Electric discharge machining (EDM) is a machining process that uses electrical sparks to erode metals. It works by maintaining a precise gap between an electrode tool and a metal workpiece submerged in a dielectric fluid. Repeated electrical sparks are generated to melt and vaporize small amounts of metal from both the tool and workpiece, allowing complex and hard-to-machine shapes to be produced. EDM can machine metals regardless of hardness and without mechanical force, giving it advantages over traditional machining methods for difficult-to-cut materials.

1. ELECTRIC DISCHARGE
MACHINING (EDM)
Prepared by : RAVI PRAKASH PANDEY

2. CONTENTS
. INTRODUCTION
. PRINCIPLE
. CONSTRUCTION
. TOOL MATERIAL
. FLUID PROPERTIES
. WORKING
. EFFECTS OF EDM ON METAL SURFACE
. ADVANTAGES
. DISADVANTAGES
. APPLICATIONS

3. INTRODUCTION
• EDM is a machining method typically used for hard
metals which are electrically conductive.
• It makes possible to work with metals for which
traditional machining techniques are ineffective.
• The use of a thermoelectric source of energy in
developing the nontraditional techniques has greatly
helped in achieving an economic machining of the
extremely low machinability materials and difficult
jobs.
• The process of material removal by a controlled
erosion through a series of electric sparks, commonly
known as EDM, was first started in the USSR around
1943. Then onwards, research and development have
brought this process to its present level.

4. PRINCIPLE
• The principle of EDM is also called electro
discharge or spark erosion or electro erosion,
is based on erosion of metals by spark
discharges.
• Since, when two current carrying
conductors/wires are allowed to touch each
other, an arc is produced.If we look closely at
the point of contact b/w the two wires, we
note that a small portion of metal has been
eroded away, leaving a small crater.

5. • In EDM,when a discharge takes place b/w two
points of the anode and the cathode, the
intense heat generated near the zone melts &
evaporates the materials in the sparking zone.
• For improving effectiveness, the w/p & tool
both are submerged in a dielectric fluid
(hydrocarbon or mineral oils).
• It has been observed that, If both the
electrodes are made of same materials, the
electrode connected to +ve terminal generally
erodes at faster rate. For this reason, the w/p
is normally made the anode.

6. . A suitable gap, known as the spark gap, is
maintained b/w the tool & the w/p surfaces.
. The sparks are made to discharge at a high
frequency with a suitable source.
. Since the spark occurs at the spot where the tool
& the w/p surfaces are the closest and since the
spot changes after each spark(bcoz of material
removal after each spark), the spark travells all
over the surface.
. This results in a uniform material removal all over
the surface, and finally the work face confirms to
the tool surface.
. Thus, the tool produces the required impression in
the workpiece.

7. CONSTRUCTION

8. .
• The main components of EDM are-
• -> Power Supply
• -> Tool (Electrode)
• -> Spark Generator
• -> Di-electric fluid
• Power Supply: Powersupply converts AC into
pulsed DC, used to produce spark b/w tool and
w/p. This high power pulsed output responsible
for generating spark between the electrodes.

9. • TOOL (ELECTRODE) : The shape of the tool should be
replica of the desired product, except that an
allowance is made for side clearance, over cuts for
broaching small holes.
• Solid tool(rod) may be used but for larger ones hollow
tools are used.
• If object have geometrical shape having symmetry
about some axis, tool symmetric to only a part of the
object will be sufficient for complete machining of the
object.
• SPARK GENERATOR : The spark generator performs the
important function of supplying sufficient voltage to
initiate & maintain the discharge.
• It also absorbs the supply of varying current intensity
and the discharge duration and controll the recurring
rhythmof the discharge.

10. .
• DI-ELECTRIC FLUID : In EDM, the dielectric fluid is
flushed through the spark gap.
• It is supplied either to a hole in the tool or from
external jet.
• This fluid works aas the spark conductor.
• The widely used dielectric fluid is kerosene;
others used are deionized water, Si oils, ethylene
glycol etc.
• The fluid must be hydrocarbon becoz
deionization occurs due to the involvment of
hydrogen in hydrocarbon.

11. TOOL MATERIALS
• The selection for tool material is depends
upon various factors. The main factor is, the
tool should have electrical conductive.
• Other factors are, volume of material to be
removed, required surface finish, desired
tolerance, wear ratio & many more.
• The various materials which can be used for
making tool may be of bross, copper, graphite.

12. FLUID PROPERTIES
• The dielectric fluid used in EDM should have
following properties-
1) It should have sufficient dielectric strength.
2) It should have low viscosity & good wetting
capacity.
3) It shoud be chemically neutral.
4) It should not evolve toxic vapors during entire
operation range.
5) The flash point should be high.
6) It should provide sufficient cooling medium.
7) It should be less costly & easily available.
8) It should flush the debris produced during
opration.

13. WORKING
• The EDM system consist of a shaped
tool(electrode) & w/p,which are connected to the
dc power supply and placed in electrically non
conducting dielectric fluid.
• When a voltage is applied to the tool, a magnetic
field causes suspended particles in the dielectric
fluid to concentrate, eventually forming a bridge
for current to flow to the w/p.
• An intense arc is then generated, causing
sufficient heating to melt a portion of w/p &
usually some of the tooling material also.
• In addition, the dielectric fluid heated rapidly,
causingevaporation of the fluid in the arc gap;
this evaporation increases resistance of interface
until the arc can no longer maintained.

14. .
• Once arc is interrupted, heat is removed from
the gas bubble by surrounding dielectric fluid,
and the bubbles collapses(cavitates).
• The gap b/w the tool & w/p called overcut is
critical; thus the downward feed of the tool is
controlled by a servomechanism, which
automatically maintains a constant gap.
• Hence, the machining of material is done by
EDM technique.

15. EFFECTS OF EDM ON METAL SURFACE
• The high temperature generated by sparks causes
the melting & vapourization of the metal &
obviously this high temperature affects the
properties of shallow layers of the surface to be
machined.
• The outer most layer is rapidly chilled, and
therefore becomes very hard.
• The hardening of the surface layerduring the
EDM imparts a better wear resistance
characteristic.
• The fatigue strength reduces due to the micro
cracks devoloped in the surface layer during
chilling.

16. ADVANTAGES
1) Hard & tough metals can be machined with
better surface finish.
2) Complex & internal shapes can be machined.
3) No cutting force due to no contact b/w metal
and w/p.
4) The surface finish is non-directional.
5) No effects of material hardness and tool wear.
6) Tolerance upto 0.4 micro meter is achieved.
7) Secondary finishing operation can be neglect.
8) No need of Heat treatment before machining.

17. DISADVANTAGES
1) Low MRR.
2) The w/p must be electric conductor.
3) The surface after machining is highly
stressed.
4) Machining time is too long.
5) Specific power conjumption is too high.
6) Excessive tool wear.

18. APPLICATIONS
1) It is used in the production of die for
fabrication of all componants.
2) EDM can be used in manufacturing of
hydraulic volve spools, gear wheels, fine
holes or slots in hard blade materials used in
gas turbines, compressors,diesel engines etc.
3) It is used in fabrication, extrusion, blanking,
stamping and embossing dies.
4) It is also used for removal of drilland tapes
from components.