JPH0661662B2 - Wire cut electrical discharge machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wire-cut electric discharge machining apparatus that electrically cuts a workpiece using a wire electrode.

[Conventional technology]

Although it has been widely known and well-known that a work piece is processed by electric energy, it is as if "a wire saw" is used by a wire-shaped electrode in a processing device which has been 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, the nozzle 6 sprays the material into the gap (interelectrode 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 for driving and controlling the X and Y axis drive motors 12, 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.

In a normal processing state, a high-frequency pulse voltage is applied from the processing power supply 15 between the work piece 1 and the wire electrode 2, and a part of the work piece 1 is melted and scattered by discharge explosion caused by one pulse. In this case, the gap between the electrodes is gasified and ionized at a high temperature, so a certain pause time is required before the next pulse voltage is applied.If this pause time is too short, the gap between the gaps will be sufficiently restored. Before that, the discharge is concentrated again at the same place, causing the wire electrode 2 to melt.

Therefore, in a normal machining power source, it is usual to process electric conditions such as a down time depending on the type of work piece, plate thickness, etc. with sufficient margin to prevent wire breakage. 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, there was a problem that the processing speed was extremely low because the wire was not broken.

The present invention has been made to solve such a problem, and an object thereof is to obtain a wire-cut electric discharge machining apparatus capable of preventing a wire electrode disconnection accident and improving a machining speed.

[Means for solving problems]

A wire-cut electric discharge machining apparatus according to the present invention includes a detection means for detecting an audio signal generated by the electric discharge when the electric discharge occurs in a gap between opposing electrodes of a wire electrode and a workpiece, and the electric discharge of the discharge based on the detection signal of the detection means. The first time when the high frequency is detected from the start and the second time when the pulse frequency of the machining power source is detected are discriminated, and the counter is detected by the detection signal of the detection means selected by the discrimination signal of the first time. And an inter-electrode gap state determination means for canceling the contents and incrementing the counter content by the detection signal of the detection means selected by the determination signal of the second timing to determine the state of the inter-electrode gap and output an abnormal signal. A control means is provided for increasing the servo gain based on the output of the abnormal signal from the inter-electrode gap state determination means and for increasing the moving speed of the wire electrode.

[Action]

In the present invention, the distribution of the frequency components of the audio signal in the gap between the electrodes at the time of occurrence of discharge is detected by the detection means, and the high frequency is detected from the start of the discharge based on the detection signal of this detection means. And a second timing at which the pulse frequency of the machining power source is detected, and the counter content is canceled by the detection signal of the detection means selected by the determination signal at the first timing to cancel the determination signal at the second timing. With the detection signal of the detection means selected in step 1, the counter gap state determination means determines whether to increase the counter content and output an abnormal signal,
When the control means receives the abnormal discharge determination signal from the inter-electrode gap state determination means, the control section increases the gap gain and the approach speed by increasing the servo gain of the inter-electrode gap length servo so that the gap state is quickly changed. When the normalization is performed and the normal determination signal is received, the servo gain is reduced, and the gap length is controlled so as to maintain the normal state so that the machining speed is improved.

〔Example〕

Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view for explaining the detection principle in the present invention, and the same parts as those in FIG. 7 are designated by the same reference numerals. A voice sensor 16 as a detection means is in contact with the wire electrode 2 stretched between the upper and lower guides 8A and 8B, and senses a voice signal between the electrodes transmitted through the wire electrode 2. Reference numeral 17 denotes an inter-electrode gap state determination means for amplifying the audio signal output from the audio sensor 16 → frequency discrimination → analysis processing.

FIG. 2 is a chart showing the relationship between the voice frequency spectrum and the gap state based on the signal obtained by the gap distance determining means 17 as shown in FIG. 2A. A slight string vibration frequency f _L (hereinafter abbreviated as f _L ) corresponding to the inter-guide span of the electrode 2 can be seen.

B, During normal discharge, string vibration (several KHz) to high frequency vibration 1
Widely distributed up to 00 KHz.

C, the string vibration is reduced immediately before the wire electrode is broken, and becomes a non-distributed sound near the frequency f ₀ (hereinafter abbreviated as f ₀ ) of the pulse from the machining power supply 15. It is considered that this is because the discharge points are concentrated and the discharge is performed in synchronization with the pulse cycle, and the reaction force due to the discharge that only causes the string vibration is reduced.

D, The string vibration is zero at the time of short circuit, and only magnetostrictive vibration is observed when the current flows from the wire electrode to the workpiece.

The frequency spectrum at the time of short circuit and immediately before the wire electrode is broken is expressed by the following equation.

The following can be seen from the frequency spectrum analysis results of FIG.

(1) When the processing is in a good state, the distribution at high frequency f _H (hereinafter abbreviated as f _H ) is large and the amount is large.

(2) High frequency f _H is almost nonexistent in the situation just before short circuit or wire electrode breakage.

(3) If the output at f ₀ is low and the output at f _H is large, it can be regarded as normal discharge.

(4) The string vibration of the wire electrode is the maximum at normal discharge and below, immediately before the wire electrode is broken → no discharge → short circuit (zero), but the span distance changes depending on the plate thickness of the work piece. However, since the frequency also changes, it is difficult to handle as a judgment factor.

From the above results, it can be seen that the abnormality in the discharge state can be identified if the state as in the item (3) can be determined.

FIG. 3 is a schematic diagram showing the inter-electrode gap state determining means 17, which basically has the same configuration as that of the frequency spectrum analyzer. The audio signal F (t) in the inter-electrode gap detected by the audio sensor 16 and amplified by the amplifier 18 is stored in the FM modulator 19
Is mixed with the output signal f (t) of the mixer 20 by the mixer 20, and only the frequency of the intermediate frequency j (t) is extracted from the sum frequency of F (t) and f (t) by the heterodyne detection. This is amplified by the intermediate frequency amplifier 21, the amplitude component is detected by the detector 22, and then amplified by the low frequency amplifier 23. The intermediate frequency amplifier 21 includes the intermediate frequency j
Usually, a tuning circuit for tuning only near (t) is provided, and this tuning circuit uses a tuning tank circuit composed of a coil and a capacitor, a crystal oscillator, a piezoelectric ceramic, and the like. Since it is well known, detailed description will be omitted.

FM modulator 19 described above, because it is by connexion frequency modulation to an analog voltage A _v, the relationship of time and frequency by changing proportionally the analog voltage A _v time becomes linear, every time It is possible to take out the amplitude of the frequency spectrum as much as the frequency of j (t) in F (t) as the output of the low frequency amplifier 23.

Therefore, the time when the analog voltage A _v becomes the voltage corresponding to the above f ₀ and f _H can be determined by the accurate oscillator 24 and the counter 25 that counts this output. 26 is a discriminator for f ₀ , and 27 is a discriminator for f _H. The contents of the counter 25
The analog voltage AV is generated by the D / A converter 28 and the F
The M modulator 19 is modulated.

In response to the timing signal from the f ₀ discriminator or the f _H discriminator, the level comparator 29 discriminates whether the amplitude amplified by the low frequency, that is, the frequency spectrum is larger or smaller than a predetermined reference value at that timing. , Based on this result, when abnormal discharge occurs, signal S _A is output. For example, f ₀ is 3KHz f _H is 5M
Hz. If the intermediate frequency is 10.7 MHz, f (t)
However, each spectrum of f _H can be detected when f ₀ is 5.700 MHz at 10.697 MHz.

The FM modulator 19 has a wide band and the input voltage is 0V.
If the D / A conversion is 16 bit type, the spectrum analyzer has a resolution of about ± 80 Hz. Also, since f ₀ is always changed every time the processing conditions are selected, (However, it is necessary to perform arithmetic control of the sum of the on-time and the off-time in the cycle T).

Regarding the abnormal discharge signal S _A , the level comparator 2 of FIG.
The detailed description of 9 will be described in more detail with reference to FIG. The output of the low-frequency amplifier 23 is output by the analog switches 30 and 31 in addition to the timings of the f ₀ discrimination and the f _H discrimination, respectively.
It is designed not to be connected to 2, 33.

Then, at the f ₀ determination timing, the spectrum amplitude V ₀
Is larger than V ₁ , the output of the comparator 32 becomes “1” and the counter 35 is counted up via the AND gate 34. Further, at the f _H determination timing, the above V ₀
There If it is greater than V _2, the output is "1" and the comparator 33, since the reset counter 35 through the AND gate 36, the counter 35 is spectral amplitude (V ₀ is V ₁ of the at f ₀ time When it is larger, the content increases and an abnormal discharge signal is output, and the spectrum amplitude V ₀ at the f _H timing is
When it is greater than V _{2, the} counter contents immediately become zero. Therefore, if there is a high frequency component, it will be zero, and if the f ₀ component is large, it will increase. Therefore, by observing the analog voltage V ₃ using the D / A converter 37, The quality of the gap between the electrodes can be determined. That is, V ₃
Is large, it means that abnormal discharge is approaching, and it is possible to easily detect a defect such as accumulation of inter-electrode gap sludge due to accumulation of machining powder.

FIG. 5 is a display circuit in which the inter-electrode gap state determined by the inter-electrode gap state determining means 17 is made easier to see as a processing monitor. In FIG. 5 (a), the normal discharge signal V ₁ <is used as a terminal. , The output of the counter 35 for supplying and applying the abnormal discharge signals V _{1 to} V ₂ to the CU terminal is connected to the display driver 38, and the bar display LED 39 is driven by the output of the display driver to form a bar shape corresponding to the content of the counter. It is an example which displays. FIG. 5 (b) shows the normal discharge signal V ₁ <when the countdown terminal C
Input to D, enter the abnormal discharge signal V ₁ ~V ₂ to count up-terminal CU, it is obtained so as to detect continuously displaying the state change.

Based on the contents of the counter 35, by changing the servo gain of the means for controlling the gap between the electrodes, that is, the sensitivity, it is possible to recover the short-circuit or open state or the state immediately before the wire electrode is broken.

That is, in the case of the bad gap state as described above, by increasing the sabot gain and increasing the speed of opening and approaching the gap, it becomes possible to quickly avoid a mechanical bad state, and Can be recovered.

An example of the control means 40 for performing the above control will be described in detail with reference to FIG. Reference numeral 100 denotes a multiplication type digital analog converter, which is an element capable of outputting in a format in which the speed command voltage F _x is multiplied according to the output of the counter 35,
AD7520 and the like manufactured by US Analog Devices, Inc. are known.
That is, it may be considered that the input signal acts as a volume. The value of this volume changes according to the output (digital value) of the counter 35.

Therefore, according to this example, the servo gain is increased by the multiplication type digital analog converter 100 in accordance with the deterioration of the gap state, and the above-mentioned speed is originally obtained via the amplifier 101 constituted by the resistors 102 and 103 and the operational amplifier 104. The speed of the table feed motor M _x is changed by connecting the input end of the motor drive amplifier 105 in the control device 14 to which the command voltage F _x was directly input to the output end of the amplifier 101.

In this example, the servo gain is increased almost linearly in proportion to the bad state between the poles, but it is not always necessary to linearly change it, and it is possible to use a quadratic function or a polygonal change. Good. When two-step control is performed using the detection signal of the counter 35, it is easy and inexpensive.

Further, according to the experiment, when the condition between the electrodes deteriorates, if there is no speed of at least 20 mm / min or more, the wire electric wire is broken, and a large amount of the processed powder stays in the gap between the electrodes.
It has been found that speeds on the order of mm / min are required. In addition, it has been confirmed that, in stable machining, the machining efficiency is high when finishing at a surface roughness of 15 μRmax or less at a speed of 5 to 10 mm / min. To be done.

〔The invention's effect〕

As described above, according to the present invention, when a discharge is generated in the gap between the electrodes facing each other between the wire electrode and the workpiece, the high-frequency frequency from the start of the discharge based on the detection signal of the detection unit that detects the audio signal due to the discharge. Discriminates between the first time when the machining frequency is detected and the second time when the pulse frequency of the machining power source is detected
The counter content is canceled by the detection signal of the detection means selected by the determination signal of the first timing, and the counter content is increased by the detection signal of the detection means selected by the determination signal of the second timing, and the counter content is increased. Since the condition of the gap between the poles is judged,
The quality of the gap state can be accurately determined with an easy and inexpensive configuration. When it is determined that there is an abnormality in the inter-electrode gap state, the servo gain of the inter-electrode gap servo means is increased in order to recover the inter-electrode gap state based on the result of the determination, and the speed of the servo motor, that is, This is to accelerate the moving speed of the wire electrode and to quickly open and close the gap in the inter-electrode gap, which has the effect of reliably preventing wire electrode disconnection accidents and improving the processing speed. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the principle of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the relationship between the frequency spectrum and the gap state, FIG. 3 is a frequency spectrum analysis circuit diagram, and FIG. 4 is a level comparator. Fig. 5 is a block diagram showing the circuit configuration of Fig. 5, Fig. 5 is a display circuit diagram of the gap state, Fig. 6 is a block diagram showing the circuit configuration of the control means, and Fig. 7 is a principle diagram showing a conventional wire-cut electric discharge machine. . Reference numeral 1 is a workpiece, 2 is a wire electrode, 16 is a detection means (voice sensor), 17 is an inter-electrode gap state determination means, and 40 is a control 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 generated. In the wire-cut electric discharge machining apparatus for machining the work piece, a detection means for detecting an audio signal due to the discharge when the wire electrode and the work piece are discharged in a gap between the electrodes facing each other, and the detection means Based on a signal, a first time when the high frequency is detected from the start of the discharge and a second time when the pulse frequency of the machining power source is detected are discriminated, and the detection is selected by the discrimination signal of the first timing. A pole for canceling the counter content by the detection signal of the means and increasing the counter content by the detection signal of the detection means selected by the discrimination signal of the second time, judging the state of the inter-electrode gap and outputting an abnormal signal. An inter-gap state determination means, and a control means for increasing the servo gain based on the output of the abnormal signal from the inter-gap state determination means to control the moving speed of the wire electrode. Wire cut electrical discharge machine.