JPS6312726B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse power source electric discharge machine.

Electric discharge machining using an electric discharge machine is widely applied to mold machining for metal drilling press equipment, etc., but in this type of electric discharge machining technology, a pulse power supply method is used to improve the machining finish condition. will be adopted. Generally, this type of electrical discharge machining is performed in oil, and the machining state is determined by the ratio of the discharge voltage pulse width applied between the tool electrode and the workpiece to the discharge time, and the closer the time width is to 1, the more This means that the applied pulse is being used effectively,
This is most desirable and means that processing efficiency is high. However, the pulse width immediately after the discharge voltage pulse is applied does not remain between the tool electrode and the workpiece, and a sustained arc discharge phenomenon occurs. Sustained arc discharge has the drawback of making the machining conditions unstable, such as locally machining the surface of the workpiece. Therefore, it is necessary to add a means to prevent this sustained arc discharge. To do this, the difference voltage between normal discharge and sustained arc discharge is detected by pulse detection, and the servo motor is driven accordingly.
There are methods that control and prevent the feeding of the tool electrode, methods that control electrical conditions such as the output pulse voltage of a pulse power source, and methods that combine these simultaneously.

FIG. 1 is a block diagram showing a method for simultaneously controlling electrode feed control and electrical condition control. In the figure, reference numeral 1 denotes a pulse power source for electric discharge machining, and its voltage is applied as a discharge voltage pulse between poles formed between a tool electrode 2 and a workpiece 3. 4 is a voltage detector between electrodes that detects the average voltage of voltage pulses between electrodes, and its output is sent to a differential amplifier 5.
is input to one of the input terminals. A voltage from a reference voltage setter 6 whose output is preset to an arbitrary value is applied to the other input terminal of the differential amplifier 5. Reference numeral 7 denotes an electrode drive device, typically a servo motor, which is activated by the output differential voltage of the differential amplifier 5 and automatically controls the feeding of the tool electrode 2. Reference numerals 8, 9, and 10 are a comparator amplifier, a reference voltage setter, and a discharge pulse control circuit that constitute a control circuit for automatically controlling the electrical conditions of the pulse power source 1, and as shown in the figure, they are a comparator amplifier, a reference voltage setter, and a discharge pulse control circuit. get the output,
It is compared and amplified with the output of the reference voltage setter 9, and the output discharge voltage pulse width from the pulse power source 1 is controlled via the discharge pulse control circuit 10, so that a normal discharge as shown in the waveform diagram 1 in FIG. 2 is performed. It is configured so that

Now, in the circuit shown in FIG. 1, if machining debris or the like is present between the tool electrode 2 and the workpiece 3, causing a short circuit, the inter-electrode voltage decreases as shown in FIG. The tool electrode 2 is moved so that the servo motor 7 is driven by a voltage difference to enlarge the gap between the electrodes.
control. At the same time, the comparison amplifier 8
Discharge pulse control circuit 1 by the output pulse from
The pulse power source 1 is controlled via the pulse power source 1 to increase the pause time of the discharge pulse to temporarily stop the discharge machining.

However, when sustained arc discharge occurs as shown in Fig. 2, this makes the condition of the machined surface unstable as described above, and the concentrated current worsens the roughness of the machined surface. Since the average voltage between the electrodes is detected and compared with the reference voltage, it is impossible to distinguish between normal discharge and sustained arc discharge 2 in FIG. In other words, rectangular waveform 3 shown in Fig. 2 has a low value as shown by voltage c, and can be distinguished from normal discharge, but sustained arc discharge 2 and normal discharge 1 are equal in voltage A, but are not normal. The time T ₀ of discharge 1 is a very short time, and the only difference is the voltage B of discharge 1 and the voltage B' of sustained arc discharge 2, and there is almost no difference in their average voltages, so it cannot be distinguished and detected. .

Therefore, in the above circuit configuration, the sustained arc discharge is treated as a normal discharge and controlled, making the machining condition unstable and locally worsening the machined surface roughness.
It was not possible to prevent so-called arcing.

An object of the present invention is to eliminate the drawbacks of the prior art described above, to stabilize the electrical discharge machining state, and to prevent sustained arc discharge.

The present invention achieves the above object by detecting the average voltage between the poles, detecting sustained arc discharge and short circuit, and controlling the machining gap and machining current based on the detection signals. Below, the third
The present invention will be explained in detail with reference to FIGS.

FIG. 3 shows an embodiment of the present invention, in which the same reference numerals as described above indicate the same parts. As shown in FIG. 3, in the same example,
The voltage applied between the electrodes is input to the inter-electrode voltage detector 4, and is also input to a newly installed first detection circuit 11 (hereinafter referred to as sustained arc discharge pulse detection circuit 11) connected in parallel with the voltage detector 4. Each output voltage is input to the differential amplifier 12, and the difference voltage obtained therefrom is used to drive and control the servo motor 7 in the same manner as described above, and the differential voltage of the differential amplifier 12 is input to the comparator amplifier 8. It is configured to control electrical conditions such as machining current. The specific circuit configuration of the sustained arc discharge pulse detection circuit 11 is shown in FIG. 4, and this figure will be explained with reference to the pulse waveform diagrams in FIGS. 5 and 6.

In FIG. 4, reference numerals 13 and 13' denote voltage dividing resistors for obtaining a predetermined voltage between electrodes. 14,1
5 and 16 are comparators which input the divided voltage between electrodes, and the output a of the voltage dividing resistors 13 and 13' is as follows.
These comparators 14, 15, and 16 are connected so as to be inputted to their respective positive terminals, negative terminals, and positive terminals. Each of these comparators 14,1
Level voltages E ₁ , E ₂ , and E ₃ for comparing and detecting normal discharge pulses, non-discharge pulses, and sustained arc discharge pulses are input to the other input terminals 5 and 16 from a voltage setting device (not shown). It has been done. 19,
20 and 22 indicate AND gate circuits, and comparator 1
4 and 15, the output of the comparator 16 obtained via the flip-flop 17, and the first timing pulse from a pulse output circuit (not shown).
T ₁ and the second timing pulse T ₂ (hereinafter simply referred to as timing pulse T ₁ and timing pulse T ₂
), T ₁ is input. Inverters 18, 21, 29 An inverter for inverting the outputs of the flip-flop 17 and the comparators 15 and 14. 23 is an OR gate circuit that receives the outputs of the AND gate circuits 20, 22, and 30; This serves as a reset signal for the first flip-flop 24 (hereinafter simply referred to as flip-flop 24), which is set by the output of the flip-flop 24. 25 and 26 are flip-flops 24
A resistor and a capacitor are connected to the output of the circuit to form an integrating circuit. A comparator 27 compares the integrated output with a level voltage set to a predetermined level, and its output is applied to the differential amplifier 12 shown in FIG. The operation of eliminating sustained arc discharge in a circuit configured as shown in FIG. 3 will be explained.

First, detection during normal discharge will be described according to the waveform diagram shown in FIG. FIG. 5A is a voltage waveform diagram between electrodes, and discharge voltage pulses and normal discharge pulses are detected at voltage level setting values E ₁ , E ₂ , and E ₃ . That is, comparator 14 in FIG.
Since the voltage _E1 at the input terminal (-) of is set as shown in FIG.
It will be as follows. Further, the output waveform of the comparator 15 is compared with the level voltage _E2 , and becomes a waveform like c.
Furthermore, the comparator 16 also adjusts the level voltage E ₃ in the same way.
A waveform d is obtained. Then, the flip-flop 17 is reset by the output voltage d of the comparator 16, resulting in an output waveform e, which has been reset in advance by the timing pulse _T2 .
As a result, an output voltage f is obtained from the inverter 18. The outputs b and c of the comparators 14 and 15 and the output f of the inverter 18 are applied to an AND gate circuit 30, and at the same time a timing pulse is applied to the AND gate circuit 30.
A pulse voltage g is obtained by applying T ₁ . That is, this pulse voltage waveform g is a normal discharge detection signal. The output pulse j is obtained from the OR gate circuit 23 by the product of this pulse voltage g and the output pulse i of the AND gate circuit 22, and is input to the reset terminal of the flip-flop 24. That is, since there is no output l from the flip-flop 24, there is no output from the sustained arc discharge detector 11 shown in FIG. 3, which means that normal discharge is occurring.

Next, the non-discharge detection shown in FIG. 5 will be described. In this case, an output pulse i in FIG. ₅₂ is obtained from the AND gate circuit 22 by the product of the timing pulse T ₁ and the inverted output h of the comparator output c by the level voltage E 2,
An output pulse j is obtained via. In this case, as in the case of normal discharge, a reset signal is applied to the flip-flop 24, and there is no output from the flip-flop 24.

Next, detection of sustained arc discharge, which is intended to be prevented by the present invention, will be described. The sustained arc discharge detection signal is obtained by pulse detection as shown in _FIG . There is no output j. However, the AND gate circuit 19
An output pulse k is obtained from the flip-flop 24 as a so-called sustained arc discharge pulse.
is input to the set terminal of flip-flop 24.
The output pulse of is obtained as a pulse waveform such as l.

Sustained arc discharge detection signal k obtained in this way
Detection signals k and j as shown in FIG. 6 are obtained from the normal or non-discharge detection signal j, and an output pulse l is obtained from the flip-flop 24, and the output voltage of the capacitor 26 constituting the integrating circuit is has a waveform like m. The output waveform m is generated by comparator 2 whose negative terminal is set to level voltage E ₄ in advance.
7 and its level voltage E ₄
When the value exceeds the value, an output pulse n is obtained.

Therefore, an output pulse is obtained from the terminal 28 only when the sustained arc discharge time or the number of sustained arc discharge pulses is large, and this sustained arc discharge pulse is applied to the differential amplifier 12 shown in FIG. The discharge pulse control circuit 10 is controlled to drive the servo motor 7 to enlarge the machining gap between the machining poles, and at the same time to decrease the machining current via the comparator amplifier 8. This prevents sustained arc discharge that adversely affects the machined surface and stabilizes the process.

However, in normal electrical discharge machining, electrical discharge machining is not necessarily performed using only normal electrical discharge. Moreover, due to the interrelationship between the feeding speed of the machining electrode 2 by the servo motor 7 and the amount (dimensions) of the workpiece 3 to be machined, the machining gap usually fluctuates between long and short.

Therefore, in normal electrical discharge machining, four discharge forms are repeated: no discharge, normal discharge, sustained discharge, and short circuit.
However, it goes without saying that the higher the proportion of normal discharges among these discharge forms, the higher the machining efficiency. The waste removed from the workpiece 3 by electrical discharge machining in the above-mentioned electrical discharge machining (hereinafter referred to as sludge)
may remain in the machining gap and cause a short circuit (hereinafter referred to as a pseudo short circuit) through this sludge, but even if this pseudo short circuit is left as it is, the machining fluid (discharge machining is performed in an insulating liquid) Since the stagnant matter is removed by the jet of water, it is often released already (about 20 ms). In this pseudo-short circuit, no sustained arc is generated, and therefore no arc traces (the main purpose of the present invention is to completely eliminate the generation of arc traces) are generated on the workpiece 3, so electrical discharge machining is performed. The above damage is not too great. However, this pseudo short circuit lasts for several milliseconds at most, but in order to distinguish it from a short circuit that occurs due to contact between the machining electrode 2 and the workpiece 3, the inter-electrode voltage detector 4
When the output decrease (average voltage) continues for about 50 to 100 ms, the processing electrode 2 is raised.

During electrical discharge machining, the gap between the machining electrode 2 and the workpiece 3 becomes smaller, and in a situation where sustained discharge and short circuit occur repeatedly, if a short circuit occurs, if it is a pseudo short circuit, arc marks will occur. Therefore, it is effective to distinguish it from sustained arc discharge and continue electric discharge machining (without raising the machining electrode).

Next, short circuit detection shown in FIG. 5 will be described. In this case, by the product of the timing pulse _T1 and the inverted output p of the comparator output b due to the level voltage _E1 , the Q
An output pulse is obtained, and an output pulse j is obtained via the OR gate circuit 23. In this case as well, the flip-flop 2
4 reset signal is applied, and there is no output l of flip-flop 24. Therefore, if a short circuit occurs following a sustained arc discharge, the flip-flop 24 will be reset at the short circuit even if it is set during the sustained arc discharge, and the terminal 28 will be reset.
The output signal 28 is not output.

Returning to the explanation of FIG. 3 again. Reference numeral 31 indicates abnormal discharge from the voltage between electrodes, i.e., sustained arc discharge and short circuit (in this case, the sustained arc detector 11 shown in FIG. 4).
(meaning a pseudo short circuit and a short circuit that occurs in a short period of time as described in the explanation section), and when abnormal discharge continues for a predetermined period of time. This is a second detection circuit (hereinafter referred to as an abnormal discharge detector) which operates to turn on the switch 32 and enable feedback. Figure 7 shows this abnormal discharge detector 31.
A circuit diagram showing this is shown. The abnormal discharge detector 31 sets the second flip-flop 24' (hereinafter simply referred to as flip-flop 24') by a short circuit signal Q corresponding to the short circuit signal Q in the sustained arc discharge detector 11 shown in FIG. The only difference is that (in FIG. 4, it was reset). In FIG. 7, parts corresponding to those in FIG. 4 are indicated by the same reference numerals with a dash (') added. 33 is an OR gate circuit which receives the outputs of AND gate circuits 19' and 30', and its output is fed to flip-flop 2.
4' becomes the set signal U. OR gate circuit 2
3' inputs the outputs of the AND gate circuits 20' and 22', and its output j is input to the flip-flop 24' which is set by the output U of the OR gate circuit 33.
This becomes the reset signal for the flip-flop 24' which is reset. Such abnormal discharge detector 31
As shown in Figure 8 1 and 2, the waveform chart for normal discharge and no discharge is the same as the waveform diagram shown in Figure 5 1 and 2, but for sustained arc discharge short circuit, it is shown in Figure 8 3 and 4. Just like that, AND gate circuit 19'
Signal K′ output from and AND gate circuit 3
An output pulse U is obtained from the OR gate circuit 33' by multiplying the signal Q' output from the OR gate circuit 33'. Then, the output pulse U causes flip-flop 2
4' is set, and its output pulse is obtained as a waveform as shown in FIG. 9l'. From the sustained arc discharge or short circuit detection signal U obtained in this way and the normal or no discharge detection signal j', detection signals l' and j ₁ ' as shown in FIG. The output voltage of 26' has a waveform m'. The output waveform m' is applied to the plus terminal of a comparator 27' whose minus terminal is previously set to the level voltage _E4 , and when the voltage reaches the level voltage _E4 or higher, an output pulse n' is obtained. The switch 32 is turned on by the output signal n' from the abnormal discharge detector 31. In other words, if sustained arc discharge and short circuit continue for more than a predetermined period of time, arc scars will be generated due to sustained arc discharge and the time during which electrical discharge machining cannot be performed will increase due to the short circuit, and the efficiency of electrical discharge machining will decrease, so these impacts should be removed. For this purpose, the machining current of the machining pulse power source 1 is reduced.
Whether or not the machining current is reduced at this time is determined by the output signal of the differential amplifier 12 and the output of the reference value setter.

Note that the resistor 2 used in Figures 4 and 7
It goes without saying that the integrator constituted by 5' and the capacitor 26' is not limited to this, and any integrator that can detect sustained arc discharge time or abnormal discharge time and compare it with a predetermined time width is sufficient. be. The operation time of the operation to widen the machining gap or the amount of gap expansion can be adjusted by using the output signal of the sustained arc detector 11 using an amplifier, a monostable multivibrator, or the like. Control using such a monostable multivibrator or amplifier means adjusting the time required to increase or decrease the discharge pulse frequency or discharge pulse pause time of the machining pulse power source 1, and the operation time for reducing the discharge current. It can also be applied when

According to the experimental results using the circuit with the above configuration, under the following machining conditions: tool electrode...copper 20φ cylindrical workpiece...SKD11 machining pulse width...500 (μsec) machining current...20 (A) When machining was done using the conventional method, sustained arc discharge occurred in about 3 minutes and machining became impossible, but according to the circuit method of the present invention, 30
Even after machining was carried out for more than a minute, no sustained arc occurred, and a good machined surface roughness was obtained, proving that the process was extremely effective. The time constant of the integrating circuit used in this experiment was 5 ms, the level of the set voltage _E4 was set to 80% of the maximum value of the waveform in Figure 6 m, and the control of the machining current was set to 50%. The current was set to decrease.

As is clear from the above-described embodiments, the present invention detects the average voltage between the machining electrodes, simultaneously detects the sustained arc discharge voltage, and calculates the machining electrode gap and the output control pulse of the machining power source by taking the detected difference voltage. It is designed to perform control. Therefore, according to the present invention, problems caused by sustained arc discharge are eliminated, the electric discharge machining state can be stabilized, and a good machined surface roughness can be obtained.

In addition, the machining state of sustained arc discharge and short circuit is distinguished, and when only sustained arc discharge occurs continuously for a predetermined period of time, the gap between the machining electrode 2 and the workpiece 3 is widened, and the short circuit state is maintained for a predetermined short period of time. If this occurs repeatedly, electrical discharge machining is continued, so even if sustained arc discharge occurs with a short circuit within a short period of time, electrical discharge machining will not be interrupted, and furthermore, arc marks will be generated at this time. This has the effect of improving machining efficiency in addition to good machined surface roughness.

[Brief explanation of the drawing]

Figure 1 is an overall circuit configuration diagram of a conventional electric discharge machine, Figure 2 is a waveform diagram of pulses applied between machining holes during electric discharge machining, and Figure 3 is an overall diagram of an electric discharge machine according to an embodiment of the present invention. Figure 4 is the circuit configuration diagram of Figure 3.
FIGS. 5 and 6, which are circuit configuration diagrams specifically showing a part of the diagram (the first detection circuit), are time charts for explaining the operation of the circuit shown in FIG. 4. FIG. 7 is a circuit diagram specifically showing a part of FIG. 3 (second detection circuit), and FIGS. 8 and 9 are time charts for explaining the circuit operation of FIG. 7. DESCRIPTION OF SYMBOLS 1... Pulse power supply, 2... Tool electrode, 3... Workpiece, 4... Voltage detector between electrodes, 5, 12... Differential amplifier, 6, 9... Reference value setter, 7... Motor, 8... Comparative amplifier, 10...Discharge pulse control circuit, 11...Sustained arc discharge pulse detection circuit, 14, 15, 1
6, 27... Comparator, 17... First flip-flop, 24... Second flip-flop, 18, 21
...Inverter, 19,20,22,30...AND gate circuit, 23,33...OR gate circuit, 25
...Resistor, 26...Capacitor, 31...Abnormal discharge detector (second detection circuit), 32...Switch.

Claims (1)

[Claims] 1. A pulse power source connected between the electrodes formed by the tool electrode and the workpiece, and a voltage detection circuit between the electrodes that detects the average voltage of the discharge pulses generated between the electrodes.
A short circuit is caused by a combination logic circuit of a comparison signal that compares the discharge pulse with a plurality of reference voltages, a first timing pulse synchronized with the falling edge of the discharge pulse, and a second timing pulse delayed by a predetermined time after the falling edge of the discharge pulse. , outputs each signal corresponding to sustained arc discharge, normal discharge, and no discharge, and outputs a pulse signal when the output of the first flip-flop set by the sustained arc discharge signal continues for a predetermined time. a first detection circuit; a differential amplifier that outputs a difference voltage signal between the average voltage signal from the electrode voltage detection circuit and the pulse signal from the first detection circuit; and an output voltage from the differential amplifier. and a reference voltage, and an electrode drive device that controls electrode feeding based on the voltage difference between the output voltage from the differential amplifier and another reference voltage, and a discharge pulse condition applied between the electrodes from the pulse power supply using the voltage difference between the output voltage from the differential amplifier and another reference voltage. and a second flip-flop whose output is set by either the sustained arc discharge signal or the short circuit signal and reset by either the normal discharge signal or the no discharge signal for a predetermined period of time. A sustained arc discharge prevention device characterized by having a second detection circuit that occasionally outputs a pulse signal, and a switch that stops or starts the control signal from the control circuit based on the pulse signal from the second detection circuit. electrical discharge machine.