JPS637890B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining apparatus, in particular, an electric discharge machining apparatus, in which an electrode and a workpiece are opposed to each other with an insulating machining liquid interposed therebetween, and an electrical discharge is generated between the opposing electrodes to machine the workpiece. This invention relates to electrical discharge machining equipment.

FIG. 1 shows a schematic configuration diagram of a conventional electric discharge machining apparatus. In FIG. 1, an electrode 10 faces a workpiece 14 placed in a processing tank 12 with an insulating processing fluid 16 in between. A processing power source 18 is connected between the electrode 10 and the workpiece 14. This machining power source 18 includes a DC power source 18a, a switching element 18b for switching on and off the machining current, a current limiting resistor 18c, and the switching element 18.
The machining current is intermittently supplied to the gap 20 between the electrode 10 and the workpiece 14 facing each other.

The above machining current I is expressed by the formula I=E-Vg/R (E is the voltage value of the DC power supply 18a, R is the resistance value of the current limiting resistor 18c, and Vg is the voltage between electrodes).
The interelectrode voltage Vg is 20 to 30 V during arc discharge, 0 V during short circuit, EV during no discharge, and 0 V when switching element 18b is in the off state.

Therefore, if this inter-electrode voltage value Vg is detected and averaged by the smoothing circuit 22, the inter-electrode gap can be controlled using this value. That is, when the gap between the electrodes is wide, discharge is difficult to occur and the average voltage value Vs is high. When the gap between the electrodes is narrow, short circuits and discharges occur easily, resulting in a decrease in the average voltage value Vs. Therefore, if this average voltage value Vs is compared with the reference voltage value Vr, and this difference is amplified by the amplifier 24 and inputted to the hydraulic servo coil 26, the hydraulic pressure generating pump 28 and the hydraulic cylinder 3
The electrode 10 can be controlled so that the inter-electrode gap 20 is approximately constant by the hydraulic servo mechanism configured with the servo mechanism 0 and 0.

When determining whether the machining state is good or bad using a conventional electrical discharge machining apparatus, the most common method is to observe the average voltage value Vs of the above-mentioned machining voltage value Vg. That is, when the average voltage value Vs is low, the impedance between the electrodes is low, and short circuits and continuous arc discharge may occur, and machining powder and sludge may accumulate between the electrodes. However, the most dangerous abnormal arc discharge in electric discharge machining is that once it occurs, carbon is generated due to thermal decomposition of the machining fluid, resulting in an electric discharge between the carbon and the workpiece, resulting in a state where the impedance between the electrodes becomes high. Become. Therefore, the average voltage value Vs
The drawback of this observation was that it was impossible to detect and eliminate the deterioration of the gap between electrodes due to abnormal arc discharge.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to detect the gap length between electrodes, determine the gap condition, and improve the condition of the electrodes so as to restore the gap condition to a good condition. increasing the amplification of the feed servo system to increase the speed and amplitude of the pole gap control movement;
It is an object of the present invention to provide an electrical discharge machining device capable of discharging sludge staying in gaps or garbage obstructing electrical discharge.

In order to achieve the above object, the present invention provides an electric discharge method for machining the workpiece by arranging an electrode and a workpiece to face each other with an insulating machining liquid interposed therebetween, and generating an electric discharge between the opposing electrodes. In the processing device, an electrode position detection means for detecting a difference between the most advanced position at which the electrode is sent to the workpiece and the current position of the electrode, and a duration for which the amount of the difference exceeds a predetermined amount, or a time period for which the amount of the difference exceeds a predetermined amount; When the product of the amount and the above duration exceeds a predetermined value, it is determined that the interpole condition is abnormal and a signal is output.
Interpole state determination that determines that the interpole state is normal and outputs a signal when the duration of the above difference exceeds a predetermined amount, or the product of the difference amount and the duration time falls below a predetermined value. and when the signal from the gap state determining means determines that the gap condition is abnormal and is output, increasing the amplification degree of an electrode feed control device that feeds the electrode to the workpiece; and means for reducing the amplification degree of the electrode feed control device that feeds the electrode to the workpiece when the signal from the gap state determining means is determined to indicate that the gap condition is normal and is output. It is characterized by:

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. 2 and 3 are schematic diagrams showing the structure of an embodiment of the present invention, in which the same parts as in FIG. 1 are denoted by the same reference numerals. In FIG. 2, the electrode support rod 3
A digital scale 34 attached to the electrode 2 generates a positive pulse Sp when the electrode 10 moves downward in the figure, and a negative pulse S _N when the electrode 10 moves upward. In order to accurately know the gap length between the poles, pulses of 10 μm or less are generated per pulse. In this example, the explanation will be made assuming 5 μm/pulse.

The above-mentioned positive direction pulse Sp is directly supplied to the negative terminal 36a of the reversible counter 36, and the negative direction pulse S _N is supplied to the positive terminal 36b via the OR gate 38. The reversible counter 36 is composed of, for example, 13 bits, and can store the amount of electrode rise corresponding to 5 μm×(2 ¹⁴ −1), that is, 82 mm. A digital-to-analog converter 40 is connected to the output side of each bit of the reversible counter 36, and this output is
_V0 and is compared with 0V by the comparator 42. Then, when the output V ₀ is 0V, that is, the counter content is 0, the output pulse of the pulse oscillator 44 is passed through the AND gate 46 and the OR gate 38 by the output of the comparator 42, and is used as the addition pulse L _P of the reversible counter 36. Positive terminal 36
supply to b.

Therefore, the reversible counter 36 adds the negative direction pulse S _N from the digital scale 34 and the above-mentioned addition pulse L _P ,
Subtract the positive direction pulse S _P from 4. As a result, the contents of the reversible counter 36 are the most advanced position at which the electrode 10 is fed into the workpiece 14 and the position at which the electrode 10
This is the difference between the current positions of That is, the addition pulse
The sum of the numbers of L _P is the most advanced position, and this, the number of minus direction pulses S _N above, and the plus direction pulse
Since the current position, which is the sum of the differences in the numbers S _P , is subtracted, the content of the reversible counter 36 is the difference between the most advanced position and the current position.

Therefore, since the output of the digital-to-analog converter 40 is a voltage proportional to the above-mentioned difference, by detecting and processing this output _V0 , it is possible to know whether the actual state of the gap between the electrodes is good or bad. i.e. the above output
If V ₀ is large, the state of the gap between the machining poles has returned from the most advanced position, which means that, for example, sludge has accumulated between the machining poles due to the retention of machining powder, or machining fluid is flowing due to an abnormal arc. Problems such as thermal decomposition of the electrode 16 and generation of carbon, or a part of the electrode being damaged and its fragments being present in the gap 20 can be easily detected.

However, the inter-electrode impedance changes constantly over a very short period of time, and even if the above-mentioned difference exists for a short time, it cannot necessarily be determined that the inter-electrode gap condition is poor. Therefore, the output of the digital-to-analog converter 40
It is necessary to determine whether the inter-electrode gap condition is good or bad by detecting that V ₀ has been present for a certain period of time or more than a predetermined value.

A voltage comparator 48 in FIG. 2 determines whether the output V ₀ of the digital-to-analog converter 40 is larger or smaller than a predetermined value V ₁ . When V ₀ >V ₁ , the output of voltage comparator 48 becomes negative, turning off switching transistor 52 via base resistor 50 . Therefore, the time measuring capacitor 54 is charged via the resistor 56, and the voltage V ₃ across the capacitor 54 is expressed by the following equation.

However, _r2 is the resistance value of the resistor 56, c is the capacitance of the capacitor 54, t is the time, the voltage across this capacitor 54, _V3, is the reference voltage.
It is compared with V ₂ by a voltage comparator 58 . During the period of V ₃ <V ₂ , the output of the voltage comparator 58 does not become negative, so
The light emitting diode 60 does not light up. And V ₀ <
When the state of V ₁ continues for a predetermined period of time and becomes V ₃ > V ₂ ,
The output of the voltage comparator 58 becomes negative, and the light emitting diode 60 is turned on via the resistor 62 to indicate the occurrence of an abnormality in the gap between the electrodes.

The switch 64 is a switch for determining whether to judge the interpole state only as a function of time or as a function of the product of the magnitude of the output V ₀ of the digital-to-analog converter 40 and time. In other words, in machining where it is difficult to determine abnormalities in the gap between the poles by simply detecting time, for example, in the machining of cemented carbide, where arc cracking or tungsten chipping occurs instantaneously, the switch 64 should be turned off. When the contact 64a is turned on as shown in the example, the occurrence of an abnormal state of the gap between the poles can be immediately detected as a function of the product of the output V ₀ of the digital-to-analog converter 40 and time. This is because if the output V ₀ is large, the charging current of the capacitor 54 increases, and the voltage V ₃ across the capacitor 54 immediately reaches the reference voltage V ₂ .

In addition, by directly observing the above output V ₀ with a voltmeter, it is possible to directly observe the difference between the most advanced position where the electrode 10 is fed into the workpiece 14 and the current position of the electrode 10, and It is clear that it can be used as a monitor of interstitial conditions.

In addition, in the above embodiment, a first-order delay circuit made up of a capacitor 54 and a resistor 56 is used to measure time when the gap condition worsens, but in order to make time measurement more accurate, an accurate integration circuit using an operational amplifier is used. It is not difficult at all to establish and implement.

FIG. 3 is a detailed explanatory diagram of the circuit GC that controls the amplification degree of the servo system based on the above detection output,
When the abnormality detection signal _V5 is "1", that is, when there is no abnormality, analog switch SW1 is closed and SW2 is closed.
is in an open state because it is connected to the inverter 70.

At this time, the pole-to-pole servo signal Va is sent to the servo amplifier 2 via an amplifier 71 having a predetermined amplification degree K.
4 and processing is performed with normal gain.

Next, an abnormal condition occurs between the poles, and _V5 becomes "0".
When this happens, the analog switch SW1 is opened and the analog switch SW2 is closed, and the amplification degree of the servo system is controlled by the multiplier type digital-to-analog converter 72. That is, this digital-to-analog converter 72 outputs an analog output V ₁ that is the product of the input voltage Va and the digital output value of the reversible counter 36, so the servo gain is determined by the difference between the most advanced value of the electrode and the current value. It will be a proportional value. As a result, the larger the above difference, that is, the more abnormal, the higher the servo gain and the faster the electrode feed speed, which makes the response of the gap more sensitive and the electrode moves more rapidly, preventing sludge from accumulating. , stagnation, or any debris can be quickly removed from the gap or scattered.

A specific example of the above-mentioned multiplication type digital-to-analog converter is manufactured by Analog Devices Inc. (USA).
AD7520 and the like are well known.

Further, in the above explanation, the servo gain is changed in response to the difference between the most advanced value and the current value of the electrode, but if an abnormality is detected more easily, the effect can be expected by simply increasing the gain. However, since the most advanced value and the current value are close to each other and the gain remains high even on the verge of a short circuit, there is a risk that the gain will be overrun. When the digital-to-analog converter described above is used, the gain is automatically controlled and decreases when it gets too close, so no bumps or hunting occur.

As described above, the present invention provides electrical discharge machining in which an electrode and a workpiece are opposed to each other with an insulating machining liquid interposed therebetween, and a sheet electric current is generated between the opposing electrodes to machine the workpiece. In the apparatus, an electrode position detection means for detecting the difference between the most advanced position at which the electrode is fed into the workpiece and the current position of the electrode, and a duration for which the amount of the difference exceeds a predetermined amount, or When the product of the amount and the above duration exceeds a predetermined value, it is determined that the state between the poles is abnormal and a signal is output, and the duration when the amount of the difference exceeds the predetermined amount, or the amount of the difference If the product of the above-mentioned duration is less than a predetermined value, it is determined that the gap condition is normal and outputs a signal, and the signal from the gap condition discrimination means is determined to indicate that the gap condition is abnormal. If it is determined that the gap is present and is output, the amplification degree of the electrode feed control device that sends the electrode to the workpiece is increased, and the signal from the gap condition determining means determines that the gap condition is normal. Since it is equipped with a means to reduce the amplification degree of the electrode feed control device that sends the electrode to the workpiece, it is possible to accurately judge the quality of the gap between the electrodes in electric discharge machining, and also to proactively Since the machining gap condition can be recovered without reducing the machining speed, not only can machining failures be prevented in advance, but also the following effects can be achieved: Be equipped. In other words, in electric discharge machining equipment, the gap impedance is constantly changing, and if a decrease in the gap impedance in a very short period of time is judged as an abnormality in the gap condition and countermeasures are taken, the machining efficiency will be reduced. This will result in a significant decline. Considering this in the light of the present invention, the amount of difference between the furthest position at which the electrode is fed into the workpiece and the current position of the electrode is very short, in other words, the amount of the difference is When the duration exceeds the above amount or when the product of the above difference and the above duration falls below a predetermined value, it is inappropriate to judge that the interpole state is abnormal, and in the present invention, in such cases, it is not normal. It is possible to provide an electric discharge machining apparatus which is also equipped with a function to determine whether there is a problem, and which enables even more highly efficient machining.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a conventional electric discharge machining device, Fig. 2 is a schematic diagram of a discharge state detection device which is an embodiment of the present invention, and Fig. 3 is a schematic diagram of a servo gain based on the output of the detection device shown in Fig. 2. FIG. 2 is a schematic diagram of a controlling device. In addition, the same reference numerals are given to the same or equivalent parts in the figure, 10 is an electrode, 14 is a workpiece, 18 is a processing power supply, 20 is a machining gap, 34 is a digital scale,
36 is a reversible counter, 40 is a digital to analog converter, 42 is a comparator, 44 is a pulse oscillator, 48 and 58 are voltage comparators, 60 is a light emitting diode, 72 is a multiplication type digital to analog converter,
24 is a servo amplifier, and Va is a servo signal.

Claims (1)

[Scope of Claims] 1. An electric discharge machining device that processes the workpiece by arranging an electrode and a workpiece to face each other with an insulating machining fluid interposed therebetween, and generating electric discharge between the opposing electrodes,
an electrode position detection means for detecting the difference between the most advanced position at which the electrode is fed into the workpiece and the current position of the electrode; A pole that determines that the interpolation state is abnormal and outputs a signal, and determines that the interpolation state is normal and outputs a signal when the duration of the above difference exceeding a predetermined amount is less than a predetermined value. When the signal from the gap state determining means and the gap state determining means determines that the gap state is abnormal and is output, the amplification degree of the electrode feed control device that feeds the electrode to the workpiece is increased. and means for reducing the amplification degree of the electrode feed control device that feeds the electrode to the workpiece when the signal from the gap condition determining means is output indicating that the gap condition is normal. An electrical discharge machining device characterized by: 2. In an electrical discharge machining device that processes the workpiece by arranging an electrode and a workpiece to face each other with an insulating machining fluid interposed therebetween, and generating an electric discharge between the opposing electrodes,
electrode position detection means for detecting the difference between the most advanced position at which the electrode is fed into the workpiece and the current position of the electrode; When the product exceeds a predetermined value, it is determined that the interpole state is abnormal and a signal is output. an inter-electrode condition determining means that determines that the inter-electrode condition is normal and outputs a signal;
When the signal from the machining gap state determining means is output as a result of determining that the machining gap condition is abnormal, the amplification degree of the electrode feed control device that feeds the electrode to the workpiece is increased, and the It is characterized by comprising means for reducing the amplification degree of the electrode feed control device that feeds the electrode to the workpiece when the signal from the state determining means determines that the inter-electrode state is normal and is output. electrical discharge machining equipment.