Gas-assisted green and efficient compound sinking machining of nickel-based alloy

Abstract

Electrical arc machining is a promising method to process nickel-based alloy. Electrical arc machining commonly adopts water-based dielectric because water has no fire hazards and good cooling capacity. However, water-based dielectric has high electric conductivity, which will lead to unstable machining, including short circuit and electrochemical reactions. The gas-based dielectric is considered a more environmental and economical dielectric than the water-based dielectric. Nevertheless, the gas-based dielectric is mainly used in electrical arc machining where the machining gap is relatively open, including milling and turning. This paper proposes a gas-assisted green and efficient compound sinking machining. The compound machining combines electrical discharge machining (EDM) and electrical arc machining. The gas-liquid two-phase flow formed by dispersing gas into the deionized water is used as dielectric, whose continuous phase is liquid. The performance of the proposed method is systemically investigated by comparing with that using pure deionized water. The effects of gas type (air, oxygen, nitrogen, and argon) and machining parameters (peak current and pulse duration) on the material removal rate (MRR) and relative electrode wear rate (REWR) are studied. The characteristics of the machined surface are also analyzed. The results demonstrate that dispersing gas into the water can improve the insulation of the dielectric and reduce the unstable discharge phenomena. Besides, it can cause electric field distortion where the gas bubble locates, thereby enlarging the machining gap, improving the gap flushing environment, and enhancing the machining stability. The combustion supporting characteristic of oxygen is also helpful for improving the machining performance; thus, oxygen has the best promoting effect. Compared with the water dielectric, the proposed dielectric can improve the machining efficiency, decrease REWR, and reduce the thickness of recast layer of the machined surface in the compound sinking machining of nickel-based alloy. The proposed method is promising to meet the increasing requirement of high efficient and sustainable machining.