JPS61125734A - Wire cut electric discharge processing device - Google Patents

Abstract

PURPOSE:To improve a processing speed by controlling tension applied to a wire electrode based on a judgement result from inter-electrode judgement means, and preventing the electrode weakened in its tension resistance from being disconnected by reducing the tension upon abnormal while reducing short-circuit by increasing the tension upon normal. CONSTITUTION:Detected troubles such as concentrated electrical discharge or wire disconnection as a result of deterioration of inter-electrode condition as a result of deterioration of inter-electrode conditions, an output is provided to a counter 26, amplified through an amplifier 106, and delivered to a controlling transistor 107 as base voltage. Hereupon, a motor current satisfies:I=Vs/R. It is found from this expression that the current I is controlled by the base voltage Vs, but the Vs is reduced and hence a drive current for a tension motor 100 is reduced to permit wire tension to be reduced, whereby disconnection of the electrode weakened in its tension resistance due to wear of the electrode can be prevented, while the device can securely be allowed to escape from abnormal processing conditions by making use of a fact of current reduction and fact that the device is brought into a non-load due to back movement. Furthermore, with the inter-electrode state being returned to a normal state the tension of the wire electrode is gradually increased, whereby rigidity of the wire electrode is increased with reduced short-circuit for improving the processing speed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a wire that generates electrical discharge between a wire electrode and a workpiece (between electrodes), and electrically cuts the workpiece using this discharge energy. The present invention relates to a cut electrical discharge machining device.

[Conventional technology]

Machining workpieces using electrical energy has been widely practiced and is well known, but it is a recent technology that has been attracting attention using wire-shaped electrodes in processing equipment.
There is a so-called wire-cut electric discharge machining device that processes a workpiece using electrical energy, as if using a ``spinning saw.''

FIG. 7 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 cut hole 1a made in advance with a drill or the like, and an insulating liquid 3 is supplied 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 .

Relative movement between the workpiece 1 and the wire electrode 2 (performed by movement of the table 11 on which the radio wave 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 the wire supply reel 7 n1
The wire passes through the lower wire guide 8A and the workpiece 1, reaches the upper guide 8Bl, and is wound up by the wire winding/tension roller 10 via the electric energy feed section 9.

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), a copying device, or a control device using a computer.

The processing power supply 15 that supplies electrical energy is composed of, for example, a DC Tt source 15a, a switching element 15b, a current limiting resistor 15C, and a control circuit 15d that controls the switching element 15b.

Next, the operation of this conventional device will be explained. Under normal machining conditions, a high-frequency pulse voltage is applied from the machining power source 15, and a part of the workpiece 1 is melted and scattered by a discharge explosion caused by one pulse. In this case Since the gap between the electrodes is gasified and ionized due to the high temperature, 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 long, the discharge will again concentrate at the same location, causing the wire electrode 2 to melt.

Therefore, with a normal machining power source, the type of workpiece, plate thickness, etc.
Normally, electrical conditions such as the down time of the machining power source 15 are set to have sufficient margin to prevent wire electrode breakage. Therefore, the machining speed has to be considerably lower than the theoretical limit value, and furthermore, if the wire electrode 2 is not uniform and the thickness changes, or if there is a protrusion or scratch on a part of the wire and the discharge is concentrated. wire electrode 2
Melting is unavoidable.

[Problem that the invention seeks to solve]

As described above, in order to prevent the wire electrode 2 from breaking, in the conventional wire-cut electric discharge machining apparatus, the output energy of the machining power supply 15 is reduced, etc., so that if the concentration of electric discharge does not occur on the wire electrode 2. The problem was that the processing speed was extremely low because it was designed to prevent the wires from breaking even if they were concentrated at one point.

Therefore, in the past, safety measures were taken to determine whether the machining condition was good or not, or whether the electrode was about to be damaged, and based on the results of this determination, automatically return to the normal machining condition or avoid damage to the electrode, thereby increasing the machining speed. Efforts are being made to prevent this from decreasing.

In this case, the most common means of determining whether the machining condition is good or not or whether the wire electrode is about to break is to observe the average value of the voltage between the electrodes. That is,
When the average voltage value is low, the impedance between the electrodes is low, and catastrophic breakdown due to discharge is likely to occur due to short circuit or accumulation of sludge or machining powder, resulting in discharge concentration (
This indicates that the main cause of wire breakage) has occurred.

However, when machining with a narrow gap (unsuitable for machining with good n-degrees), short circuits occur frequently even under normal machining conditions, so it would be difficult to detect short circuits and take safety measures. There was a problem in that the value decreased significantly.

This invention was made to solve these problems, and provides an electric discharge machining device that can accurately determine whether the machining condition is good or bad without reducing the machining speed, and can prevent electrode damage accidents. The purpose is to obtain.

[Means for solving problems]

The electric discharge machining apparatus according to the present invention includes a detection means for detecting a leakage current from the time when a pulse voltage is applied between a wire electrode and a workpiece until a discharge occurs between opposing electrodes, and the detection output thereof. The present invention is provided with a gap condition determining means for determining the condition of the gap based on the condition, and a control means for controlling the tension of the wire electric mark based on the determined condition.

[Function] When the control means of the present invention receives an abnormality determination signal from the inter-electrode state determination means, it reduces the tension of the wire electrodes to prevent wires whose tension resistance has weakened due to wear and tear from breaking. However, when a normality determination signal is received, the tension of the wire electrode is controlled to gradually increase to reduce short-circuit accidents and improve processing speed.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and the reference numeral ! -15 is exactly the same as the conventional device described above. 16
is a current detector for detecting the pulse current supplied between the machining power supply 15, and 17 is a control command signal generator, which receives the detected current from the current detector 16 and the voltage between the machining electrodes as input; Control device 14. It is configured to supply control command signals to the processing power source 15 and the like.

FIG. 2 is a time chart obtained from the current detector 16 in the circuit shown in FIG. Shaped signal 31 as signal, electrode voltage signal V
g is the threshold voltage v.

f The signal Sv for determining whether the soldering iron is in a no-load state or during discharging, and the next two signals Su obtained from the above-mentioned signals Sx and Sv.

SD is shown. That is, the signal Su in which current flows but is not discharged is expressed by the logical formula Sυ=SvaSX, indicating that leakage current exists during pulse application. Moreover, the signal 8D is expressed by the logical formula 8n=Sma・S! This indicates that there is no current at all during pulse application.

Figure 3 shows the signal group S described in the time chart of Figure 2.
Leakage current detection means 1 for obtaining r, Sv, Su, So
8 is an example of a circuit configuration. The current signal from the current detector 16 is converted into a shaped signal Sr by a waveform shaping circuit 19, which is a signal indicating the presence or absence of current.

The interelectrode voltage Vg is divided by a voltage dividing circuit rIr'2,
The level comparator 20 sets the reference threshold voltage VR.
A comparison is made to see if it is larger or smaller, and it is determined whether it is a discharge or no-load state.

The signal SU indicating the presence of leakage current is output by the AND gate 21 in the form of the above-mentioned logical formula 8a==3y*8x, and the no-load signal 8o is output by the AND gate 22 in the form of the logical formula 8n=8vaSz. Output.

According to experiments, when the above signal Sυ = 1, that is, when the leakage current is flowing under no load, it has been found that the interpolation state is as described below. (1) The leakage current is When flowing, the concentration of sludge, metal ions, etc. becomes abnormally high at a certain point in the gap between the electrodes, and the resistance becomes less than several hundred ohms.

(2) If the signal Sυ = 1 continues for several β seconds to 1 tn seconds, the interpolation state can be recovered by taking some kind of deionization countermeasure, but if it continues for several tens of milliseconds or more, , leading to unrecoverable wire breakage.

(3) If there is a protrusion or a hole on the wire electrode, the electric field strength at one point l will become stronger inside the gap between the electrodes, and the signal will become 5u=l, and the concentration of the discharge will only occur after that one point has receded. occurs in

(4) When there is no leakage current and the signal 5o=l, the ion H
e is low, the condition between the electrodes is good, and there is no concentrated discharge or abnormal arc discharge. However, even when an abnormal condition is occurring, the signal 5D may sometimes become 1. In this case, the current value does not last (8D=1 does not continue for several milliseconds).

As described above, the gap state can be detected based on the signal Sυ and the signal SD. In other words, the above (2) (
As shown in 4), if the continuous amount or generation of the signal Sυ and the signal SD can be analyzed, the interpole state can be detected.

Figure 4 shows the AND gate 23.2 for the above signals SU and 3D.
4 shows an example of a gap condition determination circuit that determines whether the gap condition is good or bad by inputting the input signal S
The numbers of υ and SD are counted by a reversible counter 25. Therefore, if the signal Su occurs more frequently than the signal SD, the counter 25 is integrated and its contents gradually increase.

When the integrated value of the counter 25 exceeds a predetermined value, for example, 100, the digital comparator 26 outputs a gap defect determination signal (hereinafter referred to as 8A) (S person=1). These signals are also applied to the negative input terminal of the AND gate 23 to eliminate the output from the AND gate, thereby preventing the contents of the counter 25 from increasing too much and overflowing or overscaling. . Further, the above-mentioned eight signals are supplied to the control means ζ to be described later to perform pole spacing recovery control I.

When the state between the poles becomes normal and the signal 5D=1 continues, the counter 25 is decremented and finally the content becomes Σ;0, so
Digital comparator 2 to prevent further subtraction.
The output signal SB of No. 7 is applied to the negative input terminal of the AND gate 24 to eliminate the output from the AND gate.

Therefore, if the contents of the counter 25 are converted into an analog quantity by the digital-to-analog converter 28 and measured, the state of the gap can be continuously monitored using the output signal SM of the converter 28.

FIG. 5 shows each signal S of the gap state discriminating circuit shown in FIG.
u, Sry, SM (SM ha7 analog tt5
F) is a time chart of the inter-electrode current signal I and the inter-electrode voltage signal Vg indicating the inter-electrode state of three people.

An example of the control means 30 that changes the tension of the wire electrode based on the contents of the counter 26 will be described below with reference to FIG. In FIG. 6, the wire electrode 2 fed out from the supply reel 7 is connected to a tension motor 100° tension reel 101. A predetermined tension is applied by the auxiliary reel 102 and the capstan 103 . Capstan roller 104. It is pulled out by the capstan motor 105 and wound up by the take-up reel 10.

When the inter-electrode condition deteriorates and the possibility of discharge concentration or wire breakage is detected, an output is generated in the counter 26, this output voltage is amplified by the amplifier 106, and is outputted to the control transistor 107 as a base voltage.

Here, if the emitter resistance 108 is R and the current flowing through the motor is I, it is expressed as follows.

Note that Vs is the motor control voltage by the counter 26, and the pace emitter I voltage VII of the control transistor 107
E is weak and constant at about 0.6 V and can be almost ignored, and the motor current is controlled by the base voltage rEVs, but the motor control voltage Vs decreases and the drive current of the tension motor 100 decreases. As a result, the wire tension is reduced, and it is possible to prevent the wire electrode from breaking due to wear (abnormal wear due to discharge concentration), which has weakened its tensile strength. By performing short-circuit back while preventing wire breakage, and by taking other measures to prevent concentration of IE emissions (current reduction, no-load due to back movement), it becomes possible to escape from the abnormal machining state more reliably.

Furthermore, since the tension of the wire electrode is gradually increased once the gap between the electrodes is in a normal state, the rigidity of the wire electrode is increased, short circuits are reduced, and processing speed is also improved.

〔Effect of the invention〕

As described above, according to the present invention, after a pulse voltage is applied between the workpiece and wS, the leakage current is detected until discharge occurs, and based on this detection result, normal discharge is determined. Since abnormal discharge is determined, it is possible to accurately determine whether the machining gap condition is good or bad without reducing the machining speed. Since the tension of the wire electrode is changed in response to the determined gap state, it is possible to reliably prevent wire electrode breakage accidents and improve the processing speed.

[Brief explanation of drawings]

Fig. IIE1 is a principle explanatory diagram showing an embodiment of the present invention, Fig. 2 is a time chart for explaining its operation, Fig. 3 is a leakage current detection circuit diagram for detecting the gap state, and Fig. 4 is a diagram illustrating the leakage current detection circuit. FIG. 5 is a time chart for explaining its operation; FIG. 6 is a block diagram showing the circuit configuration of the control means; FIG. 7 is a principle diagram showing a conventional wire-cut electrical discharge machining device; It is. 1 is a workpiece, 2 is a wire electrode, 18 is a leakage current detecting means, 29 is a gap state determining means, and 30 is a control means. Note that the same reference numerals in the figures indicate the same or corresponding parts. Patent author Mitsubishi Electric Corporation-20): Ku-〉
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Claims (1)

[Claims] A wire electrode and a workpiece are opposed to each other with an insulating machining fluid interposed between them, and a pulse voltage is applied between the two to generate an electric discharge between the opposing poles. A wire-cut electrical discharge machining apparatus for machining a wire-cut electric discharge machining device includes a detection means for detecting a leakage current after the pulse voltage is applied between the wire electrode and the workpiece until discharge occurs, and a detection output of the detection means. and a control means for controlling the tension of the wire electrode based on the output of the electrode spacing state determining means. Characteristic wire cut electrical discharge machining equipment.