Abstract: A sintered electrode for electric discharge machining comprises a continuous phase consisting of a conductive region (3), and a dispersed phase consisting of microscopic polycrystalline diamond (2) dispersed in the continuous phase. The conductive region (3) is cobalt, nickel, cobalt nickel alloy or cemented carbide and imparts conductivity to the electrode (1). The microscopic polycrystalline diamond (2) imparts excellent mechanical strength and thermal diffusion to the electrode (1). The electrode (1) and the workpiece (5) are connected to a power supply (V1) in reverse polarity and a current pulse having ON-time of 60 ? seconds or less and 1 ? second or more and peak of 15 A or less and 1 A or more is supplied to the electrode (1) from the power supply (V1).

Abstract: An adaptive apparatus for controlling the discharge current comprises a circuit for sensing the gap voltage and a circuit for sensing the gap current. Based upon these sensed conditions at the gap, the waveform of the discharge current is detected. The waveform of the current is compared to several reference levels at certain times during the waveform in order to determine the condition at the gap. The reference levels may be varied in accordance with the machining method, such as in accordance with the peak value of current. The off times for the pulses are then varied according to the conditions at the gap. The pulses of discharge current are therefore controlled in order to provide the optimal machining rate and an improved workpiece surface finish while reducing arc discharges.