Electrical discharge machining
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Electrical discharge machining (or EDM) is a method of working extremely hard materials or materials that are difficult to machine cleanly using conventional methods. It is limited, however, to electrically conductive materials. EDM can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals such as titanium, hastelloy, kovar, inconel and carbide.
Sometimes referred to as spark machining or spark eroding, EDM is a nontraditional 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 dielectric field. The EDM cutting tool is guided along the desired path very close to the work but it does not touch the piece. Consecutive sparks produce a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization. The particles are washed away by the continuously flushing dielectric fluid.
The EDM process is most widely used by the mold-making tool and die industries, but is becoming a common method of making prototype and production parts, especially in the aerospace and electronics industries in which production quantities are relatively low.
There are two main types of EDM machines, ram and wire-cut. In ram EDM, 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 Wire-cut EDM, 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.