Deep micro-hole fabrication in EMM on stainless steel using disk micro-tool assisted by ultrasonic vibration

Deep micro-hole is important in modern industries, such as aerospace, automobile, electronics, computer and medicine area, etc. Electrochemical micromachining (EMM) is a promising micro-machining method for the micro-hole fabrication. However, micro-hole with high aspect ratio is a challenge for EMM due to the difficulty of products removal in the interelectrode gap. Considering the difficulties of electrolyte refreshment in deep micro-hole drilling in EMM, the disk micro-tool was prepared and used to fabricate the micro-hole in stainless steel assisted by ultrasonic vibration in this study. Comparisons and discussions between the cylindrical and the disk-shaped cathode, drilling with and without tool vibration were done based on the Finite Element Analysis (FEA). Furthermore, influences of machining parameters on hole taper, machining speed, radial overcut, diameter, aspect ratio and surface quality were investigated on the experimental setup. Results reveal that the disk micro-tool electrode can focus the electric field on the anode and improve dissolution localization. When ultrasonic vibration was used to the micro-tool in electrochemical micro-hole machining, the machining speed and maximum depth of the machined micro-hole increases obviously, the taper and diameter decreases, the surface quality on the workpiece improves greatly than that of micro-hole machining without tool ultrasonic vibration. Deep micro-hole of Ø440 μm in entrance and Ø320 μm in exit with depth of 5.4 mm was fabricated by using the optimum parameters of voltage 9 V, pulse power 100 kHz with 0.5 off-time, amplitude 10 μm and 30 g/L NaNO3, the hole aspect ratio reaches 12.3. The proposed method will be useful for deep micro-structures fabrication in metallic material.