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Principle of EDM

EDM is a special machining method that uses the electro-erosion effect generated by the pulse discharge between the two poles immersed in the working fluid to erode conductive materials.
In 1943, the Soviet scholars Lazarenko and his wife researched and invented EDM, which developed rapidly with the improvement of pulse power supply and control system. The first pulsed power supplies used were simple resistor-capacitor loops. In the early 1950s, it was improved to circuits such as resistance-inductance-capacitance. At the same time, the so-called long-pulse power supply such as a pulse generator is also used, which improves the erosion efficiency and reduces the relative loss of the tool electrode.
Subsequently, high-frequency pulse power sources such as high-power electron tubes and thyratrons appeared, which improved the productivity under the same surface roughness conditions. In the mid-1960s, transistor and thyristor pulse power supplies appeared, which improved energy efficiency and reduced tool electrode wear, and expanded the adjustable range of rough and fine machining.
By the 1970s, power sources such as high and low voltage composite pulses, multi-circuit pulses, constant amplitude pulses and adjustable waveform pulses appeared, and new progress was made in machining surface roughness, machining accuracy and reducing tool electrode wear. In terms of the control system, from the initial simple maintenance of the discharge gap to control the advance and retreat of the tool electrode, it has gradually developed to the use of microcomputers to timely control various factors such as electrical parameters and non-electrical parameters.
During EDM, the tool electrode and the workpiece are connected to the two poles of the pulse power supply respectively, and are immersed in the working fluid, or the working fluid is charged into the discharge gap. The tool electrode is controlled to feed to the workpiece through the gap automatic control system. When the gap between the two electrodes reaches a certain distance, the pulse voltage applied to the two electrodes will break down the working fluid and generate spark discharge.
A large amount of thermal energy is instantaneously concentrated in the micro-channel of the discharge, the temperature can be as high as 10,000 degrees Celsius, and the pressure also changes sharply, so that the local trace metal material on the working surface immediately melts, vaporizes, and splashes into the working fluid explosively In the process, it condenses rapidly to form solid metal particles, which are carried away by the working fluid. At this time, a tiny pit mark is left on the surface of the workpiece, the discharge is briefly interrupted, and the working fluid between the two electrodes restores the insulating state.
Immediately after, the next pulse voltage breaks down at another point where the two electrodes are relatively close to generate spark discharge, and the above process is repeated. In this way, although the amount of metal removed by each pulse discharge is very small, due to the action of thousands of pulse discharges per second, a large amount of metal can be removed, with a certain productivity.
Under the condition of maintaining a constant discharge gap between the tool electrode and the workpiece, while the workpiece metal is etched, the tool electrode is continuously fed to the workpiece, and finally the shape corresponding to the shape of the tool electrode is processed. Therefore, as long as the shape of the tool electrode and the relative movement between the tool electrode and the workpiece are changed, various complex profiles can be processed.
Electrocorrosion-resistant materials such as copper, graphite, copper-tungsten alloy and molybdenum are commonly used for tool electrodes with good electrical conductivity, high melting point and easy processing. During the machining process, the tool electrode is also lost, but it is less than the amount of metal removal of the workpiece, and even close to no loss.
As a discharge medium, the working fluid also plays the role of cooling and chip removal during the processing. Commonly used working fluids are mediums with low viscosity, high flash point and stable performance, such as kerosene, deionized water and emulsions.
According to the form of the tool electrode and the characteristics of the relative movement between the tool electrode and the workpiece, the EDM methods can be divided into five categories: EDM machining with simple feeding motion relative to the workpiece by forming the tool electrode; EDM machining with axial movement The metal wire is used as the tool electrode, and the workpiece is moved according to the required shape and size, so as to cut the electric discharge of the conductive material. Spark grinding; EDM conjugate rotary machining for thread ring gauges, thread plug gauges, gears, etc.; small hole machining, marking, surface alloying, surface strengthening and other types of machining.
EDM can process materials and complex-shaped workpieces that are difficult to cut by ordinary cutting methods; no cutting force during processing; no defects such as burrs and tool marks and grooves; tool electrode materials do not need to be harder than the workpiece material; Realize automation; a metamorphic layer is produced on the surface after processing, which must be further removed in some applications; purification of working fluid and treatment of smoke pollution generated during processing are more troublesome.
EDM is mainly used for machining molds and parts with complex shapes of holes and cavities; machining various hard and brittle materials, such as cemented carbide and hardened steel; machining deep and fine holes, special-shaped holes, deep grooves, Slotting and cutting thin slices, etc.; processing tools and measuring tools such as various forming tools, templates and thread ring gauges.