JPS62287924A - Wire electric discharge machine - Google Patents

Abstract

PURPOSE:To improve processing efficiency through prevention of disconnection of a wire electrode, by a method wherein a pulse signal with an amount of electricity proportioning an amount of electricity at intervals of one pulse of processing current pulse is generated and smoothed by a filter circuit, and is outputted as a signal responding to an average processing current. CONSTITUTION:Signals responding to the width of the processing current pulse of a factor deciding an amount of electricity of a processing current pulse, a bath voltage, the number of select. ions of each of switching elements 4, 6, and 8, resistance values of resistors 5, 7, and 9 for limiting a current, and pulse wave shape are inputted to a pulse generating circuit 17. A pulse signal having an amount of electricity proportioning an amount of electricity at intervals of one pulse of processing current pulse is generated and smoothed by a filter circuit 18. The result is outputted as a signal responding to an average processing current value to input it to a current display unit 19 where an average processing current value is displayed. Thus, the current value can be easily and accurately grasped, and by deciding whether the current value exceeds the limit current value of a wire electrode 2 or not, disconnection is prevented from occurring, and processing efficiency can be sufficiently improved.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Industrial Field of Application] The present invention provides a method for connecting a wire electrode and a wire electrode by controlling on/off a switching element provided in a current-carrying path using a pulse signal from a pulse control circuit. Regarding wire electrical discharge machining equipment that performs machining by applying a pulsed voltage between the workpiece and generating intermittent electric discharges, it is particularly important to easily and accurately calculate the average machining current value required to judge the machining state. This invention relates to wire electrical discharge machining equipment that can be grasped.

[Conventional technology]

The circuit configuration of a conventional device of this type is shown in FIG.

In FIG. 4, 1 is a workpiece, 2 is a wire electrode running in the direction of the arrow, and these are in a state of facing each other with a predetermined gap therebetween. The positive terminal of the DC power supply 3 is a shunt resistor 15
The negative electrode is connected to the current-carrying terminal 13.14 of the wire electrode 2 through the switching elements 4, 6.8 and the current limiting resistors 5, 7.9 in series, respectively. There is. During processing, the pulse control circuit 11
The switching elements 4, 6.8 are on/off controlled by the output pulse signal of the wire electrode 2 and the workpiece 1 (
A pulsed voltage is applied between the electrodes (hereinafter referred to as the gap between the electrodes) to generate intermittent transient arc discharge. The pulse width, pulse rest time, or pulse period of the output pulse signal from the pulse control circuit 11 is set by the machining condition setting circuit 10, and the discharge state is detected from the voltage between the electrodes by the discharge state detection circuit 12, and the discharge state is detected. A signal for controlling the pulse conditions accordingly is input to the pulse control circuit 11. The current during machining is set by the shunt resistor 15, and the average machining current value is displayed on the current indicator 16.

FIG. 5 shows voltage waveforms and current waveforms in the gap of the wire electrical discharge machining apparatus configured as described above.

That is, when the switching elements 4, 6.8 are turned on by the pulse signal from the pulse control circuit 11, the DC power supply voltage E is applied between the electrodes. is applied and a discharge occurs after a delay time td1, the discharge state detection circuit 12 detects the occurrence and sends the detection signal to the pulse control circuit 11.

As a result, the pulse control circuit 11 outputs a signal to turn off the switching elements 4 and 6°8 after time t1, and after maintaining the off state for time t2, the switching elements 4 and 68 are turned off again.
6.8 is turned on. This time tzt tz is set by the processing condition setting circuit 10. Here, the current flowing through the switching elements 4, 6.8 is caused by the current limiting resistor 5.7.
9, and the peak value IP of the current flowing between the electrodes is determined by the number of switching elements selected by the processing condition setting circuit 10. The relationship between voltage and current is shown in more detail as follows. That is, switching element 1
The current I flowing through each individual is the resistance value of the current limiting resistor R1
If the arc voltage during normal discharge is E, it is given by equation (1).

At the time of a short circuit, the voltage between the poles becomes almost zero, so the current flowing through one switching element is given by equation (2).

E.

I=-(2) Figure 5(b) shows the current waveform when multiple (n) switching elements are controlled on and off simultaneously, Ip:l:nI
becomes. By sequentially shifting the turn-on timing of multiple switching elements, the current waveform becomes a step wave as shown in Figure 5(c), and by providing an appropriate inductance in the current path, the current waveform becomes a step wave as shown in Figure 5(d). You will get a triangular wave like this. In electric discharge machining, machining characteristics change by using such various current waveforms. For example, the fifth
It is known that the waveform of (c) or (d) in the figure can reduce the electrode wear rate more than the waveform of (b).

By the way, in general, wire electrodes have a maximum current value (this is called a limit current value) that can be passed within a range that does not cause wire breakage, depending on the material and wire diameter, and the average machining current value must be lower than the limit current value. In order to increase machining efficiency, it is important to maintain the value as high as possible during machining.

[Problem that the invention seeks to solve]

Conventionally, the average machining current value has been measured by directly measuring the current during machining using a shunt resistor 15 installed in the current-carrying path as shown in Fig.
Because the current falls sharply and contains high-frequency components, it is not possible to accurately measure the current value using a commercially available shunt resistor due to its own inductance.

To accurately measure the current value of a waveform that includes high frequency components,
For example, as described in pages 144 to 147 of "Discharge Application Device" by Mikio Motoki (Nikkan Kogyo Shimbun, 1966), two disk-shaped resistors facing each other with a minute interval are radially connected to each other. There is a method of using a special non-inductive resistor with a structure in which a current flows and the magnetic flux cancels each other, but it is difficult to compensate for resistance changes due to temperature and calibrate the measured value, and the average machining current with a practical machine is difficult. Not suitable for measuring values.

As mentioned above, in the past, it was not possible to easily and accurately grasp the average machining current value in wire electrical discharge machining, and therefore it was not possible to accurately determine whether the average machining current value exceeded the limit current value of the wire electrode. Therefore, there was a problem that processing efficiency could not be sufficiently increased while preventing disconnection of the wire electrode.

In addition, in high-speed switching circuits that do not use the current limiting resistors 5 and 7°9 shown in No. 4 rM, circuit impedance, especially inductance, has a large effect on the current waveform. It is also undesirable to insert the current waveform into the current waveform.

The present invention has been made to solve the above-mentioned problems, and allows the average machining current value to be easily and accurately grasped.
An object of the present invention is to provide a wire electrical discharge machining device that can accurately determine whether or not the average machining current value exceeds the limit current value of the wire electrode, and eliminates the influence of the inductance of a shunt resistor on the current waveform. shall be.

[Means for solving problems]

The present invention provides a signal corresponding to a machining current pulse width from a lap pulse control circuit that performs on/off control of a switching element, a signal corresponding to a voltage between electrodes from a discharge state detection circuit, and a signal corresponding to a switching element selected by a machining condition setting circuit. number of pieces,
A pulse generation circuit receives a signal corresponding to the resistance value of the current limiting resistor and the current pulse waveform as input, and generates a pulse signal having an amount of electricity proportional to the amount of electricity for each pulse of the machining current pulse; A filter circuit is provided to average No. 3 and output it as a signal corresponding to the average machining current value, so that the average machining current value can be indirectly understood from the output signal.

[Effect]

In the above pulse generation circuit, a pulse signal synchronized with the machining current pulse is generated, and the pulse width and peak value thereof are determined, for example, as follows.

When the discharge state detection circuit detects that the voltage between the electrodes has become lower than the DC power supply voltage E0 during the ON period of the switching element, let Ei be the voltage and R be the resistance value of the 'It current limiting resistor. , the value of the current I flowing through one switching element is obtained from equation (3).

o Ex I=-(3) If the current pulse waveform is a rectangular wave as shown in Fig. 5(b), the current peak value Ip is determined by the current value obtained from equation (3) and the machining condition settings. It is the product of the number n of switching elements selected in the circuit. The pulse generation circuit calculates the current peak value Ip, and makes the pulse width of the generated pulse signal the same as the pulse width t1 of the machining current pulse,
If the peak value e is set to have a proportional relationship with the calculated current peak value Ip, this pulse signal will have an amount of electricity proportional to the amount of electricity for each pulse of the machining current pulse, so this pulse signal By averaging the values using a filter circuit, a signal that accurately corresponds to the average machining current value can be obtained.

If the current pulse waveform is a waveform other than a rectangular wave as shown in FIG. Depending on the current value per switching element and the selected number of switching elements, each step wave is adjusted so that the electrical quantity of the generated pulse signal is proportional to the electrical quantity of each pulse of the processing current pulse. What is necessary is to set the rise amount of the step, the rise gradient of the triangular wave, etc.

Since the output pulse signal of the pulse generation circuit is ultimately used to grasp the average machining current value, it is sufficient to have an amount of electricity proportional to the amount of electricity for each pulse of the machining current pulse, and the pulse waveform is not necessarily It does not have to be similar to the machining current pulse.

The signal corresponding to the average machining current value obtained in this way is input to the current display and the average machining current value is displayed, thereby controlling the machining conditions so that the average machining current value does not exceed the limit current value. It can be used for manual setting, or input this signal into a comparison circuit and compare it with the signal from the limit current value setting circuit.

The comparison circuit outputs the determination signal to the pulse control circuit and is used to automatically control the machining conditions so that the average machining current value is always below the limit current value.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3. Reference numerals 1 to I4 in FIGS. 1 and 2 indicate the same or corresponding parts as in FIG. 4, respectively.

In the embodiment shown in FIG. 1, the pulse generation circuit 17 receives signals from the machining condition setting circuit 1O, the pulse control circuit 11, and the discharge state detection circuit 12, respectively, and generates electricity proportional to the amount of electricity for each pulse of the machining current pulse. This pulse signal is averaged by the filter circuit 18 and outputted to the current display 19 as a signal corresponding to the average machining current value, thereby displaying the average machining current value. The filter circuit 18 is a low-pass filter with a cutoff frequency of about several Hz to several tens of Hz. Current indicator 19
may be in either analog or digital display format.

In another embodiment shown in FIG. 2, the pulse generation circuit 17 and the filter 18 have the same functions as in FIG.
0 and is compared with a setting signal corresponding to the limit current value from the limit current value setting circuit 21. Filter circuit 18
When the output signal becomes larger than the setting signal from the limited current value setting circuit 21, the judgment signal of the comparison circuit 20 is output to the pulse control circuit 11, and the processing condition (current pulse width, pulse rest time or pulse period, current peak value, pulse waveform, etc.) are controlled so that the average machining current value decreases. This current control is
Generally, this is done by increasing the pulse pause time and lowering the current peak value. It is preferable that the current control is continued not only when the output signal of the filter circuit 18 is larger than the signal from the limit current value setting circuit 21, but also for a predetermined period of time after such a state ends. This is to cool the wire electrode heated by the large current, but if this time is increased, the processing speed will decrease.

FIG. 3 shows an example of the configuration of the pulse generation circuit 17. 22 is■
,=DanE'LXn The calculation section is composed of an analog calculation unit. Input A of the calculation unit 22,
Among B, C, and D, the input A corresponding to the voltage E1 between electrodes is given from the discharge state detection circuit 12, and
, 6.8, the input B corresponding to the number of selected pieces n is given from the processing condition setting circuit 10.

When the current peak value is set by the selected number of switching elements, the DC power supply voltage E. The resistance value R of the current limiting resistors 5 and 7.9 (the value of circuit impedance in a switching circuit that does not use an FFI current limiting resistor) is set as a constant to the human power C and D, respectively, but the current peak value When switching the current limiting resistors 5, 7.9 in accordance with the current limiting resistor 5, 7.9, a signal corresponding to the resistance value R of the current limiting resistor selected by the machining condition setting circuit 10 is input. In addition, in an electrical discharge machining apparatus that uses various current pulse waveforms as shown in FIG. 5(b), (c), and (d), a pattern generator is used to select waveforms from the machining condition setting circuit IO. The signal may be used to generate a pulse signal having the same waveform as the current pulse waveform. A switching section 23 is controlled by an input E corresponding to the machining current pulse width t1 from the pulse control circuit 11, and is made of a high-speed switching element that is turned on only during the period when current is flowing between the electrodes.

By intermittent output of the calculation section 22 by this switching section, a pulse signal having a similar relationship to the machining current pulse is generated as the output of the pulse generation circuit 17. Therefore, the signal obtained by averaging this pulse signal with the filter circuit 18 shown in FIGS. 1 and 2 accurately corresponds to the average machining current value. Here, as the input A corresponding to the inter-electrode voltage, the inter-electrode voltage itself, a signal obtained by dividing the inter-electrode voltage, or a signal at a predetermined voltage level corresponding to the discharge state detected by the discharge state detection circuit 12 is used. . The arc voltage during normal discharge varies depending on the combination of wire electrode and workpiece material, but it is a value of 20 to 25 V, for example, with little fluctuation, and the voltage between electrodes is almost zero during a short circuit, so it is normal. A signal with a preset voltage level depending on whether it is a discharge or a short circuit is applied to the electrode-to-electrode voltage E.
Even if the input corresponds to 1, a large error will not occur in the calculation result.

〔Effect of the invention〕

As described above, in the present invention, the processing current pulse width, the voltage between electrodes, the selected number of switching elements, the resistance value of the current limiting resistor, the pulse waveform, etc., which are the factors that determine the electrical quantity of the processing current pulse, etc. The signal is input to a pulse generation circuit, which generates a pulse signal with an amount of electricity proportional to the amount of electricity for each pulse of the machining current pulse, and this pulse signal is averaged by a filter circuit as a signal corresponding to the average machining current value. By inputting this output signal into the current display to display the average machining current value, or by comparing this output signal with the signal from the limit current value setting circuit using a comparison circuit, you can The average machining current value can be easily and accurately grasped without using a non-inductive resistor, etc., and it is possible to accurately determine whether the average machining current value exceeds the limit current value of the wire electrode, and to prevent disconnection of the wire electrode. It is possible to sufficiently increase machining efficiency while preventing this. Additionally, since there is no need to insert a shunt resistor into the current-carrying path, it is possible to prevent the current waveform from being distorted due to the inductance of the shunt resistor and deteriorating machining performance, especially in high-speed switching circuits that do not use a current-limiting resistor. There is an effect that it can be done.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, FIG. 3 is a schematic diagram showing an example of the configuration of a pulse generation circuit in the present invention, FIG. 4 is a circuit diagram of a conventional device, and FIG. 5 is a diagram of voltage and current waveforms between electrodes. 1: Workpiece 2: Wire electrode 3: DC power supply 4.6, 8 Niswitching element 5.7.9: Current limiting resistor 10: Machining condition setting circuit 11: Pulse control circuit 12:
Discharge state detection circuit 17: Pulse generation circuit 18: Filter circuit 19: Current indicator 20: Comparison circuit 21: Limit current value setting circuit Attorney Junnosuke Nakamura Figure 1 19: Current indicator Figure 2 Figure 3 E 22: Arithmetic section 23 - Switching section A: Input B corresponding to the interelectrode voltage E; Input C corresponding to the selected number of switching elements n: Input D corresponding to the resistance value R of the current limiting paper 'VL device; Input E corresponding to DC electric voltage O: Input F corresponding to machining current pulse width t1; Pulse signal output Fig. 4 Fig. 5

Claims (1)

[Claims] 1. By controlling the switching element installed in the current-carrying path on and off using pulse signals from the pulse control circuit, a pulsed voltage is applied to the gap between the wire electrode and the workpiece to generate an intermittent electric discharge, and the machining is performed. In the wire electric discharge machining apparatus, a signal corresponding to the machining current pulse width from the pulse control circuit, a signal corresponding to the inter-electrode voltage from the discharge state detection circuit, the number of the switching elements selected by the machining condition setting circuit, A pulse generation circuit that receives a signal corresponding to the resistance value of a current limiting resistor and a current pulse waveform as input, and generates a pulse signal having an amount of electricity proportional to the amount of electricity for each pulse of a machining current pulse, and this pulse signal. A wire electrical discharge machining device characterized by comprising: a filter circuit that averages and outputs a signal corresponding to an average machining current value.