JPS61111829A - Wire-cut electric discharge machinine - Google Patents

Abstract

PURPOSE:To prevent a wire electrode from breaking, by discriminating a gap state from frequency distribution of a voice signal in an electrode gap, while controlling spouting flow of a dielectric machining fluid being spouted to the gap between the wire electrode and a work according to the discriminated result. CONSTITUTION:A voice sensor 16, as a detecting device, comes into contact with a wire electrode 2 being stretched between upper and lower guides 8A and 8B, and this voice sensor 16 senses a voice signal in a gap trnsmitted via the wire electrode 2. A spark ago discriminating device 17 amplified the voice signal outputted out of the voice sensor 16, discriminating the frequency and performing an analytic process, thus it discriminates a spark gap state. According to the discriminated result, the spouted flow of a dielectric machining fluid to be spouted to the gap between the 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 wire-cut electrical discharge machining apparatus that electrically cuts a workpiece using a wire electrode.

[Conventional technology]

Machining workpieces using electrical energy has been widely practiced 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. 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 spinning hole 1a made 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
From tank 4 to pump 5, workpiece 1 and wire electrode 20
It is sprayed by the nozzle 6 into the gap (gap between the poles).

The relative movement between the workpiece 1 and the wire electrode 2 is caused 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.
Driven by. With the above configuration, the relative movement between the workpiece 1 and the electrode 2 becomes a two-dimensional subplane movement within the aforementioned X and Y axis planes.

The wire electrode 2 is supplied by a wire supply reel T,
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 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 control device using a numerical control device (NC control device), a copying device, or a computer.

The processing power supply 15 that supplies electrical energy includes, for example, a DC power supply 15a1, a switching element 15b1, a current limiting resistor 1,
5e and a control circuit 15d that controls the switching element 15b.

Next, the operation of the conventional device will be explained.

In a normal machining state, a high frequency pulse voltage is applied from the machining power supply 15 between the workpiece 1 and the wire electrode 2, 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 at 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 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 down time are usually set to have enough margin to prevent wire breakage. Therefore, the machining speed must be υ equivalent to 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 when concentrated.

The present invention has been made to solve these problems, and an object of the present invention is to provide a wire-cut electric discharge machining apparatus that can prevent wire electrode breakage accidents without reducing the machining speed.

[Means for solving problems]

A wire-cut electrical discharge machining apparatus according to the present invention includes a detection means for detecting the distribution of frequency components in an audio signal in a gap between opposing poles when a discharge occurs in a gap between opposing poles between a wire electrode and a workpiece, and the detection means A pole gap condition determining means is provided for determining the pole gap condition and outputting a signal by comparing the distribution of the detected frequency component with the distribution of the set frequency component, and based on the output of the pole gap condition determining means. and a control means for controlling the ejection flow rate of the insulating working fluid.

[For production]

In this invention, the distribution of the frequency components of the audio signal in the gap between the poles at the time of occurrence of electric discharge is detected by the detection means, and the distribution of the detected frequency components is compared with the distribution of the frequency components set in advance. A gap state determining means determines whether the gap is abnormal discharge or normal discharge, and when the control means receives an abnormal discharge determination signal from the gap state determining means, the control means controls the jetting flow rate of the machining fluid. The sludge and metal ions that increase the machining gap and cause the gap to deteriorate are discharged to return the machining gap to a normal state. When a normality determination signal is received, the jetting flow rate of machining fluid is controlled to be lowered to improve the machining gap. The impedance is lowered and the discharge frequency is increased to increase the machining speed.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. FIG. 1 is an explanatory diagram for explaining the detection principle in this invention, and the same parts as in FIG. 7 are given the same reference numerals. An audio 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 an audio signal transmitted between the electrodes via the wire electrode 2. Reference numeral 17 denotes an interpole gap state determining means that performs amplification → frequency discrimination → analysis processing on the audio signal output from the audio sensor 16.

FIG. 2 is a chart showing the relationship between the audio frequency spectrum and the inter-electrode condition based on the signal obtained from the inter-electrode gap state determining means 17, and A indicates that there is almost no sound when there is no discharge, and the wire electrode A slight string vibration frequency (hereinafter abbreviated as fL) corresponding to the span between the two guides can be seen.

B. During normal discharge, the frequency is widely distributed from string vibration (several KHz) to high frequency vibration of 100 KHz4.

C. Immediately before the wire electrode breaks, the string vibration decreases and becomes a non-distributed sound around the frequency fo (hereinafter abbreviated as fo) of the pulse from the processing power source 15. This is thought to be because the discharge points are concentrated and the discharge occurs in synchronization with the pulse cycle, and because the reaction force caused by the discharge that causes string vibration is also reduced.

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

Incidentally, the frequency spectrum at the time of a short circuit and immediately before the wire electrode is disconnected is β as shown in the following equation.

(2) is an initial value.From the frequency spectrum analysis results shown in FIG. 2, the following can be seen.

(1) When the machining is in good condition, high frequency fH (hereinafter, fl
(abbreviated as) has a large distribution and a large amount.

(2) In the situation immediately before a short circuit or wire electrode breakage, the high frequency fH hardly exists.

+3) If the output at fo is low and the output at fl is high, it can be considered normal discharge.

(8) ・ (4) The chordal vibration of the wire electrode is at its maximum during normal discharge, and then occurs in the following order: just before the wire electrode breaks → no discharge → short circuit (zero), but the span distance varies depending on the thickness of the workpiece. It changes and the frequency changes, so it can't even be treated as a determining factor.

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

FIG. 3 is a schematic diagram showing the pole gap state determining means 17, which basically has the same configuration as a frequency spectrum analyzer. The interpole gap audio signal F(t) detected by the audio sensor 16 and amplified by the amplifier 18 is mixed with the output signal f(t) of the FM modulator 19 by the mixer 20, and is converted into F(t) by heterodyne detection. and f (t)
Only the intermediate frequency j (t) is extracted from the sum of the frequencies, and this is amplified by the intermediate frequency amplifier 21, and the amplitude component is detected by the detector 22 and amplified by the low frequency amplifier 23. Ru.

The above-mentioned FM modulator 19 is frequency-modulated by the analog voltage AV, so by changing the analog voltage AV in proportion to time, the relationship between time and frequency becomes linear, and F (t) of j (t)
The amplitude of the frequency spectrum can be extracted as the output of the low frequency amplifier 23 by the frequency of .

Therefore, the time at which the analog voltage AV reaches the voltage corresponding to folfH can be determined by the accurate oscillator 24 and the counter 25 that counts its output. 26 is f
27 is a discriminator for fH. counter 2
The content of 5 is converted into an analog voltage AV by the D/A converter 28.
and modulates the FM modulator 19.

The level comparator 29 responds to the timing signal of the zero discriminator or fH discriminator Yoshi, and determines whether the low frequency amplified amplitude, that is, the frequency spectrum, is larger or smaller than a predetermined reference value at that timing, Based on this result, a signal SA is output when an abnormal discharge occurs. For example f. is 3K
Hz and fH are 5 MHz.

Also, if the intermediate frequency is 10.7 MHz, f (t)
However, when the frequency is 10.693 MHz, f. is 5.700 M
When the frequency is Hz, each spectrum of fH can be detected.

The FM modulator 19 is of broadband type, and the input voltage OV
5 MHz at O, 10 MHz at 10 V, and if the D/A conversion is 16 bit type, ±8
This is a spectrum analyzer with a resolution of about 0 Hz.

Furthermore, since fc is always changed every time machining conditions are selected, it is necessary to perform arithmetic control under fo (however, period T is the sum of on-time and off-time).

Regarding the abnormal discharge signal SA, a detailed explanation of the level comparator 29 shown in FIG. 3 will be explained in more detail using FIG. 4.

The output of the low frequency amplifier 23 is connected to the analog switch 30.31.
As a result, they are not connected to the comparators 32 and 33 except at the timing of fo discrimination and fH discrimination.

Then, at the fo determination timing, if the spectrum amplitude Vo is larger than vl, the output of the comparator 32 is "1'
``p'', the counter 35 is counted up via the AND gate 34. Also, at the fH determination timing, if the above ■o is larger than v2, the output of the comparator 33 becomes ``1'', and the AND gate 36 This counter 35 outputs an abnormal discharge signal when the spectral amplitude vo at the fo timing is greater than vl and outputs an abnormal discharge signal, and the spectral amplitude Vo at the fH timing is greater than v2. When , the counter contents immediately become zero. Therefore, if there is a high frequency component, it is zero, f
If the o-acid component is large, the state of increase will repeat, so
It is also possible to determine whether the state of the gap between the electrodes is good or bad by observing the analog voltage (5) of this counter using the D/A converter 3γ. That is, if V5 is a dog, it means that abnormal discharge is approaching, and a problem such as accumulation of sludge in the inter-electrode gap due to accumulation of machining powder can be easily detected.

FIG. 5 shows a display circuit that makes it easier to see the gap state determined by the gap state determining means 17 as a machining monitor, and FIG. 5(a) shows a normal discharge signal v1< , the display driver 38 outputs the output of the counter 35 that supplies and applies the abnormal discharge signals v1 to v2 to the CU terminal.
Bar display LED 39 is connected to the output of the display driver.
This is an embodiment in which a bar-shaped display is performed according to the contents of a counter by driving the counter.

In Fig. 5(b), a normal discharge signal v1< is inputted to the countdown terminal CD, an abnormal discharge signal vl-v2 is inputted to the countup terminal CU, and continuous state changes are detected and displayed. be.

Hereinafter, an example of the control means 40 for changing the amount of machining fluid jetted to the machining gap according to the contents of the counter 35 will be explained.
The diagram will be explained. In FIG. 6, the machining fluid 3 sucked up from the tank 4 by the machining fluid supply pump 5 is transferred to the pipe 1.
00 through liquid volume variable valve v1. v2. ■5. It is supplied to the nozzle 6 via vlI. This machining fluid flow rate is the same as that of valve v1. v2. It changes depending on the open/closed state of v and vll.

The opening and closing of the valves (1 + v2 + v3 y vll) are controlled by the outputs 26 to 2 of the counter 35, respectively. In this example, vl is 100 cc/min, v
2 is 200 cc/min, V5 is 400 cc/min, v4
Since this is a valve with a rate of 800 cc/min, a liquid amount corresponding to the quality of the inter-electrode condition is injected between the electrodes. For example, when the content of the counter 35 is 26, that is, 64 or more, 2
Since the output of 6 is "1", is VO open? )
If the flow rate is 100 cc/min, the content of counter 35 is 2.
7, that is, 192, the outputs of 26 and 27 are "1", so vl and v2 are open and 300 cc/
The machining fluid is supplied between the poles at a flow rate of 100 min.

When the value is extremely large, for example 210 or 1
024 or higher, the forced jet valve v5 is opened via the OR gate 101 to provide a liquid flow of several thousand cc/minute. On the other hand, when the difference is small, the manual valve V controls the appropriate amount of minute flow as used in normal processing. is given to the gap between the poles.

〔Effect of the invention〕

As described above, according to the present invention, the distribution of frequency components in the audio signal in the gap between opposing poles between the workpiece and the wire electrode when electric discharge occurs in the gap between the opposing poles is detected, 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 gap condition is good or bad. Since the liquid flow rate is controlled in response to the quality of the inter-electrode condition, the sludge generated in the inter-electrode gap can be efficiently discharged, and the efficiency of discharge can be significantly improved. In other words, when sludge is present in the gap between the electrodes, a discharge arc is generated along the path of electrode → sludge → workpiece, so a portion of the discharge energy is consumed in the sludge.
It is now possible to prevent the phenomenon that machining efficiency decreases and more heat is generated on the wire electrode side due to electric discharge, causing the wire electrode to break. In addition, the liquid flow is reduced when the gap between the poles is appropriate and the discharge condition is normal, so the gap and impedance between the poles are not made unnecessarily high, making discharge easier and machining stable, resulting in faster machining speed. There are effects such as

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the relationship between the frequency spectrum and the state between poles, Fig. 3 is a frequency spectrum analysis circuit diagram, and Fig. 4 is a level comparator. 5 is a block diagram showing the circuit configuration of the machining device, 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 the conventional wire-cut electrical discharge machining device. be. 1 is a workpiece, 2 is a wire electrode, 16 is a detection means (sound sensor), 17 is an inter-electrode gap state determining means, and 40 is a 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 the two, and the discharge energy is used to stimulate the workpiece. A wire-cut electrical discharge machining apparatus for machining a workpiece, a detection means for detecting the distribution of frequency components in an audio signal in the gap between opposing poles between the wire electrode and the workpiece when electric discharge is generated in the gap between the opposing poles; an inter-electrode gap state determining means for determining the state of the inter-electrode gap and outputting a signal by comparing the distribution of frequency components detected by the detection means with a preset distribution of frequency components; A wire-cut electric discharge machining apparatus characterized by comprising a control means for controlling the ejection flow rate of the insulating machining fluid based on the output of the determination means.