JPH0460765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a power supply device for electric discharge machining that is optimal when a conductive machining fluid is used as the machining fluid.

[Conventional technology]

Conventionally, this type of power supply device has been shown in the circuit diagram of FIG. In the figure, 1 is a machining DC power supply with an output voltage of E volts, 2 is a switching element, 3 is an oscillator, 4 is a variable resistor for controlling the machining current (its resistance value is R ohm), and 5 is a machining electrode 51 This is the gap formed by the workpiece 52 and the workpiece 52. Since general electrical discharge machining equipment uses an insulating liquid such as mineral oil or kerosene as its machining fluid, the voltage applied to the gap 5 is as shown in 6 in Figure 4 during no load (the period is 30). The voltage and current waveforms during processing (the period is 31) are shown as 7 and 8 in FIG. 4, respectively.

However, when using water or a machining fluid that is a mixture of water and an organic compound, since these machining fluids are conductive, there is a gap between the machining holes as shown in [1] below, as shown in Figure 5. There is a resistance value (assumed to be Rg ohms), which causes a reactive current to flow between the poles.

Rg=ρ×l/s … [1] However, ρ: Specific resistance of machining fluid (Ω-cm) l: Distance between machining electrode 9 and workpiece 10 (cm) s: Machining electrode 9 and workpiece 10 (cm ² ) Here, the following (a) to (c) are considered to be the causes of the variation in the value (Rg) of the inter-electrode resistor 11.

(a): Change in ion concentration (reciprocal of specific resistance) in the machining fluid due to electrolysis of machining fluid and sludge due to arc or reactive current during electrical discharge machining, that is, change in resistivity (ρ).

(b): Change in the gap distance (l) due to the gap servo or a change in the facing shape of the machining electrode 9 and workpiece 10 as machining progresses.

(c): Changes in the facing area s between the machining electrode 9 and workpiece 10 as electric discharge machining progresses, and substantial opposition due to gases such as hydrogen gas and methane gas generated between the electrodes due to electrolysis of the machining fluid. Change in area s.

Also, as can be easily seen from the above formula [1],
The smaller the specific resistance ρ between the electrodes and the distance l between the electrodes, and the larger the facing distance s, the smaller the value of the resistance Rg between the electrodes. It is shown in Figure 6. In addition, between poles 5
The equivalent resistor of is indicated by 11. FIG. 7 is a diagram of voltage and current waveforms in the gap 5 mentioned above. In FIG. 7, in the region where the DC voltage E is applied to the gap 5 and machining has not yet started, that is, in the no-load region period 12, a reactive current Ie of ₁ ampere flows and the no-load voltage value _V0 volts. is lower than the DC voltage E volts. When this period 12 passes and the next period 21 begins and discharge starts, the voltage between the electrodes is approximately
The discharge arc voltage Varc has constant voltage characteristics of 20-30 volts. The total current I ampere flowing through the electrode gap 5 is the sum of the discharge current Id and the reactive current _Ie2 . No-load voltage V ₀ and reactive current Ie ₁ mentioned above
and Ie ₂ , the discharge current Id flowing between the electrodes during discharge, and the total current I are respectively calculated from [2] to
[7] It is expressed by the formula. However, the voltage drop across the switching element 2 is ignored.

V ₀ = (E×Rg)/(R+Rg)=E/(1+R/
Rg) … [2] Ie ₁ = V ₀ / Rg = E / (R + Rg) … [3] Ie ₂ = Varc / Rg … [4] Id = (E-Varc) / R-Ie ₂ … [5] I =Id+Ie ₂ … [6] = (E-Varc)/R … [7] [Problem to be solved by the invention] Easier than the above formulas [2], [3], [4], and [5] So that you can guess. The interpole resistance value Rg fluctuates due to the causes (a) to (c) mentioned above, and when this becomes smaller, a large reactive current Ie ₁ flows, which causes the no-load voltage V ₀ to drop and discharge to occur. The problem was that it became difficult. In addition, if the inter-electrode resistance value Rg fluctuates unstablely, the no-load voltage V ₀
and the discharge current Id becomes unstable. Therefore, there were problems in that stable electrical discharge machining could not be performed and uniform surface roughness could not be obtained.

Conventionally, in order to solve the above problems, the specific resistance (ρ) of the machining fluid was increased using ion exchange resin, etc.
A method has been used to reduce the reactive currents Ie ₁ and Ie ₂ to prevent machining from becoming impossible, but this method has the disadvantage of higher running costs compared to using an insulating machining fluid such as kerosene. be. In addition, when machining a complex shape such as a three-dimensional shape, the resistance value Rg between the machining electrodes fluctuates due to various changes in the facing area S between the machining electrodes, which is insufficient to obtain stable electrical discharge machining. .

This invention was made to solve the above-mentioned problems.In an electrical discharge machine that uses conductive machining fluid, electrical discharge machining is possible even if the inter-molar resistance value fluctuates and this decreases or becomes unstable. The purpose of this invention is to provide a power supply device that does not become disabled or unstable.

[Means for solving problems]

The electric discharge machining power supply device according to the present invention is equipped with a DC constant voltage source whose output voltage is lower than the discharge arc voltage, and during the suspension period of the discharge voltage, the DC voltage source is connected to the DC voltage source through a current limiting resistor between the electrodes. A device that applies a voltage with the same polarity as the DC power supply for electrical discharge machining and detects the voltage or current generated between the electrodes due to the voltage, and an output signal of this detection device that detects a no-load voltage or a voltage higher than the discharge generation voltage. The device is equipped with a control device that changes and controls the internal impedance of the DC power source so as to supply a discharge current corresponding to a predetermined surface roughness.

[Effect]

The voltage or current generated between the poles by the DC constant voltage source during the pause period of the discharge voltage is detected by the detection device and input to the control device. This control device calculates the required internal impedance of the processing DC power source and controls the resistance value of the variable resistor to be changed to the calculated value.

[Embodiments of the invention]

Hereinafter, a power supply circuit according to an embodiment of the present invention will be explained with reference to the circuit diagram of FIG. In FIG. 1, elements having the same reference numerals as in FIG. 3 are the same elements. 13 is a rectifier, 14 is a discharge arc voltage Varc
DC constant voltage source with output voltage Va volts:
15 is a current limiting resistor (its resistance value is Ra ohm) that protects the machining electrode 51, workpiece 52, and DC constant voltage source 14 when the gap 5 is short-circuited;
6 is the current Ia flowing between the poles by the DC constant voltage source 14
17 is a DC constant voltage source 14
The voltage Va output by the current limiting resistor 15
A voltage measuring device 18 detects the voltage Vag that is divided by the electrode-to-electrode resistor 11 and appears between the electrodes; The current measuring device 16, voltage measuring device 17, and converter 18 are collectively referred to as a detection device. 19 is the converter 18
This is a control device that calculates the inter-electrode resistance value during the pause period of electrical discharge machining based on the current value Ia or voltage value Vag output from the control device, and changes and corrects the value R of the variable resistor 4. Then, by correcting the resistance value R, V ₀ during no-load is raised to a level higher than the discharge voltage Vd, and a discharge current Id during discharge corresponding to a predetermined surface roughness is supplied.

FIG. 2 is a voltage and current waveform diagram for explaining the operation of the embodiment device shown in FIG. 1. That is, the DC constant voltage source 14 has an output voltage Va of approximately 30
It has a discharge arc voltage Varc of volts or less, has the same polarity as the machining DC power supply 1, and is connected to the machining gap 5 via a rectifier 13 and a current limiting resistor 15. Note that the output voltage Va is applied to the electrode gap 5 only during the pause period 20 of the discharge voltage. Current Ia flowing in the gap 5 during this period 20 or voltage appearing in the gap 5
If Vag is detected by the detection device, the low resistance value Rg between poles during this period 20 can be determined from the following equation [8].

Rg=Vag/Ia=(Va-RaIa)/Ia... [8] Therefore, the value R of the variable resistor 4 that makes the voltage _V0 during the no-load voltage period 12 equal to or higher than the discharge generation voltage Vd of approximately 50V , and the value R of the variable resistor 4 that causes a predetermined discharge current Id to flow during the period 21 when the discharge has started is calculated by the control device 19 from the above-mentioned formulas [2] and [5] to find this value. is possible. The control device 19 then corrects the resistance value R of the variable resistor 4 to this calculated value.

As for the calculation method of the control device 19, there are a real-time numerical calculation method, a simple method of comparing the magnitude with a reference value, a data table method, and the like. Contrary to the above, if the output voltage Va of the DC constant voltage source 14 is higher than the arc voltage Varc, a steady arc state will occur in which discharge occurs when this voltage is applied between the electrodes and the workpiece. There may be a corresponding adverse effect.

In the above embodiment, the rectifier 13 is used, but this uses a switching element such as a transistor to switch the DC voltage source 1 only during the rest period 20 of the discharge voltage.
4 voltages may be applied. In addition, we considered a variable resistor 4 equivalent to the internal impedance of the processing DC power supply 1, but this is a method in which multiple resistors are connected in series and in parallel, and the resistance values are switched and controlled using a switching element. Any method is acceptable. Furthermore, although the above embodiments have been described with respect to a die-sinker electric discharge machine, similar effects can be obtained with a wire electric discharge machine.

〔Effect of the invention〕

As described above, according to the present invention, the inter-electrode resistance value during the suspension period of the discharge voltage is calculated and determined, and the internal impedance of the DC power supply is thereby changed and corrected, and the discharge voltage is discharged during the no-load voltage period. By applying a no-load voltage higher than the generated voltage between the electrodes and passing a predetermined discharge current during the discharge period, it is possible to improve surface roughness even when machining complex three-dimensional shapes where the electrode gap tends to be unstable. Stable machining performance such as machining speed and reproducibility of machining accuracy can be achieved with an inexpensive circuit configuration consisting only of electronic circuits. Also, in resistivity control, it is possible to set the "target" resistivity to an economical value, which brings about an extremely advantageous effect industrially.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a power supply device for electrical discharge machining according to an embodiment of the present invention, Fig. 2 is a voltage and current waveform diagram for explaining its operation, and Figs. 3 and 4 are conventional electrical discharge machining power supply devices. The power supply circuit diagram, voltage and current waveform diagrams, and Figures 5, 6, and 7 show a model diagram of the gap between the electrodes, an equivalent circuit diagram, and voltage and current waveform diagrams when a conductive working fluid is used. In the figure, 1 is a DC power supply, 2 is a switching element,
3 is an oscillator, 4 is a variable resistor, 5 is a gap between poles, 11 is a resistor between poles, 13 is a rectifier, 14 is a DC constant voltage source, 15 is a current limiting resistor, 16 is a current measuring device,
17 is a voltage measuring device, 18 is a detection device, and 19 is a control device. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In the power supply of the electric discharge machining equipment that performs machining using the discharge energy generated between the machining electrode and the workpiece, it is equipped with a DC constant voltage source with an output voltage lower than the discharge arc voltage, and during the period when the discharge voltage is inactive, a detection device that applies a voltage of the same polarity as the DC power source for electrical discharge machining between the electrodes from the DC constant voltage source through a current limiting resistor and detects a voltage or current generated between the electrodes by the applied voltage; The equivalent of the DC power supply is controlled so that the output signal of the detection device supplies a no-load voltage higher than the discharge generation voltage during the no-load voltage period and a discharge current corresponding to a predetermined surface roughness between the electrodes during the discharge period. 1. A power supply device for electric discharge machining, comprising: a control device for correcting and controlling target internal impedance.