NOVEL EDM SCREW THREADING TECHNIQUE USING
THREADED CAVITY ELECTRODE
AHMAD HISYAMUDDIIN BIN HASSAN
B050910008
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
2013
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
NOVEL EDM SCREW THREADING TECHNIQUE USING
THREADED CAVITY ELECTRODE
This report submitted in accordance with the requirement of the UniversitiTeknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Manufacturing Process) (Hons.)
by
AHMAD HISYAMUDDIIN BIN HASSAN
B050910008
871015-26-5145
FACULTY OF MANUFACTURING ENGINEERING
2013
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA
TAJUK: Novel EDM Screw Threading Technique using Threaded Cavity
ELectrode
SESI PENGAJIAN: 2012/13 Semester 2
Saya AHMAD HISYAMUDDIIN BIN HASSAN
mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti
Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:
1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis.
2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja dengan izin penulis.
3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan
pertukaran antara institusi pengajian tinggi.
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(Mengandungi maklumat yang berdarjah keselamatan
atau kepentingan Malaysiasebagaimana yang termaktub
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SULIT atau TERHAD.
DECLARATION
I hereby, declared this report entitled “Novel EDM Screw Threading Technique Using
Threaded Cavity Electrode” is the results of my own research except as cited in the
references.
Signature
:
................................................
Author's Name
:
Ahmad Hisyamuddiin Bin Hassan
Date
:
3 June 2013
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a
partial fulfillment of the requirements for the degree of Bachelor of Manufacturing
Engineering (Manufacturing Process) (Hons.). The member of the supervisory is as
follows:
...............................................
Dr Raja Izamshah Bin Raja Abdullah
Project Supervisor
ABSTRACT
The complicated geometrical design and tight tolerance of orthopedic screw such as
titanium alloys were fabricated using single-point threading and thread whirling
technique. However, there are few problem encounters with these techniques such as
rapid tool wear, limited design flexibility, low accuracy and high capital cost. The
suitable candidate to overcome this problem is using Electrical Discharge Machining
(EDM) process in which the material is removed by spark erosion. Since there is no
physical contact between tool electrode and workpiece, the tool wear rate is low and
the material hardness is not dependent. In addition, the main advantages of using
EDM technique are the accuracy and fine surface integrity which is suitable for
medical application. However, to ensure the success of EDM as an alternative
manufacturing technique for orthopedic screw required a scientific investigation
especially on the effect of EDM machining parameter. This study aims to investigate
the effect of EDM machining parameter namely current, pulse on time and pulse off
time on machining performances. A statistical response surface methodology are use
to evaluate the effect of the machining parameter on the machining performances
namely surface roughness, machining time and electrode wear. Lastly, the optimal
machining condition base on the multi-objective performance criteria will be
proposed.
i
ABSTRAK
Reka bentuk geometri yang rumit dan ketepatan yang tinggi skru ortopedik seperti
aloi titanium telah direka menggunakan satu titik ulir dan teknik “thread whirling”.
Walau bagaimanapun, terdapat beberapa masalah yang timbul dengan mengunakan
teknik-teknik ini, seperti kehausan mata alat, reka bentuk terhad, ketepatan yang
rendah dan kos modal yang tinggi. Calon yang sesuai untuk mengatasi masalah ini
adalah dengan menggunakan “Electrical Discharge Machining (EDM) proses di
mana bahan kerja dia hakis melalui teknik percikan api. Kerana tidak ada hubungan
fizikal antara elektrod alat dan bahan kerja, kadar kehausan mata alat adalah rendah
dan kekerasan bahan tidak bergantung. Di samping itu, kelebihan utama
menggunakan teknik EDM adalah ketepatan dan integriti permukaan halus yang
sesuai untuk aplikasi perubatan. Walau bagaimanapun, untuk memastikan kejayaan
EDM sebagai teknik pembuatan alternatif untuk skru ortopedik memerlukan
penyiasatan saintifik terutamanya mengenai kesan parameter pemesinan. Kajian ini
bertujuan untuk mengkaji kesan parameter pemesinan EDM iaitu arus elektrik,
“pulse on time” dan “pulse off time” di persembahan pemesinan. “Response surface
methodology” digunakan untuk menilai kesan parameter pemesinan pada
persembahan pemesinan iaitu kekasaran permukaan, masa pemesinan dan kadar
kehausan mata alat. Akhir sekali, keadaan pemesinan asas optimum pada kriteria
prestasi pelbagai objektif akan dicadangkan
ii
DEDICATION
Dedicate to my beloved parents Hassan Bin Salleh and Hasnah Binti Hamid.
Dedicated to my beloved brothers,
Dedicated to all my family and my friends.
Thank you for your support and encouragement.
You all are everything for me.
May Allah bless all of us. InsyaAllah.
iii
ACKNOWLEDGEMENTS
First and foremost, I would like to express my highest appreciation to my
supportive academic supervisor, Dr. Raja Izamshah B. Raja Abdullah for his
supervision and support in completing this thesis.
Also with the greatest thanks to my beloved parents and family who always
pray and give the encouragement while pursuing my research and project. Their
sacrifices are never being forgotten.
I would like to acknowledge to (EDM) laboratory technicians, who has been
so warmth and kind to provide sincere assistance and good cooperation during the
training period. Their co-operation is much appreciated. Last but not least, I would
like to convey my appreciation to all the staff of Faculty of Manufacturing
Engineering, FKP, my friend and colleagues for their support and their help in the
project. Thank you.
iv
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowlegment
iv
Table of Content
v
List of Tables
viii
List of Figures
ix
List of Abbreviations, Symbols & Nomenclature
xi
CHAPTER 1: INTRODUCTION
1
1.1
Background
1
1.2
Current Method Produced Screw thread
2
1.2.1
Thread Turning
2
1.2.2
Thread Rolling
3
1.2.3
Thread Whirling
4
1.3
Problem Happen Making Titanium Screw
6
1.5
Objective Of Research
6
CHAPTER 2: LITERATURE REVIEW
7
2.1
Introduction to Electrical Discharge Machining (EDM)
7
2.2
EDM Machining System
7
2.3
Process Parameter
8
2.3.1 Discharge Voltage
8
2.3.2 Peak Current
9
2.3.3 Pulse Duration
9
2.3.4 Pulse Interval
9
2.3.5 Polarity
10
2.3.6 Type of Dielectric Flushing
10
Basic EDM Setting
10
2.4
v
2.4.1 Duty Factor
10
2.4.2 Pulse Frequency
11
2.4.3 Average Current
11
2.5
Thread Specification
12
2.6
Electrode
13
2.6.1 Electrode Selection
13
2.6.2 Electrode Material
14
Related Work on EDMing Titanium
14
2.7
CHAPTER 3: METHODOLOGY
16
3.1
Introduction
16
3.2
Project Overview
16
3.3
Identify the Problem
18
3.4
Literature Review
18
3.5
Research Methodology
19
3.5.1 Control Factor and Level
19
3.5.2 Response Surface Methodology
20
Preparation of the Experiment
22
3.6.1 Specimen Preparation
22
3.6.2 Conduct the Experiment
23
3.6.3 Testing
25
Summary of This Chapter
26
3.6
3.7
CHAPTER 4: RESULT AND DISCUSSION
27
4.1
Statistical Analysis
27
4.1.1 Design Summary
28
4.2
Modelling of Machining Performance
29
4.3
Machining Time Analysis
31
4.4
Suface Roughness Analysis
32
4.5
Electrode Wear Analysis
34
4.6
Multi Objective Optimization
36
4.7
Dimension of Screw
36
4.8
Defect
38
vi
CHAPTER 4: CONCLUSION AND RECOMMENDATIONS
40
5.1
Conclusion
40
5.2
Recommendations
41
REFERENCES
42
APPENDICES
A
Gantt Chart PSM 1
B
Gantt Chart PSM 2
vii
LIST OF TABLES
1.1
Qualitative comparison between screw threading fabrication methods
6
2.1
M10 screw specification
13
2.2
Physical properties of copper
14
2.3
Material properties Ti-6Al-4V
15
3.1
The level of process parameter for copper electrode
20
3.2
The setting of EDM parameters
20
3.3
Table 3.3: Table for experiment data
21
4.1
Data of machining performance
27
4.2
Suggested parameter according to factor priority
36
viii
LIST OF FIGURES
1.1
Thread turning
3
1.2
Thread rolling
3
1.3
Thread whirling
5
2.1
Basic EDM die sinker component
8
2.2
ISO unified thread profile
12
3.1
Methodology flow chart
17
3.2
Experiment layout preparation
22
3.3a
Copper electrode
23
3.3b
Titanium workpiece
23
3.4a
Workpiece
23
3.4b
Electrode
23
3.4c
Electrode and workpiece submerged in dielectric fluid
24
3.5
EDM die sinker machine
24
3.6a
Portable surface roughness tester (SJ 301)
25
3.6b
Stereo digital imaging (EM2 – 13TR)
25
4.1
Design summary
28
4.2
ANOVA response surface linear model for machining time
29
4.3
ANOVA response surface linear model for surface roughness
29
4.4
ANOVA response surface linear model for electrode wear
30
4.5
Current vs machining time
31
4.6
Pulse on vs machining time
31
4.7
Pulse off vs machining time
32
4.8
Current vs surface roughness
32
4.9
Pulse on vs surface roughness
33
4.10
Pulse off vs Surface roughness
32
4.11
Current vs electrode wear
35
4.12
Pulse on vs electrode wear
35
ix
4.13
Pulse off vs electrode wear
35
4.14
Exp 1
36
4.15
Exp 2
36
4.16
Exp 3
37
4.17
Exp 4
37
4.18
Exp 5
37
4.19
Exp 6
37
4.20
Exp 7
37
4.21
Exp 8
37
4.22
Surface defect
38
4.13
Unspark area
38
x
LIST OF ABBREVIATIONS, SYMBOLS AND
NOMENCLATURE
CNC
-
Computer Numerical Control
EDM
-
Electric Discharge Machine
MRR
-
Material Removal Rate
EWR
-
Electrode Wear Rate
SR
-
Surface Roughness
TWR
-
Tool Wear Rate
CAD
-
Computer Aided Design
CAM
-
Computer Aided Manufacturing
%
-
Percentages
kHz
-
Kilohertz
A
-
Ampere
µs
-
Micro Second
mm
-
Milimeter
V
-
Voltage
xi
CHAPTER 1
INTRODUCTION
1.1 Background
Orthopedic medical is one of path in medical. Orthopedic is related with bone and
joint human body anatomy. Orthopedic pain mostly causes by accident or injury on
work, sport and others. Treatment on orthopedic pain taken by doctor is applying the
implant device between the fracture bone and orthopedic disease area. Medical
device is one of important requirement in orthopedic surgery. The device needs to
fulfill the criteria state on medical standard. In the criteria, material selected is
important. Recent trends in the medical industry increase the use of titanium alloys
because of its outstanding mechanical properties such as lightweight material with
greater strength and thougness, and non-corrosive.
The complicated geometrical design and tight tolerance of orthopedic screw such as
titanium alloys were fabricated using single-point threading and thread whirling
technique. However, there are few problem encounters with these techniques such as
rapid tool wear, limited design flexibility, low accuracy and high capital cost. The
suitable candidate to overcome this problem is using (EDM) process in which the
material is removed by spark erosion. Since there is no physical contact between tool
electrode and workpiece, the tool wear rate is low and the material hardness is not
dependent. In addition, the main advantages of using EDM technique are the
accuracy and fine surface integrity which is suitable for medical application.
1
1.2 Current Method Produced Screw Thread
There are many methods of generating thread including subtractive methods,
deformative methods and additive method. However for complicated geometrical
design and tight tolerance of orthopedic screw, the thread can only be produced by
method thread turning, thread rolling and thread whirling. The method chosen for
any one application is chosen based on constraint- time, cost and degree of
precision.[1]
1.2.1 Thread Turning
Thread turning is the oldest and the most widely used threading operations. It is a
process for producing external or internal threads that usually using a single point
tool. The disavantages of this method are the tool wear and costs to fabricate
orthopedic screw are high.
2
Figure1.1: Thread Turning
1.2.2 Thread Rolling
Thread rolling is a cold forming process for producing threads on a cylindrical or
conical blank. It is similar to internal roll form tapping. The tool or die displaces or
extrudes the metal from the part surface to form the thread. Thread rolling machines
are designed with two flat die rollers in a side-by-side position. The threads on the
blank, which is inserted between the rollers, are usually completed after eight
revolutions. However this method is having limitation about highly rate of tool wear.
3
Figure 1.2: Thread rolling
1.2.3 Thread Whirling
Thread whirling is a process used for internal and external threads. Whirling removes
material in a manner similar to thread milling. The process uses a special head
supporting the threading tool. The whirling head is mounted in machine spindles that
rotates eccentrically at high speed around the slowly rotating workpiece, or perform a
planetary rotation along a stationary workpiece. The cutter uses insert arranged along
the inside or the outside circumference of a ring for external and internal thread,
respectively. The most critical issues are about the cost for fabricating orthopedic
screw.
4
Figure1.3: Thread whirling
5
1.3 Problem Happen Making Titanium Screw
Table 1.1: Qualitative comparison between screw threading fabrication methods.
Turning
Rolling
Whirling
EDM
Tool Wear
High
High
Medium
Low
Accuracy
Medium
Low
High
High
Time
Medium
Medium
High
Low
Cost
High
Low
High
Low
Medium
Low
High
High
Shape Hard Material
Table 1.1 shows the comparison between screws threading technique which depicted
EDM is the most suitable as compared to other technique. Based on this justification,
EDM are chosen as an alternative screw fabrication method.
1.4 Objective of Research
Both the difficulties and disadvantages for fabricating titanium screw were causing to
initiate this project:
1. To determine the capability of EDM Die Sinking on screw threading
fabrication using threaded cavity electrode.
2. To investigate EDM machining parameter namely current, pulse on time and
pulse off time on machining performances (surface roughness, electrode wear
and machining time).
3. To propose an optimal machining condition based on multi-objective
performance criteria.
6
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction to Electrical Discharge Machining (EDM)
Electrical Discharge Machining (EDM) is the process of machining electrically
conductive materials by using precisely controlled sparks that occur between an
electrode and a workpiece in the presence of a dielectric fluid. The electrode may be
considered the cutting tool. EDM is one type of advance machining that can be
milled, drilling grinding and other machining operation. The commonly operation of
this machine are to producing mould and die component. Die-sinking or also known
as RAM type EDM machine require the electrode to be machined in the exact
opposite shape as the one in the workpiece. EDM differs from most chip-making
machining operations in that the electrode does not make physical contact with the
workpiece for material removal. Since the electrode does not contact the workpiece,
EDM has no tool force. The electrode must always be spaced away from the
workpiece by the distance for sparking, known as the sparking gap. [2]
2.2
EDM Machining System
Its three major assemblies are the machine tool, power supply and dielectric unit. The
assemblies are dependent upon one another to such an extent that the EDM system
will not function unless all assemblies are operating properly.
7
The power supply must provide each individual spark to the sparking gap for
material removal. It must also monitor the electrical conditions at the sparking gap
and direct the machine servo in advancing, retracting or maintaining the position of
the electrode, in reference to the workpiece. The dielectric unit must provide the
dielectric fluid to the machine for submersing the workpiece. In addition, the
dielectric unit must send fluid to the sparking gap for cooling purpose and to remove
the EDM chip. The dielectric unit includes a filtration system for cleaning the
dielectric fluid. [2]
Figure 2.1 Basic EDM die sinker component
2.3
Process Parameter
The process parameters that affected the properties of EDM parts need to be
identified in the first step of the experiment [3]. The parameters are listed as below:
2.3.1 Discharge Voltage
Discharge voltage in EDM is related to the spark gap and breakdown strength of the
dielectric. The preset voltage determines the width of the spark gap between the
leading edge of the electrode and workpiece. Higher voltage settings increase the
gap, which improves the flushing conditions and helps to stabilize the cut. MRR, tool
wear rate (TWR) and surface roughness increases, by increasing open circuit voltage.
8