JPH04135119A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent a crack of a pulse current by connecting a comparator circuit, which compares preset pulse current conduction time with the actual pulse current duration time, and a control device. which changes resistance of a variable resistor by an output signal of the comparator circuit, to the variable resistor and a pulse current detector. CONSTITUTION:A pulse current during machining is detected as actual pulse current duration time in a pulse current detector 9, input to a comparator circuit 10 and compared with current duration time previously input to a control unit 11. A crack is discovered by the compared result, and when a resistance value of a variable resistor 8 is judged required to be changed, a signal is fed to the control unit 11 to change the resistance value in a direction of increasing it. When the resistance value is increased, a time constant, formed between the resistance value and stray capacity, is increased, so that an influence of the increase of virtual resistance 3 in a side of an electrode 2, causing generation of a crack, is decreased, as a result to suppress the crack. When the resistance value of the variable resistor 8 is increased, interpole voltage is increased to eliminate current leakage between poles, and also to suppress the crack.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrical discharge machining apparatus for surface machining a metal workpiece.

(Prior Art) As a surface processing means for a metal workpiece, an electrical discharge machining apparatus is available that can relatively easily and efficiently produce a good finish. FIG. 10 shows the basic circuit of this electrical discharge machining apparatus. Let me explain this. 1 is a workpiece set in oil (not shown), and 2 is a workpiece tm facing the workpiece l with a predetermined gap. This electrode 2 has an apparent resistance 3 to high frequencies. The end of the electrode 2 opposite to the workpiece 1 is connected to the first side of a DC power source 4, and the end of the workpiece 1 opposite to the t-transformer 2 is connected to a plurality of resistors 5a, 5b5n (there are more than two shown) each end is connected. At the other ends of each of the resistors 5a, 5b, and 5n, there is a transistor 6 whose emitter is connected to the negative electrode side of the DC power supply 4.
The collectors of a, 6b, and 6n are connected. The terminals of the transistors 6a, 6b, 6n are connected to output terminals 7a, 7b, 7n of the control device 7, respectively. Note that the resistance values of resistors 5a, 5b, and 5n are as follows:
The resistor 5a is the largest and the resistors 5n are set to become smaller.

When performing electrical discharge machining on the surface of the cut 1 to be machined in an electrical discharge machining apparatus having a circuit configured as described above, the resistor 5a is first turned on and off by the control device 5. As a result, the current from the direct current 1za4 becomes a pulse current, which has a peak value commensurate with the value of the resistor 5a, and flows only for the ON time of the transistor 6a. This pulsed current acts on the workpiece 1 and the electrode 2, which are opposed to each other with a small gap in the oil, to process the surface of the workpiece 1. When the pulse current is small, the surface of the workpiece l is machined finely and smoothly, but when the current value is small, so-called "cracks" (pulse cracks), which are breaks in xi, occur. become. The causes of this "cracking" are phenomena specific to high frequencies, such as the skin effect (increase in apparent resistance 3) of the electrode 2 under high frequency conditions and the displacement current from the electrode 2, and maintaining a predetermined current value when the current is small. It can be considered that this occurs because the process becomes impossible, but in any case, it is undeniable that it will result in processing defects.

Assuming that the cause of "cracking" is a phenomenon peculiar to high frequencies as mentioned above, which makes it impossible to maintain a predetermined value of microcurrent, it is necessary to reduce the skin effect of the workpiece and electrode, and also reduce the displacement current. It turns out that it's fine if you let them.

Therefore, when a "cracking" occurs in this way, the transistor 6a, which had been on until then, is turned off and the transistor 6b is turned on, thereby inserting a resistor 5b with a smaller resistance value into the pulse current circuit. so that As a result, the pulse current and current increase, so that the "cracking" that occurred due to the small current value of the pulse current disappears. “Crack” in pulsed current
Since the occurrence of this also depends on the area of the workpiece l facing the electrode 2, if the Na value increases, it will not be affected by it. What was made from this viewpoint is Japanese Patent Application Laid-Open No. 197123/1983, which is the prior art of the present invention.

(Problem to be Solved by the Invention) In the prior art described above, when a "crack" occurs in the pulse current, the transistors 6a, 6b, - are sequentially switched to increase the value of the pulse current. ,in this case,
It is considered that the electrode 2 is affected by a voltage drop due to the apparent resistance 3 and the displacement current, and there is a problem in that it is not possible to prevent a drop in the machining voltage due to the collector current set in advance in the transistors 6a, 6b, and 6n. At this time, since the influence of the displacement current also overlaps, it is impossible to cope with this problem unless the current value is further increased. However, when the current value increases, even if the effect of preventing "cracking" increases, the processed surface of the non-processed object 1 becomes rough, resulting in a problem that the processed surface has worse than desired properties.

Here, we will consider the cause of the occurrence of "1 crack".

The occurrence of "cracks" can be considered to be due to the following two causes. That is, one of them is caused by the resistance and stray capacitance of the wiring immediately between the workpiece and the electrode in the circuit, and the other is caused by the displacement current from the 1i pole due to high frequency. It is. For the former, the effect of capacitance (stray capacitance) can be reduced by increasing the time constant, and for the latter, it is possible to generate a current by compensating the voltage between the workpiece and the electrode. This can be solved by.

The present invention has been made in view of this point, and is based on the idea opposite to the above-mentioned prior art, and when a "cracking" occurs, the pulse current is adjusted in the direction of decreasing, thereby eliminating the "cracking". The object of the present invention is to provide an electric discharge machining apparatus that suppresses the occurrence of.

(Means for Solving the Problems) The present invention provides a first method for solving the problems described above.
As shown in the figure, in an electrical discharge machining apparatus that processes the surface of a workpiece 1 by applying a pulse current to the gap between a workpiece 1 and an electrode 2 facing the workpiece, a series connection is made in the current supply circuit for the pulsed current. A variable resistor 8 and a pulse current detection device 9 are inserted and connected to the variable resistor 8 and pulse current detection device 9, and a comparison circuit 10 for comparing a preset pulse current conduction time and an actual pulse current duration; The configuration is such that a control device II that changes the resistance value of the variable resistor 8 according to the output signal of the comparison circuit 10 is connected.

As another means, as shown in FIG.
In an electrical discharge machining apparatus that processes the surface of a workpiece l by applying a pulse current to the gap between the workpiece l and the electrode 2 facing the workpiece l, a variable resistor 8 is connected in parallel to the workpiece l and the electrode 2. At the same time, a pulse current detection device 9 is inserted and connected in series in the pulse current energization circuit, and the preset pulse current energization time and the actual pulse current duration are compared between the variable resistor 8 and the pulse current detection device 9. A comparator circuit 10 is connected thereto, as well as a control device II that changes the resistance value of the variable resistor 8 according to the output signal of the comparator circuit IO.

Note that the variable resistor 8 in the above configuration is not a pure resistance, but an impedance whose resistance value changes with changes in frequency.

(Function) With such a configuration, in the case of a configuration in which the variable resistor 8 and the pulse current detection device 9 are inserted and connected in series in a pulse current energizing circuit, the variable resistor 8 is By increasing the resistance value, the time constant for stray capacitance in the circuit can be increased, and voltage compensation can be made for the increase in resistance 171 in electrode 2. This makes it possible to suppress the occurrence of "cracking" within the current peak value of the set conditions. In addition, in the case of a configuration in which a variable resistor 8 is connected in parallel to the workpiece l and the t pole 2, the combined resistance value of the resistance value of the variable resistor 8 and the resistance value of the resistor in the electrode 2 is set. Although there are some difficulties, similar effects can be obtained without significantly changing the current value relative to the set conditions.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, 1 is a workpiece set in oil (not shown), and 2 is a tfj opposed to this workpiece 1 with a predetermined gap.

This electrode 2 has an apparent resistance 3 to high frequencies.

1 of the DC power supply 4 is connected to the end of the workpiece 2 opposite to the workpiece 1.
The positive side is connected, and one end of each of multiple resistors 5a, 5b, 5n (there are three or more resistors shown) is connected to the opposite end of the workpiece l from the electrode 2. It is connected. At the other ends of each of the resistors 5a, 5b, and 5n, there is a transistor 6 whose emitter is connected to the negative winding side of the DC power supply 4.
The collectors of a, 6b, and 6n are connected. The bases of the transistors 6a, 6b, and 6n are connected to the output terminals 7a, 7b, and 7n of the control device i7, respectively.6The resistance values of the resistors 5a, 5b, and 5n are as follows.
The resistor 5a is set to be large at the end and gradually become smaller toward the resistor 5n.

A workpiece l and a resistor 5a, which is a pulse current energizing circuit,
5b and 5n, a variable resistor 8 (not a pure resistance but an impedance whose resistance value changes depending on the frequency of the current flowing through it, the same applies hereinafter) and a pulse current detection device t9 are inserted and connected in series. ing. The variable resistor 8 and the pulse current detection device 9 include a comparator circuit IO that compares a preset pulse current conduction time with an actual pulse current duration, and the resistance of the variable resistor 8 is determined by the output signal of the comparator circuit 10. A control device that changes the value is connected. And for these comparison circuit 1G and control device H.

A control device 7 for switching the transistors 6a, 6b, and 6n and controlling the energization time is connected to them so that they operate in conjunction with each other. An external input board 12 is further connected to the control device H, so that the 5-pulse current application time can be set in advance to the resistor and the pulse current detection device.

When performing discharge heating in this device configured as described above, the variable resistor 8 is initially set at the resistance value O, and the control device 7 is turned on as in the conventional device shown in FIG. turns on transistor 6a and turns on resistor 5a
energize. As a result, a pulse current having a small value within a predetermined range flows between the workpiece l and the t-shape 2, and electrical discharge machining is performed on the surface of the workpiece l. The pulse current during processing is detected by the pulse current detection device 9 as the actual pulse current duration.

Since this detected value is input to the comparison circuit In, the comparison circuit IO receives this signal from the external input board 12 to the control device 1.
Compare with the pulse current duration (set value) input in advance in 1. If a "cracking" is found as a result of the comparison and it is determined that the resistance value of the variable resistor 8 needs to be changed, a signal to that effect is sent to the control device 11 and the resistance value of the variable resistor 8 is determined to be changed. Change the value in an increasing direction.

As the resistance value of the variable resistor 8 increases, the time constant formed between it and the above-mentioned stray capacitance increases, which is the cause of the "cracking". The influence of the increase in the apparent resistance 3 on the second side becomes smaller, and as a result, "cracking" is suppressed. Furthermore, as the resistance value of the variable resistor 8 increases, the voltage across the conductor increases, so current leakage between the conductors is eliminated, and this also helps to suppress "cracking".

FIG. 2 shows another embodiment of the present invention, in which the connection location of the variable resistor 8 is changed. In this case, a variable resistor 8 is connected to the workpiece l and the electrode 2 in parallel. There is no change in other parts. In this circuit, the variable resistor 8 is connected in parallel with the apparent resistance 3 of the electric generator 2, so when the resistance value of the variable resistor 8 increases, the combined resistance of these changes in a complicated manner. In any case, since they are connected in parallel, the resistance value becomes smaller than when the variable resistor 8 is not connected. Therefore, in terms of current value, it does not change much from the original set value, and "cracking" can be prevented.

FIG. 3 is a flowchart for explaining the operations of FIGS. 1 and 2. FIG. When machining is started in step 20, a reset command is issued from the external input board in step 21. As a result, if the 5 reset signal is output, in step 22, the variable resistor 8 is set to the resistance fffi.
It is reset to OΩ. When the reset signal is not output, the variable resistor 8 maintains its current state as shown in step 23. A pulse current flows in the state of step 22, and when a "break" occurs in the pulse current (step 24), the variable resistor 8 is driven so that the resistance value increases beyond a predetermined resistance value (step 25). When "cracking" does not occur, the variable resistor 8 maintains its current state as shown in step 23. Note that if the "cracking" cannot be suppressed by increasing the resistance value of the variable resistor 8 shown in step 25, the current is immediately interrupted.

Those shown in FIGS. 4 to 9 are forms of high-frequency resistors (designated with the same symbols for convenience) used as the variable resistor 8, respectively. That is, the one with the planar shape shown in FIG. 4 has a frontal shape as shown in FIG.
The one having the planar shape shown in FIG. 6 has a frontal shape as shown in FIG. Furthermore, the planar shape shown in FIG. 8 has a frontal shape as shown in FIG.

Although the power source is direct current, pulsed current can be thought of as a high-frequency current with a very small period, and since high-frequency current has the property of becoming a skin current, as shown in these figures,
It has a structure that generates a predetermined impedance when a high frequency current flows through the surface. Specifically, in the case of FIGS. 4 and 5, the disc part 14 is formed integrally with the rod-shaped part 13, and in the case of FIGS. 6 and 7, a rectangular cylinder 15 is formed. A large number of 16 characters are provided. Furthermore, in the case of FIGS. 8 and 9, the outer periphery of the rectangular cylinder 17 is made of a high resistance component.

In the present invention, the resistance value of the variable resistor 8 is gradually increased when a "crack" occurs in the pulse current, so it is convenient to make the resistance value of these resistors themselves adjustable. However, in practice, it is also possible to prepare a plurality of resistors of the same type but with slightly different resistance values, and to sequentially change the connections of these resistors.

Among the devices described above, in the device shown in FIG. 1, the variable resistor 8 and the pulse current detection device 9 are
and the resistors 5a, 5b, and 5n, but if the condition is met that there is a balance with the apparent resistance 3 in the electrode 2, it may be connected between the direct a power source 4 and the electrode 2. is also possible, and even when configured in this way, the same effects as those of the embodiment described can be expected. In an electrical discharge machining device that processes the surface of a workpiece by passing a pulsed current through the gap between the electrode and the electrode, a variable resistor and a pulsed current detection device are inserted and connected in series in the energization circuit for the pulsed current, or A variable resistor is connected in parallel to the workpiece and the electrode, and a pulse current detection device is inserted and connected in series to the pulse current energization circuit, and a preset pulse is connected to the variable resistor and the pulse current detection device. Wj
It has a configuration in which a control device that changes the resistance value of the variable resistor is connected. By increasing the resistance value of the variable resistor, the voltage between the electrodes decreases, which eliminates current leakage between the electrodes and prevents the pulse current from cracking within the current peak value of the 5 setting conditions. can.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of embodiments of the present invention, FIG. 3 is a flow chart for explaining the operation of the components shown in FIGS. 1 and 2, and FIGS. 4, 6, and 8. 1 is a plan view of a resistor used as a variable resistor, FIGS. 5, 7, and 9 are front views of the same resistor, and FIG. 1O is a circuit diagram of the prior art. 1...Workpiece 2...Electrode 4...DC power supply 6a...Transistor 7.11...Control device 8...Variable resistor 9...Pulse current detection device! 0-- Comparison circuit Figure 1 Patent Applicant: Toyota Motor Corporation 4...a, tt, original 6a-r-Fungistaff, 11 Control device 8 Variable mode 9 No. 9 No. Vru or electric charge clamping device ℃・Comparison episode! Figure 3

Claims (2)

[Claims] (1) In an electric discharge machining device that processes the surface of a workpiece by passing a pulsed current through a gap between the workpiece and an electrode facing the workpiece, a variable resistor is connected in series in the pulsed current supply circuit. A pulse current detection device is inserted and connected to the variable resistor and the pulse current detection device, and a comparison circuit that compares a preset pulse current conduction time and an actual pulse current duration, and an output signal of the comparison circuit are used to connect the variable resistor and the pulse current detection device. An electrical discharge machining device characterized by being connected to a control device that changes the resistance value of the device. (2) In an electrical discharge machining device that processes the surface of a workpiece by passing a pulse current through the gap between the workpiece and an electrode facing the workpiece, a variable resistor is connected in parallel to the workpiece and the electrode. At the same time, a pulse current detection device is inserted and connected in series in the pulse current energization circuit, and the pulse current energization time set in advance and the actual pulse current duration are compared between the variable resistor and the pulse current detection device. An electric discharge machining apparatus characterized in that a control device is connected to a circuit and a control device that changes the resistance value of the variable resistor according to an output signal of the comparison circuit.