Comparison experiments of near-dry EDM ablation milling, submerged mist-jetting mode and submerged gas-jetting mode are conducted to investigate an optimal gap dielectric mode which benefits improving the process index of EDM ablation milling. Material Removal Rate (MRR), Relative Electrode Wear Rate (REWR) and surface roughness are compared. The experimental results show that the submerged gas-jetting mode gets the highest MRR of 131.86 mm3/min, increased by 7.10% and 27.42% compared to near-dry mode and submerged mist-jetting mode; this mode remains the lowest REWR of 1.81%, reducing by 72.11% and 74.64% compared to near-dry mode and submerged mist-jetting mode; the mode also achieved the largest oxygen utilization rate of 0.81%, increasing by 44.64% and 65.31% in comparison with near-dry mode and submerged mist-jetting mode. The analysis indicates submerged gas-jetting EDM ablation milling sparks in the gas-liquid stratified medium, which shows better debris removal capability than others, and therefore reduced short circuit; thus, REWR of submerged gas-jetting mode reduces sharply. The submerged gas-jetting mode also has the advantage of gathering oxygen, and consequently, is able to improve the performance of EDM ablation milling.
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