Process for shaping workpiece by electrical discharge and apparatus therefor

Abstract

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.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. A process for shaping a workpiece using electric current comprising the steps of: positioning a workpiece adjacent a working electrode such that the electrode and the workpiece are separated by a working gap,   impressing an intermittent pulse voltage across said working gap, .Iadd.said intermittent pulse voltage comprising a repeating no-load voltage followed by a discharge voltage at the commencement of which a substantial current begins to flow within said working gap followed by a quiescent period during which no voltage is present in the gap, .Iaddend.   detecting the .Iadd.no-load .Iaddend.time period between the instant at which a .Iadd.no-load .Iaddend.voltage is impressed across said working gap and the instant at which a substantial current begins to flow within said working gap; and,   controlling the length of time during which said substantial current flows directly in response to the length of said .Iadd.no-load .Iaddend.detected time period .Iadd.and independently of the length of the quiescent period. .Iaddend.   
     
     
       2. A process as in claim 1, wherein said step of controlling includes the steps of: reducing the length of time during which said substantial current flows in said working gap below a maximum predetermined length of time provided said .Iadd.no-load .Iaddend.time period is less than a predetermined interval; and,   permitting said substantial current to flow for said maximum predetermined length of time provided said .Iadd.no-load .Iaddend.time period is greater than said predetermined interval.   
     
     
       3. An apparatus for shaping a workpiece by electric current comprising: switching means for impressing a voltage across a working gap between an electrode and a workpiece, .Iadd.said voltage comprising a repeating no-load voltage followed by a discharge voltage followed by a quiescent period during which no voltage is present in the gap, .Iaddend.said voltage remaining at a no-load level until a substantial current flows in said working gap,   timing means for measuring the time period during which said no-load voltage .Iadd.exclusive of the discharge voltage and the quiescent period .Iaddend.exists across said working gap; and,   control means coupled to said no-load voltage time measuring means for controlling the duration of flow of said substantial current directly in response to the output from said no-load voltage time measuring means .Iadd.and independently of the length of the quiescent period. .Iaddend.   
     
     
       4. An apparatus as in claim 3, further comprising: a source of potential coupled to said electrode, and,   shunt resistance means coupled between said source of potential and said switching means.   
     
     
       5. An apparatus as in claim 4, wherein: said switching means comprises a plurality of transistors coupled in parallel with one another; and,   said control means includes,   discharge initiation detector means coupled to said shunt resistance means for detecting initiation of a current in said working gap by sensing a current flow through said shunt resistance means.   
     
     
       6. An apparatus as in claim 5, wherein: said timing means is coupled to and controlled by said discharge initiation detector means.