JPH10128620A - Power supply unit for electric discharge machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply unit for electric discharge machining, without causing generation of a short-circuit arc discharge condition, increasing a discharge repeating frequency, increasing a machining speed, preventing a machined surface from being damaged, reducing electrode consumption, and capable of reducing a cost. SOLUTION: A power supply unit is provided with a capacitor device set 53, 54 formed by two capacitors 53-1, 53-2, 54-1, 54-2 connected in parallel to a machining gap G formed by opposing a machining electrode 5 and a workpiece 6, also a charger 51 charging the capacitor, switching elements 57-1, 57-2, 58-1, 58-2 connected in series in a discharge circuit leading to the machining gap G from the respective capacitor, switching drive circuit 59, 60 respectively controlling on/off of the switching elements, discharge detection circuit 61 detecting generation of a discharge between electrodes, and a switching element switching circuit 62 switching one of the switching drive circuits in each capacitor device set to an operating condition in each generation of a discharge by a detection signal output by the discharge detection circuit 61.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for an electric discharge machine used in an electric discharge machine, and more particularly to a power supply device for a power storage type for an electric discharge machine.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional basic power supply for power storage type electric discharge machining. In FIG. 4, 1 is a charging device using a DC power supply, 2 is a charging resistor for limiting a charging current, 3 is a power storage device (capacitor) for storing electric energy for performing electric discharge machining, 5 is a machining electrode, and 6 is a workpiece. Each object is shown.

[0003] Next, the operation of the above-described power supply device for power storage type electrical discharge machining will be described. In the initial state, the power storage device 3 has no charge, and the processing gap G in which the processing electrode 5 and the workpiece 6 face each other is open. First, a current flows from the charging device 1 to the power storage device 3 through the charging resistor 2, and the power storage device 3 is charged. Power storage device 3 as charged
Is increased, and a voltage is applied to the processing gap G.

[0004] Then, a discharge occurs at a certain probability, and the electric energy stored in the power storage device 3 is supplied to the machining gap G through a discharge circuit to perform electric discharge machining.

FIGS. 5 (a) and 5 (b) show a voltage waveform and a current waveform, respectively, between discharge electrodes in the electric power storage type power supply device for electric discharge machining. In FIG. 5B, A indicates a current pulse during normal discharge, and B indicates a short-circuit current when a short circuit occurs.

[0006] In the above-mentioned conventional power supply for power storage type electric discharge machining, since the electric discharge is generated in a state depending on the voltage applied to the machining gap G, the machining energy varies for each electric discharge and is formed on the machining surface. The size of the discharge trace also varies.

In electric discharge machining, the surface roughness of the machined surface is determined by the largest discharge mark, and this maximum discharge mark must satisfy the required surface roughness. For this reason, in a situation where the size of the discharge trace varies, many processing traces that are much smaller than permitted due to the required surface roughness are generated, and as the discharge trace becomes smaller, the processing speed decreases, and the machining efficiency is reduced. Getting worse.

Since the charging speed of the power storage device 3 is governed by a time constant determined by the charging resistance 2 and the capacity of the power storage device 3, in order to increase the processing speed, the repetition frequency of the discharge must be increased. It is necessary to charge as quickly as possible.

However, if the charging time constant is set small by lowering the resistance value of the charging resistor 2 in order to speed up the charging, the current flowing from the charging device 1 to the power storage device 3 before the discharge ends is increased. Working gap G from charging device 1
In addition, as shown by reference numeral B in FIG.
A long-term direct current flows as a short-circuit current.
In this case, a sustained arc discharge occurs, which causes damage to the machined surface.

Therefore, the resistance value of the charging resistor 2 cannot be reduced too much, and as a result, the rise of the voltage between the electrodes becomes slow, so that the discharge frequency decreases and the machining speed cannot be improved.

In view of the above problems in the basic power storage type power supply device for electric discharge machining, see, for example, Japanese Patent Application Laid-Open No. 50-101.
As disclosed in Japanese Patent Application Publication No. 997, there is a proposal in which a plurality of charge / discharge circuits are provided in parallel, and a charge switch and a discharge switch are provided in each charge / discharge circuit. Hereinafter, such a power supply device for electric discharge machining is referred to as a power storage device switching type power supply device for electric discharge machining for convenience.

FIG. 6 shows a conventional example of a power supply unit for electric discharge machining which is switched by a storage battery. In FIG. 6, the same or corresponding parts as those of the electric discharge machining power supply device shown in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 6, 1-1 is a first charging device,
1-2 is the second charging device, 2-1 is the first charging resistor, 2
-2 is the second charging resistor, 3-1 is the first capacitor, 3-2
Is a second storage capacitor, 4-1 is a first discharge switch by a thyristor, 4-2 is a second discharge switch by a thyristor, 13 is a charge switch switching control signal circuit, 14-1
Denotes a first Zener diode, 14-2 denotes a second Zener diode, 15-1 denotes a first backflow prevention diode, 15-2 denotes a second backflow prevention diode, and 16-1 denotes a second backflow prevention diode.
Denotes a first charge switch, and 16-2 denotes a second charge switch.

Next, the operation of the above-described power supply device for electric discharge machining which is switched by a storage battery will be described. Immediately after the last discharge,
The second storage battery 3-2 has not been stored because it has discharged the internal charge, and the second charge switch 16-2 is off.

On the other hand, the first charge switch 16-1 is turned on, and the first battery 3-1 stores a charge corresponding to the time since the first charge switch 16-1 was turned on. Power is stored by one charging device 1-1. As the first capacitor 3-1 is charged, the voltage between its terminals increases. When this voltage exceeds the Zener voltage, the Zener diode 14-1 conducts and the first discharge switch 4-1 operates, and the first discharge switch 4-1 operates. One capacitor 3-1 is connected to the processing gap G. At the same time, the charge switch switching control signal circuit 13 turns on the second charge switch 16-2.

After a while, electric discharge occurs in the machining gap G, the electric charge in the first capacitor 3-1 is consumed, and the first Zener diode 14-1 becomes non-conductive. 1 charge switch 16-1
Turn off.

During this time, the second charging switch 16-2 has been turned on, so that the electric charge corresponding to the time since the second charging switch 16-2 was turned on is stored in the second battery 3-2. Power is stored by 1-2. As the second capacitor 3-2 is charged, the voltage between its terminals increases, and when this voltage exceeds the Zener voltage, the second Zener diode 14-2 conducts and the second discharge switch 4-2.
Operates, and the second electric storage device 3-2 is connected to the machining gap G. At the same time, the charge switch switching control signal circuit 13 turns on the first charge switch 16-1.

After a while, a second discharge occurs in the machining gap G, and the electric charge in the second electric storage device 3-2 is consumed.
The Zener diode 14-2 becomes non-conductive, and at the same time, the charge switch switching control signal circuit 13 sets the second charge switch 1
Turn off 6-2 and return to the initial state. Therefore, if the above operation is repeated, electric discharge machining can be continued.

[0019]

Since the conventional power supply device for electric power storage switching electric discharge machining operates as described above,
While one capacitor is being charged, electric discharge machining can be performed with the other capacitor, and the machining speed can be improved to some extent.

However, even in the above-described power supply device for switching electric discharge machine, since the discharge occurs stochastically, the voltage between the terminals of the other storage device reduces the Zener voltage before the electric charge in one storage device is discharged. May exceed. Thereafter, when a discharge occurs due to the electric charge in one of the capacitors, the electric charge in the other capacitor is also discharged following the discharge of the electric charge in the one capacitor, so that unexpected large discharge marks are formed on the surface of the workpiece, Damage occurs on the machined surface and electrode wear increases.

In the above-described power supply device for electric discharge machining switching type, if the operation of the charge switch is slow, the charging current from the DC power supply directly flows into the machining gap when electric discharge occurs, and the machining surface is damaged. become. Therefore, in the conventional power supply device for electric power storage switching electrical discharge machining, it is necessary to use a fast-operating charge switch, and there is also a problem that the device becomes expensive.

The present invention has been made in view of the above-mentioned problems, and always discharges at a constant energy.
An object of the present invention is to obtain a power supply device for electric discharge machining that increases the repetition frequency of electric discharge without causing a short circuit or arc discharge state, has a high machining speed, does not damage a machined surface, reduces electrode consumption, and is inexpensive. I have.

[0023]

In order to achieve the above-mentioned object, a power supply device for electric discharge machining according to the present invention comprises at least two power supply devices connected in parallel to a machining gap formed by opposing a machining electrode and a workpiece. A charging device that connects each of the capacitors in parallel and charges each of the capacitors; a charging resistor provided for each of the capacitors in a charging circuit including the charging device and the capacitor; A switching element provided for each capacitor in each discharge circuit including the machining gap and the machining gap; and a switching drive circuit for alternately turning on / off the switching element at a constant cycle.

In the power supply device for electric discharge machining according to the present invention,
The switching drive circuit turns on and off the switching elements of each discharge circuit alternately at a fixed cycle, and the voltage between the machining electrode and the workpiece increases in a stepwise manner, and the voltage between the electrodes becomes a voltage sufficient to generate discharge. When the temperature rises to above, discharge occurs between the electrodes of the machining electrode and the workpiece.

The power supply device for electric discharge machining according to the next invention is as follows.
A plurality of power storage device sets each including at least two power storage devices connected in parallel to a processing gap formed by facing a processing electrode and a workpiece, and each of the power storage devices of each power storage device set is connected in parallel. A charging device for charging the storage device, a charging resistor provided for each storage device in each charging circuit including the charging device and the storage device of each storage device set, the storage device and the processing gap of each storage device set; A switching element provided for each capacitor in each discharge circuit, a switching drive circuit for alternately turning on / off the switching elements of the same power storage device set at a constant cycle in each power storage device set, and the processing electrode; A discharge detection circuit for detecting generation of a discharge between the workpiece and the electrode; and a charge storage device each time a discharge is generated by a detection signal output from the discharge detection circuit. A switching element switching circuit for switching one of the switching drive circuits for each set to an operating state, and during a period until a discharge occurs, one storage device is operated by the switching drive circuit in an operating state by the switching element switching circuit. The switching elements of the device set are alternately turned on / off at a constant cycle, and when a discharge occurs, a switching drive circuit for another power storage device set is operated by the switching device switching circuit, and a plurality of power storage device sets are sequentially operated. Switching is used.

In the power supply device for electric discharge machining according to the present invention,
The discharge detection circuit detects the occurrence of discharge between the machining electrode and the workpiece, and the switching element switching circuit switches the switching drive circuit for each power storage device set every time a discharge occurs according to the detection signal output by the discharge detection circuit. Switch to one of the operating states. Until the discharge occurs, the switching elements of one power storage device set are alternately turned on / off at regular intervals by the switching drive circuit that is in the operating state by the switching element switching circuit, and the gap between the machining electrode and the workpiece is changed. When the voltage rises stepwise and discharge occurs, a switching drive circuit for another power storage device set is operated by the switching element switching circuit, and a plurality of power storage device sets are sequentially switched and used.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a power supply device for electric discharge machining according to the present invention.

(Embodiment 1) FIG. 1 shows Embodiment 1 of a power supply device for electric discharge machining according to the present invention. The power supply device for electric discharge machining includes a charging device 51 using a DC power supply,
The first to fourth connected in parallel to the charging device 51
A first power storage device set 53 including two charging resistors 52-1 to 52-4, two power storage devices (capacitors) 53-1 and 53-2, and storing electric energy for performing electric discharge machining, and two power storage devices (capacitors) A second power storage device set 54 including 54-1 and 54-2 for storing electric energy for performing electrical discharge machining, and a power storage device 53-1 of the first power storage device set 53 including switching elements 57-1 and 57-2. , 53-
A first switching element set 57 for connecting / disconnecting the charging circuit to the second switching element, and switching elements 58-1 and 58-2
A power storage device 54-1 of the second power storage device set 54,
And a second switching element set 58 for connecting and disconnecting the charging circuit to 54-2.

Further, this power supply device for electric discharge machining has a first
Switching element 57 of switching element set 57
-1 and 57-2 are alternately turned on and off at a constant cycle, and a first switching drive circuit 59, and switching elements 58-1 and 58-2 of a second switching element set 58.
A second switching drive circuit 60 for alternately turning on / off at regular intervals, a discharge detection circuit 61 for detecting the occurrence of discharge between the machining electrode 5 and the workpiece 6, and a discharge detection circuit 61. A switching element switching circuit 62 for switching the first switching drive circuit 59 and the second switching drive circuit 60 alternately to an operating state each time a discharge is generated by the output detection signal.

In this power supply device for electric discharge machining, the first power storage device is operated by the first switching drive circuit 59 or the second switching drive circuit 60 which is in the operating state by the switching element switching circuit 62 until the discharge occurs. Switching element 57-1, 57-2 or 58 for set 53 or second power storage device set 54
-1 and 58-2 are alternately turned on / off at a constant cycle, and when a discharge occurs, the switching drive circuit for another power storage device set is operated by the switching element switching circuit 62, and the first power storage device set is operated. 53 and the second power storage device set 54 are alternately used.

In other words, each time a discharge is generated by the detection signal output from the discharge detection circuit 61, the switching element switching circuit 62 connects the first switching drive circuit 59 and the second switching drive circuit 59 with each other.
And the switching drive circuit 60 of the first power storage device set 53 and the second power storage device set 54 in the period until the discharge occurs. Or 58
Switching element 57-1, 57-2 or 58-
1, 58-2 are alternately turned on and off at a constant cycle,
When a discharge occurs, an on / off operation of a switching element of another power storage device set is performed.

Next, the operation of the power supply device for electric discharge machining having the above-described configuration will be described. In the initial state, the storage devices 53-1, 53-2, 54-1, and
An electric charge is accumulated in each of 54-2.

Next, the first switching drive circuit 59 is selected by the switching element switching circuit 62. As a result, the first switching drive circuit 59, as shown in FIG.
7 so that the switching elements 57-1 and 57-2 are alternately turned on / off.

Thus, the power storage devices 53-1 and 53-2 of the first power storage device set 53 are connected to the processing electrode 5 and the workpiece 6
Are alternately connected between the poles. Switching element 57-
While 1 is on, the energy stored in the battery 53-1 is supplied between the machining electrode 5 and the workpiece 6. As a result, the voltage between the electrodes increases, and the voltage of the battery 53-1 decreases. On the other hand, during this time, the switching element 57-
Since the battery 2 is off, the battery 53-2 maintains the state charged by the energy supplied from the charging device 51.

Next, when the switching element 57-2 is turned on, the energy stored in the battery 53-2 is supplied between the machining electrode 5 and the workpiece 6. As a result, the inter-electrode voltage further increases, and the voltage of the battery 53-2 decreases. During this time, since the switching element 57-1 is off, the battery 53-1 is charged by the energy supplied from the charging device 51, and the battery 53-1 is charged.
Voltage rises and recovers.

By repeating the above on / off operation, as shown in FIG. 3, the voltage between the electrodes increases stepwise in synchronization with the on / off operation.

When the time T1 elapses from the start of switching, the voltage between the electrodes rises to a voltage sufficient to generate electric discharge, so that electric discharge occurs between the electrode between the machining electrode 5 and the workpiece 6, and Is supplied with a discharge current A, and electric discharge machining proceeds.

The discharge detection circuit 61 detects the occurrence of this discharge, and the switching element switching circuit 62
Is switched from the first switching element set 57 to the second switching element set by the discharge detection signal from the first switching element set 57.
Is switched to the switching element set 58 of FIG. As a result, the on / off operation of the switching elements 57-1 and 57-2 stops, and instead, the switching element 58-
1, 58-2 start the on / off operation. After the switching, for the switching elements 57-1 and 57-2,
The off state is maintained until the next discharge occurs between the poles,
In the meantime, the capacitors 53-1 and 53-2 are charged by the energy supplied from the charging device 51.

Until the next discharge is generated between the electrode between the machining electrode 5 and the workpiece 6, the second switching drive circuit 60 switches the switching elements 58-1 and 58 of the second switching element set 58. -2 are alternately turned on / off.

Thus, the power storage devices 54-1 and 54-2 of the second power storage device set 54 are connected to the processing electrode 5 and the work 6
Are alternately connected between the poles. Switching element 58-
While 1 is on, the energy stored in the battery 54-1 is supplied between the machining electrode 5 and the workpiece 6. As a result, the voltage between the electrodes increases, and the voltage of the battery 54-1 decreases. On the other hand, during this time, the switching element 58-
Since the battery 2 is off, the battery 58-2 maintains the state charged by the energy supplied from the charging device 51.

Next, when the switching element 58-2 is turned on, the energy stored in the battery 54-2 is supplied to the gap between the processing electrode 5 and the workpiece 6. As a result, the voltage between contacts further increases, and the voltage of battery 54-2 decreases. During this time, since the switching element 58-1 is off, the battery 54-1 is charged by the energy supplied from the charging device 51, and the battery 54-1 is charged.
Voltage rises and recovers.

By repeating the above ON / OFF operation, as shown in FIG. 3, the voltage between the electrodes increases stepwise again in synchronization with the ON / OFF operation.

When the time T2 elapses from the start of switching, the voltage between the electrodes increases again to a voltage sufficient to generate electric discharge, so that electric discharge occurs between the electrode between the machining electrode 5 and the workpiece 6 and During this time, a discharge current A is supplied, and electric discharge machining proceeds.

The discharge detection circuit 61 detects the occurrence of the discharge, and the switching element switching circuit 62 detects the discharge.
Is switched from the second switching element set 58 to the first switching element set 57 in accordance with the discharge detection signal from the first switching element set 57. Thereby, the switching elements 58-1 and 58
-2 stops on / off operation, and switching elements 57-1 and 57-2 start on / off operation instead. After the switching, the switching elements 58-1, 58-2
With respect to, the off state is maintained until the next discharge occurs between the poles, and during that time, the capacitors 54-1 and 54-2 are charged again by the energy supplied from the charging device 51.

The on / off operation as described above has an effect of eliminating the short-circuit at an early stage especially when a short-circuit occurs between the electrode 5 and the workpiece 6. That is, when a short circuit occurs between the electrode of the processing electrode 5 and the workpiece 6, a short circuit current determined by the resistance values of the charging resistors 52-1 to 52-4 flows between the electrodes. In the power supply device according to the present invention, since the on / off operation is performed at a high frequency according to the cycle t0, the short circuit is easily eliminated, and as shown by the symbol B in FIG. 3, most of the short circuit current is cut off at about t0 time. Is done.

Therefore, as shown by reference numeral B in FIG. 5 of the conventional example, there is no continuation of a short circuit for a long time, and a short circuit between the electrodes can be eliminated in a short time. With the elimination of the short circuit, the insulation is restored between the electrode of the machining electrode 5 and the workpiece 6 and the voltage rises, and the electric discharge machining is resumed. Especially t0
= 1 to 5 μs, the effect is high.

In the case where not only a short circuit but also a gap is in an arc state, the discharge is brought into a normal state in a short time by the same effect. The phenomenon of short-circuit and arc time can improve the processing efficiency by avoiding the abnormal state, and can prevent the deterioration of the processed surface roughness and the abnormal consumption of the electrode.

In the on / off operation, short-circuiting and arc continuation are prevented, and low-impedance charging resistors 52-1 to 52-4 that normally cause short-circuiting and arcing can be used. Each of the capacitors 53-1 and 53-
The charging time for 2, 54-1, and 54-2 can be reduced, and processing with a higher frequency can be performed.

The power storage device set 5 connected between the poles
By switching and using 3, 54, each of the power storage devices in the power storage device set 53 or 54 in a state where they are not connected between the poles is charged by the charging device 1 in the meantime, and therefore, is sufficiently charged continuously between the poles. A power storage device can be connected, and the rise time of the voltage between contacts can be significantly reduced.

[0050]

As will be understood from the above description, according to the power supply device for electric discharge machining according to the present invention, the switching elements of the respective discharge circuits are alternately turned on / off at a constant cycle by the switching drive circuit, so that the electric contact between the machining electrode and the machining electrode is obtained. If the voltage between the electrode and the workpiece increases stepwise and the voltage between the electrodes rises to a voltage sufficient to generate electric discharge, electric discharge occurs between the electrode and the workpiece. Arc generation can be suppressed, the quality of the machined surface can be significantly improved, and abnormal wear of the electrodes can be prevented, and highly accurate finishing can be realized.

According to the power supply device for electric discharge machining according to the next invention, the occurrence of electric discharge between the machining electrode and the workpiece is detected by the electric discharge detection circuit, and the discharge detection circuit outputs the switching element switching circuit. Each time a discharge is generated by the detection signal, the operation is switched to one operation state of the switching drive circuit for each power storage device set, and one storage device is operated by the switching drive circuit that is operating by the switching element switching circuit until the discharge occurs. When the switching elements of the set are alternately turned on / off at a fixed cycle, and the voltage between the working electrode and the workpiece increases stepwise and discharge occurs, the switching element switching circuit sets another power storage device set. Switching drive circuit is operated, and a plurality of power storage device sets are sequentially switched and used. In addition to being able to suppress the occurrence of defects, significantly improving the quality of the machined surface, preventing abnormal wear of the electrodes, and achieving high-precision finishing, the frequency of the discharge is greatly increased. Therefore, the processing speed can be greatly improved as compared with the conventional case.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing Embodiment 1 of a power supply device for electric discharge machining according to the present invention.

FIG. 2 is a waveform chart of each part showing the operation of the power supply device for electric discharge machining according to the present invention.

FIGS. 3 (a) and 3 (b) are waveform diagrams showing a gap voltage and a gap current in a power supply device for electric discharge machining according to the present invention.

FIG. 4 is an electric circuit diagram showing a conventional power supply device for electric discharge machining.

5 (a) and 5 (b) are waveform diagrams showing a gap voltage and a gap current in a conventional power supply device for electric discharge machining.

FIG. 6 is an electric circuit diagram showing a conventional example of a power supply device for a storage battery switching type electric discharge machining.

[Explanation of symbols]

5 Working electrode, 6 Workpiece, 51 Charger, 52-
1 to 52-4 charging resistance, 53 first power storage device set, 54 second power storage device set, 53-1 and 53-
2, 54-1, 54-2 Storage device, 57 First switching element set, 58 Second switching element set, 57-1, 57-2, 58-1, 58-2 Switching element, 59 First switching Drive circuit, 60
2nd switching drive circuit, 61 discharge detection circuit,
62 Switching element switching circuit.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masahiro Yamamoto 2-6-1, Otemachi, Chiyoda-ku, Tokyo Mitsubishi Electric Engineering Co., Ltd.

Claims (2)

[Claims] At least two capacitors connected in parallel to a processing gap in which a processing electrode and a workpiece are opposed to each other; a charging device that connects each of the capacitors in parallel and charges each of the capacitors; A charging resistor provided for each battery in each charging circuit including the charging device and the battery, a switching element provided for each battery in each discharging circuit including the battery and the machining gap, And a switching drive circuit for alternately turning on / off the switching element at a constant cycle. 2. A plurality of power storage device sets each including at least two power storage devices connected in parallel to a processing gap in which a processing electrode and a workpiece are opposed to each other, and each of the power storage devices in each power storage device set is connected in parallel. A charging device connected to each of the power storage devices; a charging resistor provided for each power storage device in each charging circuit including the charging device and the power storage device of each power storage device set; and the power storage device of each power storage device set. A switching element provided for each power storage device in each discharge circuit including the power supply device and the machining gap; and a switching drive circuit for alternately turning on / off the switching elements of the same power storage device set at a constant cycle in each power storage device set A discharge detection circuit that detects generation of a discharge between the machining electrode and the workpiece; and a discharge is generated by a detection signal output by the discharge detection circuit. A switching element switching circuit that switches one of the switching drive circuits for each of the power storage device sets to an operating state each time the power storage device set is operated, and a switching drive that is in an operating state by the switching element switching circuit until a discharge occurs. The circuit turns on / off the switching elements of one power storage device set alternately at a constant cycle, and when a discharge occurs, the switching element switching circuit operates a switching drive circuit for another power storage device set, and A power supply device for electric discharge machining, wherein a power storage device set is sequentially switched and used.