JPS6219322A - Electric power device for wire-cut electric discharge machining - Google Patents

Abstract

PURPOSE:To make the disconnection of a wire electrode preventable in a highly reliable manner, by making the momentary average working current grasped in squaring and calculating a signal, proportionate to pulse width, out of a pulse control circuit of a switching element so as not to exceed a critical current value for the wire electrode. CONSTITUTION:A switching element 4 is controlled for its on-off operations with a pulse signal out of a pulse control circuit 11, performing electric discharge machining for a work 2. At this time, a signal proportionate to pulse width of the pulse signal out of the pulse control circuit 11 is inputted in an operational circuit 12, squaring and calculating it. That is to say, since a quantity of electricity per pulse is proportioned to the square of an on-time t1 of the switching element 4, an output signal of the operational circuit 12 comes to an average working current. Whether this current exceeds a critical current value for a wire electrode 1 or not is compared with a comparator 13, and when exceeding it, the pulse control circuit 11 is controlled, holding it down to less than the critical current value. With this constitution, the average working current at the time of machining is easily and accurately grasped, thus the disconnection of the wire electrode is preventable in a highly responsible manner.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention applies processing pulses to the gap between a wire electrode and a workpiece by controlling on/off switching of a switching element using a pulse signal from a pulse control circuit. The present invention relates to a power supply device for wire electrical discharge machining that processes a workpiece by generating intermittent arc discharge.

[Background of the invention]

A device of this type is shown in FIG. In this figure 3, 1
A wire electrode is fed in a certain direction, for example, the direction of arrow A, and passes through the workpiece 2 in the vertical direction while facing the workpiece surface with a predetermined gap. The DC power source 3 has a positive electrode connected to the workpiece 2 and a negative electrode connected to the wire electrode 1 via a switching element 4 and a current limiting resistor 5 in series. The oscillator 6 turns the switching element 4 on and off using a pulse signal, applies a pulsed voltage between the wire electrode 1 and the workpiece 2 (hereinafter referred to as the gap), and generates intermittent arc discharge. to occur.

As described above, intermittent arc discharge occurs and the workpiece 2
When the above-mentioned discharge occurs, a nearly rectangular current flows between the electrodes as shown in FIG. 4(a). When the capacitor 7 is connected between the poles as shown by the broken line in FIG. 3, the current has a waveform close to a sine wave as shown in FIG. 4(b).

The amount of electricity i per pulse for such a pulse is as follows (
1) Given by Eq.

1 = / I p d t・・・・・・・・・
(1) Also, the average machining current T is given by the following equation (2), where f is the average discharge frequency.

1=if ・・・・・・・・・・・・(2)
By the way, it is generally known that the wire electrode 1 has a maximum current value (this is called a limiting current value) in a region where wire breakage does not occur depending on its material and diameter, and the current value during processing is It is important to perform processing while maintaining the current below the limiting current value.

However, in the past, it has been difficult to accurately determine the current value during processing. In particular, detecting the current value of a current waveform that includes high frequency components requires a special detector, as described, for example, in Mikio Motoki's "Discharge Application Device" (published by Nikkan Kogyo Shimbun, 1966), pages 144-147. At the same time, accurate measurement was difficult. It is also possible to use the pulse signal of the oscillator 6 to find the electrical quantity i per pulse, and then use the average discharge frequency f to find the average machining current using equation (2), but this would require too much calculation processing. It becomes difficult.

As described above, in the past, it was not possible to easily and accurately grasp the current value during machining, and therefore it was also impossible to easily and accurately grasp whether the average machining current exceeded the limit current value of the wire electrode 1. There was a problem in that disconnection of the wire electrode 1 could not be prevented with high reliability.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and it is possible to easily and accurately grasp the average machining current, and therefore to easily and accurately determine whether the average machining current exceeds the limit current value of the wire electrode. It is an object of the present invention to provide a power supply device for wire electric discharge machining that can be grasped and can reliably prevent disconnection of wire electrodes.

[Summary of the invention]

The device of the present invention generates an instantaneous signal by calculating the square of a signal proportional to the pulse width of a pulse signal from a pulse control circuit that controls on/off switching of a switching element (including a signal that is the same as the pulse width of the above-mentioned pulse signal). The average machining current of the wire electrode is determined, and when the average machining current exceeds the limit current value of the wire electrode, the average machining current is reduced to be below the limit current value, thereby achieving the above purpose. It is.

[Embodiments of the invention]

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a power supply device for wire electrical discharge machining according to the present invention, and numerals 1 to 4 in the figure are the same as those in FIG. 3. A second DC power supply 8 is connected in parallel to the series circuit of the DC power supply 3 and the switching element 4 via a diode 9. in this case.

The second DC power supply 8 is connected to the workpiece 2 in a polarity opposite to that of the DC power supply 3, and the diode 9 is connected in the opposite direction to the second DC power supply 8. 10 is a discharge start detection circuit that detects the occurrence of arc discharge between the poles and outputs a signal. Reference numeral 11 denotes a pulse control circuit which turns off the switching element 4 after receiving the signal from the discharge start detection circuit 10, that is, t1 time after the start of the discharge, and then turns off the switching element 4 again after a desired time t3. On/off switching control such as turning on is performed on the switching element 4 using a pulse signal. 12 is an arithmetic circuit that squares a signal proportional to the pulse width of the pulse signal of the pulse control circuit 11; 13 is a comparison circuit that compares the output signal of the arithmetic circuit 12 with a signal corresponding to the limit current value of the wire electrode 1, and when the former value exceeds the latter value, that is, the average machining current during machining is Electrode 1
When the current limit value exceeds the current limit value, the pulse control circuit 11 is controlled as follows. That is, for example, the on time tl or the off time t3 or both are controlled so that the average machining current during machining is equal to or less than the limit current value of the wire electrode 1.

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

That is, by controlling the switching element 4 to turn on and off with a pulse signal from the pulse control circuit 11, a machining pulse is applied between the poles to which ion-exchanged water or oil (not shown) is supplied, and the machining pulse is intermittently A typical arc discharge is generated, and the workpiece 2 is machined. Here, when an arc discharge occurs between the poles, the discharge start detection circuit IO detects it. After t3 hours, the switching element 4 is turned off, and after t3 hours, the switching element 4 is turned off.
is turned on, and the above-mentioned on/off switching control is performed by repeating this process.

The discharge current waveform for one pulse at this time is as shown in FIG. When the resistance of the line through which this current flows is small,
It becomes a triangular wave, and the slopes α, β and time t in the figure
is determined by the inductance of the current-carrying line and the DC power sources 3 and 8, and is generally a value specific to the device. In this case, the amount of electricity i per pulse is given by the following equation (3).

1=Kt- (3) That is, the amount of electricity i per pulse is proportional to the square of the on-time tl of the switching element 4. Therefore, if the waveform constants α and β are determined in advance, or K is determined in advance, the above i can be easily determined from time t1.

Therefore, a signal proportional to the pulse width of the pulse signal from the pulse control circuit 11 is input to the calculation circuit 12, and a square calculation is performed.
A comparator circuit 13 compares whether the output signal, that is, the average machining current exceeds the limit current value of the wire electrode 1, and when it does, the pulse control circuit 11 is controlled so that the average machining current is below the limit current value. I will make it happen. Thereby, the average machining current during machining is constantly controlled so as not to exceed the limit current value of the wire electrode 1, and disconnection of the wire electrode 1 is prevented.

Note that the arithmetic circuit 12 and the comparison circuit 13 may be configured as either digital circuits or analog circuits, but if they are configured as analog circuits, the pulse width of the pulse signal from the pulse control circuit 11 is changed. By making a voltage pulse with a constant peak voltage, passing it through a filter circuit for averaging, and then inputting it to the analog square calculation circuit, it is possible to easily obtain a signal proportional to the average machining current. .

[Effects of the Invention] ′ As described above, according to the present invention, the average machining current during machining can be easily and accurately grasped, and thereby wire electrode breakage can be prevented with high reliability. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the device of the present invention, Fig. 2 is a diagram showing an example of a discharge current waveform in the same device, Fig. 3 is a circuit diagram of a conventional device, and Fig. 4 is a discharge diagram in the same device. It is a current waveform diagram. 1... Wire electrode, 2... Workpiece, 3, 8...
DC power supply, 4... Switching element, 9... Diode, 11... Pulse control circuit, 12... Arithmetic circuit, 13... Comparison circuit.

Claims (1)

[Claims] By controlling the switching element to turn on and off using pulse signals from the pulse control circuit, a machining pulse is applied to the gap between the wire electrode and the workpiece to generate intermittent arc discharge, thereby machining the workpiece. In a power supply device for wire electrical discharge machining that performs A power supply device for wire electric discharge machining, comprising: a comparison circuit that controls a control circuit to reduce an average machining current flowing through the gap.