When we EDM the mold, both the positive electrode and the negative electrode will be corroded by different degrees of electrode, even if the corrosion amount of the two electrodes of the same material is different, we will find that one electrode is more corroded than the other electrode. This phenomenon is usually called the polarity effect. If the two electrode materials are different, the effect of polarity will be more obvious. Usually, the processing of the workpiece connected to the positive pole of the pulse power supply is called "positive polarity" processing; otherwise, the processing of the workpiece connected to the negative pole of the pulse power supply is called "negative polarity". "Processing. Taking full advantage of the polarity effect in practice can increase the processing speed and reduce the electrode wear of the tool.

During electric pulse machining, we decompose the free carbon particles of negative polarity by EDM in the oil medium. Under the appropriate pulse width and pulse-to-pulse conditions, carbon particles will be covered on the positive electrode of the discharge, which is called the coverage effect. At the same time, a certain coverage effect can be used to reduce the electrode loss, but the tool electrode must be connected to the positive electrode, and the workpiece is connected to the negative electrode, that is, the workpiece is processed by the negative polarity processing method.

The energy released by the pulse discharge of injection molding is mainly absorbed by the tool electrode and the workpiece, and is usually corroded in the form of melting or vaporization. Obviously, the higher the melting point, boiling point, thermal conductivity, latent heat of fusion, latent heat of vaporization, etc. of the tool electrode or the metal to be processed, the amount of electrical corrosion will be less and less. For the tool electrode, the loss is small and it is easy to ensure the machining accuracy; and For the processing workpiece, the processing speed is slow and the effect is poor.