EDM method and apparatus with trapezoidized short-duration pulses

Claim 1

An apparatus for machining an electrically conductive workpiece with a tool electrode by passing a succession of electroerosive machining pulses each with a predetermined current level and of a short pulse duration not in excess of 10 microseconds between the tool electrode and the workpiece across a machining gap flooded with a fluid medium, the apparatus comprising: a DC source; pulse-forming means for pulsing an output of the DC source to produce a succession of discrete, time-spaced, essentially unidirectional current pulses of a said short pulse duration for passage through said machining gap, each of said discrete current pulses having an essentially sinusoidally rising and falling current-time characteristic and a peak current in excess of said predetermined level; and pulse reforming means including a network connected in shunt across said workpiece and said electrode for clipping a peak current portion of each said essentially sinusoidal current pulse beyond said predetermined level so that the resulting current pulse has substantially a pair of steep flanks bridged by a plateau and has substantially said predetermined current level within said short duration, and passing said resulting current pulses in succession, constituting said succession of electroerosive machining pulses, between the tool electrode and the workpiece, said network including a field effect transistor.

Claim 2

An apparatus for machining an electrically conductive workpiece with a tool electrode by passing a succession of electroerosive machining pulses each with a predetermined current level and of a short pulse duration not in excess of 10 microseconds between the tool electrode and the workpiece across a machining gap flooded with a fluid medium, the apparatus comprising: a DC source; pulse-forming means for pulsing an output of the DC source to produce a succession of discrete, time-spaced, essentially unidirectional current pulses of a said short pulse duration for passage through said machining gap, each of said discrete current pulses having an essentially sinusoidally rising and falling current-time characteristic and a peak current in excess of said predetermined level; and pulse reforming means including a network connected in shunt across said workpiece and said electrode for clipping a peak current portion of each said essentially sinusoidal current pulse beyond said predetermined level so that the resulting current pulse has substantially a pair of steep flanks bridged by a plateau and has substantially said predetermined current level within said short duration, and passing said resulting current pulses in succession, constituting said succession of electroerosive machining pulses, between the tool electrode and the workpiece, said network including a field effect transistor.