Electronic discharge machining (EDM) is also known as the spark erosion process. It is metal removal by an interrupted electric spark discharge between the tool and the work. A spark gap is maintained between them, and a dielectric like kerosene, lubricant oil, paraffin oil, transformer oil having a high flash point is passed between them. Dielectric is a fluid that does not conduct current under normal circumstances. In Electronic discharge machining (EDM), it insulates, cools electrodes and workpiece, conveys the spark, flushes the removed metal. At a suitable range of voltage, the dielectric breaks down, emitting electrons ionizing the gap, liberating a temperature of 100000 C° which will melt and vaporize the metal. The tool should have high electrical conductivity, high thermal conductivity, high density, and the work should have low specific heat for a better metal removal rate process. It also defined as Electronic discharge machining the metal is removed by erosion caused by rapidly recurring spark discharges between the tool (cathode) and work (anode) separated by flooded dielectric fluid through a small gap ( about 0.02-0.5), the spark frequency is normally in the range 200-500,000 Hz. An MRR(removal rate) up to 300 mm'3/ Mon can be obtained with this process. The efficiency and the accuracy of performance have been improved when a forced circulation of the dielectric fluid is provided.
The dielectric is used to control the spark discharges, help in the sparks' movement, and act as a coolant. The tool material comprises cast iron, brass, copper steel, silver, graphite, and copper tungsten alloy. The Electronic discharge machining can machine the hardest material and produces a high degree of surface finish.
# Dielectric Fluid
The use of liquid dielectric provides the following main advantages
It acts as a vehicle to derive away from the chips, thus preventing them from sticking to the tool's surface.
— It helps increase the MRR(Metal removal rate) by promoting spark between tool and work.
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— Acts as coolant medium.
# The rate of material removal from the cathode is comparatively less than that from the anode due to the following reasons:
— The momentum with which the stream of electrons strikes the anode is much more than that due to the stream of the positive ions impinging on the cathode through the mass of an individual Electron is less than that of positive ions.
—The pyrolysis of the dielectric fluid creates a thin film of carbon on the cathode.
— A compressive force is developed on the cathode surface
# Requirement of Dielectric
— Low viscosity
— Nontoxic vapors
— Noninflammable
— Chemically stable
— Low cost
— Easily available
# The inaccuracies introduced during the EDM operation are mainly the following
—Taper of the hole machined
—Overcut due to the spark at the side faces of the electrode
— Errors due to gradual change in the electrode shape and size.
# Electrode material: The selection of the Electrode material depends on the
— MMR( Material metal removal)
— wear ratio
— Ease of shaping electrode
— Cost
# Advantage
— High MRR(Metal removal rate)
— Good surface finish
— Complex cavities can be cut
# Disadvantage
—High tool wear
—Tool wear limits the accuracy
— Only good conductors can be machined
Application:
Electronic discharge machines (EDM) are widely used for stamping (press tool), dies and punches diecasting, mold cavities for plastic molding, Blind Complex cavities.
Spark Electronic Discharge Machine (EDM) is used for simple tools and diesinking operation, whereas wire Electronic Discharge Machine is for a complex profile.
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