JPS6014651B2 - Power supply device for electrical discharge machining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrical discharge machining, which performs electrical discharge machining of a workpiece by causing electrical discharge to occur in a machining gap formed between opposing electrodes and the workpiece through a machining fluid. The present invention relates to a power supply device for use in electric discharge machining, and is particularly suitable as a power supply device for wire-cut electrical discharge machining.

Hereinafter, the configuration and operation of an example of a wire-cut electric discharge machining apparatus used from a subordinate position will be explained with reference to the drawings.

In FIG. 1, 1 is a workpiece, 2 is a wire electrode, 3 is a machining fluid stored in a tank 4, 5 is a pump for feeding this machining fluid 3, and 6 is a wire for distributing this machining fluid 3. This is a nozzle for spraying into the machining gap formed between the machining part 2A of the electrode 2 and the workpiece 1.

7 is a supply V supply reel for the wire electrode 2; 8B and 8A are upper and lower wire guides that define the position of the machining section 2A of the wire electrode 2; and 9 is a current for electrical discharge machining to the wire electrode 2; a power supply unit for supplying 1
0 is a winding reel that winds up the wire electrode 2 while applying appropriate tension to it.

11 is a table on which the workpiece 1 is placed, and 12 and 13 are an X-axis drive motor and a Y-axis drive motor that drive the table 11 in the X direction and the Y direction, respectively.

14 is a drive control device that controls the X-axis drive motor 12 and the Y-axis drive motor 13, which generally includes a copying control device, an N/C device, a fin calculator, etc.;
4 moves the table 11 in the It controls the motor 13.

Reference numeral 15 denotes a power supply device for electric discharge machining that supplies machining current for electric discharge machining between the wire electrode 2 and the workpiece 1 via the power supply unit 9, and this power supply device 15 includes a capacitor 18 for electric discharge,
Charging circuit 1 for charging this discharging capacitor 18
It is composed of 5A.

This charging circuit 15A includes a DC power supply 16 that is a source of machining energy, a switching element 17 that controls charging of a discharging capacitor 18, and a charging current limiting resistor 19.
For example, the switching element 17 is turned on at a certain period.
The control circuit 20 includes a switching element 17 and a control circuit 20 including an oscillator that is turned off.

FIG. 2 shows the machining power supply 15 of the wire-cut electric discharge machining apparatus shown in FIG. 1, the workpiece 1 and the wire electrode 2.
FIG. 2 is a diagram illustrating the operation of the main parts of this wire-cut electrical discharge machining apparatus, which is composed of a machining gap formed by facing a machining section 2A.

The discharging capacitor 8 is charged via the limiting resistor 19 while the switching element 17 of the charging circuit 15A is in the N state, and the voltage Vc between the terminals of the discharging capacitor 8 after charging for t hours is equal to the DC power supply 16. If the voltage of is E, the capacity of the discharge capacitor 8 is C, and the resistance value of the limiting resistor 19 is R, then vC=E(, -exp- point)...・'
The battery should be charged as shown by the curve 1'.

However, even during charging of the discharge capacitor 8, a leakage current flows through the machining fluid 3 into the machining gap formed between the machining part 2A of the wire electrode 2 and the workpiece 1.
As shown in the figure, this is equivalent to connecting a leakage resistor with a resistance value of 1 to the machining gap, and in this case, the discharge capacitor 1
The charging characteristic curve of No. 8 is shown by the following equation. VC = three seven (1-
eXp bribe),. ．． 、． Here, the resistance value y of the leakage resistance
In addition to being related to the specific resistance of the machining fluid 3, is constantly changing due to the influence of machining waste generated during machining, machining conditions, flow rate and flow velocity of the machining fluid 3, etc. The actual situation is that the charging characteristic curve of the voltage Vc between the terminals of the discharging capacitor 18 shown by is constantly changing during processing.

When the discharge capacitor 18 charged in this way starts discharging into the discharge gap, the voltage Vc between the terminals of the discharge capacitor 18 is defined as the discharge start voltage Vo. It constantly changes due to the influence of the change in the charging curve in No. 18, and especially when the leakage current is small (when the leakage resistance value y is large), the rising speed of Vc is fast, and as a result, the discharge starting voltage becomes abnormally high. Something happened.

On the other hand, when discharge starts in the discharge gap at the discharge starting voltage Vo, the energy W released from the discharge capacitor 18 is expressed by the following equation.

w=yoV.

2. ．． ...[3] That is, the machining energy released from the discharge capacitor 8 into the discharge gap is the discharge starting voltage V.

squared, V. 2, when the discharge starting voltage VD is increased, the amount of cutting of the workpiece 1 in one discharge increases, but the amount of wear of the machined part 2A of the wire electrode 2 also increases, and the discharge If the starting voltage Vo increases, there is a risk of wire breakage in the processing section 2A of the wire electrode 2. Therefore, when it is necessary to increase processing efficiency, the voltage E of the DC power supply 16 is set high to prevent wire breakage. Applying energy close to the limit of , to the machining gap,
Ideally, machining should be performed at high speed, but when setting the voltage E of the DC power supply 16, the fluctuation of the resistance value y of the leakage resistance during machining is taken into account to ensure that wire breakage does not occur even under the worst conditions. As a result, the machining speed cannot be made very high and the machining efficiency cannot be made very high.

Furthermore, since the amount of cutting of the workpiece 1 is related to the discharge starting voltage Vo in the machining gap and Vo2, the discharge starting voltage V during machining.

It also had the disadvantage that when the value of the machining process changed, the machining process changed at the same time, resulting in poor processing accuracy. In order to eliminate these drawbacks, it is necessary to limit the discharge starting voltage Vo to a constant value Vs or less during machining. For example, as shown in FIG. A method has been proposed in which the voltage limit control circuit 21 is connected to prevent the voltage Vc from rising above a desired constant voltage Vs. FIG. 4 shows a specific example of this voltage limit control circuit 21, in which a plurality of zener diodes ZD
,,ZD2,ZD3・・・・・・・・・・・・・ZDn
It is possible to select the required number of zener diodes with the selector switch SW, and set the zener voltage between the two terminals to be equal to the desired constant voltage Vs. It was designed so that By connecting this voltage limit control circuit 21A in parallel to the discharge capacitor 18, the voltage between the terminals of the discharge capacitor 18 is
Until c reaches a constant voltage Vs, it increases according to the curve shown in the above equation (2), but when Vc=Vs, the charging current supplied thereafter is not charged to the discharging capacitor 18, and the voltage limit control circuit The voltage Vc between the terminals of the 21A Zener diode is maintained at Vc=Vs.

Therefore, the voltage Vc between the terminals of the discharging capacitor 18 is always VcminVs, and the discharge start voltage Vo is always VominVs, and is no longer higher than the desired constant voltage Vs.

FIG. 5 shows a specific example of 8U of the voltage limit control circuit 21,
A series body of a second capacitor 22 having a capacitance Co sufficiently larger than that of the discharging capacitor 18 and a rectifying element 23 for preventing backflow is connected between the terminals of the transformer 26 and the rectifier whose output voltage can be adjusted by switching the switch SW2. Consisting of 25
DC power supply 24 with adjustable output voltage and second capacitor 2
The second discharge resistor 27 is connected in parallel to the second capacitor 22.

Therefore, this second capacitor 22 is always charged to a desired constant voltage Vs by the DC power supply 24 whose output voltage is adjustable. This voltage limit control circuit 2
1B is connected in parallel to the discharge capacitor 18, until the voltage Vc between the terminals of the discharge capacitor 18 reaches the constant voltage Vs, the voltage Vc between the terminals is expressed by the formula '2] as in the above specific example. Therefore, it increases, but Vc=V
The inter-terminal voltage Vc after a further t time has reached s is connected in parallel with the second capacitor 22 having a capacitance Co, so VC=support (E-VS) {1-eXPRyC~.

t1} 10VS ‐‐‐‐‐‐{41 Here, C+Co》C, so the first term of formula [4} is 7 E−vS){, −eXp−R }±
o...It can be seen as t51. Furthermore, since the second capacitor 22 is constantly discharging via the discharge resistor 27, in practice, after Vc reaches Vs, Vc=Vs...[61
It can be considered that the relationship holds.

Therefore, it can be seen that the discharge starting voltage is always VoVs. FIG. 6 shows a modified part of the voltage limiting control circuit 21B shown in FIG. 5, in which a series body of a second capacitor 22 and a rectifying element 23 for preventing backflow is connected between the terminals e. A series body of a PNP transistor 28 and a resistor 29 is connected in parallel with the second capacitor 22 as a discharge circuit for the second capacitor 22, and an output voltage is set between the e terminal and the base of the transistor 28. A desired constant voltage Vs is applied from a DC power source 24 for regulation.

This DC power supply 24 is configured to divide the output of a constant voltage DC power supply 31 by a variable resistor 30, but it can also be used even if the output of a voltage variable transformer is rectified.
This voltage limit control circuit 21C is the discharge capacitor 18
When connected in parallel with the charging circuit 1, both the discharging capacitor 18 and the second capacitor 22 are connected in parallel to the charging circuit 1 at the start of machining.
Charged by 5A.

Once the second capacitor 22 is charged to a constant voltage Vs, even if discharge starts in the machining gap, the rectifying element 23 prevents discharge from the second capacitor 22 into the discharge machining gap. The voltage Vs is maintained. In this state, the discharging capacitor 18 is charged to a constant voltage Vs, and the charging current is also charged to the second capacitor, and the voltage between its terminals Vc becomes Vc>Vs, but at this time, the emitter voltage of the transistor 28 Since V8 is Vz=Vc, it is higher than the base voltage VB, so the transistor 28
Since conduction occurs between the emitter and the collector, and the charges in the second capacitor 22 and the discharge capacitor 18 are discharged via the resistor 29, it can be seen that the relationship between Vc and Vs is always maintained. I can do it.

Therefore, even by installing this voltage limit control circuit 21C, the discharge starting voltage Vo can always be maintained at a constant voltage Vs.
The following is true. However, in this way, the voltage limit control circuit 2
1 as a bias circuit, after the voltage Vc between the terminals of the discharging capacitor 18 reaches the constant voltage Vs, a charging current larger than necessary flows to the voltage limiting control circuit 21, and this voltage limiting control circuit 21, and if the power consumed by this voltage limit control circuit 22 is Ps, then
13'Ps is expressed by the following formula.

, 3=(E1VS) ----PS=ra-VS=(Eichigo)-VS...■Here, as an example of commonly used processing conditions, E=300V, Vs=
Assuming 150V and R=200, the result of calculating Pw from the above formula and formula (2) is Ps = 1125W. This power Ps is not only wasted as energy, but also becomes heat, so the device This also resulted in the problem of having to take measures to dissipate heat in order to reduce the effect on each part.

The present invention eliminates the drawbacks and problems of the conventional apparatus, enables high-performance and highly efficient electrical discharge machining, and reduces power loss generated within the apparatus.
This was done with the aim of obtaining a highly efficient power supply device for electrical discharge machining.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In this embodiment, in the voltage limit control circuit 21C shown in FIG. 6, after the voltage Vc between the terminals of the discharging capacitor 18 reaches the constant voltage Vs, more energy than necessary is supplied from the charging circuit 15A to the charging circuit 15A. The circuit configuration diagram is shown in FIG. 7. In the figure,
The same reference numerals as in the past indicate the same or equivalent parts, and 40 is a transformer whose input is the current 13 discharged from the second capacitor 22 through the transistor 28, which is replaced by the resistor 29 shown in FIG. This is for absorbing the charging energy that is released from the second capacitor 22 and is more than necessary.

The output current 14 of this transformer 40 is rectified by a rectifier 41, and then connected to the DC power supply 16 of the charging circuit 15A and the smoothing large capacitor 42 of this circuit.
This discharged charging energy in excess of what is necessary is returned to the charging circuit 15A again. However, charging circuit 1
When the discharging capacitor 22 continues to be charged from 5A, the current 13' continues to flow in the same direction, so the iron core of the transformer 40 becomes saturated, and the energy charging circuit 15
There will be no return to A.

Therefore, switching element 1 7 of charging circuit 15A
The control circuit 20 that controls ON/OFF of the transformer 40 is inputted with the output voltage of the transformer 40 as a detection signal sens,
When an output voltage is generated in the transformer 40 and energy return begins, the switching element 17 of the charging circuit 15A is turned off to control charging of the discharging capacitor 22 to be stopped.

FIG. 8 shows the switching element 17 of this charging circuit 15A.
FIG. 2 is a circuit diagram showing an example of an ON-OFF control circuit 20 of FIG.

The switching element 17 of the charging circuit 15A is driven by a driving transistor 44, a resistor 45, and a cutoff bias power supply 46 for the switching element 17.

That is, when the transistor 44 is ON, the switching element 17 is OFF, and when the transistor 44 is OFF,
The switching element 17 is turned on. Typically, the base input of transistor 44 is connected to oscillator 48 via base resistor 47.

In this oscillator 48, 49 and 50 are NAND gates consisting of logic elements having a high threshold (threshold level).
As the NAND gates 49 and 50, HNILAPB12 manufactured by NEC Corporation is used. 51 and 52 are variable capacitor capacitors that adjust the oscillation cycle of this oscillator 48, and when the detection signal sens is not input, the switching of the charging circuit 15A is performed at the cycle set by the variable capacitors 51 and 52. The charging circuit 15A continues to charge the discharging capacitor 18 by turning the element 17 ON and OFF.

Charging continues in this way, and the discharging capacitor 1
When the voltage between the terminals of 8 reaches Vc, a current 12 flows to the input side of the transformer 4, and an output voltage is generated on the output side.
As energy begins to be returned to the charging circuit 15A,
The detection signal Sens is input to two control circuits.

This detection signal Se is applied to the base of the transistor 44,
This transistor 4 is inputted via the base resistor 53.
4 is turned on, the switching element 17 of the charging circuit 15A is turned off and charging is stopped. In this way, when charging of the discharging capacitor 8 is stopped, the current 13
Since the current stops flowing, the detection signal Sens is also no longer generated, and the switching element 17 of the charging circuit 15A responds to the output of the oscillator 46 and repeats ON/OFF to resume charging the discharging capacitor 18.

As explained above, the electric discharge machining power supply device of this embodiment repeatedly charges and stops the discharge capacitor 8, and the voltage Vc between its terminals does not exceed the predetermined constant value Vs, and moreover, The charging energy is transferred to charging circuit 1 again.
It is reduced to 5A and can be reused.

In addition, the charging circuit 15A can also control the charging current of the discharging capacitor 18 by using a reactor 60 instead of the charging current limiting resistor 19 by appropriately controlling ON/OFF of the switching element 17. It's now possible.

By controlling the charging current of the discharge capacitor 18 using the reactor 60, it is possible to eliminate heat loss due to the current limiting resistor 19, and the elements that generate heat loss from the electric discharge machining power supply device are almost eliminated, improving the efficiency of the device. Further improvement is possible. Here, the switching element 17
The reactor 60 is connected to the charging circuit 15A on the collector side of the
When used for current control, switching element 1
A diode 43 is installed in order to circulate back electromotive force generated at the moment 7 is turned off, thereby preventing troubles caused by the generation of abnormal voltage.

When the power supply device for electrical discharge machining according to the present invention is used in a wire-cut electrical discharge machining device, even if the conditions for wire-cut electrical discharge machining are set to a machining speed close to the limit at which wire breakage occurs, the charging voltage of the electrical discharge capacitor 18 remains constant. Since it is regulated to be below a predetermined value Vs, there is no risk of wire breakage due to an abnormal rise in the discharge starting voltage Vo due to changes in leakage current in the machining gap, and the machining speed can be kept close to the limit value. As a result, machining efficiency can be greatly increased, and variations in discharge starting voltage Vo can be reduced, resulting in improved machining accuracy.

In addition, when this electric discharge machining power supply device is used not only as a power source for wire-cut electric discharge machining equipment but also for general electric discharge machining equipment, an abnormally high discharge starting voltage will not occur, and its variation will be reduced, so the discharge It was possible to solve problems such as surface roughness and changes in clearance caused by variations in starting voltage, and in this case as well, it became possible to improve processing accuracy. As explained above, the electric discharge machining power supply device according to the present invention limits the voltage between the terminals of the machining capacitor that generates discharge in the machining gap formed between the electrode and the workpiece to a desired constant voltage. By using this power supply device, it is possible to improve the machining accuracy and machining efficiency of electrical discharge machining, and also to recharge the discharge capacitor with the energy generated by the excess charging current supplied from the charging circuit to the discharge capacitor. Since it is configured to be returned to the circuit and reused, it is possible to provide an extremely efficient power supply device for electrical discharge machining, which has an extremely high energy-saving effect, and its economic value is highly evaluated. It can be said that this is something that should be done.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of an example of a subordinate wire-cut electrical discharge machining apparatus, and FIG. 2 is a diagram illustrating the operation of the main parts thereof. FIG. 3 is a diagram explaining the operation of the main parts in the improved example of the above-mentioned subordinate device, and FIGS. It is a circuit diagram. FIG. 7 is a diagram illustrating the operation of the main parts of a wire-cut electrical discharge device which is an embodiment of the present invention, and FIG.
It is a circuit diagram of the ON-OFF control circuit of the switching element of the charging circuit. In the drawings, the same symbols indicate the same or corresponding parts, 1 is the workpiece, 2 is the wire electrode, 3 is the machining fluid, 12 is the x-axis drive motor, 13 is the Y-axis drive motor,
15 is a power supply device. 15A is a charging circuit, 16 is a DC power supply, 17 is a switching element for the charging circuit, 18 is a discharging capacitor, 19 is a resistor, an ON-OFF control circuit for the switching element,
21 is a voltage limit control circuit, 22 is a second capacitor, 2
Reference numeral 4 indicates a DC power supply with adjustable output voltage, and reference numeral 28 indicates a transistor. 40 is a transformer, 41 is a rectifier, 42 is a smoothing capacitor, 44 is a transistor, 48 is an oscillator, 49 and 50 are NAND gates, 51 and 52 are variable capacitance capacitors, and 60 is a reactor. Figure 1 Figure 3 Figure 4 Figure 5 Figure 2 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A discharge capacitor that performs electrical discharge machining on a workpiece by causing discharge to occur in a machining gap formed between an electrode and a workpiece through a machining fluid, and A power supply device comprising a charging circuit, a circuit for controlling the voltage between the terminals of the capacitor to prevent it from exceeding a desired constant value, and a circuit for returning excess charging energy of the capacitor to the charging circuit. A power supply device for electric discharge machining, characterized in that it is equipped with a circuit for. 2. The electric discharge machining power supply device according to claim 1, which is used for wire cut electric discharge machining. 3. The charging circuit includes a DC power supply that charges the capacitor, a switching element that controls charging of the capacitor,
3. A power supply device for electric discharge machining according to claim 1 or 2, characterized in that the power supply device comprises a series body with a reactor that limits charging current.