JPH0234732B2 - HODENKAKOYODENGENNOSEIGYOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a power source for electric discharge machining using a conductive machining fluid as the machining fluid.

A conventional power supply device of this type is shown in FIG. In the figure, 1 is a DC power source, 2 is a switching element, 3 is an oscillator, 4 is a variable resistor that controls the machining current, and 5 is a gap formed between the electrode and the workpiece. In general electric discharge machining, an insulating liquid such as mineral oil or kerosene is used as the machining fluid, so the voltage applied between the poles has a value of E ₀ when there is no load, and the voltage and current waveforms during machining are shown in Figure 2a and 2, respectively. The voltage waveforms 6 and 7 and the current waveform 8 of b. However, when using water or a machining fluid that is a mixture of water and organic compounds, the impedance between the electrodes is determined by the distance between the electrode and the workpiece, g, and the distance between the electrode and the workpiece, since the machining fluid is conductive. If the opposing area is S and the specific resistance of the machining fluid is ρ, then as shown in Figure 3, R = ρg/S (1), and the narrower the gap and the larger the opposing area, the higher the impedance. decreases. Therefore, the inter-electrode waveform in this case is as shown in Fig. 4, and when the inter-electrode voltage is applied, a current based on Ohm's law flows due to the decrease in inter-electrode impedance, resulting in a reactive current 13, and the voltage applied to the inter-electrode 12. decreases. Thereafter, when discharge starts, the voltage shifts to arc voltage 7 and the machining current shifts to 8. However, as the machining area further increases, as shown in Fig. 5, the voltage applied to the machining gap does not increase and the voltage waveform becomes only about 16, so no discharge occurs, and the reactive current 14 increases, eventually resulting in Since electric discharge is impossible, when machining a large machining area, it is necessary to increase the specific resistance of the machining fluid using an ion exchange resin or the like. Therefore, the running cost is high compared to the case where kerosene or the like is used as the machining fluid.

The present invention was made in order to eliminate the drawbacks of the conventional electric discharge machining power supply as described above.In one electric discharge machining power supply, a voltage is applied between the poles, and a voltage is applied between the electrodes during the no-load time until discharge occurs. By controlling the internal impedance of the power supply to be sufficiently smaller than the impedance between the electrodes, a voltage sufficient to generate a discharge between the electrodes is applied, and when it is detected that a discharge has occurred between the electrodes, the predetermined machining current waveform is set. By controlling the internal impedance of the power supply to a value corresponding to this machining current so as to supply the machining current, and then repeating this series of operations after a predetermined pause time, it is possible to The objective is to realize machining of large areas and micro-machining conditions using conductive machining fluids.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 6, 17 is a discharge detection device that detects the occurrence of discharge between electrodes, 18 is its output signal line, 19 is a logic circuit that selects the drive of switching elements 21 to 25, and 20a to 20e are AND circuits. , 26-30 are resistors for selecting the machining current value connected in series with the switching element, and 31-35 are outputs of the logic circuit 19.

Next, the operation of this circuit will be explained with reference to FIGS. 7 and 8.

At the start of processing, the logic circuit 19 sends ON signals to all switching elements 21-25. At this time, the oscillator 3 generates a pulse signal P as shown in FIG. The machining current waveform 37 shown in FIG. 8b is supplied.

Next, when a discharge occurs between the electrodes, the discharge detection device 17
outputs the discharge detection signal D as shown in FIG. 7, the logic circuit 19 turns off the switching elements 23 to 25, and leaves the switching elements 21 and 22 on. In this embodiment, the resistors 26 and 27 are the internal impedances of the power supply for obtaining the original predetermined discharge current. That is, applying a voltage between the poles,
During the no-load time until discharge occurs, all of the switching elements 21 to 25 are turned on, and the internal impedance of the power source is controlled to a sufficiently small value compared to the inter-electrode impedance. When a discharge occurs between the electrodes, the switching elements 21 to 25 are switched and controlled to obtain the original predetermined discharge current, and the internal impedance of the power source is controlled to a predetermined value. If all switching elements are not turned on during no-load time,
As shown in FIGS. 8a and 8b, the voltage waveform between the poles is 16, and the current waveform is 14.

In this way, by applying a voltage between the electrodes and controlling the internal impedance of the power supply to a sufficiently small value compared to the impedance between the electrodes during the no-load time until discharge occurs, a discharge is generated between the electrodes. Sufficient voltage is generated to enable stable machining even during machining of large area electrodes and finishing machining, thereby eliminating the drawbacks of conventional machining.

In the above embodiment, a general-purpose electric discharge machine was described, but the same effect can be obtained with a wire-cut electric discharge machine.

As described above, according to the control method of the present invention, it is possible to process large areas and finishing areas, which were conventionally impossible to process, without increasing running costs, which is extremely effective industrially.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional electric discharge machining power supply, Figure 2
The figure shows the voltage and current waveforms of a conventional electrical discharge machining power supply, Figure 3 is a conceptual diagram of the machining gap when using conductive machining fluid, and Figures 4 and 5 show the drawbacks of the conventional power supply. 6 is a circuit diagram showing an embodiment of the present invention, FIG. 7 is a timing chart of the power supply in FIG. 6, and FIG. 8 is a diagram of voltage and current waveforms between poles of the power supply in FIG. 6. be. In the figure, 1 is a DC power supply, 3 is an oscillator, 17 is a discharge detection device, 19 is a logic circuit, 21 to 25 are switching elements, and 26 to 30 are resistors. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. During the no-load time until discharge occurs due to the voltage applied between the electrodes, the internal impedance of the power source is determined by the distance between the electrode and the workpiece, the opposing area, and the specific resistance of the machining fluid. A method for controlling a power source for electrical discharge machining, wherein the internal impedance of the power source is selected to be smaller than the inter-electrode impedance, and after the occurrence of electric discharge, the internal impedance of the power source is selected to be larger than the internal impedance. 2. The method of controlling a power source for electric discharge machining according to claim 1, wherein the internal impedance of the power source is selected from a group of impedances arranged in advance. 3. Claim 1, characterized in that the internal impedance of the power supply is selected by a logic circuit.
A method of controlling a power supply for electric discharge machining described in Section 1.