JPS61111824A - Wire-cut electric discharge machinine - Google Patents

Abstract

PURPOSE:To keep off a disconnection accident in a wire electrode without entailing any drop in a machining rate, by discriminating a gap state from frequency distribution of a voice signal in an electrode gap, while controlling spouting pressure in a dielectric machining fluid 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 transmitted via the wire electrode 2. A spark gap state discriminating device 17 amplifies the voice signal outputted out of the voice sensor 16, discriminating the frequency and performing an analytical process, thus it discriminate a spark gap state. According to the discriminated result, spouting pressure in a dielectric machining fluid to be spouted to the spark gap between a work 1 and the wire electrode 2 through a nozzle 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]

Processing workpieces using electrical energy has been widely used and is well known, but a recent technology that has been attracting attention is the use of wire-shaped electrodes in processing equipment, which makes it possible to process workpieces using electrical energy, as if it were a ``string saw.'' There is a so-called wire-cut electrical discharge machining device 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
The nozzle 6 sprays the liquid 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'llll drive motor 13' and an X-axis motor 12. With the above configuration, the relative motion between the workpiece 1 and the electrode 2 becomes a two-dimensional plane motion within the inner surface of the flat axis of the aforementioned XXY axes.

The wire electrode 2 is supplied to a wire supply reel 7,
The wire passes through the lower wire guide 8A and the workpiece 1 to reach the upper guide 8BK, 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 XXY 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 includes, for example, a DC power supply 15&, a switching element 15b1, a current limiting resistor 1
5c 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, it is normal to process the electrical conditions such as the down time, which depends on the type of workpiece, plate thickness, etc., with sufficient margin to prevent wire breakage. Therefore, the processing speed must be considerably lower than the theoretical limit value.Furthermore, if the wire electrode 2 is not uniform and its thickness varies, or if there is a protrusion or scratch on a part of the wire electrode, If the discharge is concentrated, the wire electrode 2 will inevitably be blown out.

[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 electrical discharge machining apparatus that can prevent wire electrode breakage accidents and improve 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 state determining means is provided which determines the multi-pole gap state by comparing the distribution of the detected frequency component with the distribution of the set frequency component and outputs a signal, and the output of the pole gap state determining means is Based on the above, the spout L of the insulating machining fluid! -Equipped with control means f for controlling force.

[Effect]

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 comparison result between the distribution of the detected frequency components and the distribution of the frequency components set in advance is determined. The machining gap state determining means determines whether the machining gap is an abnormal discharge or a normal discharge, and when the control means receives an abnormal discharge determination signal from the machining gap state discriminating means, the control means adjusts the machining fluid injection pressure. is controlled to increase the sludge discharge capacity, thereby eliminating discharge concentration caused by a drop in impedance within the sludge dormitory and preventing wire electrode breakage.

[Embodiments] 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 the 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 determination means 1T. The string vibration frequency fL (hereinafter abbreviated as fL) corresponding to the span between the guides of the electrode 2 is slightly illuminated.

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

Immediately before the C1 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 because the discharge points are concentrated and the discharge is synchronized with the pulse cycle, and the reaction force due to the discharge that only generates string vibration is also reduced.1. Because I'm there, I can't stand the place.

D. When short-circuited, the string vibration is zero, and only the magnetostrictive vibration is observed when the electric current, IAt, flows from the wire 1111 pole to the workpiece.

Incidentally, the frequency spectrum at the time of a short circuit and immediately before the wire electrode is disconnected is expressed by the following equation.

The initial value of V is found from the frequency spectrum analysis results shown in FIG. 2 as follows.

(1) When machining is in good condition, high frequency fa (hereinafter fH
(abbreviated as ) is large in distribution and quantity.

(2) There is almost no high frequency fu in the situation immediately before a short circuit or disconnection of the wire electrode.

(If the output at 31fo is low and the output at fn is high, it can be considered as 5 normal discharge.

(4) The chordal vibration of the wire electrode is at its maximum during normal discharge, and the order is immediately before the wire electrode breaks → no discharge → short circuit (zero), but the span distance changes depending on the thickness of the workpiece. Since the frequency also changes, it cannot even be treated as a determining factor.

The above result! D, (It can be seen that if it is possible to determine that the battery is in the state described in Section 31, it becomes possible to identify an abnormality in the discharge state.

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)
Of the frequencies of the sum of , only the intermediate frequency j (t) is extracted, which is amplified by the intermediate frequency amplifier 21 , whose amplitude is detected by the detector 22 and amplified by the low frequency amplifier 23 .

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 is linear, and F ( j of t) (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 fo, fH can be determined by the accurate oscillator 24 and the counter 25 that counts its output. 26 is a discriminator for fo, and 27 is a discriminator for fH. The contents of the counter 25 are converted into analog voltage A by the D/A converter 28.
V and modulates the FM modulator 1B.

The level comparator 29 responds to a timing signal from the fo discriminator or the tn discriminator, and determines whether the low frequency amplified amplitude, that is, the frequency spectrum, is large or small compared to a predetermined reference value at that timing. , Based on this result, a signal S is issued when an abnormal discharge occurs. For example, fo is 3KH
Assume that z and fa are 5 MHz.

Also, when the intermediate frequency is 10.7 MHz, when f (t) is 10.693 Mffz, fo is 5.700 MHz.
When z, each spectrum of fu can be detected.

The FM converter 19 is of a wide band type, and the input voltage QV
5MHz when O, 10MHz when IOV, D/
If A conversion is 16 bit type, ±80Hz
It becomes a spectrum analyzer with a resolution of about

Furthermore, since fc is always changed every time machining conditions are selected, it is necessary to carry out arithmetic control such that fc='' (however, period T is the sum of on-time and off-time).

With respect to the abnormal number signal S, the level comparator 29 shown in FIG. 3 will be explained in detail with reference to 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 fu discrimination.

Then, at the 10th discrimination timing, if the spectrum amplitude vo is larger than vl, the output of the comparator 32 is "1°
"tona fi, counter 35 via AND gate 34
count up. Further, at the fa determination timing, if the above vo is larger than V2, the output of the comparator 33 becomes "1" and the counter 35 is reset via the AND gate 36, so that the counter 35 is
When the spectrum amplitude Vo at the timing is larger than ■1, the content increases and an abnormal discharge signal is output, and the spectrum amplitude V at the fH timing.

When is greater than v2, the counter contents immediately become zero.

Therefore, by observing the analog voltage V5 using the D/A converter 37 of the contents of this counter, it is possible to change the state between zero and increase when the high frequency component is large. It is possible to determine whether the gap condition is good or bad. That is, if ■3 is large, it means that abnormal discharge is approaching, and for example, a problem in the sludge where sludge has accumulated in the gap between the poles due to the retention 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 1T as a machining monitor, and FIG. 5 (&) indicates the normal number
is applied to the R terminal, and the output of the counter 35, which applies the abnormal discharge signals v1 to v2 to the CV terminal, is applied to the display driver 3.
8 and bar display I, ED3 with the output of the display driver.
9 is driven to display a bar-like display according to the contents of the counter. FIG. 5(b) shows that the normal discharge signal Vl<
is input to the countdown terminal CD, and the abnormal discharge signal V
1-V2 is input to the count-up terminal CV, and continuous state changes are detected and displayed.

Hereinafter, an example of a control means 4001 for changing the machining fluid ejection pressure to the gap between the poles in accordance with the abnormal discharge signal Sm 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 is transferred to a pipe 10 via an electromagnetic pulp 101 and a manual pulp 102.
3 to the 9 nozzle 6. This processing fluid pressure is observed by a fluid pressure meter relay 105, and when it exceeds a predetermined pressure, a feedback signal SB is fed back from the fluid pressure meter relay 105 to the controller 106, and the electromagnetic pulp 101 is controlled by the output of this controller 106. Maintain proper set pressure.

Note that the manual pulp 102 is used to maintain the lowest pressure when the electromagnetic pulp 101 is operating and operating.

When the machining condition worsens and machining powder stays in the gap between the poles, the counter 35 outputs the fc signal Sm and inputs it to the pulp controller 106, so the 11L magnetic pulp 101 is opened and the hydraulic meter relay 105 It continues to open until the feedback signal SB is output from.

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 restored, the signal S is no longer output, the electromagnetic pulp 101 closes, and the pressure returns to the low pressure set only by the manual pulp 102.

Regarding why two types of pressure are necessary, in general, when the pressure is around 0.05 K@/d, the inter-electrode impedance is most appropriate (moderately dirty materials are easier to discharge and provide stable machining). ), and if it exceeds 0.5 V-, the impedance of the gap between the poles is too high and the gap length for discharge is too narrow, making short circuits more likely to occur and unstable machining. Due to problems such as
Normally, it is desirable to process at 0.05 Kl/- or less, and a leakage liquid flow is required only when the gap between the electrodes is too dirty or when processing sludge accumulates in a part.

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 processing by suction.

〔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 condition is good or bad. Since the machining fluid ejection pressure is controlled in response to the quality of the gap between the machining plates, the machining powder produced in the gap between the machining plates can be efficiently discharged, and machining efficiency can be significantly improved. In other words, when machining powder is present in the gap between the machining electrodes, sparks from the discharge are generated along the path of electrode → machining powder → workpiece, so a large proportion of the discharge energy is spent on thermal decomposition of machining powder and machining fluid. , it is possible to prevent the phenomenon that the machining speed decreases, and it is possible to prevent local wear of the wire electrode and disconnection due to concentration of electric discharge.

[Brief explanation of drawings]

Figure 1 shows an embodiment '4 of this invention - J principle 1llp
, Figures 1 and 2 are explanatory diagrams showing the relationship between the frequency spectrum and the polarity, Figure 3 is a frequency spectrum analysis circuit diagram, and Figure 4 is the circuit configuration of the level comparator. FIG. 5 is a circuit diagram showing the machining gap state, FIG. 6 is a schematic diagram of the control means, and FIG. 7 is a principle diagram showing a conventional wire-cut electric discharge machining apparatus. 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 electrical discharge machining apparatus comprising a control means for controlling the jetting pressure of the insulating machining fluid based on the output of the determining means.