JPS61249213A - Electric power source apparatus for wire electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent the softening of the worked surface and improve energy efficiency by setting the polarity of a workpiece to negative electrode on dielectric breakdown and to positive electrode on the generation of main electric discharge, when working is performed by the main electric discharge for working which is generated in the working gap after dielectric breakdown. CONSTITUTION:A condenser 20e for electric discharge is charged by turning-ON a switching element 20b and turning-OFF a switching element 21b. Then, the electric discharge for dielectric breakdown is started in a working gap Q, and said dielectric breakdown is detected by a voltage detecting circuit 22a, and output into a pulse control circuit 22b is performed. Then, the switching element 20b is turned-OFF, and the switching element 21b is turned-ON for the time t1. At this time, the dielectric breakdown voltage can be arbitrarily set. When a prescribed time t2 lapses after the switching element 21b is turned-OFF, the switching element 20b is turned-ON, and the above-described procedures are repeated. Thus, the softening of the worked surface can be prevented, and the dimension precision can be improved, and the energy efficiency can be improved, and the dielectric breakdown voltage can be arbitrarily set.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a wire electrical discharge machine, and particularly to an improvement of a power supply device used for generating electrical discharge in the wire electrical discharge machine.

[Background of the invention]

In recent years, both the machining speed and machining accuracy of wire electric discharge machines have been greatly improved, but as the machining speed increases, the machining accuracy tends to decrease. Particularly, in those using a high-speed machining power source, the power source generates a relatively large electrolytic reaction, resulting in a reduction in machining accuracy.

This will be explained below based on FIG. 4. FIG. 4 is a schematic configuration diagram of a conventional wire electric discharge machine equipped with the above-mentioned power supply device, and 1 in the figure indicates a wire electrode.

This wire electrode 1 is guided by rollers 2 and 3 and faces the processing surface of the workpiece 4, and the electrode 1 and the workpiece 4
The relative position of is controlled by a motor 5.6 of a positioning device operated by a command from a numerical control device (not shown). A machining fluid supply nozzle 7.8 supplies ion-exchanged water, which is a machining fluid, to the machining gap Q formed between the electrode l and the workpiece 4, and the electrode l is connected to a current-carrying terminal 9.8. 1O, and a source of stains is supplied from the power supply 11 between the electrode 1 and the workpiece 4 (machining gap Q). The power supply device 11 is composed of a DC power supply 12, a switching element 13 and its on/off control circuit 14, a current limiting resistor 15, and a discharge circuit including a discharge capacitor 16.

As shown in FIG. 5(a), the voltage waveform in the machining gap Q by the power supply device 11 increases exponentially after the switching element 13 is turned on, and the capacitor 16 is charged up to the voltage of the DC power supply 12. When the electric discharge is generated in the machining gap Q, the oscillating current flows and becomes zero, as shown in FIG. 5(b). The oscillating current waveform is
It is determined by the inductance and resistance value of the current-carrying system from the capacitor 16 to the machining gap Q, and the capacitance of the capacitor 16, but generally the waveform is as shown in FIG. 5(b).

Furthermore, a power supply device having a circuit configuration in which the capacitor 16 in FIG. 4 is removed has also been used in the past, and the voltage and current waveforms in this case are as shown in FIGS. 6(a) and (b). In either power supply device, the polarity of the applied current at the time of dielectric breakdown is such that the workpiece 4 is the anode. This is because it has been confirmed through experiments that it is better to flow the current from the workpiece 4 to the electrode 1 as the polarity that increases the speed at which the workpiece 4 is processed.

However, in such conventional devices, since water is normally used as the machining fluid, an electrolytic reaction occurs when a voltage is applied to the machining gap Q, and the machining surface of the workpiece 4 becomes soft, resulting in a machining problem. The quality of the surface deteriorated. This amount of deterioration extends from several micrometers to more than ten micrometers from the machined surface, which has been a major obstacle when performing high-precision processing with dimensional accuracy on the order of several micrometers.

For the above problem, the average voltage between the power supply poles is OvK
There is a method of applying a bipolar voltage to make the difference, but according to this method, there is a method of applying a bipolar voltage to make the difference. The problem remains that the machining speed decreases because the frequency of the pulse decreases.

Further, in the conventional apparatus described above, when the dielectric breakdown voltage is changed, the machining current also changes, so there is a problem that the setting of the dielectric breakdown voltage is restricted by the machining current.

[Purpose of the invention]

The present invention was made to solve the above-mentioned problems, and it prevents softening of the machined surface caused by electrolytic reaction in the machining gap without reducing the machining speed, and improves the quality of the machined surface. It is an object of the present invention to provide a power supply device for a wire electric discharge machine, which can improve the dimensional accuracy, and whose dielectric breakdown voltage can be arbitrarily set without being restricted by the machining current.

[Summary of the invention]

The device of the present invention is a power supply device for a wire electric discharge machine that performs dielectric breakdown of a machining gap, then generates a main discharge for machining in the machining gap, and repeatedly performs machining. By setting the polarity to the cathode when performing the dielectric breakdown and the electrode when generating the main discharge, it is possible to prevent the machining surface from softening due to electrolytic reaction without reducing the machining speed, and to prevent the machining gap from becoming soft. The electromagnetic energy generated in the current-carrying system when the switching element of the main discharge circuit that generates discharge is turned off is introduced by a diode to be reused as a DC power source for the dielectric breakdown/earth circuit to improve energy efficiency. An output voltage variable means of the dielectric breakdown/fault circuit is provided outside the introduction path of the electromagnetic energy to the DC power supply, thereby making it possible to arbitrarily set the dielectric breakdown voltage.

[Embodiments of the invention]

The present invention will be described in detail below with reference to FIGS. 1 to 3. FIG. 1 is a circuit diagram showing an embodiment of a power supply device for a wire electrical discharge machine according to the present invention, and 1.4.9 and 10 in the figure.
is the same as in FIG. 20 is a wire electrode! and a dielectric breakdown circuit that performs dielectric breakdown of the machining gap Q between the workpieces 4, a DC power supply of 20 m, and a switching element 20b.
, its on/off control circuit 20c, current limiting resistor 20d, and discharge capacitor 20e.

It consists of a diode 20f and a variable DC power supply 20g as an output voltage variable means. A main discharge circuit 21 generates a main discharge for machining in the machining gap Q, and is composed of a DC power supply 21a, a switching element 21b, and its on/off control circuit 21c. n is a processing control circuit, which includes a voltage detection circuit 22m for the electrode 1 and the workpiece 4, an on/off control circuit 20c,
21e and the pulse control circuit 22b, the switching elements 20b and 21b, that is, the pulse control circuit 21 and the pulse control circuit 22b, are connected to the switching elements 20b and 21b, that is, the pulse control circuit 21 and the pulse control circuit 22b to repeatedly generate the main discharge after the dielectric breakdown. Control.

Reference numeral 23 denotes a diode, which transfers electromagnetic energy generated in the current-carrying system when the switching element 21b is turned off to the DC power supply 20.
The main discharge circuit 21 is connected to the main discharge circuit 21 and the loop circuit 21 in order to introduce it into the main discharge circuit 21. This is an output terminal for connection to a workpiece connected to the cathode of the DC power source 20m and the anode of the DC power source 21m. Reference numeral 25 denotes an output terminal for connecting wire electrodes, which is connected to the anode of the DC power source 20m via the diode 20f, current limiting resistor 20d, and switching element 20b, and further via the variable DC power source 20g. DC power supply 21 via 21b
connected to the cathode of a. Note that the diode 23 is
The switching element 2 is configured so that the machining current does not change due to the setting of the output voltage (breakdown voltage) of the pulse circuit 20.
It is connected between the output terminal δ side of 1b and the anode of the DC power supply 20&.

Next, the operation of the above-mentioned device of the present invention will be explained.

First, the signal shown in FIG. 2(c) is input from the pulse control circuit 22b to the switching element on/off control circuit 20a, and the switching element 20b is turned on. At this time, the switching element 21b is off (Fig. 2 (
d)). A discharge capacitor 20e is charged from the DC power sources 20a and 20g via a switching element 20b and a resistor 20d as shown in FIG.

This charging is carried out at a voltage (
This is continued until the voltage reaches the sum of the voltage E□ of the power source 20m and the voltage EI12 of the power source 20g. As a result, when a dielectric breakdown discharge starts in the machining gap Q, the discharge capacitor 2Q
The discharge mudflow flows out from the machining gap QK through the diode 20f. The voltage detection circuit 22a detects that the discharge has started, that is, that the dielectric breakdown of the machining gap Q has occurred, and outputs a signal to the 9 pulse control circuit 22b. And, from the pulse control circuit 22b to the switching element 20b
Switching element on/off control circuit 2
0c, and also outputs the signal shown in FIG. 2(d) to the switching element on/off control circuit 21e to turn on the switching element 21b for a time t1. At that time, the machining current flowing through the machining gap QK has a waveform shown in 2-Ql+). The reason why current flows through the machining gap Q even after the switching element 21b is turned off is because electromagnetic energy generated in the current-carrying system and accumulated in the inductance of the wiring flows through the diode 23 to the DC power supply 20a Ic. . The waveform of the current from the main discharge circuit 21 at this time is the second waveform.
As shown in Figure 3), it is approximately triangular, and its slope β is determined by the voltage Ea1 of the DC power supply 20&.

In other words, NoJ? Output voltage Eat + E of loop circuit
Even if s2 (breakdown voltage) is changed by adjusting the power supply 20g, the machining current does not pass through the power supply 20g and flows to the power supply 20m, so the waveform shown in Figure 2 (b) does not change, and the breakdown voltage can be adjusted arbitrarily. Configurable.

When the switching element 21b is turned off and a predetermined time t2 has elapsed, the signal shown in FIG. ,
The above-mentioned operation is performed, and electrical discharge machining is performed by repeating this operation.

As shown in FIG. 2, there is a delay of time t3 from when the capacitor 20e starts discharging until the switching element 21b turns on. This is because the voltage detection circuit 22
After detecting the start of discharge at m, the switching element 21b
This is because the signal processing time required for turning on the element used is 200 to 500 ns at the shortest, and the time t3 is 200 to 500 ns or more.

Further, the time 11 and t2 or t2' are usually controlled to be constant, but may be changed depending on the state of discharge. Also, the signal of (d) in Fig. 2 is changed to tl as shown in (d').
' may be set to ts + t3 or tx + ta' (here, O(ts' (t3)).

In the above embodiment, the discharging capacitor 20e is used in the dielectric breakdown pulse circuit 20, but the same effect can be obtained even without using this. Further, in the above embodiment, the voltage detection circuit 2 is used to detect the start of discharge of the discharge capacitor 30.
2 m is used, but the same effect can be obtained by detecting the current flowing in the machining gap Q or the discharge current from the discharge capacitor 30.Furthermore, in the above-mentioned embodiment, the output voltage when the 9 pulse circuit is applied. Although a variable DC power supply of 20 g was used as the variable means, it is not limited to this, for example, as shown in FIG. 3, a voltage dividing resistor of 2
It may be configured by the 0h1 voltage dividing variable resistor 201 and the capacitor 20j. In this case, the voltage El of the DC power supply 20 &
f is divided into voltages adjusted by a variable resistor of 20% and applied to the capacitor 20j, charged, and the charging voltage becomes
This is the output voltage (breakdown voltage) of the 9-rus circuit 20. Note that the output voltage variable means illustrated in FIG. The output voltage variable means illustrated in FIG.
This is applied when ll is less than or equal to the maximum set voltage.

〔Effect of the invention〕

As described above, the present invention is a power supply device for a wire electric discharge machine that generates a main discharge for machining in the machining gap after dielectric breakdown of the machining gap, and repeatedly performs machining. The polarity of the workpiece is set to cathode when performing dielectric breakdown and anode when generating main discharge, so that the polarity of the machined surface caused by electrolytic reaction in the machining gap can be reduced without reducing the electrical discharge machining speed. It can prevent softening. Therefore, the quality of the machined surface is improved and the dimensional accuracy can be improved. Furthermore, since the electromagnetic energy generated in the current-carrying system when the switching element of the main discharge circuit is turned off is introduced into the DC power supply of the dielectric breakdown/mirror circuit by means of a diode, there is also the effect of high energy efficiency. Furthermore, since the output voltage (breakdown voltage) variable means is provided outside the introduction path of the electromagnetic energy to the DC power supply by the diode, there is an effect that the breakdown voltage can be arbitrarily set without changing the machining current.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the device of the present invention, FIG. 2 is a timing chart for explaining the operation of the device, and FIG. 3 is a circuit diagram showing another embodiment of the device of the present invention. Figure 4 is a schematic configuration diagram of a wire electrical discharge machine equipped with a conventional device;
6 and 6 are voltage and current waveform diagrams of the machining gap in the conventional apparatus shown in FIG. 4, respectively. DESCRIPTION OF SYMBOLS 1... Wire electrode, 4... Workpiece, 20... Dielectric breakdown/Grus circuit, 21... Main discharge circuit, 22...
... Processing control circuit, 23... Diode, Q... Processing gap.

Claims (1)

[Claims] An output voltage variable means is provided between a first DC power supply whose cathode is connected to the workpiece and a first switching element, and the voltage set by this means is applied to the wire electrode and the workpiece by the first switching element. A dielectric breakdown pulse circuit that applies voltage to the machining gap between objects to cause dielectric breakdown thereof, and a second DC power source whose anode is connected to the workpiece through a second switching element to apply the voltage to the machining gap for machining. a main discharge circuit that generates a main discharge; a processing control circuit that controls the first and second switching elements to repeatedly generate the main discharge after the dielectric breakdown; and a processing control circuit that controls the first and second switching elements to repeatedly generate the main discharge after the dielectric breakdown; a diode connected between the first DC power supply and the output voltage variable means and between the second switching element and the wire electrodes in order to introduce electromagnetic energy generated in the system into the first DC power supply; A power supply device for a wire electrical discharge machine, comprising: