JPS6059097B2 - Power supply device for electrical discharge machining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply device for electrical discharge machining that performs electrical discharge machining by generating electrical discharge in a machining gap formed between an electrode and a workpiece through a machining fluid. It is particularly suitable as a power supply device for wire-cut electrical discharge machining using wire electrodes.

FIG. 1 is a configuration diagram showing an example of a conventional wire-cut electrical discharge machining device, in which 1 is a workpiece, 2 is a wire electrode, 3 is a machining fluid stored in a tank 4, and 5 is a pump for pumping this machining fluid 3. 6 is a nozzle that injects the machining fluid 3 into the opposing machining gap between the machining part 2A of the wire electrode 2 and the workpiece 1; 7 is the supply reel for the wire electrode 2; 8A and 8B are the upper and lower parts of the wire electrode 2; An upper wire guide and a lower wire guide that define the position of the processing section 2A, 9 a power supply section for the wire electrode 2, 10 a winding roll for winding the wire electrode 2 while applying appropriate tension to the wire electrode 2; 11 is a table on which the workpiece 1 is placed, 12 and 13 are this table 11
an X-axis drive motor and a Y-axis drive motor that respectively drive the
2 and the Y-axis drive motor 13 to move the table 11 in the X-Y direction so that the workpiece 1 draws a desired shape relative to the processing portion 2A of the wire electrode 2. This equipment generally consists of copying equipment, N/C equipment, electronic computers, etc.

15 is a machining power supply device for electric discharge machining, which is a DC power supply 16
, a switching element 17, a discharging capacitor 18, a charging current limiting resistor 19 of this capacitor 18, and a control device 20 that controls ON/OFF of the switching element 17. It consists of an oscillator that turns on and off the switching element 17 periodically.

Figure 2 shows the machining power supply 15 of this device and the workpiece 1.
FIG. 4 is a diagram illustrating the operation of the main part constituted by the machining gap where the wire electrode 2 and the machining section 2A of the wire electrode 2 face each other.

The discharging capacitor 18 is charged via the resistor 19 while the switching element 17 is ON, and the voltage Vc between the terminals of the discharging capacitor 18 after charging for t hours is equal to the voltage of the DC power supply 16 compared to the voltage of the E1 discharging capacitor. If the capacitance of 18 is C and the resistance value of resistor 19 is R, charging should occur as shown by the curve.

However, a leakage current flows through the machining fluid 3 into the machining gap between the machining part 2A of the wire electrode 2 and the workpiece 1, and a leakage resistor with a resistance value r is connected to the machining gap as shown in the figure. The charging characteristic curve of the discharging capacitor 18 in this case is expressed by the following equation.

Here, the leakage resistance value r is not only related to the specific resistance of the machining fluid 3, but also changes constantly due to the influence of machining waste generated during machining, machining conditions, flow rate and flow rate of the machining fluid 3, etc. The reality is that the charging curve of the terminal voltage Vc of the discharging capacitor 18 expressed by equation (2) is constantly changing.

If the voltage Vc between the terminals when the discharging capacitor 18 charged in this way starts discharging into the discharging gap is the discharging starting voltage ■D, then this discharging starting voltage V.

changes constantly under the influence of the change in the charging curve . As a result, the discharge starting voltage ■. sometimes became abnormally high. On the other hand, the discharge starting voltage V.

The energy W released from the discharge capacitor 18 when discharged into the discharge gap is expressed by the following equation. In other words, the machining energy released into the discharge gap is the discharge starting voltage■.

It is related to the square of the discharge starting voltage V. If the value is increased, the amount of cutting of workpiece 1 in one discharge will increase, but on the other hand,
The amount of wear on the processed portion 2A of the wire electrode 2 also increases,
If the discharge starting voltage V was too high, there was a risk of wire breakage. Therefore, when it is necessary to increase machining efficiency, it is ideal to set the voltage E of the DC power supply 16 high to apply energy close to the limit of wire breakage to the machining gap and process at high speed. When setting the voltage E of the power supply 16, it must be set to a low value so that wire breakage does not occur even under the worst conditions, taking into account the fluctuation of the leakage resistance value r, and as a result, the machining speed may not be too high. The disadvantage was that the machining efficiency was poor.

Moreover, since the cutting amount of the workpiece 1 is related to the square of the discharge starting voltage ■D, if this discharge starting voltage VO changes widely, the machining groove width will also change, which has the disadvantage of deteriorating the machining accuracy. I had both.

In order to eliminate this drawback, it is necessary to suppress the discharge starting voltage V・D below a certain value. For example, as shown in FIG. It is sufficient to provide a circuit 21 for bypassing the voltage, and this bypass circuit is generally composed of a constant voltage element such as a Zener diode.

However, when the bypass circuit 21 is provided in this way, after reaching the terminal voltage Vc of the discharging capacitor 18, a current of 13 shown by the following equation flows through this circuit.
1 consumes power of Ps.

Here, examples of values generally used as processing conditions are E=300■, VS=150V, . When R=20Ω, PS=1125W, and this power is not only wasted, but also becomes heat, resulting in the problem that the heat must be dissipated. In particular, in wire-cut electrical discharge machining, which requires accuracy of several microns, thermal distortion of the machine body due to such a large amount of heat is
This was unfavorable in terms of accuracy and had a fatal flaw.

In order to eliminate the above-mentioned drawbacks, a method shown in FIG. 4 has been proposed in which the generation of wasteful power is prevented by only switching.

The same reference numerals in the figures indicate the same or corresponding parts, 31, 32
, 33, and 34 have resistance values R1, R2, and R3, respectively.
, R4 resistor, R2/(R1+R2)=R4/(R
3+R4), and operates as a voltage dividing resistor to divide the voltages E1 and E2 at both ends of the discharge capacitor 18 with respect to the reference point G at the same ratio to obtain voltages 11 and 12 at controllable levels. ing.

22 inputs these voltages e1 and E2 and calculates the difference (E2-
FIG. 5 shows an example of a difference detection circuit that outputs e1).

In this figure, 35, 36, 37, 38 are the resistance values R,...
R6, R7, and R8 are all equal resistors, and 23 is an operational amplifier, whose output voltage is set to EOl (+) side voltage by ε2, (
1) If the side voltage is ε1, ε2 and j1 can be expressed by the following equation. Here, since the amplification degree of the operational amplifier 23 is set to a value close to infinity, the potential difference between the (+) and (-) input terminals is approximately O.
■, and it can be seen that ε1=ε2, and as a result e1
/2+EO/2=E2/2 is obtained, and the output E of the operational amplifier 23 is obtained.

is the difference between e1 and E2 (E2-e1) and operates as the difference detection circuit 22. 24 is a comparator that compares the output (E2-e1) of this difference detection circuit 22 with a reference voltage Vref set as a value proportional to the constant voltage ■S, and when (E2-e1)>Vref, the switching element 17, outputs a signal to set it to 0FF.

25 is an AND circuit into which the output of the comparator 24 and the output of the oscillator 20 are input, and outputs a signal that turns the switching element 17 ON only when both signals that turn the switching element 17 ON are given.

26 is an amplifier that amplifies the output of this AND circuit 25;
The switching element 17 is controlled ON-OFF by this output.

In the power supply device configured in this way, the terminal voltage Vc of the capacitor 18 is controlled by 0FF of the switching element 17.
Since this prevents the voltage from rising, there is no wasteful heat generation, but the switching element 17 actually has a "delay" problem, and the time from when the predetermined voltage is reached until the switching element 17 turns 0FF is Usually takes about 1 ps.

For example, if the capacitor 18 is set to 0. ? F, and when you want to set the terminal voltage ■C to 100V, assuming that the original DC voltage is 300V and the charging resistance is 10Ω, the charging current at this time is 2
Since it is 0A (1=81??11), the capacitor 18
The voltage ΔV that rises after being charged during 1 psec is as follows.

After this, due to the leakage current between the electrodes, the capacitor 18
Since the terminal voltage ■C becomes less than 100V again, the switching element 17 is turned on, and almost at the same time it becomes more than 100■ and a 0FF signal is output, but it becomes 140■ again.The process repeats, so the original defect is solved. It won't be. The present invention aims to eliminate the above-mentioned drawbacks, stabilize and smooth the voltage peak value, and prevent the generation of wasteful thermal energy.

FIG. 6 is a circuit diagram showing one embodiment of the present invention, which will be described in detail below.

Large capacity capacitor C. has the function of preventing the voltage of the processing capacitor 18 from rising rapidly and keeping the average value of the peak voltage constant. The capacitor C. teeth,
Anti-reverse diode D. Therefore, even if current flows from the machining gap, no machining current flows. Resistor R9 is the capacitor C mentioned above. This is a leak resistance that prevents the terminal voltage VCO from increasing. Now, the above capacitor C. The terminal voltage ■COl, that is, the voltage corresponding to the average value of the peak voltage, is divided by the voltage dividing resistors R1 and Rll, and the voltage corresponding to the average value of the peak voltage is divided by the voltage dividing resistors R1 and Rll. This output voltage is the difference voltage from the terminal voltage Vc of the capacitor 18 in the machining gap.If the comparison voltage of the comparator 24'' is 0V, if Vc>VCO. At this time, the switching element 17'' is set to 0FF via the driving amplifier 26'' of the N1 gate 255 switching element 17', and when Vc<VCO, the signal from the oscillator 20 is applied to the switching element 17'', and the switching element 17'' is turned off. 17'' repeats ON-OFF. Switching element 1
The collector resistance Rl2 of 7" is larger than the resistance 19 of the main circuit, and is approximately equivalent to the leakage resistance of the processing gap. According to the above configuration, due to the delay of the switching element 17 of the main circuit, The terminal voltage Vc of the capacitor 18 is set to a value larger than the voltage determined by the reference value ■Ref, but after that it is maintained near VCO by the weak current generated by the resistor Rl2 and the switching element 17'.
Vc no longer has a large ripple as in the circuit shown in the figure. The setting value Vref is set by Vref during machining.
If the selection is made while looking at CO, the desired peak voltage can be set without any problem even if there are variations in the delay of the switching element 17. The power supply device according to the present invention is configured as described above, and when used in a wire-cut electric discharge machining device, even if the machining conditions for wire-cut electric discharge machining are set to a machining speed close to the limit of wire breakage, the electric discharge Since the charging voltage of the capacitor is regulated, there is no risk of wire breakage due to an increase in the discharge starting voltage D due to changes in leakage current in the machining gap, and it is possible to increase the machining speed to the limit. As a result, machining efficiency is greatly increased, and variations in discharge starting voltage VD can be reduced, resulting in improved machining accuracy.

In addition, the power supply device according to the present invention does not generate an abnormally high discharge starting voltage even in general electrical discharge machining equipment as well as wire-cut electrical discharge machining equipment, and the variation in the discharge starting voltage is reduced. It is possible to solve problems such as changes in clearance and clearance, and improve machining accuracy.

As explained above, the power supply device for electrical discharge machining according to the present invention can limit the terminal voltage of the discharge capacitor to a desired constant voltage, so by using this power supply device, machining accuracy and machining efficiency can be improved. In addition to being able to perform measurements, it is also efficient as a power supply device, and the economic effects of this invention and the effects on improving the quality of processed products are extremely large.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing the configuration of a conventional wire-cut electrical discharge machining device, Fig. 2 is an explanatory diagram of the operation of its main parts, Figs.
FIG. 5 is a circuit diagram of a difference detection circuit, and FIG. 6 is a circuit diagram of an embodiment of a power supply device according to the present invention. In the figure, 1 is a workpiece, 2 is a wire electrode, 3 is a machining fluid, 15 is a power supply device, 16 is a DC power supply, 17 and 17'' are switching elements, 18 and C0 are discharge capacitors, and 23
, 23'' are difference detection circuits, and 24 and 2C are comparators.

Claims (1)

[Scope of Claims] 1. A DC power supply that charges a first capacitor that performs electrical discharge machining by causing discharge to occur in a machining gap formed between an electrode and a workpiece via a machining fluid, from this DC power supply. In the device comprising a plurality of switching elements for controlling charging of the first capacitor, when the voltage between the terminals of the first capacitor exceeds a desired constant value, the first A first control circuit that controls not to charge the capacitor, a second capacitor that maintains the average value of the peak voltage of the first capacitor, and a second capacitor that compares the voltage of the first capacitor and calculates the A second control circuit is provided for controlling the remaining switching elements so as not to charge the first capacitor when the voltage across the terminals of the first capacitor becomes equal to or higher than the voltage across the terminals of the second capacitor. Features of electrical discharge machining power supply device. 2. The electric discharge machining power supply device according to claim 1, which is used for wire cut electric discharge machining.