In the previous issue of EDM Today we presented the evolution and application of die sinking generators. We saw that the generator is able nowadays to master the discharges and shape them. This article deals with the wire cutting EDM generators, and illustrates a few current and voltage pulses used in this technology. The WEDM generators must provide, for the main cut, needle like current pulses of some hundreds of amps, at voltages in the range of 300V In order to work with the electronic current only (from the wire to the workpiece), it is important that the pulses be shorter than 2.5 us. After about 3 us the ionic current (from the workpiece to the wire) becomes important, removing the wire material, depositing it on the workpiece, closing the gap and eventually welding the wire to the part, and breaking it. The pulses are then scaled down for the trim cuts, down to few amps and tens of nanoseconds at high frequencies. This machine used wires with a diameter of 30 to 40 μm, out of tungsten or molybdenum. The early WEDM machines could cut only very easy geometries, without tapering functionality, at very low speed. This limited their industrial acceptance. The booming market for the Wire machines developed only years later, with the first NC controlled machines (AGIE, 1969) and the CNC controlled ones (Seibu, 1972).
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