JPH0767648B2 - Electric discharge machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention is designed to process a workpiece by utilizing a discharge phenomenon when a voltage is applied between the workpiece electrode and the discharge electrode. Electric discharge machine

"Prior Art" It was thought that in order to stably repeat the discharge in the wire cut electric discharge machining, a sufficient discharge pause time was required for each discharge (JP-A-56-89434). .
Japanese Patent Application No. 59-53193, which is the applicant's own earlier application,
With a focus on this point, it has a programmable timer that determines the sum of the discharge pause time and the discharge time to be constant, and a delay circuit that generates an off signal when the discharge time set by the surface roughness selection switch has elapsed from the start of discharge. And a flip-flop circuit which is reset by the OFF signal of the delay circuit and is set by the drive signal of the programmable timer. Then, as shown in FIG. 4, an indeterminate no-load time TC determined by the voltage of the power source and the size and state of the machining gap, a discharge time (load time) Ta determined by the surface roughness, etc. Electric discharge machining was performed with a total time of a sufficient fixed discharge pause time Tb as one cycle time To, but in this conventional electric discharge machine, the discharge time Ta and the discharge pause time Tb are set by a programmable timer. It was difficult to increase the machining efficiency by increasing the number of discharge pulses within a predetermined time because the sum of the above was determined in advance.

That is, in this type of electric discharge machine, if the number of electric discharge pulses within a predetermined time is increased, the machining speed of the workpiece can be increased, but if the number of electric discharge pulses is too large, the electric discharge pulse that causes the electric discharge pulse is generated. Depending on the time required to replace (break) an electrode (for example, a wire electrode) and replace it,
There is a risk that the total processing efficiency will rather decrease.

Therefore, in the above-mentioned conventional electric discharge machine, the sum of the discharge time Ta and the discharge rest time Tb is set to a small value within a range in which the discharge electrode is not damaged, thereby increasing the number of discharge pulses within a predetermined time. In this case, as shown in FIG. 4, one cycle time To of electric discharge machining, that is, the electric discharge cycle includes an indeterminate no-load time Tc, so that the actual electric discharge cycle (discharge interval) is It becomes larger than the limit value that can withstand, and the machining efficiency cannot be maximized.

Therefore, it is possible to set the sum of the discharge time Ta and the discharge rest time Tb to be smaller than the above limit value in anticipation of the no-load time Tc, but in this case, a cycle with a small no-load time Tc If continuous, the actual discharge cycle becomes smaller than the limit value, which may damage the discharge electrode.

That is, in the above-mentioned conventional electric discharge machine, the minimum value of the electric discharge cycle cannot be reliably set, and as a result, the number of electric discharge pulses within a predetermined time is increased to the limit that the electric discharge electrode can withstand, and the machining efficiency is increased. It was difficult to improve.

"Problems to be Solved by the Invention" The present invention has been made in view of the above problems, and provides an electric discharge machine capable of increasing the number of electric discharge pulses and improving the machining efficiency. The purpose is to

[Means for Solving the Problems] According to the present invention, the discharge electrode and the workpiece electrode are connected to each other on the discharge path between the electrodes, and the discharge is performed so as to generate the discharge in the machining gap therebetween. A switching element that opens and closes a path to apply a voltage between the two electrodes from the power source, and a discharge that generates a detection signal by detecting that a discharge has occurred between the two electrodes when the switching element is turned on. Generation detection means, first delay means connected to the discharge generation detection means and outputting an operation signal after a first set time based on the detection signal of the detection means, and the detection signal of the discharge generation detection means Irrespective of the pulse signal generating means for generating a pulse signal every second set time, and the switching element is turned on in response to the generation of the pulse signal by the pulse signal generating means. Further, there is provided an electric discharge machine comprising: a switching control unit that holds the turn-on state and turns on the switching element based on an operation signal of the first delay unit.

[Operation] In the electric discharge machine of the present invention configured as described above, the pulse signal generating means generates a pulse signal at every second set time, and the switching control means responds to the generation of the pulse signal. The switching element is turned on and the turn-on state is maintained.

Then, the switching element applies a voltage from the power supply between the discharge electrode and the workpiece electrode, and in that state, when discharge occurs between the electrodes, the discharge generation detection means causes the discharge between the electrodes. Is detected and a detection signal is output, and the first delay means outputs an operation signal after a first set time based on the detection signal. And
When the actuation signal is output from the first delay means, the switching control means turns on the switching element, whereby the voltage application to the discharge electrode and the workpiece electrode is stopped.

Then, when a pulse signal is generated from the pulse signal generating means in the next cycle, the switching control means turns on the switching element again, and the above operation is repeated.

That is, in the electric discharge machine of the present invention, a first set time (discharge time) at which discharge should be continued according to surface roughness and the like,
The second set time, which is the cycle of applying the voltage to the discharge electrode and the work piece electrode, is set independently of each other, and the voltage is applied to both electrodes every second set time. A series of operations such as discharge between both electrodes and suspension of voltage application to both electrodes are performed.

In some cases, the size of the machining gap fluctuates, and the time from when the switching element is turned on by the switching control means to when discharge occurs (no-load time) is longer than the second set time. However, the switching element is held in the ON state, and discharge will eventually occur (for example, in the next cycle). Therefore, even if discharge does not occur within the second set time that is the pulse signal generation gap, for example, when viewed from a long time until the processing of the workpiece is completed, the second set A discharge pulse is generated every time.

As described above, in the electric discharge machine of the present invention, the sum of the electric discharge time and the electric discharge rest time is not set to be constant as in the conventional apparatus, but the cycle of applying the voltage to the electric discharge electrode and the workpiece electrode (first (2nd set time) is set to a constant value, and basically a discharge pulse is generated every second set time, so the actual discharge cycle does not become shorter than the second set time. . Therefore, according to the electric discharge machine of the present invention, the minimum value of the electric discharge cycle, as the second set time, can be reliably set to the limit value that the electric discharge electrode can withstand, and by extension, the machining efficiency. You can easily improve to the maximum.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the entire electric discharge drive circuit of an electric discharge machine according to this embodiment, FIG. 2 is a circuit diagram showing the relationship between the electric discharge control circuit and a central processing unit, and FIG. 3 is an electric discharge control circuit. 2 is a timing chart of.

One end of a DC power source 1 as a power source is connected to the workpiece 2 and also to one pole of the charging capacitor 3 which also forms an electrode. The wire electrode 4, which is opposed to the workpiece 2 through the machining gap G and is relatively movable, is composed of a field effect transistor (hereinafter simply referred to as FET) 5 as a switching element, a diode 6, and a non-inductive resistance. The wire electrode 4 is connected to the other end of the DC power supply 1 via the current detection resistor 7 and the diode 8, and the wire electrode 4 is connected to the other pole of the charging capacitor 3 via the FET 5. Also,
A current detection circuit 9 for detecting discharge having an isolator having a well-known configuration is connected to both ends of the current detection resistor 7, and an output signal path of the current detection circuit 9 is introduced to a discharge control circuit 10 for discharge control. The output signal path of circuit 10 is FET5
Has been introduced to the gate terminal of. A diode 11 and a resistor 12 are provided in parallel with both ends of the workpiece 2 and the wire electrode 4.
The series circuit of is connected.

As shown in FIG. 2, the current detection circuit 9 is connected with a delay circuit 13 which constitutes a first delay means. This delay circuit 13 outputs an actuation signal by a short pulse after a set time t _D corresponding to the load time after the signal is input, and this set time t _D is the central processing unit (CPU) 1
4 is set arbitrarily according to the operation of the surface roughness selection switch 15. In the discharge control circuit 10, the current detection circuit 9
A programmable timer 16 is provided which generates a pulse signal of a very short time every predetermined set time (discharge cycle time) t _S irrespective of the detection signal.
The programmable timer 16 serves as a pulse signal generating means, and its discharge cycle time t _S is determined by operating the keyboard 17 provided in the CPU 14 so that the plate thickness of the workpiece 2
It is set according to the processing conditions such as the wire diameter of the wire electrode 4, the electric conductivity of the water supplied to the processing gap G, and the discharge energy (time to turn on the FET 5). The programmable timer 16 is connected to a clock terminal CLK of a flip-flop (hereinafter simply referred to as FF) 18 that forms a switching control means and generates a high-level output signal based on the output signal of the timer 16. FF18 clear terminal C
The output signal of the delay circuit 13 is introduced into the LR, and when the output signal of the delay circuit 13 is at high level, the FF 18 is cleared and the output signal disappears (becomes low level).

The output signal of the FF 18 is introduced to the gate terminal of the FET 5 via the AND gate 19 for controlling the start of the discharge control circuit 10.

[Operation] In the above configuration, when the start signal Dis on is introduced to the AND gate 19, the AND gate 19 is opened, and it becomes possible to give the output signal from the FF 18 of the discharge control circuit 10 to the gate terminal of the FET 5. .

As shown in FIG. 3, when the programmable timer 16 generates the first pulse, this pulse is applied to the clock terminal CLK of FF18. Since the output signal of the delay circuit 13 is not generated, the clear terminal CLR of the FF18 is at the low level, so this FF18 is set and a high level output signal is generated at the output terminal Q, and the FET5 is output via the AND gate 19.
This output signal is applied to the gate terminal of and FET5 turns on. Then, the DC power supply 1 and the charging capacitor 3
From, a voltage is applied to the workpiece 2 and the wire electrode 4. When some no-load time elapses, a discharge is generated in the discharge gap G, and a detection signal SG is generated from the current detection circuit 9 and added to the delay circuit 13. The delay circuit 13 generates a pulse signal for a short time when the load time t _D has elapsed from when the detection signal SG was applied, and this signal is generated by the clear terminal CL of the FF18.
Add to R. FF18 eliminates the output signal of the output terminal Q by adding a signal to the clear terminal CLR.
Turns on because it cannot apply a signal to the gate terminal. Then, the discharge of the discharge gap G ends after a very short time.

When the second pulse is generated by the programmable timer 16 after the discharge cycle time t _S , this pulse is FF.
By being applied to the clock terminal CLK of 18, the FF 18 generates an output signal at the output terminal Q at the rising time of this pulse, and this output signal is applied to the gate terminal of the FET 5 via the AND gate 19, so that the FET 5 becomes When turned on, a voltage is applied to the work piece 2 and the wire electrode 4 from the DC power source 1 and the charging capacitor 3, and after a little no-load time, a discharge is generated in these discharge gaps G. A detection signal SG is generated from the current detection circuit 9, and a short pulse is generated from the delay circuit 13 after the load time t _D. Delay circuit 13 pulse is FF
When applied to the clear terminal CLK of 18, the FF 18 extinguishes the output signal of the output terminal Q and turns on the FET 5.

When the third pulse is generated by the programmable timer 16 after the discharge cycle time t _S , in the example shown in FIG. 3, since the pulse of the delay circuit 13 falls, the FF 18 is Since the clear terminal CLR is at low level, the pulse of the programmable timer 16
It is set by being added to K, and an output signal is generated at the output terminal Q. Then, through the AND gate 19, FE
Since this output signal is applied to the gate terminal of T5, FET5
Is turned on. At this time, the FET 5 is turned on after the load time t _D according to the detection of discharge, and then the FET 5 is turned on at an interval much shorter than the time interval of the discharge cycle time t _S. After that, discharge is generated in the discharge gap G. The detection signal SG is generated from the current detection circuit 9, the delay circuit 13 generates a pulse signal after the load time t _D from the rising time point of this detection signal SG, and the rising edge of this pulse signal causes the FF 18 to disappear the output signal. FET5 is turned off.

When the fourth pulse is generated from the programmable timer 16 after the discharge cycle time t _S has elapsed, the FF18 is set to generate an output signal, and the output signal is added to the gate of the FET5, whereby the FET5 is Turned on, discharge gap G
A voltage is applied to. When a discharge occurs in the discharge gap G after some no-load time, the current detection circuit 9 generates a detection signal SG, and the delay circuit 13 generates a short-time pulse signal after the load time t _D and outputs a short pulse signal. Apply this pulse signal to the clear terminal CLR. The FF 18 extinguishes the output signal when the pulse signal of the delay circuit 13 rises, and turns off the FET 5.

Even if the fifth cycle time t _S arrives while the output signal of the delay circuit 13 is present (at the high level), and the pulse from the programmable timer 16 enters the clock terminal CLK of the FF18, it goes to the clear terminal CLR of the FF18. Since the output signal of the delay circuit 13 is input, the FF 18 is not set and the output signal is not output to the output terminal Q of the FF 18. Then, the FET 5 is turned on by the next sixth pulse of the programmable timer 16.

(Advantages of the Embodiment) In the above embodiment, the set time t _D of the delay circuit 13 is the discharge time (load time) at which the discharge should be continued, and the cycle time t _S of the programmable timer 16 is the workpiece 2 And the cycle of applying the voltage to the wire electrode 4 is independently set, and a series of machining operations such as voltage application, discharge, and suspension of voltage application are performed at each cycle time t _S. I am trying.

Therefore, according to the above-described embodiment, the minimum value of the cycle in which discharge occurs (discharge cycle) can be reliably set to the limit value at which the wire electrode 4 is not broken, and the wire electrode 4 is cut. Without, it is possible to improve the processing efficiency to the maximum.

Further, according to the above embodiment, the set time t of the delay circuit 13
_D is automatically set by the CPU 14 according to the operation of the surface roughness selection switch 15, and the cycle time t _S of the programmable timer 16 is automatically set by the CPU 14 according to various processing conditions input from the keyboard 17. Therefore, there is an advantage that the setting by the user is easy. However, the present invention is not limited to the configuration of the above embodiment.

"Effect" As described above, the electric discharge machine of the present invention has the above-mentioned configuration, and the switching element is closed by the pulse generated every second set time set according to the machining conditions. Since a voltage is applied between both electrodes, the number of discharge pulses within a predetermined time can be determined by comparing the number of discharge pulses within a predetermined time with the conventional method in which the discharge pause time is fixed to a necessary and sufficient value regardless of the processing conditions. The number can be safely increased within a range that does not cause damage, and further, the processing efficiency of the workpiece can be further improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the entire electric discharge drive circuit of an electric discharge machine according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the relationship between the electric discharge control circuit and a central processing unit, and FIG. The timing chart of the control circuit, FIG. 4 is a waveform diagram for explaining the discharge cycle in the conventional electric discharge machine. 1 ... DC power supply, 2 ... Workpiece, 3 ... Charging capacitor, 4 ... Wire electrode, 5 ... Field effect transistor (FET), 7 ... Current detection resistor, 9 ... Current detection circuit, 1
0 ...... discharge control circuit, 13 ...... delay circuit, 14 ...... CPU, 16 ...... programmable timer, 18 ...... flip-flop (FF), G ...... machining gap, SG ...... detection signal, t _D ...
… Load time, t _S …… Discharge cycle time.

Claims (1)

[Claims] 1. A discharge electrode and a workpiece electrode are moved relative to each other, and a voltage is applied between these electrodes to generate an electrical discharge in a machining gap between them, and the workpiece is machined by the discharge energy. In the electric discharge machine, a switching element, which is connected on the discharge path between the electrodes and a power supply, opens and closes the discharge path so as to generate an electric discharge in the machining gap, and applies a voltage between the electrodes from the power supply. And a discharge generation detecting means for generating a detection signal by detecting the occurrence of a discharge between the two electrodes in a state where the switching element is turned on, and a detection of the detection means connected to the discharge generation detecting means. A first delay unit that outputs an operation signal after a first set time based on the signal, and a pulse signal every second set time regardless of the detection signal of the discharge occurrence detection unit. A pulse signal generating means for generating a signal, and turning on the switching element in response to the generation of the pulse signal by the pulse signal generating means, maintaining the turned-on state, and based on the operation signal of the first delay means. An electric discharge machine comprising: a switching control means for turning on a switching element;