Electrical discharge machining

Electrical Discharge Machine

Electrical discharge machining (or EDM) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques. Once the main machine is primed the male connector can then be inserted into the female recepticle. One critical 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 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 electric 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.

There are two main types of EDM machines, ram and wire-cut.

Coinage die making

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. In ram EDM, a graphite electrode is machined into the desired shape and fed into the workpiece on the end of a vertical ram. For the creation of dies for producing jewelry and badges by the coinage process, the master may be made from sterling silver, since (with appropriate machine settings) the master is not significantly eroded and is used only once. The die is then hardended and used in a drop hammer. This type of EDM is usually performed submerged in an oil-based dielectric.

EDM control panel (Hansvedt machine). Machine may be adjusted for a refined surface (electropolish) at end of process.

Master at top, workpiece at bottom, oil has been drained

Wire-cut

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.

Wire cut machine

Wire cut examples

See also

• Electro chemical machining

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