 µm. The excitation energy is optically provided

by high intensity electric-discharge lamps or laser diodes. Compared to gas laser, the

rod-shaped Nd:YAG laser crystal is optically active and decreased the output beam

quality while the power output is increased. So, the Nd:Yag beam quality is lower

than CO2 laser beam quality. However, the laser may achieve similar focus spot

sizes since it has shorter wavelength. 6 kW is the maximum CW output power of