JPS61111835A - Wire-cut electric discharge machinine - Google Patents

Abstract

PURPOSE:To prevent a wire electrode from breaking without fail, by discriminating a gap state from a time distribution state till causing discharge generation, while controlling spouting pressure in a dielectric machining fluid according to the discriminated result. CONSTITUTION:A switching transistor 15b, which impressed voltage on a spark gap and makes a discharge current 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, spouting pressure in a dielectric machining fluid to be spouted to the gap between a wire electrode 2 and a work 1 is controlled.

Description

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

[Conventional technology]

Processing the sound of a workpiece using electrical energy has been widely practiced and is well known, but it is now possible to use wire-shaped electrodes in processing equipment, which has been attracting attention as a recent technology. Yo K.

4) There is a wire-cut electric discharge machining apparatus in which a workpiece is pressurized with electrical energy.

FIG. 7 shows the above-mentioned wire cut electric discharge machining apparatus m? FIG. Reference numeral 1 denotes a workpiece, in which a wire hole and a pole 2 are passed through a spinning hole 1a that has been drilled in advance with a drill, etc., and an insulating liquid 3 is entirely 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
A nozzle 6 injects the liquid from the tank 4 into the gap between the workpiece 1 and the wire electrode 2 using the pump 5 .

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 entirely placed.

The table 11 has a Y-axis drive motor 13 and an X-axis motor】2
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 X1Y axis plane.

The wire electrode 2 is supplied by a wire supply reel 7,
The wire passes through the lower wire guide 8A, the workpiece 1 and reaches the upper guide 8B, where it is wound up by the wire winding and tension roller 10 via the electrical energy supply s9i.

The control device 14 that drives and controls the drive motors 12 and 13 for the X and Y axes is a numerical control device (NC control device) f-copying device or a control device using a computer.

A processing power source 15Fi that supplies all electrical energy, for example,
It is composed of a DC power supply 15a, a switching element 15b1, a current limiting resistor 15c, and a control circuit 15d that controls the switching element 15bi.

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 the next full pulse voltage is applied. 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 machining power source 15 is normally operated under electrical conditions such as downtime that 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 to be solved by the invention 3 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 source 15 is reduced, etc. Since the electric discharge was concentrated at one point on the wire electrode 2, there was a problem that the machining speed was extremely low because the wire was not broken even if it was concentrated at one point.

Therefore, conventional attempts have been made to extract various signal components from between the poles and detect the warning sound 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 KIIz. Therefore, there is a problem in that this causes a disturbance, making it extremely difficult to accurately detect the state between the poles.

This invention has been made to solve these problems, and provides a wire that can accurately detect the state of the gap between electrodes and utilize the detection results to reliably prevent wire electrode breakage accidents. The overall purpose is to obtain a cut electric discharge machining device t.

[Means for solving problems]

The wire-cut electric 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. Periodically sample only the time when discharge occurs and discharge in the gap between the electrodes.
a detection means for detecting a time distribution state after the voltage is applied; and a distribution state indicating the quality of the electrode gap state, which is a preset time distribution state detected by the detection means from the voltage application to the occurrence of the discharge. The apparatus is equipped with a gap condition determining means for comparing the gap condition, determining the gap condition and outputting a signal, and a control means for controlling the ejection pressure of the insulating machining fluid based on the output of the gap condition determining means. be.

[Effect]

In this invention, after voltage is applied between the electrodes, the time distribution state up to the occurrence of discharge is detected by the detection means while eliminating the influence of string vibration of the cable wire electrode, and this detected time distribution state and the preset polarity are detected. The control means compares the distribution state indicating the quality of the gap state with the distribution state by the gap state discrimination means. When the control means receives an abnormality determination signal from the gap state discrimination means, the control means increases the injection pressure of the machining fluid and discharges the sludge. Control is performed to increase the capacity, eliminate discharge concentration caused by impedance reduction due to sludge factors, and completely prevent wire electrode disconnection.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be fully explained based on the drawings. Figure 1 shows the discharge voltage waveform between the electrodes to fully explain the detection principle of the electrode gap state in this invention, and the distribution state of the no-discharge time from voltage application to the start of discharge in each of the seven discharge voltage waveforms. This is the result obtained by experiment.

Note that since the release 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 electrode state (the state where the electrodes and workpiece are completely separated and are not being processed), the rate of discharge starting within 2 μs after voltage application is high.

(11) When the wire electrode is about to break, the rate of full discharge starting within 2 microseconds exceeds 70.

(C) During normal discharge, the distribution is about 30% up to 2 μs after voltage application, and then the distribution gradually decreases.

(2) When the gap between the poles is made extremely narrow, it becomes similar to the state immediately before the wire breakage in 0 above, but still 2 to 1
There are more than 10 distributions during 0 μs.

[F] When servoing between poles is performed so that the gap between poles is widened, 1
From 0 to 20 inches, the discharge occurs within 2 microseconds, and then it gradually decreases.

(g) No discharge occurs during short circuit.

Note that the above 翰~(g) corresponds to 翰~■ in Figure 1.

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 more than 10 pulses that start discharging in 2 to 10 μs.

(2) The ratio of pulses discharged within 24 seconds does not exceed 50.

(3) τ, but the ratio of no discharge does not exceed 50ch.

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. A pulse pause signal input to this switching amplifier 16 is generated by a 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 at least 1 I Ml - I2, which is also used for sampling the time until the discharge of the voltage applied between the electrodes.

In Figure 2, 19 is a circuit that detects the fall of the voltage between electrodes,
The voltage is divided by the resistor rl r't, and the signal sound at the time when the voltage falls below the reference voltage Vr at the comparator 19a, the resistor r
1 and a falling differential circuit composed of a capacitor C, which extracts the signal S.

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 pole distance tPi:, all disturbance elements due to string vibration can be eliminated by the above-mentioned differential circuit.

The inter-electrode state determination circuit 20 receives the clock pulse CI from the clock pulse generator 18, the signal SI from the pulse pause generation circuit 17, and the signal Stk from the differentiation circuit, and determines the discharge state between the inter-electrode. The operations of steps 7 and 7 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 an OR game is performed.
22. ~22n is in a gate open state every time.

For example, OR gate 22. The output is II for 0 to 5 μs.
It is IH. During this time, discharge occurs 1. A voltage falling signal S is input to the 121st and ANI) gates.
Counter 24.1 through 231-23nk. .about.24n, the number of pulses along the radiation #M1 distribution for each section in a predetermined period of time is counted. As the predetermined time, 10 to 30 msec is considered to be appropriate based on experimental results, in view of the continuous change in the state of the gap between the poles. These counters 241 to 24
The contents of n are determined by the digital comparator 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 determined to be abnormal and a distribution determined to be normal, and if the distribution is not determined to be abnormal, the counter 26 further counts this distribution.

- Also, if the distribution is judged to be normal, the counter 26
Since the counter 26 is reset, when it is determined that an abnormal state exists, that is, when the rate of discharge within 2 μs after voltage application is 50 or more, or the rate of not discharging even after 20 μs is 50 or more, the counter 26 is set. Counter self-answer increases, 2
2) The counter 26 is reset as soon as more than 1O- pulses are present. Therefore, if it is normal, it r, r '4, and if it is abnormal, the counter content increases. Using r, AJ-u
By observing v0 for gummies, it is possible to distinguish between -C4, extremely gap-shaped cap, σ, and bulge. In other words, if the arithmetic voltage and pressure v0 are large, it means that abnormal discharge is approaching, and problems that occur immediately before the wire electrode breaks, such as sludge being trapped in the gap between the electrodes due to the accumulation of workpiece powder, can easily occur. Can be detected.

However, in a very short period of time, the pole gap state is constantly changing, and even if the analog voltage v0 is present for a short time, it cannot necessarily be determined that the pole gap state is bad. Therefore, it is necessary to detect whether the output X0 of the digital-to-analog converter 27 has been greater than a predetermined value for a certain period of time, and to judge whether the gap state is good or bad.

The voltage comparator 28 in FIG. 5 determines whether the output Va of the digital-to-analog converter 27 is larger or smaller than a predetermined value V11. When Vo>VoK, the output of the voltage comparator 28 becomes negative, and the switching transistor 30 is turned off via the pace resistor 29. Therefore, the time measuring capacitor 31L1 is charged via the time measuring capacitor 31L1. The voltage V across this capacitor 31 is expressed by the following equation.

-yuVs+ = V4111 exp) only 1
~ "The resistance value C of the resistor 32 is the capacitance t of the capacitor 31. The voltage V □ across the capacitor 310 is the reference voltage V and the current r.
Compare with E comparator 33. During the period of V□<Vll, the output of the voltage comparator 33 does not become negative, so the light emitting diode 34 does not light up. Set Vo＞■3. When the state continues for a predetermined time and becomes V, I > vtI, the voltage comparator 33
The output becomes negative, and the 34 light emitting diodes are turned on through the resistors 351 to indicate the occurrence of an abnormality in the gap between the poles.

The switch 36 is a switch for switching whether to judge the pole gap state only as a function of time or as a function of the product of the magnitude of the output y0 of the digital-to-analog converter 27 and time. In the case of machining in which it is difficult to determine abnormalities in the gap between poles by detecting only time, if the switch 36 is turned to the contact 36a side as shown in the example,
As a function of the product of the output v0 of the digital-to-analog converter 27 and time, the occurrence of an abnormality in the pole gap state can be immediately known. This is because when the above-mentioned output V0 is large, the charging current of the capacitor 31 increases by t, and the electric current FEV across the capacitor 31 immediately reaches the reference value of 1V, 1[V□.

In addition, the above output V. It is clear that it can be used as a monitor of the polar gap state by observing -r at Yamaguchi and Kawaguchi 1.

Hereinafter, the abnormality detection count 2 of the gap state determining means 20 will be described below.
An example of a control means 3701 for changing the pressurized liquid ejection pressure to the gap between the poles in accordance with the detection signal SA from 6 will be described with reference to FIG. In FIG. 6, the machining fluid 3 sucked up from the machining fluid tank 4 by the machining fluid supply pump 5 passes through a pipe 103 via an electromagnetic pulse 11011 and a manual valve 102, and is guided to the nozzle 6. This machining fluid pressure is observed by the fluid pressure meter relay 105, and if it exceeds a predetermined pressure, -
Feedback from hydraulic pressure meter relay 105
B is fed back to the controller 106, and the output of the controller 106 controls the electromagnetic valve 101 to maintain the appropriate set pressure.

Note that the manual valve 102 is operated by the electromagnetic valve 101 [
- This is to maintain the lowest pressure at all times.

Processing conditions worsen [-1 If processing powder stays in the gaps,
Since the detected 4W SA output from the abnormality detection counter 26 is input to the valve controller 106, the electromagnetic valve 101 is opened and continues to be opened until the feedback signal SB is output from the hydraulic meter relay 105.

Due to this strong ejection pressure, the machining powder present in the gap between the mazes is quickly removed, and the state between the mazes is restored to its normal state. When the pressure is recovered, the detection signal 8 no longer outputs n2, the electromagnetic valve 101 closes, and the pressure returns to the weak pressure set only by the manual valve 102.

Regarding why two types of pressure are necessary, in general, when the pressure is about 0.05 mm/cIIi, the impedance between the electrodes is most appropriate (moderately dirty ones are easier to discharge and improve machining stability). ), and 0.5kt/-
If this happens, the impedance of the gap between the poles will become too high and the gap length for discharge will become too narrow, making short circuits more likely to occur and machining becoming unstable. It is desirable to process at less than .051w/c+J, as the gap between the machining parts may become too dirty or sludge from processing may accumulate in some areas.1. Only when high-pressure fluid flow is required.

〔Effect of the invention〕

As described above, the present invention is based on the time distribution state of the string vibration of all wire electrodes after applying 1111E between the workpiece and the wire electrode, leading to the generation of W. r J
Detect by dividing JI, and based on the detection result, calculate V1. IE always
ll 1! and abnormal discharge is determined.
It is possible to accurately determine whether the gap condition is good or bad. It was determined that: Since the machining fluid ejection pressure sound is controlled in response to the quality of the machining gap, the machining powder generated in the machining gap can be efficiently discharged, and the machining efficiency group L <It can be improved. In other words, if machining powder is present in the gap between the machining plates, sparks from the discharge will be generated along the path of electrode → machining powder → workpiece, so a considerable proportion of the discharge energy will be spent on thermal decomposition of machining powder and machining fluid. This has the effect of preventing the phenomenon of a decrease in machining speed, and preventing local wear of the wire 'fjL pole and wire breakage due to concentration of electric discharge.

In addition, although this example has been explained using examples of ejection and injection,
It is clear that exactly the same effect can be obtained in the case of machining using suction.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of 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 pole gap state determining means, and FIG. 4 is a diagram of the circuit operation of FIG. 3. A time chart for explanation, FIG. 5 is a display circuit diagram of the determination result of the pole gap state, FIG. 6 is a schematic configuration diagram showing one example of a control means for controlling the jetting pressure of machining fluid according to the determination signal, and FIG. The figure is a principle diagram showing a conventional wire-cut electric discharge machining device. 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. A gap condition determining means for comparing the gap condition to determine the gap condition and outputting a signal, and a control means for controlling the ejection pressure of the insulating machining fluid based on the output of the gap condition determining means. Wire cut electrical discharge machining equipment featuring: