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A Project Report
on
“EXPERIMENTAL STUDY ON EFFECT OF PROCESS
PARAMETERS ON PERFORMANCE MEASURE OF EDM”
submitted to
Gujarat Technological University
for Partial Fulfillment Towards the
Subject : PROJECT-I (170001), Semester VIIth
in the Field of
“MECHANICAL ENGINEERING”
Submitted by
PATEL PAVANKUMAR I. (080170119037)
PARMAR KAUSHIK C. (080170119027)
PATEL DARSHIL D. (090173119005)
MODI TARUN D. (090173119002)
Under the Guidance of
Prof. S.R Pandya
Asst. Professor,
Department of Mechanical Engineering
Vishwakarma Government Engineering College , Chandkheda
Department of Mechanical Engineering
Vishwakarma Government Engineering College,
Chandkheda – 382424 NOV/DEC 2011
Certificate
This is to certify that the project report entitled “EXPERIMENTAL STUDY ON
EFFECT OF PROCESS PARAMETERS ON PERFORMANCE MEASURE OF
EDM”
submitted by
PATEL PAVANKUMAR I. (080170119037)
PARMAR KAUSHIK C. (080170119027)
PATEL DARSHIL D. (090173119005)
MODI TARUN D. (090173119002)
towards the partial fulfillment of the requirement for the subject PROJECT-I (Subject
Code: 170001) (Semester VIIth
) in the field of “MECHANICAL ENGINEERING” of
Gujarat Technological University is a record of the bona-fide work carried out by him/her
under my guidance and supervision. The work submitted, in my opinion, has reached to a
level required for being accepted for the examination.
.
Guide:
Prof. S.R.Pandya
Asst. Professor,
Department of Mechanical Engg.
Vishwakarma Government Engg.College ,
Chandkheda
Prof. Rupal. P Vyasa
Head of Department
Department of Mechanical Engg.
Vishwakarma Government Engg. College ,
Chandkheda
Certificate of Examiner
The Project Report entitled
“EXPERIMENTAL STUDY ON EFFECT OF PROCESS
PARAMETERS ON PERFORMANCE MEASURE OF EDM”
Submitted By
PATEL PAVANKUMAR I. (080170119037)
PARMAR KAUSHIK C. (080170119027)
PATEL DARSHIL D. (090173119005)
MODI TARUN D. (090173119002)
As a partial fulfillment of the requirement
for the
Subject : PROJECT-I (170001)
Semester-VIIth
of Gujarat Technological University in the field of
“MECHANICAL ENGINEERING”
is hereby approved.
Internal Examiner External Examiner
Date :
Place :
ACKNOWLEDGEMENT
I express my cavernous sense of obligation and gratitude to my guide Shri S R
PANDYA for his genuine guidance and constant encouragement throughout this project
work. I am highly obliged as my honourable guide have devoted his valuable time and
shared his expertise knowledge.
I extend my sincere thanks to HOD, Department of Mechanical Engineering and
Principal, Vishwakarma Government Engineering College, Chandkheda for providing me
such an opportunity to do my project work in my college.
I also wish to express my heartfelt appreciation to my friends, colleagues and many who
have rendered their support for the successful completion of the project, both explicitly
and implicitly.
PATEL PAVANKUMAR I. (080170119037)
PARMAR KAUSHIK C. (080170119027)
PATEL DARSHIL D. (090173119005)
MODI TARUN D. (090173119002)
7th
/Mechanical
Date:
Place:
ABSTRACT
Electron discharge machining is one of the earliest non-traditional machining
processes. EDM process is based on thermoelectric energy between the work piece and
an electrode. Material removal rate (MRR) is an important performance measure in EDM
process. Figure 3.1 shows various process parameters and performance measure of EDM
process. Low MRR is the disadvantage in EDM therefore no. Of ways are explored to
improve and optimize MRR.
This project works on mainly concentrated on analyzing the effect of process
parameters like current, voltage, Ton , Toff on MRR of EDM process. For that a
experiment is to be carried out on EDM machine and result to be analyzed. Further, by
taking into consideration the result obtained and feasibility of application, a solution to
increase MRR is to be suggested and applied.
NOMENCLATURE
Vo Open Circuit Voltage
Vw The Working Voltage
Io The Maximum Current
P
W
t
Ton
Density
Weight
Operation Time
The Pulse Time On
Toffᵟᵟ
ᵟ
The Pulse Time Off
Spark Gap
LIST OF FIGURES
3.1. EDM Process Layout 5
3.2. Working Principle of EDM 6
3.3
3.4.
3.5.
Pressure Flushing Through electrode
Pressure Flushing Through workpiece
Suction Flushing Through Electrode
17
18
18
3.6. Suction Flushing Through Work piece 19
3.7.
3.8.
3.9.
3.10.
6.1.
6.2.
6.3.
Jet Flushing
Vertical Flushing
Rotary Flushing
Orbiting Flushing
Current Vs.MRR.
Ton Vs.MRR.
Toff Vs.MRR.
20
21
22
22
33
33
34
LIST OF TABLES
1. Observation table of MRR rate at varying current.
2. Observation table of MRR rate at varying Ton time
3. Observation table of MRR rate at varying Toff time.
31
31
32
INDEX
Acknowledgement
Abstract
Nomenclature
List of Figures
List of Tables
i
ii
iii
iv
v
1. INTRODUCTION 1-2
1.1 Motivation And Objective Of Project 1
1.2 Organization Of The Project 2
2. LITRATURE REVIEW 3-4
3. FUNDAMENTALS OF EDM 5-25
3.1 History Of EDM 5
3.2 Working Principle of EDM 6
3.3 Electrodes. 7
3.4 Die-electric Fluid. 9
3.5 Flushing Techniques. 15
3.6 Characteristic of EDM. 23
3.7 Application of EDM. 24
4. EXPERIMENT WORK. 26-30
4.1 Process Parameters. 26
4.2 Performance Parameters. 28
4.3 Procedure. 28
4.4 machine Specification 29
4.5 Working Details 29
5. OBSERVATIONS. 31-32
6. RESULT & DISCUSSIONS. 33-35
6.1 By Varying Current. 33
6.2 By Varying Ton Time. 33
6.3 By Varying Toff Time. 34
6.4 Expected Outcome. 34
7. FUTURE WORK. 36-37
REFERENCES. 38
CHAPTER 1
INTRODUCTION
With the increasing demand for new, hard, high strength, hardness, toughness
and temperature resistance material in engineering, the development and application
of EDM has become increasingly important. EDM has been used effectively in
machining hard, high strength and temperature resistance materials. Material is
removed by means of rapid and repetitive spark discharges across the gap between
electrode and work piece.
Since the EDM process does not involved mechanical energy the removal rate
is not affected by hardness, strength or toughness of the work piece material.
Therefore, comprehensive study of effects of EDM parameters on the machine
characteristics such as electrode wear rate, material removal rate, surface roughness
& etc., is of great significance and could be of necessity.
1.1 MOTIVATION AND OBJECTIVE OF PROJECT
To gain of full appreciation of state of art in EDM. Ten research paper read
and analyzed. To appropriately summarized the paper and applied then to project
intended. The following questions are asked of each paper.
1. What is definition of EDM?
2. What are strength and weakness of the EDM process?
3. What types of parts are being machined by EDM and in what materials are they
being machined?
4. What is the minimum/maximum features has been machined?
5. How quickly are the parts being made or what is the machining rate?
6. What is the method that improves the EDM process?
The main strength of EDM process is that it can machine the complex shape
machine into any conductive material with very low forces. The forces are very small
because the tool and work piece do not come in contact during machining process.
There are two important weaknesses to the EDM process the first is that it is a very
slow machining process and the second weakness that while the work piece electrode
is being machined the tool electrode also wears at significant rate. This tool wear
leads to shape in accuracies.
The research on EDM can be divided into three categories.
1. Attempting to improve speed EDM.
2. Attempting to improve accuracy and shape complexity of EDM parts.
3. Applying EDM process to new type of materials.
Among these three areas the goals set for these project were to increase general
understanding of EDM process & increase the speed of EDM process.
1.2 ORGANIZATION OF THE PROJECT
Chapter-1 Provides a brief introduction about the EDM, objective of the EDM & the
need for an implementation of this project.
Chapter-2 provides a literature Review of EDM.
Chapter-3 about the fundamental of EDM in which includes history of EDM, working
principle of EDM, electrodes, die-electric properties, various flushing techniques,
characteristic & application of EDM.
Chapter-4 Discuss about the experiment work, in which includes Process&
Performance parameter.
Chapter-5 About observation of EDM which include the observation tables under
different condition.
Chapter-6 Discuss the Result and graphs and its effect on MRR.
Chapter-7 About the future work which include the various methods to improve the
MRR.
CHAPTER 2
LITRATURE REVIEW
A Study on dry EDM by Samuel M.P. ,Philip P.K.[1], studied various Aspect of
EDM using powder metallurgy electrode & concluded that powder metallurgy
technique have an advantage over other fabrication technique. They studied that
there is better control over the properties of PM electrodes properties of the
electrode can be controlled by adjusting the compacting & sintering condition.
A study on “surface modification” by EDM by S.kumar R.singh[2]., studied the
surface modification by EDM using conventional electrode, powder metallurgy
electrode, powder suspended in dielectric.
A study on EDM of Hastelloy using copper chromium powder metallurgy
electrode using reverse polarity, technical journals online.com by Dinesh kumar,
Naveen Beri, Anil kumar, saurabh Sharma[3] has been used mostly in the tool &
die industry & the material normally used as electrode are copper, tungsten,
graphite, brass, silver, copper tungsten & copper chromium alloys. In the present
work, Hastelloy steel is used as a work piece for investigating using partially
sintered electrode of copper chromium with reverse polarity setup in standard EDM
oil. The input parameters selected in the study are current, voltage, duty cycle, pulse
on time & flushing pressure, in which current & voltage are varied & other input
parameters are kept constant on average value. The output parameters are MRR,
tool wear rate, percentage wear rate & surface roughness.
A study on dry EDM by M.kunieda, B. lauwers,k.p. rajurker[4], with copper as tool
electrode & steel as workshop reveal that in case of EDM in Air, the tool electrode
wear ratio was much lower & MRR much higher when tool electrode was negative.
In the case of EDM in a liquid there was more tool of electrode wear & lower MRR
when the polarity of tool is negative. Hence negative polarity was found to be
desirable for material transfer from the tool electrode.
A study on EDM by S.K. Hoa,D.K. Aspinwall[6], they reported that powder
metallurgy electrode produced greater alloying than the solid electrode. This was a
function conductivity & the level of bonding between the copper particles, with the
pelleted electrodes. It was observed that powder metallurgy electrodes used with
positive produced polarity, thicker recast layers. When using a solid copper
electrode under negative work piece hardness was in general of lower or of
comparable hardness to the bulk material.
A Study by Singh, S., Kansal & H.K., Kumar [7], the amount of energy applied
during machining is controlled by peak current and pulse duration. Longer pulse
duration results in higher material removal resulting in broader and deeper crater
formation. However, too much pulse duration is counter productive and once
optimal value for a particular work piece- electrode combination is exceeded,
material removal rate starts decreasing. Pulse interval influences the speed and
stability of the cut. In theory, the shorter interval results in faster machining
operation. But if the interval is too short, the ejected work piece material will not be
swept away by the flow and the fluid will not be deionized resulting in unstable
next spark.
A study by Zhao, W.S., Meng, Q.G., Wang [8] & Z. Wong, Y.S., Lim, L.C.,
Rahuman[9], I Powder mixed electric discharge machining (PMEDM) is one of the
new innovations for the enhancement of capabilities of electric discharge machining
process. In this process, a suitable material in fine powder is properly mixed into
the dielectric fluid. The added powder improves the breakdown characteristics of
the dielectric fluid. The insulating strength of the dielectric fluid decreases and as a
result, the spark gap distance between the electrode and work piece increases.
Enlarged spark gap distance makes the flushing of debris uniform. This result in
much stable process thereby improving material removal rate and surface finish.
CHAPTER 3
FUNDAMENTAL OF EDM
Electron discharge machining is basically a non –conventional material removal
process which is widely used to produce dies, punches, moulds, finishing parts for
aerospace, automotive industry, and surgical components. This process can be
successfully employed to machine electrically conductive parts only.
Fig 3.1 EDM Process
There are mainly three types of EDM:
EDM Die sinking
EDM Wire cutting
Micro EDM.
3.1 HISTORY OF EDM.
In 1770, English physicist Joseph Priestley noted in his research the erosive effect
of electrical discharges on various metal. Based off of Priestley's earlier research, during
a separate study to eliminate the erosive effect on electrical contacts, the Soviet
researchers B.R. and N.I Lazarenko had the idea of exploiting the destructive effects of
an electrical discharge and develop a controlled process for machining of metals. In 1943,
they developed a spark machining process, thus called because of the fact that a
succession of sparks (electrical discharges) took place between two electrical conductors
immersed In a dielectric fluid. The discharge generator effect then used, known as the
Lazarenko Circuit, was used for a long time in the construction of generators of EDM
machines. Improved, this type of generator is still used today for some applications.
The spectacular changes in EDM are due also to the perseverance of several other
researchers who contributed to the highlighting the fundamental characteristics of this
machining method and to obtaining, at present, the best possible advantages from this
process. In 1952, the manufacturer Charmilles, because interested in spark erosion
machining, created the first machine using this machining process was presented for the
first time at the European Machine Tool Exhibition in Milan in 1955. Numerical control
and feedback loops with ultra fast servos were added in the 1970's.
Today, full 3-D CAD/CAMS feed the controls of the machines with code generated to
control path and spark characteristics.
3.2 WORKING PRINCIPLE OF EDM
Fig 3.2 Working Principle of EDM
The working principle of EDM process is based on the thermoelectric energy.
This energy is created between a work piece and a electrode submerged in dielectric fluid
with the passage of electric current. The work piece and electrode are separated by small
gap called spark gap. Pulses are discharges occur in this gap filled with an insulating
medium, preferably a dielectric liquid like hydrocarbon oil or did-ionized water.
In this process the electrode move toward the work piece reducing the spark
gap so that the applied voltage is enough to ionize the dielectric fluid. The material is
removed from tool and work piece with erosive effect.
3.3 ELECTRODES.
Electrical discharge machining (EDM) makes it possible to work with metal for
which traditional machining techniques are ineffective. It only works (except by specific
design) with materials that are electrically conductive. Using recurring electric discharge,
it is possible to cut small, odd-shaped angles and detailed contours or cavities in hardened
steel as well as exotic metals such as titanium and carbide.
Types of EDM Electrode Materials
EDM electrode materials need to have properties that easily allow charge and yet resist
the erosion that the EDM process encourages and stimulates in the metals it machines.
Alloys have properties which provide different advantages based on the needs of the
application.
Brass is an alloy of copper and zinc. Brass materials are used to form
EDM wire and small tubular electrodes. Brass does not resist wear as well as
copper or tungsten, but is much easier to machine and can be die-cast or extruded
for specialized applications. EDM wire does not need to provide wear or arc
erosion resistance since new wire is fed continuously during the EDM wiring
cutting process.
Copper and copper alloys have better EDM wear resistance than brass, but are
more difficult to machine than either brass or graphite. It is also more expensive
than graphite. Copper is, however, a common base material because it is highly
conductive and strong. It is useful in the EDM machining of tungsten carbide, or
in applications requiring a fine finish.
Copper tungsten materials are composites of tungsten and copper. They
are produced using powder metallurgy processes. Copper tungsten is very
expensive compared to other electrode materials, but is useful for making deep
slots under poor flushing conditions and in the EDM machining of tungsten
carbide. Copper tungsten materials are also used in resistance welding electrodes
and some circuit breaker applications.
Graphite provides a cleaning action at low speeds. Carbon graphite was one of
the first brush material grades developed and is found in many older motors and
generators. It has an amorphous structure.
Molybdenum is used for making EDM wire. It is the wire of choice for small slot
work and for applications requiring exceptionally small corner radii. Molybdenum
exhibits high tensile strength and good conductivity, making it ideal where small
diameter wire is needed for demanding applications.
Silver tungsten material is tungsten carbide particles dispersed in a matrix of
silver. Silver offers high electrical conductivity and tungsten provides excellent
erosion resistance and good anti-welding characteristics in high-power
applications. This composite is thus the perfect choice for EDM electrode
applications where maximizing conductivity is crucial.
Tellurium copper is useful in EDM machining applications requiring a fine
finish. Tellurium copper has a machinability that is similar to brass and better than
pure copper.
Selection Properties
When selecting EDM electrodes, the most important considerations alongside its
form and function are the material’s conductivity (or resistivity) and it’s erosion
resistance. Conductivity promotes cutting efficiency, since electric current is the “cutting
tool”. Erosion resistance (a factor of melting point, hardness, and structural integrity)
gives the electrode a longer service life and lowers the frequency of replacement. These
properties, which vary almost exclusively by the type of alloy or material used, must be
the deciding factors when selecting an electrode.
3.4 DIE-ELECTRIC FLUID
A. Functions of a Dielectric Fluid.
The sinker EDM process has primarily used oil for the dielectric fluid, and the balance
of this article will focus on dielectric oils. The dielectric oil in a Sinker EDM serves a
number of functions:
• The dielectric oil acts as a medium through which controlled electrical discharges
occur.
• The dielectric oil acts as a quenching medium to cool and solidify the gaseous EDM
debris resulting from the discharge.
• The dielectric oil acts as a medium used to carry away the solidified EDM debris from
the discharge gap to the filter system.
• The dielectric oil acts as a heat transfer medium to absorb and carry away the heat
generated by the discharges from both the electrode and the work piece.
B. Properties & Characteristics of Dielectric Oils
EDM dielectric oil properties and characteristics as they relate to the functions
of the dielectric oil in the EDM process:
Viscosity
Viscosity is the property that describes a fluids resistance to flow. Viscosity is
commonly measured by two Different units:
• Centistokes (cST)
• Say bolt Universal Seconds (SUS)
This often causes a great deal of confusion, as dielectric manufacturers often do
not use the same units to specify viscosity, making comparison difficult. Another point of
confusion results from the fact that a viscosity specification is always associated with the
temperature at which the test was performed, again rendering comparisons meaningless
unless both fluids were tested at the same reference temperature. Regardless of the
system used, a lower number means a thinner (less viscous) fluid. Generally, a thinner
fluid will flush better than a thicker fluid, and for most oils, the oil will get thinner as the
oil temperature increases.
Flash Point
“The flash point of a flammable liquid is the lowest temperature at which it can
form an ignitable mixture in air.”
The Flash Point is usually reported in units of ºF and is often measured by the
Cleveland Open Cup (COC) procedure. “The sample is contained in an open cup (hence
the name) which is heated, and at intervals a flame is brought over the surface.” The oil
temperature at which ignition of the resulting vapor occurs is the Flash Point. Flash
points for common liquids are listed below:
• Gasoline -40º F
• Ethanol 55º F
• Kerosene 120º F
• Diesel 143º F
• Vegetable Oil 620º F
The flash point for commonly used EDM dielectric oils ranges from 160º F to
255º F. Obviously for reasons of safety, the higher the flash point the better.
Dielectric Strength
For a given configuration of dielectric material and electrodes, the dielectric
strength is the minimum electrical field that produces breakdown. The dielectric strength
is commonly measured in units of either MV/m, or V/mil. Unfortunately, reported values
of dielectric strength are highly dependent upon test conditions, and therefore are subject
to a great deal of variability. It has been my experience that in actual practice, the
reported values for this parameter in commonly used dielectric oils doesn’t seem to have
much effect upon EDM performance.
Pour Point
The pour point of an oil is the temperature below which the oil no longer pours
freely. This is also sometimes called the gel point, since at temperatures below the gel
point the oil begins to gel. The pour point is usually stated in units of ºF. Since EDM oil
is normally used at or above room temperature, one might surmise that this property is
not worthy of consideration. However, if your drums of dielectric fluid are stored in an
unheated area in the winter, and that fluid has a relatively high pour point, the dielectric
will gel and cannot be pumped from the drum until it is warmed to room temperature.
Some EDMers believe that, all other properties being equal, a dielectric fluid with low
pour point is preferable to a dielectric fluid with a high pour point because is has less
dissolved paraffin wax or long chain molecules.
Volatility
Volatility is a measure of the tendency of a dielectric fluid to vaporize. While
most all dielectric fluids will exhibit some degree of evaporation, the more volatile
dielectric fluids will evaporate significantly more rapidly than their less volatile cousins.
Volatility in dielectric oils is generally related to flash point. Volatility is often not listed
in the specifications for dielectric oil, however an oil with low volatility is clearly more
desirable.
Oxidation Stability
Oxidation stability is a measure of the dielectric fluids tendency to react with
oxygen. Having greater oxidation stability means that the dielectric fluid will resist
degradation longer, retaining its clarity, initial viscosity, and give longer service life.
Oxidation stability is often not listed in the specifications for dielectric oil; however oil
with high oxidation stability is clearly more desirable.
Acid Number
The acid number is used to quantify the amount of acid present in a sample of
dielectric oil. Excessive levels of acid in dielectric oil could lead to corrosion in the
dielectric system. The acid number is expressed in units of mg KOH/g, or the amount of
Sodium Hydroxide necessary to neutralize the acid present in an oil sample.
Color
The color of dielectric oil can be classified by an ASTM test. Ideally, a dielectric
fluid should be water white for maximum visibility of the work piece. There are some
dielectric oils on the market that are intentionally colored with dye. I have seen both
green and blue. These colors have no effect upon the properties and performance of
dielectric oil. The color is often filtered out over a period of time, especially by a low
micron filter system.
Odor
The odor of a dielectric fluid is an important property, especially for those that
work with or near the dielectric fluid. Quite frankly, no one wants to work in a smelly
environment, and no one wants to go home smelling like an EDM machine. Thus, odor is
an important consideration in maintaining a decent work environment for the employees.
Unfortunately, there is no standard measure or specification of dielectric odor.
Effects on the Skin
EDM dielectric oils can adversely affect the skin of EDM operators in a number
of ways:
• EDM dielectric oils often have solvent properties which result in the removal the
natural oils and fat from the skin (With certain dielectric oils, if you dip your hand in a
drum of fresh oil, the skin on your hand will turn white when you remove your hand and
dry it off) Repeated exposure to the solvent action of the dielectric oil will often lead to
Cracking of the skin and dermatitis.
• EDM dielectric fluids can infiltrate the pores of the skin and cause all kinds of nasty
skin reactions.
C. Dielectric Fluid Types
Mineral Oils
“Mineral oil or liquid petroleum is a by-product in the distillation of petroleum.”
Kerosene
Kerosene was one of the first popular dielectric oils. Its primary benefit is that it
has very low viscosity and flushes very well. Unfortunately, it has many drawbacks:
• Low flash point
• High volatility
• Odor
• Skin reactions
In the “old days”, there were numerous EDM fires and explosions attributed to the
use of kerosene. It is no longer used as a dielectric, except in Third World countries.
Mineral Seal
Mineral seal oil takes its name from the fact that it originally replaced oil derived
from seal blubber for use in signal lamps and lighthouses. Mineral seal is a petroleum
based product that has many industrial applications, and was adopted by a number of
aerospace companies as a dielectric fluid in the early days of EDM. In fact, it is still listed
as an approved aerospace dielectric oil today. Unfortunately, it has been identified as
having some potentially carcinogenic components, and thus its use is no longer
recommended.
Transformer Oil
Transformer oil is another mineral oil based product that was adapted for use in
EDMs due to its dielectric properties. Earlier generations of transformer oil were
compounded with PCBs. Transformer oil has no current application in EDM.
EDM Oils
There are currently numerous choices of mineral oils formulated specifically for
EDM. They are available with a wide range of properties and pricing. These oils are
currently the most commonly used sinker dielectric fluids.
Synthetic Oils
“Synthetic oil is oil consisting of chemical compounds which were not originally
present in crude oil (petroleum), but were artificially made (synthesized) from other
compounds.” Synthetic oil is used as a substitute for oil refined from petroleum, stated, to
provide superior mechanical and chemical properties than those found in traditional
mineral oils. In the EDM industry, there is considerable controversy among dielectric oil
manufacturers as to whether certain oils are truly synthetic or merely super refined
mineral oils. I’ leave that controversy for the chemists to resolve. The fact of the matter is
that synthetic EDM dielectric oil is revolutionary in terms of the benefits provided:
• Longer life
• Low evaporation and volatility
• Extremely low odor
• Improved health and safety for operators
3.5 .FLUSHING TECHNIQUES
A. Proper Flushing
The most important factor in EDM is to have proper flushing. There is an old
saying among EDMers: “There are three rules for successful EDMing: flushing, flushing,
and flushing.”
Flushing is important because eroded particles must be removed from the gap
for efficient cutting. Flushing also brings fresh dielectric oil into the gap and cools the
electrode and the work piece. The deeper the cavity, the greater the difficulty for proper
flushing.
Improper flushing causes erratic cutting. This in turn increases machining time.
Under certain machining conditions, the eroded particles attach themselves to the work
piece. This prevents the electrode from cutting efficiently. It is then necessary. to remove
the attached particles by cleaning the work piece. The danger of arcing in the gap also
exists when the eroded particles have not been sufficiently removed. Arcing occurs when
a portion of the cavity contains too many eroded particles and the electric current passes
through the accumulated particles. This arcing causes an unwanted cavity or cavities
which can destroy the work piece. Arcing is most likely to occur during the finishing
operation because of the small gap that is required for finishing. New power supplies
have been developed to reduce this danger.
B. Volume , Not Pressure
Proper flushing depends on the volume of oil being flushed into the gap, rather than
the flushing pressure. High flushing pressure can also cause excessive electrode wear by
making the eroded particles bounce around in the cavity. Generally, the ideal flushing
pressure is between 3 to 5 psi. (.2 to .33 bars).
Efficient flushing requires a balance between volume and pressure. Roughing
operations, where there is a much larger arc gap, require high volume and low pressure
for the proper oil flow. Finishing operations, where there is a small arc gap, requires
higher pressure to ensure proper oil flow. Often flushing is not a problem in a roughing
cut because there is a sufficient gap for the coolant to flow. Flushing problems usually
occur during finishing operations. The smaller gap makes it more difficult to achieve the
proper oil flow to remove the eroded particles.
C. Type Of Flushing
There are four types of flushing: pressure, suction, external, and pulse
flushing. Each job needs to be evaluated to choose the best flushing method.
1. Pressure Flushing
Pressure flushing, also called injection flushing, is the most common and
preferred method for flushing. One great advantage of pressure flushing is that the
operator can visually see the amount of oil that is being used for flushing. With
pressure gauges, this method of flushing is simple to learn and use.
a. Pressure Flushing thought electrode.
Pressure flushing may be performed in two ways: through the electrode or
through the work piece.
Fig.3.3 Pressure Flushing through electrode
With pressure flushing, there is the danger of a secondary discharge. Since
electricity takes the path of least resistance, secondary discharge machining can
occur as the eroded particles pass between the walls of the electrode and the work
piece, as presented in Figure 12:3. This secondary discharge can cause side wall
tapering. Suction flushing can prevent side wall tapering.
b. Pressure Flushing Through Work piece.
Pressure flushing can also be done by forcing the dielectric fluid through a
work piece mounted over a flushing pot. See Figure 3.4. This method
eliminates the need for holes in the electrode.
Fig.3.4 pressure flushing through work piece
2. Suction Flushing
Suction or vacuum flushing can be used to remove eroded gap particles. Suction
flushing can be don through the electrode or through the work piece, as in Figure.
Fig3.5 Suction Flushing through Electrode
Fig.3.6 Suction Flushing through Work piece
Suction flushing minimizes secondary discharge and wall tapering.
Suction flushing sucks oil from the work tank, not from the clean filtered oil as in
pressure flushing. For suction cutting, efficient cutting is best accomplished when
the work tank oil is clean.
A disadvantage of suction flushing is that there is no visible oil stream as
with pressure flushing. Also, gauge readings are not always reliable regarding the
actual flushing pressure in the gap. A danger of suction flushing is that gases
may not be sufficiently removed; this can cause the electrode to explode. In
addition, the created vacuum can be so great that the electrode can be pulled from
its mount, or the work piece pulled from the magnetic chuck.
3. Combined Pressure and Suction Flushing
Pressure and suction flushing can be combined. They are often used for
molds with complex shapes. This combination method allows gases and eroded
particles in convex shapes to leave the area and permit circulation for proper
machining.
4. Jet Flushing.
Jet or side flushing is done by tubes or flushing nozzles which direct the
dielectric fluid into the gap, as shown in Figure. Pulse flushing is usually used
along with jet flushing.
Fig. 3.7 Jet Flushing
5. Pulse Flushing
Three types of pulse flushing are:
a. Vertical flushing: the electrode moves up and down.
b. Rotary flushing: the electrode rotates.
c. Orbiting flushing: the electrode orbits.
A. Vertical Flushing
In vertical flushing, the electrode moves up and down in the cavity. This
up and down motion causes a pumping action which draws in fresh dielectric oil.
Many machines are now equipped with jump control which causes the electrode
to jump rapidly in and out of the cavity which aids in flushing out the eroded
particles. See Figure.
Fig. 3.8 Vertical Flushing
B. Rotary Flushing
In rotary flushing, the electrode rotates in the cavity as in Figure. Rotating the
electrode aids in flushing out the EDM particles from the cavity.
Fig. 3.9 Rotary Flushing
C. Orbiting Flushing
Orbiting an electrode in a cavity allows the electrode to
mechanically force the eroded particle from the cavity, as pictured in Figure.
Fig. 10 Orbiting Flushing
3.6 CHARACTERSTICS OF EDM
Characteristics Description
Mechanics Of Material Removal Melting and evaporation aided by
cavitations
Medium Die-electric Fluid
Tool Material Cu, Brass, Cu-W alloy, Ag-W alloy,
Graphite
MRR/TWR 0.1-10
Gap 10-125 µm
Max. Material Removal Rate 5 x 10^3 mm^3/min
Specific Power Consumption (Typical) 1.8 W/mm^3/min
Critical Parameters Voltage, capacitance, spark gap, die-
electric circulation, melting temperature
Material Application All conducting metals and alloys
Shape Application Blind complex cavities, micro holes for
nozzles, through cutting of non-circular
holes, narrow slots
Limitation High specific energy consumption (about
50 times that in conventional machining);
when forced circulation of die-electric is
not possible, removal rate is quite low;
surface tends to be rough for larger
removal rates; non applicable to non-
conducting materials.
3.7 APPLICATION OF EDM
Prototype production
The EDM process is most widely used by the mold-making tool
and die industries, but is becoming a common method of making prototype and
production parts especially in the aerospace, automobile and electronics industries in
which production quantities are relatively low. In Sinker EDM, a graphite, copper
tungsten or pure copper electrode is machined into the desired (negative) shape and fed
into the work-piece on the end of a vertical ram
Coinage dies making
For the creation of dies for producing jewelry and badges by the coinage
(stamping) process, the positive master may be made from sterling silver, since (with
appropriate machine settings) the master is significantly eroded and is used only once.
The resultant negative die is then hardened and used in a drop hammer to produce
stamped flats from cutout sheet blanks of bronze, silver, or low proof gold alloy. For
badges these flats may be further shaped to a curved surface by another die. This type of
EDM is usually performed submerged in an oil-based dielectric. The finished object may
be further refined by hard (glass) or soft (paint) enameling and/or electroplated with pure
gold or nickel. Softer materials such as silver may be hand engraved as a refinement.
Small hole drilling
Small hole drilling EDM is used in a variety of applications. On wire-cut EDM
machines, small hole drilling EDM is used to make a through hole in a work piece in
through which to thread the wire for the wire-cut EDM operation. A separate EDM head
specifically for small hole drilling is mounted on a wire-cut machine and allows large
hardened plates to have finished parts eroded from them as needed and without pre-
drilling.
Small hole EDM is used to drill rows of holes into the leading and trailing edges
of turbine blades used in jet engines. Gas flow through these small holes allows the
engines to use higher temperatures than otherwise possible. The high-temperature, very
hard, single crystal alloys employed in these blades makes conventional machining of
these holes with high aspect ratio extremely difficult, if not impossible.
Small hole EDM is also used to create microscopic orifices for fuel system
components, spinnerets for synthetic fibers such as rayon, and other applications.
CHAPTER 4
EXPERIMENTAL WORK
4.1 PROCESS PARAMETERS
In EDM process parameters we can say that the process parameters of EDM & the
process parameters of Micro EDM are quite similar this is because the working principle
is same which that both of the machining use EDM were electrode discharge pulses & cut
away the metal with help of Die electric fluid for better machining accuracy.
1. Discharge Voltage
The spark gap & the brake-down strength of the die electric is related to
the discharge voltage in EDM process. Current will flow in to the system &
before it happened the open gap voltage increase until it has created a path that
will go through die electric the path that is mentioned before is called the
ionization path.
2. Peak Current
Peak current is known as the amount of power used in discharge
machining which this parameter is measure in Amperage and above all this is the
most important parameters in EDM machining. During each on time pulse the
current increase until it reaches a present level which is express as the peak
current.
3. Pulse Duration & Pulse Interval
Expressed in unit of micro seconds the cycle has an on time & off time.
On the one time all the work is produce and as a result the duration of these pulses
and the number of cycle per second are important. Metal removal is directly
proportional to the amount of energy applied during the on time. Pulse duration &
Pulse off time is called Pulse interval.
4. Pulse Waveform
The normal pulse waveform that we always see is rectangle, but now new
shapes have been developed pulse wave is a Non Sinusoidal wave form that is
similar to the square wave. By using trapezoidal wave generators are relatives tool
wear can be reduced to a very low value.
5. Polarity
Polarity can be either positive or negative. The current will pass through
the gap & create high temperature causes the material to evaporate at both the
electrodes spots. Polarity is determined by experimented & is a matter if tool
material, Work material, Current density & pulse combination. Modern power
supplies insert an opposite polarity “Swing Pulse” at fixed intervals to prevent
arcing. A typical ratio is 1 swing for every 15 standard pulses.
6. Electrode Gap
The tool servo mechanism is one of the most important in the efficient
working of EDM process in the servo mechanism function is to control the
working gap to the set value. An electro mechanical & hydraulic system are used
and normally designed to respond to average gap voltage. In order to obtain good
performance, gap stability & the reaction speed of the system needs to the account
for where the presents of backlash are particularly undesirable. Gap width is not
measured directly but can be inferred from the average gap voltage.
The process parameters in EDM are mainly related to the waveform
characteristics.
The open circuit voltage - Vo
The working voltage - Vw
The maximum current - Io
The pulse on time – the duration for which the voltage pulse is applied - Ton
The pulse off time - Toff
The gap between the work piece and tool – spark gap - δ
The polarity – straight polarity – tool (-ve)
The dielectric medium
External flushing through the spark gap.
4.2 PERFORMANCE PARAMETERS
1. Material Removal Rate
Based from the journal “Influence of the pulsed power condition on the
machining properties in EDM”. Shows that the source energy electro
discharge between the tool electrode and the workspace is an electric one
which power can be determined by the supply voltage and current.
2. Tool Wear Rate
The ratio of amount of electrode to the amount of work piece removal is
defined as wear ratio. There are four methods that are known to evaluate the
electrode wear ratio by means of measuring weight, shape, length and total
volume respectively. A common one is by calculating the volumetric wear
ratio usually we will measure the weight difference and transfer them into the
volumes by the density of materials. However this method is unsuitable for
Micro EDM because the weight change is so small making it difficult to
measure it accurately. Therefore it is important to measure an analyzed
removed material directly.
4.3 PROCEDURE
First of all mounting of work piece on work table, work piece is Mild steel.
Electrode clamping on quill, electrode material is copper
Alignment of electrode and work piece.
Before switching mains on, checking of all the subsystem of EDM, weather all
are working properly or not.
Priming of pump, if pump not getting started.
Once all subsystems are working properly, press mains on.
Manually move the quill down and keep some distance between electrode and
work piece.
Turn auto mode on, press auto pose on, LED grows and electrode come down.
When electrode touches job, buzzer starts and electrode goes up by sense pot.
Press pump switch on, indicator on.
Pump motor starts, dielectric fluid flows in tank.
Control its flow and hence level in dielectric tank, with the help of flow control
valves.
Press erosion on switch, if erosion indication on voltage is shown.
Electrode come down, sparking takes place.
4.4 MACHINE SPECIFICATION
Company Name: - Sparkonix India Pvt. Ltd.
Model No: - S-25
Work Tank 600x400x275mm
Work Table: - 400x300mm
X-Travel: - 200mm
Y-Travel: - 150mm
Z-Travel: - 200mm
Pulse Generator: - 25A
4.5 WORKING DETAILS
WORK CONDITION DESCRIPTION
Electrode - Copper – 10x10mm
Work-piece - M.S.-65x50x6mm
Voltage - 55-70V
Pulse Duration - 0-10
Die-electric Fluid - Hydro-Carbon oil
Polarity - Straight
Machining Time - 20min
Equipment
EDM machine has the following major subsystem
Dielectric reservoir, pump and circulation system
Power generator and control unit
Working tank with work holding device
X-Y table accommodating work table
The tool holder
The servo system to feed the tool
CHAPTER 5
OBSERVATIONS
OBSERVATION TABLE: 1
Sr
No.
I (amp) I. Weight F. Weight Difference
1 6 141.01 139.87 1.14
2 8 141.23 139.42 1.81
3 10 140.40 137.87 2.53
MRR rate at Varying Current.
Ton = 6
Toff = 6
T = 20 min.
Calculation:-
MRR-1 = [(weight Difference)/density] x Time
= [(1.14x10⁶ )/7.84] x 20min = 2.9081x10⁶ mm3/min.
OBSERVATION TABLE : 2
Sr
No.
Ton I. Weight F. Weight Difference
1 2 139.78 139.65 0.13
2 4 139.42 138.51 0.91
3 6 137.87 136.17 1.70
MRR rate at varying Ton value:
I = 8A
Toff = 6
T = 20min.
OBSERVATION TABLE : 3
Sr
No.
Ton I.Weight F. Weight Difference
1 2 139.65 137.54 2.11
2 4 138.51 136.57 2.24
3 6 136.17 134.68 1.49
MRR rate at varying Toff value :
I = 8A
Ton = 6
T = 20 min.
CHAPTER 6
RESULTS AND DISCUSSION
6.1 BY VARYING CURRENT
Fig.6.1 Current Vs MRR
As per graph between Current & MRR it is observed that increasing in
current the value of MRR increase continuously with variation of Current.
As increasing the current value more energy librated at work-piece thus
increasing in MRR.
6.2 BY VARYING Ton TIME
Fig.6.2 Ton Vs MRR
On the Ton time all the work is produced and as a result the duration of
these pulses and the numbers of cycles per second are important.
Metal removal is directly proportional to the amount of energy applied
during the Ton time.
The energy applied during the Ton time; control the peak amperage and
the length of the Ton time.
6.3 BY VARYING Toff TIME
Fig.6.3 Toff Vs MRR
Graph describe Toff time increasing while the MRR rate decreasing due
to increasing in time interval between work piece and tool, results in
increasing in surface finish and decreasing in MRR rate .
6.4 EXPECTED OUTCOME
To get in sight of expected outcome a small experiment has been
performed on EDM machine to evaluate effect of process parameters on
MRR of EDM process.
In the same manner more no. Of readings are to be taken to improving the
accuracy of results obtained.
And it is expected the MRR should increased with increasing in current,
voltage Ton and with decreasing in Toff.
CHAPTER 7
FUTURE WORK
As expectation as well as result obtained from the experiment carried out
concluded that MRR increases with increases in current, voltage, Ton and
decreases with Toff. Also non electric parameter like flushing of die-electric
has major effect of MRR.
So, depending upon the feasibility of application a method is to be applied
to improve MRR of EDM process.
Again MRR will be measured after application of suggested method is to be
compared with initial result.
Following are the various suggested methods to improve MRR of EDM
process.
1.By Electrode Design
2.By Controlling Process parameters
3.By EDM variation
4.By powder Mixed Die-electric
1. By electrode design.
Trying different kind of electrode geometries and designs to improve the
MRR.
Investigating suitable electrode material for a particular work piece material to
improve optimizes the MRR.
2. By controlling process parameters.
The material removal can be controlled and improve by controlling process
parameters. The first parameter which affects the MRR is peak current.
During each pulse on-time the current increases up to prevent value called
peak current. the peak current is governed by surface area of cut. Higher
amperage improves MRR but at a cost of tool wear and surface quality.
The amount of energy applied during machining is controlled by peak current
and pulse duration. Longer the pulse duration results in higher material
removal resulting broader and deeper crater formation.
Material removal rate is highly affected by types of dielectric and method of
flushing. Better flushing condition results in increase in both MRR and
TWR.
3.By EDM variations.
Study can be possible on effect of vibrated work piece. The vibration can be
introduce on the work piece then the flushing effect can be increase .
An introduced a new kind of electrical discharge machining technology
named tool electrode ultrasonic vibration assisted EDM in gas medium.
Experimental result shown that material removal rate could be increased
greatly by introducing ultrasonic vibration.
4. By Powder mixed die-electric.
Powder mixed electric discharge machining is one of the new innovations for
the enhancement of capabilities of EDM process.
In this process, a suitable material in fine powder properly mixed into the
die-electric fluid.
The added powder improves the break down characteristics of the die-electric
fluid.
An addition of an approximate amount of the powder into the die-electric
causes considerable improvement in MRR
REFERENCES
1. Samuel M P., Philip P. K. “powder metallurgy tool electrodes for electrical
discharge machining” , international journal of machine tool manufacturing,
vol. 37, Issue 22, 1997, pp. 1625-1633.
2. S. Kumar, R. Singh, “surface modification” by EDM. Journal of material of
material processing issue, april-2009
3. Dinesh Kumar, Naveen Beri, Saurabh Sharma, Anil Kumar, Some studies on
electric discharge machining of Hastelloy using Copper Chromium Powder
metallurgy electode using reverse polarity, technical journals online.com
4. M. Kunieda, B. Lauwers, K. P. Rajurker, B. M. Schumacher, Advancing EDM
through fundamental insight into the process journal of annals of the CIRP,
46/1, 143-146.
5. Unconventional machining by Mishra
6. S.K. Hoa, D.K. Aspinwall, W. Voice, ”use powder metallurgy compacted
electrodes for electrical discharge surface alloying/modification of Ti-6AL-
4V,” Journal of material processing technology 191 (2007) 123-126
7. Singh, S., Kansal, H.K., Kumar, P., 2005, “Parametric optimization of
powder mixed electrical discharge machining by response surface
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436.
8. Zhao, W.S., Meng, Q.G., Wang, Z. L. 2002, “The application of research on
powder mixed EDM in rough machining”, Journal of materials processing
technology, 129, 30–33.
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