Study on surface characteristics in ultrasonic vibration-assisted WEDM-LS based on spatial vibration of electrode wire

The spatial vibration model of the electrode wire in ultrasonic vibration (USV)-assisted low-speed wire electrical discharge machining (WEDM-LS) under continuous discharges is proposed for analyzing its vibration state, and subsequently, a theoretical model of material removal from the TiNi-01 shape memory alloy workpiece is established by means of Gaussian heat source in single-pulse discharge process and the principle of the nearest-point discharge breakdown. Then, the topological matrix of the surface morphology is developed for investigating the surface characteristics and the distribution of discharge points by simulation. Finally, the experiment of photographing the discharge channel position is accomplished to validate the reliability and feasibility of the model. The results show that the discharge channels are more uniformly distributed in the hybrid process, which enhance effectively the success rate of the discharge pulses and decrease the surface roughness. In addition, a mathematical model to evaluate the uniformity of the discharge point distribution is employed as an evaluation index of the burn degree on the workpiece surface. The distribution uniformity coefficient obtained by the compound process is higher than that of the traditional WEDM-LS. This is consistent with the phenomenon of alleviated surface burn under the hybrid machining technology, and the average errors of the simulated and experimental values of the uniformity coefficient of traditional WEDM-LS and the hybrid process are 4.9% and 3.4%, respectively. The maximum errors of surface roughness between simulated value and experimental value about the WEDM-LS and hybrid process are 7.4% and 8.2%, respectively. It is demonstrated that the model can effectively and accurately predict the surface roughness and the surface burn of the workpiece.