GB780242A - Improvements in methods and apparatus for cutting electrically conductive materials - Google Patents

Abstract

780,242. Removing metal by electro-erosion. SPARCATRON, Ltd. May 19, 1953 [April 30, 1952], No. 10872/52. Addition to 637,872. Class 83 (4). In apparatus for cutting electrically conductive materials comprising a cutter electrode which is maintained in close relation to the workpiece forming the other electrode, a current supply source is included so that electric discharges are continuously produced between the cutter and workpiece which alternate between a spark discharge for evaporating material and an arc discharge for preheating the material and means are provided for flowing fluid through the cutting zone to remove disintegrated material and to cool the zone. The workpiece and electrode may be kept in relative motion and rubbing contact may be maintained, the contact pressure exerted being less than the vapour pressure exerted by the evaporation so that the cutter floats on the vapour. A capacitor may be connected between the cutter and the work to discharge intermittently, each discharge commencing with a spark and terminating.in an arc. Adjustable capacitance may be provided. The circuit is preferably made non- oscillatory by being critically damped or overdamped when the number of discharge periods may be above 5000/sec. The change-over of spark discharge to arc discharge may be caused by impressing an additional intermittent and/or cyclically variable electric motoric force upon the circuit of the cutter and workpiece. The discharges and intervals may be obtained by using a D.C. source and interrupting or diminishing the flow of current during the intervals by including an interrupting device, e.g. a thermionic valve in the circuit. A pilot spark may be used to trigger the spark discharge. As an alternative to the pilot spark the gap between the cutter and the work may be reduced by a vibrating device. The cutter may be made the anode during arcing and the cathode during sparking. An A.C. supply may be provided for sparking and arcing which may be weakened to produce the intervals. D.C. supply is preferable and electronic valve gear is used to effect polarity reversal.