GB1062593A - Improvements relating to electrolytic machining - Google Patents

Abstract

A method of electrolytic machining comprises forcing an electrolyte flow through a restricting electrode gap between end faces of a tool and a workpiece connected respectively to opposite poles of a direct current source, applying a substantially constant bias force which tends to reduce the electrode gap size, while maintaining constant the mass flow rate of the electrolyte to suit an actual machining operation. Thereby the size of the electrode gap is maintained constant during machining. Fig. 1 shows a workpiece component 2 with a cylinder 3 mounted on it in which a piston 4 carries a hollow electrode tool 5. The tool comprises a brass or stainless steel tube 14 electrically insulated at 15. A pump 17 circulates electrolyte upwardly at a constant mass flow rate through the tool. Hydraulic fluid, such as oil, is supplied under pressure at the upper side of the piston 4 by a pump 19. Instead of the hydraulic arrangement, the piston may be connected to a spring mechanism. An electrically insulating resilient pad 24 beneath the workpiece 2 makes it possible to machine right through the work. Fig. 2 (not shown) illustrates apparatus for simultaneously machining both sides of a workpiece <PICT:1062593/C6-C7/1> <PICT:1062593/C6-C7/2> component (32), e.g. a turbine blade. Tools (36, 37) are carried by pistons (34, 35) and electrolyte is supplied and exhausted through ducts (38, 39) at constant mass flow. Oil is supplied to the ends of a cylinder (33) from a pump (43). A mechanical linkage (44) links the pistons (34, 35) so that they move equally in opposite directions. In a modification the pistons (34, 35) are moved by connecting rods from pistons in cylinders remote from the cylinder (33) and the linkage between the pistons (34, 35) is hydraulic. Also the movement of the pistons (34, 35) may alternatively be controlled by a spring movement. A sodium chloride electrolyte, tools e.g. of austenitic steel, brass and mild steel, and workgaps of 0.003-0.005 inch are specified. Fig. 3 illustrates apparatus embodying a servomechanism. A hollow tool 53 is moved relative to a workpiece 52 by a hydraulically operated piston 84. Electrolyte is circulated at constant mass flow between a reservoir 63 and the tool 53 by a pump 64 via a filter 65. Hydraulic fluid, e.g. oil, is supplied under pressure to both sides of the piston 84 from a supply 81. 88 is a variable restriction. A servo control valve 75 compares the pressures in the electrolyte and hydraulic systems and effects controls to maintain the tool-workpiece gap constant. The apparatus could be used to control two or more tools.