According to Wikipedia.org:
EDM (electrical discharge machining) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques. One important limitation, however, is that EDM only works with materials that are electrically conductive.
EDM can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals such as iconel, hastelloy, kovar, titanium and carbide. Sometimes referred to as spark eroding or spark machining, EDM is a method of removing material by a series of rapidly recurring electric arcing discharges between an electrode (the cutting tool) and the work piece, in the presence of an energetic electric field.
The EDM cutting tool is guided along the desired path very close to the work but it doesn't touch the piece. Rapidly occurring consecutive sparks produce a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization. The constantly flushing dielectric fluid washes away the particles.
The EDM Machining process is becoming a common method of making production and prototype parts, though it has been most widely used by the mold-making tool and die industries. Particularly in the aerospace and electronics industries in which production quantities are relatively low.
Types of EDM Machines
The two main types of EDM machines are "ram" and "wire-cut". In the Ram method a graphite electrode is machined into the desired shape and fed into the workpiece on the end of a vertical ram. This type of EDM is usually performed submerged in an oil based dielectric. In the Wire-cut method, a thin single-strand metal wire, usually brass, is fed through the workpiece.
The wire, which is constantly fed from a spool, is held between upper and lower guides. The guides move in the X-Y plane, and sometimes the upper guide can also move independently giving rise to transitioning shapes (circle on the bottom square at the top). This gives the Wire-cut EDM the ability to be programmed to cut very intricate and delicate shapes. The wire-cut uses water as its dielectric with the water's resistivity and other electrical properties carefully controlled by filters and de-ionizer units.
A good source of information on this topic is edmmachining.com.
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