Patent GB-1072952-A (GB)
Title: Method of and apparatus for the electrochemical machining of conductive workpieces
IPC: B23H5/12
Filed: 1964-05-13
Abstract: <PICT:1072952/C6-C7/1> <PICT:1072952/C6-C7/2> In electrolytically machining a conductive workpiec by means of a spacedly juxtaposed electrode, turbulence is promoted in electrolyte in the gap between the electrode and workpiece by passing a gas through the electrolyte to maintain a substantially uniform electric current flow between the electrode and workpiece across the gap and reduce ionic contamination.  The gas may be air, N2, CO2 or H2.  Turbulence may be further promoted, where electrolyte is introduced to the gap through a hollow electrode, by one or more constrictions in the electrode. Ionic contaminents may be mechanically dislodged by applying to the electrode a mechanical oscillation towards and away from the workpiece at a relatively low or sonic frequency and/or applying to the electrolyte a supersonic vibration.  Fig. 1 shows an electrode 17 and a workpiece 15, the electrode 17 being movable towards the workpiece 15 by a rack 43 and pinion 44.  The workpiece 15 can be displaced transversely relative to the electrode 17 by means of a mounting block 12 provided with a rack 13 engageable by a worm 14. Electrolyte is pumped through the electrode 17 from a Venturi nozzle 29 and entrains gas at 30.  The electrolyte is recirculated via a filter 48.  The nozzle 29 is oscillated axially at sonic frequency by means of an elecromagnetic coil 34 to produce a succession of electrolyte pulses and the electrolyte is oscilated ultrasonically by a transducer 38.  Turbulence is further promoted by the constriction 30 and an enlarged chamber 25.  A servo control which controls the advance of the electrode 17 responds to the voltage across the electrodeworkpiece gap 16 in order to maintain the gap constant. Fig. 3 (not shown) illustrates an electrode having a restriction (57) and a screen (52) across the end of the electrode, both of which promote turbulence of the electrolyte, the screen (52) also serving to maintain a substantially uniform current density throughout the gap.  Fig. 5 (not shown) illustrates an axially disposed conductive body (62) within an electrode.  Fig. 6 shows a workpiece 71 and an electrode 73 through which electrolyte and gas are passed.  A layer 81 of dielectric such as kerosene overlies the electrolyte to prevent splattering of the electrolyte.  The electrolyte and overflowing dielectric are recirculated via a filter screen 80.  A three-phase current supply 85 provides machining current via a three-phase transformer 86, saturable core reactor 89 and rectifiers 88a-c.  The circuitry is such as to maintain the power supplied to the electrode proportional to the width of the working gap, a transformer 92 and condenser 93 comprising a sensing device responsive to pulsating D.C. voltage applied across the working gap.  A variable capacitor 97 constitutes a current reversing element operable to permit machining of materials such as WC.  An a.c. source 98 applies HF-AC across the electrode and workpiece to reduce ionic contamination.  Figs. 7-11 (not shown) illustrate various electrode constructions for promoting turbulence of the electrolyte.  In an arrangement having two apertured discs a vortex is produced in the electrolyte.  Fig. 12 (not shown) illustrates an electrode where gas introduced through passages (146) draws electrolyte into the electrode via an injector (147).  A gas control valve (149), which in this case regulates both gas and electrolyte flow is itself controlled by a servo system (150) in response to gap width (152). When the gap increases, valve 149 opens to increase the rate of gas flow and flow of electrolyte entrained thereby.  Examples I-IV are of machining a high carbon steel using a working gap of 250 microns and an electrolyte of a 25% solution of NaCl in H2O.