Spark erosion (EDM – Electrical Discharge Machining) is a modern, thermal erosive machining process for all electrically conductive materials (steel, aluminum, copper, brass, hard metals, conductive ceramics). In result of short voltage pulses, in a non-conductive medium (dielectric fluid) there are generated electrical discharges (flashover) coming quickly after another between electrode/wire and workpiece. These discharges heat the workpiece at the point with the smallest distance between electrode/workpiece so much that small areas of material are melted and removed. Depending on current and material property during this process deep craters can arise in workpiece.

It is distinguished between wire and sinking EDM. The, so called “bore eroding” or “EDM turning” can be reduced to the above mentioned two methods.