Effects of workpiece polarity and flushing pressure on the arc plasma and the crater of single-pulsed arc discharges

Electro-arc machining (EAM) is a novel type of electrical discharge machining (EDM) that adopts high-energy arc discharges to erode workpiece materials. The workpiece polarity and the dielectric medium flushing have complex effects on the machining process and the EAM results. To fully understand these effects is beneficial to reveal the mechanism of EAM. Two single-pulsed arc discharge experiments with factors, namely, workpiece polarity and flushing pressure, were conducted. As the experimental results, the craters were measured using the microscopy images and surface profiles. The experiments found clear evidence of the polarity effect. The arc root diameter of positive workpiece polarity was smaller than that of negative workpiece polarity, while the crater diameter of positive workpiece polarity was bigger than that of negative workpiece polarity. Additionally, the effects of flushing are obvious. The arc plasma was moved along the flushing direction, which turned the common round crater into a crater with a tail. The crater depth was unaffected by workpiece polarity in the experiments and grew bigger when flushing was adopted, which means that flushing was beneficial to the material removal in EAM. It was deduced that the material removal appeared in the head of the crater mostly while the tail was composed of neglectable pits. The bulge height was increased slowly with an increase in flushing pressure, which was against good gap state and high material removal. Based on the results of the experiments, it is suggested that the EAM processes should adopt both arc-breaking methods to get better machining results.