The polarity effect in the process of EDP machine tool processing is that the surface of positive and negative electrodes is bombarded by negative electrons and positive ions respectively, and the instantaneous heat source acts on them. The energy distribution on the surface of the two electrodes is different, so the electrolyte produced by melting and vaporization is different. The mass and inertia of electrons are small, and it is easy to obtain high speed and acceleration at the beginning of breakdown discharge. In the initial stage of breakdown discharge, a large number of electrons rush to the positive electrode, transferring energy to the surface of the positive electrode, so that the cathode material melts and vaporizes rapidly. However, due to the increase of mass and inertia, the start-up and acceleration of positive ions are slow, and only a few of them are in the initial stage of breakdown discharge. Divide the positive ions in time to reach the negative surface and transfer energy. Selecting the processing polarity, when using short pulse processing, the etching speed of positive material is faster than that of negative material, and the workpiece should be connected with the positive electrode; when using long pulse processing, the positive ions with large mass and inertia will have enough time to accelerate and reach and bombard the negative surface. Because of the large mass of positive ions, the bombardment damage to the negative surface is strong, and when using long pulse, the negative surface will be damaged strongly. The corrosion rate of the pole is greater than that of the positive pole, and then the workpiece receives the negative pole.

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