Modeling and Analysis of Discharge Process in Electrical Discharge Machining of NiTi Shape Memory Alloys

The material is removed by thermal effect by wire electrical discharge machining (WEDM) and a thermal damage layer is formed on the machined surface, which affects the function and performance of NiTi shape memory alloys (NiTiSMAs). However, the material removal process and thermal damage of WEDM are not clear. Therefore, by establishing the empirical formula of discharge channel radius, and based on the theory of heat transfer field and fluid mechanics, the finite element mode of crater morphology evolution and material removal process of WEDM is established in this paper. The results show that the reaction force of the vaporized metal and the gradient of surface tension caused by temperature are the fundamental reasons for driving the molten flow in the pit to both sides and forming bulges. The spatter of molten material is caused by the reaction force of metal vapor greater than the surface tension. When the material absorbs and transfers heat at a rate close to the same level during removal, a steady state effect will be formed, so that the recast layer changes within a certain range. Under the same machining conditions, the simulation and experimental results agree well with the geometry of the dent. The error of the crater depth is 14.6 %, while the error of the crater diameter is only 5.8 %. Therefore, the established model can provide insights into the material removal and thermal damage formation of NiTi-SMAs machined by WEDM