3 Types of EDM Machining and Their Differences

EDM (electrical discharge machining) is among the newer metal processing techniques, compared to rotating cutters, shearing, and forging. Rapidly pulsed high-voltage electrical discharges (sparks) are passed across the gap between the electrode and the grounded workpiece, removing material from the workpiece by erosion. Even the hardest and most intractable material can be cut and machined with very little bulk heating and virtually no application of macro forces, provided that the material is electrically conductive. This results in very low distortion and no addition of meaningful residual stresses to the workpiece.

The first EDM method, developed by Stark, Harding, and Beaver (and in parallel Lazarenko in the USSR), was hole-drilling EDM. Its earliest application was in the mid-1940s for the removal of sheared-off bolts and taps in high-value aluminum castings. Out of this relatively simple drilling method, the second branch of EDM processing developed: ram EDM or sinker discharge machining. This technique is essentially identical to EDM drilling, except that a complex form can be added to the end of the “drill” electrode. This process allows a finished, refined, and precise cavity-bottom shape to be formed in a single action. The third EDM type is wire-cut, which uses a straight wire electrode to cut a vertical or angled slot (slightly wider than the wire), as the wire is slowly fed through the cut to maintain ‘new’ electrode at all times.

This article will describe EDM machining, discuss the three main EDM methods, highlight important technical aspects of each, and identify applications that use each EDM method. It will also focus on practical applications, selection of the appropriate method, and the primary benefits of each method.