Combination of capacitance and conductive working fluid to speed up the fabrication of a narrow, deep hole in electrical discharge machining using a dielectric-encased wire electrode

An attempt was made to increase the machining speed of a new electrical discharge machining system for fabricating narrow, deep holes in metal. The method employs a wire encased in a dielectric jacket as the tool electrode, in contrast with the conventional pipe electrode. The role of the dielectric jacket is to completely suppress unnecessary secondary discharges occurring between the sidewalls of the wire and the fabricated hole. In the present study, the effectiveness of the combination of conductive working fluid and a capacitor connected to the work piece and the tool electrode was examined. Although electrode wear was severe, machining speed with this combination (saline water at 150–250 μS/cm and capacitance at ∼8 μF) was twice as fast compared with fabricating a hole (∅ 0.8–0.9 mm) without a capacitor and saline water in a 20-mm thick carbon steel block. The mechanisms involved are discussed based on electrical circuit theory and electrochemical corrosion.