GB1076633A - Ion-control system for electrochemical machining - Google Patents

Abstract

In electrolytically machining a workpiece, a current having a waveform similar to that shown in Fig. 2 or Fig. 3 is employed. Fig. 1 illustrates an embodiment wherein a workpiece 211 is first electrochemically machined and then finished by spark discharge machining. During working, a hollow electrode 210 is fed forward by a servomotor 215 which keeps the work gap constant. During electrolytic machining, electrolyte, e.g. aqueous NaCl and optionally an inert gas such as N2 is pumped through the electrode and, during sparking, dielectric liquid such as kerosene is used. The dielectric and electrolytic liquids are separated within a reservoir 220 as a consequence of their different specific gravities. A three-phase current supply 230 provides current via transformers 233 and 234 for electrolysis and sparking respectively. The secondary windings of the transformers are connected with windings of saturable core reactors 235 and 2351. In the electrolysis circuitry, rectifiers 200A-C provide half-wave rectification of the three-phase current. When one of the switches 239A-C is closed, an impedance is bridged across the rectifier means 200B and the waveform of the current supplied to the electrodes is as shown in Fig. 2. H.F.-A.C. from a supply 209 may be superimposed on this. Network 237, 238 is responsive to the potential across the work-gap and maintains the power supply thereto substantially constant. Fig. 6 (not shown) illustrates alternative circuitry for producing a current waveform as shown in Fig. 2. The examples are of electrolytically machining I) a body composed of 60% by weight of WC and 40% by weight of Co using an aqueous NaCl electrolyte. After initial machining, the workpiece was finished by spark discharge in a kerosene dielectric. II) Electrolytically machining a tungsten-steel workpiece using a Cu electrode. <PICT:1076633/C6-C7/1>