EDM is a machining technique for electrically conductive materials in which the tool consists of a fast and controlled continuous series of electric arcs between an electrode and the workpiece.
The process is as follows:
Between the workpiece and the electrode, separated from each other by an insulating liquid (dielectric), a potential difference ΔV is applied.
The electrode approaches the workpiece until the electric field (ΔV/cm) becomes equal to the breakdown voltage of the dielectric and the latter “breaks down” thereby conducting the electric current by means of an electric arc.
The electric arc causes a very concentrated local heating of the workpiece, causing the material to evaporate (or, putting it more accurately, to sublime).
The electrode can be a either a wire (Wire Electrical Discharge Machining or WEDM), or the negative of the engraving to be machined into the workpiece (plunge EDM).