UNIVERSITI TEKNIKAL MALAYSIA MELAKA

Faculty of Manufacturing Engineering

LASER PROCESSING OF NON-LINEAR INCLINE CUTTING

Turki Diwan Hussein

Master of Manufacturing Engineering

(Manufacturing System Engineering)

2013

LASER PROCESSING OF NON-LINEAR INCLINE CUTTING

TURKI DIW AN HUSSEIN

A thesis submitted

in fulfilment of the requirements for the degree of Master of Manufacturing Engineering

(Manufacturing System Engineering)

Faculty of Manufacturing Engineering

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

2013

DECLARATION

I declare that this thesis entitled "Laser Processing of Non-Linear Incline Cutting" is the

results of my own research except as cited in references. The thesis has not been accepted for

any degree and is not concurrently submitted in candidature of any other degree .

Signature

Name

Date

.. ~,y. . ., ~ .......... Turki Diwan Hussein

.... 6 .. / .. 1 .. ; ... ;Lo .. J .. 3

APPROVAL

I hereby declare that I have read this thesis and in my opnion this thesis is sufficient in terms

of scope and quality for the award of Master of Manufacturing Engineering (Manufacturing

System Engineering).

Signature

Supervisor

Date

Prof. Madya. Ir. Dr. Sivarao Subramonian

............. fi./.1./.~~J ............... . fiRIIWTAl li.MAAO-

Fallulti Kejuruteraan Pemt>uatan Universiti T9knikal Malaysia Melat.a

Durian Tungga~ Melaka.

ABSTRACT

This research is to find the optimal parameters of machining process. The research conduct based on Design of Experiment DOE analysis. In this research the experiment designed to find out the interaction between the variables to evaluate the high performance responses of machining process. The experiment is design based on the objectives that want to be achieved in this research. The analysis is run by using the Minitab Software. In this research, Response Surface Methodology and factorial design used to compared in term of modeling capabilities. The input parameters evaluated were gas pressure, power supply, and cutting speed; meanwhile the output responses being kerf width and surface roughness. The laser cutting process is one of the widely used techniques for cut various thickness of material for many applications such as fiber, steel, wood etc. In the area cutting material, it can be improved drastically with the application of difficult cutting material. Application of cut on mild steel for various machining techniques, such as bevel linear and bevel non-linear cutting, requires different cut characteristics. From that, being highly dependent on the process parameters under which they were performed. To efficiently optimise and customise the kerf width and surface roughness characteristics, machining of laser cutting conduct via modelling using RSM methodology was proposed. In this research, non-linear incline cutting is done on critical laser processing of mild steel materials optimization . This research predominantly focuses to investigate the correlation between laser machining parameter with the responses kerf width and surface roughness. This research also highlights the experimental control parameters of mild steel laser processing with the responses.

ABSTRAK

Kajian ini adalah untuk mencari parameter optimum dalam proses pemesinan. Kajian penyelidikan ini berdasarkan "Design of Experiment". Dalam kajian ini "DOE" bertujuan untuk mengetahui interaksi antara pembolehubah untuk menilai respons prestasi tinggi dalam proses pemesinan. Analisis ini dijalankan dengan menggunakan perisian Minitab itu. Dalam kajian ini, "Response Surface Methodology" dan "Factorial Design" akan digunakan untuk dibandingkan dari segi keupayaan model. Parameter input dinilai ialah tekanan gas, bekalan kuasa, dan kelajuan pemotongan; sementara itu maklumbalas adalah Iebar garitan dan kekasaran permukaan. Proses pemotongan laser adalah salah satu teknik yang digunakan secara meluas untuk pelbagai ketebalan potong bahan untuk banyak aplikasi seperti serat, besi, kayu dan lain-lain Dalam bidang memotong bahan, ia boleh diperbaiki secara drastik dengan permohonan memotong bahan yang sukar. Pengunaan pemotongan pada keluli lembut untuk pelbagai teknik mesin, seperti serong linear dan memotong serong bukan linear, memerlukan ciri-ciri yang berbeza dipotong. Dari itu, Proces paramter memainkan peranan penting dalam menentukan potongan terbaik. Dengan mengoptimumkan dan menyesuaikan Iebar garitan dan ciri-ciri kekasaran permukaan, pemesinan pemotongan dijalanakan melalui model dengan menggunakan kaedah RSM telah dicadangkan. Dalam luljian ini, pemotongan serong bukan linear dilakukan di laser pemotongan. Kajian ini terutamanya memberi tumpuan untuk menyiasat hubungan antara parameter pemesinan laser dengan maklumbalas Iebar garitan dan kekasaran permukaan. Kajian ini juga menunjukkan parameter kawalan eksperimen untuk pemotongan keluli lembut

DEDICATION

I would like to present my work to those who did not stop their daily support since I was

born, my dear mother and my dear wife. They never hesitate to provide me all the facilities

to push me foreword as much as they can. This work is a simple and humble reply to their

much goodness I have taken over during that time. I don't forget my brothers, sisters, son,

daughter, uncle and those entire how I love. Also to my father, grandfather, aunt and uncle

(Allah's mercy them).

CJ'urkf diwan J{ ussein

ACKNOWLEDGEMENT

First and foremost, praise be to Allah, for giving me this opportunity, the strength and the

patience to complete my thesis finally, after all the challenges and difficulties. I would like

to thank my supervisor, Prof. Madya. Ir. Dr. Sivarao Subramonian for his high motivation

and most significant contribution in this thesis.

I would also like to thank Ministry of Higher Education and Scientific Research of Iraq,

the Dean of Faculty of Manufacturing Engineering Prof. Madya. Dr. Mohd Rizal Salleh

and Prof. Madya. Dr. Mohd Warikh Bin Abd Rashid. Furthermore, I want to thank my

friends who have helped and motivated me throughout. May Allah reward them all

abundantly, Sincere thanks to all.

Turf& <Diwan Jfussein

lV

TABLE OF CONTENT

PAGE

ABSTRACT i

ABSTRAK ii

DEDICATION iii

ACKNOWLEDGEMENT iv

TABLE OF CONTENT v

LIST OF TABLES vii

LIST OF FIGURES ix

LIST OF SYMBOLS xi

LIST OF APPENDICES xii

CHAPTER 1

1. INTRODUCTION 1

1.1 Background 1

1.2 Laser Parameters 2

1.2.1 Laser Cut Quality Characteristics 3

1.3 Problem statement 4

1.4 Research Objective 5

1.5 Research Scopes 5

2. LITERATURE REVIEW 6

2.1 Introduction 6

2.2 Metal Cutting Process 7

2.3 Laser Cutting 9

2.3.1 Types of Cutting 12

2.3 .1.1 Laser Fushion Cutting 12

2.3.1.2 Laser Flame Cutting 12

2.3.1.3 Laser Sublimation 12

2.4 Laser Types 13

v

2.4.1 C02 Laser 14

2.4.2 Nd:Y AG Laser 15

2.4.3 Fibre Laser 16

2.4.4 Laser Gas Assistance 17

2.4.5 Oxygen as Assist Gas 18

2.4.6 Nitrogen as Assist Gas 19

2.5 Laser Cut Quality 20

2.5.1 Laser Cutting Typical Imperfection 23

2.6 Optimization of Cutting Process Parameters 24

2.6.1 Fuzzy Logic 24

2.6.2 Genetic Algorithm 25

2.6.3 Taguchi Technique 25

2.6.4 Artificial Neural Network (ANN) 26

2.6.5 Response Surface Methodology (RSM) 27

2.7 Related Work 29

2.8 The Research Work 31

3. METHODOLOGY 32

3.1 Research Methodology 32

3.2 Initial Design 33

3.3 Flow Chart of Research Methodology 34

3.4 Work Material 35

3.5 Cutting Parameter 35

3.6 Cutting Machine and Laser Cutting 39

3.7 Analytical Tool 42

3.7.1 Response Surface Methodology (RSM) 43

4. RESULT & DISCUSSION 45

4.1 Modelling of the Cut Kerf Width and Roughness 45

4.2 RSM Modelling of Kerf Width With Respect to Laser 46

Cutting Process Parameters

4.3 Response Surface Regression: Kerf versus Pressure, 57

Power, Speed

4.4 Discuss Interpreting the Results 59

4.5 Interpretting the Results 56

4.6 Response Optimization 57

4.7 Discuss Interpretting the Results Optimization Plot 58

4.8 Interpretting the Results 59

4.9 Response Surface Regression: Roughness versus Pressure, 60

Power, Speed

4.10 Interpretting the Results and Discussion 68

4.11 Response Optimization 72

5. CONCLUSION 74

5.1 Conclusion 74

5.2 New Contributions to Body of Knowledge 76

5.3 Future Work 76

REFERENCE 78

APPENDIX A: Measuring for Laser Process Kerf Width 87

Non-Linear Incline Cutting

APPENDIXB: Measuring for Laser Process Surface Roughness 97

Non-Linear Incline Cutting

APPENDIXC: Experimental for Laser Process Kerf Width and 102

Surface Roughness Non-Linear Incline Cutting

APPENDIXD: Experimental for Laser Process Kerf Width and 104

Surface Roughness of Non-Linear Incline Cutting

LIST OF TABLES

TABLE TITLE PAGE

2.1 Parameters for Laser Cutting of Mild Steels with Laser 13

Cutting Oxygen Including Pressure and Volume

Requirements

3.1 Parameters Range 36

3.2 Parameters Values during the Central Composite Design 37

3.3 Experimental Layout for Response 38

4.1 Experimental Results for Laser Process Kerf Width 47

Non-Linear Incline Cutting of Bevels and Reading Measured

Specified Three of Top Area x~, x2, and x3 at Bevel Angle 22°

4.2 Experimental Results for Laser Process Kerf Width Non-Linear 48

Incline Cutting and Reading Measured Specified Three of

Bottom Area X~, X2, And X3 at Bevel Angle 22°

4.3 Experimental Results for Laser Process KerfWidth Non-Linear 49

Incline Cutting of Bevels, Top And Bottom Area Average

4.4 Estimated Regression Coefficients for Kerf 50

4.5 Analysis of Variance for Kerf 51

4.6 Estimated Regression Coefficients for Kerf Using Data in 52

Uncoded Units

4.7 Predicted Responses for New Design Points Using Model for 53

Kerf

4.8 Parameters Response Optimization 57

4.9 Starting Point 57

4.10 Global Solution 57

4.11 Predicted Responses 57

4.12 Experimental Results for Laser Process surface roughness 60

Non-Linear Incline Cutting and Reading Measured Specified

Three of Area x~, x2, and x3 at Bevel Angle 22°

4.13 Experimental Run and Results of Surface Roughness 61

(Non-Linear Incline Cutting)

4.14 Experimental Run and Results ofKerfWidth and Surface 62

Roughness

4.15 Estimated Regression Coefficients for Roughness 63

4.16 Analysis of Variance for Roughness 64

4.17 Responses for New Design Points Using Model for Residual 65

4.18 Estimated Regression Coefficients for Roughness using Data 66

in Uncoded Units

4.19 Predicted Responses for New Design Points Using Model for 67

Roughness

4.20 Surface Roughness Optimization 72

4.21 Starting Point 72

4.22 Global Solution 72

4.23 Predicted Responses 72

LIST OF FIGURES

TABLE TITLE PAGE

1.1 Laser Parameters 3

2.1 Basic Principle of Laser Cutting 9

2.2 N2 and 02 Laser 15

2.3 Nd:Y AG Laser 16

2.4 Fiber Laser 17

2.5 Schematic Mechanism of Striations Formation during Laser 23

Cutting

2.6 Formation ofDross: a- Formation of a Droplet, b- Growing, 24

c- Merging of the Droplet with Previous Molten Material

3.1 Flow Charts of Research Methodology 34

3.2 RSM Central Composite Designs for 3 Factors at Two Levels 36

3.3 Laser Cutting Machine L VD 39

3.4 Workpiece before Laser Cutting 40

3.5 Workpiece after Laser Cutting 41

3.6 The Work Pieces Base at an Angle of22° 42

3.7 Overall Approach of Laser Process Non-Linear Incline 44

Cutting Study

4.1 Residual Plots for Kerf Width 54

4.2 Contour Plot of Kerf vs. Power, Pressure 55

4.3 Selects the First Factor, in This Case Pressure, for the Vertical 56

Axis, and the Second Factor, Power, for the Horizontal Axis.

4.4 Optimization Plot 58

4.5 Graph Window Output 59

4.6 Residual Plots for Roughness 68

4.7 Contour Plot 69

4.8 Surface Plot 70

4.9 Contour of Roughness 71

4.10 Surface Roughness Optimization. 73

X

5.1 Laser Cutting Process as Applied to the Cutting KerfWidth

and Surface Roughness Hard Cutting.

Xl

74

KIW

C02

I,V,Y

DC

RF

Nd:YAG -

K=l

K< 1

cw Psi

RSM

LBC

XRD

SEM

OP

ANOVA

CCD

02

N2

LIST OF SYMBOLS

Kerf Width

Carbon Dioxide

Type of Bevel

Direct Current

Radio Frequency

Neodymium-Doped Yttrium Aluminum Gamet

For an ideal Gaussian

For real laser radiation.

Continuous Wave

Pounds per square inch

Response Surface Methodology

Laser Beam Cutting

X-Ray Diffraction

Scanning Electrical Microscopy

Optical Microscopy

Analysis of Variance

Central Composite Design

Oxygen

Nitrogen

Xll

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Measuring for Laser Process Kerf Width Non-Linear Incline 87

Cutting

B Measuring for Laser Process Surface Roughness Non-Linear 97

Incline Cutting

c Experimental for Laser Process Kerf Width and Surface 102

Roughness Non-Linear Incline Cutting

D Experimental for Laser Process Kerf Width and Surface 104

Roughness ofNon-Linear Incline Cutting

xm

CHAPTER!

INTRODUCTION

1.1 Background

This 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, and high continuous or pulsed power density and mono - chromaticity

(Majumdar and Manna, 2003). One of its main applications is his ability to act as a heat

source 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 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 non- contact process, 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

by Eltawahni et. al., (201 0):

1. Solid state crystal or glass laser- Nd:Y AG, Ruby

11. Semiconductor laser- AlGaAs, GaAsSb and GaAlSb lasers

111. Dye or liquid lasers solutions of dyes in water/alcohol and other solvents

IV. Neutral or atomic gas lasers- He-Ne laser, Cu or Au vapor laser

v. Ionized gas lasers or ion lasers- argon. ArC I and krypton .KrC I ion lasers

VI. Molecular gas lasers - C02 or CO laser

v11. Excimer laser- XeCl, KrF, etc

vm. Fiber laser- ytterbium

However, there are main obstacles that limit the lasers extensive use in applications

of routine material processing such as beam size limitation, high cost of installation and

replacement, additional and costly accessories, and need for skilled workers (Majumdar

and Manna, 2003).

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 1.1 below.

LASER CUTTING PARAMETERS

Processing parameters

- Laser power - Cutting speed - Focal length - Focal point position -Type and pressure of

assist gas - Nozzle diameter

Parameters ad.iusted by operator

Figure 1.1 Laser Parameters (Wandera, 2010)

Researchers studied the impact of different lasers parameters on cut edge quality,

kerf dimensions, roughness and surface finish. Kar et. al., (1996) studied the process

parameters impacts such as laser power, spot size and dimensions, and cutting speed on the

resulting kerf size. Yilbas (2008) studies on the effect of laser power and oxygen gas

pressure on the kerf width variation. Researchers Ghany and Newishy (2005) indicated a

positive relationship between laser cutting quality and the laser power, pulse frequency,

cutting speed and focus position.

1.2.1 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.

1.3 Problem Statement

The common metal machining is performed by using a laser machine with vertical

cutting head. The literature did not explain clearly the impact of the nonlinear incline

cutting process parameters on the surface quality, and did not compare this effect with the

linear cutting.

The nonlinear incline cutting is very important in assembling parts or appliances or

in welding pieces together as some of the parts and by design must have incline surfaces

for ease of their linking and assembling. Therefore, incline cutting laser machine should be

available, but this machine probably not is available, in addition to being expensive. For

this reason, will use the available vertical cutting machine to address this problem, where

we will be control the incline degree ofthe work piece usually at an angle of22° under the

vertical head to get the incline cutting. After that test process on the impact of incline

cutting process parameters in term of surface quality will conduct. This project focuses on

research on alternative process acetylene oxygen cutting material in machine CNC because

of their defects on the metal surface and the changing characteristics at mechanical

physical and safety of the surface and transactions thermal and other. Therefore, the

existence of machine laser CNC using oxygen gas best for the safety of the surface and the

characteristics of mechanical and other through literature review of cutting mild steel,

stainless steel, crystal steel, duplex steel.

1.4 Research Objectives

The main objective of this research is to conduct a comprehensive study on the

processing parameters effects during incline laser cutting of thin sheet mild steel. The

effect of processing parameters is evaluated in terms of surface finish and kerf width. The

research aims to achieve the following objectives:

1. To identify the significant laser material processing that affecting inclined cutting

parameter.

11. To establish significant design parameters for high cut quality of non-linear

inclined cutting.

111. To model the optimal laser processing of non-linear inclined cutting

1.5 Research Scope

The aim of this research is to identify which parameters in incline laser cutting

process play the major role in producing very low roughness cuts and surface finish, which

improve the end product quality. The laser oxygen assist will be used for non-linear incline

cutting process of a thin sheet of mild steel of 6 mm thickness.

The response surface methodology RSM will be applied to construct a

mathematical relationship between the laser cutting process parameters, laser power, speed

and pressure and between the quality of the responses namely quality of cut edge and

surface roughness during an incline 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.

CHAPTER2

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. 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 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 and Shirley, 201 0).

Laser machining is one of the AMPs utilized to cut various types of materials

economically. Laser beam machining has wide application because it gives a finer finish to

the end product as compared to conventional cutting methods (Choudhury and Shirley,

2010). Lasers are commonly used to cut or machine different types of materials, especially

difficult-to-cut materials, in many industrial applications, due to its advantages over the

6

conventional cutting processes (Eltawahni et al., 2010). Compared with other conventional

mechanical processes, laser cutting removes little material, 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 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 and Dahotre, 2009). Metal working 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 oxyfuel

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). Emergence of advanced engineering materials, stringent design requirements,