Observation and simulation investigation for the crater formation under discharge plasma movement in RT-WEDM

Abstract

Observations of the discharge gap were conducted to investigate the discharge plasma motion in reciprocated traveling wire electrical discharge machining (RT-WEDM). It was found that a discharge plasma continuously slides on the surface of a workpiece. An oscillating moving heat source is proposed to better describe the characteristics of discharge plasma motions. Based on an oscillating moving heat source, a novel thermal-fluid coupling model by adopting a level-set method is proposed to investigate the formation of a crater and the effects of machining parameters on craters. Discharge plasma sliding, latent heat, and molten pool forces are comprehensively considered in the proposed model. Simulation and experimental results show that a sliding discharge plasma has a significant effect on a crater. At the end of a discharge, a considerable proportion of molten materials remains in the molten pool. A high sliding speed of discharge plasma can lead to a low aspect ratio in a crater and a thin recast layer. Due to discharge plasma sliding, an increase in pulse duration can significantly increase the length of a crater and decrease the aspect ratio, while an increase in peak current can significantly increase the depth and volume of the crater. Simulation and experimental results also show that morphologies of the simulated crater and experimental craters are consistent, verifying the feasibility and accuracy of the proposed simulation model in explaining the mechanism of crater formation in RT-WEDM.