GB776172A - Improvements relating to cutting or shaping electrically conductive materials by spark discharges - Google Patents

Abstract

776,172. Spark erosion. G.K.N. GROUP SERVICES, Ltd. Dec. 6, 1954 [Sept. 7, 1953], No. 24725/53. Class 83 (4). A method of machining a workpiece 13 by electric spark discharges comprises a tool electrode 14 of wire or strip form supported in tension and extended formation in the sparking zone 23 and fed therethrough from a bulk supply so that each part of the wire or strip is used once only during the whole of the feed movement. The wire electrode 14, preferably of brass, is supported on either side of the sparking zone by wire-drawing dies 24, 25 and fed through the zone 23 from a storage reel (not shown) to a receiving reel (not shown) by means of a motor 20 driving through reduction gearing 21 a tapered sleeve 22 on which the wire is lapped. The die 24, in the approach path of the wire, has an aperture of less area than the crosssection of the wire and the die 25 has an aperture equal to or smaller in size than that of the die 24. The wire may be fed continuously or intermittently, the speed of feed or the period of dwell respectively being such that no significant erosion of the wire occurs. The workpiece 13 is carried by a member 12 which may be mounted on the machine frame 10 so as to be adjustable transverse to the wire electrode in the horizontal and/or vertical directions and also, if desired, angularly about an axis perpendicular to the electrode. Such adjustments may be controlled manually or automatically by motors controlled by the spark discharge voltage. The workpiece, electrode, and dies are immersed in a cooling liquid 17, such as paraffin oil supplied to and drained from a receptacle 16 by pipes 18 and 19 respectively. The positive and negative contacts of the spark producing circuits are connected respectively to the workpiece and the die 24. The invention is particularly applicable to forming holes in tungsten carbide or other hard materials or to forming wire-drawing dies, the electrode wire passing through a pilot pole in the workpiece which is traversed normal to the electrode or angularly adjusted with respect thereto to produce the required shape of the hole.