shivajee yadav

1. CONTENT
What is EDM
Working principle
Elements of EDM
Process capabilities
Measurement of MRR and Electrode wear
Applications
Advantages
Disadvantages

2. ELECTRIC DISCHARGE MACHINING
It is thermal energy based advance machining process. Numerous tiny
sparks created between two electrodes (Tool and Workpiece) are
responsible for melting and vaporization of work material.

3. WORKING PRINCIPLE
EDM is a thermoelectric process in which heat energy of a spark is used to
remove material from the workpiece in the presence of dielectric fluid.
The workpiece and tool should be made of electrically conductive material.
The frequency of sparking may be as high as thousand of spark per second.
The material removed from w/p in the form of craters. Particles erode from
electrode known as debris.
Electrodes are submerged in dielectric so that energy concentrated into
small area. Cooling of electrodes is also function of dielectric.
Localized spark energy Very high temperature
Melting & vaporization
of tool & w/p

4. Pulse On-time and Pulse Off-time
• Pulse On-time: The duration time of the EDM
spark measured in microseconds. During the
on-time there will be vaporization of material
i.e. melting of electrode material, The larger
the on time the more the metal erodes.
• Pulse Off-time: As soon as the off-time of a
pulse starts, the pressure drops instantaneously
allowing the superheated metal to evaporate.
The amount of material eroded from the work
piece and the tool will depend upon the
contributions (in the form of K.E) of electrons
and ions.

5. DIELECTRIC SUPPLY SERVO SYSTEM
POWER SUPPLY TOOL & WORKPIECE
ELEMENTS OF EDM

6. DIELECTRIC SUPPLY SERVO SYSTEM
POWER SUPPLY TOOL & WORKPIECE
ELEMENTS OF EDM
Power supply converts AC to DC by using solid state rectifier to
produce spark between tool and workpiece.
Power supply should also be able to control the parameters like
voltage, current, duration and frequency of a pulse, electrode polarity
etc.
EDM power supplies are also equipped with cut-off protection circuit.

7. DIELECTRIC SUPPLY SERVO SYSTEM
POWER SUPPLY TOOL & WORKPIECE
ELEMENTS OF EDM
Both electrodes (tool & w/p) should be electrically conductive.
The material to be used as tool electrode should possess desirable
properties like easily machinable, low wear rate, good conductor of
electricity and heat, cheap, and readily available.
Graphite, copper, brass, copper tungsten, cast aluminium, copper
boron, and silver tungsten are some of the materials that are used for
making the tools for EDM. However, copper and graphite are more
commonly used

8. DIELECTRIC SUPPLY SERVO SYSTEM
POWER SUPPLY TOOL & WORKPIECE
ELEMENTS OF EDM
It consists of dielectric fluid, reservoir, filters, pump, and delivery devices.
A good dielectric fluid should possess certain properties, it should:
1.have high dielectric strength (i.e. remain electrically non-conductive
until the required breakdown voltage between the electrodes is attained),
2.take minimum possible time to breakdown (i.e. ignition delay time).
3.deionize the gap immediately after the spark has occurred,
4.serve as an effective cooling medium,
5.have high degree of fluidity.
fluids commonly used as dielectric are transformer oil, paraffin oil,
kerosene, lubricating oils, and deionized water.

9. DIELECTRIC SUPPLY SERVO SYSTEM
POWER SUPPLY TOOL & WORKPIECE
ELEMENTS OF EDM
A servo system is used to maintain a predetermined gap between tool
and workpiece.
There is a gap voltage sensor in power supply, which sends signals to
the servo system.
The servo system will keep the tool reciprocating towards the
workpiece.
Tool wear during EDM also reduces length of tool. For accurate
machining, electrode feeding can be done manually or automatically.

10. PROCESS CAPABILITIES

11. Measurement of MRR and / Electrode Wear
MRR is calculated from weight difference of work piece before and after the
performance trial.
MRR = (Wi -Wf)1000/(7.8 t) mm³/min
Where,
Wi = Initial weight of work piece in gms, before trial
Wf = Final weight of Work piece in gms, after trial
t = Period of trials in minutes.
7.8 = Density of steel in gms/cc.

12.  The wear of copper electrodes is calculated from the weight difference in electrode weight
before and after the performance trial and is expressed as a percentage of MRR.
Absolute Wear = (Ei - Ef)1000/(8.9 t) mm³/min
Where,
Ei = weight of copper electrode in gm. Before trial
Ef = weight of electrode in gms. After trial
t = Period of trial in minutes.
8.9= Density of cu in gms/ cc.
 The wear of graphite electrodes is calculated from the loss in length of electrode during
performance trial,
Absolute Frontal Wear = AL/t mm³/min
Where,
A=frontal area – (mm²)
L =Loss in length of electrode -mm
t = Period of trial in minutes.
Percentage wear=100(Absolute frontal wear) / MRR percentage

13. APPLICATIONS
Drilling of micro holes.
Manufacturing of gears.
Fine holes or slots.
Threat cutting.
Engraving operations.
Rotary form cutting.
Manufacturing of tool having complicated profile.

14. ADVANTAGES
It can produce complex shapes, which otherwise would be
difficult to produce using conventional machining processes.
Tolerance of plus or minus 0.005 can be achieved.
Good surface finish can be obtained economically.
There is no distortion, or vibration of tool or w/p, as there no
physical contact between the tool and workpiece.
Required less machining time.

15. DISADVANTAGES
High power consumption.
Excessive tool wear during machining.
This process is only applicable for metallic or
conductive materials.
Material removal rate or MRR is very slow.
High cost and maintenance cost are required.