JP2572416B2 - Electric discharge machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining apparatus which copes with interruption of electric discharge during electric discharge duration in electric discharge machining, that is, a so-called arc interruption phenomenon, and particularly relates to finishing and fine machining. The present invention relates to an electric discharge machining apparatus suitable for high precision due to low electrode consumption.

[Conventional technology]

In the electric discharge machining, machining is performed by repetitive electric discharge by a machining pulse supplied to a machining gap formed between a machining electrode and a workpiece, and the input energy of the machining pulse is relatively small, for example, a finishing machining area or a fine machining area. in order peak value I _P of the machining current pulses less and less 4A, difficult to maintain the discharge, in an unstable state. Therefore, an arc that interrupts the discharge arc once generated during the application of the machining pulse due to some phenomenon that occurs in the machining gap, or an effect that is considered to be due to the resonance phenomenon due to the floating capacitance and the inductance and resistance of the wiring existing in the discharge circuit. Cutting phenomenon occurs,
For this reason, it was confirmed that the machining current pulse was divided and a machining current pulse having a pulse width smaller than the set value was generated.

In the electric discharge machining characteristics, if the current peak value _Ip is the same in the range of stable machining, the current pulse width and the electrode wear rate are in an inverse relationship, and thus the occurrence of arc break development increases the electrode wear rate. . Here, the time width of the arc interruption varies, and for example, there is a very short time width of 100 ns or less. It was confirmed that such short-time arc interruption can be ignored with respect to an increase in the electrode consumption rate. Therefore, it is necessary to control arc breaks of a predetermined time width or more to reduce the processing current pulse having a short width. However, heretofore, there has not been found any technology relating to this kind of arc interruption and its time width control.

[Problems to be solved by the invention]

As described above, conventionally, no consideration has been given to arc breaks and their time widths, and arc breaks frequently occur in finishing or micromachining areas where the processing energy is relatively small, and short-width processing current pulses are continuously generated. Therefore, there is a problem that the electrode consumption rate increases and the accuracy decreases.

The object of the present invention is caused by an arc break. An object of the present invention is to provide a high-precision electric discharge machine by reducing the frequency of occurrence of machining current pulses having a width shorter than a predetermined value and suppressing an increase in the electrode wear rate.

[Means for solving the problem]

The above object is to perform on / off switching control of a switch element so as to extend application of a machining pulse by a preset discharge duration from a time point at which an arc break is detected for a predetermined time width or more, when the arc break disappears. This is achieved by:

[Action]

The detection of an arc break of a predetermined time width or more is performed by comparing the detected value of the discharge voltage, discharge current, or impedance of the machining gap with a predetermined value for a predetermined period during the discharge duration, and the detected value satisfies the condition of the arc break. If the time width is equal to or more than the predetermined value, and the arc break has disappeared during the application of the normal machining pulse, the time width is further compared with the predetermined value. The switch element is controlled to extend the application. As a result, since the processing pulse is conventionally turned off regardless of the occurrence of the arc break, a short-width processing current pulse that has been generated after the disappearance of the arc break does not occur, thereby suppressing an increase in the electrode consumption rate. be able to. Further, if an arc break of a predetermined time width or more is detected and the arc break disappears during the application of a normal processing pulse, a processing current having a desired width is generated from the disappearance point, so that the processing speed is not impaired.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, 1 is a working electrode, 2 is a workpiece,
A machining gap g is formed facing these. Reference numeral 3 denotes a power supply for processing, which is supplied to a processing gap g via a switch element 4 of a transistor and a current limiting resistor 5 in series. Reference numeral 6 denotes an RS flip-flop for controlling ON / OFF switching of the switch element 4. The RS flip-flop 6 is an underflow signal of the down counter 7 for measuring the discharge duration and the down counter 8 for measuring the off time, and is reset by a signal from the output terminal MIN. Operation and set operation are performed. Reference numeral 9 denotes a clock pulse oscillating circuit for the counters 7 and 8, and the output clock pulse is input to the clock input terminals CK of the counters 7 and 8, respectively. Numerals 10 and 11 denote discharge duration and off time setting circuits, respectively. The setting time is a product of the set value and the oscillation cycle of the oscillation circuit 9.

Reference numeral 12 denotes an operation amplifying circuit as a circuit for detecting the voltage of the machining gap g. The output voltage thereof is output from a voltage setting circuit 14 for setting a voltage corresponding to the level at which the arc is cut off by a voltage comparison circuit 13 (e.g. ), And the H signal which is a logic high level if the arc break level is exceeded,
If it is less than this, the low level L signal is applied to one input terminal of the AND circuit 15 which is the final stage of the first discriminating circuit. Reference numeral 16 denotes a detection circuit for detecting a discharge duration. The output voltage of the amplifier circuit 12 corresponding to the voltage of the machining gap g and the control signal of the switch element 4 start the discharge after the application of the machining pulse to reduce the arc voltage. An H signal is output after the generation until the processing pulse is turned off. The output signal of this detection circuit 16 is applied to the other input terminal of the AND circuit 15 and A
As the output of the ND circuit 15, a pulse signal of an arc interruption which becomes H level only when an arc interruption occurs is obtained. On the other hand, the detection circuit 16
The level of the output signal is inverted by the NOT circuit 17 and input to the enable terminal of the counter 7 to stop the wave counting operation during the discharge delay time even during the application of the machining pulse, and to count only during the discharge duration time. Can work.

Reference numeral 18 denotes a one-shot circuit which detects the rising of the arc break and outputs a pulse having a set time width of the arc break. The time width is set by the variable resistor 19 (for example, 100 ns). The output of the AND circuit 15, which is the pulse signal of the arc cut, is corrected by the delay circuit 20 by the signal propagation delay time of the one-shot circuit 18, and the AND circuit 21 performs AND with the signal of the inverted output terminal of the one-shot circuit 18. Ask.
As a result, the H signal is generated at the output terminal of the AND circuit 21 only when the pulse signal of the arc break exceeds the set time. This signal is input to the one-shot circuit 22, where only the falling edge at the time when the arc is extinguished is detected, and an L signal pulse having a constant width is generated at its output terminal. This signal and the control signal of the switch element 4 are applied to an AND circuit 23 which is the final stage of the second discriminating circuit, and the output thereof is supplied to a load signal input terminal ▲ ▼ of the set value (preset data) of the counter 7. Added. Thereby, when the arc break does not occur, the normal count operation is performed by the control signal of the switch element 4, while the arc break occurs, and the arc break occurs before the turning off of the machining pulse (applied voltage pulse). When the arc is extinguished and the arc break time exceeds the set value, the count operation can be performed again by the set value of the discharge duration from the time when the arc break has disappeared.

The counting operation of the machining pulse off time is performed as follows. That is, to load the set value of the off-time, the signal of the inverted output terminal of the flip-flop 6 is input to the load signal input terminal ▲ ▼ of the counter 8, and the count stop during the processing pulse on-time is performed by the terminal of the flip-flop 6. This can be performed by inputting a signal obtained by inverting the signal by the NOT circuit 24 (or a signal at the output terminal Q of the flip-flop 6) to the enable terminal of the counter 8.

In FIG. 2, (a), (b), and (c) are waveform diagrams of the applied voltage pulse (machining pulse), discharge voltage, and machining current of the above embodiment, or (d), (e). , (F)
FIG. 3 is a waveform diagram of an applied voltage pulse (machining pulse), a discharge voltage, and a machining current in a conventional apparatus. In these waveform diagrams, A, D, H, and L are waveforms when an arc break occurs and its time width is short. B, E, J,
M is a waveform when an arc break occurs and the applied voltage pulse is turned off before the arc break disappears. A, D
, H, L, B, E, and J and M, there is no difference between the case of the apparatus of the present invention and the case of the conventional apparatus. on the other hand,
C, F, G and K, N, and P are waveforms when arc breaks occur and their time widths are wide and the arc breaks disappear before the applied voltage pulse is turned off. In actual machining, Waveforms A, D, H, L and waveforms C, F, G,
The frequency of occurrence of K, N, P is relatively high. In this case, in the conventional apparatus, a current pulse having a short width like the waveform P after the disappearance of the arc is extinguished, so that the electrode consumption rate is significantly increased. As described above, since the current pulse having the width of the set discharge duration is generated, the electrode consumption rate does not increase. Therefore, high processing accuracy can be maintained.

In the above-described embodiment, the processing pulse off time is configured to be constant. However, the configuration may be such that the processing pulse off time can be changed depending on the processing state or the like. The arc break detection period may be any section as long as it is within the discharge duration. For example, a section of 10% of the discharge duration from the start of discharge does not detect the arc break, and then the machining pulse The arc break detection may be performed until is turned off. Also,
The time width for determining whether the arc has been cut may be variable depending on the machining state or the like.

〔The invention's effect〕

According to the present invention, it is possible to reduce the frequency of occurrence of a current pulse having a width shorter than a predetermined width due to the arc breaking phenomenon, and thereby reduce the electrode wear rate without lowering the processing speed. There is an effect that an electric discharge machine can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the device of the present invention, and FIG. 2 is a waveform diagram for explaining the effect of the above device in comparison with the case of the conventional device. 1 ... working electrode 2 ... work piece 3 ... working power supply 4 ... switch element 5 ... current limiting resistor 6 ...
RS flip-flop, 7: Down counter for measuring discharge duration, 8: Down counter for measuring off time, 12
…………………………………………………………………………………………………………………………………………………………………………………………. 21,23 …… AND circuit, g …… Working gap.

Claims (1)

(57) [Claims] 1. An electric discharge machining method in which a machining pulse is supplied to a machining gap formed between a machining electrode and a workpiece by facing on / off switching control of a switch element to generate an intermittent arc discharge for machining. In the apparatus, a detection circuit for detecting a discharge voltage, a discharge current, or an impedance of a machining gap at the time of supplying the machining pulse, and a value detected by the detection circuit is compared with a predetermined value only for a predetermined period during a discharge duration, and When a predetermined condition is satisfied, a first discriminating circuit for discriminating a discharge interruption (arc interruption) and outputting a pulse signal of the arc interruption for the arc interruption time, and an output pulse signal of the first discrimination circuit. A second determination circuit that compares the pulse width with a preset value, and outputs a signal when the pulse width is equal to or greater than the set value and the processing pulse is not turned off; And a switching control circuit for controlling on / off switching of the switch element so as to extend the application of the machining pulse by a preset discharge duration immediately after the generation of the output signal of another circuit. apparatus.