Automatic Stripping of Dielectric-Encased Wire Tool Electrode Used in Electrical Discharge Machining

A new electrical discharge machining (EDM) system using a wire encased in a dielectric jacket is proposed as an alternative to conventional hole-fabrication EDM systems. The jacket suppresses secondary discharges occurring between the sidewalls of the wire and the fabricated hole, which allows fabrication of holes with higher aspect ratios compared to those formed by a conventional EDM system using naked pipe electrodes. In this new system, the tip of the wire electrode is stripped by displacing the jacket, which produces continuous sparks for workpiece erosion and keeps the bore and shape of the fabricated holes constant. In the present study, we developed a control system to maintain the exposed length of the tip without the need for visual observation and without the assumption that wear is constant over time. The exposed length of the tip of the wire electrode is related to the feed speed (toward the workpiece) of the electrode system. The jacket was displaced when the feed speed of the electrode system exceeded a threshold value, which resulted in slowing of the electrode system feed. The feed speed was kept within the specified range by determining a threshold value, which led to maintenance of a constant exposed length of the tip. This control system was validated in actual drilling tests. Optimizing the threshold feed speed contributed to a higher machining speed.