Research on ultrasonic vibration-electrical discharge machining of curved holes based on gravity driven flexible electrode

: Curved hole channel structures are crucial for high-end equipment (e.g., aerospace and energy) to optimize fluid flow and heat transfer. This study investigates ultrasonic vibration-assisted electrical discharge machining (UV-EDM) of curved holes using a gravity driven flexible electrode. The effect of ultrasonic vibration (UV) applied to the workpiece on flexible electrode motion was examined. An industrial camera was used to observe the discharge process and voltage waveforms with and without UV. The results indicate that UV induces stable periodic variation in the discharge gap, thereby improving discharge stability. A mathematical model of ball electrode motion under UV excitation was established to determine the trajectory of the ball electrode in the working fluid and to provide a theoretical basis for parameter optimization. Simulation results show that UV generates alternating pressure at the hole bottom, which promotes dielectric circulation. Curved hole forming experiments were then conducted to evaluate the effects of peak current and ultrasonic amplitude on the bottom and hole wall regions using SEM, confocal laser microscopy, and roughness measurement. At a fixed amplitude, increasing the peak current intensified erosion and deposition. A peak current index of 40 produced superior sidewall quality, with Ra = 0.266 μm. At a fixed peak current, an amplitude of 3 μm yielded a more uniform surface, with sidewall Ra = 0.285 μm. Finally, an exponential relationship between machining time and depth was fitted to support depth prediction and path planning. The successful machining of multi-segment curved holes verifies the controllability of the proposed approach.