The principle of spark machining is usually connected to the positive pole of the power supply. If negative polarity machining is used, it will lead to reverse machining. That is, the electrode loss is large, and reverse processing can only be used when processing the same kind of data, which is often referred to as iron punching. During EDM, the tool electrode and the workpiece are respectively connected to the two poles of the pulse power supply, and immersed in the working fluid, or the working fluid is filled into the discharge gap. The tool electrode is controlled to feed the workpiece through the gap automatic control system. When the gap between the two electrodes reaches a certain distance, the pulse voltage applied on the two electrodes will break down the working fluid and generate spark discharge.

A large amount of heat energy is temporarily concentrated in the micro-channel of the discharge, the temperature can be as high as 10000 ℃, and the pressure also changes sharply, so that the local trace metal materials on the working surface of this point melt and gasify immediately, and splash into the working liquid explosively, quickly condensing to form solid metal particles, which are taken away by the working liquid. At this time, a tiny pit mark is left on the surface of the workpiece, the discharge stops for a short time, and the working fluid between the two electrodes returns to the insulating state.

Then, the next pulse voltage breaks down at another point where the two electrodes are relatively close to each other, generating a spark discharge, and the above process is repeated. In this way, although the amount of metal removed by each pulse discharge is very small, because there are thousands of pulse discharges per second, more metal can be removed, and a certain productivity is achieved.

Under the condition of maintaining a constant discharge gap between the tool electrode and the workpiece, the metal of the workpiece is etched away while the tool electrode is continuously fed to the workpiece, and finally a shape corresponding to the shape of the tool electrode is machined. Therefore, as long as the shape of the tool electrode and the relative motion pipeline between the tool electrode and the workpiece are changed, various complex profiles can be processed. Tool electrode commonly used good conductivity, high melting point, easy processing of electrical corrosion resistance data, such as copper, graphite, copper tungsten alloy and so on. In the process of machining, the tool electrode is also lost, but less than the amount of metal erosion of the workpiece, and even close to no loss.

As a discharge medium, the working fluid also plays a role in cooling and chip removal during the machining process. The commonly used working fluid is a medium with low viscosity, high flash point and stable performance, such as kerosene, deionized water and emulsion. Electric spark machine is a kind of self-excited discharge, its characteristics are as follows: spark discharge between the two electrodes in front of the discharge with a higher voltage, when the two electrodes close, during the dielectric breakdown, then spark discharge. With the breakdown process, the resistance between the two electrodes decreases sharply, and the voltage between the two electrodes also decreases sharply. The spark channel must be extinguished in time after maintaining a short time (usually 10-7-10-3s) to maintain the "cold pole" characteristic of spark discharge (I. e. the heat energy converted by the channel energy cannot be transferred to the depth of the electrode), so that the channel energy acts on a very small range. The effect of channel energy can make the electrode locally corroded. The method of using the corrosion phenomenon generated by spark discharge to process the data is called EDM. Electrical discharge machining is a spark discharge in a liquid medium in the lower voltage range. According to the form of tool electrode and the characteristics of relative movement between tool electrode and workpiece, EDM pipelines can be divided into five categories: EDM forming process using forming tool electrode to make simple feed movement relative to workpiece; Wire EDM process using axially moving metal wire as tool electrode and workpiece moving according to required shape and size to cut conductive data; Wire EDM process using metal wire or forming conductive grinding wheel as tool electrode, EDM grinding for small hole grinding or forming grinding; EDM conjugate rotary processing for processing thread ring gauge, thread plug gauge, gear, etc. Small hole processing, engraved British surface alloying, surface strengthening and other types of processing. EDM can process data and workpieces with complex shapes that are difficult to cut by ordinary cutting methods. No cutting force during processing; No defects such as burrs and tool marks grooves are produced. Tool electrode data need not be harder than workpiece data; Direct use of electric energy for processing is convenient for automation. After processing, metamorphic layer is generated on the surface, which must be further removed in some applications. Purification of working fluid and treatment of smoke pollution generated in processing are more troublesome.