The desired shape is "cut" into the workpiece by eroding the material around the "cutter" using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between the positive and negative sides of the machines plattens while separated by a dielectric fluid (which is inherently non-conductive) and subject to an electric voltage. Usually the upper platten is where the cutting tool or "electrode" is located and the table would hold the "workpiece".
When the distance between the two pieces is decreased, the intensity of the electric field in the volume between the electrodes becomes greater than the strength of the dielectric (at least in some point(s)), which breaks, allowing current to flow between the two electrodes. This phenomenon is the same as the breakdown of a capacitor (condenser) (see also breakdown voltage). As a result, material is removed from both the electrodes. Once the current flow stops (or it is stopped – depending on the type of generator), new liquid dielectric is usually conveyed into the inter-electrode volume enabling the solid particles (debris) to be carried away and the insulating proprieties of the dielectric to be restored. Adding new liquid dielectric in the inter-electrode volume is commonly referred to as flushing. Also, after a current flow, a difference of potential between the two electrodes is restored to what it was before the breakdown, so that a new liquid dielectric breakdown can occur.
A little history about the process. In 1770, English phsicist Joseph Priestley noted in his research the erosive effect of electrical discharges on various metals. Based off of Priestley's earlier research, during a separate study to eliminate the erosive effect on electrical contacts, the Soviet researchers B.R. and N.I Lazarenko had the idea of exploiting the destructive effects of an electrical discharge and develop a controlled process for machining of metals. In 1943, they developed a spark machining process, thus called because of the fact that a succession of sparks (electrical discharges) took place between two electrical conductors immersed in a dielectric fluid. The discharge generator effect then used, known as the Lazarenko Circuit, was used for a long time in the construction of generators of EDM machines. Improved, this type of generator is still used today for some applications. The spectacular changes in EDM are due also to the perseverance of several other researchers who contributed to the highlighting the fundamental characteristics of this machining method and to obtaining, at present, the best possible advantages from this process. In 1952, the manufacturer Charmilles, because interested in spark erosion machining, created the first machine using this machining process was presented for the first time at the European Machine Tool Exhibition in Milan in 1955.
A lot has changed over the years, but some things are still very much the same and at Able Wire EDM, Inc. we are proud to use Charmilles Die Sinker equipment, the industry founders.