Determining the Importance of Polarity Change in the Electrical Discharge Machining

Abstract

The polarity change in spark erosion is still a problem and is often carried out in a completely unmotivated or arbitrary manner. Primarily, the polarity designation must be assigned to the removal electrode. For EDM, this is usually the cathodic workpiece electrode. The objective of the chapter is to describe the removal conditions on the anode and cathode, and to explain the changing removal behavior of both electrodes. From this, the reversal point of the pulse duration can be determined, which is important for the material combination of the electrodes, the process energy source (PES) used and the load conditions. Experimental results with copper, aluminum and iron are compared in combination of the same and different electrode materials in order to validate the phenomenological models. In a second section, literature references are analyzed with the objective of investigating a polarity change. The direct polarities are primarily selected in order to maximize the removal and at the same time ensure low wear. Secondly, reverse polarities are used to achieve low surface roughness in finishing. In these applications, which have by far the largest share in the literature, a high level of wear must always be accepted. In the literature, the polarity is almost not associated with the PES and/or the load conditions of the PES, which neglects an important factor in the discussion of the results. Another factor that requires a polarity change is the use of electrical discharge in combination with other machining processes, such as electrochemical machining (ECM). The main removal mechanism is an additional influencing factor.