Electrochemical machining for micro holes with high aspect ratio on metal alloys using three-electrode PPS in neutral salt solution

To get micro holes with high aspect ratio on metal alloys by electrochemical machining (ECM) process, the mutual restricted problems between machining localization and efficiency are researched. By analyzing the thickening process of passive film, the mechanism of gas inhibition and dissolution promotion (GIDP) is explored. Thereby, a three-electrode pulse power supply (PPS) is designed to acidize on the workpiece/solution interface, for both better machining localization and efficiency. Micro ECM experiments, using the three-electrode PPS in neutral salt solution as electrolyte, are carried out on 304 stainless steel and 18CrNi8 alloy, in which a micro hollow electrode is used to flush electrolyte under high-pressure supply. It is found that the material removal rate (MRR) is increased by at least 80% and surface roughness R_a is dropped by 40%, compared to those of two-electrode PPS. Micro array holes with diameter of about 175 μm are machined through metallic plates with thickness of 0.5 and 1.1 mm respectively. The micro array holes obtained have high consistent precision, good surface quality, and aspect ratio up to 6.5. Experimental results show the feasibility of micro ECM techniques proposed for micro hole with high aspect ratio.