Electric Discharge Machining Apparatus and Power Supply therefor

• Main Authors: EVERARD MOTT WILLIAMS, TERRY OLIVER HOCKENBERRY
• Format: Patent
• Language: English
• Published: 02.07.1969
• Subjects: MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR; PERFORMING OPERATIONS; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL; TRANSPORTING; WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OFELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKESTHE PLACE OF A TOOL

1,156,951. Electro-erosion. SILTRONICS Inc. 21 Feb., 1967, No. 8304/67. Heading B3V. [Also in Divisions G3 and H1] A spark-erosion machine has a working capacitor 341 charged through a rectifier 281 and transformer 501 having a leakage leg 541. The transformer may be single phase, but is preferably three-phase with primary winding 361 and secondary winding 381 which may be connected in a wye-wye, delta-wye or wye-delta network. The primary and/or the secondary windings may be tapped at 163, 154 and connected to tap switches such as 156. The secondary winding is connected to a full wave rectifier network 281 whose output is connected across the capacitor 341 and to the electrode 121 and workpiece 141. The capacitor 341 may comprise a bank of capacitors 160 coupled to a tap switch 162 which may be interconnected with the tap switch 156 controlling the transformer secondary. Erosion is performed in a bath of kerosene 181 and the spark gap 104 is controlled by the electrode feed screw 110 driven through gearing 116, 120, 122, 124 by a reversible electric motor 861. The latter has its armature energized by a D.C. source and is shunted by a rectifier 921 to facilitate motor reversals. Separate field winding 821 and 841 are provided for forward and reverse motion and are controlled automatically from the transformer 501. On at least one and preferably on each leakage leg 541 there is provided a control winding 561 connected through low-pass filter network 641 to full wave rectifier network 130. The output therefrom is connected to transistor amplifier 701 where it is compared with an adjustable reference voltage from source 761. The differential output of the amplifier controls the field windings 821, 841. Each leakage leg 541 may have a second tapped winding 164 connected through tap switch 170 and selector switch 178 to a capacitance 174 or an inductance 176 for effecting small changes in voltage-current ratio. Alternatively, this ratio may be controlled by movable tapered slugs (212), Fig. 11 (not shown), inserted into the air gaps (59) of the leakage legs 541. Reference is made to the erosion of metal carbide, hardened steel and alloys of titanium, zirconium and vanadium.