Electrodischarge machining, commonly known as EDM,
removes workpiece material by an electrical spark erosion
process in which a large potential (voltage) difference is
established between the workpiece to be machined and an
electrode. A large burst (spark) of electrons travels from the
electrode to the workpiece. When the electrons impinge on
the workpiece, workpiece material is eroded away.
The EDM process (Figure M-105) takes place in a
dielectric (nonconducting) oil bath. The dielectric bath concentrates
the spark and also flushes away the spark-eroded workpiece
A typical EDM system consists of a
power supply, dielectric reservoir, electrode, and workpiece.
The EDM machine tool has many of the same features as
its conventional counterpart. These include worktable positioning
mechanisms and measurement devices.
Many EDM machine tools are equipped with computer numerical control
Thus the versatility of CNC for workpiece positioning
and tool control functions can be effectively used in
In the EDM process, the shape of the electrode controls the
shape of the machined feature on the workpiece. EDM electrodes
be made from
metal or carbon
Figure M-105 EDM system.
Servo, maintains electrode gap
Arc occurs between
electrode and work
shaped by molding or machining to the desired geometry.
The electrode erodes as well during the EDM process. In
time it becomes unusable. To circumvent this problem, a
roughing electrode may be used to generally shape the workpiece
and then a finish electrode
be applied to
and establish final dimensions and geometry.
The grades of graphite for EDM electrodes can greatly
influence tool life as well as the degree of precision obtained
by the electrode tooling. The electrode material may be classified
graphite particle size, usually ranging
from about 1 micrometer ( ) up to 100
Denser graphites have superior wear characteristics and may
be more easily machined to accommodate fine details without
EDM graphite electrodes may be
checked by examining the microstructure of the material
under a microscope.