GB974338A - Apparatus suitable for forming holes electrolytically in a metallic workpiece - Google Patents

Abstract

A hole is formed electrolytically with or without arcing in an anodic workpiece 33, such as a turbine or compressor blade, by advancing the workpiece 33, mounted in a holder 35, 36 37, at a predetermined rate towards a hollow cathode electrode 55 through which electrolyte is supplied and, at the same time, rotating the workpiece relative to the cathode by means of a projection 41 engaging a groove 40 in a cylindrical portion 37 of the advancing workpiece holder 35, 36, 37. The electrode 55 shown in Fig. 1 has an insulating outer coating and terminates in an enlarged uninsulated working tip 70 which forms a hole of elliptical cross-section. Rotation of the workpiece causes the ellipse axes to rotate as the depth of the hole increases. Alternatively, an electrode as shown in Fig. 3 may be used which forms a circular hole. The workpiece holder 35, 36, 37 is <PICT:0974338/C6-C7/1> mounted in a carriage 9 movable over guide shafts 10, 11 by means of a motor 23 acting through a shaft 22. An arm 35, forming part of the workpiece holder, has an aperture 59 which makes a press fit over a boss 58 which slidably surrounds the cathode 55. The electrolyte is circulated by pumps 65, 68, is filtered at 69 and, to prevent its conductivity from varying, its temperature is maintained constant by a thermostatically controlled electric heater 66a. A relay in the circuitry switches off the electrolysing current if the electrode should contact the workpiece. Upward movement of the carriage 9 is limited by a stop 50. The electrode shown in Fig. 3, for forming holes which are circular in cross-section, comprises a hollow stainless steel stem 81, which is insulated at 84 with a phenolic epoxy resin, and at 86 with a polyvinyl chloride coating on top of a primer 85 and has an uninsulated working tip 83. An electrode may be reciprocated rapidly to cause intermittent arcing between itself and the work. Further, an electrode for forming circular holes can be rotated. Electrolysing conditions referred to are an electrolyte of brine of specific gravity 1.172 at 140 DEG F. and at 100 p.s.i. for holes over 0.70 inch diameter and at 300 p.s.i. for holes of less than 0.070 inch and a voltage of 4 to 30. Alternatively Na2SO4 with or without 5% borax may be used.