JPS61111831A - Wire-cut electric discharge machinine - Google Patents

Abstract

PURPOSE:To keep off a disconnection accident in a wire electrode without fail, by discriminating a gap state in a way of detecting a time distribution state till causing discharge generation, while controlling a peak value of a pulse current energizing an electrode gap according to the discriminated result. CONSTITUTION:A switching transistor 15b, which impresses voltage on a spark gap and makes a discharge cuttent flow, is driven by a switching amplifier 16, A falling of gap voltage is detected by a detecting device 19, and the output is inputted into a spark gap state discriminating circuit 20. This spark gap state discriminating circuit 20 discriminates a discharge state of the gap, and according to this discriminated result, a peak value of a pulse current to be energized to the gap between a work 1 and a wire electrode 2 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a processing device that electrically cuts a workpiece using a wire electrode.

[Conventional technology]

Machining workpieces using electrical energy has been widely used and is well known, but a recent technology that has been attracting attention is the use of wire-shaped electrodes in processing equipment, which is similar to a ``string saw.'' There is a so-called wire-cut electrical discharge machining apparatus that processes a workpiece using electrical energy.

FIG. 8 is a configuration diagram showing the wire-cut electrical discharge machining apparatus. Reference numeral 1 denotes a workpiece, in which a wire electrode 2 is passed through a spinning hole 1a that has been drilled in advance with a drill or the like, and an insulating liquid 3 is interposed between the hole wall and the wire electrode 2.

The above-mentioned insulating liquid 3 will be hereinafter referred to as a processing liquid. The processing fluid is
The liquid is sprayed from the tank 4 by the pump 5 into the gap between the workpiece 1 and the wire electrode 2 through the nozzle 6 .

The relative movement between the workpiece 1 and the wire electrode 2 is performed by moving the table 11 on which the workpiece 1 is placed.

The table 11 is driven by a Y-axis drive motor 13 and an X-axis motor 12.
Driven by. With the above configuration, the relative movement between the workpiece 1 and the electrode 2 becomes a two-dimensional plane movement within the aforementioned X and Y axis planes.

The wire electrode 2 is supplied by a wire supply reel 7,
The wire passes through the lower wire guide 8A and the workpiece 1, reaches the upper guide 8B, and is wound up by the wire winding/tension roller 10 via the electric energy supply section 9.

The control device 14 that drives and controls the drive motors 12 and 13 for the upper g6x and y axes is a numerical control device (NC control device).
A control device using a computer, a copying device, or a computer is used.

The processing power supply 15 that supplies electrical energy includes, for example, a DC power supply 15a1, a switching element 15b, and a current limiting resistor 1.
5C and a control circuit 15d that controls the switching element 15b.

Next, the operation of the conventional device will be explained. A high-frequency pulse voltage is applied between the workpiece 1 and the wire electrode 2 from the machining power supply 15, and a part of the workpiece 1 is melted and scattered by a discharge explosion caused by one pulse.

In this case, the gap between the electrodes is gasified and ionized by the high temperature, so a certain pause time is required before applying the next pulse voltage, and if this pause time is too short, the insulation between the electrodes will not recover sufficiently. Before this occurs, the discharge concentrates again at the same location, causing the wire electrode 2 to melt.

Therefore, with a normal machining power source, depending on the type of workpiece, plate thickness, etc., the electrical conditions such as the down time of the machining power source 15 are usually set to have enough margin to prevent wire breakage. . Therefore, the machining speed must be considerably lower than the theoretical limit value. Furthermore, if the wire electrode 2 is not uniform and its thickness changes, or if a portion of the wire electrode has protrusions or scratches and discharge is concentrated, fusing of the wire electrode 2 is unavoidable.

[Problem that the invention seeks to solve]

As described above, in the conventional wire-cut electric discharge machining apparatus, in order to prevent the wire electrode 2 from breaking, the output energy of the machining power supply 15 is reduced, etc., so that the electric discharge concentrates on one point on the wire electrode 2. The problem was that the processing speed was extremely low because it was designed to prevent wire breakage even if the wires were concentrated.

Therefore, conventional attempts have been made to extract various signal components from the gap between the poles and detect the state between the poles.

However, the wire electrode 2 vibrates within the workpiece due to string vibration (standing wave vibration between the wire guides), and during machining, the state of gap open → discharge → short circuit → discharge → open is repeated at a frequency of several KH2. Therefore, there was a problem in that this caused a disturbance and it was extremely difficult to accurately detect the state between the poles.

This invention has been made to solve such problems, and is a wire cutter that can accurately detect the state of the gap between electrodes and use the detection result to reliably prevent wire electrode breakage accidents. The purpose is to obtain electrical discharge machining equipment.

[Means for solving problems]

The wire-cut electrical discharge machining apparatus according to the present invention eliminates the open state and short-circuit state caused by the string vibration of the wire electrode in the gap between the opposing poles of the wire electrode and the workpiece. A detection means that periodically samples only the time when the occurrence occurs and detects the distribution state of the time after voltage application when the discharge occurs in the gap between the electrodes, and a detection means that detects the time distribution from the voltage application to the occurrence of the discharge detected by the detection means. Comparing the time distribution state with a preset distribution state indicating the quality of the gap state, determining the gap condition and outputting a signal, based on the output of the gap condition determining means. and control means for controlling the peak value of the pulse current flowing through the gap between the electrodes.

[Effect]

In this invention, the time distribution state from the time when a voltage is applied between the electrodes until the occurrence of discharge is detected by the detection means, excluding the influence of the string vibration of the wire electrode, and the detected time distribution state and the time distribution state are set in advance. The inter-electrode gap state determining means compares the distribution state indicating the quality of the inter-electrode gap condition with the distribution state, and when receiving an abnormality determination signal from the inter-electrode condition discriminating means, the control means determines the peak value of the pulse current flowing through the inter-electrode gap. In addition to sensing the wear of the wire electrode and preventing the wire electrode from breaking, the gap between the electrodes is restored to a normal state, and when a normal discharge determination signal is received, the peak value of the pulse current is increased to reduce the machining speed. Control to improve.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Figure 1 shows the discharge voltage waveform between the electrodes and the distribution of the no-discharge time from voltage application to the start of discharge in each discharge voltage waveform to explain the principle of detecting the electrode gap state in this invention. , are the results obtained through experiments.

Note that since the discharge start point is detected at the time when the voltage falls, a signal is also output when the pulse turns from on to off. The following has been found from the relationship between this distribution state and the interpolar state.

(A) Except for the open state between the electrodes (the state where the electrodes and the workpiece are completely separated and are not being processed), the rate of discharge starting within 2 μs after voltage application is high.

in) When the wire electrode is about to break, the above 2.
The ratio of starting discharge within μ seconds exceeds 70.

(Q During normal discharge, the distribution up to 2 μs after voltage application is 3
The distribution is around 0, and then gradually decreases.

(1) When the gap between the poles is extremely narrow, the above (B)
Although it resembles the state just before the wire breakage in 2.
The distribution between ~10 μsec is 10% or more.

(If the servo between the poles is performed so that the gap between the poles is widened, 10
~20fi is discharged within 2 μs and then gradually decreases.

(g) No discharge occurs during short circuit.

Note that the above (Al-(g)) is equivalent to (Al-(g)) in Figure 1.
corresponds to

Based on the above results, it can be determined that the pole gap state is not abnormal, that is, it is a normal state, if the following conditions exist.

During the period of opening → discharge → short circuit → discharge → open between the electrodes due to string vibration of the wire electrode, only the discharge time is sampled, and in the distribution state of the no-load voltage application time from voltage application to discharge occurrence during the discharge, (1 ) There are 10 or more pulses that start discharging in 2 to 10 μsec.

(2) The ratio of pulses discharged within 2 microseconds does not exceed 50 inches.

(3) The ratio of no discharge even under r p does not exceed 50%.

FIG. 2 is a schematic diagram including this embodiment. A switching transistor 15b, which applies a voltage to the gap between poles and causes a discharge current to flow, is driven by a switching amplifier 16. The pulse pause signal input to the switching amplifier 16 is generated by the pulse pause generation circuit 17.

The basic clock pulses of this pulse pause generation circuit 17 are generated by a clock pulse generator 18. The frequency of the clock pulse needs to be higher than IMIIz because it is also used for sampling the time until the voltage applied between electrodes is discharged. In FIG. 2, 19 is a circuit for detecting the fall of the voltage between electrodes, and resistors r1. The voltage is divided by r2, and the signal at the time when it falls below the reference voltage vr by the comparator 19a is
A falling differential circuit composed of a resistor r3 and a capacitor C1 extracts the signal as a signal S2.

When the electrode gap is open and shorted due to string vibration of the wire electrode,
Since there is no rise or fall of the inter-electrode voltage, the disturbance element due to string vibration can be removed by the above-mentioned differential circuit.

The inter-electrode state determination circuit 20 receives the clock pulse CLK from the clock pulse generator 18, the signal S1 from the pulse pause generation circuit 17, and the signal S1 from the differentiation circuit, and determines the discharge state between the inter-electrode. The operation will be explained below using FIGS. 3 and 4. A voltage is applied to the gap between the poles, the ring counter 21 operates, and the OR gate 2
21 to 22 are in a gate open state every time. For example, OIt gate 22. The output for 0 to 5 μs is “1”
''. During this time, when discharge occurs and the voltage fall signal S2 is input, the counters 241 to 24n receive a signal corresponding to the discharge distribution for each section in a predetermined period of time via the AND gates 23, to 23. The number of pulses is counted.The predetermined time is 10 to 3, considering the speed of change in the state of the gap between the poles.
0 msec is considered appropriate based on experimental results. The contents of these counters 241 to 24n are stored in the digital comparators 25. .about.25n, and it becomes clear how many or fewer pulses are discharged in a predetermined period of time and with what kind of no-load voltage application time distribution.

As described above, the distribution status is classified into a distribution that is determined to be abnormal and a distribution that is determined to be normal, and when it is determined that the distribution is abnormal, this is further counted by the counter 26.

Furthermore, in the case of a distribution that is determined to be normal, the counter 26 is reset, so this counter 26 is determined to be in an abnormal state, that is, when the rate of discharge within 2 μs after the application of voltage or pressure is 50 chips. or when the rate of non-discharge is 50 or more even after 20μ seconds, the counter contents increase and 2
The counter 26 is immediately reset when there are 10 or more pulses that are discharged in ~10 microseconds. Therefore, if it is normal, the counter value is zero, and if it is abnormal, the counter value increases. Therefore, by using the digital-to-analog converter 27 and observing the analog voltage VO, it is also possible to check whether the pole gap condition is good or not. Can be distinguished. In other words, if the analog voltage ■o1 is large, it means that it is close to an abnormal discharge, and it is easy to detect a problem in the state where the wire electrode is about to break, such as sludge accumulated in the gap between the electrodes due to the accumulation of workpiece powder. can.

1 to 1. However, for a very short period of time, the inter-electrode gap condition constantly changes t2, and even if there is a short-time analog voltage v (h, it cannot always be determined that the inter-electrode gap condition is bad.) ,
It is necessary to determine whether the pole gap condition is good or not by detecting that the output Vo of the digital-to-analog converter 27 remains at a predetermined value or more for a certain period of time.

The voltage comparator 28 in FIG. 5 is the output ■ of the digital-to-analog converter 27. It is determined whether the value is a dog or smaller than a predetermined value Vll. When Vo>Vll, the output of the voltage comparator 28 becomes negative, turning off the switching transistor 3o via the base resistor 29. Therefore, the time measurement capacitor 31 is charged via the resistor 32.

The voltage V across this capacitor 31 is expressed by the following equation.

Vas = V41 (1-ex, re) where r
is the resistance value C of the resistor 32 and the capacitance t of the capacitor 31 is the time IQt FE V s r across the capacitor 31 is compared with the reference tlf and IEV by the voltage comparator 33.

During the period when Vat<V+, the output of the voltage comparator 33 is not the same, so the light emitting diode 34 does not light up. That's V. 〉The state of Vll continues for a predetermined period of time (V s t )
When V□, the output of the voltage comparator 33 becomes negative,
The light emitting diode 34 is turned on via the resistor 35 to indicate the occurrence of an abnormality in the gap between the bars.

The switch 36 determines the pole gap condition only as a function of time or the output of the digital-to-analog converter 27 (12). This is a switch for determining whether to make a judgment as a function of the product of the magnitude and time. That is, in the case of machining in which it is difficult to determine abnormalities in the gap between poles by detecting only time, when the switch 36 is turned to the contact 36a side as shown in the example, the output voltage of the digital-to-analog converter 27 is
As a function of the product of and time, the occurrence of an abnormality in the polar gap state can be quickly detected. This is because if the output vo is large, the charging current of the capacitor 31 increases, and the voltage V across the capacitor 31 immediately reaches the reference voltage V, lK.

Furthermore, it is clear that by directly observing the above output ①o with a voltmeter, it can be used as a monitor for the state of the gap between the poles.

Hereinafter, an example of the case where the control means 37 for controlling the peak value of the pulse current based on the output signal Sm from the counter 26 of the gap state determination means 2o is controlled by changing the voltage of the main current circuit will be explained. This will be explained using the principle diagram in FIG. 6 and the waveform diagram in FIG. 7.

Two pulse current supply circuits are connected to the machining current pulse feeder 9. One of the circuits is composed of a fixed voltage power supply 100, a switching element 101, a current limiting impedance element 102, and a reverse current prevention diode 103. The switching element 101 is controlled to be conductive or non-conductive at a constant cycle according to the output of a switching control circuit 104. be done.

Due to the conduction of the switching element 101, a voltage is applied from the fixed voltage power source 100 between the workpiece 1 and the wire electrode 2, and the applied voltage breaks the insulation in the gap between the electrodes, causing a pulse current to flow. Therefore, the width of this pulse current, the pause time, etc. are controlled by the switching control circuit 104.

Next, another current supply circuit includes a variable voltage power supply 105,
Switching element 106, current limiting impedance 10
7 and a backflow prevention diode 108, the switching element 106 becomes conductive when it detects that a current is supplied between the electrodes from the pulse current supply circuit, and when the switching element 104 reaches the rest time, the switching element 106 also becomes conductive. It is set to be in the off state. The output voltage of the variable voltage power supply 105 is controlled by a voltage control circuit 110, and this voltage control circuit 110 is operated by the output of the abnormality detection counter 26.

Therefore, - the peak value of the pulse current p is the voltage E1 of the fixed voltage power supply 100, the current limiting impedance 102,
107 each 2. ．． 2. and variable voltage power supply 105
If the voltage is E2, then the trap will be as follows. Note that ``■'' is the arc voltage during discharge, and is approximately 20 to 35V.

Therefore, according to the circuit configuration shown in FIG. 6, when the gap condition deteriorates and a signal is output from the abnormality detection counter 26, the voltage control circuit 110 responds to reduce the voltage E of the variable voltage power supply 105. to lower the current peak value.

As shown in the waveform diagram of Fig. 7, the open circuit voltage between the electrodes is set at the fixed power source 100 El and the discharge pulse current peak value
Only p is variable power supply E! controlled by When the signal 5A from the abnormality detection counter 26 is O, that is, when the machining condition is good, the peak value ■p of the pulse flow is the high peak value Ip1, and once an abnormality occurs and the signal Sm becomes 1. , the current peak value ■, becomes ■,2.

In wire-cut electrical discharge machining, when the current peak value 1 is large, the machining speed is also high, but the amount of electrode consumption of the wire electrode is also large, so the wire electrode is likely to break.

Current peak value ■When p is small, electrode consumption 1゛ decreases1
(approximately proportional to the flow peak value), and wire electrode breakage can be prevented.

As mentioned above, the reason why only the peak value of the pulse current is changed is that if the surface texture of the machined surface is experimentally changed only by the peak value, it is difficult to be affected, and it has a large effect on the machining speed and wire electrode wear. This is because it has.

In the above example, the peak value I is obtained by changing the voltage.

is controlled, but the current limiting impedance 107
The peak value can also be controlled by changing .

〔Effect of the invention〕

As described above, according to the present invention, the time distribution state from the voltage application between the workpiece and the wire electrode until the occurrence of electric discharge is detected by eliminating the influence of string vibration of the wire electrode, and the detection result is Since normal discharge and abnormal discharge are determined based on this, it is possible to accurately determine whether the inter-electrode condition is good or bad. When an abnormal condition is detected, the peak value of the pulse current flowing between the electrodes is reduced to reduce wear on the wire electrodes, prevent wire electrode breakage, and return the electrode gap to a normal state. In this case, the above-mentioned peak value is increased and the machining speed can be improved.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a schematic diagram of the device configuration of the present invention, FIG. 3 is a circuit configuration diagram of the interpolar gap state determining means, and FIG. 4 shows the circuit operation of FIG. 3. A time chart for explanation, FIG. 5 is a display circuit diagram of the pole gap state determination result, FIG. 6 is a circuit diagram showing an example of a control means for controlling the peak value of the pulse current according to the determination signal, and FIG. 7 is a signal waveform diagram of the circuit, and FIG. 8 is a principle diagram showing a conventional wire-cut electrical discharge machining apparatus. 1... Workpiece, 2... Wire electrode, 3...
Machining fluid, 19... Detection means (fall detection circuit of inter-electrode voltage), 20... Inter-electrode gap state determination means, 37.
...control means. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] A wire electrode and a workpiece are placed facing each other with an insulating machining fluid interposed between them, and a pulse voltage is applied between the wire electrode and the workpiece to generate an electric discharge between them, and the discharge energy is used to drive the workpiece. In a wire-cut electric discharge machining device for machining, an open state and a short-circuit state caused by string vibration of the wire electrode in the gap between opposing poles between the wire electrode and the workpiece are removed, and electric discharge is performed in the gap between the poles. a detection means for detecting a distribution state of time after voltage application at the time of the discharge; and a distribution state indicating the quality of the electrode gap state, which is a preset distribution state of the time detected by the detection means from the voltage application to the occurrence of discharge. an inter-electrode condition determining means for comparing the inter-electrode conditions, determining the inter-electrode condition and outputting a signal; and a control means for controlling the peak value of the pulse current flowing through the inter-electrode gap based on the output of the inter-electrode condition determining means. A wire cut electrical discharge machining device characterized by comprising: