JPH0661659B2 - Wire cut electrical discharge machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a processing apparatus that electrically cuts a workpiece using a wire electrode.

[Conventional technology]

It has been widely known that an object to be processed by electric energy has been widely used in the past, and it is well known that a wire-shaped electrode is used in a processing device, which is attracting attention as a recent technique. There is a so-called wire-cut electric discharge machining apparatus for machining a work piece with electric energy as described above.

FIG. 7 is a block diagram showing the wire-cut electric discharge machine. Reference numeral 1 denotes a work piece, in which a wire electrode 2 is passed through an initial hole 1a made by a predrill or the like, and an insulating liquid 3 is interposed between the hole wall and the wire electrode 2.

The insulating liquid 3 will be hereinafter referred to as a working liquid. The working fluid is
From the tank 4 to the pump 5, a nozzle 6 sprays the material into the gap between the workpiece 1 and the wire electrode 2.

The relative movement between the workpiece 1 and the wire electrode 2 is performed by the movement of 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. With the above configuration, the relative movement between the work piece 1 and the electrode 2 is a two-dimensional plane movement within the above-mentioned X and Y axis planes.

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

As the control device 14 that drives and controls the X and Y axis drive motors 12 and 13, a numerical control device (NC control device), a copying device, or a control device using a computer is used.

The processing power supply 15 for supplying electric energy is, for example, a DC power supply 15a, a switching element 15b, a current limiting resistor 1
5c, and a control circuit 15d for controlling the switching element 15b.

Next, the operation of the conventional device will be described. 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 the electric discharge explosion caused by one pulse. In this case, since the gap is gasified and ionized due to the high temperature, a certain rest time is required until the next pulse voltage is applied, and if the rest time is too short, the gap will be insufficient. Before the insulation is restored, the electric discharge is concentrated again in the same two places and the wire electrode 2 is melted.

Therefore, in a normal machining power source, it is usual to process electric conditions such as a down time of the machining power source 15 depending on the type of work piece, plate thickness, etc., with a sufficient margin not to cause wire breakage. is there. Therefore, the processing speed must be considerably lower than the theoretical limit value. Further, when the wire electrode 2 is not uniform and changes in thickness, or when the discharge is concentrated due to protrusions or scratches on a part of the wire electrode, fusing of the wire electrode 2 cannot be avoided.

[Problems to be solved by the invention]

As described above, in the conventional wire-cut electric discharge machining apparatus, in order to prevent the wire electrode 2 from being broken, the output energy of the machining power supply 15 is reduced and the electric discharge is concentrated at one point of the wire electrode 2. However, since the wire was not broken, the processing speed was extremely low.

Therefore, conventionally, various signal components are extracted from the gap to detect the gap state. However, the wire electrode 2 vibrates in the work piece due to the string vibration (standing wave vibration between the wire guides), and the state of inter-electrode opening → discharge → short circuit → discharge → open is repeated at a frequency of several KHz during processing. For,
This is a disturbance, and there is a problem that it is extremely difficult to accurately detect the gap state.

The present invention has been made to solve such a problem, and can accurately detect a gap between electrodes, and use the detection result to reliably prevent a wire electrode disconnection accident. The purpose is to obtain an electric discharge machine.

[Means for solving problems]

The wire-cut electric discharge machining apparatus according to the present invention is only for electric discharge except for the inter-electrode open state and the short-circuit state due to the string vibration of the wire electrode in the gap between the electrodes facing each other between the wire electrode and the workpiece, that is, the wire. Detecting means for detecting the distribution state of time after voltage application when periodically discharging only during a time when discharge occurs in string vibration of the electrode and discharging in the gap between the electrodes, and voltage detected by this detecting means A distribution state of time from application to discharge is compared with a distribution state indicating the quality of a preset gap state, and a gap state determination means for determining a gap state and outputting a signal, and this gap state. And a control means for controlling the feed speed of the wire electrode based on the output of the discrimination means.

[Work]

In the present invention, the time distribution state after the voltage is applied between the electrodes and before the electric discharge is generated is detected by the detecting means while eliminating the influence of the string vibration of the wire electrode, and the detected time distribution state is set in advance. The distribution state indicating the quality of the inter-electrode gap is compared by the inter-electrode state determination means, and when the control means receives the abnormality determination signal from the inter-electrode → state determination means, the wire electrode feed speed is increased to increase the discharge point. And the electrode wear per unit length of the wire electrode are reduced to prevent the wire from breaking.

〔Example〕

Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a discharge voltage waveform between electrodes for explaining the principle of detection of the electrode state in the present invention, and a distribution state of no discharge time from the application of voltage to the start of discharge in each discharge voltage waveform. , The results obtained by the experiment.

Since the discharge start point detects the time when the voltage falls, a signal is output even when the pulse is turned on and off. The following has been found from the relationship between this distribution state and the interpolar state.

(A) 2μ after voltage is applied, except the condition that the gap between the electrodes is open (the electrode and the work piece are completely separated from each other and are not processed)
The rate of starting discharge within a few seconds is high.

(B) In the state immediately before the wire electrode is broken, the ratio of starting discharge within 70 μs exceeds 70%.

(C) During normal discharge, the distribution up to 2 μs after voltage application is 3
The distribution is about 0%, and then the distribution gradually decreases.

(D) When the gap between the poles is made extremely small, it becomes similar to the state just before the wire break of (B) above, but it is still 2-10μ.
There is 10% or more distribution during the second.

(E) When the servo between poles is performed so that the gap between poles opens, 10
-20% discharges within 2 microseconds, and decreases gradually thereafter.

(F) No discharge occurs at short circuit.

The above (A) to (E) correspond to (A) to (E) in FIG.

From the above results, it can be determined that the inter-electrode gap state is not abnormal, that is, the normal state, in the following states.

In the distribution state of the no-load voltage application time between the voltage application during the discharge and the occurrence of the discharge during the discharge, the sampling is performed only during the cycle of the inter-electrode open due to the string vibration of the wire electrode → discharge → short-circuit → discharge → open. ) There are 10% or more of pulses that start discharge in 2 to 10 μsec.

(2) The ratio of pulses discharged within 2 μsec does not exceed 50%.

(3) The ratio of not discharging does not exceed 50% even with τ _P.

FIG. 2 is a schematic diagram including this embodiment. The switching transistor 15b for applying a voltage to the gap between the electrodes and flowing a discharge current is driven by the 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 pulse of the pulse pause generation circuit 17 is generated by a clock pulse generator 18. Since the frequency of the clock pulse is also used for sampling the time until the discharge of the voltage applied between the electrodes, a frequency of 1 MHz or higher is required.

In FIG. 2, 19 is a circuit for detecting the fall of the voltage between contacts,
The voltage is divided by the resistors r ₁ and r ₂ , and the comparator 19a
Then, the signal at the time when it becomes lower than the reference voltage V _r is taken out as the signal S _{2 by the} falling differentiation circuit composed of the resistor r ₃ and the capacitor C ₁ .

At the time of opening and shorting between the electrodes due to the string vibration of the wire electrode,
Since there is neither rise nor fall of the voltage between contacts, the disturbance element due to the string vibration can be removed by the differentiating circuit.

The gap state determining circuit 20 receives the clock pulse CLK from the clock pulse generator 18, the signal S ₁ from the pulse pause generating circuit 17, and the signal S ₂ from the differentiating circuit, and determines the discharge state between the electrodes. The operation will be described below with reference to FIGS. 3 and 4. The voltage is applied to the gap between the electrodes, the ring counter 21 operates, and the OR gate 2
2 ₁ through 22 _n is a gate open state every time. For example, the output of the OR gate 22 ₁ is “1” for 0 to 5 μsec.
It is said. When discharge occurs during this period and the voltage falling signal S ₂ is input, the number of pulses along the discharge distribution for each section in a predetermined time is counted by the counters 24 _{1 to} 24n via the AND gates 23 _{1 to} 23n. It The predetermined time is 10 to 30 m in view of the speed of change in the gap between the electrodes.
Seconds are also considered appropriate from experimental results. The contents of these counters 24 _{1 to} 24 n are discriminated by the digital comparators 25 ₁ to 25 n, and it is clear how many or less pulses are discharged in what distribution of no-load voltage application in a predetermined time. Become.

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

If the distribution is judged to be normal, the counter 26 is reset, so that when the counter 26 is judged to be in an abnormal state, that is, the discharge rate is 50% or more within 2 μsec after the voltage application, or When the rate of not discharging even at 20 μs is 50% or more, the counter content increases,
The counter 26 is immediately reset when 10% or more of the pulses are discharged in 10 μsec. Therefore, since the state of zero is normal if it is normal and the counter content is increased if it is abnormal, it is possible to observe the analog voltage V ₀ by using the digital analog converter 27 for this counter content. The quality of can be determined. That is, if the analog voltage V ₀ is large, it means that abnormal discharge is approaching, and there is a problem in the state immediately before the wire electrode is broken, such as sludge accumulating in the gap between the electrodes due to the accumulation of the powder to be processed. It can be easily detected.

However, the inter-electrode gap state constantly changes for a very short time, and it cannot be determined that the inter-electrode gap state is bad even if the analog voltage V ₀ is present for a short time. Therefore, it is necessary to detect the existence of the output V ₀ of the digital analog converter 27 equal to or more than a predetermined value for a certain period of time to judge whether the inter-electrode gap state is good or bad.

The voltage comparator 28 in FIG. 5 determines whether the output V ₀ of the digital analog converter 27 is larger or smaller than the predetermined value V ₁₁ . When V ₀ > V ₁₁ , the output of the voltage comparator 28 becomes negative and the switching transistor 30 is turned off via the base resistor 29. Therefore, the time measuring capacitor 31 is charged via the resistor 32. The voltage V across the capacitor 31 is expressed by the following equation.

Here, r is the resistance value of the resistor 32, c is the capacitance of the capacitor 31, and t is time. The voltage V ₃₁ across the capacitor ₃₁ is compared with the reference voltage V by the voltage comparator 33. Since the output of the voltage comparator 33 does not become negative during the period of V ₃₁ <V ₂₁ , the light emitting diode 34
Does not light. Then, when the state of V ₀ > V ₁₁ continues for a predetermined time and becomes V ₃₁ > V ₂₁ , the output of the voltage comparator 33 becomes negative, and the light emitting diode 34 is turned on via the resistor 35 to cause an abnormality in the inter-electrode gap state. It shows the occurrence.

The switch 36 is a switch for switching between the judgment of the inter-electrode gap state based only on the function of time or the judgment of the state as a function of the product of the output V ₀ of the digital analog converter 27 and the time. That is, in the case of machining in which it is difficult to determine the abnormality of the inter-electrode gap state by simply detecting only the time, when the switch 36 is closed to the contact 36a side as shown in the drawing, the output V ₀ of the digital analog converter 27 and the time As a function of the product, it is possible to promptly know the occurrence of the anomaly in the gap between the poles. If the output V ₀ is large, the capacitor 3
This is because the charging current of 1 increases and the voltage V across the capacitor 31 reaches the reference voltage V ₂₁ immediately.

Further, it is apparent that the output V ₀ can be used as a monitor of the inter-electrode gap state by directly observing the output V ₀ with a voltmeter.

Hereinafter, the control means 37 for changing the feed speed of the wire electrode based on the output from the inter-electrode state determination means 20
It will be described with reference to the drawings. The wire electrode 2 sent from the supply reel 7 is a tension motor 10 for generating wire tension.
0, tension reel 101, auxiliary reel 102 applies a predetermined tension, and pulls through the machining gap by pulling capstan 103, capstan roller 104, capstan motor 105, and by take-up reel 10. Being rolled up.

In the wire electrode feeding mechanism configured as described above,
When the condition of the gap between electrodes is deteriorated and the concentration of discharge and the precursory condition of wire breakage are detected, the output from the counter 26 is output to the control means 37.
The control transistor 107 is amplified by the internal amplifier 106.
Is supplied as a base voltage V ₂ to the base of the.

If the emitter resistance 108 is R and the current flowing through the capstan motor 105 is I, Is represented.

Note that Vs is a motor control voltage by the counter 26, and is the base-emitter voltage V of the control transistor 107.
_BE is weak and constant at about 0.6 V, and can be almost ignored. The motor current is controlled by the base voltage Vs. This base voltage Vs becomes a high voltage based on the output of the counter 26, and the motor current is increased to increase the wire electrode 2.
Increase the feed rate of. The discharge points are forcibly moved and dispersed by the high speed running of the wire electrode, the discharge concentration is eliminated, and the electrode consumption amount per wire unit length is reduced to prevent the wire electrode from breaking.

The faster the feeding speed of the wire electrode 2 is, the better the sludge discharging action is, the more the short circuit is reduced and the processing speed is increased.
It is not economical because the consumption of wire electrodes increases. When the gap condition deteriorates, feed quickly, and if the gap condition is good,
Control to send slowly. Also, in the unprocessed state,
In the conventional device, the wire electrode is fed, which is uneconomical, but by controlling as described above, the wire electrode is fed slowly, which is economical.

〔The invention's effect〕

As described above, according to the present invention, after the voltage is applied between the workpiece and the wire electrode, the time distribution state up to the occurrence of electric discharge is detected by eliminating the influence of the string vibration of the wire electrode, and the detection result is obtained. Since the normal discharge and the abnormal discharge are discriminated on the basis, it is possible to accurately discriminate the quality of the gap state. Then, when the abnormality of the gap between the electrodes is determined, the feed speed of the wire electrode is changed so as to be increased, so that the wire electrode disconnection accident can be reliably prevented and the wire electrode can be economically used. There is an effect.

[Brief description of drawings]

FIG. 1 is a diagram illustrating 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 inter-electrode gap state determining means, and FIG. 4 is a circuit operation of FIG. Time chart for explaining, FIG. 5 is a display circuit diagram of the result of determination of the inter-electrode gap state, and FIG. 6 is a circuit diagram showing an example of control means for controlling the feed speed of the wire electrode according to the determination signal. FIG. 7 is a principle view showing a conventional wire-cut electric discharge machine. 1 is an object to be processed, 2 is a wire electrode, 3 is a working liquid, 19 is a detecting means (falling voltage detecting circuit between electrodes), 20 is an interelectrode gap state determining means, and 37 is a controlling means. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A wire electrode and a work piece are opposed to each other with an insulating working liquid interposed therebetween, a pulse voltage is applied between the wire electrode and the work piece to generate an electric discharge therebetween, and the discharge energy is used. In a wire-cut electric discharge machine for machining the work piece, only during an electric discharge other than an inter-electrode open state and a short-circuit state caused by the string vibration of the wire electrode in the gap between the electrodes facing each other between the wire electrode and the work piece. The detection means for detecting the time distribution state after the voltage application and the distribution state of the time from the voltage application to the discharge generation detected by the detection means are compared with the distribution state indicating the preset gap quality Then, the inter-electrode state determining means for determining whether the inter-electrode state is normal or not, and the feeding speed of the wire electrode is reduced based on the normal determination output from the inter-electrode state determining means. Wire-cut electric discharge machining apparatus characterized by comprising a control means for quickly feeding speed of the wire electrode based in the abnormality determination output.