a process for shaping a workpiece using an electrical discharge and an apparatus for practicing the process is disclosed . according to the process , a workpiece is shaped by intermittently impressing a voltage pulse across a working gap between the workpiece and an appropriately shaped electrode . the process includes the step of controlling the duration of the electrical discharge in the working gap in accordance with operating conditions in the working gap to control the average current flow . the apparatus includes a control circuit having a capacitor circuit which controls the duration of the current discharge depending directly upon the time during which the no - load voltage exists in the working gap .