Patent GB-1310701-A (GB)
Title: Method and apparatus for electrolytically etching a workpiece
IPC: B23H3/02
Filed: 1970-06-23
Abstract: 1310701 Electrolytic machining MITSUBISHI ELECTRIC CORP 23 June 1970 [23 June 1969] 30493/70 Heading C7B  A method of electrolytically etching a workpiece (whereby the working-gap between the workpiece and a working electrode can be kept constant) comprises feeding one or both of the workpiece and working electrode towards the other at a constant speed and controlling the working voltage in accordance with the sum of (a) a signal proportional to the specific resistance of the electrolyte supplied to the working-gap, (b) a signal proportional to the ratio of the amount of gas to the amount of electrolyte within the working-gap and optionally (c) a signal corresponding to the electrolyzing voltage. (The electrolyzing voltage is a constant component of the working voltage unrelated to current. The electrolyzing voltage is the voltage at zero current which is obtained by extrapolating a current/working voltage curve to the working voltage axis.) The gas referred to at (b) includes gas generated by the electrolytic etching such as H 2 , and any extra gas added to the electrolyte such as air, CO or CO 2 . The ratio of the amount of gas to the amount of electrolyte within the working-gap may be controlled so as to be maintained constant. The electrolyte may be salt water, the current may be 3,000-5,000 amps at 5-20 volts. As shown in Fig.1, a workpiece 12 is electrolytically etched by means of a working electrode 16 fed towards the workpiece at constant speed by a motor M. Electrolysing current is derived from a source 34 via a transformer 36 and rectifier 52. The working voltage V is controlled by means of a saturable reactor 42. Electrolyte is fed to the working-gap 20 by a pump 24 via a flowmeter 27 which gives rise to a signal proportional to electrolyte flow. Gas is generated by the electrolysis and its amount is proportional to the electrolyzing electric current. Thus, a transformer 132 produces a signal proportional to gas flow in the electrolyte. The specific resistance of the electrolyte is detected at 110 and a signal produced. A signal proportional to the electrolysing voltage is generated at 210. The circuitry is such that at signal comparison circuit 100, a voltage V' proportional to the working voltage is compared with the sum Vs of voltages proportional to, the specific resistance, the ratio of gas flow to electrolyte flow, and electrolyzing voltage. The output from the comparison circuit 100 controls the operation of thyristors 92, 94 and thus the reactance of reactor 42 and thereby controls the working voltage V such that V' and V a  become equal. Fig.4, (not shown) illustrates a modification where in addition to the electrolytically produced gas, extra gas is supplied to the electrolyte from a source (302). A signal proportional to the quantity of this gas is supplied by a signal generator (306). Fig. 6, (not shown) illustrates a modification of the apparatus shown in Fig. 1, wherein the amount of electrolyte flow through the electrolyzing gap 20 is controlled by operation of a valve 29 in a by-pass pipe 28 so as to keep constant the ratio of the amounts of gas flow to electrolyte flow in the electrolysing gap 20. Fig.8, (not shown) illustrates apparatus including the modifications of both Figs. 4 and 6, (not shown).