Measurement-based analysis of discharge-state evolution and surface characteristics in low-voltage micro-arc discharge-grinding hybrid machining of Inconel 718

To alleviate the conflict between high material removal efficiency and acceptable surface quality in machining difficult-to-cut alloys such as Inconel 718, a low-voltage micro-arc discharge-grinding hybrid machining (LV-MADG) process is proposed. The process combines low-voltage, high-current discharge with in-situ grinding, so that discharge-assisted thermal softening and abrasive removal occur within the same machining gap. An in-situ monitoring system integrating high-speed imaging with synchronized voltage-current acquisition was established to analyze discharge-state evolution during the hybrid process. Unlike previous EDM-grinding studies that mainly emphasized process feasibility or parameter optimization, this work focuses on measurement-based identification of discharge-state evolution and its relation to surface generation under low-voltage micro-arc conditions. Comparative experiments with conventional low-voltage micro-arc discharge machining (LV-MAM) under identical conditions show that LV-MADG produces a smoother surface, a thinner recast layer, and higher dimensional fidelity. Compared with copper-electrode LV-MAM, LV-MADG increases MRR by 24.66% and reduces Sa by 88.54%, while decreasing REWR from 0.40% to 0.18%. The effects of feed rate, duty cycle, spindle speed, and voltage on MRR, REWR, Sa, and RLT were also evaluated. Within the tested range, a feed rate of 0.8–1.0 mm/min, a spindle speed of 1000–1200 r/min, a voltage of 18–20 V, and a duty cycle not exceeding 70% provide a favorable window for balancing removal efficiency and surface quality. These results indicate that LV-MADG is a promising approach for improving both efficiency and surface quality in the machining of Inconel 718.