Electro-discharge machining is a metalworking process in which the desired shape is obtained by using electrical discharge.

An EDM consists of an electrode and a workpiece immersed in an insulating liquid such as oil or other dielectric liquid. The electrode and workpiece are connected to a power source. The power supply generates electrical potential between the two parts. As the electrode approaches the workpiece, the dielectric fluid breaks down into a plasma channel and creates small sparks. These sparks occur in large quantities at seemingly random places between the electrode and the workpiece. As the base metal erodes and the spark gap increases, the electrode is automatically lowered by the machine so that the process can continue uninterrupted. Several hundred thousand sparks are produced per second and the actual work cycle is precisely controlled by setting parameters.