GB1081902A - Electrolytic machining - Google Patents

Abstract

<PICT:1081902/C6-C7/1> In a generating method of electrolytic machining (i.e. one where the finished form of the workpiece depends directly on the relative movement between the tool and the workpiece, though it may be affected by the shape of the tool) the tool presents a conductive surface comprising a first portion which in the direction of relative movement faces the anode or workpiece and a second portion in the form of a land which extends generally in the direction of relative movement during machining and in that direction follows the first portion and effects the finishing stage of the machining operation, and the electrolyte is caused to approach the land in a path the cross-section of which has a decrease in the flow direction towards the land without any increase between the decrease and the land. The voltage drop, the relative feed rate between the workpiece and tool, and the conductivity of the electrolyte may all three be maintained substantially constant. However, small variations in profile may be produced by adjustment of any of these three factors, e.g. to produce a slightly tapered hole. Jerkiness in feed is avoided by using an electric feed motor controlled by a known electronic comparison circuit. Fig. 1 shows a cathodic template 12 machining a workpiece 11, electrolyte being supplied to the apparatus at 16 and removed through the template holder 13. The template may be of mild or stainless steel, brass, or Cu and the holder 13 may be insulated by a stoved plastic coating, epoxy resin or plastic insulating tape. There may be a central hole 14 or parallel bores through the holder and template for removal of electrolyte but, where holes are to be enlarged, the electrolyte circulation may be by way of a hole in the workpiece in which case the template and holder will be solid. Fig. 2 (not shown) illustrates the shaping of the outer surface of a shaft, electrolyte being supplied through a hollow template holder. Templates may be such as to produce splined or square holes or solid cross-sections. The electrolyte and control of its temperature, concentration and circulation may be as specified in the parent Specification (No. 1497/64). A workpiece, prior to final sizing electrolytically, may be rough profiled, e.g. by spark discharge machining or electrolytically.