Electrochemical machining mechanism with bipolar pulses and auxiliary electrode elucidated by analyzing behavior of electric double layer

Electrochemical machining (ECM) has become one of the most promising technologies in non-conventional machining due to its high quality in surface finish, no tool wear, and no residual stress. To achieve high-precision machining with highly-localized material dissolution in ECM, effective measures need to be taken to overcome stray corrosion, which is the critical issue hindering ECM accuracy. Previous work has shown that electrochemical machining with bipolar pulses and auxiliary electrode (BPAE-ECM) can greatly improve machining accuracy and efficiency. However, the underlying mechanism of the proposed method is still unclear, especially the role of the behavior of the electric double layer (EDL). This study clarifies the mechanism through analyzing the behavior of the EDL based on signal processing of the electrochemical system. Briefly, the mechanism involves a neutralizing effect, in which the reverse charges provided by the negative-pulse are utilized to counteract the positive-pulse charges in the EDL of the non-machining area, which effectively reduces the Faradaic current to improve machining accuracy. The mechanism was verified by simulations and experiments. In contrast to conventional ECM with unipolar pulse (UP-ECM), the signals from the simulated equivalent circuit show that the EDL overpotential and Faradaic current of the non-machining area can be reduced greatly by BPAE-ECM. Corresponding experimental results show that stray corrosion is significantly reduced. Furthermore, structures with high shape accuracy are machined to demonstrate the capability of BPAE-ECM.