Long before Corey Feldman’s doppelganger started dropping sick beats, there was another, much more useful and pleasant-sounding EDM: electrical discharge machining. Sometimes known as “spark machining”, “die sinking”, “wire erosion”, and “what?”, EDM is a unique manufacturing process that, as the official name suggests, uses electrical discharge to cut the desired part shape from metal materials.
A Brief Explanation of the EDM Process
In electrical discharge machining, material is removed from the workpiece (the “raw” material) by a series of fast, nearly-constant electrical current discharges between two electrodes, both of which are sunk in a dielectric liquid and goosed with electric voltage. The first electrode, called the tool-electrode, moves across the workpiece, as needed, to make the necessary cuts; the second electrode, called the workpiece-electrode, is just the workpiece itself—it pretty much just sits there.
There are two basic types of electrical discharge machining, sinker EDM and wire EDM, both of which operate on the same general principals.
Sinker EDM generally uses oil as the dielectric fluid. As the tool approaches the workpiece, the fluid breaks down, creating a plasma channel through which sparks jump. Sparks strike the workpiece one at a time, hundreds of thousands of times per second. Microsecond control of spark time (length) allows for cleaner or rougher cuts, as the part(s) being made require. Sinker EDM is used to create complex, 3D part shapes.
Wire EDM uses a thin, single strand of electrified wire (often brass) to cut through the workpiece like a cheese slicer (kind of). To prevent the ongoing electrical erosion from breaking the wire, it’s constantly fed from a spool through upper and lower CNC-controlled guides that maneuver the electrified wire through the material to cut the desired part shape. Wire EDM can cut intricate or delicate shapes in metal plate as thick as 30 cm. Deionized water is the most common dielectric fluid for wire EDM.
A Brief History of EDM
Joseph Priestly, an 18th century English physicist with the most 18th-century-English-physicist-sounding name ever, was the first to realize the erosive effect of electrical discharges of metal materials. It was not until the early 1940s, however, that the EDM process was refined for use in manufacturing. The Lazarenko brothers, noted Russian scientists, somewhat accidentally invented an early EDM system. Whilst working on a different project, they discovered that the erosive effects of electrical sparks are much more effective and easy to control when the electrode and workpiece are submerged in dielectric liquid. Their first EDM machine, created to machine difficult materials like tungsten, utilized an RC circuit to charge the electrodes. Hence, it was known as an RC-machine at the time.
At roughly the same time, a team of American scientists developed a rudimentary EDM machine to help remove broken drills and tapes from aluminum castings. As they refined their first designs, they added automatic spark repetition capabilities via an electromagnetic interrupter that could produce 60 carefully controlled sparks per second. This was further refined in later iterations, using vacuum tube circuits to increase the output to thousands of sparks per second. The more plentiful and more consistent the sparks, they found, the cleaner the cut.
Wire EDM machines were developed in the 1960s, and the earliest (pre-CNC, mechanical-“computer” operated) NC machines were built on modified punched-tape milling machines. Once again, the Russkies were the first to develop a commercially viable version, debuting a wire EDM system in the USSR in 1967. The first true CNC-controlled wire EDM machine was produced by the Andrew Engineering Company in 1976, based on R&D by a group led by American scientist David H. Dulebohn.