GB1310702A - Method and apparatus for electrolytically etching a workpiece - Google Patents

Abstract

1310702 Electrolytic machining MITSUBISHI ELECTRIC CORP 23 June 1970 [23 June 1969] 30494/70 Heading C7B A method of electrolytically etching a workpiece (whereby the gap between the workpiece and working electrode can be kept constant) comprises moving either or both of the workpiece and working electrode towards the other at constant speed and controlling the working voltage in dependence on a signal which represents the sum of a signal proportional to the instantaneous specific resistance of the electrolyte supplied to the working gap and a fixed or settable signal corresponding to the electrolyzing voltage. (The electrolyzing voltage is defined as having a constant value regardless of the current density, which value the electrolyzing voltage approaches as the current density approaches zero). As shown a workpiece 12 is electrolytically etched using a working electrode 16. Electric current is provided from a three phase A.C. source 34 via a transformer 36 and rectifier 52. The working electrode is moved at a constant speed towards the workpiece by a motor M. A first signal proportional to the working voltage is taken from resistance 102. A second signal proportional to the specific resistance of the electrolyte is derived from a detector 108. A third signal of constant magnitude corresponding with the electrolysing voltage is generated at 128. The second and third signals are added and amplified and compared with the first signal at comparison point 100. Any difference between the compared signals causes control through a saturable reactor 42 of the voltage supplied to the transformer 36. This control is effected through circuitry wherein the firing phase of thyristors 92, 94 can be altered. Specified conditions are a working-gap of 0À1 to 0À5 mm, a salt water electrolyte and use of a voltage source providing 5-20 volts and 3,000 to 5,000 amps.