JPS641252B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention detects the difference between the most advanced position of the electrode and the current position, and automatically adjusts the electrical processing conditions in response to this difference to restore the gap state to a good state. The present invention relates to a switchable electrical discharge machining device.

FIG. 1 shows a conventional electric discharge machining apparatus, in which an electrode 1 faces a workpiece 3 placed in a machining tank 2 and an insulating machining fluid 4 with a machining gap G interposed therebetween. The machining power supply P/S consists of a DC power supply E, a switching element SW for switching on and off the machining power supply, and a current limiting resistor R.
and an oscillator OSC for controlling the on/off of the switching element, and supplies an intermittent current I between the electrode 1 and the workpiece 3. Intermittent current I is I
It is expressed by the formula =E-Vg/R, and during arc discharge, the voltage between electrodes Vg is 20 to 30V, when short-circuited it is 0V, during no discharge it is E, and when the switching element SW is in the OFF state, the voltage between electrodes Vg is 20 to 30V. becomes 0V. So this Vg
If this value is detected and averaged by the smoothing circuit 5, the interpole gap can be controlled from this value. That is, when the inter-electrode gap is wide, it is difficult for discharge to occur and the average voltage VS becomes high, whereas when the inter-electrode gap is narrow, short circuits occur and discharge occurs easily, resulting in a decrease in the average voltage. Therefore, if this voltage VS is compared with the reference voltage Vr and this difference is input to the inter-electrode servo circuit, that is, it is amplified by the amplifier 6, and input to the hydraulic servo coil 7, the electrode feeding device, that is, the hydraulic pressure generating pump P. The hydraulic servo mechanism constituted by the hydraulic cylinder 8 is controlled so that the gap G between the poles is approximately constant.

As described above, the most common way to determine whether the machining condition is good or bad with conventional electrical discharge machining equipment is to observe the average machining voltage Vg, and when this is low, the machining impedance is low, and this state Possible causes include short circuits, continuous arc discharge, and accumulation of machining powder and sludge between the machining plates. 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. Therefore, there was a problem in that it became impossible to detect the deterioration of the gap state based on the average voltage.

The present invention has been made in order to eliminate the drawbacks of the conventional ones as described above, and includes a device that can detect the gap length between poles and determine the state of the gap, and based on the determination by this device. Electrical machining conditions that are compatible with the above gap condition, i.e. discharge peak current value,
The object of the present invention is to provide a device that can automatically set values such as discharge duration, pause time, applied voltage, etc., and can optimally control discharge energy.

Hereinafter, one embodiment of the present invention will be described in detail using FIGS. 2 and 3. Reference numeral 9 in FIG. 2 is a digital scale, which is attached to the electrode support rod 10, and generates a positive direction pulse Sp when the electrode 1 moves downward, and a negative direction pulse Sn when it moves upward. In order to accurately determine 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. Reference numeral 11 denotes a reversible counter serving as a discriminating device between electrodes, which has 13 bits and can store the amount of electrode rise equivalent to 5 μm×(2 ¹⁴ −1), that is, 82 mm. Reversible counter 11
A digital-to-analog converter D/A is connected to the output of each bit, and this output is Vo. D/
The output of A is compared with 0V by the comparator 12, and if it is 0V, that is, the counter content is 0.
Then, the output pulse of the pulse oscillator 13 is
OR as addition pulse Lp via AND gate
Since it is added to the reversible counter via gate 15,
The reversible counter 11 adds the amount of increase and the addition pulse, and subtracts the amount of decrease. Yotsutte reversible counter 11
The content of is the difference between the most advanced position and the current electrode position.
That is, the sum of the addition pulses Lp is the most advanced position, and since the current value, which is the sum of the difference between the descent and the ascent, is subtracted from this, the content of the reversible counter 11 is the difference between the most advanced position and the current position. Therefore, since the output of the digital-to-analog converter D/A 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 poles is good or bad. In other words, if the above V ₀ is large,
Since the machining gap condition has returned from the most advanced value, there may be some kind of problem, such as sludge accumulating in the processing powder, or carbon generation due to thermal decomposition of the processing fluid due to abnormal arcing. It is easy to detect whether a part of the electrode is damaged and its fragments are present between the electrodes. However, the inter-electrode impedance changes constantly over a very short period of time, and even if the above difference exists for a short time, it cannot necessarily be determined that the inter-electrode condition is bad _.
It is necessary to detect and make a judgment that the existence of has continued for a certain period of time. Reference numeral 16 in FIG. 2 is a voltage comparator, which determines whether the difference voltage V ₀ is larger or smaller than a predetermined value V ₁ . When V ₀ becomes larger than V ₁ , the output of the voltage comparator 16 becomes negative, and the transistor Tr is turned off via the base resistor r ₁ . The time measurement capacitor C is charged through the resistor _r2 , and the voltage _V3 across the capacitor is expressed as follows.

Therefore, the output of the voltage comparator 17 does not become negative until the capacitor voltage V ₃ reaches the reference voltage V ₂ , so the light emitting diode 18 does not light up. If the voltage _{V 0 indicating} the difference continues to be greater than the above V ₁ for a predetermined time determined by the reference voltage V 2 , the output of the voltage comparator 17 becomes negative, and the light emitting diode 1
8 lights up, and it is possible to know that an abnormality has occurred in the gap state.

The switch 19 is a switch that serves as a switching means for determining whether to judge the state between poles only as a function of time or as a function of the product of the magnitude of the difference voltage V ₀ and time, and is located at the position shown in Fig. 2. By switching, arc cracking or tungsten chipping can occur instantaneously in machining that is difficult to detect by simply detecting time, such as machining copper or silver and tungsten powder alloy electrodes with iron and cemented carbide. In some cases, the occurrence of an abnormality can be immediately known as a function of the product of differential voltage and time. In other words, if the difference is large even for a short time, capacitor C
The charging current increases and immediately the capacitor voltage V ₃
This is because it reaches V ₂ . That is, since the condition of powder alloys deteriorates rapidly due to the falling of powder (20μ to 50μ diameter), it is effective to judge the condition as a function of the product of the differential voltage and time.

In addition, when machining graphite electrodes versus iron, if the current flows in a locally concentrated manner, the machining fluid (light oil, kerosene, etc.) carbonizes and adheres to the graphite.
If current concentration is not prevented, the interelectrode gap condition will deteriorate instantly, so it is effective to judge it as a function of the product of the difference voltage and time.

On the other hand, if the switch 19 is switched to the +V side as shown in FIG. 2, the state between poles can be determined only by a function of time, which is effective in the following cases, for example.

In other words, when processing copper electrodes versus iron, the distance is 10 to 15 m.
It is impossible to determine whether it is a true defect unless it is detected continuously for about sec. In addition, when machining iron electrodes versus iron or stainless steel, eluates from the workpiece generate bridges during machining, and judgment is required in 0.1 to 0.3 seconds, so the state of the gap between the electrodes can be determined only as a function of time. It is effective to do so.

Furthermore, by directly observing the voltage difference V ₀ with a voltmeter, the difference between the most advanced value and the current value can be directly observed, and it is clear that it can be used as a monitor of the state between the poles.

Then, the output of the above-mentioned inter-pole abnormality occurrence detection device
_V5 is sent to the machining power source P/S together with the binary digital values of outputs ²⁰ to ²¹³ of the counter 11 that detect the difference between the most advanced position and the current position, and these signals cause the machining power source P/S to I am trying to control this.

FIG. 3 is a detailed diagram of the machining power source P/S, and this embodiment shows an example in which the discharge pause time and the applied voltage are controlled by the above-mentioned signals. Although the discharge pause time and the applied voltage have an influence on the discharge gap, they have the characteristic that they do not have a large effect on the roughness of the machined surface or the wear of the electrode. It goes without saying that similar control can be performed depending on the processing purpose regardless of the conditions.

Reference numeral 30 in FIG. 3 is a multi-digit coincidence determination circuit, which determines whether the value of the reversible counter 11 for position difference detection is equal to the pause time setting counter 19, and if they match, an AND gate 20 and an OR gate 21 are used.
The R-S flip-flop 22 is reset via the RS flip-flop 22. However, the rest time setting counter 19 can be set by the manual preset rotary switch 23 when the gap state detection signal _V5 is not present, that is, when the logic is "1". In this case
AND gate 20 is closed. The output of the R-S flip-flop 22 drives the final stage switching element SW by the amplifier AMP, and supplies on/off pulses of the voltage of the DC power source E between its poles. The pulse duration is arbitrarily set by a pulse width setting counter 25 and a switch 26 for selecting this value to a predetermined value. The output of the oscillator 27 is connected to the output Q of the R-S flip-flop 22, and
are alternately selected by AND gates 28 and 29,
Used to set pause width and pulse width.

The operation shown in FIG. 3 will be explained in detail. First, the AND gate 24 is open when the gap state detection signal _V5 is not present, and the AND gate 20 is open when there is an abnormality. Therefore, the rest time is the value set by the manual preset rotor switch 23 in normal times, and the value of the reversible counter 11 in abnormal times.

When the counter 19 finishes counting the rest time, the R-S flip-flop 22 is reset and the output switches the switching element SW.
turns on and starts supplying pulses between the poles.
Further, the counter 25 starts counting by the output, and when it reaches the value set by the switch 26, the R-S flip-flop 22 is set.
Due to the loss of output, the switching element SW
Turn it off and it's time for a break.

In this way, when the abnormal state detection signal V ₅ becomes logic "0", a value corresponding to the difference between the most advanced value and the current value is automatically selected as the pause width, and the larger the difference, the shorter the pause width is. This increases the length, reduces the amount of processing, reduces the production of processed powder, and normalizes the machining distance. Conversely, when the difference is small, the predetermined set value is reached.

In addition, the applied voltage E is adjusted by the voltage regulator 31 so that when the gap widens due to an abnormality in the gap, it becomes a low voltage, and the gap length that has widened due to easy discharge due to the influence of machining powder etc. It is starting to get closer to normal values again. In this way, the difference between the most advanced position at which the electrode is fed into the workpiece and the current position of the electrode is detected, and the electrical conditions are controlled in accordance with the amount of abnormality between the electrodes so that the above difference is reduced. Therefore, the optimum gap length between the poles can be maintained at all times, and high-precision machining can be achieved.

Furthermore, the state of the gap between the electrodes can be determined by the switching means, either as a function of time alone or as a function of the product of the magnitude of the difference and time. It is possible to appropriately determine the abnormal state between poles depending on the type.

In addition to the above embodiments, it is clear that the discharge peak current value, current waveform, voltage waveform, pulse width, etc. can be controlled in a similar manner within the range that does not adversely affect the intended processing content. be.

As described above, in the present invention, the electrode and the workpiece are opposed to each other with an insulating working fluid interposed therebetween, and servo control is performed to maintain the gap between the electrode and the workpiece at a predetermined value. In an electric discharge machining device that processes the workpiece by generating an electric discharge between opposing electrodes between the electrode and the workpiece, the most advanced position at which the electrode is fed into the workpiece and the current position of the electrode are an electrode position detection means for detecting a difference; and a time period during which the difference between the most advanced position of the electrode and the current position is greater than a predetermined value, or a time period during which the difference between the most advanced position of the electrode and the current position is greater than a predetermined value. a selection means for selectively selecting the time at which the electrode is located and the value of the product of the difference; a time during which the difference between the most advanced position of the electrode selected by the selection means and the current position is greater than a predetermined value;
Alternatively, if the value of the product of the time and the difference exceeds a predetermined value, it is determined that the gap condition is in a bad condition and outputs a signal, and the signal of the gap condition discrimination means is inputted. , and a device that controls the electrical machining conditions in order to restore the machining gap to a good condition in response to this, it is possible to determine the machining gap condition and restore the machining gap to a good condition, and also to control the electrical machining conditions. Since the machining conditions are controlled, the response is quick.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing a conventional electrical discharge machining device, Fig. 2 is a principle diagram showing an embodiment of the electrical discharge machining device according to the present invention, and Fig. 3 is an embodiment of an automatic switching device for machining electrical conditions. FIG. In addition, the same reference numerals in the figures indicate the same or equivalent parts, 1 is an electrode, 2 is a processing tank, 3 is a workpiece, 8 is a hydraulic cylinder, 9 is a digital scale, 11
13 is a reversible counter, 13 is a pulse oscillator, D/A is a digital-to-analog converter, 16 and 17 are voltage comparators, and P/S is a processing power source.

Claims (1)

[Claims] 1. The electrode and the workpiece are faced to each other with an insulating working fluid interposed between them, and servo control is performed to maintain the gap between the electrode and the workpiece at a predetermined value. In an electrical discharge machining device that processes the workpiece by generating electrical discharge between opposing poles,
an electrode position detection means for detecting a difference between the most advanced position at which the electrode is fed into the workpiece and the current position of the electrode; and a time period during which the difference between the most advanced position of the electrode and the current position is greater than a predetermined value. , or selection means for selectively selecting the time during which the difference between the most advanced position of the electrode and the current position is greater than a predetermined value and the value of the product of the difference; When the difference between the most advanced position and the current position is greater than a predetermined value, or the product of that time and the difference exceeds a predetermined value, it is determined that the gap between poles is in a bad state and a signal is output. The present invention is characterized by comprising: a gap condition determining means; and a device to which a signal from the gap condition determining means is input, and in response to the signal, controls electrical processing conditions in order to restore the gap condition to a good state. electrical discharge machining equipment.