Electrical discharge machining is a non-traditional machining process that removes metal by using a series of electrical discharges between an electrode tool and a workpiece. Small particles of metal are melted and vaporized from the workpiece by the high temperature of the electric sparks. A dielectric fluid is continuously flushed between the tool and workpiece to carry away removed material and prevent overheating. Key factors in EDM include the current, voltage, spark gap distance, material removal rate, taper, and surface finish. It can machine any electrically conductive material regardless of hardness and produce complex, burr-free parts without mechanical contact or heat distortions.

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ELECTRICAL DISCHARGE MACHINING
j. satyanarayana

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•Electrical discharge machining, sometimes referred to as spark
machining and disintegrating
•Removing metal by a series of rapidly recurring electrical
discharges between an electrode (the cutting tool) and the
workpiece in the presence of a dielectric fluid.
•Minute particles of metal or chips, generally in the form of
hollow spheres, are removed by melting and vaporization.
are washed from the gap by the dielectric fluid which is
continuously flushed between the tool and workpiece.
•Metal removal in EDM operations takes place as a result of the
generation of extremely high temperature generated by the high
intensity of the discharge current
ELECTRICAL DISCHARGE MACHINING

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ELECTRICAL DISCHARGE MACHINING

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Dielectric
fluid
Tool
electrode
(anode)
work piece
(anode)
pump
Head
feed
direction
DC - generator
filter

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Methods of dielectric distribution:-
•Normal flow
•Immersion flushing.
ELECTRICAL DISCHARGE MACHINING

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ELECTRICAL DISCHARGE MACHINING

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ELECTRICAL DISCHARGE MACHINING

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Dielectric fluids:-
•petroleum based hydrocarbon
•mineral oils
•kerosene
•deionized water
•etc
The function of the dielectric fluid is to serve as a coolant,
conductive medium for spark, preventing oxide layer
formation due to heating and flushing the gap. The best
dielectric fluid is KEROSENE.
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The choice of the dielectric has been dictated mainly by the following factors:-
• The dielectric fluid should have sufficient and stable dielectric strength to serve as
insulation between tool and work piece.
• It should deionise rapidly after the spark discharge has taken place.
• It should have low viscosity and wetting capacity.
• It should be chemically neutral so as not to attack the electrode (tool), the table,
the work piece and the working chamber.
• Its flash point must be sufficiently high to avoid any fire hazards.
• It should not emit any toxic vapours or have unpleasant odours.
• Additives are added to inhibit the formation of bubbles and remove the char of
petroleum odor.
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Electrode material:-
• Copper graphite
• Copper
• Tellurium copper
• Brass
• Copper tungsten
• Silver tungsten
• Tungsten carbide
• Steel
• Aluminum
• Zinc.
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Guide to select Electrode Material .

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Adv & disadv of various materials for Electrodes

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Important Process parameters:-
•Current and voltage
•Electrode wear
•Spark gap ~ 0.013-0.13mm
•Material removal rate ~ 16.4mm3/hr to 245cm3/hr
•Taper range 0.005-0.05 mm/cm.
•Surface char ~ 2-4microns to 500 microns
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Application:-
•Tool & Die industries
•Aerospace
•Electronic Industries
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•Any electrically conductive material regardless of its
hardness.
•Machining will be done at hardened stage so heat
treatment distortions are avoided.
•Burr free process
•Thin fragile features machined without deformation.
•Stress free process due to no contact with work.
•Secondary operations are not required
ELECTRICAL DISCHARGE MACHINING
Advantages:-

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•slow process.
•Cavities produced are tapered due to dielectric flow.
•Materials have to be electrically conductive.
•Electrodes less than dia70 microns are impractical.
•Slight case hardening will occur this may not be permissible in
some cases.
•Tool wear, which leads to use of two or three tools per
operation, thus results in high tool manufacturing cost.
ELECTRICAL DISCHARGE MACHINING
Disadvantages:-

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