Research on servo feed control of electrostatic induction feeding micro-ECM

• A new servo feeding control system with the peak voltage method was developed.
• The lower reference voltage resulted in higher material removal rate and smoother surface finish.
• The material removal rate was higher with larger feeding capacitance C1.
• Through-hole of 50 μm in diameter were machined on a stainless steel (SUS304) plate of 50 μm in thickness.

This paper researches about the machining characteristics and servo feeding control of micro electrochemical machining (ECM) with the electrostatic induction feeding method. Since current can flow only in the rising and falling time of pulse voltage, short pulses in the order of several tens of nanoseconds can easily be obtained, realizing significantly narrow gap widths. To avoid short circuit in the small working gap of several micrometers, a servo feeding control system based on monitoring the peak of gap voltage was developed. Compared with the old method, which monitors the average gap voltage, controllability of the working gap width with higher response was obtained because of the higher S/N ratio. The influence of the reference voltage on the material removal rate (MRR) and machining accuracy was investigated. The results showed that higher MRR and smoother surface can be obtained with lower reference voltages, due to the higher current density in the working gap obtained with higher current efficiency. However, the MRR decreased when the reference voltage was too low, as a result of the interruption of machining by the frequent retreat of the tool electrode due to short circuit. On the other hand, the MRR increased with increasing feeding capacitance C1, because electric charge per each pulse duration increased in proportion to C1. The inlet side gap width was independent of C1, due to the higher MRR and shorter machining time with larger C1. Based on the preliminary study, through-holes of 50 μm in diameter were machined on a stainless steel (SUS304) plate with a thickness of 50 μm to investigate the straightness of the holes. The diameter of the hole at the inlet and outlet sides was 58.5 μm and 55.5 μm, respectively.