Electrical discharge machining ( EDM), also known as spark machining, is a metal processing process by which the desired shape is achieved by using electrical discharges (sparks). 

The material is removed from the workpiece by a series of rapidly repetitive current discharges between two electrodes separated by a liquid dielectric and exposed to electrical voltage. One of the electrodes is called an instrument-electrode, or simply an instrument or electrode, and the other is called a workpiece-electrode or workpiece. The process depends on the tool and the workpiece, which are not in physical contact.

When the voltage between the two electrodes increases, the electrical field strength in the volume between the electrodes becomes greater, causing a dielectric breakdown of the fluid and causing an electrical arc. As a result, the material is removed from the electrodes. As soon as the current stops (or stops, depending on the type of generator), the new liquid dielectric moves into the interelectrode volume, allowing the solid particles (debris) to be carried away and the insulating properties of the dielectric to be restored. . The addition of a new liquid dielectric to the inter-electrode volume is usually called a working fluid. After the current flow, the voltage between the electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur to repeat the cycle.

Machining of splines using EDM process
Production of bevel gears utilizing EDM machines