The phenomenon of electrical erosion in CNC EDM was discovered as early as the end of the 19th century. For example, the electric spark generated when plugs and switches are opened and closed will cause damage to the contact surface. In the early 20th century, when Lazarinko of the Soviet Union studied the phenomenon and causes of the corrosion damage of the switch contacts by spark discharge, he found that the instantaneous high temperature of the electric spark would melt and vaporize the local metal and be etched away, thus created and invented the CNC EDM method, and in 1943, the world's first practical CNC EDM-device was developed using the principle of electric erosion, and the phenomenon of electric erosion was really applied to actual production and processing. China began to study the EDM equipment in the early 1950s, and in the early 1960s developed the first wire EDM hole drilling machine.
(1) EDM drilling
The punch processing of EDM drilling machine is the most widely used type of CNC EDM, and is often used to process shaped holes (round holes, square holes, polygon holes, special-shaped holes), curved holes, 4qL, micro holes, etc., such as cold stamping dies, drawing dies, extrusion dies, nozzles, various types of holes and small holes on the spinneret.
The dimensional accuracy of the perforation is mainly guaranteed by the size of the tool electrode and the gap of the spark discharge. The cross-sectional contour size of the electrode is evenly smaller than the size of the pre-machined hole by a machining gap, and its dimensional accuracy is one level higher than that of the workpiece, generally not lower than IT7 level, the surface roughness value is smaller than that of the workpiece, and the straightness, flatness and parallelism are not greater than 0.01mm on a 100mm length.
(2) EDM cavity machining
The EDM cavity processing includes forging dies, die casting dies, extrusion dies, bakelite dies, plastic dies, etc. The cavity machining is more difficult, mainly because it is non-through hole machining, the amount of metal corrosion is large, the working fluid circulation and the removal conditions of electro-corrosion products are poor, and the tool electrode cannot be compensated by feed after wear; secondly, the machining area changes greatly, and due to the cavity is complex and the electrode wear is uneven, which has a great impact on the machining accuracy, so the cavity machining productivity is low and the quality is difficult to guarantee. In order to improve the machining accuracy of the cavity, in terms of electrodes, pure copper and graphite with high corrosion resistance should be used as electrodes. In addition, the CNC EDM is also used for the surface grinding of some small plastic molds.