We use electrical energy to cut the material to
final shape and size. The work piece (anode) and
tool (cathode) are separated by a dielectric
fluid medium. The workpiece is made anode
(positive) and tool is made cathode (negative)
in order to remove maximum metal and minimum
wear on tool.
We pass high current between the tool and work piece. When we reduce the
distance between tool and work piece, the dielectric medium ionizes and
electric current flow between the two electrodes which causes the spark
discharge. The spark will be developed into an arc if potential
difference is maintained. This results in localized heating of workpiece
which raises the local temperature of the order of 10,000°C. This
results in melting of work surface and erosion. Some of the removed
particles are vaporized and fine particles are carried away by
dielectric medium. The surface is quenched by the surrounding fluid. A
true replica is produced on the workpiece in this process.
The spark gap is generally maintained 0.01 to 0.5 mm by a Servomotor.
Higher gap decreases the spark frequency. If the potential difference
decreases, the fluid will de-ionize and discharge will cease. The gap
between the tool and work piece is varied to match metal removal rate.
The greatest erosion takes place upon positive electrode (anode) if both
electrodes are made of same material.
The shape/profile of tool is produced on work piece so any complicated
shape that can be produced on tool can be reproduced on the work piece.
All electrically conducted metals and alloys can be machined by this
process so it is used in tool manufacturing.
Complicated jigs and fixtures are not required to hold the job.
Mainly paraffin, kerosene or transformer oil is used as dielectric fluid
medium. It is pumped through tool or workpiece at a pressure of 2 kg/cm2
or less. An automatic controller ensures a constant level of dielectric
The tool used in EDM can be metallic, no-metallic, and combination of
metallic and non-metallic.
- Any hard material can be machined by this process which can not be
machined otherwise. Example – Ceramic carbide.
- Very thin section can be machined by this method.
- Very close tolerances of up to 0.04 μm can be achieved.