Phenomena Accompanying Transient Low-Voltage Discharges in Liquid Dielectrics III-Anomalous Cathode Erosion for Arcs of Millisecond Duration

This is the third of a series1,2 of papers concerned with the electrode erosion phenomena accompanying lowvoltage (LV) discharges in liquid dielectrics. Data given are the results of investigations into the significant phenomena in the electric-spark machining art.3,4 In the electric-spark machining process, a succession of high-current discharges are caused to pass between a work piece and a tool electrode having the cross section of a shape to be formed in the work piece. Electrode and work piece are immersed in a dielectric fluid, in which the discharge is initiated by a breakdown, or sparkover. The material removal accompanying the discharge corresponds at the work piece to "useful" work and at the tool electrode to tool "wear." The electrode spacing is adjusted so that sparkover takes place at voltages of the order of 40 to 200 volts and this electrode spacing is maintained, as the machining progresses, at a relatively constant value, usually by automatic means. As a substitute for industrial diamond tools in the machining of hard materials and as a means of forming intricate shapes in a single operation with all types of conducting materials, electricspark machine tools have attracted wide interest. They are in wide use in the Soviet Union and ils western Europe. Several types of machines of United States, British, Swiss, and Japanese manufacture are commercially available in this country.