PERFORMANCE AND EVALUATION OF GRAPHITE WHEN MACHINING
HARDENED STEEL ASSAB 718
RADWAN AHMED SAEED AHMED
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
NOVEMBER 2009
iii
To My Beloved Father, Mother, Wife, Brothers,
Sisters and my Daughter
Last but not least to all the prayers, courage, and confidence and trust that
you all gave to me. May Allah bless all people that I love and it is my honor to share
this happiness with my loved ones.
iv
ACKNOWLEDGMENTS
First and foremost, I would like to express my deepest, sincerest gratitude to
my supervisors Associate Professor Dr izman sudin and Associate Professor
Hamidon Musa for their guidance and advice, without which I would never have
been able to accomplish the objectives of my project. Their intelligence and
determination have been a source of inspiration, their demands for quality and
perfection, a challenge which taught me lessons beyond the reach of my classroom
textbook.
Secondly, I would like to dedicate my thanks to all the technical staff at
Production Lab, Metrology Lab and Material Science Lab especially to En. Ali, En.
Aidid, En. Sazali, En.Ayub for lending me their help and support in completing this
project. Their time and patience for providing many useful advices and ideas through
the trials and tribulations during this project execution are very much appreciated.
Lastly, I would also like to express my special thanks to my wife, Mother and
my family members for believing in me and continuously supporting me throughout
this project. Last but not least, I would like to thank those who have contributed
directly or indirectly towards the success of this research study.
v
ABSTRACT
This project presents the machining of ASSAB718 hardened steel using
sinker electro-discharge machining involving two different graphite electrodes.
POCO EDM4 and POCO EDM200 The main purpose of this study was to
investigate the influence of various parameters on the machining characteristics,
namely, surface roughness (Ra), Material removal rate (MRR), Electrode wear rate
(EWR), and Microcracks depth after undergoing sinker EDM process. The Full
Factorial Design of Experiment (DOE) approach with two-levels was used to
formulate the experimental plan and, to analyze the effect of each parameter on the
machining characteristics four factors under study were pulse interval (A), pulse
duration on (R), peak current (P) and servo voltage (SV). Confirmation tests were
conducted for the optimum conditions for each machining characteristics in order to
verifying and comparing. Design Expert software was utilized to analyze the above
results. The, servo voltage and pulse of signal have appeared to be significant to all
responses investigated. Overall, the results from the confirmation tests showed that
the percentage of performance was acceptable due to all the results obtained were
within the allowable value which was less than 11% of margin error for EDM200
and 7.23% for EDM4 electrodes respectively.
vi
ABSTRAK
Projek ini mengkaji pemesinan keluli keras (ASSAB718) menggunakan
pemesinan nyahcas elektrik (EDM) melibatkan dua jenis elektrod grafit. Tujuan
utama kajian ini ialah untuk mengkaji pengaruh pelbagai parameter dalam EDM
pembenam acuan, iaitu kekasaran permukaan (Ra), kadar pembuangan bahan
(MRR), kadar kehausan elektod (EWR) dan kedalaman mikrorekahan selepas
melalui proses EDM pembenam acuan. Pendekatan reka bentuk eksperimen (DOE)
faktoran penuh melibatkan dua aras digunakan untuk menyediakan susun atur
eksperimen, untuk menganalisis pengaruh setiap parameter ke atas ciri pemesinan
dan untuk menganggarkan penetapan optimum bagi setiap parameter EDM iaitu sela
denyutan (A), tempoh denyutan on, (R), arus puncak (P), dan voltan servo (SV).
Ujian pengesahan juga dijalankan pada keadaan optimum bagi setiap ciri pemesinan
bertujuan untuk membanding dan mengesahkan keputusan anggaran secara teori
menggunakan perisian Design Expert. Dalam kajian ini, pemesinan dilakukan
menggunakan mesin EDM CNC jenis Roboform 100 (4 paksi). Pengukuran Ra pula
menggunakan Mitutoyo Formtracer CS-5000 dan kedalaman mikrorekahan diukur
menggunakan Mikroskop Imbasan Elektron XL40. Umumnya, keputusan yang
diperolehi menunjukkan yang denyutan on dan arus puncak adalah bererti terhadap
kesemua sambutan yang dikaji. Secara keseluruhannya, keputusan ujian pengesahan
boleh diterima kerana kesemua hasil memberikan jidar ralat kurang daripada 11%.
vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xi
LIST OF FIGURES
xiii
LIST OF SYMBOLS
xv
LIST OF APPEENDICES
xvi
INTRODUCTION
1.1
Introduction
1
1.2
Background of the Project
1
1.3
Problem Statement
2
1.4
Objective
3
1.5
Scope
3
1.6
Significance of study
4
1.7
Project Structure
4
viii
2
LITERATURE REVIEW
2.1
Introduction
5
2.2
EDM Die Sinking process:
6
2.2.1
Limitation of EDM
9
2.3
EDM Electrodes
9
2.4
3
2.3.1
Electrodes Material
10
2.3.2
Graphite Material
10
2.3.3
Graphite Grades within Classifications
11
EDM Machining Parameter
16
2.4.1
Discharge voltage:
17
2.5.2
Pulse (On-time) and pulse interval (Off)
18
2.5.3
Polarity
19
2.5.4
Electrode gap
20
2.5.5
Dielectric Fluid
20
2.5.6
Concentration of EDM
21
2.5.7
Type of dielectric flushing
23
2.5.8
Surface Finish
23
2.5.9
Surface Integrity
24
2.5.10 White Layer
25
2.5
Machining Characteristics
30
2.7
summary
32
METHODOLOGIES
3.1
Introduction
33
3.2
Research Methods and Procedures
33
3.1.2
Workpiece Material
36
3.2.2
Electrode Materials
36
3.2.3
Machining Parameters
37
3.3 4
Measuring of Responses
39
3.3.1
Volumetric relative wear
40
3.3.2
Material Removal rate (MRR)
40
3.3.3
Microcracks
41
3.3.4
Surface Roughness
41
ix
3.4
4
41
RESULTS AND DATA ANALYSIS
4.1
Introduction
46
4.2
Experimental Results EDM4
46
4.2.1
Machining Time
47
4.2.2
Weighing Process
48
4.2.3
Surface Roughness
49
4.2.4
Microcracks
50
4.2.5
ANOVA Analysis
51
4.3
4.4
5
Experimental Equipment
4.2.5.1 Analysis Results for Ra
52
4.2.5.2 Analysis Results for MRR
54
4.2.5.3 Analysis Results for EWR
56
4.2.5.4 Analysis Results for Microcracks
58
4.2.6
60
Confirmation Tests
4.2.6.1 Comparison Tests for EDM4
61
4.2.7
62
Comparison of Test Results for EDM4
Experimental Results EDM200
64
4.3.1
Weighing Process
64
4.3.2
Microcracks
65
4.3.3
ANOVA Analysis
66
4.3.3.1 Analysis Results for Ra
67
4.3.3.2 Analysis Results for MRR
69
4.3.3.3 Analysis Results for EWR
71
4.3.3.4 Analysis Results for Microcracks
73
4.3.4
Confirmation Tests for EDM200
76
4.3.5
Comparison of Test Results for EDM200
77
summary
78
DISCUSSIONS
5.1
Introduction
78
5.2
Surface Roughness, Ra
79
x
6
5.3
Material Removal Rate MRR
79
5.4
Electrode Wear Rate EWR
80
5.5
Microcracks
80
5.6
Summary
81
CONCLUSIONS
6.1
Conclusions
82
6.2
Recommendations
84
REFERENCES
85
Appendices A-E
88-114
xi
LIST OF TABLES
NO.
TITLE
PAGE
2.1
POCO Graphite grade EDM4
12
2.2
Graphite electrode weights
13
2.3
Classification of EDM Graphite Electrodes
14
2.4
Specification of electrodes
16
2.5
peak current and pulse duration effect to work machined surface
27
2.6
sinking EDM parameters affect the surface integrity of hardened steel
28
2.7
sinking EDM parameters affect the tool wear of hardened steel
29
3.1
Classification for the material to be used in the experiment
36
3.2
electrode properties
37
3.3
General machining parameter
38
3.4
The parameters and the value used in experiment
39
4.1
Machining Time when using EDM4, EDM200
47
4.2
Weighing of workpiece (lift) and Weight of EDM$ electrode (right)
48
4.3
MRR &EWR for Electrode EDM4
49
4.4
Surface Roughness (Ra) for Electrodes EDM4 and EDM200
50
4.5
Machining response results for Electrode EDM4
51
4.6
ANOVA for surface roughness, Ra
52
xii
4.7
ANOVA for Material Removal Rate MRR
54
4.8
ANOVA for Electrode Wear Rate EWR%
57
4.9
ANOVA for Microcracks
59
4.10
Quality characteristics of the machining performance.
61
4.11
Confirmation test results for surface roughness, Ra)
61
4.12
Confirmation test results for Microcracks
61
4.13
Confirmation test results for Material Removal Rate MRR.
62
4.14
Confirmation test results for Electrode Wear Rate EWR %.)
62
4.15
Comparison test results for all responses. EDM 4
63
4.16
Weighing of workpiece (lift) and Weight of EDM200 electrode (right)
64
4.17
MRR &EWR for Electrode EDM4
65
4.18
Machining response results for Electrode EDM200
66
4.19
ANOVA for surface roughness, Ra
67
4.20
ANOVA for surface roughness, MRR.
70
4.21
ANOVA for Electrode Wear Rate (EWR %)
72
4.22
ANOVA for Microcracks
74
4.23
Quality characteristics of the machining performance200.
76
4.24
Confirmation test results for surface roughness, Ra.
76
4.25
Confirmation test results for microcracks
76
4.26
Confirmation test results for Material Removal Rate MRR
77
4.27
Confirmation test results for Electrode Wear Rate EWR%
4.28
Comparison test results for all responses.EDM200
78
5.1
The comparison of setting parameters with previous researchers
92
.
77
xiii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
CNC EDM Die Sinking Machine Roboform 100 (4 Axis)
6
2.2
The Process die sinking1
8
2.3
The Process die sinking2
8
2.4
The Process die sinking3
8
2.5
EDM4 specification
15
2.6
EDM200 specification
15
2.7
List of process factors for EDM
17
2.8
Actual profile of a single EDM pulse
18
2.9
jet flushing using flushing nozzles
21
2.10
Structure material layers
26
2.11
Sparking gap
31
3.1
Overall summary of Research Methodology
34
3.2
The view of work piece
36
3.3
Electrode cross-section view
37
3.4
CNC EDM Die Sinking Machine Robform 100 (4 Axes)
42
3.5
The Digital Rockwell Hardness Tester machine
42
3.6
Formtracer CS - 5000 Mitutoyo
43
3.7
High Power Optical Microscope – Zeiss Axiotech
43
3.8
Balancer device
44
3.9
MECATONE T201A
44
3.10
The sand grind and the polish machine
45
4.1
Half Normal probability plots for Ra EDM4
53
4.2
Main Interactions for Ra EDM4
53
4.3
Half Normal probability plots for MMR EDM4
55
xiv
4.4
Interaction plot for MMR EDM4
56
4.5
Half Normal probability plots for EWR%. EDM4
57
4.6
Interaction plot for EWR%. EDM4
58
4.7
Half Normal probability plots for Microcracks EDM4
59
4.8
Interaction plot for microcracks EDM4
60
4.9
Half Normal probability plots for Ra.EDM200
68
4.10
Interaction plot for Ra EDM200
69
4.11
Half Normal probability plots for MRR. EDM200
70
4.12
Interaction plot for MRR EDM200
71
4.13:
Half Normal probability plots for EWR% EDM200
72
4.14:
Interaction plot for EDM200
73
4.15
Half Normal probability plots for Microcracks EDM200
75
4.16
Interaction plot for EDM200
75
xv
LIST OF SYMBOLS
EDM
-
Electrical Discharge Machining
WEDM
-
Wire Electrical Discharge Machining
MRR
-
Material Removal Rate
EWR
-
Electrode Wear Ratio
Ra
-
Surface Roughness
LMC
-
Length of Microcracks
SEM
-
Scanning Electron Microscopy
V
-
Machining Voltage
P
-
Peak Current
A
-
Pulse Duration (On-time)
R
-
Pulse Interval Time (Off-time)
CNC
-
Computer Numerical Control
DOE
-
Design of Experiment
ASSAB718
Hardened Steel Working Material, ASSAB Steel Grade
EDM4, 200
Electrode Grade Level
We
Weight of Electrode
Wm
Weight of Working Material
xvi
LIST OF APPENDICES
APPENGIXS
TITLE
PAGE
References
98
A
The overall results for surface roughness EDM4
103
B
The overall results for surface roughness EDM200
109
C
The overall results for Microcracks structure EDM4
115
D
The overall results for cracks structure EDM200
122
1
CHAPTER 1
INTRODUCTION
1.1
Introduction
This chapter discusses the basic ground of the project. It is followed by
Problem statement, project objective, scopes and finally project structure.
1.2
Background of the Project
Electrical discharge machining, commonly known as EDM, is a process that
is used to remove metal through the action of an electrical discharge of short duration
and high current density between the tool and the work piece. There are no physical
cutting forces between the tool and the workpiece involved. EDM has proved
valuable especially in the machining of super-tough, electrically conductive materials
such as the new space-age alloys. It can be used to produce parts with intricate shape
that is impossible when using conventional cutting tools.
2
This machining process is continually finding further applications in the
metal machining industry. It is being used extensively in the plastic industry to
produce cavities of almost any shape in metal moulds. Other applications include
production of critical parts for aerospace, electronics and medical industries.
Although the application of EDM is limited to the machining of electrically
conductive work piece materials, the process has the capability to cut these materials
regardless of their hardness or toughness (Li Li, Y.S. Wong January 2001)
In recent years, EDM researchers have explored a number of ways to improve
the sparking efficiency including some unique experimental concepts that depart
from the EDM traditional sparking phenomenon. Despite a range of different
approaches, this new research shares the same objectives of achieving more efficient
metal removal coupled with a reduction in tool wear and improved surface quality
.Research areas in EDM fall under three major headings. The first relates to
machining performance measures such as material removal, tool wear and surface
quality (SQ). The second area describes the effects of process parameters including
electrical and non-electrical variables, which are required to optimize the stochastic
nature of the sparking process on the performance measures. Finally, research
concerning the design and manufacture of electrodes has also been reported (S.T.
Newman 2003)
1.3
Problem Statement
EDM is commonly used in tool, die and mould making industries for
machining heat-treated tool steel materials. The heat-treated tool steel material falls
in the difficult-to-cut material group when using conventional machining process.
3
1) Comparing the Performance of POCO EDM4 and POCO EDM200 electrodes
from material removal rate MRR, electrode wear rate EWR, achievable
roughing surface finish and Microcracks.
2) To evaluate the optimal condition for each electrode. by using DOE soft wear
and conformations tests
1.4
Objectives
The objectives of this research were:
1. To evaluate the performance of sinker electro-discharge machine(EDM)on
hardened steel(ASSAB718)
2. To evaluate the performance of graphite electrode in term of surface
roughness, material removal rate, electrode wear rate and microcracks
1.5
Scope
The scopes of this project were limited to the following
1. Workpiece material used was hardened steel ASSAB 718 with hardness up to
59 HRC
2. Electrode material was limited to two types of graphite materials.
4
3. Variable machining parameters were limited to current, voltage, pulse off/on
and pulse width while other parameters were fixed.
4. Chermill Robofirm 100 Electrical discharge machine EDM die sinking were
used. for conducting experimental.
1.6
Significance of study
The current study focused on the evaluation of the performance of graphite
electrodes when machining hardened steel material. It was hoped that the findings
could be used by industrial practitioners to select the most suitable cutting
parameters for hardened steel and realizing its economic potential to the fullest.
Generally, the significance of study can be summarized by the following
points:
1. Better understanding of graphite electrode behaviors when machining
hardened steel at various conditions.
2. Information gathered from the study becomes useful especially for die and
mould making industries to consider graphite as a candidate for replacing
copper electrode particularly for varying works
1.7
Project Structure
This project were include about six chapters with references and appendixes
were all illustrated in the contents
5
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
This chapter discusses the effects of EDM machining parameters and the
working principle of each EDM parameters.
2.2
EDM Die Sinking Process
The electrical discharge process is based on thermal effects; electrical
discharges between two electrodes, the tool and the work-piece have material
removing potential. Electro-discharge machining (EDM) is a widely used method for
shaping conductive materials. EDM removes material by creating controlled sparks
between a shaped electrode and an electrically conductive work piece. As part of the
material is eroded, the electrode is slowly lowered into the work piece, until the
resulting cavity has the inverse shape of the electrode. Dielectric fluid is flushed into
6
the gap between the electrode and work piece to remove small particles created by
the process and to avoid excessive oxidation of the part surface and the electrode.
The applications of EDM lie mainly in the tooling industry where it is applied
on materials which are too hard to be machined with conventional techniques, such
as milling or turning. The parts for these applications are usually larger than 1 mm;
therefore conventional methods can be applied for fabricating the electrodes. Due to
the fact that EDM can achieve very fine surface finishes, it has been trialed in the
micromachining of conductive materials. For this purpose, two grades of graphite
electrodes (EDM4 and EDM200) are used with CNC EDM Die Sinking Machine
Rob form 100 (4xis) have been used as die-sinking electrodes.
Figure 2.1 shows the EDM die sinking machine that available at Universiti
Teknologi Malaysia (UTM).
Figure 2.1: CNC EDM Die Sinking Machine Rob form 100 (4 Axis)
During the EDM process, a series of non-stationary, timed electrical pulses
remove material from a work piece. The electrode and the work piece are held by the
7
machine tool, which also contains the dielectric. A power supply controls the timing
and intensity of the electrical charges and the movement of the electrode in relation
to the work piece. At the spot where the electric field is strongest, a discharge is
initiated. Under the effect of this field, electrons and positive free ions are
accelerated to high velocities and rapidly form an ionized channel that conducts
electricity.
The plasma zone quickly reaches very high temperatures, in the region of
8,000 to 12,000' Centigrade, due to the effect of the ever-increasing number of
collisions; this causes instantaneous local melting of a certain amount of the material
at the surface of the two conductors. When the current is cut off, the sudden
reduction in temperature causes the bubble to implode, which projects the melted
material away from the work piece, leaving a tiny crater,
The eroded material then re-solidifies in the dielectric in the form of small
spheres and is removed by the dielectric. All this without the electrode ever touching
the work piece Making EDM a no-contact machining process allowing you to
achieve tighter tolerances and better finishes in a wide range of materials that are
otherwise difficult or impossible to machine with traditional processes.
The physical principle working of EDM can be explained as EDM machining
is performed, as an electric sparks who jump between two electrodes subjected to a
given voltage in the submerged of insulating liquid (dielectric fluid). Figures 2.2, 2.3
and 2.4 show how the electricity used to machining the electrode materials. Since the
two electrodes are in a dielectric or insulating medium, the voltage applied to them
must be sufficient to create an electric field which is greater than the dielectric
rigidity of the fluid.
8
Figure 2.2: The process of die sinking
As a result of the action of this electrical field, free positive ions and electrons
are accelerated, creating a discharge channel which becomes a conductor, and it is
precisely at this point where the spark jumps. This causes collisions between the ions
(+) and the electrons (-). A channel of plasma is thus formed.
Figure 2.3: The process of die sinking
These collisions create high temperatures in both poles and a ball of gas is
formed around the plasma channel, which begins to grow. At the same time, the high
temperatures in the two poles melt and vaporize part of the material of the part, while
the electrode itself suffers only very slight wear.
Figure 2.4: The process of die sinking
9
2.2.1
Limitation of EDM
Clearly, the benefits of EDM are considerable, and it is often appropriate to
EDM instead of using conventional manufacturing processes. Below show some of
the restrictions of EDM:
i.
EDM tapering: The maximum taper angle is ±45 degrees. The maximum
height/angle is 30 degrees at 40.64 cm high. In the maximum electrical
resistance for work piece and fixture is approximately 0.5-5.0 ohm centimeter
for sinker EDMs.
ii.
The accuracy of an EDM is limited to about ±0.00245mm(2.5µm)
iii.
Surface finish is about (5.08 micro meter) for EDMs sinkers.
2.3 EDM Electrodes
The EDM electrodes are the important component in this process. This is
because of the reaction between the work piece and the electric currents through this
electrode. These electrodes should be a conductor of electricity so that they can
conduct this current from the machine to the work piece. The shape of this electrode
will affect the shape of the product. In this study round shape electrodes are used for
experimental involving copper electrode and square shape for electrode graphite.
The basic characteristics need for electrodes:
i.
Good conductors of electricity and heat
ii.
Easily machined to shape that is needed
iii.
Produce efficient metal removal from the work piece
iv.
Resist deformation during the erosion process
v.
Exhibit low electrode (tool) wear rates
10
2.3.1
Electrodes Materials
Electrical discharge machining (EDM) is a non-conventional machining
process where material is removed electro-thermally by a series of successive
discrete discharges or sparks between two electrically conductive objects, i.e., the
electrode and the machined work piece. The performance of the EDM process, to a
large extent, is dependent on the material and the design of the electrodes. EDM
electrode material must have basic properties such as electrical and thermal
conductivity, a high melting temperature, low wear rate, and resistance to
deformation during machining.
In general, the electrode is the ―cutting‖ tool in the EDM process. With
normal EDM machining applications, the work piece is the positive terminal of the
power supply and called anode. The electrode, called the cathode is the negative
terminal. The size and shape of the electrode determines the size and shape of the
work piece produced with the clearance that existed.
2.3.2
Graphite Materials
One of the electrodes used is graphite. Graphite is a crystalline form of
carbon having a layered structure of basal planes or sheets of close-packed carbon
atoms. Although brittle, graphite has high electrical and thermal conductivity and
resistance to thermal shock and high temperature [although it begins to oxidize at
500°C (930°F)]. It is therefore an important material for application such as
electrodes, heating elements, brushes for motors, high-temperature fixtures and
furnace parts, mold material such as crucibles for melting and casting of metals, and
seals (because of low friction and wear). Unlike other materials, the strength and
stiffness of graphite increase with temperature. This material is available in many
different grades from large grain sizes (200 μm), used in rough EDM operations, to
11
very fine grains (1 μm) for finish EDM operations, particularly in steel. The costs of
graphite vary from inexpensive, for coarse-grain sizes, to very expensive for finegrain sizes. It provides a high material removal rate and low electrode wear depending on the EDM parameter settings - as compared to metallic electrodes. At
the present there is a trend to incorporate the entire geometrical configuration of the
work piece onto a single large electrode, instead of partitioning the tool in many
small pieces. Thus, the weight of the electrode becomes very important because it
affects many factors in handling construction and use of the electrode. Graphite has a
much lower density than copper, which makes it the best material for large
electrodes. Although graphite is very abrasive it is relatively easy to be machined by
all the conventional machining processes. Milling, drilling, turning, grinding and
ultrasonic machining provide excellent finishes in graphite. The major drawback of
graphite is the fine dust it produces during its machining. It is able to settle on the
guides of the machine tool and when mixed with the machine's cutting fluid it will
act like a lapping compound, which eventually reduces the accuracy of the machine.
Precautions must be taken when machining graphite.
3.3.3
Graphite Grades within Classifications
The physical properties of each grade of graphite determine the ranking
within classifications. The properties that influence performance are particle size,
flexural strength and shore hardness. These properties along with a photomicrograph
of the microstructure are the best tools for predicting graphite performance.
The best graphite in any classification has tightly packed particles with little
variation in size. This kind of uniform material resists wear caused by the thermal
nature of the EDM process. Particle size is generally stated as an average size. When
particle size spans a small range, the microstructure of the material becomes more
uniform with reduced porosity. The porosity in the graphite is boundary between
12
particles. The particles are bound together by chemical or mechanical means and the
failure of this system is what releases particles into the gap when EDMing. If the
material's particles are small, uniform in size and tightly packed, erosion of the
electrode is minimal. Particle size has a bearing on the minimum surface finish that
the material will produce. Since the electrode reproduces its structure in the cavity,
fine surface finishes cannot be obtained with graphite grades that have large particle
and non-uniform microstructure. [www.moldmakingtechnology.com].
The following tables 2.1 and 2.2 shows the different grade of EDM machined
with proper suitable graphite electrode types, according to POCO Graphite
Production:
Table 2.1 POCO GRAPHITE GRADE
13
Table 2.2 Graphite Electrode Weights
a) EDM Graphite Electrodes
Graphite is isotropic, very fine grain graphite with high strength, high density,
electrical conductivity, providing high metal removal rate, excellent surface finish,
and high resistance to electrode wear makes it an excellent EDM electrode material.
Spark Graphite is light in weight, dimensionally stable and is easily machining into
any size or shape from larger size EDM graphite electrode to thin and intricate EDM
graphite electrodes.
14
Table 2.3 Classification of EDM Graphite Electrodes
Classification of EDM
Graphite Electrodes
Fine
Application
Large Forging Dies, Die Casting Dies and Plastic Moulds.
Precision Forging Dies , Die Casting ,Plastic Moulds,
Superfine
Rubber & Glass Moulds
Very precision - Threading Electrodes, Engraving,
Ultrafine
Stamping Dies & Aerospace Applications
Fine detailed Engraving electrodes, Delicate electrode &
Angstrofine
intricate Mould and Dies
PRODUCT SPECIFICATIONS OF POCO GRAPHITE
Grade
Average Flexurl Compres
Classification Particle Strength Strength
Size
(psi)
(psi)
Electrical
Hardness Resistivity
(Shore)
Microohm/inch
EDMAF5
Angstrofine
<1
17,000
27,000
87
680
EDMC3
Ultrafine
<5
16,500
30,000
67
120
EDM-4
Ultrafine
<4
15,800
23,000
76
500
EDM-3
Ultrafine
<5
13,500
21,500
76
540
EDM-2
Ultrafine
<5
10,000
18,000
73
620
EDM-1
Ultrafine
<5
7,500
15,000
70
740
EDM200
Superfine
10
9,000
16,000
64
480
EDMC200
Superfine
10
13,000
23,000
60
70
EDM150
Fine
14
7,800
14,500
68
570
EDM100
Fine
20
6,500
12,500
58
480
COA
PHI
15
b) EDM-4
4
Poco‘s EDM-4 is the premier offering in the ultrafine grain classification.
This highly isotropic grade combines extraordinary strength with moderate hardness,
yielding superior electrode fabrication characteristics. EDM-4 has superior EDM
performance characteristics for metal removal rates, wear and surface finish.
c) Superfine-Graphite-EDM-200
Poco's EDM-200 is anisotropic superfine particle graphite providing good
strength, surface finish, and wear resistance. Moderately priced, EDM-200 provides
excellent repeatability from electrode to electrode and from job to job. Table 2.3 and
Figure2.5, 2.6 below shows the specification of the graphite electrode
Figure 2.5 EDM4 specification
Figure 2.6 EDM200 specification
16
Table 2.4: Specification of electrodes
Physical properties
EDM4
EDM200
Electrical resistivity (μΩ/inch)
500
480
Hardness ss (shore)
76
64
Compressive vies strength (psi)
23000
16000
Melting point (°C)
3350
3125
Flexural strength (µsec)
15800
9000
classification
ultrafine
Super
fine
Coefficient of thermal expansion (×10 −6 °C−1) 7.8
2.4
6.9
EDM Machining Parameter
Generally, EDM parameters are categorized into two groups which have
electrical and non-electrical parameters. The electrical parameters comprise of
polarity, peak current, pulse duration and power supply voltage. The non-electrical
parameters include circumferential speed of the electrode, reciprocating speed, gap
size and flushing of dielectric. According to Mohd. Amri the electrical group usually
has more significant affects to the machining characteristics than non-electrical
group. This is based on his research that showed the most significant parameter in
machining tungsten carbide is pulse duration, followed by machining voltage, peak
current and interval time.
By referring to figure 2.7 there are many factors that can affect machining
characteristics in EDM process found by previous researcher ,however, in this study
the emphasis will be given more on the electrical parameters only such as machining
voltage, peak current, pulse duration (on-time) and interval time (off-time).
17
Figure 2.7 List of process factors for EDM.
Furthermore, many researchers also have suggested that it is more desirable
and economical to familiar with parameters that would control the machining process
before planning and designing the machining process. Therefore, in order to have
better understanding of EDM parameters, they are briefly explained as below based
on reports and journals written by former researchers:
2.4.1
Discharge voltage
Discharge voltage in EDM is related to the spark gap and breakdown strength
of the dielectric (Kansal.italic 2005). Before current can flow, the open gap voltage
increases until it has created an ionization path through the dielectric. Once the
current starts to flow, voltage drops and stabilizes at the working gap level. The
preset voltage determines the width of the spark gap between the leading edge of the
electrode and work piece. Higher voltage settings increase the gap, which improves
the flushing conditions and helps Fig.2.8
Actual profile of a single EDM pulse (Fuller, 1996).To stabilizes the cut.
MRR, tool wear rate (TWR) and surface roughness increases, by increasing open
circuit voltage, because electric field strength increases. However, the impact of
changing open circuit voltage on surface hardness after machining has been found to
be only marginal.
18
Figure 2.8 Actual profile of a single EDM pulse
2.4.2
Pulse duration (On-time) and pulse interval (Off-time)
Each cycle has an on-time and off-time that is expressed in units of
microseconds. Since all the work is done during on-time, the duration of these pulses
and the number of cycles per second (frequency) are important. Metal removal is
directly proportional to the amount of energy applied during the on-time (Singh
italic. 2005).
This energy is controlled by the peak amperage and the length of the on-time.
Pulse on-time is commonly referred to as pulse duration and pulse off-time is called
pulse interval. With longer pulse duration, more work piece material will be melted
away. The resulting crater will be broader and deeper than a crater produced by
shorter pulse duration. These large craters will create a rougher surface finish.
Extended pulse duration also allow more heat to sink into the work piece and spread,
which means the recast layer will be larger and the heat affected zone will be deeper.
However, excessive pulse duration can be counter-productive. When the
optimum pulse duration for each electrode—work material combination is exceeded,
19
material removal rate starts to decrease. A long duration can also put the electrode
into a no-wear situation. Once that point is reached, increasing the duration further
causes the electrode to grow from plating build-up. The cycle is completed when
sufficient pulse interval is allowed before the start of the next cycle.
Pulse interval will affect the speed and stability of the cut. In theory, the
shorter the interval, the faster will be the machining operation. But if the interval is
too short, the ejected work piece material will not be swept away by the flow of the
dielectric and the fluid will not be deionizer. This will cause the next spark to be
unstable. Unstable conditions cause erratic cycling and retraction of the advancing
servo. This slows down cutting more than long, stable off-times. At the same time,
pulse interval must be greater than the deionization time to prevent continued
sparking at one point (Fuller, 1996), typical ranges are from 2to 1000 second.
Therefore, the selection of EDM parameters is important in determining and
getting the accuracy and surface finish for a particular application, all the pervious
parameters descried can be adjusted either the manually or by using CNC control
unit or programmable controllers.
2.4.3
Polarity
The polarity of the electrode can be either positive or negative. The current
passing through the gap creates high temperatures causing material evaporation at
both electrode spots. The plasma channel is composed of ion and electron flows. As
the electron processes (mass smaller than anions) show quicker reaction, the anode
material is worn out predominantly. This effect causes minimum wear to the tool
electrodes and becomes of importance under finishing operations with shorter ontimes. However, while running longer discharges, the early electron process
predominance changes to positron process (proportion of ion flow increases with
20
pulse duration), resulting in high tool wear. In general, polarity is determined by
experiments and is a matter of tool material, work material, current density and pulse
length combinations.
2.4.4
Electrode gap
The tool servo-mechanism is of considerable importance in the efficient
working of EDM, and its function is to control responsively the working gap to the
set value. Mostly electro-mechanical (DC or stepper motors) and electro-hydraulic
systems are used, and are normally designed to respond to average gap voltage. The
most important requirements for good performance are gap stability and the reaction
speed of the system; the presence of backlash is particularly undesirable. The
reaction speed must be high in order to respond to short circuits or open gap
conditions. Gap width is not measurable directly, but can be inferred from the
average gap voltage (Crook all and Heuvelman, 1971).
2.4.5
Dielectric Fluid
The EDM setup consists of a power supply whose one lead is connected to
the work piece immersed in a tank having dielectric coil. The tank is connected to a
pump, oil reservoir, and a filter system. The pump provides pressure for flushing the
work area and moving the oil while the filter system removes and traps the debris in
the oil. The oil reservoir restores the surplus oil and provides a container for draining
the oil between the operations as shown in figure 2.9.
21
(a)
(b)
Figure 2.9 Jet flushing using flushing nozzles
The main functions of the dielectric fluid are:
i.
To flush the eroded particles produced during machining, from the discharge
gap and remove the particles from the oil to pass through a filter system.
ii.
To provide insulation in the gap between the electrode and the work piece.
iii.
To cool the section that was heated by the discharge machining.
For most EDM operations kerosene is the common die electric used with
certain additives that prevent gas bubbles. Silicon fluids and mixture of these fluids
with petroleum oils have excellent results.
2.4.6
Concentration of EDM
Flash point: This is the temperature at which the vapors of the fluid will
ignite. This explanation is a little simplistic as conditions for testing are more
involved but for the sake of discussion and safety‘s sake, the higher this number, the
better.
22
Dielectric strength: This is the ability of the fluid to maintain high resistivity
before spark discharge and in turn the ability to recover rapidly with a minimal
amount of OFF time. Oil with a high dielectric strength will offer a finer degree of
control throughout the range of frequencies used, especially those used when
machining with high duty cycles or poor flushing conditions. This will provide for
better cutting efficiency coupled with a reduced potential arcing.
Viscosity: The lower the viscosity of the fluid the better is the accuracy and
finishes that can be obtained. In mirror finishing or close tolerance operations, spark
gaps can be as small as 0.005 or less. With such tight, physical restrictions such as
this, it is much easier to flush small spark gaps with lighter and thinner oil. Good
finishing EDM oils are on the thin side.
Specific gravity: Often confused with viscosity, this is the ―weight‖ of a
substance measure by a hydrometer. The ―lighter‖ the oil or lower its specific
gravity, faster the heavier particles (chips) settle down. This reduces the gap
contamination and possibilities of secondary discharge and/or arcing.
Color: All dielectric oils will eventually darken with use, but it seems only
logical to start with a liquid that is as clear as possible to allow viewing of the
submerged part. Clear or ―water-white‖ should be your choice, because any fluid that
is not clear when brand new certainly contains undesirable or dangerous
contaminants.
Preventive Maintenance: Depending on the use of the oil and maintenance
the oils can last several years. Regularly filtered oil prevention of water
contamination will extend its useful life considerably. Water contamination cannot
be eliminated completely as condensation will occur on the electrode surface when
the surface heats up. Graphite electrodes will contribute more to the condensation
than the metallic electrodes as they have a porous structure and absorb moisture from
23
the air. That is the reason why the graphite electrodes should be stored in dry areas.
Some shops will keep the electrodes in dry ovens the night before they are used.
2.4.7
Type of dielectric flushing
Basic characteristics required of a dielectric in EDM are high dielectric
strength and quick recovery after breakdown, effective quenching and flushing
ability. TWR and MRR are affected by the type of dielectric and the method of its
flushing (Wong et al., 1995). Most dielectric fluids are hydrocarbon compounds or
water. Demonized water is used for wire-EDM and high precision die-sinking
because of its low viscosity and carbon-free characteristics. The dielectric fluid is
flushed through the spark gap to remove gaseous and solid debris during machining
and to maintain the dielectric temperature well below its flash point. A control
feature that is available on many machines to facilitate chip removal is vibration or
cyclic reciprocation of the servo-controlled tool electrode to create a hydraulic
pumping action. Orbiting of the tool or work piece has also been found to assist
flushing and improve machining conditions (Levy and Ferroni, 1975).
2.4.8
Surface Finish
During each electrical discharge, intense heat is generated, causing local
melting or even evaporation of the work piece material. With each discharge, a crater
is formed on the work piece and a smaller crater is formed on the tool electrode. Of
the molten material produced by the discharge, only 15% or less is carried away by
the dielectric [Serope Kalpakjian, (1992)]. The remaining melt re-solidifies to form
an undulating terrain. After magnification, the surface is observed to be covered with
overlapping craters, globules of debris, and pockmarks or ‗chimneys‘, formed by
entrapped gases escaping from the re-deposited material.
24
The crack formation usually occurred due to the development of high thermal
stresses exceeding the ultimate tensile strength of the material, as well as with plastic
deformation [Mohd. Amri, L. (2002). - Sandvik CIC Rolls]. According to Lee et al.
[V.García Navasa] cracks normally exist in the recast layer, initiating at its surface
and traveling down perpendicularly towards the parent material. In the vast majority
of cases, the cracks terminate within the white layer or just on the interface of the
white layer and the parent material. Sometimes the cracks also may observe within
the crater as the result of thermal stress during discharge. It has been observed that
the occurrence and the extension of the cracks can be greatly influenced by choosing
suitable operating conditions [Earaerts, W. (2004).].
2.4.9
Surface Integrity
Surface integrity is defined as the inherent or enhanced condition of a surface
produced in a machining or other surface generating operation. The nature of the
surface layer has been found in many cases to have a strong influence on the
mechanical properties of the part. This association is more pronounced in some
materials and under certain machining operations. Surface integrity has two
important parts. The first is surface texture, which governs principally surface
roughness, which essentially is a measure of surface topography. This subject has
been and being pursued by many investigators. The second is surface metallurgy
which is a study of the nature of the surface layer produced in machining. Surface
integrity of a surface produced by a metal removal operation includes the nature of
both surface topography as well as surface metallurgy on the mechanical and
physical properties of a material in its chosen environment.
Typical surface integrity problems include:
i.
Grinding burns on high strength steel landing gear components.
ii.
UN tempered marten site in drilled holes.
iii.
Effect of cutting fluid on the stress corrosion properties of titanium.
iv.
Grinding cracks in root section of cast nickel base gas turbine buckets.
25
v.
Lowering of fatigue strength of parts processed by EDM or ECM.
vi.
Distortion of thin components.
vii.
Residual stress induced in machining and its effect on distortion, fatigue, and
stress corrosion.
Surface integrity broadly defined not only topological (geometric) features of
surfaces and their physical and chemical properties, but also the metallurgical and
mechanical state of the machined surface. It‘s can be assessed using micro hardness
measurements
or
micro
structural
analyses
which
reveal
cracks,
phase
transformation, melted and re-deposited layers and similar features. Surface integrity
is an important consideration in manufacturing operations because its influences
properties, such as fatigue strength, resistance to corrosion and service life.
Several defects produced during manufacturing operation these defects are
usually caused by combination of factors, such as:
i.
Defect in the original material, caused by a casting or metal working process
ii.
The method by which the surface is produced
iii.
Lack of proper control of process parameter, which can result in excessive
stresses, excessive temperature or surface deformation.
2.4.10 White Layer
White layer also known as recast layer that occur in EDM machining because
of the machining parameters used in experiment. Due to thermal nature of the electro
discharge machining process, a heat-affected zone, consisting of several layers is
created at the surface of the work piece. The white layer includes some particles resolidified on the surface and not flushed away. This material was taken to the molten
state but neither ejected nor removed by the flushing action of the dielectric.
26
According to [Luo, Y. F. and Mater, J. (1998) Process Technology] under the
white layer, other layers may be seen, and the number of layers differs from sample
to sample also reported that a white layer has been observed to form under all
machining conditions even when using water as dielectric, though this white layer
differs from the one found on samples machined in an oil dielectric. The average
thickness of the white layer decreases with a decrease in energy. The thickness of the
layer also appears thicker when machining with a graphite electrode as compared
when machining with a copper electrode.
Due to high temperature during EDM process, a molten pool is formed at the
surface of the work piece and the dielectric takes place resulting in diffusion carbon
in the material. This carbon goes into solution in the molten metal. The iron and the
carbon combine to form iron carbides, which solidify in dendrite structures, oriented
along the direction of the highest cooling gradient, which is perpendicular to the
surface. This phenomenon leads to a significant increase in the micro hardness value
of the white layer. Based on the findings of the different workers, it is found that
irrespective of the EDM machining conditions used (such as pulse current and pulse
on-time) the occurrence of the white layer depends on two main factors, namely, the
initial carbon content of the work piece and the type of dielectric fluid used. If these
two conditions are met, then the resulting thickness of the white layer will depend
upon the magnitude of the pulse energy (pulse current and/or pulse on-time). The
white layer or recast layer shown on figure 2.11
Figure 2.10 Structure material layers
27
i.
A summary of previous researchers regarding the effects of EDM parameters
on the surface roughness on various types of steel is shown in Table 2.5.
Table 2.5 Peak current and pulse duration effect to work machined surface
EDM process
and electrode
types
Lee S H and Die sinking
Ki X P(2001) Graphite,
copper and
[Lee, S.H.
and Li, X.P. copper
tungsten.
(2001).]
Author
(Year)
Mohd Amri
(2002)
[Lauwers,
B., Liu, W.
and
Earaerts, W.
(2004).]
Puerto‘s et
al.
(2004)
[C.F. Hu
Y.C. Zhou ,
Y.W. Bao
(2006).‖]
work piece
Steel (en31)
Findings
i) For all three electrodes used the surface
roughness of the work piece increases
with the increasing peak current.
ii) Copper exhibits the best performance
with regard of surface finish and graphite
is the poorest.
iii) The negative tool polarity gives better
surface roughness.
iv) Surface roughness increase with the
increase of open-circuit voltage, peak
current and pulse duration.
.
i) To obtain minimum surface roughness
(Ra), minimum voltage and peak current
coupled with maximum pulse duration
and interval time.
ii) For higher surface roughness, must
inverse the parameters.
iii) The results showed peak current have
the major influenced to Ra, followed by
interval time, machining voltage and pulse
duration.
iv) Optimal machining parameters for Ra
are machining voltage -120 V, peak
current 8 A, pulse duration 50 µm and
interval time 800 µm,
Die sinking
Graphite:
(ELLOR30)
negative
polarity,
Ø 9 mm
AISI P20
tool steel
Die sinking
Copper:
negative
polarity, jet
flushing
pressure 20
kPa
AISI P20 tool i) Design factor of intensity have great
steel
influence on surface roughness for any
value of duty cycle.
ii) Duty cycle is less influenced in surface
roughness parameter.
iii) To obtain good surface finish of AISI
P20
tool steel, low value of both intensity and
pulse time must be used.
Most of the researchers also agreed that peak current and pulse duration have
the significant effect to work machined surface. Other factors such as flushing
pressure and duty cycle have no significant influenced to surface roughness.
28
However, without proper flushing used during EDM process, good machining
conditions cannot be achieved [Sandvik CIC Rolls].
ii.
A summary of previous researchers regarding the effects of EDM parameters
On the Cracks (surface integrity) on various types of steel is shown in Table 2.6
Table 2.6 Sinking EDM parameters affects the surface integrity of hardened steel is
Author
(Year)
Rebelo
Morao
Dias(1997)
EDM
process and
electrode
types
Die sinking
Graphite,
copper
work piece
Findings
HRC55 i) The dimensions of random overlapping
surface
craters
increase
with
machining pulse energy and density
and penetration depth of the cracks in
the re-cast layer increases with the
machining pulse energy.
ii) Network crack formation is
associated with the development of
high tensile stresses
. Luis,
Die sinking conductive
i) Flushing pressure, it was verified
Puertas
Graphite,
ceramic
that an increase in the latter (within the
and G.
(siliconise considered work interval, 20–60 kPa)
Villa
d silicon resulted in a decrease in The wear on
(2003)
carbide)
the electrode.
(SiSiC)
ii) Factors over material removal rate
(MRR) and Electrode wear (EW)
has been carried out. . intensity (I),
pulse time (ti), duty cycle (η), opencircuit voltage (U) and flushing
pressure (P),
iii) Large micro cracks formed in
materials B, D And E (depth = 10
µm).
. Hu , Zhou Die sinking Ti3SiC2
i) The acceleration of the material
and Y.W.
Graphite,
removal rate increases with the
Bao (2006) copper
discharge current and working voltage,
but decreases with increasing pulse
duration
ii) Melting and decomposing are
confirmed as the Main material
removal mechanisms.
iii) Despite the formation of micro
cracks in the re-solidified layer and the
loose grains in the subsurface
29
Lee and
Die sinking
Tai
Graphite,
reported,
copper
(2006)
[C.F. Hu
Y.C. Zhou
, Y.W. Bao
(2006).‖]
H13 tool
i) The surface roughness is broadly
steel and D2 similar for D2
and H13, and, in both cases, it is
found to increase as pulse current and
pulse-on Duration increase.
ii) white layer thickness, it is noted
that the thickness of this layer on H13
is slightly Greater than the layer on
D2.
iii). white layer thickness increases as
pulse current and pulse-on duration
increase
The literature reports showed that the information on details how sinking
EDM parameters affects the surface integrity of hardened steel is still scarce and
rather vague in the open literature. Particularly, a systematic study on how sinking
EDM parameters affect the surface integrity especially in the presence of cracks.
iii.
A summary of previous researchers regarding the effects of EDM parameters
on the Tool Wear on various types of steel is shown in Table 2.7
Table 2.7 Sinking EDM parameters affect the tool wear of hardened steel
EDM
process and
Author (Year)
electrode
types
Die sinking
Amorim,
Graphite,
Weingaertner copper
October-366
work
piece
Findings
AISI P20 (a) For electrodes at positive
tool steel polarity, graphite and copper
presented similar results in terms of
the values of Vw. Probably the 10
μm grain size of the graphite used
for the experiments should be
applied with higher discharge
currents, when the working gap
width would be larger and the EDM
performance could be more stable.
(b) The lower levels of volumetric
relative wear J were attained for
EDM with graphite and copper at
positive polarity despite the EDM
30
parameter settings.
(c) The best surface roughness Ra
was obtained for copper electrodes
under negative polarity.
. Che Haron. Die sinking
Ghani,
Graphite,
.Burhanuddin, copper
Y.K. Seong,
C.Y. Swee
2007
XW42 tool 1. The material removal rate of
steel
XW42 tool steel with copper
electrode is greater than that with
graphite electrode.
2. Copper electrode is suitable for
roughing process, whilst graphite
electrode is suitable for finishing
process. Combination of both
electrodes will improve machining
characteristics and surface finish.
3. The electrode wear rate of
copper is lower than graphite
electrode when machining XW42
tool steel.
The literature reports showed that the information on details how sinking
EDM parameters affects the tool wear of hardened steel material is still scarce and
rather vague in the open literature. Particularly, a systematic study on how sinking
EDM parameters affect the tool wears especially in the presence of wear.
2.5
Machining Characteristics
In this section, the machining characteristics that investigate are cracks,
surface roughness, and thickness of recast layer in the previous study. Each of this
features are usually occurred at the machined surface and may caused failure to the
work piece. These defects are explained in the following:
31
i.
Cracks
Since surface cracking is a potential source of component failure, it is
necessary to qualify the degree of cracking by means of some objective standard.
However, to quantify the cracking in terms of an estimation of width, length or depth
of crack, or even the amount of cracking is not easy. In this study, crack is defines as
a ―surface crack density‖, for instances the total length of cracks (cm) in a unit area
(cm2).
ii.
Sparking gap
Spark gap of the electrode used during machining is measured using optical
microscope in order to study the correlation between the machining parameters and
the spark gap. The unit used in this measurement is mm. Figure 2.12 showed the
actual length of spark gap in the mathematical equation.
Figure 2.11 Sparking gap
32
2.7
Summary
1) Most of the researchers also agreed that peak current and pulse duration have
significant effect to work machined surface. Other factors such as flushing pressure
and duty cycle have no significant influenced to surface roughness. However,
without proper flushing used during EDM process, good machining conditions
cannot be achieved [Sandvik CIC Rolls].
2) The literature reports showed that the information on details how sinking
EDM parameters affects the surface integrity of hardened steel is still scarce and
rather vague in the open literature. Particularly, a systematic study on how sinking
EDM parameters affect the surface integrity especially in the presence of cracks.
3) The literature reports showed that the information on details how sinking
EDM parameters affects the tool wear of hardened steel material is still scarce and
rather vague in the open literature. Particularly, a systematic study on how sinking
EDM parameters affect the tool wears especially in the presence of wear.
33
CHAPTER 3
METHODOLOGY
3.1
Introduction
This chapter describes the research methods and procedures covered in this
study it consist of four main elements namely, research design and data analysis,
variables, research procedures and instrumentations
3.2
Research Methodology
The flow chart in Figure 3.1 shows the overall steps involved in the
experimental works. It is divided in to three main parts, i.e.
1) Workpiece and electrode materials
2) EDM machine and parameters to vary
3) Responses to be evaluated
Detailed descriptions of those are explained in the following section.
34
Work piece Material
Equivalent ASSAB 718 High steel material with hardness range 55HRC
Electrode Graphite
Graphite
Parameters
Current (A)
Voltage (v)
24-48
Pulse interval (µSec)
80-120
100-400
Pulse Duration
0.2-3.8
Measuring Response
Material Rate
Removal MRR
Electrode Wear
Ratio EWR
Electronic Balance/weighing m/c
Surface
Roughness Ra
Microcrack
Surface Roughness Tester
Measuring Equipments
CNC EDM Die
sinking M/c
Robform
100(4axis)
Mitutovo
Formtracer
CS-5000
Scanning Electronic
Micro Scopy SEM
(XL40)
Figure 3.1: (a) Overall summary of Research Methodology
35
Workpiese Material: ASSAB718 (59HRC)
Material
Electrode Material: Poco EDMK4 & EM200
Chermilles
Machine: Roboform 100
Experiment
Trials
Experimental Method: Full factorial, 2level, 4fectors
&4cener points
Parameters to vary:
Current:
Voltage:
Pulse Interval:
Pulse duration:
24-48
80-120
100-400
0.8-3.2
A
V
µsec
µsec
Material removal
Rate (MRR)
Using Electronic
balance
Responses
Electrode Wear
Ratio (EWR)
Roughness (Ra)
Microcracks (LOC)
Formtraser CS5000
Scanning Electron (µ/scope)
High power (µ/scope)
Figure 3.1: (b) Overall summary of Research Methodology
36
3.2.1
Workpiece Material
Work piece of hardened steel ASSAB718 was cut to the cube shape with
dimension of 10mm x10mmx10mm and cut by the EDM Wire Cut. Figure 3.5
shows the shape and dimension of the work piece. Table 3.1 provides the
specification of the working material.
Work piece size = 10x10x10 mm
Hole size = 5x 5x5 mm
Figure 3.2: The view of work piece
Table 3.1 Classification for the material to be used in the experiment (ASSAB718)
ASSAB718
C
Nominal composition (wt. %) 0.33
3.2.2
Cr
Ni
W V
F
e
0. 1.8
0.9
0
0
Mn Si
1.4
Hardness
59 HRC
Density
7.87kg/cm³
0
Electrode Materials
Two different types of electrodes were examined in this project for rough
EDM machining hardened steel .These two electrodes were poco EDM4 and
EDM200.
37
Table 3.2 shows the properties of poco electrodes used in the experiment,
while the cross-section view shows in figure 3.3
Table 3.2 electrode properties
Grade
EDM4
EDM200
Average
Classification Particle
Size
Flexural
Strength
(psi)
Compress
Hardness
Strength
(Shore)
(psi)
Electrical
Resistivity
Microohm/inch
Ultrafine
<4
15,800
23,000
76
500
Superfine
10
9,000
16,000
64
480
5mm
5mm
5mm
(a)
5mm
(b)
Figure3.3 Electrode cross-section view
3.2.3
Machining Parameters:
The experiments were conducted using Charmilles CNC EDM Machine
Roboform 100 the machine is equipped with energetic generator, which means that
it is possible to set , among others EDM parameters , the discharge duration (te) and
pulse interval (to) which control the ignition delay time (td) as a percentage of (te).
In this work (td) was kept as 30% of (te) for all the experiments It means that low
energy would be applied with longer ignition delay time. The detailed specifications
of EDM used in this experiment are given in table 3.3 appendix
38
The selection of EDM parameters is important in determining the accuracy
and surface finish for a particular application. The parameters that were used in EDM
machining include voltage, current, pulse On-time and also pulse Off-time. These
parameters were manually adjusted using CNC control unit or programmable
controllers.
This research the parameters were varied include pulse voltage, pulse current,
pulse-on duration (ON-time), and pulse-off duration (OFF-time).Table 3.3
summarized the factors and levels of the parameters
Table 3.3 General machining parameter
Level
Factor
Low (-)
High (+)
Discharge Voltage (V) volt
80
120
Peak Current (P) amp.
24
48
Pulse interval (A) µsec
100
400
Pulse duration( Off /On- time ) (R) µsec
0.8
3.2
Table 3.4 shows the planning of experimental trials after considering all
factors and levels given in table 3.3
39
Table 3.4: The parameters and the value used in experiment
No of Trial
3.2.4
Voltage
Peak Current
Pulse Interval
Pulse Duration
V (volt)
P(Ampere)
A(µsec)
R(µsec)
1
-1
-1
-1
-1
2
+1
-1
-1
-1
3
-1
+1
-1
-1
4
+1
+1
-1
-1
5
-1
-1
+1
-1
6
+1
-1
+1
-1
7
-1
+1
+1
-1
8
+1
+1
+1
-1
9
-1
-1
-1
+1
10
+1
-1
-1
+1
11
-1
+1
-1
+1
12
+1
+1
-1
+1
13
-1
-1
+1
+1
14
+1
-1
+1
+1
15
-1
+1
+1
+1
16
+1
+1
+1
+1
17
-1
-1
-1
-1
18
+1
-1
-1
-1
19
-1
+1
-1
-1
20
+1
+1
-1
-1
Measuring of Responses
There are four (4) responses variables evaluated in this experiment and are
discussed in the following section.
40
3.2.4.1 Volumetric relative wear
This value represents the ratio of electrode wear rate to material removal rate
and expressed in percentage. Electrode wear ratio (EWR) can be defined as electrode
wear weight divided by work piece removal weight. [Khairul Nizar bin Omar (2004)]
The efficiency of the electrode used, calculated
EWR% =
𝑊𝑒₁−𝑊𝑒₂
𝑊𝑚₁−𝑊𝑚₂
X100
3.1
Where,
We₁=
Weight of electrode before machining
We₂=
Weight of electrode after machining
Wm₁ =
Weight of material before machining
Wm₂ =
Weight of material after machining
Or,
Electrode wear ratio (EWR) can be expressed by the following
expression
EWR
=
volume of material removed from electrode
Volume of material removed from part
3.2.4.2 Material Removal Rate (MRR)
This response variable was selected for this study r to indicate the speed of
the EDM process, in removing workpiece
MRR =
reduction in weight of work piece or electrode (gm)
Density of work piece or electrode (g/mm³) × machining time (min)
3.2
41
3.2.4.3 Microcracks
Scanning electron microscopy (SEM) was used to measure cracks on the
specimens after machining with EDM die sinking. The specimens were grind using
silicon carbide paper with grit size from 400 to 4000 to obtain smooth surface. Final
polishing was performed on rotating disc of cotton cloth followed by slevyt cloth.
The diamond of 6µm particles was used during polishing with cotton cloth. The
slevyt cloth was used together with a suspension solution consisting of SiO₂ particle
to get better result. Then specimens were examined under the optical image analyzer
and SEM.
3.2.4.4 Surface Roughness
The surface finish of machined specimens was measured using a surface
roughness tester. (Mitutoyo Formtracer CS5000). The length of measurement was
1.5mm and measure with 0.8mm cut off. The Ra values were measured three times
for each trial to get the average value
3.4
Analytical Equipments
Figure 3.4 shows the EDM die sinking machine that is available at the
production laboratory, Unversti Teknologi Malaysia. All the experimental trail were
conducted using this machine
42
Figure 3.4: CNC EDM Die Sinking Machine Robform 100 (4 Axes)
Hardness of the specimens was tested using Digital Rockwell hardness tester
machine (see figure 3.5)
Figure 3.5 The Digital Rockwell Hardness Tester machine
Mitutoyo Formtracer CS-5000) was used to measure the surface finish of
specimens (see figure 3.6)
43
Figure 3.6 Formtracer CS - 5000 (Surface Roughness machine
Calibration block was used to calibrate the surface roughness taking before
measurement was took place. Each specimen was measured using and 0.8mm cut off
Style.
Brand/Model
: (Mitutoyo Formtracer CS-5000)
Accuracy
: 0.001 µm
The Philips XL40 Microscope Scanning Electron was used to measure cracks
on the specimens that occur after EDMed machining. The sample was sectioned prior
to the measurement of cracks. At low magnification, high power optical Microscope
(see figure 3.7) was used to capture the specimens images on cracks
Figure 3.7: High Power Optical Microscope – Zeiss Axiotech.
44
Figure 3.13 shows the balancer used to weigh the workpiece materials
ASSAB 718 and the electrodes (EDM4 and EDM200) before and after machining.
(See figure 3.8)
Figure 3.8 Weighing Machine
MECATONE was used to section the workpiece material prior to
microcracks measurements by using Scanning Electron Microscope (see figure 3.9)
Figure 3.9 MECATONE T201A
45
The measured workpieces were grind with sand paper and polish with polishing
machine. Figure 3.10 shows these equipements
Figure 3.10: The sand grind and the polish machine
3.5
Summary
This chapter discusses the research methodology used in this project. Any
others, the experiment plane, workpiece and electrode materials and finally the
analytical equipments used to measure and evaluate the response variables
46
CHAPTER 4
RESULTS AND DISCUSSIONS
4.1
Introduction
This chapter presents the experimental results on Sinker EDM of hardened
steel material using graphite electrodes (EDM200 and EDM4). As was noted earlier,
the full factorial design was used for both designing and analyzing the experiment.
DOE was used to determine the significant process variables surface roughness (Ra),
electrode wear rate (EWR), material removal rate (MRR) and length of Microcracks
(LMC).
4.2
Experimental Results-EDM4
In this study, randomization of the run order to be carried out and analysis
sequences were carried out according to the run order organized by Design Expert
software as summarized table 3.4. Full factorial design of four factors with two levels
each was conducted which consist of 16 runs plus four center points which resulted
in a total number of 20 trials. The machining responses that were record are surface
47
roughness (Ra), Electrode wear rate (EWR), Material removal rate (MRR) and
Length of Micro-Cracks (LMC).
4.2.1
Machining Time
The time consumed for each run in this study was recorded by the machine
time indicator. Machining time starts as the electrode touch the workpiece and ends
at a fixed distance of 5 mm
Table 4.1 Machining Time when using EDM4, EDM200
No of
Trial
Run
(volt)
V
Peak
Current
(Ampere)
P
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
15
12
8
6
5
1
2
4
13
12
9
10
17
14
11
17
16
20
16
3
80
120
120
120
80
80
120
120
80
120
80
80
80
120
80
120
80
120
120
120
24
48
24
48
24
24
24
24
48
48
24
24
24
48
48
48
48
48
48
24
Voltage
Pulse
width
(µsec)
A
400
400
100
100
100
100
400
100
400
100
400
100
100
100
400
100
100
400
100
400
Pulse
Off/On time
(µsec)
R
Machining
Time
(minute)
EDM4
Machining
Time
(minute)
EDM200
0.8
0.8
0.8
3.2
0.8
0.8
0.8
3.2
3.2
0.8
3.2
0.8
3.2
0.8
0.8
0.8
3.2
3.2
0.8
3.2
100.8
29.01
45.06
57.14
67.45
35.32
112.34
85.03
105.42
46.63
178.36
21.48
67.00
38.20
34.15
19.94
65.42
89.49
29.46
265.80
96.31
25.55
41.22
55.38
51.15
54.40
97.09
105.2
274.30
35.07
218.28
107.58
144.09
62.01
137.30
21.09
226.26
373
82.46
179.0
48
4.2.2` Weighing Process
With the help of electronic balancer we got the differences weight between
the working material and cutting tool electrode before and after machining operations
as shown in Table 4.2.While machining responses (MRR and EWR) shown in Table
4.3 are calculated by equations shown after.
Table 4.2 Weighing of workpiece (lift) and Weight of EDM$ electrode (right)
No. of
Initial
Weight
(gm)
Final
Weight
(gm)
Difference
In Weight
(gm)
Initial
Weight
(gm)
Final
Weight
(gm)
Difference
In Weight
(gm)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
8.0315
8.1542
7.5692
8.2895
7.7863
8.0420
7.9130
8.0214
8.1260
7.8731
7.9125
7.9788
7.9965
7.7665
7.8792
7.9324
8.0300
7.8265
8.1424
6.8180
6.9258
6.5780
7.1650
6.7008
7.0116
6.8560
7.0756
6.9748
6.6947
6.9900
6.9760
7.2670
6.8000
6.7660
6.9380
7.3200
6.6740
6.8920
1.2135
1.2284
0.9912
1.1245
1.0855
1.0304
1.0570
0.9458
1.1512
1.1784
0.9225
1.0028
0.7295
0.9665
1.1132
0.9944
0.7100
1.1523
1.2504
4.7128
4.7821
4.3722
4.6032
4.8508
4.7130
4.8099
4.5894
4.9623
5.2364
4.5247
4.4120
4.4920
4.3757
4.7792
4.4060
4.7160
4.7640
5.2912
4.6660
4.7140
4.3300
4.5567
4.8088
4.6692
4.7900
4.5760
4.9580
5.2262
4.4770
4.3280
4.4440
4.3240
4.7290
4.3540
4.6536
4.7110
5.1895
0.0468
0.0681
0.0422
0.0465
0.0488
0.0438
0.0199
0.0134
0.0043
0.0102
0.0477
0.0840
0.0480
0.0517
0.0502
0.0520
0.0624
0.0050
0.1017
20
7.9898
6.9360
1.0538
4.6067
4.5552
0.0510
Trial
49
Table 4.3 MRR &EWR for Electrode EDM4
No. of
Trail
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
4.2.3
Volume of
material
Removal
(mm³)
155.179
157.084
126.752
143.798
138.8107
131.765
135.166
120.480
147.210
150.690
11.795
128.240
93.280
123.590
142.350
127.160
90.079
147.350
159.890
134.750
Machining
Time
(min.)
Response 1
(MRR)
mm³/min
Response 2
(EWR)‰
100.8
29.01
45.06
57.14
67.45
35.32
112.34
85.03
105.42
46.63
178.36
21.48
67.00
38.20
34.15
19.94
65.42
89.49
29.46
265.80
1.5395
5.4148
2.8129
2.5155
2.0579
3.7306
1.2032
1.4169
1.3964
3.2316
0.0661
5.9699
1.3923
3.2354
4.1685
6.3772
1.3878
1.6466
5.4274
0.5069
3.8566
5.5438
4.2575
4.1352
4.4915
4.2508
1.8827
1.4168
0.3735
0.8656
5.1707
8.3764
6.5798
5.3492
4.5095
5.2293
8.7887
4.3391
8.1334
4.8396
Surface Roughness
Table 4.4 shows the summary of surface roughness measurements for 20
trials. All the measurements were conducted using Mitutoyo Formtracer CS-5000
with 5 µm stylus tip and 40º of tip angle. Each section was measured for three times
before the average results were obtained. However, the data indicated in Table 4.4 is
only the summary of measurements obtained and the full measurement results of
surface roughness can be seen in Appendix B.
50
Table 4.4 Surface Roughness (Ra) for Electrodes EDM4 and EDM200
No. of
Trail
surface roughness for bottom
surface
EDM4 µm
surface roughness for bottom
surface
EDM200 µm
Ttrail
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
4.2.4
Ra1
Ra2
Ra3₃
Av. Ra
Ra1
Ra2
Ra3
Av. Ra
7.765
10.110
8.631
8.784
10.716
9.858
10.105
9.981
11.688
12.923
10.865
11.585
10.222
11.939
10.412
10.317
10.579
8.377
8.951
9.165
11.182
9.282
9.672
9.948
10.243
10.381
9.985
10.148
8.670
13.618
9.531
9.100
8.334
8.594
8.178
8.322
8.457
8.862
9.831
8.659
10.023
9.424
9.567
9.645
11.270
9.862
10.025
9.943
9.903
10.242
9.789
9.931
9.325
12.167
10.018
9.671
11.473
10.588
10.260
8.737
15.118
8.924
8.825
10.260
4
8798
7.610
8.120
8.162
11.732
22.241
11.305
11.518
10.661
10.957
9.885
10.347
11.336
11.972
9.235
11.654
8.787
9.583
9.028
9.107
9.392
8.282
8.631
8.456
11.567
11.080
10.871
11.097
5.254
10.640
9.516
10.078
7.686
11.083
8.726
9.055
7.240
8.123
10.670
7.681
9.488
10.801
9.256
9.700
10.360
9.794
9.600
9.697
11.057
9.800
10.012
10.220
13.894
13.790
14.977
13.842
9.720
10.344
9.157
9.594
9.600
11.769
9.351
9.475
11.569
11.724
11.462
11.554
11.181
10.028
9.820
9.924
12.667
11.957
11.213
1.755
9.530
12.998
9.725
9.627
9.032
12.172
9.320
9.961
10.447
11.150
10.266
10.356
12.179
8.324
9.251
9.751
17.996
18.380
17.403
18.188
Microcracks
Table 4.5 shows the summary of Length of Microcracks for 20 trials, all the
measurements were conducted using Scanning Electron Microscope (SEM) Philips
XL40. Each section was measured for three times before the average results were
51
obtained. However, the data indicated in Table 4.5 shows the machining results
response for EDM4 electrode.
Table 4.5 Machining response results for Electrode EDM4
Factors
No
of
Trial
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Response
V
(volt)
P
(amp)
A
(µsec)
R
(µsec)
80
24
400
0.8
120
120
120
80
80
120
120
80
120
80
80
80
120
80
120
80
120
120
120
48
24
48
24
24
24
24
48
48
24
24
24
48
48
48
48
48
48
24
400
100
100
100
100
400
100
400
100
400
100
100
100
400
100
100
400
100
400
0.8
0.8
3.2
0.8
0.8
0.8
3.2
3.2
0.8
3.2
0.8
3.2
0.8
0.8
0.8
3.2
3.2
0.8
3.2
Ra
µm
8.784
11.585
9.165
10.148
8.322
9.645
9.931
10.260
8.162
10.347
9.107
11.097
9.055
9.700
10.220
9.594
11.554
1.755
9.961
9.751
L.MC
µm
MRR
mm³/min
EWR
‰
100.38
1.5395
3.8566
63.12
5.4148
5.5438
96.35
2.8129
4.2575
71.42
2.5155
4.1352
25.63
2.0579
4.4915
64.7
3.7306
4.2508
40.1
1.2032
1.8827
28.56
1.4169
1.4168
55.1
1.3964
0.3735
56.85
3.2316
0.8656
34
0.0661
5.1707
55.93
5.9699
8.3764
72.62
1.3923
6.5798
44.2
3.2354
5.3492
89.57
4.1685
4.5095
40.77
6.3772
5.2293
50.93
1.3878
8.7887
95.53
1.6466
4.3391
69.91
5.4274
8.1334
84.12
0.5069
4.8396
4.2.5. ANOVA Analysis
All data obtained for Electrode EDM4 were then used as input to the Design
Expert software for further analysis, according to steps outline for full factorial
design Table 4.5
52
4.2.5.1 Analysis Results for Surface Roughness, Ra
Based on Table 4.6, there are only three factors affecting the surface
roughness, Ra. According to the analysis done in the Design Expert software, when
the values of probability (Prob>F) are less than 0.05, it shows that the factor is
significant. In this case, the pulse 0ff (off) and servo voltage (SV) and peak current
(IP) were significant to the Ra, but there were no interaction of any of these factors
observed in the ANOVA table. For the other factors namely pulse on (ON), is not
significant since the probability values were greater than 0.1. Therefore, they will not
show in the Table 4.9. In this investigation, 95% of confidence interval (CI) is used.
Table 4.6 ANOVA for surface roughness, Ra
Based on Figure 4.1, the significant factors were observed better in the half
normal probability plot of the standardized effects. As displayed in the Figure 4.1,
the significant factors highlighted were pulse off time (OF) servo voltage (SV) and
53
peak current (IP)which denoted as A, B and AD respectively. In order to have clearer
observation and better understanding of the response, the main effect plot is
available. Therefore, only the main effect of Ra which are pulse off time (OF) servo
voltage (SV) and peak current (IP) were showed.
Figure 4.1 Half Normal probability plots for Ra.
From the interactions plot, it was clearly showed that whenever peak current
(IP) increased from 24 µs to 48 amps. The value of (Ra) also increased dramatically
from 9.3315 to 10.2777. Meanwhile, a reverse result was observed for SV effect as
the graph showed that Ra increased 9.64425 to 10.5055 when SV increased from 80
volt to 120 volt. Therefore, no interaction graph can be show in this section. In order
to obtain better Ra during EDM Sinker of hardened steel, IP should be set at 48A.and
SV at 120 V.
Figure 4.2 Main Interactions for Ra
54
4.2.5.2 Analysis results for Material Removal Rate MRR
Next analysis is to determine which factor and interaction affecting the
response of material removal rate (MRR). This was done by considering the result
from ANOVA obtained from the software. According to Table 4.7, there is only one
factor affecting the material removal rate (MRR). According to the analysis done in
the Design Expert software, when the values of probability (Prob>F) are less than
0.05, it shows that the model is significant. In this case, and pulse width was
significant to the MRR, but there were no interaction of this factor observed in the
ANOVA table. For the other factors namely pulse off (OFF), servo voltage (SV) and
peak current (IP), are not significant since the probability values were more than
0.05. Therefore, they will not show in the Table 4.7. In this investigation, 95% of
confidence interval (CI) is used. The information was better illustrated in half normal
probability plot as shown in Figure 4.3. This graph is required in order to check for
normality of residuals of the factors studied.
Table 4.7 ANOVA for Material Removal Rate MRR
55
As displayed in the Figure 4.3, the significant factors highlighted were the
pulse on (ON)only while the other parameter was not significant which denoted as C
and ABD In order to have clearer observation and better understanding of the
response, the main effect plot is available. Therefore, only the main effects of MRR
which are pulse on (ON) were show.
Figure 4.3 Half Normal probability plots for MRR.
Figure 4.4 show the interaction plot, it was clearly showed that when SV
increased from 80 volt to 120 volt. The increasing of MRR was from 2.68275 to
3.07. Meanwhile, the value of (Ra) also increased dramatically. From 2.62075 to
4.16325 Based on the ANOVA analysis, IP and SV were affecting the MRR In order
to obtain better MRR during EDM Sinker of hardened steel; IP should be set at
48A.while SV at 120 V.
56
Figure 4.4 Interaction plot for MMR
4.2.5.3 Analysis Results for Electrode Wear Ratio (EWR %)
The third analysis is to determine which factors and interaction that affects
the Electrode Wear Ratio (EWR), similar procedures were done in analyzing the
significant factor and the possible interaction as discussed in previous section,
whatever factors that have the “Prob>F” less than 0.05 are considered significant for
EWR with the confidence interval (CI) used is 95%.
Therefore, based on ANOVA analysis and half normal probability plot shown
in Table 4.8 and Figure 4.5 respectively, only CD which is the products of C and D
factors were effects on the Electrode Wear Ratio (EWR). In this section, the
interaction plot is given in Figure 4.6 in order to provide a better illustration of the
phenomena.
57
Table 4.8 ANOVA for Electrode Wear Rate EWR%
Figure 4.5 Half Normal probability plots for EWR%.
58
Results in Figure 4.6 showed that, Electrode Wear Ratio (EWR) was affected
by the product of pulse on (ON) and pulse off (OFF), Based on the graph, EWR
increased dramatically from 1.69625 to 5.4165 mm/min as ON was increased
Meanwhile, EWR was observed to decrease as OFF were decreased from [4.5815 to
3.01074] Based on this relationship, maximum EWR. Can be obtained when the
parameters are set at ON = 400 µs, OFF = 3.2 µs, IP = 24 A and SV = 80 V.
Figure 4.6 Interaction plot for EWR%.
4.2.5.4 Analysis Results for Microcracks
Results of the ANOVA Table 4.9 and the half normal probability plot figure
(4.7) indicated that all factors are not significant. As explained before, although pulse
off (OFF) as shown in the ANOVA and normal probability plot, it was not
considered as the main factor because of the “Prob>F” value was more than 0.05.
However, it is indicated in the variance analysis in order to support the hierarchy in
the experiment design analysis. For clearer observation and understanding on the
response and main effects of the results obtained, the main effect plot and the
interaction plot were provided.
59
Table 4.9 ANOVA for Microcracks
Figure 4.7 Half Normal probability plots for Microcracks
60
From the graph shown in Figure 4.8, it was obvious that both factors were
able to increase the microcracks when the setting parameters were increasing. as
shown in the graphs, cracks an increment from50.2 to 87.2 µm when servo voltage
was increased from 80v to 120 v. Similar pattern was observed as pulse off was
increased from 0.8 to 3.8µs the increment of microcrack was 54.8 to
55.02.Apparently based on the analysis, the maximum length of crakes can be
achieved by setting pulse-off and SV at 0.8 µs and 120 V respectively.
Figure 4.8 Interaction plot for Microcracks
4.2.6
Confirmation Tests
Once the analyzing process for all the four responses were completed, the
factors need to be confirmed according to the effects correlation and met with the
objective and goal of each response. In the other words, the confirmation tests needs
to be carried out in order to ensure that the theoretical predicted roles suggested by
the software were accepted. All the parameters used in the confirmation tests were
suggested by the Design Expert software. Three confirmation tests were conducted in
order to compare the experimental results from the prediction made. Table 4.10
indicates the expected of quality characteristics for each response that required in the
61
process optimization. This is followed by the confirmation test results for Ra, EWR,
MRR and microcracks as shown in Tables 4.11 to 4.14 respectively. All data and
related pictures involved in this analysis were attached in Appendix B and C.
4.2.6.1 Comparison Tests for EDM4
Table 4.10 Quality characteristics of the machining performance.
Machining Characteristics
Quality Characteristics
Surface roughness (Ra)
Maximum
Material Removal Rate (MRR)
Maximum
Electrode Wear Rate (EWR)
Minimum
Microcracks
Minimum
Table 4.11: Confirmation test results for surface roughness, Ra.
Exp. Trial
Trial condition
Repeat 1
Ra (µm)
19
ON = 100µs
OFF = 3.2 µs
IP = 2.4 A
SV = 120 v
12.667
Repeat 2
Ra (µm)
Repeat 3
Ra (µm)
Total
Average
(µm)
11.957
11.213
11.755
Table 4.12: Confirmation test results for Microcracks
Confirmation test results for micro-cracks
Exp.
Trial
Trial Condition
14
ON = 400µs
OFF = 0.8 µs
IP = 48 A
SV = 120 v
Repeat 1
(µm)
Repeat 2
(µm)
Repeat 3
(µm)
Total Average
(µm)
35.46
52.94
38.5
44.2
62
Table 4.13: Confirmation test results for Material Removal Rate MRR.
Exp.
Trial
Trial
Condition
17
ON = 100µs
OFF =.0.8 µs
IP = 48 A
SV = 120 v
Material Removal Rate MRR Confirmation Test
Results
Repeat 1
Repeat 2
Total Average
mm³/min
mm³/min
mm³/min
6.85
5.88
6.38
Table 4.14: Confirmation test results for Electrode Wear Rate EWR%.
EWR%. Confirmation Test Results
Exp.
Trial
Trial Condition
20
ON = 400µs
OFF = 0.8 µs
IP = 48 A
SV = 120 v
Repeat 1
Repeat 2
Repeat 3
Total Average
4.51
4.39
3.85
4.26
4.2.7. Comparison of Test Results
As mentioned before, three confirmation runs were conducted in order to
measure the reliability of optimization solutions obtained from the software analysis.
The comparison of test results between the theoretically prediction and confirmation
test results was the final consideration that will evaluate whether the optimum
parameters predicted were in the allowable range. The margin of error from the
prediction and experimental results was set at 7.523% (below than 10 %.)Margin
error was calculated using the equation below
Margin error % = [(Confirmation on test result – Predicated result) / Predicated result] * 100%
4.1
63
According to the Final Equation in Terms of Coded Factors and Final
Equation in Terms of Actual Factors given in ANOVA table analysis ,we can found
the value of the prediction and confirmation test results which illustrated in appendix
(E)
Prediction equation = f x (Duty fact, pulses, current, SV)
4.2
Tables 4.22 indicated the comparison of test results between theoretical
prediction and confirmation runs for Ra (7.01%), micro-cracks (2.31%), MRR
(11.54%) and EWR% (9.23%) respectively. Therefore, the overall margin of error
percentage was 7.523%
Table 4.15: Comparison test results for all responses. EDM 4
Response
factors
Prediction
(Design Expert)
Experimental
(Confirmation Test)
Error
Margin (%)
Ra
10.99
11.76
7.01
MRR
5.72
6.38
11.54
EWR
3.90
4.26
9.23
Crack
43.20
44.2
2.31
64
4.3 Experimental results –EDM200
All the experiment results were shown in the following sections.
4.3.1
Weighing Process
With the help of electronic balancer we got the differences weight between
the working material and cutting tool electrode before and after machining operations
as shown in Table 4.16.While machining responses (MRR and EWR) shown in
Table 4.17 are calculated by equations shown after.
Table 4.16 Weighing of workpiece (lift) and Weight of EDM200 electrode (right)
No of
Trial
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Initial
Weight
(gm)
Final
Weight
(gm)
Difference
In Weight
(gm)
Initial
Weight
(gm)
Final
Weight
(gm)
Difference
In Weight
(gm)
8.0632
7.1004
0.9628
4.1023
4.0588
0.0435
8.0185
7.1110
0.9075
4.4130
4.3668
0.0462
8.1592
7.1648
0.9944
4.3747
4.3320
0.0427
7.9248
6.8942
1.0306
4.0363
3.9905
0.0458
7.7323
6.7100
1.0223
4.5191
4.4760
0.0431
7.9010
6.8828
1.0182
3.9890
3.9542
0.0348
7.9580
6.8975
1.0605
4.4513
4.4149
0.0364
8.1092
7.1504
0.9588
4.2383
4.2005
0.0378
7.9875
7.0192
0.9683
4.2586
4.2185
0.0401
8.1262
7.1210
1.0052
4.3277
4.2885
0.0392
8.0758
7.1261
0.9497
4.6044
4.5608
0.0436
7.9325
6.9220
1.0105
4.2129
4.1698
0.0431
8.0131
7.1668
0.9895
4.2982
4.2610
0.0372
8.1027
7.0236
0.9419
4.2101
4.1740
0.0361
7.8302
6.7683
1.0619
4.4089
4.3780
0.0309
7.8288
6.8537
0.9751
4.1270
4.0931
0.0339
8.0213
6.9717
1.0496
4.4649
4.4187
0.0462
7.7778
6.7855
0.9923
4.4168
4.3623
0.0545
8.0244
7.1329
0.8916
4.5265
4.4940
0.0325
706267
6.7200
0.9067
4.2685
4.2420
0.0215
65
Table 4.17 MRR &EWR for Electrode EDM4
No. of
Trail
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
4.3.2
Volume of
material
Removal
(mm³)
0.1231
0.1161
0.1272
0.1318
0.1307
0.1302
0.1356
0.1226
0.1238
0.1289
0.1214
0.1292
0.1265
0.1204
0.1358
0.1247
0.1342
0.1268
0.1140
0.1159
Machining
Time
(min.)
Response 1
(MRR)
mm³/min
Response 2
(EWR)‰
96.31
25.55
41.22
55.38
51.15
54.40
97.09
105.2
274.30
35.07
218.28
107.58
144.09
62.01
137.30
21.09
226.26
373
82.46
179.0
1.2782
4.5440
3.0859
2.3799
2.5558
2.3934
1.3966
1.1654
0.5030
3.6755
0.5602
1.2009
0.8779
1.9416
0.9891
5.9127
0.6100
0.5100
1.3825
0.7082
4.5181
5.0910
4.2940
4.4440
4.2159
3.4178
3.4323
3.9424
4.1413
0.0389
4.5909
4.2652
3.7595
3.8327
2.9098
3.4766
4.4016
5.4922
3.6451
2.3712
Microcracks
Table 4.18 shows the summary of Length of microcracks for 20 trials, all the
measurements were conducted using Scanning Electron Microscope (SEM) Philips
XL40. Each section was measured for three times before the average results were
obtained. However, the data indicated in Table 4.5 shows the machining results
response for EDM200 electrode.
66
Table 4.18 Machining response results for Electrode EDM200
Factors
Response
No
of
Trial
V
(volt)
P
(amp)
A
(µsec)
R
(µsec)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
80
24
400
4.3.3
120
120
120
80
80
120
120
80
120
80
80
80
120
80
120
80
120
120
120
48
24
48
24
24
24
24
48
48
24
24
24
48
48
48
48
48
48
24
400
100
100
100
100
400
100
400
100
400
100
100
100
400
100
100
400
100
400
Ra
µm
L.O.C
µm
MMR
mm³/min
EWR
‰
0.8
9.981
35.13
1.2782
4.5181
0.8
10.317
26.54
4.5440
5.0910
0.8
9.9477
40.88
3.0859
4.2940
3.2
9.100
66.9
2.3799
4.4440
0.8
8.659
45.26
2.5558
4.2159
0.8
9.943
21.41
2.3934
3.4178
0.8
9.671
75.45
1.3966
3.4323
3.2
8.825
71.11
1.1654
3.9424
3.2
11.518
152.35
0.5030
4.1413
0.8
11.654
35.18
3.6755
0.0389
3.2
8.456
207.85
0.5602
4.5909
0.8
10.078
40.1
1.2009
4.2652
3.2
7.681
219.2
0.8779
3.7595
0.8
9.697
38.49
1.9416
3.8327
0.8
13.842
60.35
0.9891
2.9098
0.8
9.475
80.5
5.9127
3.4766
3.2
9.924
44.04
0.6100
4.4016
3.2
9.627
82.42
0.5100
5.4922
0.8
10.356
37.77
1.3825
3.6451
3.2
18.188
64.25
0.7082
2.3712
ANOVA Analysis
All data obtained for Electrode EDM4 were then used as input to the Design
Expert software for further analysis, according to steps outline for full factorial
design Table 4.19
67
4.3.3.1 Analysis Results for Surface Roughness, Ra
Based on Table 4.19, there are two factors affecting the surface roughness,
Ra. According to the analysis done in the Design Expert software, when the values of
probability (Prob>F) are less than 0.05. In this investigation, 95% of confidence
interval (CI) is used. The information was better illustrated in half normal probability
plot as shown in Figure 4.9. This graph is required in order to check for normality of
residuals of the factors studied.
Table 4.19 ANOVA for surface roughness, Ra
68
As displayed in the Figure 4.9, the significant factors highlighted were pulse
width (ON) and servo voltage (SV) which denoted as A,C,AD,CD, and ABD
respectively. In order to have clearer observation and better understanding of the
response, the main effect plot is available.. Therefore, only the main effects of Ra
which are pulse width (ON) and servo voltage (SV) were showed.
Figure 4.9 Half Normal probability plots for Ra.
From the interaction plot, it was clearly showed that whenever IP increased
from 24 A. to 48 A, the value of Ra also decreased dramatically. From 10.905to
9.0625, meanwhile, a reverse result was observed for SV effect as the graph showed
that Ra decreased when SV increased from 80 volt to 120 volt. The decreasing of Ra
was 11.48 to 8.11. Based on the ANOVA analysis, to obtain better Ra during EDM
Sinker of hardened steel, IP should be set at 48A.while SV at 80 V.
69
Figure 4.10: Interaction plot for Ra
4.3.3.2 Analysis Results for Material Removal Rate MRR
Next analysis is to determine which factor and interaction affecting the
response of material removal rate (MRR), this was done by considering the result
from ANOVA obtained from the software. According to Table 4.20, there is no any
factor affecting the material removal rate (MRR). According to the analysis done in
the Design Expert software, when the values of probability (Prob>F) are less than
0.05, it shows that the entire factors are not significant. In this investigation, 95% of
confidence interval (CI) is used. The information was better illustrated in half normal
probability plot as shown in Figure 4.11.
Based on Figure 4.11, the significant factor was observed better in the half
normal probability plot of the standardized effects. In order to have clearer
observation and better understanding of the response, the main effect plot is
available, .therefore, only the main effects of MRR which are peak current (IP) and
pulse ON were showed.
70
Figure 4.11 Half Normal probability plots for MRR.
Table 4.20 ANOVA for surface roughness, MRR
71
Figure 4.12: Interaction plot for MRR
Figure 4.12 show the main effects plot, it was clearly showed that when IP
increased from 24 amps to 48 amps. The decreasing of MRR was about 2.4975 to
1.805 meanwhile, but, when pulse ON increasing from100µs to 400µs. the
decreasing of MRR from 1.9375 to 1.0125.Based on the ANOVA analysis, ON and
IP were affecting the MRR, therefore, in order to obtain better MRR during EDM
Sinker of hardened steel, ON should be set at 100 µs while IP at 24 A.
4.3.3.3 Analysis Results for Electrode Wear Rate (EWR %)
The third analysis is to determine which factors and interaction that affects
the Electrode Wear Ratio (EWR) Similar procedures were done in analyzing the
significant factor and the possible interaction as discussed in previous section,
whatever factors that have the “Prob>F” less than 0.05 are considered significant for
EWR with the confidence interval (CI) used is 95%.Therefore, based on ANOVA
analysis and half normal probability plot shown in Table 4.21 and Figure 4.13
respectively, all factors were effects were are not significantly .
72
Table 4.21 ANOVA for Electrode Wear Rate (EWR %)
Figure 4.13 Half Normal probability plots for EWR%
73
Figure 4.14 shows that, Electrode Wear Ratio (EWR) was affected by servo
voltage SV, and peak Current IP, Based on the graph, EWR increased dramatically
from 3.805 to 4.5325 Meanwhile, EWR was observed to decrease as SV increased,
were decreased from 4.1575 to 4.0575.Based on this relationship, maximum EWR.
Can be obtained when the parameters are set at IP = 48 A, and SV = 120 V.
Figure 4.14: Interaction plot for EWR%
4.3.3.4 Analysis Results for Microcracks
Last analysis is to determine which factor and interaction affecting the
response of microcracks, this was done by considering the result from ANOVA
obtained from the software, according to the table 4.22, the factors which are
affecting the Microcracks are servo voltage S.V and pulse off, according to the
analysis done in the Design Expert software, when the values of probability (Prob>F)
are less than 0.05, it shows that factors are significant to the microcracks, in this
investigation, 95% of confidence interval (CI) is used. The information was better
illustrated in half normal probability plot as shown in Figure 4.15. This graph is
required in order to check for normality of residuals of the factors studied.
74
Table 4.22 ANOVA for Microcracks
Based on Figure 4.15, the significant factors were observed better in the half
normal probability plot of the standardized effects. As displayed in the Figure 4.15,
the most significant factors highlighted were pulse OFF and servo voltage (SV)
which denoted as A, D, and AD respectively. In order to have clearer observation
and better understanding of the response, the main effect plot is available. Therefore,
only the main effects of micro-cracks which are servo voltage (SV) and pulse off
were showed.
75
Figure 4.15 Half Normal probability plots for microcracks
From the interaction plot, it was clearly shown that whenever IP increased
from 24 A to 48 A, the value of microcracks will be decreased dramatically from
96.1275µm to 65.1325 µm. Meanwhile, when SV increased from 80 v to 120 v, the
decreasing of microcracks from 112.98 µm to 30.405 µm. In order to obtain better
Microcracks during EDM Sinker of hardened steel, IP should be set at 48A.while SV
at 80 volt.
Figure 4.16: Interaction plot for Microcracks
76
4.3.4
Confirmation Tests for EDM200
Table 4.23 Quality characteristics of the machining performance.EDM200
Machining Characteristics
Quality Characteristics
Surface roughness (Ra)
Maximum
Material Removal Rate (MRR)
Maximum
Electrode Wear Rate (EWR)
Minimum
Micro-cracks
Minimum
Table 4.24: Confirmation test results for surface roughness, Ra.
Exp.
Trial
Trial condition
Repeat 1
Ra (µm)
Repeat 2
Ra (µm)
Repeat 3
Ra (µm)
Total Average
(µm)
12
ON = 100µs
OFF = 3.2 µs
IP = 24 A
SV = 120 v
17.996
18.38
17.40
18.21
Table 4.25: Confirmation test results for microcracks
Confirmation test results for micro-cracks
Exp.
Trial
Trial Condition
2
ON = 400µs
OFF = 0.8 µs
IP = 48 A
SV = 120 v
Repeat 1
(µm)
Repeat 2
(µm)
Repeat 3
(µm)
Total Average
(µm)
34.27
41.27
37.01
37.72
77
Table 4.26: Confirmation test results for Material Removal Rate MRR.
Exp.
Trial
Trial
Condition
6
ON = 100µs
OFF =.0.8 µs
IP = 44 A
SV = 120 v
Material Removal Rate MRR Confirmation Test
Results
Repeat 1
Repeat 2
Total Average
mm³/min
mm³/min
mm³/min
6.01
5.88
5.91
Table 4.27: Confirmation test results for Electrode Wear Rate EWR%.
EWR%. Confirmation Test Results
4.3.5
Exp.
Trial
Trial Condition
2
ON = 100µs
OFF = 0.8 µs
IP = 48 A
SV = 120 v
Repeat 1
Repeat 2
Repeat 3
Total Average
3.41
4.01
3.65
3.645
Comparison of Test ResultsEDM200
As mentioned before, three confirmation runs were conducted in order to
measure the reliability of optimization solutions obtained from the software analysis.
The comparison of test results between the theoretically prediction and confirmation
test results was the final consideration that will evaluate whether the optimum
parameters predicted were in the allowable range. The margin of error from the
prediction and experimental results was set below than 11 %.( 10.72%) Margin error
was calculated using the equation below
Margin error % = [(Confirmation on test result – Predicated result) / Predicated result] x 100%
78
According to the Final Equation in Terms of Coded Factors and Final
Equation in Terms of Actual Factors given in ANOVA table analysis ,we can found
the value of the prediction and confirmation test results which illustrated in appendix
(E)
Prediction equation = f x (Duty fact, pulses, current, SV)
Table 4.28: Comparison test results for all responses.EDM200
Response
factors
Prediction
(Design Expert)
Experimental
(Confirmation Test)
Error
Margin (%)
Ra
16.49
18.19
10.31
MRR
4.68
5.91
26.28
EWR
3.05
4.26
39.67
Crack
56.62
37.72
-33.38
NOTE:
All the mathematical relations for prediction result and confirmation test are
illustrated in appendix (E).
4.4
Summary
This chapter discusses the results and discussions on this project. The
experimental results for EDM4 and EDM200, where each one included the
experiment results tables, ANOVA ANALYSIS and confirmation tests and finally to
determined the margin of error from the prediction and experimental results for each
EDM electrodes.
78
CHAPTER 5
PERFORMANCE COMPARISON BETWEEN GRAPHITE ELECTRODES
5.1
Introduction
This chapter focuses more on the significant parameters that have great
influence on the performance of machining characteristics such as, surface roughness
(Ra), Material Removal Rate (MRR), Electrode Wear Rate (EWR) and Microcracks.
Additionally, an explanation on why there was almost no observation of Microcracks
presence in this study will also is included. Although DOE has greatly contributed to
the analysis of all studied responses, the information provided was still lacking in
understanding the EDM sinker process for ease of optimization. The information
which was provided through statistically process was only based on numbers and
plotted graphs; therefore it is required for further interpretation and discussion in
terms of relating them back to the actual machining process. In this chapter, the
discussions are made unilaterally according to each response.
79
5.2
Surface Roughness, Ra
According to the results obtained from the Design Expert software tables 4.6
and 4.19, servo voltage (SV) was the main factors that affect on the roughness
response (Ra) were found that when SV increase from 80 volt to 120 volt., Ra (for
EDM4) increased from 9.64425 to 10.5055 while for EDM200 decreased 11.48 to
8.11 While the maximum value found with EDM4 which is about 11.7µm while with
EDM200 only 18µm.Therefore, the optimal signal setting to get maximum amount
for Ra with EDM4 are ON = 100µ ,OFF = 3.2 µs ,IP = 2.4 A and SV = 120 v. and
for EDM200 was ON = 100µs, OFF = 3.2 µs, IP = 24 A and SV = 120 v Finally, the
margin error obtained from the comparison test for the Surface Roughness, Ra
EDM4 was 7.01%.,while for EDM200 was 10.31%
5.3
Material Removal Rate MRR
From the analysis it could be see that the servo voltage and pulse width ON
are the most significant factor compared to another factors. As given by the Design
Expert software tables 4.7 foe EDM4, but with EDM200 there were no significant
factors. Therefore, the maximum value of material removal rate for EDM4 was
6.4mm/min, while for EDM200 the maximum value of material removal rate was 5.9
mm/min where the value of the servo voltage is increased from 80 v to 120 v. the
increasing of MRR was from 2.68275 to 3.07mm/min, while in EDM4 was.
Increased from 2.68275 to 3.07mm/min .Therefore, the optimal signal setting to get
maximum amount for MRR with EDM4 are ON = 100µs, OFF =.0.8 µs, IP = 48 A
and SV = 120 v., and for EDM200 was ON = 100µs, OFF =.0.8 µs, IP = 44 A and
SV = 120 v .finally, the margin error obtained from the comparison test for the
material removal rate for the EDM4 was 6.38%. While for EDM200 was 26.28%
80
5.4
Electrode Wear Rate EWR
From the analysis it observed that the pulse off and pulse width ON are the
most significant factor compared to another factors, as given by the Design Expert
software tables 4.8 foe EDM4, but with EDM200 there were no significant factors.
Therefore, the maximum value of electrode wear rate for EDM4 was 8.8, while for
EDM200 the maximum value of electrode wear rate was 5.49 where the value of the
pulse off is increased from 0.8 v to 3.8 µsec. the increasing of EWR from 3.805 to
4.5325 while in EDM4 was increased dramatically from 1.69625 to 5.4165
Therefore, the optimal signal setting to get maximum amount for EWR with EDM4
ON= 400µs ,OFF = 0.8 µs ,IP = 48 A ,and SV = 120 v., and for EDM200 was ON =
100µs, OFF =.0.8 µs, IP = 48 A and SV = 120 v .finally, the margin error obtained
from the comparison test for the material removal rate for the EDM4 was 9.23%.
While for EDM200 was 39.6%
5.5
Microcracks
According to the results obtained from the Design Expert software tables 4.9
and 4.22, servo voltage (SV) and pulse off was the main factors that affect on the
microcracks were found that when SV increase from 80 volt to 120 volt., cracks (for
EDM4) increased from50.2 to 87.2 µm while for EDM200 decreased 112.98 µm to
30.405 µm While the maximum value found with EDM4 which is about 11.7µm
while with EDM200 only 18µm.Therefore, the optimal signal setting to get
maximum amount for Ra with EDM4 are ON = 400µ ,OFF = 0.8 µs ,IP = 48 A and
SV = 120 v. and for EDM200 was ON = 400µs, OFF = 0.8 µs, IP = 48 A and SV =
120 v Finally, the margin error obtained from the comparison test for the Surface
Roughness, Ra EDM4 was 2.31%.,while for EDM200 was -33.38%
81
5.6
summary
Generally, the result obtained and data analysis is acceptable. All the results
obtained one in agreement with the general trends obtained by other researchers.
According to the actual design of experiment, replication of experiment is important
to ensure that all data is accurate and acceptable..But due to several difficulties
during this project ,only one replicate has been done for each electrode experiment
and these experiment just follow the P-value from the response surface analysis ,also
this experiment has been conducted 100%random manner .
The die-sinking electrical discharge machine model Chamilles ROBOFORM
100 is a CNC machine if the machining conditions are not suitable for the machine,
the machine stops or the duration of interval between two pulses and the withdrawal
time duration of pulsation are changed automatically. This affected the accuracy of
the responses.
EDM requires that the axis of the electrode be parallel to the direction of feed
for true reproduction of the electrode shape .It was difficult to obtained this because
of the way that the tool were machined and the machine`s condition which also
effected on the accuracy of responses .
82
CHAPTER 6
CONCLUSION AND RECOMMENDATIONS
6.1
Conclusions
Basically, this study evaluates the machining performance of hardened steel
material (ASSAB718) when machined using two different grades of graphite
electrodes. All the experiments trials, planning and analysis were executed using
two-level full factorial design of experiment. The purposes of DOE method applied
in this study were to determine the optimum condition of machining parameters and
the significance of each parameter to the performance of machining characteristics.
The total experiment runs performed in this study was 20 trials for each electrode
using randomized parameters and analyzed using by Design Expert software. The
following conclusions are drawn based on the performance of machining
characteristics studied in this research work.
1) Within the range of parameters tested using EDM4 electrode material the
recommended condition to get maximum MRR are the machining voltage at level
120 v, peak current 48 A, and pulse ON time at 100 µsec .While for EDM200
electrode, the recommended conditions to get maximum MRR are the machining
voltage at level 80 v, peak current 48 A, and pulse ON time at 400µsec. The
83
machined workpiece surface roughness increases steadily with increasing MRR;
therefore, referred to the overall machining results tables in chapter 4 EDM4 is better
to used for hardened steel material to produced high Material Removal Rate (MRR),
low roughness, less length of Microcracks and short machining time, but with high
EWR%.
2) The most significant factors that effecting the quality of machining
Characteristic is the servo voltage was the most significant factor affecting the
responses, According to ANOVA ANALAYSIS tables studied in chapter 4.
Finally, the objective of this project is generally achieved. From the design of
experiment methodology, it is found that the, servo voltage and pulse of signal have
appeared to be significant to all responses investigated. Overall, the results from the
confirmation tests showed that the percentage of performance was acceptable due to
all the results obtained were within the allowable value which was less than 11% of
margin error for EDM200 and 7.23% for EDM4 electrodes respectively .Even
though there is a lot of variation influencing the data. The results in this project could
be used as a basis for further investigation in electrical discharge machining of
hardened steel ASSAB718
6.2
Recommendations
Based on the current findings, the following recommendations for future
works are proposed as follows:
1. Use of different grades of graphite as the tool electrode for better understands
84
its effect upon the machined surface and machining parameters in machining
hardened steel material.
2. Study the effects of additives in dielectric fluid increasing the effectiveness
of material removal rate
3. Study on the effect of residual stress on the specimens after being machined
at high removal rate.
4. Different flushing methods need to be investigated as opposed to continuous
pressure flushing employed in this study.
85
References
Ahmet, H. and Caydas, U. (2004). “Experimental study of wire electrical discharge
machining of AISI D5 tool steel.” Journal of Materials Processing
Technology. 148: pp. 362–367.
Benedict, G. F. (1987). “Electrical Discharge Machining (EDM), Non Traditional
Manufacturing Processes.” New York & Basel: Marcel Dekker, Inc.
C.H. Che Haron∗, J.A. Ghani, Y. Burhanuddin, Y.K. Seong, C.Y. Swee (1992)
Copper and graphite electrodes performance in electrical-discharge
Machining of XW42 tool steel. Department of Mechanical and Materials
Engineering, Faculty of Engineering, National University of Malaysia, 43600
Bangi, Selangor, Malaysia
C.J. Luis, I. Puertas , G. Villa (2005).” Material removal rate and electrode wear
study on the EDM Silicon Carbide”. Journal Mechanical, Energetics and
Materials Engineering Department, Manufacturing Engineering Section,
Public University of Navarre,
C.F. Hu, Y.C. Zhou, Y.W. Bao (2006).” Material removal and surface damage in
EDM of Ti3SiC2 ceramic” Journal. Shenyang National Laboratory for
Materials Science, Institute of Metal Research, China
86
C.F. Hu Y.C. Zhou , Y.W. Bao (2006).” Material removal and surface damage in
EDM of Ti3SiC2 ceramic” Journal. Shenyang National Laboratory for
Materials Science, Institute of Metal Research, China
Fred L. Amorism Emeritus Member, ABCM Federal University of Santa CatharinaUFSC Department of Mechanical Engineering. (1970). The Behavior of
Graphite and Copper Electrodes on the Finish Die-Sinking Electrical
Discharge Machining (EDM) of AISI P20 Tool Steel Department of
Mechanical Engineering 80040-970 Florianopolis, SC. Brazil
H.T.Lee and T.Y.Tai (2003).”Relationship between EDM parameters and Surface
Crack Formation”. Department of Mechanical Engineering, National Cheng
Kung University, Taiwan.Journal
J.C. Rebelo, A. Morao Dias, D. Kremer, J.L. Lebrun (1997).” Influence of EDM
pulse energy on the surface integrity of martensitic steels” Journal. Faculdade
de Cieˆncias e Tecnologia da Uni6ersidade de Coimbra, Portugal
K.H. Ho, S.T. Newman.(2003) State of the art electrical discharge machining
(EDM) International Journal of Machine Tools & Manufacture
Khairul Nizar bin Omar (2004) (www.elsevier.com/locate/jmatprotec) Surface
modification by electrical discharge machining: Electrical Discharge
Machining of Aluminum Alloy
Li Li, Y.S. Wong, J.Y.H. Fuh, L. L (2000) EDM performance of Tic copper-based
sintered electrodes Department of Mechanical Engineering, National
University of Singapore, 10 Kent Ridge Crescent, Singapore’
Llanes, L., Casas, B., Idan˜ez, E., Marsal, M. and Anglada, M. (2004). Surface
Integrity Effects on the Fracture Resistance of Electrical-DischargeMachined WC–Co Cemented Carbides.” Journal of Advanced Ceramic
Society. 87: pg. 1687–1693.
Lauwers, B., Liu, W. and Earaerts, W. (2004). “Influence of the composition of WC-
87
based cermets on the manufacturability by Wire-EDM.”University of
Katholieke Leuven.
Lee, L.C., Lim, L.C., Wong, Y.S. and Fong, H.S. (1992). “Crack susceptibility of
electro-discharge machined surfaces.” Journal of Materials Processing
Technology. 29: pg. 213-221.
Lee, S.H. and Li, X.P. (2001). “Study of the Effect of Machining Parameters on the
Machining Characteristics in Electrical Discharge Machining of Tungsten
Carbide.” Journal of Materials Processing Technology. 115: pg. 344-358.
Mohd. Amri, L. (2002). “Study on Machining Parameters Optimization in EDM of
Tungsten Carbide Using the Taguchi Method.” Universiti Teknologi
Malaysia: Master Thesis.
Mhd Fareed Fahmy bin Mhd Yunin (2005).”Study of Crack Formation in EDM of
Tool Steel”. UTM Skudai
Serope Kalpakjian, (1992). “Manufacturing Engineering and Technology”, second
edition, Addison-Wesley Publishing Company,Inc.
V.García Navasa, I. Ferreresb , J.A. Marañónb , C. Garcia-Rosalesa and J (April 2007.)
Electro-discharge machining (EDM) versus hard turning and grinding—
Comparison of residual stresses and surface integrity generated in AISI O1
tool steel
Yan, B. H., Wang, C. C., Liu, W. D. and Huang F. Y. (2002). “Machining
Characteristics of Al2O3 / 6061 Al Composite Using Rotary EDM with a
Dislike Electrode.” The International Journal of Advances Manufacturing
Technology, 16: pp. 322-333.
88
APPENDIX A
THE OVERALL MEASUREMENT RESULTS
FOR SURFACE ROUGHNESS
EDM4 ELECTRODE
89
RUN #1:
RUN#2
RUN #3:
RUN #4
90
RUN #5:
RUN #6:
7)
RUN #8:
RUN #7:
91
9)
RUN #9:
11)
RUN #11
10)
RUN #10
12)
RUN #12
92
13)
RUN #13
14)
RUN #14
15)
RUN #15
16)
RUN #16
93
17)
RUN #17
18)
RUN #18:
19)
RUN #19
20)
RUN #20
94
APPENDIX B
THE OVERALL MEASUREMENT RESULTS
FOR SURFACE ROUGHNESS
EDM200 ELECTRODE
95
1)
3)
RUN #1:
RUN #3:
2)
RUN #2:
4)
RUN #4:
96
5)
RUN #5:
6)
RUN #6:
7)
RUN #7:
8)
RUN #8:
97
9)
RUN #9:
10)
RUN #10:
11)
RUN #11:
12)
RUN #12:
98
13)
RUN #13:
14)
RUN #14:
15)
RUN #15:
16)
RUN #16:
99
17)
RUN #17:
18)
RUN #18:
19)
RUN #19:
20)
RUN #20
100
APPENDIX C
THE OVERALL MEASUREMENT RESULTS
FOR MICROCRAKES STRUCTURE
EDM4 ELECTRODE
101
1) RUN #1:
2)
RUN #2
4) 3)
4)
RUN #4
RUN #1:
102
5) RUN #5
6)
RUN #6
7) RUN #7
8)
RUN #8
103
9) RUN #9
10)
RUN #10
11) RUN #11
12)
RUN #12
104
13)
15)
RUN #13
RUN #15
14)
RUN #14
16)
RUN #16
105
17)
RUN #17
18)
RUN #18
19) RUN #19
20)
RUN #20
106
The microcracks on the surface of EDM machining at 250x magnification on trial 2
of graphite electrode
Microcracks at 160volt, 64amperes, and 50µsecond of pulse interval (magnification
2500x) on graphite electrode
107
APPENDIX D
THE OVERALL MEASUREMENT RESULTS
FOR MICROCRAKES STRUCTURE
EDM200 ELECTRODE
108
1) RUN 1
2)
RUN 2
1) RUN 3
4)
RUN 4
109
6) RUN 5
7) RUN 7
6)
9)
RUN 8
RUN 6
110
8) RUN 9
10)
RUN 10
10) RUN 11
12)
RUN 12
111
13) RUN 13
14) RUN 15
14)
16)
RUN 14
RUN 16
112
17) RUN 17
17) RUN 19
18)
20)
RUN 18
RUN 20
113
NOTE: All the above diagrame of creacs are taken with magnification
optical (10 *50) 500x
Microcracks at 80volt, 48amperes, and 100µsecond of pulse interval (magnification
2500x) on graphite electrode EDM4
Microcracks at 80volt, 24amperes, and 4000µsecond of pulse interval (magnification
2500x) on graphite electrodeEDM200
114
APPENDIX E
THE OVERALL ANALYSIS RESULTS
FOR PREDICTED AND ACTUAL COMFORIMATION TESTS
FOR EDM200 AND EDM4 ELECTRODES
115
EDM4
Analysis Results for Surface Roughness, Ra
116
Analysis Results for Material Removal Rate MRR
117
Analysis Results for Electrode Wear Ratio (EWR)
118
Analysis Results for Microcracks
119
Analysis of Results for EDM200 electrode
Analysis Results for Surface Roughness, Ra
120
Analysis Results for Material Removal Rate MRR
121
Analysis Results for Electrode Wear Ratio (EWR)
122
Analysis Results for Microcracks