High-accuracy and high-surface-quality electrical discharge machining using bipolar hybrid pulses

Abstract

Electrical discharge machining (EDM) predominantly employs a single machining polarity. Generally, machining with one polarity achieves relatively high efficiency, but the accuracy and surface quality are poor. Conversely, machining with the opposite polarity can improve machining accuracy and surface quality to some extent, but it significantly reduces machining efficiency and has limited applicability in engineering. Hence, single-polarity EDM struggles to simultaneously achieve high accuracy, excellent surface quality, and good machining efficiency. This study proposes a novel bipolar EDM method that compounds positive and negative EDM via bipolar hybrid pulses. For the first time, the electrical parameters of positive and negative pulses are independently controllably adjusted, fully leveraging the polarity effects of EDM to enhance machining performance comprehensively. The mechanism of bipolar EDM is disclosed, and the influences of electrical parameters on machining performance are investigated. Results show that the compound of positive and negative pulses enables the discharge gap of bipolar EDM to be larger than that of negative EDM. This larger discharge gap facilitates the timely removal of machining debris, enhancing machining stability and further improving accuracy and surface quality. Therefore, compared with negative EDM that exhibits better accuracy and surface quality in single-polarity EDM, bipolar EDM reduces the included angle by 6.7°, surface roughness by 19.2 % and recast layer thickness by 74.8 %. Moreover, few significant pores or cracks are observed on the machined surface, and the material removal rate increases by 1.5 times. The proposed bipolar EDM method has promising applications in precision machining.