Verfahren und Schaltungsanordnung zur Bearbeitung von Metallen durch Elektroerosion

1,196,644. Pulse circuits. INGERSOLL MILLING MACHINE CO. 26 July, 1967 [27 July, 1966], No. 34262/67. Headings H3P and H3T. [Also in Division B3] In the spark erosion machining of a conductive workpiece 16, a relatively high voltage source 20 is first connected across the gap 17 to effect ionization followed by a relatively low voltage high power machining source 22. The source 20 is connected through a switch 28, consisting of a tube or transistor controlled by a pulse generator 24. Source 22 is connected through a similar switch 42 also controlled by the pulse generator through a delay timer 36. Instead of or in addition to the timer, a diode 50 may be used to prevent application of the power source 22 until the gap has been ionized. The voltage pulses produced across the gap have a loading peak of short duration merging into a low constant voltage portion of longer duration, Fig. 2 (not shown). In modified embodiments, Figs. 3, 3a, 4 (not shown), a pulse transformer (54) and/or an R-C network are connected between the switch 28 and the gap. In another embodiment, Fig. 7 (not shown), an "and" gate (140) is connected between the timer (154) and power switch (142). This gate is supplied with an reference voltage (160) and is arranged to open the power switch (142) in the event of a short circuit in the gap. In another embodiment, Fig. 5 (not shown), the high voltage switch (102) is controlled by a flip-flop circuit (98) and the power switch (116) by a monostable vibrator (112). A detection device (90) connected across the gap provides a signal to the flip-flop when the gap has been deionized and a further signal to the vibrator when the gap has been ionized by the high voltage source. The flip-flop circuit (98) ensures that the high voltage switch (102) is opened when the power switch (116) closes. In a further embodiment, Fig. 9, a pulse generator 230, whose frequency is variable between 100 c.p.s. and 500 k.c.p.s., and whose duty cycle is also variable between 5% and 95%, feeds a pulse through a differentiating circuit 234 to a firing pulse amplifier 238 which feeds it through conductor 240 to the gap 17. Simultaneously a high voltage switch circuit 250 is energized to provide the gap with sufficient power to erode away any burns in the gap causing a short circuit. A pulse is also fed through gate 258 and inverter circuits 270, 276-to a bank of transistors or tubes 286 acting as a power switch. The latter delivers a machining pulse from variable voltage