Electrical discharge machining (EDM), also known as spark erosion machining, is a nontraditional method of removing metal by a series of rapidly recurring electrical discharges (that are the equivalent of tiny lightning bolts) between an electrode (the cutting tool) and the workpiece in the presence of dielectric fluid. Minute particles of metal or chips, generally in the form of hollow spheres, are removed by melting (at 10,000°C) and vaporization. The process occurs on such a tiny scale that the resulting metal removal can be precisely controlled.
The electrode in EDM takes different forms. Wire EDM machines use a process similar in configuration to bandsawing, except in the case of the wire EDM, the “saw” is a small diameter wire electrode.
Ram EDM machines, however, which are also called “die sinkers,” use electrodes that are custom machined into 3D shapes. The EDM process then produces a cavity in the part that is opposite or a female version of the “male” electrode form. These electrodes are usually machined from graphite.
Similar to the ram EDM machine is the small-hole EDM machine. On this machine, the electrode is a cylinder used to machine a hole. Often, these machines are used simply to provide starter holes for wire EDM, but the technology may also be used to machine finished holes in materials that are too difficult to drill. Small hole EDM is also used to create microscopic orifices for fuel system components, spinnerets for synthetic fibers such as rayon, and other applications.
Besides having the ability to drill very fine holes, the advantages of EDM include: the production of complex shapes that would otherwise be difficult to produce with conventional cutting tools; the ability to machine extremely hard material to very close tolerances; and the ability to machine very small workpieces.
EDM is popular in the mold-making and die industries, but is also becoming a common method of making prototype and production parts, especially in the aerospace, automobile and electronics industries in which production quantities are relatively low.