JP4381223B2 - EDM power supply - Google Patents

Description

  The present invention relates to an electric discharge machining power supply device, and more particularly, to an electric discharge machining power supply device that improves the machining surface roughness of a workpiece.

  In general, an electrical discharge machining device continuously applies a high DC voltage between the electrodes and the workpiece or periodically applies a high voltage pulse to induce a discharge in the gap between the electrodes and the workpiece. A pulse generating power source that is used for both electrical discharge induction and electrical discharge machining that breaks down and processes a workpiece. When electric discharge starts due to dielectric breakdown, machining waste accumulates and a short circuit occurs, so that a pause is provided in which no voltage is applied between the electrode and the workpiece to prevent this.

  When DC high voltage is continuously applied, discharge starts due to dielectric breakdown after voltage application, that is, when the search time ST for starting discharge elapses, the τON voltage is continuously applied for a predetermined time to perform discharge machining. After that, the DC high voltage is applied again after waiting for the rest time τOFF. The electric discharge machining is performed by repeating such electric discharge induction, electric discharge machining, and pause operations.

  When applying a high voltage pulse periodically, when discharge starts due to dielectric breakdown, in the pulse period, the pause time during discharge machining is longer than the pause time when the discharge is induced before discharge machining. Electric discharge machining is performed by applying a pulse voltage.

  An electric discharge machining apparatus called a capacitor system is known. In this method, the voltage of a capacitor charged by a DC voltage source is applied between the electrode and the workpiece, and electric discharge machining is performed by periodically repeating discharge induction, electric discharge machining, and pause operations. Since the insulation state between the electrode and the workpiece is constantly changing, it is not determined at which voltage of the capacitor voltage that changes with the time constant CR of the charging resistance R and the capacitance C of the capacitor during charging. . Therefore, the electric discharge machining voltage is not determined and the surface roughness of the workpiece becomes non-uniform.

  Moreover, the detection of dielectric breakdown, that is, the start of electric discharge machining is usually performed by detecting the fall of the voltage between the electrodes, and after the detection, charging from the power source to the capacitor is stopped. If this detection is delayed due to the characteristics of the electric circuit, electric discharge machining will be performed while charging continues for that delay time, and therefore the electric discharge machining current will also increase, making it unsuitable for machining with fine surface roughness. . In addition to the charging capacitor, the power feeding circuit has a stray capacitance, so that the combined capacitor capacity increases, and therefore the electric discharge machining current also increases, making it unsuitable for machining with fine surface roughness.

  A capacitor-type electric discharge machining apparatus is disclosed in Patent Document 1. This device releases the charge from the power supply to the capacitor after the capacitor charge is almost saturated, applies the voltage of the charged capacitor between the electrodes, induces discharge, performs electrical discharge machining by dielectric breakdown, When the discharge voltage is almost zero volts, the discharge circuit from the capacitor to the pole is cut off, and the peak value of the charge voltage during charging is compared with the reference voltage when the discharge machining is stopped. A series of cycles for detecting whether or not is good is executed. This peak value is lowered when insulation is defective.

JP-A-5-337738 (see paragraph numbers [0010] to [0013] of the specification and FIGS. 1 to 3 of the drawings).

As described above, in the electric discharge machining power supply device of the capacitor type according to the prior art, the inter-electrode voltage at the start of discharge changes every cycle of the pulse voltage application, so the machining current also changes and the surface roughness of the workpiece is made uniform. There is a problem that it cannot be processed.
Also, in the electric discharge machining power supply device of the prior art, a delay occurs in the detection of the dielectric breakdown between the electrodes, and the capacitor capacity including the stray capacitance is increased, so that the electric discharge machining current is increased and the fine surface roughness of the workpiece is increased. There is a problem that it is not suitable for processing.

  In the device described in Patent Document 1, the capacitor must be sufficiently charged before the capacitor charging voltage is applied between the electrodes in order to induce discharge, and it takes time until the discharge is induced. If there is a problem that the efficiency deteriorates and no discharge occurs after the charging voltage is applied, it is impossible to judge whether the insulation state between the electrodes is good or not when the electric discharge machining is stopped. There arises a problem that the concentrated discharge occurs to deteriorate the machining quality of the workpiece.

  The electric discharge machining power supply device of the present invention is mainly intended to machine a workpiece with a uniform surface roughness during finishing machining, and has another object to enable machining with a fine surface roughness. Furthermore, another object of the electric discharge machining power supply apparatus of the present invention is to enable the determination of good / bad of the insulation state between the electrodes even when no discharge occurs every time the charging voltage is applied.

The electric discharge machining power supply device according to the present invention that achieves the above object is an electric discharge machining power supply device that applies electric voltage between the electrode and the workpiece to discharge-machine the workpiece.
A DC power supply for applying a high-value pulse voltage that induces a discharge between the electrodes;
A first switching element connected in series to one side of a line connecting the DC power source and the poles;
A capacitor connected in parallel to the first switching element and having a constant or variable capacitance;
An inductor inserted at a position separating the line in which the electrode, the workpiece, and the capacitor are connected in series to the DC power source from the DC power source;
A voltage monitoring circuit that monitors a charging voltage of the capacitor and determines whether the gap is in an insulated state or an energized state; and
A second switching element that opens and closes a closed circuit in which the DC power source and the inductor are connected in series;
A first control circuit that opens and closes the first and second switching elements to control charging / discharging of the capacitor and supply electric power of a low DC voltage that does not induce discharge between the electrodes, and a determination result of the voltage monitoring circuit A pause time setting circuit for setting a pause time from application to application of the next pulse voltage, and opening and closing the first and second switching elements to generate a high pulse voltage capable of inducing a discharge between the electrodes from the DC power supply A control circuit comprising a second control circuit ;
It is comprised and comprises.
With the above configuration, the electric charge of the capacitor when a pulse voltage is applied between the electrodes for electric discharge machining is constantly emptied, and machining can be performed so that the surface roughness of the workpiece is uniform.
In the electric discharge machining power supply device, the capacitance of the capacitor is variable. Thereby, the surface roughness of the workpiece can be varied, and processing with a fine surface roughness is enabled.

With the above configuration , the insulation state between the poles is detected and feedback control is performed so that the processing time can be shortened so that it can be judged whether the insulation state between the poles is good or bad even when no discharge occurs every time the charging voltage is applied. Can do.

With the above configuration, a DC power supply that supplies a low voltage without providing a high-voltage pulse power supply for inducing discharge, an inductor, a second switching element, and a second switching control circuit that controls opening and closing of the second switching element, Thus, a high voltage short pulse width pulse for inducing discharge can be applied between the electrodes.

According to the present invention, due to the switching element, the capacitor, and the switching control circuit, the electric charge of the capacitor is constantly emptied when the electric discharge machining pulse is applied between the electrodes, and the voltage between the electrodes at the start of discharge becomes substantially constant. Therefore, the surface roughness of the workpiece becomes uniform. By varying the capacitance of the capacitor, the surface roughness of the workpiece can be varied, and processing with fine surface roughness is possible. In addition, by providing a voltage monitoring circuit and a control circuit, it is possible to determine whether the gap is short-circuited or insulated, and feedback control of the determination result eliminates the cause of the short-circuit or provides a pulse voltage pause time. Electrical discharge machining can be performed under conditions with good machining efficiency.
Also, without using a high voltage pulse power supply, a low voltage DC power supply, an inductor, a second switching element, and a second switching control circuit can supply a pulse voltage with a short pulse width between the electrodes, Fine processing with improved surface roughness is realized.

  FIG. 1 is an electric circuit diagram of an electric discharge machining power supply apparatus according to the first embodiment of the present invention. The electric discharge machining power supply apparatus shown in FIG. 1 is one that performs electric discharge machining between the electrode 1 for machining and a workpiece 2 that is a workpiece, that is, within a gap GAP. This device induces a discharge between the electrode 1 and the work 2 and a relatively high pulse power source PG that applies a pulse voltage of, for example, 100 volts, which can induce a discharge between the electrode 1 and the work 2. A DC power source V1 for supplying power of a DC voltage lower than, for example, several tens of volts, a switching element S1 having an anode connected to the work 2 and a cathode connected in series to the cathode of the DC power source V1, and a switching element S1 A switching control circuit (not shown) for controlling opening and closing (on / off), a capacitor C1 connected in parallel to the switching element S1, and a voltage monitoring circuit MC for monitoring a charging voltage of the capacitor C1 and determining a state between the electrodes And a control circuit (not shown) for controlling the time until the next pulse voltage application according to the state. The smaller the capacitance of the capacitor C1, the smaller the current during electric discharge machining, so that the surface roughness of the workpiece 2 can be improved. The capacitance of the capacitor C1 may be a constant value according to the surface roughness to be obtained, and the minimum value of the capacitance of the capacitor C1 is a stray capacitance of the line.

  The workpiece 2 is placed in the processing tank 3 so as to face the electrode 1, and oil is injected into the processing tank 3 as a processing liquid 4. The electrode 1 is moved toward the machining position of the workpiece 2 by driving a servo motor (not shown) so that the discharge gap GAP with the workpiece 2 has a predetermined length.

FIG. 2 is a time chart of the operation of the electric circuit shown in FIG. In FIG. 2, the horizontal axis represents time, the vertical axis represents the voltage for the pulse voltage VPG and the charging voltage VC1, the current for the charging current IC, and the switching element S1 being on at high level and off at low. Show by level.
At the first time t0, the pulse voltage VPG having a predetermined cycle is not applied between the electrode 1 and the work 2 from the pulse power source PG, and the switching element S1 is off. In the first step, a pulse of the pulse voltage VPG is applied between the electrode 1 and the work 2 from the pulse power source PG at a predetermined cycle from the time t1 while the S1 is turned off.

  In the second step, dielectric breakdown occurs due to the application of the fifth pulse at time t2, discharge starts, charging current IC flows from DC voltage source V1 to capacitor C1, and capacitor C1 is charged at the same time. At t3, the charging voltage VC1 across the capacitor C1 rises to the saturation voltage. In addition, the gap voltage VG between the electrodes 1 and the workpiece 2 gradually decreases as the charging progresses between times t2 and t3, the GAP insulation is restored, and the charging current IC is interrupted at time t3. After the application of the pulse voltage VPG from the time t1, immediately after the fifth pulse application, if the charging voltage VC1 rises, either the GAP is induced to discharge and break down or a short circuit occurs. That is, if there is no increase in the charging voltage VC1 just after the application of the first to fourth pulses, the induction of discharge has swung.

  It is determined by the voltage monitoring circuit MC that monitors the charging voltage VC1 of the capacitor C1 whether the discharge gap GAP is induced to cause a dielectric breakdown, a short circuit has occurred, or the discharge induction is lost. The voltage monitoring circuit MC compares the charging voltage VC1 with the first comparator level CL1, and determines that the dielectric breakdown occurs when VC1 ≧ LV1, and determines that the discharge induced idling occurs when VC1 <LV1. The voltage monitoring circuit MC compares the charging voltage VC1 with the second comparator level CL2 (CL1 << CL2 <V1, where V1 is the voltage of the DC voltage source V1), and determines that a short circuit occurs when VC1 ≧ LV2. When VC1 <LV2, it is determined that dielectric breakdown or discharge-induced idling occurs.

  The advantage of this voltage monitoring circuit MC is that, in order to detect the occurrence of dielectric breakdown between the electrodes due to the conventional discharge induction, the voltage between the electrodes must be measured when a short pulse is applied. Although the measurement result is obtained, the voltage monitoring circuit MC only needs to measure the charging voltage of the capacitor C1, not the voltage between the electrodes, and can measure within a relatively long time when a short pulse is not applied. Therefore, stable and reliable measurement results can be obtained.

  The control circuit applies the next second to fifth pulses from the pulse power supply PG if the charging voltage VC1 does not increase as immediately after the first to fourth pulses are applied. If the charging voltage VC1 rises immediately after the fifth pulse is applied, the suspend time τOFF is waited in the second step, the switching element S1 is turned on at time t11 in the third step, and the capacitor C1 is turned on. Start discharging the charged charge.

  Next, after the switching element S1 is turned off at time t12, the charge charged in the capacitor C1 becomes empty, and if there is no increase in the charging voltage VC1 of the capacitor C1, the GAP is in an insulated state, and there is an increase in the charging voltage VC1. Then, GAP determines with a short circuit state. This determination is performed by the voltage monitoring circuit MC that monitors the charging voltage VC1 of the capacitor C1 by comparing VC1 with the first comparator level CL1. As after the fifth pulse application, the charge charged in the capacitor C1 after the switching element S1 is turned off at time t12 is empty, so that the charging voltage VC1 does not increase and the GAP is insulated. If so, the next sixth pulse is applied from the pulse power source PG at time t13. As in the case of the sixth pulse application, the electric charge of the capacitor C1 when the pulse is applied for electric discharge machining is constantly empty, so that the surface roughness of the workpiece can be made uniform, That is, the discharge traces of the workpiece 2 can be made uniform.

  On the other hand, after the eighth pulse application, the switching element S1 is turned on at time t21, the discharge of the charge charged in the capacitor C1 is started, and then the switching element S1 is turned off at time t22. After the charging voltage VC1 is increased and the voltage monitoring circuit MC determines that the GAP is in a short-circuited state, in the fourth step, after applying the next ninth pulse in order to urge the discharge again at time t23. , Wait for the downtime τOFF. Here, without applying the ninth pulse, it is determined that a short circuit has been detected by the voltage monitoring circuit MC, and the machining is interrupted. For example, the machining axis jump operation is performed for the purpose of removing machining debris between the electrodes. For example, the machining may be resumed after removing the cause of the short circuit. This determination is performed by the voltage monitoring circuit MC that monitors the charging voltage VC1 of the capacitor C1 by comparing VC1 with the second comparator level CL2.

  In the fifth step, the switching element S1 is turned on again at time t31, and discharging of the charge charged in the capacitor C1 is started. If the charging voltage VC1 does not increase at time t32, it is determined by the voltage monitoring circuit MC that the GAP has returned to the insulated state, and the next tenth pulse is applied from the pulse power source PG at time t33. To resume. On the other hand, when the charging voltage VC1 rises at time t32 and the voltage monitoring circuit MC determines that the short circuit state of GAP is continuing, the processing is interrupted and the processing is performed after removing the cause of the short circuit as described above. You may resume.

  As described above, by monitoring the charging voltage VC1 of the capacitor C1 by the voltage monitoring circuit MC, it is possible to determine whether the discharge gap GAP is in an insulated state or an energized state including a short circuit state, and according to the determination result. The control circuit can determine how long the rest time is to be waited for and then apply the pulse voltage between the electrodes, thereby reducing the machining time. Specifically, if the discharge gap GAP is in an insulated state after the induction of discharge, the next pulse voltage is applied between the electrodes after a short period of T pause, as in the case of applying the second to fifth pulses. If the discharge gap GAP is in an energized state later, the next pulse voltage is applied between the electrodes with a τOFF pause for a long time, as in the application of the sixth pulse.

  FIG. 3 is an electric circuit diagram of the electric discharge machining power supply apparatus according to the second embodiment of the present invention. The electric discharge machining power supply apparatus of the second embodiment is the electric discharge machining power supply apparatus shown in FIG. 1, in which an inductor L1 and a switching element S2 are arranged instead of the pulse power supply PG, as shown in FIG. A switching control circuit (not shown) for controlling on / off is provided to generate a high voltage pulse with a short pulse width from the DC power supply V1. The switching control circuit for turning on / off the switching element S2 is incorporated in the switching control circuit (not shown) for turning on / off the switching element S1 described with reference to FIG.

  Next, generation of a high voltage pulse by the electric discharge machining power supply device of the second embodiment shown in FIG. 3 will be described below. Initially, both switching elements S1, S2 are off. In the first step, S2 is turned on while S1 is turned off. Then, a current flows from the DC power supply V1 through S2.

  In the second step, S2 is turned off instantaneously while S1 is turned off. Then, since the current flowing through S2 from the DC power supply V1 is instantaneously interrupted, the inductor L1 between the positive terminal of V1 and the open end side of S2 has a peak value several to several tens of times higher than the voltage of V1. Is induced and applied to the electrode 1. In order to make the peak value of the pulse voltage VP higher and to make the pulse width longer, it is necessary to take a longer time to turn on S2. The peak value and the pulse width are determined by the pulse voltage at the time of interruption, the interruption current, the inductance of the closed circuit before the interruption, and the turn-off response characteristic of the switching element S2.

  In the third step, S1 is turned on while S2 is turned off. Then, the electric charge charged in the capacitor C1 flows through S1 and is discharged. Thus, by repeatedly executing the first to third steps, a pulse having a pulse width shorter than the response time of the switching element is supplied without supplying a high voltage pulse between the electrode 1 and the workpiece 2. Thus, fine processing with improved surface roughness of the workpiece 2 is realized.

  As described above, according to the electric discharge machining power supply device of the present invention, machining can be performed so that the surface roughness of the workpiece is uniform, processing of fine surface roughness is possible, and machining efficiency is excellent. Can be. In addition, the electric discharge machining power supply device of the present invention can determine whether the insulation state between the electrodes is good or bad even when no discharge occurs every time the charging voltage is applied, by the voltage monitoring circuit that monitors the charging voltage of the capacitor. Can detect the insulation state.

The electric discharge machining power supply apparatus according to the present invention can process a workpiece with a surface roughness suitable for the machining conditions by varying the capacitance of the capacitor.
In this embodiment, the workpiece is connected to the anode of the DC power source and the electrode to the cathode. However, depending on the processing conditions such as the electrode material and workpiece material, there is a connection of reverse polarity.

It is an electric circuit diagram of the electric discharge machining power supply device according to the first embodiment of the present invention. It is a time chart of operation | movement of the electric circuit shown in FIG. It is an electric circuit diagram of the electric discharge machining power supply device according to the second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Work 3 ... Processing tank 4 ... Processing liquid V1 ... DC power supply PG ... Pulse power supply S1, S2 ... Switching element C1 ... Capacitor MC ... Voltage monitoring circuit GAP ... Discharge gap L1 ... Inductor

Claims (1)

In an electric discharge machining power supply device that applies electric voltage between the electrode and the workpiece to perform electric discharge machining on the workpiece,
A DC power supply for applying a high-value pulse voltage that induces a discharge between the electrodes;
A first switching element connected in series to one side of a line connecting the DC power source and the poles;
A capacitor connected in parallel to the first switching element and having a constant or variable capacitance;
An inductor inserted at a position separating the line in which the electrode, the workpiece, and the capacitor are connected in series to the DC power source from the DC power source;
A voltage monitoring circuit that monitors a charging voltage of the capacitor and determines whether the gap is in an insulated state or an energized state; and
A second switching element that opens and closes a closed circuit in which the DC power source and the inductor are connected in series;
A first control circuit that opens and closes the first and second switching elements to control charging / discharging of the capacitor and supply electric power of a low DC voltage that does not induce discharge between the electrodes, and a determination result of the voltage monitoring circuit A pause time setting circuit for setting a pause time from application to application of the next pulse voltage, and opening and closing the first and second switching elements to generate a high pulse voltage capable of inducing a discharge between the electrodes from the DC power supply A control circuit comprising a second control circuit ;
An electric discharge machining power supply device comprising:

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