JPS6258849B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for setting optimum values of machining stability factors for an electric discharge machine.

Conventionally, in order to perform electrical discharge machining stably, the effective discharge rate is determined, and the set voltage, pulse duty factor, and hunting are set so that the effective discharge rate exceeds a preset value. Control factors such as cycle and machining fluid pressure were controlled individually.
However, normally, when the electrode shape, material, material of the workpiece, etc. change, the effective discharge rate fluctuates significantly, so the control factors are automatically controlled as described above so that the effective discharge occurrence rate is equal to or higher than a predetermined value. There were times when things became impossible. That is, in the past, whenever the shape and material of the electrode or workpiece was changed, the above-mentioned predetermined values had to be set based on experience and intuition, and the control range of each factor was not fixed. As a result, the optimum value was not necessarily set, resulting in an extremely low machining efficiency.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques and to improve the machining stability factor of an electric discharge machine so that stable and high electric discharge machining efficiency can be obtained even if the shape and material of the electrode and workpiece change. An object of the present invention is to provide an optimum value setting device.

The present invention provides a method for controlling any one of machining stability factors such as set voltage, pulse duty factor, hunting period, and machining fluid pressure in a predetermined order and in a predetermined control range according to the shape of the material to be processed. While detecting the effective discharge rate that occurs in the machining gap between the electrode and the workpiece by changing it sequentially at intervals, for the set value of the changed control factor,
The effective discharge rate is determined, and this effective discharge rate is searched in correspondence with the above set value, and the value of the predetermined control factor is controlled so as to reach the optimal value of the control factor that maximizes the effective discharge rate. Even if the material of the electrode or workpiece changes during machining, the optimum value is always automatically determined, enabling efficient and stable electrical discharge machining. This is an optimum value control device for the machining stability factor of an electrical discharge machine, characterized in that it detects arc discharge and also uses a continuous abnormal arc discharge prevention circuit to prevent abnormal marks from occurring on the workpiece.

Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

1 and 2 are explanatory diagrams of the operation of the circuit according to the present invention, and FIG. 3 shows an embodiment of the optimum value setting device according to the present invention. FIG. 1 shows the relationship between the set voltage (target setting value of the electrode gap following servo circuit and corresponds to the machining gap) among the machining stability factors and the effective discharge rate, that is, the machining speed. This effective discharge rate is determined by the machining pulse 1, as shown in detail in Figure 4.
This is a percentage obtained by integrating and correcting the actual discharge time for each pulse.

In FIG. 1, the optimal setting voltage is determined as described below. In Figure 1,
A graph curve is shown. Although this varies depending on the material to be processed, etc., the curve will be explained here. First, the initial value of the set voltage is set to Us (50V in this example), and as the set voltage is gradually lowered, the effective discharge rate follows a curve with one peak. In this example, the optimal value of the set voltage is 40V, which is the Um point where the effective discharge rate is maximum. The curve shown in FIG. 1 mainly shows the characteristics when machining steel materials, but the curve shows the characteristics when machining cemented carbide. Therefore, the optimum value differs depending on the processed material. Figure 2 shows the relationship between machining fluid pressure and effective discharge rate, where the curve shows the case when steel material is machined, and the curve shows the case when cemented carbide is machined. For the machining characteristics of cemented carbide shown in the curve, the search range for machining fluid pressure is 0.7 to 1.5 kg/
The maximum value of the effective discharge rate must be determined between cm ² and the machining fluid pressure control range must be 0.05 to 0.3 Kg/cm ² when machining the steel material shown in the curve. In other words, if machining of cemented carbide were controlled within the range of 0.05 to 0.3 Kg/cm ² as with steel, the effective discharge rate would be extremely low, making it impossible to obtain the best machining speed. It becomes impossible. In addition, if the search range for machining fluid pressure is between 0.05 and 1.5 Kg/cm ² to cover both materials, in principle the optimum value can always be found, but when looking at one material, it becomes unnecessary. However, if the machining process is performed with a value that is far from the appropriate value, the machining efficiency will be reduced and the efficiency will be extremely poor. Although not shown, the same can be said of the pulse duty factor. For example, for copper or copper alloy electrodes, the duty factor value should be between 50% and 95%, and for steel-based electrodes, the value should be between 20% and 50%. In this way, the search range must be changed depending on the electrode and workpiece material.

The present invention will be explained below based on the embodiment shown in FIG. 1 is a pulse power supply, 2 is an electrode, 3
4 is a workpiece, and 4 is a discharge state detection circuit for detecting an effective discharge rate and a sustained abnormal arc discharge. 5
6 is an electrode raising circuit for raising the electrode in response to a sustained abnormal arc discharge detection signal; 6 is a pulse pause circuit for suspending the pulse power supply in response to a sustained abnormal arc discharge detection signal; 7 is an analog-to-digital converter; 8 is a maximum value Memory, 9 is shift register, 1
0 is a size discrimination circuit for determining the size of the contents of the maximum value memory 8 and the contents of the number register 9; 11
is an AND gate and one input is a size discrimination circuit 10
The output signal of the one-shot multivibrator 13 is applied to the other input. AND
The output of gate 11 is applied to a control input of shift register 12 and a control input of maximum value memory 8. A reversible counter 14 is connected to the parallel input of the shift register 12.
The parallel output signal of the shift register 12 passes through the switch 15 and is sent to the reversible counter 19.
given to parallel inputs. A signal from an initial setting circuit 16 is applied to the other parallel input of the switch 15. A search sequence circuit 23 is connected to the control input of the switch 15.
A control signal is given from The output signal of the AND gate 19 is given to the (+) input of the reversible counter, the output of the rotary switch 18 for determining the control range is given to one input of the AND gate 19, and each switching terminal of the rotary switch The output signal of the decoder 17 is given to the input of the decoder 17. A parallel output signal from the reversible counter 14 is applied to the input of the decoder 17 . AND gate 1
A search clock signal is applied to the other input of 9 from a search clock generator 22 through a search sequence circuit 23 at a predetermined clock period. The search clock signal obtained from the search sequence circuit 23 is applied to the (-) side input of the reversible counter 14 through one input of the AND gate 20. The output side of the rotary switch 26 is applied to the other input terminal of the AND gate 20, and the output side of the decoder 27 is connected to each terminal on the input side of the rotary switch. A parallel output signal from the reversible counter 14 is applied to the input of the decoder 27 . Rotary switch 26 and rotary switch 1
Each output of 8 is connected to two inputs of an OR gate, and its output passes through a one-shot multivibrator 24 and is inputted to a load input terminal of a reversible counter 14 through an OR gate 21. The other input of the OR gate 21 is given an initial value load signal from the search sequence circuit 23, and the signal is given to the load signal input of the reversible counter 14. The parallel digital output of the reversible counter 14 is digital -
Through an analog converter 28, a control drive circuit 29 is provided with a set voltage or working fluid pressure, a pulse duty factor, an electrode up and down hunting period, etc.

Next, the operation of the above circuit configuration will be explained.

The operation will be explained in the case of machining having the characteristics shown in the curve of FIG. First, search sequence circuit 1 for a processing start signal (not shown)
1, a code control signal is sent from the search sequence circuit 23 to the reversible counter 14 and a switching signal to the switch 15 through the OR gate 21, and the initial value set by the initial value setting circuit 16, that is, the curve shown in FIG. The value of the set voltage U _s of approximately 50 V is then loaded in parallel to the reversible counter 14 through the switch 15 . The contents of the reversible counter 14 are simultaneously converted into an analog value by a digital-to-analog converter 28, the details of which serve as a reference voltage for an electrode feed follower servo (not shown), and electrical discharge machining is started at a predetermined gap. Next, search clock generator 22
The clock signal passes through the search sequence circuit 23 and the AND gate 20 to the (-) side of the reversible counter 14.
The content of is subtracted by one pulse. As a result, the analog output of the digital-to-analog converter 28 is set to a set voltage that is lowered by one step, for example, 45V. In this way, the set voltage is lowered by several volts per step, and the U _E shown in the curve in Figure 1 is approximately 30V.
If the output of the reversible counter 14 is also input to the decoder 27, the output of the rotary switch 26 becomes "L" when the content of the reversible counter 14 is reached by selection of the rotary switch 26.
level, the AND gate 20 closes, and no further input is made to the (-) input of the reversible counter 14. That is, the lower limit of the search range is set by the decoder 27 and rotary switch 26. While operating up to the lower limit of the search range, the analog value of the effective discharge rate detected by the discharge state detection circuit 4 is converted into a digital value by the analog-digital converter 7, and is first stored in the maximum value memory of the effective discharge rate at the start of machining. 8 is stored. Next, the value of the effective discharge rate when the set voltage is lowered by one step is transferred to the shift register 9, and the magnitude determination circuit 10 determines the magnitude of the contents of the maximum value memory 8 and the contents of the shift register 9. After the determination delay time provided in the multivibrator 13, if the contents of the shift register 9 are large, an output signal is obtained from the magnitude discriminator 10, and this output signal determines the effective discharge of the digital-to-analog converter 7. The value of the rate is newly stored and updated in the maximum value memory 8. At the same time, the output signal of the magnitude discriminator 10 is passed through an AND gate 11 to a shift register 1.
2, and the contents of the reversible counter 14 are transferred to the number register 12. Following similar operations, the maximum value of the effective discharge rate is finally set to the maximum value memory 8.
The optimum value of the set voltage is stored in the shift register 12, a search end signal is given from the one-shot multivibrator 24 to the load input of the reversible counter 14, and the optimum value is passed from the shift register 12 to the switch 15, and is then transferred to the reversible counter 14. is set to
After that, it is processed using the optimum value.

Next, the case of determining the optimum value of the machining fluid pressure shown in the curve and in FIG. 2 will be explained using FIG. 3. The circuit to find the optimum value of machining fluid pressure is
In FIG. 3, reference numerals 1 to 11, 13, 22 and 23 are common elements, and although parts with other reference numbers must be manufactured separately, the circuit configuration is the same. In order to find the optimal value of machining fluid pressure, first,
Taking the curve as an example, the initial value setting circuit 16 sets the initial value to 0.6 kg/cm ² and discharge machining is started, and the search is continued until the upper limit of the search is approximately 1.5 kg/cm ² . This purpose is achieved by setting the search upper limit value by selecting the output obtained by decoding the contents of the reversible counter 14 by the decoder 17 using the rotary switch 18, thereby closing the AND gate 19. In the case of curve (1), the machining fluid pressure is set to 0.05Kg/ ^cm2 as the initial value, and the upper limit is set to 0.3Kg/cm2.
The positions of the initial value setting circuit 16 and the rotary switch 18 may be selected so that the distance is cm ² . Further, the search range for the optimum value of the pulse duty factor may be set to the value as described above. Naturally, the initial value setting circuit 16 and the rotary switches 18 and 26 are used to determine the search range depending on the electrode and material of the workpiece.
Although the switching may be set separately, it goes without saying that they can be set in conjunction with each other using a relay or the like.

These operations are performed at a relatively slow speed with a clock cycle of about 10 to 20 seconds from the search clock generator. If abnormal arc discharge persists during this search, it is necessary to avoid this. By using a specific circuit shown later, the electrode raising circuit 5 and the pulse stopping circuit 6 are operated to prevent abnormal machining traces from occurring on the machined surface.

Next, the discharge state detection circuit 4 of FIG. 3 will be specifically explained using FIG. 4. In the figure, 1 is a pulse power source, 2 is an electrode, 3 is a workpiece, 401 is a timing pulse generator, 402, 403, 404
are a first level setter, a second level setter, and a third level setter, and the levels E ₁ , E ₂ , and E ₃ are 405, 406, and 407, respectively. , to one input of the third comparison amplifier. 408 is an AND gate to which the outputs of comparison amplifier 405 and comparison amplifier 406 are applied. The input of the AND gate 410 is the output of the comparison amplifier 405 and the timing pulse generator 4.
A timing pulse _T2 obtained from 01 is applied, and the output of AND gate 410 is applied to the reset input. D of D type flip-flop 412
The (data) input is given the output of the R-S flip-flop, and the clock input (T input) is given a signal obtained by inverting the timing pulse _T1 generated by the timing pulse generator 401 by an inverter 409. The output of the D-type flip-flop passes through an integrating circuit consisting of a resistor 413 and a capacitor 414, and is applied to a comparator amplifier 415.
The other input of comparison amplifier 415 is given E ₄ by level setter 416 . AND gate 40
8 is given to the inputs of AND gates 418 and 419, the output of the comparison amplifier 415 is given to the other input of the AND gate 418, and the output signal of the comparison amplifier 415 is given to the other input of the AND gate 419. 417 provides an inverted signal. The output of AND gate 418 is resistor 4
20 and a capacitor 422, the current is exchanged to direct current, and an effective discharge rate detection signal is obtained from a terminal 424. Further, the output of the AND gate 419 is converted into direct current by an integrating circuit consisting of a resistor 421 and a capacitor 423, and a sustained abnormal arc discharge detection signal is obtained from a terminal 425. Terminal 424, 4
25 is applied to the electrode rise circuit 5 and pulse pause circuit 6 shown in FIG. 3, and control is performed respectively.
The operation will be explained below based on the waveforms of each part shown in FIG. When a pulse with waveform A is applied from the pulse power source 1 between the electrodes and electrical discharge machining is performed, the inter-electrode voltage waveform becomes as shown in B. By the first and second level setters 402 and 403
E ₁ and E ₂ are the first and second comparison amplifiers 405 and 4
06, these outputs are applied to the inputs of AND gate 408, whose output has the waveform shown in C. In waveform B, B ₁ to _{B 6} and B ₁₃
indicates that a discharge occurred after the pulse was applied, and the time width of the discharge is detected as shown in waveform C. In waveforms B ₇ to _{B 12} , the pulse was applied before the ions in the electrode gap were annihilated, so the current flows simultaneously with the pulse application, so the so-called
This is called abnormal arc discharge. If this condition continues, abnormal traces will appear on the machined surface. Detection of this continuous abnormal discharge is performed as follows.
When the voltage between the poles is above the level _E3 , the output of the comparator amplifier 407 goes to the "1" level, and the AND gate 410 resets the flip-flop 411 through the timing pulse _T1 , which is set by _T2 , so that waveform F is obtained. . When this is applied to the D-type flip-flop 412, a waveform G is obtained in synchronization with the rising edge of the waveform obtained by inverting the timing pulse _T1 . Waveform G is integrated by an integrating circuit consisting of resistor 413 and capacitor 414 to obtain waveform H.
Waveform H is at the level set by level setter 416
When E ₄ or more, waveform I is obtained from the comparator amplifier 415. The output of the comparator amplifier 415 is a signal "L" when the abnormal arc discharge continues at a predetermined level _E4 , that is, for a predetermined time or more, and the discharge time detection signal obtained from the AND gate 408 is output to the output of the AND gate 418. It will no longer be done. Conversely, when the abnormal arc discharge lasts for a predetermined period of time or less, it is considered to be an effective discharge. The output of the AND gate 418 is integrated by a resistor 420 and a capacitor 422, and is obtained as an effective discharge rate detection signal from a terminal 424, and experiments have shown that this signal has a one-to-one correspondence with the machining speed. . Further, the output of the AND gate 419 is converted into a direct current as a continuous abnormal arc discharge detection signal by an integrating circuit consisting of a resistor 421 and a capacitor 423, and is outputted to a terminal 425. As the machining shape becomes more complex or the machining progresses, one of the above control factors must be sequentially repeated and searched again. In such a case, the search sequence circuit 23 should be changed in advance, for example, after searching all the control factors mentioned above in the initial search, in the re-search, the machining fluid pressure and the electrode vertical hunting cycle may be changed independently or alternately at regular intervals. You may search repeatedly. Note that when the number of signals output from the sustained abnormal arc detection signal output terminal 425 of the discharge state detection circuit 4 exceeds a predetermined number, the electrode raising circuit 5 is activated to separate the electrode 2 from the workpiece 3. Alternatively, it goes without saying that the processing pulse can be stopped by activating the pulse pause circuit 6.

As described above, the present invention adjusts any of machining stability factors such as set voltage, pulse duty factor, hunting period, machining fluid pressure, etc. in a predetermined order and within a predetermined control range according to the shape of the workpiece material. , while detecting the effective discharge rate that occurs in the machining gap between the electrode and the workpiece by changing the order with a predetermined gap, and calculating the effective discharge rate for the set value of the changed control factor. This effective discharge rate is searched in correspondence with the above setting value, and electric discharge machining is performed by controlling the value of the predetermined control factor so that the effective discharge rate becomes the optimum value of the control factor that maximizes the effective discharge rate. Because it is an electric discharge machining control device,
Even if the material of the electrode or workpiece changes, the optimum value of the control factor is always automatically determined, and efficient and stable electrical discharge machining can be performed. Further, since sustained abnormal arc discharge is detected and the electrode is raised and the pulse is stopped, it is possible to prevent abnormal traces from occurring.

[Brief explanation of the drawing]

1 and 2 are characteristic diagrams for explaining the present invention, FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 is a circuit specifically showing a part of FIG. 3. 5 is a timing chart explaining the operation of FIG. 4. DESCRIPTION OF SYMBOLS 1... Pulse power supply, 2... Electrode, 3... Workpiece, 4... Discharge state detection circuit, 5... Electrode raising circuit, 6... Pulse pause circuit, 7... Analog-digital converter, 8 ... Maximum value memory, 9 ... Shift register, 10 ... Size discrimination circuit, 12 ...
Shift register, 13...multivibrator,
14... Reversible counter, 15... Switching circuit, 16
...Initial value setting circuit, 17, 27...Decoder,
18, 26...Loader switch, 22...Clock circuit, 23...Search sequence circuit.

Claims (1)

[Claims] 1. In a control device that determines the optimum value of the machining stability factor of an electric discharge machine, an effective discharge detector is used to detect the effective discharge rate, and a search for the set voltage, pulse duty factor, machining fluid pressure, and hunting period is required. A circuit that variably sets the initial value, upper limit value, and lower limit value to predetermined values in conjunction with switching of electrodes and workpieces; a search sequence circuit for repeatedly searching within the range, a maximum value discrimination circuit for determining the maximum value of the effective discharge rate during the search, and each machining stability factor corresponding to the maximum value of the effective discharge rate during the search. An electrical discharge machining control device comprising a storage device for storing an optimum value of.