Master drawings were later produced by computer numerical controlled (CNC) plotters for greater accuracy. Dulebohn's group in the 1960s at Andrew Engineering Company for milling and grinding machines. Machines that could optically follow lines on a master drawing were developed by David H. The first commercially available NC machine built as a wire-cut EDM machine was manufactured in the USSR in 1967. The earliest numerical controlled (NC) machines were conversions of punched-tape vertical milling machines. To avoid the erosion of the wire causing it to break, the wire is wound between two spools so that the active part of the wire is constantly changing. The tool electrode in wire EDM is simply a wire. The wire-cut type of machine arose in the 1960s for making tools ( dies) from hardened steel. Later machines based on their design used vacuum tube circuits that were able to produce thousands of sparks per second, significantly increasing the speed of cutting.
Stark, Harding, and Beaver's machines were able to produce 60 sparks per second. But more powerful sparking units, combined with automatic spark repetition and fluid replacement with an electromagnetic interrupter arrangement produced practical machines. Initially constructing their machines from under-powered electric-etching tools, they were not very successful. Simultaneously but independently, an American team, Harold Stark, Victor Harding, and Jack Beaver, developed an EDM machine for removing broken drills and taps from aluminium castings. The Lazarenkos' machine is known as an R-C-type machine, after the resistor–capacitor circuit (RC circuit) used to charge the electrodes. This led them to invent an EDM machine used for working difficult-to-machine materials such as tungsten. They failed in this task but found that the erosion was more precisely controlled if the electrodes were immersed in a dielectric fluid.
Lazarenko, were tasked in 1943 to investigate ways of preventing the erosion of tungsten electrical contacts due to sparking. The erosive effect of electrical discharges was first noted in 1770 by English physicist Joseph Priestley.
Once the current stops (or is stopped, depending on the type of generator), new liquid dielectric is conveyed into the inter-electrode volume, enabling the solid particles (debris) to be carried away and the insulating properties of the dielectric to be restored. As a result, material is removed from the electrodes. When the voltage between the two electrodes is increased, the intensity of the electric field in the volume between the electrodes becomes greater, causing dielectric break down of the liquid, and produces an electric arc. The process depends upon the tool and work piece not making physical contact. One of the electrodes is called the tool-electrode, or simply the tool or electrode, while the other is called the workpiece-electrode, or work piece.
Material is removed from the work piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. Electrical discharge machining ( EDM), also known as spark machining, spark eroding, die sinking, wire burning or wire erosion, is a metalįabrication process whereby a desired shape is obtained by using electrical discharges (sparks).