CN1069856C - Wire cutting electrical discharge machining control method and device - Google Patents

Abstract

The invention provides a linear cutting discharge machining control method and a device, which can avoid the electrolysis phenomenon of a workpiece and improve the quality of a die; the composition comprises: the pulse generator, the negative low-voltage power supply circuit, the positive low-voltage power supply circuit and the negative high-voltage power supply circuit; controlling the discharge waveform on a full-crystal discharge structure, detecting the condition of a machining gap by using low voltage before applying high-voltage discharge each time, judging whether the discharge is normal discharge, arc discharge or open circuit, and adjusting high-voltage discharge energy to obtain high-speed and stable machining; and according to the output of the low-voltage ignition commutation control circuit, the polarity of the ignition voltage is switched, so that the purpose of alternating-current ignition is achieved.

Description

Wire cutting electrical discharge machining control method and device

The present invention relates to a control method and device for wire-cut electric discharge machining, in particular to a control method and device for wire-cut electric discharge processing with high-voltage discharge energy and high-speed detection of machining gap conditions with AC ignition low voltage.

The traditional wire-cut electric discharge machining circuit uses a unipolar power supply for ignition and processing, as shown in Figure 1, 1 is a pulse generator, 2 is a negative high-voltage power supply circuit, 3 is a negative low-voltage power supply circuit, and 4 is a wire Pole, 5 is the workpiece. Its operation method is as follows: First, the pulse generator 1 generates a control signal to turn on the switch 6 (ON), and the negative low voltage source 7 applies a voltage to the discharge gap between the wire electrode 4 and the workpiece 5 for ignition detection. If the voltage is lower than the reference voltage Vref, it means that the ignition is successful, then the switch 6 is turned off (OFF) and the switch 10 is turned on, then the supply voltage of the negative high voltage source 11 will be applied to the gap through the switch 10 for processing, after a period of processing Finally, the switch 10 is also turned off, so the discharge gap enters the state of resting insulation recovery, and after a period of OFF, the switch 6 is turned on again for the next complete ignition discharge cycle. Resistor 8 in the negative low voltage power supply circuit 3 is a current limiting resistor to prevent excessive current during discharge; diode 9 is used to prevent the voltage of negative high voltage power supply 11 from entering negative low voltage power supply 7 in reverse during discharge. Because this discharge structure and control method adopt the unipolar power supply, the workpiece 5 is always in the positive polarity, and the line pole 4 is in the negative polarity. Electrolysis will also occur while being processed, so electrolytic cracks will occur on the surface of the workpiece 5, resulting in oxidation and rust. As a result, not only the roughness of the processed surface will deteriorate, but also the life of the mold will be reduced.

The object of the present invention is to provide a wire cutting EDM control method and device for detecting the condition of the discharge gap and adjusting the discharge energy according to the ignition result.

Another object of the present invention is to provide a wire-cut electric discharge machining control method and control method that utilizes a timing circuit to record the accumulated time of low-voltage ignition, and adjusts the polarity of the ignition voltage according to the accumulated time to achieve AC ignition and avoid electrolysis. device.

The wire cutting EDM control method of the present invention includes the following steps:

(1) First, the polarity of the low-voltage ignition is determined according to the output of the low-voltage ignition commutation control circuit. If it is a negative polarity ignition, the switch of the negative low-voltage power supply circuit is turned on, and a detected negative voltage is applied in the discharge gap. If For positive ignition, the switch of the positive low-voltage power supply circuit is turned on, and a detected positive voltage is applied to the discharge gap;

(2) After a period of time T1, start to detect the level of the discharge gap voltage. If the gap voltage does not enter the window shape comparison range established by the reference voltage Vref1 and Vref2, it means that the discharge is a normal discharge or an open circuit; if the gap If the voltage has entered the range of the reference voltage Vref1 and Vref2 at this time, it means that the discharge is an arc discharge; if the voltage has not entered the range of Vref1 and Vref2 after a longer time T2, it means that the discharge gap remains open ;

(3) If the discharge is a normal discharge or an arc discharge, turn on the switch of the high-voltage power supply circuit, apply a high discharge voltage in the discharge gap, and control different discharge times (On Time), so that the arc discharge time It is about half of the normal discharge time; after discharge, the switch of the high-voltage power supply circuit is turned off, and a different off time (Off Time) is imposed;

(4) If the discharge is in an open circuit state, the switch of the high-voltage power supply circuit is not turned on, and directly enters the short rest time T3;

(5) After the rest time T3 ends, enter the next ignition discharge cycle;

(6) In the process of low-voltage ignition, use a set of timers to time the low-voltage ignition time. If the cumulative ignition time of the same polarity does not reach the set time T4, the same polarity is allowed for the next ignition. If the same polarity If the accumulative ignition time has reached the set time T4, the next ignition will change the voltage polarity to make the ignition voltage AC change.

The wire cutting EDM control device of the present invention comprises: a negative low voltage power supply circuit, a positive low voltage power supply circuit, a high voltage power supply circuit, and a pulse generator, and the pulse generator controls the negative low voltage according to different discharge conditions. The power supply sequence of the power supply circuit, the positive low voltage power supply circuit, and the high voltage power supply circuit; the high voltage power supply circuit uses the negative low voltage power supply circuit or the positive low voltage power supply circuit to detect the status of the processing gap before each high voltage discharge , judge whether the discharge is normal discharge, arc discharge or open circuit, and then adjust the high-voltage discharge energy; and switch the polarity of the ignition voltage according to the output of the low-voltage ignition commutation control circuit to achieve the purpose of AC ignition.

From the following detailed description, in conjunction with the accompanying drawings, the above-mentioned purpose and other advantages of the present invention will become more apparent, wherein:

Fig. 1 is the circuit diagram of known wire-cut electrical discharge machining device;

Fig. 2 is the circuit diagram of the wire-cut electrical discharge machining device of the present invention;

Fig. 3 is the circuit block diagram of the pulse generator in the wire-cut electrical discharge machining device of the present invention;

Fig. 4 is the circuit diagram of the low-voltage ignition commutation control in the wire-cut electrical discharge machining device of the present invention;

Fig. 5 is a schematic diagram of the action of the window comparator in Fig. 3;

Fig. 6 is the waveform and sequence diagram of the wire-cut electric discharge machining device of the present invention during normal discharge;

Fig. 7 is a waveform and sequence diagram of the wire-cut electric discharge machining device of the present invention during arc discharge;

Fig. 8 is the waveform and sequence diagram of the wire-cut electrical discharge machining device of the present invention when it is open;

FIG. 9 is a timing diagram of the wire-cut electrical discharge machining device in the low-voltage ignition commutation controller of the present invention.

The circuit diagram of the wire-cut electrical discharge machining device of the present invention is as shown in Figure 2, wherein 1a is a pulse generator, which produces control signals that make transistor switches 6, 10, 12 turn on or off respectively (signal waveforms are respectively S1, S2 , S3); resistor 8, diode 9, switch 6 and negative low voltage source 7 form a negative low voltage power supply circuit; resistor 8, switch 12, diode 13 and positive low voltage source 14 form a positive low voltage power supply circuit; 2 is a negative High-voltage power supply circuit; the upper current limit resistor 8 of the ignition circuit prevents the current from being too large during discharge, and the diodes 9 and 13 are used to limit the current path of the ignition circuit.

The wire-cut electric discharge processing device of the present invention controls the timing of the switches 6, 10, 12 by the pulse generator 1a according to different discharge conditions, and the method is as follows:

(1) First, the polarity of the low-voltage ignition is determined according to the output of the low-voltage ignition commutation control circuit. If it is a negative polarity ignition, the switch 6 is turned on, and a detection voltage V1 (negative voltage) is applied in the discharge gap. If it is a positive polarity The permanent ignition makes the switch 12 conduct, and applies a detection voltage V3 (positive voltage) in the discharge gap. (2) After a period of T1 (about 1μs-2μs), start to detect the level of the discharge gap voltage. If the voltage does not enter the window-shaped comparison range established by the reference voltage Vref1 and Vref2, it means that the discharge is a normal discharge. Or an open circuit; if the gap voltage has entered the range of the reference voltage Vref1 and Vref2 at this time, it means that the discharge is an arc discharge; if after a longer time T2 (about 40μs-60μs), the voltage has not yet entered Within the range of Vref1 and Vref2, it means that the discharge gap remains open.

(3) If the discharge is a normal discharge or an arc discharge, turn on the switch 10, apply a discharge voltage V2 in the discharge gap, and control different discharge times (On Time), so that the time of the arc discharge is approximately the normal discharge half of the time, in order to prevent excessive energy during arc processing and cause disconnection, and at the same time increase the processing speed, after the discharge, the switch 10 is turned off, and a different off time (Off Time) is applied to facilitate the discharge gap Restore insulation.

(4) If the current discharge is in an open circuit state, the switch 10 is not turned on, and directly enters a short rest time (about 40 μs-60 μs).

(5) After the off time (Off Time) ends, enter the next ignition discharge cycle.

(6) In the process of low-voltage ignition, use a set of timers to time the low-voltage ignition time. If the cumulative ignition time of the same polarity does not reach the set time (about 40μs-60μs), the next ignition is allowed to use the same polarity. Polarity, if the cumulative ignition time of the same polarity has reached the set time, the next ignition will change the voltage polarity, so that the ignition voltage will produce AC changes.

The circuit block diagram of the pulse generator 1a in FIG. 2 is shown in FIG. 3 . The voltage feedback between the workpiece 5 and the wire electrode 4 is introduced into the window comparator (Window Comparator) 15 through the discharge gap, and the output signal of the window comparator 15 enters the logic control circuit 16 to judge the discharge state of the gap. The discharge time (On Time) and the rest time (Off Time) are set by the main control computer (Host Computer) 17 via the input port 18 to set the initial state of the counting circuit 19, and the time base generation circuit (Time-base Generator) 20 is used to Generate the reference time base required for counting and logic control, the low-voltage ignition commutation control circuit (Phase-convert control circuit for low-voltage ig-nition) 21 is used to determine the voltage source used in the next ignition cycle, and finally control the signal 23 The on/off of the transistor switches 6 , 10 , 12 is controlled by the output port 22 .

The circuit block diagram of the low-voltage ignition commutation control circuit 21 in FIG. 3 is shown in FIG. 4 . The signal S1 applied to the switch 6 and the signal S3 applied to the switch 12 are respectively ignition signals of different voltage polarities, and the high-frequency clock pulse signal (Clock) of the time base generation circuit 20 is used as the carrier wave, as the timer 24, 25 Up-counting trigger signal, respectively counting the conduction time of S1 and S3, the output signals S1-disable and S3-disable are respectively the prohibition signals of S1 and S3, which are used to control the polarity of the ignition voltage, T-SET1 and T-SET2 The signal is used to set the count value (40 μs-60 μs) of the timer 24 and the timer 25 , which can be determined by the main control computer 17 . The inputs 27, 28, and 29 of the OR gate 26 are status signals of normal discharge (Normal), arc discharge (Arc), and open circuit (Open), respectively.

When the polarity of the low-voltage ignition is determined according to the output S1-disable and S3-disable of the low-voltage ignition commutation control circuit 21, if it is a negative polarity ignition, the switch 6 (signal S1) is turned on, and a detection voltage V1 is applied in the discharge gap (negative voltage), if it is a positive ignition, the switch 12 (signal S3) is turned on, a detection voltage V3 (positive voltage) is applied in the discharge gap, and the window comparator 15 of the pulse generator 1a starts to detect the attenuation The gap voltage Vgap.

After a period of time T1 (about 1μs-2μs), if the voltage does not enter the window-shaped comparison range established by the reference voltage Vref1 and Vref2, it means that the discharge is normal discharge (Normal) or open circuit (Open), if If the gap voltage has entered the range of the reference voltage Vref1 and Vref2 at this time, it means that the discharge is an arc discharge (Arc). In the range of Vref2, it means that the discharge gap remains open.

If this discharge is a normal discharge or an arc discharge, turn on the switch 10, apply a discharge voltage V2 in the discharge gap, and control different discharge times (On Time), so that the arc discharge time (Arc on time) is approximately Half of the normal on time to prevent wire breakage caused by excessive energy during arc machining, and at the same time increase the machining speed. After the discharge, the switch 10 is turned off, and different off-times (Off Time) are imposed, so as to restore the insulation of the discharge gap. The timing diagram of normal discharge is shown in Figure 6, and the timing diagram of arc discharge is shown in Figure 7.

If the current discharge is in an open circuit state, the switch 10 is not turned on, and a short rest time (about 4 μs-6 μs) is directly entered. Once an open circuit occurs, the polarity of the ignition voltage will be changed in the next ignition cycle to obtain an AC voltage change and avoid electrolysis. The timing diagram of the open circuit is shown in Figure 8.

FIG. 5 is a schematic diagram of the operation of the window comparator 15 in FIG. 3 . The reference voltage Vref1 is the reference voltage of the first comparator (CMP1), and the reference voltage Vref2 is the reference voltage of the second comparator (CMP2). In this example, the positive voltage of Vref1 is higher than the absolute value of the negative voltage of Vref2. When the detected discharge gap voltage Vgap does not enter the window-shaped comparison range established by the reference voltages Vref1 and Vref2, it indicates that the discharge is a normal discharge or an open circuit; if the gap voltage Vgap has entered the range of the reference voltages Vref1 and Vref2 at this time , it means that the discharge is an arc discharge; if after a longer period of time, the voltage still does not enter the range of Vref1 and Vref2, it means that the discharge gap remains open. Vs in the figure is the output signal waveform of the window comparator 15, and the Vs signal enters the logic control circuit 16 to judge the discharge state of the gap.

Fig. 6 is a waveform and timing chart of normal discharge. The pulse generator 1a generates control signals S1, S2, S3 for turning on or off the transistor switches 6, 10, 12 respectively. DMP is the cycle start signal for turning on the transistor switches 6 and 12. After the switch 6 is turned on for a period of time T1 (about (1 μs-2 μs), it starts to detect the level of the discharge gap voltage Vgap. In this example, during the detection time After T1, the voltage Vgap does not enter the window-shaped comparison range established by the reference voltages Vref1 and Vref2, indicating that the discharge is a normal discharge or an open circuit, but then the discharge gap voltage Vgap detected within a predetermined period of time enters Vref1 and Vref2 In the established window shape comparison range, so this discharge is a normal discharge. During the normal discharge machining, the voltage V2 is applied to the discharge gap to generate the machining current Igap of the triangular wave. After the machining discharge, the switch 10 is turned off (S2 signal ), give off time (Off Time), in order to restore the insulation of the discharge gap.

Fig. 7 is a waveform and sequence chart of arc discharge. If the gap voltage Vgap has entered the range of the reference voltage Vref1 and Vref2 within T1 after the switch 6 is turned on, it means that the discharge is an arc discharge; in the discharge time (On Time), the time of the arc discharge is approximately normal Half of the discharge time to prevent wire breakage due to excessive energy during arc machining. After the arc discharge, the switch 10 is turned off, and different off-times (Off Time) are imposed, so as to restore the insulation of the discharge gap.

Figure 8 is the waveform and sequence diagram of the open circuit. If after a longer time T2 (about 40μs-60μs), the gap voltage Vgap still does not enter the range of Vref1 and Vref2, it means that the discharge gap remains open, and the OPN signal is used to make the transistor switches 6 and 12 turn on. The waveform of the open cycle T2. If the current discharge is an open circuit state, the switch 10 is not turned on, and directly enters a short rest time (about 4 μs-6 μs).

Figure 9 is a timing diagram of the low-voltage ignition commutation control circuit. In the process of low-voltage ignition, use a set of timers to time the low-voltage ignition time. If the cumulative ignition time of the same polarity does not reach the set time (about 40μs-60μs), the same polarity is allowed for the next ignition. If the cumulative ignition time of the same polarity has reached the set time, as shown in the figure, the cumulative time of CNT1 of the timer 24 three times before S1 ignition has reached the set time, then the next ignition will change the voltage polarity, that is, it will become S1- The dis-able signal is enabled, and the S3-disable signal is disabled, so that the ignition voltage produces AC changes, and the CNT2 of the timer 25 accumulates time.

The ignition voltage V1 and V3 in Fig. 2 of the embodiment of the present invention and the ignition counting time T-SET1 and T-SET2 in Fig. 4 are all adjustable, if V1=V3 and T-SET1=T-SET2, then the ignition can be made The average voltage is 0. If you want to improve the effect of electrolytic control, you can make V3>V1 or T-SET2>T-SET1, so as to ensure that the workpiece is negative with respect to the wire.

Using the wire-cut EDM control method and device of the present invention to control the discharge waveform can control the discharge energy in the most appropriate range, and has the function of automatic phase change of the ignition voltage to obtain the processing effect of high speed, continuous wire, and preventing electrolysis.

Although the present invention has been described by examples, it should be understood that without departing from the broad spirit and viewpoint defined in the scope of the appended claims of the present invention, various changes or modifications shall fall within the scope of the present invention.

Claims (9)

1. A control method for wire-cut electrical discharge machining, the method comprising the following steps: (1) Use the low-voltage ignition commutation control circuit to time the low-voltage ignition time. If the cumulative ignition time of the same polarity does not reach the set time T4, it is allowed to use the same polarity for the next ignition. If the cumulative ignition time of the same polarity T4 has reached the set time, the next ignition will change the voltage polarity; (2) Determine the polarity of the low-voltage ignition according to the output of the low-voltage ignition commutation control circuit. If it is a negative polarity ignition, a detected negative voltage will be applied in the discharge gap. If it is a positive polarity ignition, a detected negative voltage will be applied in the discharge gap. positive voltage; (3) Use the first reference time signal with a period of T1 and the second reference time signal with a period of T2 to detect the change of the gap voltage, where T1<T2, use the window comparator to judge whether the discharge is a normal discharge, Arc discharge or open circuit, if the gap voltage enters the range of the reference voltage Vref1 and Vref2 of the window comparison within the time T1, it means arc discharge occurs, and if the gap voltage enters the window comparison within the time T1 and T2 If the reference voltage is within the range of Vref1 and Vref2, it means normal discharge; if it does not enter the range of the reference voltage Vref1 and Vref2 for window shape comparison after T2, it means keep open circuit; (4) If the discharge is normal discharge or arc discharge, apply discharge voltage in the discharge gap, and control different discharge time (On Time), so that the time of arc discharge is half of the normal discharge time; after discharge, Apply different off time (Off Time); and (5) If the current discharge is in an open circuit state, no discharge voltage will be applied, and a short rest time T3 will be entered directly; the voltage polarity will be changed for the next ignition to obtain the effect of AC ignition. 2. The wire cutting EDM control method according to claim 1, wherein the T1 is 1 μs-2 μs; T2 is 40 μs-60 μs; T3 is 4 μs-6 μs; T4 is 40 μs-60 μs. 3. A wire cutting electrical discharge machining control device, comprising: Negative low voltage power supply circuit to detect the status of the machining gap with negative low voltage; The positive low voltage power supply circuit detects the status of the machining gap with positive low voltage; A high-voltage power supply circuit for machining with a high-voltage discharge applied to the machining gap; and The pulse generator controls the power supply timing of the negative low-voltage power supply circuit, the positive low-voltage power supply circuit, and the high-voltage power supply circuit according to different discharge conditions; In this way, the high-voltage power supply circuit uses the negative low-voltage power supply circuit or the positive low-voltage power supply circuit to detect the status of the machining gap before applying high-voltage discharge each time, and judges whether the discharge is normal discharge, arc discharge or open circuit. , and then adjust the high-voltage discharge energy, and switch the polarity of the ignition voltage according to the output of the low-voltage ignition commutation control circuit to achieve the purpose of AC ignition. 4. The wire cutting electric discharge machining control device according to claim 3, wherein the high voltage power supply circuit is a negative high voltage power supply circuit. 5. The wire-cut electric discharge machining control device according to claim 3, wherein all the wire-cut electric discharge machining control devices are transistor structures. 6. The wire cutting electric discharge machining control device according to claim 3, wherein the pulse generator includes a window comparator and a logic control circuit, and feeds back the voltage between the workpiece and the wire to the window comparator, and the window comparator The output signal of the comparator is sent to the logic control circuit to judge the discharge state of the gap. 7. The wire-cut electric discharge machining control device according to claim 3, wherein the low-voltage ignition commutation control circuit uses the count-up trigger signal of the timer to count the conduction time of the negative low-voltage power supply circuit and the positive low-voltage power supply circuit respectively, The commutation of the polarity of the ignition voltage is controlled by comparing with the reference time. 8. The wire-cut electric discharge machining control device according to claim 3, wherein the value of the positive low-voltage power supply is greater than the absolute value of the negative low-voltage power supply. 9. The wire cutting electric discharge machining control device according to claim 7, wherein the reference time compared with the conduction time of the positive low voltage power supply circuit is greater than the reference time compared with the conduction time of the negative low voltage power supply circuit .

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