JPH0472645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a wire electrode breakage prevention circuit for wire electrical discharge machining, which prevents wire electrode breakage in wire electrical discharge machining.

[Background of the invention]

In wire electrical discharge machining, supply pulse current or pulse period (pulse
OFF time) and increases the discharge energy to perform machining.

However, the wire electrode used in wire electrical discharge machining is extremely thin, measuring 0.02 to 0.3 mm in diameter, and therefore, the current capacity that can be passed through the wire electrode is limited to 5 to 50 A, and if more current is applied, the wire will break. Therefore, it is possible to prevent wire breakage by turning off the pulse when the current capacity of the wire electrode is exceeded.
In actual processing, the wire electrode sometimes broke even when the current capacity was less than the above-mentioned current capacity. This is because machining debris, air bubbles, etc. generated during machining are locally stationary in the machining gap, where electric discharge is concentrated and heated.

For this reason, conventionally, machining was performed by setting pulse conditions such that the average machining current was 40 to 50% less than the current capacity of the wire electrode, but this new method slowed down the machining speed. A problem arose.

[Purpose of the invention]

The present invention was made in order to solve the above problems, and without reducing the processing speed,
An object of the present invention is to provide a wire electrode breakage prevention circuit for wire electrical discharge machining that can accurately and effectively prevent wire electrode breakage when current is flowing below the current capacity due to concentrated discharge.

[Summary of the invention]

The circuit of the present invention accurately detects whether or not there is a concentrated discharge state in wire electrical discharge machining, and
Detects whether the machining average current is above a predetermined value, and reduces the arc discharge energy when the machine is in a concentrated discharge state and the machining average current remains above the predetermined value for a predetermined period of time or more. In this way, the above objective is achieved.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the wire electrode disconnection prevention circuit for wire electrical discharge machining according to the present invention. In FIG. 1, 1 is a wire electrode, 2 is a workpiece, 3 is a machining fluid supply nozzle, and 4 is a pulse power source that supplies processing pulses between the wire electrode 1 and the workpiece 2. Numerals 5 and 6 are feeders for supplying the processing pulses to the wire electrode 1, and are arranged above and below the workpiece 2, respectively. 7
and 8 are rollers for guiding the wire electrode 1, and the wire electrode 1 is fed out from a wire feeding bobbin (not shown) via these rollers 7, 8, and wound up by a winding drive device (not shown). Further, the workpiece 2 is placed on a table (not shown) that is movable on the XY-axis plane by a drive device such as a numerical control device. 9 is an oscillator, 1
0 is the T _ON circuit that sets the ON time of the machining pulse,
11 is a T _OFF circuit that sets the OFF time of the machining pulse; ON time and OFF time setting signals from these circuits 10 and 11 are given to the pulse power source 4, and the pulse power source 4 sets the predetermined ON and OFF times. Generates a machining pulse with

12 is a current detector for measuring the machining current flowing through the upper feeder 5, and 13 is an amplifier for amplifying the minute current detected by the current detector 12. The output terminal of this amplifier 13 is connected to a filter circuit 14.
It is connected to the input terminal of the differentiating circuit 15 via. 1
6 and 17 are comparison amplifiers, and comparison amplifier 16
The output terminal of the differentiating circuit 15 is connected to the positive input terminal of the comparator amplifier 17 and the negative input terminal of the comparator amplifier 17. Moreover, the output terminals of these comparison amplifiers 16 and 17 are
Each is connected to a different input terminal of the OR gate 18. The output terminal of OR gate 18 is connected to one input terminal of OR gate 19. Note that the circuit from the current detector 12 to the OR gate 18 is referred to as a concentrated discharge detection circuit.

20 is a current detector that detects the total machining current flowing through the upper and lower side feeders 5 and 6; 21 is a filter circuit 2 that amplifies the output current of this current detector 20;
2. 23 is a comparison amplifier,
The output terminal of the filter circuit 22 is connected to the negative input terminal, the output terminal of the setting device 24 is connected to the positive input terminal, and the output terminal of the comparison amplifier 23 is connected to the other terminal of the OR gate 19. connected to the input end of the In addition, from the current detector 20 to the comparison amplifier 2
The circuit leading to 3 is called a processing average current detection circuit.

25 is a counter, its count input terminal T is connected to the clock output terminal T of the oscillator 26, its reset input terminal R is connected to the output terminal of the OR gate 19, and its output terminal Q is connected to the clock output terminal T of the oscillator 26;
It is connected to each control input terminal of the T _ON and T _OFF circuits 10 and 11. Note that the circuit from the OR gate 19 to the T _ON and T _OFF circuits 10 and 11 is referred to as a control circuit.

Reference numeral 27 denotes a comparison amplifier, the positive input terminal of which is connected to the output terminal of the amplifier 21, and the negative input terminal thereof to the output terminal of the setting device 28, respectively. 29 is an AND gate, one input terminal of which is connected to the output terminal of the comparator amplifier 27, and the output terminal thereof connected to the set input terminal S of the D-type flip-flop 30, respectively. 31 is
This is a delay circuit that delays the pulse signal from the T _ON circuit 10 and supplies it to the check pulse generation circuit 32. The output terminal of the check pulse generating circuit 32 is connected to the other input terminal of the AND gate 29 and the clock input terminal T of the D-type flip-flop 30, respectively. The data input terminal D of the D-type flip-flop 30 is grounded and has a logic value of "0", and the output terminal Q thereof is connected to the input terminal of the integrating circuit 33. The output terminal of the integrating circuit 33 is connected to a differential amplifier 34.
and the negative input terminal of the differential amplifier 35, respectively. The differential amplifier 34 has -
The side input terminal is connected to the output terminal of the setter 36, and the output terminal is connected to the negative input terminal of the comparator amplifier 16, respectively. Further, the differential amplifier 35 has its + side input terminal connected to the output terminal of the setter 37 and its output terminal connected to the + side input terminal of the comparator amplifier 17, respectively. Note that the circuit from the comparison amplifier 27 to the differential amplifiers 34 and 35 is referred to as a sensitivity correction circuit.

Next, the operation of the above-mentioned circuit of the present invention will be explained.
First, the supply of insulating machining fluid from the machining fluid supply nozzle 3 between the wire electrode 1 and the workpiece 2 is started. Further, the ON and OFF times of the signal of a predetermined frequency generated by the oscillator 9 are set by the T _ON and T _OFF circuits 10 and 11 as shown in waveform A in Figs. 2 and 3, and based on this, the ON and OFF times are set. A machining pulse is applied between the wire electrode 1 and the workpiece 2, to which machining fluid is supplied, from a pulse power supply 4 operating in a power switching manner, and an electric discharge is generated. At this time, the workpiece 2 is processed and fed by a table drive device (not shown), and thereby the workpiece 2 is subjected to electrical discharge machining into a desired shape.

Here, when discharge occurs, the inter-electrode voltage waveform becomes an arc voltage Va as shown by waveform B in FIG. Now, when the discharge occurs at the lower part of the workpiece 2, the distance from the discharge point to the lower side feeder 6 becomes short, and the distance from the upper side feeder 5 becomes long. As a result, the machining current (discharge current) satisfies I _U <I _D as seen from I ₁ and I ₁ ' of waveforms C and D in FIG.
Here, _IU indicates a machining current flowing through the upper side feeder 5, and _ID indicates a machining current flowing through the lower side feeder 6. The sum of these currents I _U + I _D contributes to electrical discharge machining as total electrical discharge energy. Contrary to the above, if electrical discharge occurs at the top of workpiece 2, the machining current will be
I _U > I _D , and the waveforms flow with the magnitudes shown by I ₂ and I ₂ ' of waveforms C and D in FIG. In addition, when electric discharge occurs in the center of the workpiece 2, I _U = I _D , that is, as shown in I ₃ , I ₃ ′ and I ₄ , I ₄ ′ of waveforms C and D in FIG. Both currents become equal. During this period, the output signal from the filter circuit 14 becomes as shown in waveform E in FIG. That is, when discharge occurs at a fixed location (discharge point is fixed), the output waveform of the differentiating circuit 15 does not vary as shown by waveform F in the current I ₃ and I ₄ sections. In this case, the signal obtained from the differentiating circuit 15 is
7 and is compared with the set voltages +E ₀ and -E ₀ from the differential amplifiers 34 and 35, and the comparison amplifier 1
The output signals 6 and 17 are respectively given to the OR gate 18, and the output signal waveform of the OR gate 18 is as shown in waveform G in FIG. this
The output signal of the OR gate 18 is applied to the reset input terminal R of the counter 25 through the OR gate 19, and when the logic value is "1", the counter 25 is reset. That is, in the current I ₁ and I ₂ sections where the discharge point is not concentrated in one place, a signal with a logical value of "1" is output from the output terminal of the OR gate 18, and the counter 25 is reset.
An output signal with a logical value of "1" is not obtained from the counter 25, and no control signal is given to the T _ON and T _OFF circuits 10 and 11. Therefore, T _ON , T _OFF circuit 10,
Electric discharge machining is performed using machining pulses with ON and OFF times preset in step 11. Also,
As can be seen from the waveform G, in the current I ₃ and I ₄ sections where the discharge points are concentrated in one place, a signal with a logical value of "1" cannot be obtained from the output terminal of the OR gate 18.
On the other hand, the total electric discharge machining current is detected by a current detector 20, voltage amplified by an amplifier 21, high frequency components are removed by a filter circuit 22, and the detected machining current is averaged and given to a comparison amplifier 23. It will be done. When the input average value of the detected machining current exceeds the value set by the setter 24, the output signal of the comparator amplifier 23 becomes a logical value "0" and is applied to the input terminal of the OR gate 19. At this time, as mentioned above, the output signal of the OR gate 18 is also the logical value "0", so the OR gate 19
The output signal of the counter 25 also becomes a logical value "0", and the counter 25
Cancels the reset state. That is, the output signal of the OR gate 19 becomes a logical value "0" when a machining average current of a predetermined value or more flows and discharge continues at a certain point, and the reset state of the counter 25 is released. As a result, the counter 25 counts clocks of a predetermined frequency generated from the oscillator 26, and when the predetermined count is reached, the output signal becomes a logic value "1" and the T _ON and T _OFF circuits 10 and 11 given, the machining pulse ON time T _ON
The T _ON and T OFF circuits 10 and 11 are controlled to shorten the processing pulse OFF time T _OFF or to lengthen the machining pulse OFF time T _OFF .

As described above, when the average machining current (total machining current) increases above a predetermined value and concentrated discharge is detected,
The machining pulse is controlled to lower the discharge energy when the duration reaches a predetermined time or more, and this effectively prevents the wire electrode 1 from breaking during wire electric discharge machining even when a concentrated discharge occurs. Machining speed will be improved.

Next, the sensitivity correction operation in concentrated discharge detection will be described. The above explanation is based on the case where the discharge itself occurs normally, but if the wire electrode 1 and the workpiece 2 are short-circuited during machining, the machining current will change as shown by _Is of waveform H in Fig. 3. increases. this
When I _s occurs continuously, the waveform E in FIG. 2 changes, and it is detected as if the discharge point had changed. Therefore, when such a short circuit occurs, it is necessary to correct the current detection sensitivity of the concentrated discharge detection circuit to lower it. According to experiments, the current during the above short circuit
Since I _s increases by about 15% compared to the machining current I _p during normal discharge, the sensitivity can be reduced by this proportion, and the sensitivity correction circuit performs such sensitivity correction. In other words, the machining current shown in waveform H in Fig. 3
I _s (or I _p ) is given to a comparator amplifier 27 and compared with the set value E _s from the setter 28, and the result is
It is applied to one input terminal of AND gate 29.
On the other hand, since the check pulse from the check pulse generation circuit 32 shown in waveform J in FIG. 3 is applied to the other input terminal of the AND gate 29, if the short circuit occurs, the waveform As shown in FIG. 2, the output signal of the AND gate 29 becomes a logical value "1" when a check pulse is input. As a result, the D-type flip-flop 30 enters the set state and outputs a signal shown in waveform L in FIG. This signal L is averaged by an integrating circuit 33 and then sent to a differential amplifier 34.
and the negative input terminal of the differential amplifier 35. As a result, the differential amplifier 34 outputs a set voltage +E ₀ that is 15% higher than the value given and output by the setter 36 during normal operation.
It is applied to the negative input terminal of the comparator amplifier 16, and from the differential amplifier 35, it is sent to the setting device 37 during normal operation.
A set voltage -E ₀ that is 15% lower than the output value given by is outputted and applied to the + side input terminal of the comparator amplifier 17. Therefore, the signal F from the differentiating circuit 15 of the concentrated discharge detection circuit is the set voltage +E ₀ , −E ₀ (the voltage indicated by the two-dot chain line in FIG. ), and the sensitivity is lowered. This prevents the output signal G of the OR gate 18 from erroneously becoming the logic value "1" when the wire electrode 1 and the workpiece 2 are short-circuited, and it is clearly distinguished from the case where the discharge point actually fluctuates. Focused detection becomes more accurate.

Specific examples of the effects achieved by the circuit of the present invention described above are shown below.

Wire electrode 1: Made of brass, 0.3mmφ Workpiece 2: Made of SKD11, 60mm thick Pulse ON time T _ON : 4μsec Pulse OFF time T _OFF : 12μsec Peak current: 500A Oscillation frequency of oscillator 26: 1msec Abnormal overcurrent and concentrated discharge When wire electrical discharge machining is performed using the circuit of the present invention, the number of counts at which the output signal of the counter 28 becomes logical value "1" after the occurrence of 10 is 10, and the setting value of the setting device 24 is 40A, the machining speed is 3.6 mm/ min, an improvement of 20% compared to the conventional method (machining speed of 3 mm/min).

In the embodiment shown in FIG. 1, a case is shown in which the current detector 12 for detecting concentrated discharge is provided in the current-carrying path leading to the upper side feeder 5; It is also possible to provide the same effect as in the above-mentioned embodiment.

In addition, the concentrated discharge detection circuit, the machining average current detection circuit, the control circuit, the sensitivity correction circuit, and the like are not limited to the configurations shown in the above embodiments. In particular, regarding the sensitivity correction circuit, in the above embodiment, the comparison amplifier 1
Sensitivity correction was performed by changing the set voltages +E ₀ and -E ₀ given to amplifiers 6 and 17, but this
This may be done by changing the input sensitivity or amplification degree of No. 3.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to accurately and effectively prevent wire electrode breakage when current is applied below the wire electrode current capacity due to concentrated discharge, and therefore, it is possible to accurately and effectively prevent wire electrode breakage caused by concentrated discharge. This eliminates the need to reduce the current, increases machining speed, and enables long-term unmanned machining.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the circuit of the present invention, and FIG.
The figure is a diagram of signal waveforms at various parts of the same circuit, and FIG. 3 is a diagram of signal waveforms at various parts at the time of a short circuit. 1... Wire electrode, 2... Workpiece, 3... Machining liquid supply nozzle, 4... Pulse power supply, 5, 6...
Feed electron, 9, 26... Oscillator, 10, 11...
T _ON , T _OFF circuit, 12, 20...Current detector, 1
3, 21... Amplifier, 14, 22... Filter circuit, 15... Differential circuit, 16, 17, 23, 27
... Comparison amplifier, 18, 19 ... OR gate, 2
4, 28, 36, 37...Setter, 25...Counter, 29...AND gate, 30...Flip-flop, 31...Delay circuit, 32...Check pulse generation circuit, 33...Integrator circuit, 34,
35...Differential amplifier.

Claims (1)

[Claims] 1. While supplying machining fluid between the wire electrode and the workpiece, machining pulses from a pulse power source are supplied via feeders provided above and below the workpiece, respectively. A circuit for detecting a waveform of a machining current flowing through at least one of the feeders, and a machining current waveform detected by this circuit, in wire electric discharge machining in which the workpiece is machined by generating intermittent arc discharges. a concentrated discharge detection circuit that outputs a concentrated discharge detection signal as being in a concentrated discharge state when the machining current unchanged state is detected in the wire electrode; A detector that detects the total machining current flowing, a circuit that removes high frequency components from the total machining current detected by this detector and outputs it as a machining average current value, and the machining average current value from this circuit is the current capacity of the wire electrode. A machining average current detection circuit comprising a circuit that outputs a machining average current detection signal of a predetermined value or more when the machining average current exceeds an arbitrarily set predetermined value as described below; This machining average current detection circuit and the concentrated discharge detection A circuit in which the output terminals of the circuit are connected to different input terminals, and detects the simultaneous input of the concentrated discharge detection signal and the machining average current detection signal of a predetermined value or more, and the state of the simultaneous input by this circuit continues for a predetermined time or more. a circuit that counts the number of pulses, and reduces the energy of the arc discharge by shortening the ON time or lengthening the OFF time of the pulse ON and OFF times of the pulse power supply when the simultaneous input state continues for a predetermined time or more. A wire electrode disconnection prevention circuit for wire electrical discharge machining, characterized by comprising a control circuit.