here is an introduction to electric discharge machining

1. Muhammad Umair Akram
Advance Manufacturing Process
Electrical Discharge Machining
EDM is a nontraditional machining operation
in which tool does not comes in direct contact with the
work piece. The principle of electric discharge
machining (EDM), also called spark-erosion machining
or electro discharge machining is based on erosion of
metals by spark discharges. As in general view we know
that when the two current conducting wires come in
contact with each other an arc is produced. When these
points on contact are closely examined so we will find
small amount of metal eroded and leaves a small carter.
EDM process removes metal by discharging electric
current from the pulsating DC power supply across a
thin inter-electrode gap between the tool and the work
piece.
The EDM system consist of shaped tool
(electrode) and the workpiece, which are connected to a
DC power supply and placed in a dielectric (electrically
nonconducting) fluid. The fluid becomes ionized at the
point where the gap is narrow. The ionization of
dielectric fluid creates a condition path in which spark is
produced.
The two different types of EDM exist based on
the shape and the tool electrode used. In ram EDM also
known as sinker EDM or simply EDM, the electrode is a
die in the shape of the negative of the cavity to be
produced in a bulk material. By feeding the die into the
workpiece, the shape of the die is machined into the
workpiece. The EDM process can be used on any
material that is an electrical conductor. The melting
point and latent heat of melting are important physical
property that determines the volume of metal to be
removed per discharge.
Electrodes for EDM are usually made of
Graphite, Brass, Copper, Copper-Tungsten alloy may be
used. The tools are shaped by forming, casting, powder
metallurgy, or machining. Tool wear is an important
factor because it adversely affects dimensional accuracy
and the shape produced. tool wear can be minimize by
maintaining the current flow i.e. keeping the voltage at
low value that this will also help the tool to produce the
finish surface at the end of machining operation.
EDM processes are slow, compared to more
conventional methods of machining and they produces
finish surface composed of many small craters, while
feed rate in EDM is very slow. EDM can still compete
with conventional machining since it can easily produce
the complex geometries, particularly in hardened
materials.