JPS6311219A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To enable discharge current to be accurately controlled by measuring current flowing through two electrolytic current measuring electrodes and a working electrode to directly detect the electrolytic current during discharge for controlling the discharge current at a desired constant value. CONSTITUTION:Working current flowing through a variable limiting resistor 3 flows to a workpiece 4 through a working electrode 5 and electrolytic current measuring electrodes 6, 7. Here, the sum Ia of discharge current and electrolytic current flowing through the working electrode 5 and electrolytic currents Ib, Ic flowing through the electrolytic current measuring electrodes 6, 7 are respectively measured by current measuring devices 9-11. And a detector 12 obtains electrolytic current IE during discharge of working electrode 5 and further discharge current ID=Ia-IE from current values Ia-Ic and interpolar distances a, a+b, a+c so that the variable limiting resistor 3 is controlled by a control unit 15 to set the discharged current to a desired constant value. Thus, the discharge current can be controlled with higher accuracy and speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electric discharge machining apparatus that uses a conductive machining fluid as a machining fluid.

[Prior Art] Conventionally, there has been an electric discharge machining apparatus as shown in FIG. 2 as this type of electric discharge machining apparatus.

In the figure, (1) is a DC power supply, (2) is a switching element, (3) is a variable limiting resistor, and (4) is an electrode facing area S.
(cm2), (5) is the workpiece (5
), and (13) is the switching element (2).
(14) is a voltage detection transmitter, (15)
is the control device.

In the electric discharge machining apparatus having the above configuration, it is known that when a conductive machining fluid is used as the machining fluid, an electrolytic current that does not contribute to machining flows.

Therefore, not only the machining current for machining the workpiece (4) decreases, but also the electrolytic current and the discharge current fluctuate as the gap state changes, causing the machining current to deviate from a desired value.

In order to prevent and control such situations, conventionally a predetermined voltage is applied between the poles, and the machining current is controlled by a control device (
15) as follows.

That is, FIGS. 3(a) and 3(b) are characteristic diagrams showing fluctuations in the inter-electrode voltage and inter-electrode current when the vertical axis represents the inter-electrode voltage and the inter-electrode current, and the horizontal axis represents time.

In the same figure, (16) is the electrode-to-electrode voltage in the pre-discharge state where only electrolytic current is flowing, and these are denoted by v and o.

Moreover, (17) is the interelectrode current in the above-mentioned pre-discharge state, and this is designated as Iro.

In addition, (18) in the figure is an electrolytic current IED that does not contribute to machining.
shows.

Therefore, conventionally, the inter-electrode resistance has been calculated by measuring the inter-electrode voltage VGO and the inter-electrode current IEO in the pre-discharge state shown in FIG. 3, etc.

That is, if the inter-electrode resistance is R, then this inter-electrode resistance Rf
is calculated from the following equation (1), and the discharge current and electrolytic current are indirectly detected on the assumption that the electrode-to-electrode resistance is the same during discharge as before discharge.

Rg=v9o/lEo...Equation (1) However,
Conventionally, the control device! ! The discharge current was controlled via (15).

[Problems to be solved by the invention] The discharge current in conventional electrical discharge machining equipment is controlled based on indirect calculation results as described above, but during discharge, sludge and gas actually flow between the machining electrodes. Therefore, the interelectrode resistance value is considered to be quite different between when discharging and when not discharging, and it is said that indirect discharge current detection as described above cannot accurately control the discharge current. There was a problem.

This invention was made to solve the above-mentioned problems, and instead of detecting the discharge current indirectly, the present invention separates and directly detects the discharge current and electrolytic current even during discharge. The purpose is to accurately control the discharge current based on the results.

C. Means for Solving Problems] The electric discharge machining apparatus according to the present invention includes two electrolytic current measuring wires, which have different distances from each other and are insulated and fixed to the machining electrode, in addition to the machining electrode. It is equipped with electrodes for

[Function] The electrical discharge machining apparatus of the present invention measures the current flowing through three electrodes including the electrolytic current measuring electrode and the machining electrode with the current measuring device, and from these current values,
The electrolytic current during discharge is directly detected by a detection device, and the current is controlled so that the discharge current is at a desired constant value.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the structure of an electric discharge machining apparatus according to the present invention.

In the figure, (6) and (7) are the processing electrodes (5)
The electrolytic current measuring electrode is integrally fixed to the processing electrode (5) via an insulating support (11) so as to have an inter-electrode distance different from the inter-electrode distance between the electrode and the workpiece (4). .

Here, the electrolytic current measuring electrode (6).

(7) each has a unit area of electrode facing area, and the distance between the electrolytic current measuring electrode (G) and (7) is different from each other.

(9), (10), (11) are the machining electrodes (
5) and the electrolytic current measuring electrodes (6) and (7), respectively.

Now, the electrode facing area S of the processing electrode (5), this processing electrode (5), and the electrolytic current measuring electrode (6).

(7) The distance between the poles is a as shown in FIG.

a+b, a+c (where b≠c).

In addition, the current flowing through the machining electrode (5) and the electrolytic current measurement electrode (6), (?) during discharge is I a
* I b * I C.

Here, 1. is the sum of the discharge current and electrolytic current flowing through the machining electrode (5), and Ib and Ic are the electrolytic currents flowing through the electrolytic current measuring electrodes (6) and (7), respectively. Further, the electrolytic current flowing through the machining electrode (5) is IE, the specific resistance of the machining fluid is p, and the discharge voltage is V arc.

Furthermore, a processing electrode (5) and an electrolytic current measuring electrode (6
), (7) and the workpiece (0) are respectively R4-Rh + Re.

Incidentally, the inter-electrode resistance R, can be calculated from the following equation (2).

R9=ρ・1/S ・・・・・・Formula (2) However, R
1; Resistance between electrodes [Ω] ρ: Specific resistance of machining fluid [Ω・cml l: Distance between electrodes [C] S: Electrode facing surface m [0 wet 2J Therefore, the resistance between electrodes Ra - Rb * Re using, 1
1, Ib, and Ie are expressed as follows.

Next, by using the above equations (3) and (0) and eliminating Varc/ρ and a from equation (5), the electrolytic current IE is expressed by the following equation.

As mentioned above, the electrolytic current IE during the discharge of the machining electrode (5)
can be obtained without depending on the distance jlla.

Here, for example, if c=2b is set, then if the above-mentioned analog calculation is configured with an electric circuit in the detection device (12), it is possible to detect the electrolytic current during discharge, which was impossible with conventional methods. Can be done.

Further, as shown in the first-order equation (8), the discharge current can be directly detected in real time, and the machining current (discharge current) Io can be controlled.

I O= I a −I E・・・・・・・・・・・・
...Equation (8) [Effects of the Invention] As described above, according to the present invention, in addition to the processing electrode, two electrodes having mutually different interpolar distances and insulated and fixed to the processing electrode are provided. The electrolytic current during discharge is directly detected from the current value flowing through the three electrodes including these electrolytic current measuring electrodes and the processing electrode, and the discharge current is kept at a desired constant value. Since the structure is configured to control the current so that the discharge current is controlled more accurately and at a higher speed, the current This method is more effective in elucidating the discharge phenomenon in wet machining fluids.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an electric discharge machining apparatus according to the present invention, and FIG. 2 is a block diagram of a conventional electric discharge machining apparatus using a conductive machining fluid.
FIGS. 3(L) and 3(b) are characteristic diagrams showing variations in the inter-electrode voltage and inter-electrode current, with the vertical axis representing the inter-electrode voltage and inter-electrode current, and the horizontal axis representing time, respectively. (1)...DC power supply, (2)...Switching element, (3)...Variable limiting resistor, (0...Workpiece, (5)...Processing electrode, (6)
, (7)...electrode for electrolytic current measurement, (8)...
Insulating support stand, (9), (1G), (11)... Current measuring device, (12)... Detecting device, (13)... Transmitter, (15)... Control device.

Claims (1)

[Claims] In an electric discharge machining device that generates an electric discharge between a machining electrode and a workpiece and processes the workpiece with the discharge energy at that time, the machining electrode has different distances between the machining electrodes, and two electrolytic current measuring electrodes that are insulated and fixed to the processing electrode, a current measuring device that measures the current flowing through the three electrodes including these electrolytic current measuring electrodes and the processing electrode, and this current. An electrical discharge machining device characterized by having a detection device for directly detecting an electrolytic current during discharge from a current value measured by a measuring device and controlling the current so that the discharge current becomes a desired constant value. .