PERFORMANCE EVALUATION OF COPPER AND …eprints.uthm.edu.my/8781/1/SURAYA_BINTI_LAILY.pdf ·...
Transcript of PERFORMANCE EVALUATION OF COPPER AND …eprints.uthm.edu.my/8781/1/SURAYA_BINTI_LAILY.pdf ·...
PERFORMANCE EVALUATION OF COPPER AND
GRAPHITE ELECTRODE IN ELECTRICAL
DISCHARGE MACHINE (EDM) OF ALUMINIUM
ALLOY LM6
SURAYA BINTI LAILY
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
STATUS CONFIRMATION FOR MASTER’S PROJECT REPORT
THE STUDY OF PERFORMANCE DIFFERENT ELECTRODE
MATERIALS IN ELECTRICAL DISCHARGE MACHINE (EDM) OF
ALUMINIUM ALLOY LM6
ACADEMIC SESSION : 2014/2015
I, SURAYA BINTI LAILY agree to allow this Master Thesis to be kept at the Library under the
following terms:
1. This Master Thesis is the property of Universiti Tun Hussein Onn Malaysia.
2. The library has the right to make copies for educational purposes only.
3. The library is allowed to make copies of this report for educational exchange between
higher educational institutions.
4. ** Please Mark (√)
CONFIDENTIAL
(Contains information of high security or of great
importance to Malaysia as STIPULATED under the
OFFICIAL SECRET ACT 1972)
RESTRICTED
(Contains restricted information as determined by
the Organization/institution where research was
conducted)
FREE ACCESS
_________________________
Approved by,
__________________________
(SURAYA BINTI LAILY)
(DR. BUKHARI BIN MANSHOOR)
Permanent Address :
NO34, JALAN BELATUK MAS 2,
TAMAN BELATUK MAS,
76100 DURIAN TUNGGAL,
MELAKA.
Date: ___________________
Date : ________________________
NOTE:
** If this Master Thesis is classified as CONFIDENTIAL or RESTRICTED, Please
attach the letter from the relevant authority/organization stating reasons
and duration for such classifications.
This thesis has been examined on
and is sufficient in fulfilling the scope and quality for the purpose of awarding
Degree of Master.
Chairperson:
Faculty of Mechanical and Manufacturing Engineering
Universiti Tun Hussein Onn Malaysia
Panels:
PERFORMANCE EVALUATION OF COPPER AND GRAPHITE ELECTRODE
IN ELECTRICAL DISCHARGE MACHINING (EDM) OF ALUMINIUM ALLOY
LM6
SURAYA BINTI LAILY
A thesis submitted in
fulfillment of the requirement for the award of the
Degree of Master
Faculty of Mechanical and Manufacturing Engineering
Universiti Tun Hussein Onn Malaysia
January,2016
iii
I hereby declare that the work in this thesis is my own except for quotations and
summaries which have been duly acknowledged.
Student : ……………………………………………………
SURAYA BINTI LAILY
Date : …………………………………………………….
Supervisor : …………………………………………………….
DR. BUKHARI BIN MANSHOOR
Co Supervisor : …………………………………………………….
DR. MOHD AMRAN BIN MD. ALI
iv
For my beloved husband, son, parents, for their endless support.
v
ACKNOWLEDGEMENT
In the name of Allah, Praise is to Allah, the Most Gracious and Most Merciful. I
would like to thank Dr. Bukhari bin Manshoor, my supervisors for his support,
encouragement, motivation and help along my master study period. My special
thanks also to my co-supervisor, Dr Mohd Amran bin Md. Ali for his support and
guidance through my master education. Besides, thanks to research group under
MTUN vot C027 grant for their help and financial support.
My appreciation go to my beloved husband, Mohammad Ikmal bin
Mohamed and my son Ammar Hadif bin Mohammad Ikmal for their love and care
and also my dearest parents for their support.
Highly heartfelt thanks for the cooperation and guidance from technical
support and others lecturer for their brilliant idea given. It was a very interesting
team work environment along my journey to complete my master project with all
their kindness and helpful. Last but not least, I would like to thank for those who
directly and indirectly contributed to complete my master project.
vi
ABSTRACT
Electrical discharge machining (EDM) which is very famous among the non-
conventional machining methods is expected to be used quite extensively in
machining aluminium alloys due to the advantages that it can offer. This thesis is to
study on the influence of operating parameters of LM6 (Al-Sil2) on machining
characteristics such as material removal rate, electrode wear rate, surface roughness,
surface hardness thickness of recast layer. Copper and graphite were selected as
electrode with positive polarity. The experiment was done using SODICK AQ35L
EDM machine. Three level approach of Taguchi Method Design of Experiment
(DOE) was applied to design the experimental table of trials, analyze the significant
factors that affecting the machining characteristics for EDM process. Total of 27
experiments were conducted included 3 time repetition of every run. The weight of
electrode and workpiece were measured before and after machining using weight
scale and surface roughness tester was used to measure the Ra for each specimen.
Scanning Electron Microscope (SEM) has been used to measure the thickness of
recast layer while Vickers Hardness tester was used to measure surface hardness of
workpiece material. The experimental data was analysed by using ANOVA analysis
and the optimal combination of the process parameters can be predicted. From the
usage of copper electrode, it can be conclude that peak current was significantly
affect material removal rate (MRR), electrode wear rate (EWR) and surface
roughness (Ra) and surface hardness (Hv).While pulse on time mainly effected
thickness of recast layer by using copper and graphite electrode . Meanwhile, by
using graphite electrode, peak current also mainly affected material removal rate,
electrode wear rate, and surface roughness. Moreover, surface hardness was affected
by peak current while others parameters which are voltage, pulse on time and pulse
off time gave equally affect on surface hardness of the workpiece.
vii
ABSTRAK
Pelepasan mesin elektrik (EDM) yang sangat terkenal antara kaedah pemesinan
bukan konvensional dijangka akan digunakan agak meluas dalam pemesinan aloi
aluminium kerana kelebihan yang ia boleh tawarkan. Tesis ini adalah untuk
mengkaji pengaruh parameter operasi LM6 (Al-Sil2) ciri-ciri pemesinan seperti
kadar pembuangan bahan, elektrod kadar haus, kekasaran permukaan, ketebalan
kekerasan permukaan lapisan menyusun semula. Tembaga dan grafit telah dipilih
sebagai elektrod dengan kutub positif. Eksperimen telah dilakukan menggunakan
mesin SODICK AQ35L EDM. Tiga pendekatan tahap Taguchi Kaedah Rekabentuk
Eksperimen telah digunakan untuk mereka bentuk rangka eksperimen , menganalisis
faktor-faktor penting yang mempengaruhi ciri-ciri mesin untuk proses EDM.
Sebanyak 27 eksperimen telah dijalankan termasuk 3 kali pengulangan setiap jangka.
Berat elektrod dan benda kerja diukur sebelum dan selepas pemesinan menggunakan
skala berat badan dan penguji kekasaran permukaan telah digunakan untuk
mengukur Ra bagi setiap spesimen. Mikroskop Imbasan Elektron (SEM) telah
digunakan untuk mengukur ketebalan lapisan menyusun semula sementara Vickers
kekerasan ujikaji digunakan untuk mengukur kekerasan permukaan bahan bahan
kerja. Data eksperimen dianalisis dengan menggunakan analisis ANOVA dan
gabungan optimum parameter proses dapat diramalkan. Daripada penggunaan
elektrod tembaga, ia boleh membuat kesimpulan bahawa puncak semasa telah ketara
memberi kesan kepada kadar penyingkiran bahan (MRR), kadar haus elektrod
(EWR) dan kekasaran permukaan (Ra) dan kekerasan permukaan (Hv) .
viii
Semasa nadi pada masa ketebalan terutamanya dilaksanakan untuk menyusun
semula lapisan dengan menggunakan tembaga dan elektrod grafit. Sementara itu,
dengan menggunakan elektrod grafit, semasa puncak juga terutamanya dipengaruhi
kadar pembuangan bahan, elektrod kadar haus, dan kekasaran permukaan. Lebih-
lebih lagi, kekerasan permukaan dipengaruhi oleh arus puncak manakala parameter
yang lain seperti voltan, nadi pada masa dan nadi kira masa sama dia memberi kesan
kepada kekerasan permukaan bahan kerja.
ix
TABLE OF CONTENT
CHAPTER TITLE PAGE
TITLE i
DECLARATION iii
ACKNOWLEDGEMENT v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENT viii
LIST OF TABLES xi
LIST OF FIGURES xiv
LIST OF ABBREVIATIONS AND SYMBOLS xvii
LIST OF APPENDICES xviii
CHAPTER 1 INTRODUCTION 1
1.1 Project Background 1
1.2 Problem Statement 2
1.3 Objective 3
1.4 Scope of Study 4
1.5 Outline of the report thesis 4
CHAPTER 2 LITERATURE RIVIEW 6
2.1 Introduction 6
2.2 Various electrical discharge machine 6
2.3 EDM die-sinking process 8
2.4 Types of materials 10
2.4.1Workpiece Materials Machined by EDM die sinking 10
x
2.4.2 Type of Electrode 13
2.4.2.1 Graphite Electrode 13
2.4.2.2 Copper Electrode 13
2.4.3 Die Electric Fluid 14
2.5 Material Aluminium Alloy LM6 (Al–Sil 12.30%) 17
2.6 Machining Parameters 18
2.6.1 Current (A) 19
2.6.2 Pulse Duration Time/Pulse ON time (μs) 20
2.6.3 Pulse Interval Time/Pulse OFF time (μs) 20
2.7 Summary 23
CHAPTER 3 METHODOLOGY 24
3.1 Introduction 24
3.2 Project Planning 25
3.2.1 Flowchart of Methodology Process 25
3.3 Design of Experiment (DOE) 27
3.3.1 Set Objectives 29
3.3.2 Select Process Variables 29
3.3.3 Identify Response Variables 29
3.3.4 Taguchi Method and ANOVA analysis 30
3.3.5 Material Aluminium Alloy LM6 32
3.3.6 Conduct Experiment 33
3.3.7 Analyze Result 34 28
3.4 Dielectric Fluid 34
3.5 EDM Die-Sinker Machine 35
3.6 Machine Responses Parameter 36
3.6.1 Electrode Wear Rate (EWR) 36
3.6.2 Metal Removal Rate (MRR) 36
3.6.3 Surface Roughness (Ra) 38
3.6.4 Surface integrity measurement (recast layer) 40
3.6.5 Surface Hardness 44
CHAPTER 4 RESULT AND DISCUSSION 50
4.1 Result of Experiment 50
4.2 Analysis of Result 54
xi
4.4 Analysis Result of MRR 54
4.4.1 Analysis Result MRR using Graphite electrode 54
4.4.2 Analysis Result MRR using Copper electrode 60
4.5 Analysis Result of EWR 64
4.5.1 Analysis result EWR using Graphite electrode 64
4.5.2 Analysis Result EWR using Copper electrode 70
4.6 Analysis Result of Ra 75
4.6.1 Analysis Result Ra using Graphite electrode 75
4.6.2 Analysis Result Ra using Copper electrode 80
4.7 Analysis of recast layer 84
4.7.1 Analysis result of recast layer by using copper
electrode
84
4.7.2 Analysis result of recast layer by using graphite
electrode
91
4.8 Surface hardness 97
CHAPTER 5 CONCLUSION AND RECOMMENDATION 102
5.1 Conclusion 102
5.2 Recommendation 104
REFERENCES 105
APPENDICES 112
xii
LIST OF TABLES
TABLE TITLE PAGE
2.1 The Physical Properties of Copper Electrode 9
2.2 Percentage of Composition LM6 (%) 13
2.3 Machining Parameter and Levels of Setting Conditions 16
2.4 Process parameters and their levels 17
2.5 Parameters and their levels 17
3.1 Factors and Levels Selected for the Experiment 23
3.2 Factorial Design Models 25
3.3 Mechanical,Physical, Electrical and Thermal properties of LM6 26
4.1 Results of experimental material MRR, EWR and Ra for
graphite electrode
52
4.2 Results of experimental material MRR, EWR and Ra for copper
electrode
53
4.3 Design of experiments and experimental results for MRR and
calculated S/N ratio
55
4.4 Average S/N Ratio and Main Effect of MRR 56
4.5 Optimum parameters combination for MRR 57
4.6 One-way ANOVA for MRR 58
4.7 The comparison between higher experimental MRR and
optimize MRR.
59
4.8 Design of experiments and experimental results for MRR and
calculated S/N ratio
60
4.9 Response Table for Signal to Noise Ratios of MRR 61
4.10 Optimum parameters combination for MRR 62
xiii
4.11 One-way ANOVA for MRR 63
4.12 The comparison between higher experimental MRR and
optimize MRR
64
4.13 Design of experiments and experimentalresults for EWR
and calculated S/N ratio
65
4.14 Average S/N Ratio and Main Effect of EWR 66
4.15 Optimum parametric combination for EWR 67
4.16 One-way ANOVA for EWR 68
4.17 The comparison between higher experimental EWR and
optimize EWR
69
4.18 Design of experiments and experimental results for EWR and
calculated S/N ratio
70
4.19 Average S/N Ratio and Main Effect of EWR 71
4.20 Optimum parameter combination for EWR 72
4.21 One-way ANOVA for EWR 73
4.22 The comparison between higher experimental EWR and
optimize EWR
74
4.23 Design of experiments and experimental results for Ra and
calculated S/N ratio using graphite electrode
76
4.24 Average S/N Ratio and main effect of surface roughness (Ra) 77
4.25 Optimum parameters combination for surface roughness (Ra) 78
4.26 One-way ANOVA for surface roughness (Ra) 79
4.27 The comparison between higher experimental Ra and optimize
Ra
79
4.28 Design of experiments and experimental results for EWR and
calculated S/N ratio using graphite electrode
80
4.29 Average S/N Ratio and main effect of surface roughness (Ra) 81
4.30 Optimum parameters combination for surface roughness (Ra) 82
4.31 One-way ANOVA for surface roughness (Ra) 83
4.32 The comparison between higher experimental Ra and optimize
Ra
83
xiv
4.33 Result of Recast Layer (RL) with different peak current, pulse
on time, pulse off time and voltage by using copper electrode
84
4.34 Result of Recast Layer (RL) with different peak current, pulse
on time, pulse off time and voltage by using graphite electrode
91
4.35 Result on hardness value by using copper electrode 98
4.36 Result on hardness value with process parameters for copper 98
4.37 Result on hardness value by using graphite electrode 100
4.38 Result on hardness value with process parameters for graphite 100
xv
LIST OF FIGURES
FIGURE TITLE PAGE
2.1 Wire EDM 6
2.2 Die Sinker EDM 6
2.3 Small Hole EDM Drilling 7
2.4 Ram-type EDMs plunge a tool 8
2.5 Powder Metallurgy Process of Composite Material 11
2.6 Classified Research Area in EDM Machining Process 16
3.1 Experimental Methodology 25
3.2 Design of Experiment Process Flow 27
3.3 Electrode and Work piece shape use 33
3.4 EDM die sinking Sodick AQ35L Series 35
3.5 Precise Digital Balance 37
3.6 Surface Roughness Equipment (Mitutoyo SJ- 301) 37
3.7 Scanning Electron Machine (SEM) 38
3.8 The heat-affected zone between white layer and
workpiece under Scanning Electron Microscopy (SEM)
38
3.9 Vickers Hardness test 39
3.10 Schematic view on Vickers Hardness Testing 40
4.1 Signal to noise graph for material removal rate ( MRR) 57
4.2 Main Effects Plot for Signal to Noise Ratios of MRR 62
4.3 Signal to noise graph for electrode wear rate ( EWR) 67
4.4 Signal to noise graph for electrode wear rate ( EWR) 72
xvi
4.5 Signal to noise graph for surface roughness (Ra) 78
4.6 Signal to noise graph for surface roughness (Ra) 82
4.7 Signal to noise graph for Recast Layer (RL) 85
4.8 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=2A, V=21V,
Pon=1µs, Poff=1µs]
86
4.9 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=2A, V=25V,
Pon=200µs, Poff=5µs]
86
4.10 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=2A, V=30V,
Pon=400µs, Poff=9µs]
87
4.11 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=15A, V=21V,
Pon=200µs, Poff=9µs]
87
4.12 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=15A, V=25V,
Pon=400µs, Poff=1µs]
88
4.13 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=15A, V=30V,
Pon=1µs, Poff=5µs]
88
4.14 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=30A, V=21V,
Pon=400µs, Poff=5µs]
89
4.15 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=30A, V=25V,
Pon=1µs, Poff=9µs]
89
4.16 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=30A, V=30V,
Pon=200µs, Poff=1µs]
90
4.17 Signal to noise graph for Recast Layer (RL) 92
xvii
4.18 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=2A, V=21V,
Pon=1µs, Poff=1µs]
93
4.19 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=2A, V=25V,
Pon=200µs, Poff=5µs]
93
4.20 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=2A, V=30V,
Pon=400µs, Poff=9µs]
94
4.21 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=15A, V=21V,
Pon=200µs, Poff=9µs]
94
4.22 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=15A, V=25V,
Pon=400µs, Poff=1µs]
95
4.23 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=15A, V=30V,
Pon=1µs, Poff=5µs]
95
4.24 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=30A, V=21V,
Pon=400µs, Poff=5µs]
96
4.25 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=30A, V=25V,
Pon=200µs, Poff=1µs]
96
4.26 SEM showing the cross-sectional view of the recast layer
of aluminium LM6 after EDM with [I=30A, V=30V,
Pon=200µs, Poff=1µs]
99
4.27 Signal to noise graph for hardness value by using copper
electrode
101
4.28 Signal to noise graph for hardness value by using
graphite electrode
101
xviii
LIST OF ABBREVIATIONS
DOE - Design Of Experiment
EDM - Electrical Discharge Machine
EWR - Electrode Ware Rate
MRR - Material Removal Rate
Ra - Surface Roughness
Hv - Surface hardness
RL - Recast layer
CCD - Charge Coupled Device
SEM - Scanning Electron Microscope
xix
LIST OF APPENDIX
Appendix A - List of published journal
1
CHAPTER 1
INTRODUCTION
1.1 Project Background
Aluminium-metal matrix composite (AMMC) such as Aluminium LM6 has been the
most exploited material for its low density and the ease of fabrication. AMMC
composes of a metallic base material called matrix, which is reinforced with
reinforcing agent such as ceramic, silicon and others (Mohan et al., 2004). Because
of this, AMMC has a high strength, hardness and stiffness that contributed more
application in aerospace, defence and automobile industries (Mohan et al., 2004).
However, in term of fabrication process, it faces difficulty during machining process
due to the presence of the abrasive reinforcing phase which cause severe tool wear.
Aluminium LM6 as an example, due to silicon content it is hard to machine by
conventional machine. The application of aluminium LM6 itself was make this
material more suitable to machine by advance machining. As an example making
microhole on shaft as one of automotive parts that need advance machining to make
precise hole. Besides, complex shape also can be done by advance machine since
most of the automotive and defence industry parts are .One of the fabrication process
that can be machined with either electroplated diamond-grinding wheel or with
carbide poly crystalline diamond cutting tools (Dhar et al., 2007). Thus, non-
conventional machining, that is electrical discharge machining (EDM) offered an
effective alternative way to cut the AMMC.
EDM Die-Sinking is controlled material removal technique where high
frequency electric spark are used to erode the workpiece which takes a shape
corresponding to that the electrode (Amri et al., 2009). The process was started when
2
electrode is moved down to workpiece until the gap is enough to ionize the dielectric
fluid. The erosion take effect when it is removed the material from workpiece and
electrode through dielectric fluid. The melted material get expelled from surface and
carried away by constantly circulated dielectric fluid.
EDM has proved in machining super tough alloy such as titanium alloy,
stainless steel and aluminium alloy. According to Lee and Li (2001), using
conventional method, these tough material is difficult to machine, even to make a
simple shape. EDM Die-Sinking offers many advantages such as non-contact with
the workpiece during the machining process Kumar et al., (2013), can cut deep slot
Hussein et al., (2008) and the ability to machine any conductive material especially
material with high hardness (Singh et al., 2004). Furthermore, EDM Die-Sinking is a
well established machining option for manufacturing geometrically complex or hard
material parts that are extremely difficult to machine by conventional machining
processes. Dhar et al., (2007) investigated the capability of EDM die-sinking process
of Al-4Cu-6Si alloy using brass electrode to see the effect of current, pulse on time,
and air gap voltage on material removal rate (MRR), tool wear rate (TWR), and
radial over cut (ROC). They found that MRR, TWR and ROC increase significantly
in non-linear fashion with increase current while MRR and ROC increase with
increase in puse duration.Besides that, Karthikeyan et al., (1999) was used copper
electrode on LM 25 Al alloy-SiC composites to see the effect of volume percent of
SiCp, current and pulse duration on MRR, TWR, and surface roughness.
1.2 Problem Statement
In this recently advance engineering area, advance machining was being the most
widely used to produce dies and mould. It is also being used by automotive and
aerospace industry in term of making small part with high precision. For example
shaft making in car’s part and small hole in bearing. These critical parts are need to
machine by advance machining like EDM Die-sinking due to avoid severe tool wear,
mechanical stress and vibration problem. The addition of hard reinforcement
materials into AMMC was categorized it as one of the most difficult materials to be
machined. Using conventional machining process significantly more difficult and
3
leads to severe tool wear and work piece damage. In many critical application and
shaped like pocket geometrical, deep slot shape and microhole, conventional
machining process method is difficult to achieve while machining AMMC.
Achieving the desired surface quality is of great importance for the effective use of
product (Lui et al., 2008). Besides, using conventional method, good surface finish is
difficult to achieve while machining AMMC due to the fracture and pull out the
reinforcing particles. Because of these, this research come out with the solution by
improving machinability of AMMC and developing machining data in order to
convince designers and manufacturers to use AMMC in their application. Non-
conventional machining such as EDM die-sinking is developed to perform
machining of AMMC in order to encounter difficulties during machining
conventional like high tool wear, and poor surface finish (Karthikeyan et al., 1999).
1.3 Objective
The main objective of the study are:
(a) To investigate the effect of various EDM parameters i.e. voltage, peak
current, pulse on time and pulse off time on the machining characteristics
of aluminium LM6 alloys which are MRR, EWR, surface roughness,
recast layer and surface hardness.
(b) To analyze the interaction between EDM parameters and machining
characteristics using two types of electrode.
(c) To identify the significance parameters using Taguchi method and
analyze its percentage contribution for each response investigated using
ANOVA.
4
1.4 Scope of the Study
Below shows the workpiece, electrode, machine parameters, EDM die-sinking
machine and equipments used for this project.
Copper and graphite with 12mm diameter are used as the main electrode
material for this research.
LM6 (Al–Si 12.30%) alloys with size 50mm (L) x 50mm (W) x 10mm (H) is
selected as workpiece.
Machining parameters of peak current,Ip (2A-30A), voltage,V(21V-30V),
pulse on time,ton(1µs-400µs) and pulse off time,toff(1µs-9µs) are selected as
the process input parameters.
Machining characteristic to be investigate are material removal rate (MRR),
electrode wear rate (EWR), surface roughness (Ra), recast layer and surface
hardness.
Kerosene oil is used as dielectric fluid.
Weighting Digital Scale is used to measure the weight of material and
electrode for before and after the process.
Surface Roughness tester will be use to measure surface roughness of
material after machining using EDM.
EDM die sinking Sodick AQ35L Series machine is the main equipment of
this project.
Minitab software with three levels of Taguchi method design and analysis of
variance (ANOVA) are employed to evaluate the data.
1.5 Outline of the Report Thesis
This report consists of five basic structures of chapters which are:
1. Introduction
This chapter describes the aim, objectives and scope of the research as
well as the structure of the thesis.
5
2. Literature Review
The literature review is written the published works by other research that
directly related to the thesis, providing information on theories and
technique.
3. Methodology
This important chapter explains the samples, instruments, materials,
procedures and data gathering methods used in the research.
4. Result and discussion
This chapter explains the data analysis technique and result through
written figures, text, tables and graph.
5. Conclusion and recommendation
Conclusion is drawn based on the research findings and their
implications. Future works are also discussed.
6
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This literature review explores the dominant themes includes study and research of
published materials like journals, thesis, case study, technical document, and online
library. Generally, the purpose of a review is to analyze critical segment of a
published body of knowledge through summary, classification and comparison of
previous research studies, reviews of literature, and theoretical articles. This chapter
will describe topics that related to EDM on LM6 which consist of their process,
parameter and material used and their application.
2.2 Various Electric Discharge Machine
There are three basic electric discharge machining method which are wire, die-
sinking and small hole EDM. All of these method based on principle of spark erosion
where spark generated between electrode and workpiece in a maintain gap to erode
the workpiece (Carl et al., 2011). Wire EDM is used to make through hole on the
workpiece. As shown in Figure 2.1, the spark jumps from wire electrode to the
workpiece and erode metal both from the wire electrode and the workpiece (Carl et
al., 2011).
7
Figure 2.1: Wire EDM (Carl et al., 2011)
EDM Die-Sinking usually to produce complex shape that removed the material from
workpiece and electrode through dielectric fluid. Figure 2.2 shows the schematic
view on how the EDM Die-Sinking process has done (Carl et al., 2011).
Figure 2.2 : Die Sinker EDM (Carl et al., 2011)
While the last common EDM process is small hole EDM drilling. The process was
done by drilled hole by eroding material from the workpiece. Usually material with
high hardness value like titanium alloy are to be machined by EDM Drilling where
there is a limitation to be machine by conventional machine (Hussein et al., 2011).
Figure 2.3 shows small hole EDM drilling schematic view.
8
Figure 2.3 : Small Hole EDM Drilling (Carl et al., 2011)
In this project, EDM process is used to machine aluminium alloy LM6. Next, detail
EDM Die-Sinking process is described.
2.3 EDM Die-Sinking Process
EDM is a non-traditional process that is used to remove metal through the action of
an electrical discharge of short duration and high current intensity between the
electrode and the work piece. There are no physical cutting forces between the tool
and the work piece. This process is finding an increasing demand owing to its ability
to produce geometrical complex shapes. EDM also have its ability to machine hard
materials that are extremely difficult to machine when using conventional process.
Mohan and Chandan, (2008) have stated that EDM has proved valuable especially in
the machining of super tough, hard and electrically conductive materials such as the
new space age alloys and have been agreed by (Lee and Li, 2001).
Other than that, since that the usage of hard, high strength, hardness and
toughness materials increasingly lately, EDM is one of the application machining
method that has getting important. It was proved by Amri et al., (2009), where
tungsten carbide have been machined using EDM Die-Sinking which has the highest
hardness in reinforcement. By using peak current, voltage, pulse duration and
interval time as the main parameters, they have found that peak current of EDM is
mainly effects the electrode wear rate (EWR) and surface roughness (Ra) while the
pulse duration was effected the material removal rate (MRR). Others present studies
also examine the effect of EDM parameters such as peak current, voltage, pulse on
9
time and pulse off time on EDM machining characteristic such as material removal
rate, electrode wear rate, surface roughness and surface integrity (Lonardo and
Bruzzone, 1999). EDM die-sinking also is one of the important process for
machining difficult to machine materials like metal matrix composite (MMC).As
such, Karthikeyan et al., (2009) had studied the effect of current, pulse duration and
percentage volume of SiC on MRR, EWR and Ra. It was found that MRR, EWR and
Ra were increased with increasing in current while EWR and Ra were perpendicular
with percentage volume of SiC. In addition, Singh et al., (2004) was agreed where
they found pulse duration was affected most of the responses by using MMC as the
main workpiece material.
Figure 2.4 : Ram-type EDMs plunge a tool (Bahari, 2007)
Figure 2.4 shows the process of EDM Die Sinking where the electrode is
moved towards the work piece until the gap is small enough, so that the impressed
voltage is great enough to ionize the dielectric fluid. A servomechanism is used to
maintain a gap between the electrode and the work piece. Hence, prevent them from
touching each other. The erosion take effect on part as it is removed the material
from work piece and electrode through dielectric fluid. The materials melts or
vaporizes and gets expelled from the surface of electrode and work piece, the eroded
particles are carried away by constantly circulated dielectric fluid.
10
In this research, peak current Ip, voltage V, pulse on time ton and pulse off
time toff are selected. It is due to several tipper utilized by others Karthikeyan et al.,
(2009)
2.4 Types of Materials
For this project, LM6 (Al–Sil 12.30%) alloys will be use as workpiece while copper
and graphite electrode will be use as the electrode material that need to differentiate
in term of machine characteristic.Further explaination on types of materials used and
their application will be explained .
2.4.1 Workpiece Materials Machined by EDM Die Sinking
There are a various type of material have been used for EDM Die Sinking machine.
Since this various of material have their various type of application, classification of
suitable material with their matched machining process are needed. Since that EDM
Die Sinking just allow conductive material to machine with, there are a huge
limitation to machine non-conductive materials. It is coincided with the EDM
process itself where electric spark were generated between electrode and workpiece
are used to erode the workpiece. These are caused the material of workpiece and
electrode must be conductive material. As such, Amri et al., (2009) used Tungsten
Carbide ceramic and graphite as the main workpiece and electrode material. While
Samsul, (2012) was used Copper Beryllium as the main workpiece, where it is
included in the copper alloy family.
Accordance with the development of processing method, material use is also
increasingly developing rapidly. Composite is one of them and there is some of
reseachers have been used these type of material to machine by EDM Die-Sinking.
Matrix composite material have been widely used in EDM. Properties on the based
material was to be integrated well enough with the properties on the ceramic to
improve the properties of new material. Due to the presence of hard and brittle
ceramic reinforcement, these type of materials are hard to machine by conventional
11
machine. Metal matrix composite as such, have been used by Kumar et al., (2013) as
the main workpiece material. In their present works LM6-5% SiCp composite, which
are fabricated by stir casting process were machine by EDM Die-Sinking. Dhar et al.,
(2007) used Al-4Cu-6Si alloy composite to machine by EDM with brass as an
electrode. Same technique fabricated with Kumar et al., (2013), they found that
Metal Matric Composite (MMC) are well know for their superior mechanical
properties and because of that, non-contact material removal process offer an
effective alternatives. Venkat, (2011) have stated that Aluminium–silicon alloys are
one of the most commonly Aluminium Metal Matrix Composite (AMMC) used
foundry alloys because they offer many advantages such as high strength to weight
ratio, good thermal conductivity, excellent castability, pressure tightness, wear and
corrosion resistance and good weldability. Because of these, they are well suited to
automotive cylinder heads, engine blocks, aircraft components, pipe fittings and
military applications.
Besides, Lau et al., (1990) have machine carbon fibre composite materials
where it is now widely used in aero-space, nuclear, shipping and chemical
industries.The process have been done with low current density since high current
density would cause the epoxy resin to smear over the surface leading to reduce
material removal rate.
Metal matrix composite is one of the matrix composite family where there are
four of them. Others are polymer matrix composite (PMC), ceramic matrix
composite (CMC) and the latest one is cement matrix composite (CeMC). According
to Kaczmar et al., (2000) metal matrix composite are produced by casting and
powder metallurgy methods. Casting is a process where molten alloy matrix was
reinforcing by dispersion particles and short fibre through blending them together.
There are direct squeeze casting and indirect squeeze casting where these two
processes have different usage of application. Direct squeeze casting is applied for
the production of composite elements characterised by relatively simple shape, and
the dies usually simple and reasonable price. The application of indirect squeeze
casting is more complex composite part and more expensive casting dies.
While powder metallurgy method, Kaczmar et al., (2000) also stated the
process are more classic where matrix powder and reinforcing elements was blending
together, continue with cold pressing and sintering followed by forging and extrusion.
Fligier et al., (2008) have stated that powder metallurgy method is mixing materials
12
with different properties in various proportions to make material properties easily to
control. Normally, this method is applied for production that uses magnesium alloy
matrix, aluminium alloy matrix and copper matrices.
Figure 2.5: Powder Metallurgy Process of Composite Material (The Metal
Casting.com)
Aluminium metal matrix composite (AMMC) have move to many
developments in term of characteristic material where in which mixed with hard and
brittle component such as ceramic. AMMC have good corrosion resistance, low
density, and high thermal stability and improved mechanical properties. AMMC that
reinforced with ceramic such as SiC, alumina and fly ash combine the high ductility
and toughness of aluminium with high hardness and tensile strength of ceramic
(Venkat et al., 2011). They studied the influence of peak current, flushing pressure
and pulse on time on MRR, EWR and Ra of AlSi10Mg alloy by means of Taguchi
method and design of experiment (DOE) technique. It was determined that peak
current was the most significant parameter influencing the responses, followed by the
pulse on time and flushing pressure. These result further strengthen the result of
machined aluminium LM6 by using copper and graphite where peak current mainly
dominant affected most of the responses. Karthikeyan et al., (1999) used ANOVA
analysis technique for optimization of EDM parameter such as current, pulse
duration and volume fraction of SiC with consideration of multiple responses like
MRR, EWR and Ra. The MRR was found to decrease with an increase in the present
13
volume of SiC while the EWR and the Ra increase with increase in the volume of
SiC in LM25 aluminium matrix. According to Dhar et al., (2007), MRR, EWR and
radial over cut (ROC) increase significantly in non-linear fashion with increase in
current by three factor, three level full factorial design and ANOVA analysis. It was
determined that peak current, pulse on time and voltage are the significant factor that
effect the response parameters by using Al-4Cu-6Si alloy as workpiece and brass as
electrode.
2.4.2 Type of Electrode
There are several types of electrode that can be used for EDM Die-sinking process
depending on the application. The selection of the most appropriate EDM Die
Sinkeing electrode material is a key decision in the process plan for any EDM Die
Sinking job. In this project, copper and graphite electrode is used as the main
electrode.
2.4.2.1 Graphite Electrode
Graphite has extremely high melting point. It does not melt at all, but sublimes
directly from a solid to a gad (just as the Carbon Dioxide in dry ice) at a temperature
thousands of degrees higher than the melting point of copper, this resistance to
temperature makes graphite an ideal electrode material. Besides, graphite is
significantly lower mechanical strength properties than metallic electrode material. It
is neither as hard, as strong, nor as stiff as metallic electrode materials.
2.4.2.2 Copper Electrode
In Europe and Asia, copper has been a popular electrode material, this is due to
several factors. First, the early EDM machines that were predominant in those areas
used R-C (Resistor Condenser) power supplies. Metallic electrodes, such as Copper,
Brass, Copper Tungsten, and others were the only electrode materials that would
perform effectively with an R-C EDM. When the next generation of machines was
developed, Copper was already firmly entrenched as the most popular electrode
14
material (McGeough and Regius, 1998) . Copper also has the qualities for high stock
metal removal. It is a stable material under sparking conditions. Its wear can be
comparable with graphite.
Indeed with some workpiece materials, it yields a finer surface finish. Copper
are easily obtainable, consistent in quality and low in cost. Copper has melting point
which is only about 1100°C. The temperature in the gap is in the range of a few
thousands of degree, hence there is rapid electrode wear (Bahari, 2007). Roger
(2008) have stated that Copper is compatible with the polishing circuits of certains
advanced power supplies. Most of the manufacturing industry in both Europe and
Japan still prefer to use Copper as the primary electrode material, due to their tool
making culture that is averse to the utidiness of working with graphite. Due to the
structural integrity, Copper can produce very fine surface finishes, even without
special polishing circuits. In addition to graphite, copper is used as an electrode to
machine aluminium LM6. Table 2.1 belows shows the physical properties of copper
electrode:
Table 2.1 : The Physical Properties of Copper Electrode (Bahari, 2007)
Physical Properties Value
Electrical resistivity (µΩ/cm) 1.96
Electrical conductivity compared with silver (%) 92
Thermal conductivity (W/mK) 268-389
Melting point (°C) 1083
Specific heta (cal/g°C) 0.092
Specific gravity at 20°C(g/cm3) 8.9
Coefficient of thermal expansion (x 10°C-1
) 6.6
2.4.3 Die Electric Fluid
There are many different types of fluid available. According to Krar, et al. (1998),
the workpiece and the electrode are submerged in the electric oil, an electrical
insulator that helps to control the arc discharge. The oil also acts as a coolant, and is
15
pumped through the arc gap to wash away the chips. A die electric fluid performs
three important functions:
i. Electrode /workpiece gap was insulated and prevents a spark from
forming until the gap and voltage are correct. When this happens,
the oil ionizes and allows the discharge to occur.
ii. Coolant act to cool the work, the electrode, and the molten metal
particles. Without coolant, the electrode and the workpiece would
become dangerously hot.
iii. Besides, coolant also flush the metal particles out of the gap. Poor
flushing will cause erratic metal removal, poor machining
conditions, and increase machining time and cost.
For most EDM operation, kerosene is the common dielectric used with
certain addictives that prevent gas bubble and deodorant. Silicon fluids and mixture
of these fluids with petroleum oils have excellent results. Other dielectric fluids such
as aqueous solution of ethylene glycol, water in emulsion and distilled water. All
dielectric oil will change in darken colour after use, but it seem only logical to start
with liquid that is as clear a possible to allow viewing of the submerged part
(McGeough and Regius 1998). In this project, kerosene is used as the dielectric fluid.
Figure 2.6 show the basic EDM research that most of the researchers have
done. This project is under improving the performance measurement where the
objectives and scope of the project are to study the interaction between EDM Die
Sinking parameters with the machine responses which are MRR, EWR, surface
roughness, recast layer and surface hardness.
16
Figure 2.6: EDM Research Area
PROJECT
AREA
17
2.5 Material Aluminium Alloy LM6 (Al–Sil 12.30%)
In the past, various studies have been carried out on metal matrix composites. SiC,
TiC and TaC are the most commonly used particulates to reinforce in the metal or in
the alloy matrix or in the matrices like aluminum or iron, while the study of silicon
dioxide reinforcement in LM6 alloy is still rare and scarce. This is due firstly to their
tendency to drag and secondly to the rapid tool wear caused by the high silicon
content. LM6 is based on British specifications that conform to BS 1490–1988 LM6.
LM6 alloy is actually an eutectic alloy having the lowest melting point that can be
seen from the Al–Si phase diagram. The main composition of LM6 is about 85.95%
of aluminium , 11% to 13% of silicon. It is widely used in many fabrication devices
due to its characteristics properties, such as the applications for motor housings,
manifolds, marine components and pumping cases. However, very limited studies
have been reported and so the information and the data available on the mechanical
properties
In term of strength at elevated temperatures, tensile strength and hardness of
LM6 decrease fairly regularly with increasing temperature and become relatively
poor at temperatures of the order of 250˚. LM6 exhibits excellent resistance to
corrosion under both ordinary atmosphere and marine conditions. LM6 can be
anodized by any of common processes, the resulting protective film ranging in colour
from grey to dark brown. The details of the LM6 alloy composition is shown in
Table 2.2.
18
Table 2.2: Percentage of composition LM6 (%)
2.6 Machining Parameters
There are varieties of parameters that can be used as factor in order to operate EDM
machine. However, there are a few common parameters that researcher always used
which are peak current, voltage, pulse on time and pulse off time. It was observed
that surface roughness of workpiece and electrode were influenced by pulsed current
and pulse time, higher values of these parameters increased surface roughness.
Lower current, lower pulse time and relatively higher pulse off time have produced a
better surface finish (Kiyak and Akir, 2007).
The machining performances depend on various EDM parameters (variables).
Wang and Yan , (2000) categorized the parameters into two groups :
1. Electrical Parameters
I. Polarity
II. Peak current
III. Pulse duration
IV. Power supply voltage
Composition Percentage (%)
Al 85.95
Cu 0.1
Mg 0.1
Si 12
Fe 0.6
Mn 0.5
Ni 0.1
Zn 0.1
Lead 0.1
Tin 0.05
Titanium 0.2
Others 0.2
19
2. Non electrical parameters
I. Rotational of speed electrode
II. Injection flushing pressure
In the other hand, Van Tri (2002) categorized the parameters into five groups:
I. Dielectric fluid which is type of dielectric, temperature, pressure,
flushing system.
II. Machine characteristics; servo system and stability stiffness,
thermal stability and accuracy.
III. Tool, material, shape, accuracy
IV. Work piece
V. Adjustable parameters; discharge current, gap voltage, pulse
duration polarity, charge frequency, capacitance and tool materials.
There are varieties of parameters that can be used as factor in order to operate
EDM machine. It was observed that surface roughness of workpiece and electrode
were influenced by pulsed current and pulse time, higher values of these parameters
increased surface roughness. Lower current, lower pulse time and relatively higher
pulse off time have produced a better surface finish (Kiyak and Akir, 2007). In this
project, the parameters that have been concerned are current, pulse on time, pulse off
time and voltage.
2.6.1 Current (A)
Pulse current is the amount of power used in discharge machining, measured in units
of amperage. In both vertical and wire applications, the maximum amount of
amperage is governed by the surface area of the “cut” the greater the amount of
surface area, the more power or amperage that can be applied. Higher amperage is
used in roughing operations and in cavities or details with large surface areas (Bud ,
1997). During EDM process, the average current is the average of the amperage in
the spark gap measured over a complete cycle. This is read on the ammeter during
the process. The theoretical average current can be measured by multiplying the duty
20
cycle and the peak current (maximum current available for each pulse from the
power supply or generator). Average current is an indication of the machining
operation efficiency with respect to material removal rate. The concept of maximum
peak amperage that can be applied to the electrode is an important factor (Adnan,
2001). Plus, very high currents are not used as they often lead to heat damage of the
work surface, the depth of the recast layer might not entirely clean up, the intense
heat generated can sink deeply into the surrounding areas of the work piece which
might undergo an uncontrolled heat treating or annealing process. The overcut will
be determined by the amount of current and the on time, but usually when elevated
temperatures are applied, it is an under size electrode which will leave sufficient
material to be removed later in subsequent finishing modes using less power and
orbiting, or by changing to larger, finishing electrodes (Adnan, 2001).
2.6.2 Pulse Duration Time/Pulse ON time (μs)
All the work is done during on time. The spark gap is bridged, current is generated
and the work is accomplished. The longer the spark is sustained more is the material
removal. Consequently the resulting craters will be broader and deeper. Therefore,
the surface finish will be rougher. Obviously with shorter duration of sparks the
surface finish will be better. With a positively charged work piece the spark leaves
the tool and strikes the work piece resulting in the machining. More sparks produce
much more wear. Hence, this process behaves quite opposite to normal processes in
which the tool wears more during finishing than roughing (Adnan, 2001).
2.6.3 Pulse Interval Time/Pulse OFF time (μs)
While most of the machining takes place during on time of the pulse, the off time
during which the pulse rests and the deionization of the die-electric takes place, can
affect the speed of the operation in a large way. More is the off time greater will be
the machining time. But this is an integral part of the EDM process and must exist.
The Off time also governs the stability of the process. An insufficient off time can
lead to erratic cycling and retraction of the advancing servo, slowing down the
operation cycle (Adnan, 2001).
21
Hussien et. al. (2008) have stated that the main parameter of EDM machining
which are voltage, peak current, and pulse off time were the most dominant factors
that effecting the material removal rate (MRR). While they found that peak current
and pulse on time were clearly effected electrode wear rate (EWR). Table 2.3 below
showed the machining parameter and levels of setting condition while conducting
EDM machine.
Table 2.3: Machining Parameter and Levels of Setting Conditions (Hussien et.
al. 2008)
Machining Parameter Setting Conditions
Electrode Polarity Positive
Work piece Polarity Negative
Dielectric Fluid Kerosene
Level
Low(-1) High(+1)
Voltage (V) 70 100
Peak Current (A) 3 9
Pulse on Time (µsec) 30 50
Pulse off Time (µsec) 30 50
Other than that, Wang et. al., (2000) used experiment condition with
workpiece material 3.2mm thickness and the tool electrode material is a kind of
carbide. The machine holes diameter is 0.2mm and the machining voltage is 100V.
The current limiting resistor is 330Ω and the gap capacitance is about 5000pF.
Karthikeyan (1999) have used three levels full factorial design for
experimentation and mathematical models with linear, quadratic and interactive
effects of the parameters was developed. Table 2.4 shows the process parameters and
their level in order to get the interaction between parameters and response which are
MRR, EWR and Ra.
22
Table 2.4: Process parameters and their levels, (Karthikeyan, 1999)
Process parameters Level
0 (low) 1(intermediate) 2(high)
Volume of SiC (%) 6 13 20
Current (A) 2.5 7.5 12.5
Pulse Duration (µs) 200 600 1000
Besides, Venkat et. al., (2011) was studied about influence of EDM process
parameters which are peak current, flushing pressure, pulse on time on Ra, MRR and
EWR by using AlSi10Mg as material based on Taguchi method. It was determined
that peak current was the most significant parameter influencing the responses
followed by pulse on time and flushing pressure. Table 2.5 shows the parameters and
their levels.
Table 2.5: Parameters and their levels, (Venkat et. al., 2011)
Level Peak Current, I
(A)
Flushing Pressure, P
(kg/cm2)
Pulse on time, Ton
(µs)
1 10 0.5 80
2 20 1.0 280
3 30 1.5 480
23
2.7 Summary
From all previous study and researched, found that in term of machining parameter,
some of the them said that there are four parameters that play important significant in
EDM machining process. They are voltage, peak current, pulse on duration and pulse
off time. These parameters give a huge effect on MRR, EWR, Ra, recast layer and
surface hardness which are the responses that need to measure. Based on the
objectives stated before, this research want to investigate the effect of voltage, peak
current, pulse on duration and pulse off time on the material removal rate
(MRR) ,electrode wear rate (EWR), surface roughness (Ra), recast layer and surface
hardness.
24
CHAPTER 3
METHODOLOGY
3.1 Introduction
In this chapter, the working procedure and method that have used were briefly
explained. There are some methodologies such as data collections, research study
and analysing the data to accomplish have describe the structure of the research
whereby it can be the guideline in managing. Besides that, the equipment, the
material and the machine involve in designing the experiment study had form and
state in this chapter. Start with project planning of this research, followed by design
of experiment (DOE), planning the matrix by using Taguchi method, discussed
about the material used and parameters setting. Besides, in this chapter, the
techniques and procedure of using the equipments have been discuss. All the steps
taken during the measuring data are recorded and analysed. Taguchi method with
design of experiment were the main technique to analyse the data with the clearly
graph plotted. Other than that, this chapter also briefly about the machine set up and
the measuring technique of every machine used. Lastly, end up with the EDM Die-
Sinking machine set up.