The Effectiveness of Non-Rectangular Current-Pulse Forms in Electro-Discharge Machining

Although the advent of rectangular current-pulse generators in EDM has represented a most significant advance in performance, nevertheless the problem of electrode wear persists, and the question arises whether alternative pulse forms are more effective still. By using a specially constructed transistorized pulse generator, giving considerable flexibility in the choice of machining current waveform, results delineate a machining region where the use of non-rectangular current pulses gives a clear improvement upon the performance of rectangular pulses. An ‘optimum’ pulseform is identified which produces an improvement in volumetric wear ratio of up to three times, when machining steel with a copper electrode to a given level of surface finish. This improvement in wear ratio can only be obtained when using medium or long pulse times and there is virtually no advantage to be gained in using non-rectangular current pulses for pulse times less than 30 μSec. Furthermore when machining steel with a graphite electrode, and using the ‘optimum’ pulseform, no improvment in wear ratio has been found at any value of pulse time.