JP4425056B2 - 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 suitable for fine machining.

  In general, an electric discharge machine applies a DC high voltage continuously between the electrode and the workpiece or periodically applies a high voltage pulse to induce a discharge in the gap between the electrode 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.

In electric discharge machining, finishing is generally performed after rough machining to increase the surface roughness of the workpiece. Regarding the relationship between the surface roughness and the pulse for electric discharge machining, Patent Document 1 discloses that the surface roughness of the workpiece is the product of the pulse application time (pulse width) PW (= τ _ON ) and the electric discharge current I during electric discharge machining. Therefore, it is disclosed that the pulse width PW or the discharge current I may be reduced to improve the surface roughness of the workpiece.

JP-A-58-28054 (refer to the second page of the specification, lines 3 to 5, page 7, Table 1 and FIG. 1 of the drawings).

As described in Patent Document 1, in order to improve the surface roughness of the workpiece, when the pulse width PW is reduced, the power source and the electrode or the electrode or the electrode or the electrode is periodically applied between the electrode and the workpiece. Since the switching element arranged between the workpiece and the workpiece has an on-time pulse width, a pulse having a pulse width shorter than the response time of the switching element cannot be generated, and the high-speed response characteristic of the element has a manufacturing limit. Therefore, there is a limit to reducing the pulse width PW.
In addition, there are two types of electric discharge machining apparatuses according to the prior art that induce electric discharge using only a large-capacity electric discharge machining power source, and one that includes a small-capacity electric power supply for electric discharge machining. Since the power source induces electric discharge and causes dielectric breakdown, a DC voltage of 70 V is required for low voltage and 100 to 300 V is required for high voltage depending on processing conditions. That is, the electric discharge machining apparatus according to the conventional technique has a problem that a special power source for supplying a high voltage pulse is required and the cost is increased.

  In order to solve the above-described problem, the present invention does not supply a high voltage pulse between the electrode and the workpiece, and supplies a pulse having a short pulse width PW, particularly during finishing, thereby reducing the surface roughness of the workpiece. An object of the present invention is to provide an electric discharge machining power supply device that enables improved machining.

An electric discharge machining power supply apparatus according to the present invention that achieves the above object is an electric discharge machining power supply apparatus that applies a pulse voltage between an electrode and a workpiece to perform electric discharge machining on the workpiece, and the power supply that applies a DC voltage between the electrodes. A first switching element connected in parallel to the power source, a second switching element connected in series between the first switching element and one end between the poles, an anode of the power source, and the first switching element And a control circuit for controlling the opening and closing of the first switching element and the second switching element, wherein the second switching element is turned off, switches on the first switching element from oFF, while the second switching element is turned off, turning on the first switching element Then, the pulse voltage obtained by boosting and converting the DC voltage of the power source is applied between the electrodes to break the insulation between the electrodes, and the discharge current passing between the electrodes is connected to one end between the electrodes. was charged in the floating capacitance generated line, the switching predetermined time to turn on the second switching element from the off the first switching element remains turned off, the control so as to discharge electrostatic charges charged in the stray capacitance And a control circuit for generating a pulse having a pulse width shorter than the response time of the first switching element .
With the above configuration, a pulse voltage having a short pulse width obtained by boosting the DC voltage of the power supply by the switching control of the first switching element can be applied between the electrodes, and the line of the electric discharge machining power supply apparatus can be controlled by the switching control of the second switching element. The charge charged in the stray capacitance is discharged.

In the electric discharge machining power supply apparatus comprises a pre-Symbol parallel connected capacitor to the second switching element. It is desirable that the inductance value of the line or inductor having the inductance and the capacitance value of the capacitor are variable.
More the inductor, can increase the pulse width of the pulse voltage applied between the electrode and eventually can increase the power supplied to the machining gap, and can be applied to various processing object. In addition, by adding the capacitor, the applied voltage at the time of dielectric breakdown between the electrodes is constant, so if the capacitor charge is emptied before the start of dielectric breakdown, at the time of electric discharge machining after dielectric breakdown Since the pulse voltage is applied under the same conditions, the discharge traces can be made uniform.
In the electric discharge machining power supply device, the peak value of the pulse voltage is variable. Thereby, the setting according to the dielectric breakdown voltage which changes with process conditions, such as an electrode, a workpiece | work, and a process liquid, can be performed.

According to the present invention, a pulse voltage having a short pulse width obtained by boosting the DC voltage of the power source by the opening / closing control of the first switching element can be applied between the electrodes, and It is possible to discharge the electric charge charged in the stray capacitance of the line or the capacitor connected in parallel to the second switching element. By repeatedly executing this step, a pulse having a pulse width shorter than the response time of the switching element can be supplied without supplying a high voltage pulse between the electrode and the workpiece, and the surface roughness of the workpiece can be reduced. Improved microfabrication is realized.
Further, the peak value of the pulse voltage obtained by boosting the voltage can be set in accordance with the dielectric breakdown voltage that varies depending on the machining conditions, thereby realizing fine machining of the workpiece.

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 device shown in FIG. 1 includes a DC voltage source V ₁ for applying a pulse having a low voltage of, for example, several tens of volts between the electrode 1 for machining and a workpiece 2 that is a workpiece, It has high-speed switching elements S1 and S2 made of a semiconductor such as an FET, and a control circuit (not shown) for controlling opening and closing (on / off) of the switching elements S1 and S2. 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 degree of insulation can be increased with oil rather than with water that is easily ionized as the working fluid. The electrode 1 is fed toward the machining location 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.

  The on / off control of the switching elements S1 and S2 by the control circuit during the finishing process after the roughing is performed as follows. Initially, both S1 and S2 are off. In the first step, S1 is turned on while S2 is turned off. Then, a current flows from the DC voltage source V1 through S1.

  In the second step, S1 is turned off instantaneously while S2 is turned off. Then, since the current flowing through S1 from the DC voltage source V1 is instantaneously interrupted, the line LINE (having inductance L0) between the positive terminal of V1 and the open end side of S1 is several times as large as the voltage of V1. A pulse voltage VP having a peak value ˜several times higher is induced and applied to the electrode 1. In order to increase the peak value of the pulse voltage VP and increase the pulse width, it is necessary to increase the time for turning on S1. 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 interruption, and the turn-off response characteristic of the switching element S1.

In the third step, when the discharge gap GAP breaks down due to the pulse voltage VP, a stray capacitance Cf is generated between the work 2 and the negative electrode of the DC voltage source V1, and the discharge current passing through the discharge gap GAP is charged into the stray capacitance Cf. To do. S2 is turned on while S1 is turned off. Then, the charge charged in Cf flows through S2 and is discharged.
As described above, by repeatedly executing the first to third steps, a pulse having a shorter voltage than the response time of the switching element can be obtained without supplying a high voltage pulse between the electrode 1 and the workpiece 2 as in the prior art. By supplying a pulse having a width, fine processing with improved surface roughness of the workpiece 2 can be realized.

  FIG. 2 is an electric circuit diagram of an electric discharge machining power supply device showing a modification of the first embodiment. The switching element S2 of FIG. 1 is provided between the anode of the DC voltage source V1 and the electrode 1. Also in this case, S2 is turned on after the discharge current passing through the discharge gap GAP is charged to the stray capacitance Cf. Then, as in the case of FIG. 1, the electric charge charged in the stray capacitance Cf flows through S2 and is discharged, and fine processing with improved surface roughness of the workpiece 1 is realized.

  FIG. 3 is an electric circuit diagram of the electric discharge machining power supply apparatus according to the second embodiment of the present invention. 1 is different from the electric circuit of the electric discharge machining power supply apparatus according to the first embodiment shown in FIG. 1 in that an inductor L1 is inserted into the line LINE in FIG. 1 and a capacitor C1 is connected in parallel to the switching element S2 in FIG. . In FIG. 3, voltages at both ends of the switching elements S1 and S2 are denoted as VS1 and VS2, respectively, current flowing through the switching element S1 is denoted as IS1, and current flowing through the discharge gap GAP between the electrode 1 and the work 2 is denoted as IG. Next, the procedure for on / off control of the switching elements S1 and S2 in the circuit shown in FIG. 3 during the finishing process after the roughing will be described with reference to the drawings.

  FIG. 4 is a time chart of the operation of the electric circuit shown in FIG. In FIG. 4, the horizontal axis indicates time, and the vertical axis indicates switching elements S1 and S2 with on being high and off with low level, IS1 with current and VS1 with voltage. The pulse application time when S1 is on in FIG. 4 is set to a constant time of 100 to 500 nS, for example, and the pause time when S1 is off is set to a constant time of 100 μS, for example. The timing for turning on S2 is set in a period in which S1 is off, and the time in which S2 is on is set to, for example, a constant time of 100 nS.

At the first time t0, the switching elements S1 and S2 are both off.
At time t1, S2 is turned on for a predetermined time while S1 is turned off. Then, the electric charge charged in the capacitor C1 flows through S2 and is discharged.
At time t2 (first step), S1 is turned on while S2 is turned off. Then, a current IS1 flows from the DC voltage source V1 through the inductor L1 and the switching element S1.

  At time t4 (second step), S1 is turned off instantaneously while S2 is turned off. Then, since the current IS1 flowing through S1 from the DC voltage source V1 is instantaneously cut off, the inductor L1 between the positive terminal of V1 and the open end side of S1 is several times to several tens of times higher than the voltage of V1. A pulse voltage VP having a peak value is induced and applied to the electrode 1. In order to increase the peak value of the pulse voltage VP and increase the pulse width, it is necessary to increase the time for turning on S1. 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 interruption, and the turn-off response characteristic of the switching element S1.

At time t11 (third step), S2 is turned on for a predetermined time while S1 is turned off. Then, the electric charge charged in the capacitor C1 flows through S2 and is discharged.
In this way, by repeatedly executing the first to third steps, a pulse width shorter than the response time of the switching element without supplying a high voltage pulse between the electrode 1 and the workpiece 2 as in the prior art. By supplying this pulse, fine processing with improved surface roughness of the workpiece 2 can be realized.

Between times t51 and t54, when the switching element S1 is turned on, it continuously changes until the current IS1 is saturated due to the transient response and the inductance of the inductor L1. More specifically, the rate of increase of current IS1 is constant from time t52 to t53, but gradually decreases from time t53 and saturates at time t54. At the time of saturation, IS1 is highest, and immediately after this, S1 is turned off. By utilizing this fact to control the switching timing of the switching element, the cutoff current can be varied, and a pulse voltage having an arbitrary surge voltage can be obtained.
In the second embodiment, the minimum values of the capacitor C1 and the inductor L1 correspond to the stray capacitance Cf and the line LINE in the first embodiment.

As described above, according to the electric discharge machining power supply apparatus of the present invention, the workpiece is not supplied by supplying a pulse having a short pulse width PW without supplying a high voltage pulse between the electrode and the workpiece during finishing machining. Fine processing with improved surface roughness can be achieved.
In the electric discharge machining power supply device, it is desirable that the pulse width of the pulse voltage is 10 nanoseconds to several tens of nanoseconds. This is suitable for fine processing.
In this embodiment, the machining electrode is connected to the anode of the DC voltage source and the workpiece is connected to the cathode. However, depending on the machining conditions such as the electrode material and the 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 an electric circuit diagram of the electric discharge machining power supply device showing a modification of FIG. It is an electric circuit diagram of the electric discharge machining power supply device concerning a second embodiment of the present invention. It is a time chart of operation | movement of the electric circuit shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Work piece 3 ... Processing tank 4 ... Processing liquid V1 ... DC voltage source S1, S2 ... Switching element GAP ... Discharge gap LINE ... Line Cf ... Stray capacitance L1 ... Inductor C1 ... Capacitor

Claims (4)

In an electric discharge machining power supply apparatus that applies a pulse voltage between the electrode and the workpiece to perform electric discharge machining on the workpiece,
A power source for applying a DC voltage between the electrodes;
A first switching element connected in parallel to the power source;
A second switching element connected in series between the first switching element and one end between the poles;
A line or inductor having an inductance connected in series between the anode of the power source and the first switching element;
A control circuit for controlling opening and closing of the first switching element and the second switching element,
Switching the first switching element from off to on while keeping the second switching element off;
With the second switching element turned off, the first switching element is instantaneously switched from on to off, and a pulse voltage obtained by boosting the DC voltage of the power supply is applied between the electrodes to insulate the electrodes from each other Charging the stray capacitance generated in the line connected to one end between the poles, and the discharge current passing through between the poles,
Wherein while the first off the switching element switching the second switching element a predetermined time from OFF to ON, controls so as to discharge electrostatic charges charged in the stray capacitance, than the response time of the first switching element A control circuit for generating a pulse with a short pulse width ;
An electric discharge machining power supply device comprising: Discharge machining power supply device according to claim 1, further comprising a pre-Symbol parallel connected capacitor to the second switching element. The electric discharge machining power supply device according to claim 2, wherein values of the inductance of the line or inductor having the inductance and the capacitance of the capacitor are variable.   The electric discharge machining power supply device according to any one of claims 1 to 3, wherein a peak value of the pulse voltage is variable.

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