GB940264A - Improvements in or relating to methods and apparatus for the spark machining of work-piece edges - Google Patents

Abstract

940,264. Removing metal by spark erosion. SONDURE ELECTRIQUE LANGUEPIN. Nov. 13, 1959 [Nov. 14, 1958], No. 38636/59. Heading B3V. A method of spark machining an edge of a workpiece 1 comprises placing the latter in a dielectric bath 10 on a support 2 having substantially free lateral movement and connected to one side of a spark generator, and centring and locating the workpiece by a vertically movable gear 9 including an electrode 6 having a surface progressively fitting the surface to be machined. The support may be mounted on a spring 3 or alternatively on a slender resilient rod, connected to an electrically conductive tank 4 containing the dielectric 10 which may be a mineral oil. An insulated chuck 9 connected to a pair of vertical displacement mechanisms 12, centres the sleeve-like workpiece 1 and the conical head electrode 6 is then lowered to machine and de-burr the inner edge of the sleeve. The spark gap is regulated by mechanism 11 controlled by the gap voltage. In another embodiment, Fig. 1 (not shown), the chuck 9 is connected rigidly to the electrode 6. The electrode and/or the tank may be vibrated during sparking. In another embodiment, Fig. 5, the support 27 is wholly or partly immersed in mercury 28 which conducts current from the tank to the support and permits its lateral movements. The workpiece is a helical spring 26 whose outer edge is machined by an electrode 19 and whose inner edge may be machined by a conical head electrode. If the surface to be machined is elliptical the axis of the conical electrode is inclined to the axis of the workpiece, Fig. 6 (not shown). An insulated replaceable sleeve 36 forms a loose guide for the support 27 and is connected to a vibrator 38 to thereby cause vibrations in the mercury 28 and hence the workpiece 26. Different sizes of sleeves produce different amplitudes of vibration. In a similar embodiment, Fig. 3 (not shown), the electrode is vibrated and the workpiece is guided by a peg projecting upwards from the tank floor; three springs may be machined simultaneously, Fig. 4 (not shown). A continuous process for machining both ends of springs 26, Fig. 8, is performed at a plurality of stations A-H. Each spring is mounted in a tank 4 carried stepwise through the stations on a rotatable table 55. At A the spring is passed into the tank from hopper 44, at B the upper inner edge is machined by electrode 45; at C the upper outer edge is machined by electrode 46; at D and E the spring is inverted by mechanism 47-50; at F and G the other edges are machined and at H the spring is withdrawn by an extractor 53.