surface itegrity evaluatio o titaium alloy after...

SURFACE ITEGRITY EVALUATIO O TITAIUM ALLOY AFTER

EDM MACHIIG USIG DIFFERET GRAPHITE ELECTRODES

MAZLA BI MAT JUSOH

A project report submitted in partial fulfilment 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

DEDICATIO

First of all, all the praises and thanks be to Allah S.W.T for His Love,

This thesis is dedicated to my family,

To my beloved parent, Mat Jusoh Bin Latif & Siti Sarah Bt Daud.

My wife, Suriyati Bt Idris.

My daughters, +ur Alya Maisarah and +ur Ain Madiihah.

And last but not least to all my relatives and my close friends.

Thank you very much for your unstinting help and encouragement

May Allah bless all people that I love.

Sorry if I forgot to mention any name.

iv

ACKOWLEDGEMET

I would like to thank Allah Almighty for blessing me and giving me strength

to accomplish this thesis. In particular, I wish to express my sincere appreciation to

my thesis supervisor, Assoc. Professor Dr. Izman Bin Sudin from Universiti

Teknologi Malaysia for encouragement, guidance, critics and friendship.

I am indebted to my parents, Mat Jusoh Bin Latif and Siti Sarah Bt Daud, my

wife, Suriyati Bt Idris, my daughters, Nur Alya Maisarah and Nur Ain Madiihah, my

brother and sister, Siti Faridah, Mat Rahim, Aziz, Mohd Zulkifli, Siti Azizah, Nurul

Azira and Mohd Anuar, without whose help, encouragement and patience I would

never have gotten this thesis completed and who made it all worthwhile.

Many thank to Reazul Haq from UTHM and all of the technicians from UTM

and UTHM especially Mr. Tarmizi and Mr. Anuar, Technicians in Advance

Manufacturing Laboratory (UTHM), Mr. Ayub Technician in Material Science

Laboratory (UTM) and other technical staff for their cooperation and assisting me in

the various laboratory tasks. I am also grateful to my fellow postgraduate students

should also be recognized for their support. My sincere appreciation also extends to

all my colleagues and others who have provided assistance at various occasions.

Their views and tips are useful indeed. Unfortunately, it is not possible to list all of

them in this limited space.

Finally, thank you to MARA and all the other people who have supported me

during the course of this work. Thank You!

v

ABSTRACT

The quality of an EDM product is usually evaluated in terms of its surface

integrity, having these specific characteristic like the surface roughness, existence of

surface cracks and residual stresses. Many process variables affect the surface

integrity such as Pulse Duration, Peak Current, Open Gap Voltage and electrode

Polarity. Other than that, material properties of the tool electrode, workpiece and

dielectric liquid in fact even the size of the electrode affects the surface integrity. The

purposes of this study are to investigate the influences of the parameters involved in

EDM especially on the machining characteristics, namely recast layer (white layer),

heat affected zone, surface topography, micro cracks and voids on the titanium alloys

using POCO 3 and POCO C3 as an electrode. The specimens were examined using

Optical Microscope (Zeiss), Scanning Electron Microscope (SEM) XL-40 with

EDAX analysis and X-Ray Diffraction (Siemens - D5000). The Full Factorial Design

of Experiment (DOE) approach was used to analyze the effect of each parameter

such as Pulse ON (ON), Pulse OFF (OFF), Peak Current (IP) and Servo Voltage

(SV) on the EDM machining characteristics. In general, the Peak Current and Pulse

ON have the most significant effect to the responses studied. EDMed with POCO 3

gives the better results compared to POCO C3 in term of recast layer thickness and in

contrary with the HAZ thickness. The mathematical models for average recast layer

thickness and average heat affected zone thickness were developed to predict the

effects within the factors investigated.

vi

ABSTRAK

Kualiti sesuatu produk yang dihasilkan oleh proses EDM biasanya dinilai

berdasarkan kepada integriti permukaannya yang dicirikan kepada kekasaran

permukaan, keretakan permukaan dan tegangan sisa yang terbentuk. Terdapat

beberapa pembolehubah yang mempengaruhi integriti permukaan, sebagai contoh,

tempoh denyut (ON), masa rehat (OFF), voltan dan kekutuban elektrod. Selain itu,

sifat elektrod, bahan kerja dan cecair ‘dielectric’ dan saiz elektrod juga

mempengaruhi integriti permukaan. Tujuan utama kajian ini adalah untuk mengkaji

faktor-faktor yang terlibat dalam pemesinan EDM bagi respons seperti lapisan

tuangan semula (RL), zon kesan daripada haba (HAZ), topografi permukaan,

keretakan kecil dan ruang kosong pada titanium aloi yang telah dimesin dengan

menggunakan POCO 3 dan POCO C3 sebagai elektrod. Spesimen tersebut diperiksa

dengan menggunakan Mikroskop Optik (Zeiss), Scanning Electron Microscopy

(XL40) dengan analisis EDAX dan x-ray diffraction (Siemens - D5000). Full

Factorial Experiment (DOE) adalah pendekatan yang digunakan untuk menganalisis

kesan daripada setiap parameter seperti tempoh denyut (ON), masa rehat (OFF), arus

puncak (IP) dan voltan servo (SV) terhadap pemesinan. Secara umumnya, arus

puncak (IP) dan tempoh denyut (ON) merupakan pembolehubah yang sangat

mempengaruhi respons yang dikaji. POCO 3 memberikan hasil yang lebih baik

berbanding dengan POCO C3 bagi lapisan tuangan semula (RL) dan sebaliknya

berlaku kepada HAZ. Model matematik dibangunkan bagi menilai anggaran kesan

kepada lapisan tuangan semula dan HAZ bagi julat faktor yang telah dikaji.

vii

TABLE OF COTETS

CHAPTER TITLE PAGE

DECLARATIO ii

DEDICATIO iii

ACKOWLEDGEMETS iv

ABSTRACT v

ABSTRAK vi

TABLE OF COTETS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xv

LIST OF APPEDICES xvi

1 ITRODUCTIO

1.1 Introduction 1

1.2 Background of Problem 4

1.3 Research Statement 5

1.4 Problem Statement 5

1.5 Objectives of Study 6

1.6 Scopes of Study 6

2 LITERATURE REVIEW

2.1 Introduction 7

2.2 Research Trends for EDM 8

2.3 Electro Discharge Machining (EDM) 9

2.3.1 Material Removal Theories 12

2.3.1.1 Electro Mechanical Theory 12

viii

2.3.1.2 Thermo Mechanical Theory 12

2.3.1.3 Thermo Electric Theory 13

2.3.2 EDM Process Mechanism 13

2.3.3 EDM Parameter 16

2.3.3.1 Peak Current 18

2.3.3.2 Discharge Voltage 18

2.3.3.3 Pulse ON Time 19

2.3.3.4 Pulse OFF Time 19

2.3.4 Electrode 20

2.3.5 Dielectric Fluid 22

2.4 EDM Surface Layer 24

2.5 Titanium Alloys 27

2.5.1 Introduction 27

2.5.2 Classification of Titanium Alloy 28

2.5.2.1 Commercially Pure (CP) Titanium 28

2.5.2.2 Alpha and Near-Alpha Alloys 29

2.5.2.3 Alpha-beta Alloys 30

2.5.2.4 Beta Alloys 30

2.5.3 EDM of Titanium Alloys 33

2.5.3.1 Machining Titanium Alloys with EDM 31

2.5.3.2 Surface Integrity in EDM of Titanium Alloys 33

2.6 Design of Experiment (DOE) 34

2.6.1 Two Level Factorial Design 35

3 RESEARCH DESIG

3.1 Introduction 36

3.2 Research Design Variables 36

3.2.1 Machining Parameters 37

3.2.1.1 Workpiece Material 37

3.2.1.2 Electrode Material 39

3.2.2 Two Level Factorial Design 39

3.2.3 Response Parameters 43

3.2.3.1 Recast Layer and Heat Affected Zone 43

3.2.3.2 Surface Topography 43

ix

3.2.3.3 Micro crack and Void 43

3.3 Experimental Machines and Analytical Equipments 44

4 RESULT AD DATA AALYSIS

4.1 Introduction 48

4.2 Experimental Results 48

4.2.1 EDM with POCO 3 and POCO C3 49

4.3 Recast Layer 53

4.3.1 Recast Layer with POCO 3 53

4.3.2 Recast Layer with POCO C3 59

4.3.3 Discussion on Recast Layer Between

POCO 3 and POCO C3. 65

4.4 Heat Affected Zone (HAZ) 67

4.4.1 Heat Affected Zone with POCO 3 67

4.4.2 Heat Affected Zone with POCO C3 76

4.4.3 Discussion on Heat Affected Zone

Between POCO 3 and POCO C3. 85

4.5 Surface Topography 87

4.5.1 Surface Topography with POCO 3 87

4.5.2 Surface Topography with POCO C3 92

4.5.3 Discussion on Surface Topography Between

POCO 3 and POCO C3 96

4.6 Micro-crack and Void 99

4.6.1 Micro-crack and Void with POCO 3 100

4.6.2 Micro-crack and Void with POCO C3 101

4.6.3 Discussion on Micro-crack and Void Between

POCO 3 and POCO C3. 103

5 COCLUSIO AD RECOMMEDATIO

5.1 Introduction 105

5.2 Conclusion 105

5.3 Recommendation 107

REFERECES 108

Appendices A - E 111 - 142

x

LIST OF TABLES

TABLE O. TITLE PAGE

2.1 Properties of Graphite and Copper Electrode 21

3.1 Machining Parameters 37

3.2 Chemical Properties of Ti-6Al-4V (wt.%) 38

3.3 Mechanical Properties of Ti-6Al-4V 38

3.4 Specification of Electrode Material 39

3.5 Factors and Levels for EDM with POCO 3 and POCO C3 40

3.6 Two-level full factorial experiment with four factors 40

4.1 Experimental plan for EDM with POCO 3 and POCO C3 50

4.2 Experimental Results for EDM with POCO 3 51

4.3 Experimental Results for EDM with POCO C3 52

4.4 ANOVA Table for Recast Layer for POCO 3 54

4.5 ANOVA Table for Recast Layer (RL) for POCO C3 60

4.6 Summary of Significant Factors (ARLT) 65

4.7 ANOVA Table for Heat Affected Zone (HAZ) for POCO 3 69

4.8 ANOVA Table for Heat Affected Zone (HAZ) for POCO C3 78

4.9 Summary of Significant Factors (Average HAZ) 86

xi

LIST OF FIGURES

FIGURE O. TITLE PAGE

2.1 Classification of Major EDM Research Area 8

2.2 Classification of EDM Process 9

2.3 Schematic of an Electro Discharge Machining (EDM) 10

2.4 The Lazarenko RC Circuit (McGeough, 1988) 11

2.5 Steps during EDM Cycle 14

2.6 Characteristic of Dielectric Fluid 23

2.7 Surface Layers formed by EDM Process 25

2.8 EDMed Surface layer for Ti6AL4V 26

3.1 Microstructure of Ti-6Al-4V (SEM Magnification 1000X) 38

3.2 Flowchart of the Specimens Inspection 42

3.3 Sodick AQ55L CNC EDM die sink 44

3.4 Grinder and Polisher 45

3.5 Optical Microscope 46

3.6 Scanning Electron Microscope (SEM) 46

3.7 X-Ray Diffraction (XRD) Machine 47

4.1 Normal Probability Plots of Residuals of RL for EDM

with POCO 3 55

4.2 Residual vs Predicted Response of RL for EDM with

POCO 3 55

4.3 Outlier T Plot of RL for EDM with POCO 3 56

4.4 Main Effect Plot of RL for EDM with POCO 3 57

xii

4.5 Interaction between Servo Voltage (A) and Pulse ON (C)

Plot of RL for EDM with POCO 3 57

4.6 Perturbation Plot of RL for EDM with POCO 3 58

4.7 Normal Probability Plots of Residuals of RL for

EDM with POCO C3 61

4.8 Residual vs Predicted Response of RL for EDM

with POCO C3 61

4.9 Outlier T Plot of RL for EDM with POCO C3 62

4.10 Pulse ON Time Effect Plot of RL for EDM with POCO C3 63

4.11 Pulse OFF Time Effect Plot of RL for EDM with POCO C3 63

4.12 Interaction between Servo Voltage (A) and Peak Current (B)

Plot of RL for EDM with POCO C3 64

4.13 Perturbation Plot of RL for EDM with POCO C3 Electrode 65

4.14 Normal Probability Plots of Residuals of HAZ for EDM with

POCO 3 70

4.15 Residual vs Predicted Response of HAZ for EDM with POCO 3 71

4.16 Outlier T Plot of HAZ for EDM with POCO 3 71


Plot of HAZ for EDM with POCO 3 73


Plot of HAZ for EDM with POCO 73

4.19 Interaction between Servo Voltage (A) and Pulse OFF (D)


4.20 Interaction between Peak Current (B) and Pulse OFF (D)


4.21 Interaction between Pulse ON (C) and Pulse OFF (D)


4.22 Perturbation Plot of HAZ for EDM with POCO 3 76

4.23 Normal Probability Plots of Residuals of HAZ for EDM

with POCO C3 79

xiii

4.24 Residual vs Predicted Response of HAZ for EDM

with POCO C3 80

4.25 Outlier T Plot of HAZ for EDM with POCO C3 80


Plot of HAZ for EDM with POCO C3 82



4.28 Interaction between Servo Voltage (A) and Pulse OFF (D)


4.29 Interaction between Peak Current (B) and Pulse ON (C)


4.30 Interaction between Peak Current (B) and Pulse OFF (D)


4.31 Interaction between Pulse ON (C) and Pulse OFF (D)


4.32 Perturbation Plot of HAZ for EDM with POCO C3 85

4.33(a) SEM Photographs show EDMed surface using POCO 3

(SV=60V, Ip=20A, tO+=150µs, tOFF=150µs) 88

4.33(b) SEM Photographs show EDMed surface using POCO 3


4.34(a) SEM Photographs show EDMed surface using POCO 3


4.34(b) SEM Photographs show EDMed surface using POCO 3


4.35(a)Spectrum of EDAX Analysis for Ti64 Surface after EDM

with POCO 3 91

4.35(b) EDAX Analysis for Ti64 Surface after EDM with POCO 3 91

4.36(a) SEM Photographs show EDMed Surface using POCO C3

(SV=120V, Ip=10A, tON=50µs, tOFF=50µs) 92

4.36(b) SEM Photographs show EDMed Surface using POCO C3


xiv

4.37(a) SEM Photographs show EDMed Surface using POCO C3


4.37(b) SEM Photographs show EDMed Surface using POCO C3


4.38(a) Spectrum of EDAX Analysis for Ti64 Surface after EDM

with POCO C3 95

4.38(b) EDAX Analysis for Ti64 Surface after EDM with POCO C3 95

4.39 X-ray Diffraction of Ti6Al4V Surface before EDM 98

4.40 X-ray Diffraction of Ti6Al4V after EDM with POCO 3 98

4.41 X-ray Diffraction of Ti6Al4V after EDM with POCO C3 99

4.42 Micro-crack on Specimen No. 6 with POCO 3 100

4.43 Micro-crack and Void on Specimen No. 16 with POCO 3 101

4.44 Micro-crack and Void on Specimen No. 16 with POCO C3 102

4.45 Micro-crack and Void on Specimen No. 12 with POCO C3 102

xv

LIST OF SYMBOLS

Al - Aluminium

ANOVA - Analysis Of Variance

C - Carbon

EDAX - Energy Dispersive X-Ray Spectroscopy

EDM - Electro Discharge Machining

ARLT - Average Recast Layer Thickness

AWLT - Average White Layer Thickness

EWR - Electrode Wear Rate

HAZ - Heat Affected Zone

MRR - Material Removal Rate

SEM - Scanning Electron Microscopy

SR - Surface Roughness

ON - Pulse On Time (Pulse Duration)

OFF - Pulse Off Time (Pulse Interval)

IP - Peak Current

SV - Servo Voltage

Ti - Titanium

XRD - X-Ray Diffraction

θ - Angle

Ø - Diameter

µ - Micro

Ω - Ohm

xvi

LIST OF APPEDICES

APPEDIX TITLE PAGE

A Electrodes for EDM (Mahajan, 1981) 107

B1 SEM of Recast Layer and Heat Affected Zone for

POCO 3 108

B2 SEM of Recast Layer and Heat Affected Zone for

POCO C3 116

C1 Experimental Results of EDM with POCO 3 123

C2 Experimental Results of EDM with POCO C3 124

D1 SEM of Surface Topography with POCO 3 125

D2 SEM of Surface Topography with POCO C3 130

E1 SEM of Micro crack and Void with POCO 3 135

E2 SEM of Micro crack and Void with POCO C3 137

1

CHAPTER 1

ITRODUCTIO

1.1 Introduction

Machining is one of the most important processes in manufacturing. There are

two types of machining processes; traditional machining and non-traditional machining.

The traditional also known as conventional machining requires the presence of a

tool that is harder than the workpiece to be machine and this tool should penetrate the

workpiece into a certain depth. Moreover, a relative motion between the tool and

workpiece is responsible for forming or generating the required shape. Without of these

elements such as the absence of tool – workpiece contact or relative motion makes the

process a nontraditional one.

The expectations from present day manufacturing industries are very high in

term of high economic manufacturing with high performance precision and complex

parts made of very hard high strength materials. Every customer demands products to

2

suit their own taste or choice; there is a need for high-quality low-cost parts made in

small batches and large variety (Jain, 2002). Furthermore, there is a trend in the market

for miniaturization of parts with high degree of reliability.

The traditional machining methods, even with added CNC features, are unable to

meet such stringent demands of various industries such as aerospace, electronics,

automobiles, etc. As a result, a new class of machining processes has evolved over a

period to meet such demands, named non-traditional, unconventional, modern or

advanced machining processes (Jain, 2002, Benedict, 1987, McGeough, 1988). These

advanced machining processes (AMP) become still more important when one considers

precision and ultra-precision machining. In some AMPs, materials were able to remove

even in the form of atoms or molecules individually or in groups. These advance

machining processes was base on the direct application of energy for material removal

by mechanical erosion, thermal erosion or electro-chemical / chemical dissolution.

Developments in materials science have led to the evolution of difficult to

machine, high-strength temperature-resistant materials with many amazing qualities.

Nano-materials and smart materials are the demands of the day. To make different

products in various shapes and sizes, traditional manufacturing techniques are often

founds not fit for that purposes. One needs to use non-traditional or advanced

manufacturing techniques in general and advanced machining processes in particular

(Jain, 2002).

The search for new, lightweight material with greater strength and toughness has

led to the development of new generation of materials, although their properties may

create major challenges during machining operations. Having greater hardness and

reinforcement strength, these materials are difficult to machine by the traditional

methods. Although these materials can be machine conventionally, sub-surface damages

3

such as metallurgical alterations, work hardening, micro cracks and others can occur

under certain circumstances that cause a damaging effect on the performance of the

machined component.

Titanium alloys are generally use for a component that requires the greatest

reliability and then the surface integrity must be maintained. Therefore, when machining

any component it is essential to satisfy surface integrity requirements (Harun and

Jawaid, 2005).

The conventional machining processes are sometimes unable to provide good

machining characteristics on titanium alloys. The non-conventional machining such as

electric discharge machining (EDM) and laser machining were consider one of the best

ideal techniques in dealing with these materials.

EDM electrodes are manufacture in variety of forms depending on the EDM

electrode materials used and the application. Copper is a common base material and

used as electrode because it is highly conductive and strong. A copper zirconium

diboride electrode is similar to a copper tungsten electrode, but has much higher erosion

resistance and is more expensive to produce. Other EDM electrode materials include

graphite, silver, and molybdenum. A metal graphite electrode is the most common type

of EDM electrode because it is easily too machined, has high wear resistance and

operating temperature capabilities, and is cost effective. A molybdenum electrode is

typically use for special applications, such as small electrodes or EDM wire designed for

high strength and arc erosion resistance. A silver tungsten electrode may be use in deep

slot applications that function under poor flushing conditions. Tungsten has a high

melting point, which makes it a useful EDM electrode material in combination with

more conductive metals. Tungsten carbide and other metal carbides were use for EDM

electrode materials because they have high hardness qualities and are wear-resistant.

4

1.2 Background of Problem

Titanium alloys have been found to have a very wide application area such as

aerospace especially in jet engine and airframe components, automotive, medicine and

dentistry due to their excellent corrosion resistance, lightweight and mechanical

properties (Ezugwu, 1997). These metals would have been difficult to machine by

conventional methods, but EDM has made it relatively simple to machine intricate

shapes that would be impossible to produce with conventional cutting tools (Lee, 2003).

The machinability of titanium and its alloys is consider rather poor due to several

inherent properties of materials. Poor thermal conductivity, chemically reactivity and

low elastic modulus are the common problems. EDM does not make direct contact

between the electrode and the workpiece where it can eliminate mechanical stresses

chatter and vibration problems during machining. Materials of any hardness can be cut

as long as the material can conduct electricity (Hascalic, A., and Caydas, U., 2007).

Hence, titanium, although difficult to cut material can be machined effectively by EDM

(Wang, C.C., and Yan, B.H., 2000).

The overall research of machining process is to study the interaction of the

cutting parameter and the workpiece in order to optimize the cutting conditions and

maximize the product quality. Many researchers have actively tried to carry out the

innovative research work with the main objectives such as tool life, material removal

rate, cutting force etc. However, less attention given to improve the surface quality

especially in the heat affected zone layer. In this case, the selection of EDM parameters

is important in determining the accuracy and surface finish obtained for a particular

application.

For the past years, there are researches and developments have being carried out

to develop a new type of graphite with improve features. One of them is mixing copper

5

into graphite or known as copper-graphite. This new type of electrode may contribute to

a better result in machining titanium as other electrodes are less effective to do so. It is

claim that the performance of these new graphite supposed to be much better compared

to the earlier type of graphite. The aim of this study is fulfilling a detailed investigation

of electrical discharge machining characteristic of titanium alloys Ti6Al4V in relation to

process parameters and different graphite electrode materials.

1.3 Research Statement

Electrical Discharge Machine of materials using a new type of graphite electrode

will improve the machining characteristics.

1.4 Problem Statement

Does POCO EDM-C3 (graphite infiltrated with copper) perform better in terms

of Surface Integrity of titanium alloys (Ti-6Al-4V) compared to POCO EDM 3?

6

1.5 Objectives of Study

The objectives of this study were:

a) To investigate the effect of the different graphite electrodes on the surface

integrity such as Recast Layer, Heat Affected Zone, Surface Topography,

Micro-cracks and Void of machined titanium alloy.

b) To determine the significance of EDM parameters that affect machined

surface integrity.

1.6 Scopes of Study

The scopes of study were limited to the following:

i. The types of graphite electrodes under study were limited to POCO EDM

3 and POCO EDM-C3 only.

ii. The work material used in this study was limited to Ti-6Al-4V.

iii. The surface integrity under investigation includes Recast Layer, Heat

Affected Zone, Surface Topography, Micro-cracks and Void.

iv. The equipments used to analyse surface integrity were limited to Optical

Microscope, Scanning Electron Microscope (SEM) with EDAX and X-

Ray Diffraction (XRD) analysis.

v. The machining parameters to vary were servo voltage, peak current, pulse

ON time and pulse OFF time.

vi. Design of Experiment (DOE) tool was used for analysis of recast layer

(RL) and heat affected zone (HAZ).

surface itegrity evaluatio o titaium alloy after...

Documents