EDM principle?

Electrical spark is a self-excited discharge, in the discharge before the two electrodes with a high voltage between the two electrodes, when the two electrodes are close, the medium between them is broken, then spark discharge, along with the breakdown process, the two electrodes between the resistance of the two electrodes dramatically smaller, the voltage between the two electrodes is also drastically lower, the spark channel must be maintained in the shortest period of time (usually 10-7-10-3s) after the timely quench to maintain the Spark discharge "cold pole" characteristics (that is, the channel energy conversion of thermal energy to the electrode depth), so that the channel energy in a very small range, the role of the channel energy, the electrode can be localized corrosion. The use of spark discharge when the corrosion phenomenon on the size of the material processing method, called electric discharge machining, also known as electrical discharge machining or electrode machining, the English abbreviation for EDM. In 1943, the Soviet Union scholars, Mr. and Mrs. Lazarenko invented the electric discharge machining, and then with the improvement of the pulse power supply and control system, and the rapid development of up. Initially, the pulse power supply was a simple resistance-capacitance circuit, and in the early 1950s, it was improved to a resistance-inductance-capacitance circuit. At the same time, the pulse generator and other so-called long pulse power supply, so that the etching efficiency, tool electrode relative loss reduction. Subsequently, the emergence of high-power tubes, gate current tubes and other high-frequency pulse power supply, so that in the same surface roughness conditions under the productivity can be improved. 60's, the emergence of transistors and silicon pulse power supply, improve the efficiency of energy utilization and reduce the tool electrode loss, and expand the roughness and finish machining of the adjustable range. To the 70's, the emergence of high and low voltage composite pulse, multi-circuit pulse, equal amplitude pulse and adjustable waveform pulse power supply, in the processing of surface roughness, machining accuracy and reduce the loss of tool electrodes and other aspects of new progress. In the control system, from the initial simple to maintain the discharge gap, control the tool electrode in and out, and gradually developed to the use of micro-computers, electrical parameters and non-electrical parameters and other factors for timely control.　　EDM processing, tool electrode and workpiece are connected to the two poles of the pulse power supply, and immersed in the working fluid, or the working fluid into the discharge gap. Through the gap automatic control system to control the tool electrode to the workpiece feed, when the gap between the two electrodes reaches a certain distance, the two electrodes on the pulse voltage applied to the working fluid breakdown, resulting in spark discharge.　　In the discharge of the micro-channel instantaneous concentration of a large amount of thermal energy, the temperature can be as high as 10,000 degrees Celsius or more, the pressure also has a sharp change, so that the surface of this point of the work of the local trace of the metal material immediately melted, gasification, and explosive splash to the work of the liquid, rapid condensation, the formation of solid metal particles, be taken away from the work of the liquid. At this time on the surface of the workpiece will leave a small pit trace, the discharge briefly stopped, the two electrodes between the working fluid to restore the insulation state. Immediately thereafter, the next pulse voltage in the two electrodes relatively close to another point of breakdown, spark discharge, repeat the above process. In this way, although the amount of metal etched by each pulse discharge is very small, but because there are thousands of pulses per second discharge effect, it can be etched more metal, with a certain productivity. Under the condition of maintaining a constant discharge gap between the tool electrode and the workpiece, while etching the metal of the workpiece, 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 you change the shape of the tool electrode and tool electrode and the relative movement between the workpiece, you can process a variety of complex surfaces. Tool electrode commonly used good electrical conductivity, high melting point, easy to process corrosion-resistant materials, such as copper, graphite, copper-tungsten alloy and molybdenum. In the process, the tool electrode also has loss, but less than the amount of workpiece metal etching, or even close to no loss. Working fluid as a discharge medium, in the process of processing also plays a cooling, chip removal and other roles. Commonly used working fluid is lower viscosity, high flash point, stable medium, such as kerosene, deionized water and emulsion. According to the form of tool electrode and the relative movement between the workpiece and the characteristics of EDM processing can be divided into five categories: the use of molding tool electrode, relative to the workpiece for a simple feed movement of the EDM molding process; the use of axial movement of the metal wire as a tool electrode, the workpiece in accordance with the required shape and size of the trajectory of the movement to cut electrically conductive materials of EDM wire-cutting process; the use of metal wire or molding of conductive grinding wheel for Tool electrode, for small hole grinding or molding grinding EDM grinding; for the processing of thread ring gauge, thread plug gauge, gears, etc. EDM **** yoke rotary machining; small hole machining, engraving, surface alloying, surface enhancement and other types of processing.

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