Research on the Plasma Channel Expansion Behavior of Cathode in Electrical Arc Machining

Abstract As a thermal erosion process, the performance of electrical arc machining (EAM)—including material removal rate (MRR) and tool wear ratio (TWR)—is greatly influenced by arc plasma in the gap between the workpiece and the electrode. Therefore, it is necessary to study plasma channel expansion behaviour (PCEB) to disclose the EAM mechanism. By far, negative polarity EAM is usually adopted to achieve a higher MRR; most current research concentrates on the PCEB of the anode side for it directly relates to the MRR. However, in electrical machining, the plasma ignites from the cathode side, and positive polarity EAM is also recommended to improve the surface quality. Thus, the PCEB of the cathode is also very important. In this paper, a set of single discharge observation experiments was implemented to investigate the PCEB at cathode side by utilizing a four-frame high-speed camera. Based on time solved imaging of single discharge, the relationship between the PCEB and primary electrical parameters, including discharge time and peak current, was studied. Besides, the PCEBs of three conventional electrode materials were compared to find the mutual relationship between the material properties and expansion behaviour. The PCEB formulations of these materials under the specific parameters were further deduced and applied to simulate the single discharge crater. Finally, to elaborate the validity of the formulations, the simulation results above were compared with the results obtained by using uniform plasma diameter.