Reduction of Tool Wear in Non-contact Electrostatic Induction Feeding EDM

Abstract

In this study, the authors aimed to decrease tool wear ratio in non-contact electrostatic induction feeding for micro electrical discharge machining (EDM). Since this electrostatic induction feeding method is capable of non-contact electric feeding to the tool electrode, the tool electrode can be rotated at a high speeds of 50,000rpm or more. Accordingly, both material removal rate and machining accuracy can be improved. With this method however, since discharges occur with alternating polarity, the tool electrode wear rate is higher than conventional unipolarity pulse discharge where the polarity of the workpiece is positive. Thus, in this study, circuit impedance was switched alternately to decrease the tool wear ratio, so that the discharge peak current becomes high when the workpiece is negatively charged, and low when positively charged. As a result, the tool wear ratio equivalent to conventional unipolarity discharge was achieved.

High Spindle Speed Wire Electrical Discharge Grinding Using Electrostatic Induction Feeding Method

“…Fig. 1 shows the high spindle speed micro EDM system [3]. The rod electrode was fixed to the metallic electrode holder which was held by the chuck of the motorized spindle (Nakanishi NR-2531).…”

“…This is because drilling was difficult with constant feed speeds of the tool electrode. To avoid short circuiting, the working gap voltage was measured by the non-contact monitoring method to control the gap width using the servo feed control system newly developed [3].…”

“…In this method, since a pulse voltage source is coupled to the tool electrode by capacitance that is formed in the gap between the feeding electrode and tool electrode, non-contact electric feeding to the rotating tool electrode is possible. In the previous report [3], it was shown that the material removal rate of micro drilling EDM can be increased by increasing the rotational speed up to 20000rpm. In micro drilling EDM, however, it is difficult to evaluate the effects of high spindle speed on the machining characteristics because the peripheral velocity is not high near the rotating center of the tool electrode.…”