JPH05177437A - Wire-cut electric discharge machine - Google Patents

Abstract

PURPOSE:To quickly predict the generation of an abnormal discharge and prevent the disconnection of a wire electrode. CONSTITUTION:A pulse voltage is applied to a working gap G formed by mutually opposing a wire electrode 1 and a material 6 to be machined, and pulse discharge is repeated for working. The discharge suspension from the end of the discharge every pulse during the working and the start of the following voltage application is detected by a stoppage detecting circuit 44, and the integrated value obtained by successively integrating each dead time during a plurality of discharge suspensions in a determined sampling time is calculated by a dead time integrating circuit 34. The integrated value is compared with a standard value, and when the integrated value exceeds the standard value within the determined sampling time, the following working condition is controlled on discharge suppressing side such as laying a switching element 16 into OFF state until the determined sampling time passes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire cut electric discharge machine for machining a work by applying a predetermined voltage between a wire electrode and the work.

[0002]

2. Description of the Related Art Conventionally, when an abnormal discharge such as a concentration of arc discharge or a short circuit occurs between an electrode of an electric discharge machine and a work piece, the consumption of the electrode and the surface roughness of the work piece are affected. It is known that a control is performed so that arc discharge or short circuit does not occur. For example, JP-A-55-70
As disclosed in Japanese Patent No. 524, attention is paid to a decrease in no-load time from application of a voltage between an electrode and a workpiece to the start of discharge as a precursory phenomenon in which abnormal discharge such as arc discharge occurs. Then, the no-load time is measured every predetermined sampling time. It is known that the idle time is increased when the no-load time is decreased, and conversely, the idle time is decreased when the no-load time is increased to prevent abnormal discharge and improve the machining efficiency. Has been.

[0003]

However, in the wire cut electric discharge machine, the time during which the abnormal electric discharge is concentrated immediately before the wire electrode is broken is shorter than the predetermined sampling time. Further, in the conventional device, after the predetermined sampling time has elapsed, the no-load time within the predetermined sampling time is integrated. Then, when the no-load time is reduced, the idle time is controlled to be increased. That is, after the lapse of a predetermined sampling time, the increase / decrease of the no-load time within the predetermined sampling time is determined, and the control for increasing / decreasing the pause time is performed.

Therefore, an abnormal discharge may occur before the increase / decrease control of the pause time, for example, before a predetermined sampling time elapses, and the control for preventing the abnormal discharge cannot be performed in time, and the wire electrode is disconnected. There is a problem that may occur. Therefore, an object of the present invention is to provide a wire cut electric discharge machine in which the occurrence of abnormal discharge is predicted quickly and wire electrode breakage is prevented, with the object of solving the above problems.

[0005]

In order to achieve such an object, the present invention has the following constitution as a means for solving the problem. That is, as illustrated in FIG. 1, the wire electrode M1
In the wire-cut electric discharge machine having a machining means M3 for applying a predetermined pulse voltage to a machining gap where the workpiece M2 and the workpiece M2 face each other and repeatedly performing pulse discharge while controlling the machining condition to a predetermined machining condition. Pause detection means M4 for detecting a discharge pause from the end of discharge for each pulse by M3 to the start of application of the next voltage, and an integrated value obtained by sequentially integrating each pause time during the plurality of discharge pauses within a predetermined sampling time. When the integrated value exceeds the reference value within the predetermined sampling time, the rest time integration means M5 for calculating And a suppression control means M6 for controlling the machining conditions by the machining means M3 to the electric discharge suppressing side. Is it.

[0006]

The function of the wire cut electric discharge machine having the above construction is
The machining means M3 applies a predetermined pulse voltage to the machining gap in which the wire electrode M1 and the work piece M2 face each other, and repeats the pulse discharge while controlling the predetermined machining condition to process the work piece M2. Then, the pause detecting means M4 detects a discharge pause from the end of discharge for each pulse to the start of application of the next voltage, and the pause time integrating means M5 sets each pause time during a plurality of discharge pauses within a predetermined sampling time. Then, the integrated value obtained by sequentially integrating is calculated. Further, the suppression control means M6 compares the integrated value with a predetermined reference value, and when the integrated value exceeds the reference value within a predetermined sampling time, the processing conditions by the processing means M3 thereafter until the predetermined sampling time elapses. Is controlled to the discharge suppression side.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a schematic configuration diagram of a wire cut electric discharge machine which is an embodiment of the present invention. Reference numeral 1 is a wire electrode, and the wire electrode 1 is stretched substantially vertically with a predetermined tension between a pair of wire guides 2 and 4 arranged at a predetermined interval. The wire electrode 1 is configured to be supplied at a predetermined supply rate by a supply device (not shown).

The workpiece 6 arranged with the wire electrode 1 penetrating is movably supported by a pair of feed motors 8 and 10 in a horizontal plane orthogonal to the wire electrode 1. The workpiece 6 is placed in a liquid tank (not shown) and is immersed in an insulating processing liquid.
This machining fluid is circulated by a pump or the like not shown,
It is supplied to the processing gap G between the wire electrode 1 and the workpiece 6.

Further, a power supply electron 12 which is in contact with the wire electrode 1 and capable of supplying power to the wire electrode 1 is provided. The power supply electron 12 and the negative electrode side of the DC power supply 14 use a transistor in this embodiment. The power line 18 is connected via the switching element 16. In addition, the DC power supply 14
The positive electrode side of is connected to the workpiece 6 by the power line 20 and is grounded.

The switching element 16 is controlled to be turned on / off by the drive circuit 22, and the drive circuit 2
2 is controlled according to the output signal from the electronic control unit 24. The electronic control unit 24 is a well-known CPU 26, RO
An input / output circuit configured by M28 and RAM30 as the center of the logical operation circuit and performing input / output with the outside, here, a drive output circuit 32, a pause time integration circuit 34, a motor drive circuit 3
6. The keyboard input circuit 38 and the like are connected to each other via a common bus 40.

The CPU 26 inputs processing conditions set by the keyboard 42, for example, a discharge cycle, a discharge current value, a wire feed speed, a predetermined sampling time, etc. through a keyboard input circuit 38 and stores them in a predetermined address of the RAM 30. To do. Further, the CPU 26 counts the signal from the pause detection circuit 44 by the pause time integration circuit 34 and inputs the integrated value.

As shown in FIG. 3, the pause detecting circuit 44 includes a buffer amplifier 46 that receives the voltage of the wire electrode 1.
And a comparator 48 for comparing the output voltage from the buffer amplifier 46 with a predetermined threshold voltage Vt set by dividing the power supply voltage. This threshold voltage Vt
As shown in FIG. 5, a voltage is applied to the machining gap G between the wire electrode 1 and the workpiece 6, and is set to a value lower than the voltage between the machining gap G until the discharge is completed. There is.
The pause detecting circuit 44 functions as the pause detecting means M4.

Then, the output voltage from the comparator 48 is input to the pause time integrating circuit 34. Rest time integration circuit 3
4 is an inverting circuit 5 for inverting the output voltage from the comparator 48.
0, an output signal from the inverting circuit 50 and a predetermined clock signal from the clock circuit 52, about 1M in this embodiment.
An AND circuit 54 that receives a clock signal of Hz and a counter 56 that counts the clock pulse signal from the AND circuit 54 are provided. The integrated value of the counter 56 is configured to be input to the CPU 26. still,
The down time integration circuit 34 functions as the down time integration means M5.

On the other hand, these data and signals and the ROM 2
8. Based on the data in the RAM 30, the CPU 26
A drive signal corresponding to the processing conditions is output to each of the feed motors 8 and 10 via the motor drive circuit 36 to control the moving speed of the workpiece 6. In addition, a control signal is output to the drive circuit 22 via the drive output circuit 32,
The switching element 16 is controlled to be turned on / off based on an applied pulse having a predetermined cycle according to the processing conditions to apply a pulse voltage to the processing gap G between the wire electrode 1 and the workpiece 6, and at the same time for each pulse. The discharge current is controlled so that the discharge energy becomes almost constant. The electronic control unit 24, the drive circuit 22, the switching element 16
Serves as the processing means M3.

Next, the disconnection prevention control process performed by the electronic control unit 24 will be described with reference to the flowchart shown in FIG. First, a predetermined sampling time is set from the keyboard 42 via the keyboard input circuit 38 and stored in a predetermined address of the RAM 30 (step S).
1, hereinafter referred to as S1. The same applies below. ). The predetermined sampling time may be an integral multiple of the discharge cycle, for example, 1 mS which is 100 times 10 μS. However, the predetermined sampling time is not limited to an integral multiple of the discharge cycle, and abnormal discharge can be detected from the integrated value of the counter 56 before abnormal discharge occurs, that is, before arc discharge concentrates or a short-circuit state continues. Just have time.

Next, 1 within a predetermined sampling time
The value is set from the keyboard 42 using 80% of the number of MHz clock signals as a reference value (S2). In this embodiment, the reference value is set to 80%, but not limited to this, the reference value is
It may be set according to processing conditions and the like. Before the integrated value of the counter 56 exceeds the reference value, a value obtained by experiments or the like may be used so that abnormal discharge does not occur.

Subsequently, an applied pulse corresponding to the machining conditions is output to the drive circuit 22 via the drive output circuit 32, and a pulse voltage is applied to the machining gap G between the wire electrode 1 and the workpiece 6 (S3). The counter 56 of the pause time integration circuit 34 is reset (S4). When the pulse voltage is applied to the machining gap G, as shown in FIG. 5, the pulse voltage is applied depending on the state of the machining gap G, for example, the distance of the machining gap G or the amount of machining chips in the machining gap G. The time from the start of discharging to the end of discharging is not constant.

Then, the pause detecting circuit 44 compares a predetermined threshold voltage Vt with the voltage of the wire electrode 1, and when the threshold voltage Vt is exceeded, the pause time integrating circuit 34.
And a low level signal in response to a discharge pause from the end of discharge until the next voltage is applied. In the pause time integration circuit 34, this signal is inverted by the inversion circuit 50 to be a high level signal in the section corresponding to the discharge pause from the end of discharge to the application of the next voltage. In the AND circuit 54, the clock signal is output to the counter 56 during the period corresponding to this high-level discharge pause, and the counter 56 counts this clock signal.

In response to the applied pulse, a voltage is applied to the machining gap G between the wire electrode 1 and the workpiece 6 to cause discharge. Then, the discharge pause section is detected, the clock signals in the section are counted, and the integrated value is calculated.
The integrated value is compared with the reference value (S5), and if the integrated value is less than or equal to the reference value (S5, NO), the discharge pause period for each pulse is maintained until the predetermined sampling time elapses (S6). The clock signal is counted and the integrated value is calculated.

When the predetermined sampling time has elapsed,
When the integrated value is less than or equal to the reference value (S6, YES), the counter 56 is reset (S4), the clock signal is counted again in accordance with the discharge pause section, and the integrated value is calculated. The process of comparing with the reference value is repeated (S5, 6).

The length of the discharge pause section varies depending on the state of the machining gap G, and the integrated value within a predetermined sampling time also varies each time. When the machining gap G is in a state where discharge is likely to occur, the time from applying a voltage to the machining gap G until the discharge starts becomes short,
The discharge pause section becomes longer. Therefore, the integrated value within the predetermined sampling time becomes a large value. On the other hand, when the discharge is difficult to occur, the discharge pause period becomes shorter and the integrated value also becomes smaller.

When the state in which discharge easily occurs continues, the integrated value increases, and when the integrated value exceeds the reference value (S5.Y
ES), immediately before the elapse of a predetermined sampling time, an off signal is immediately output to the drive circuit 22 to turn off the switching element 16 (S7). As a result, no voltage is applied to the machining gap G between the wire electrode 1 and the workpiece 6.

Thereafter, it is determined whether or not the predetermined sampling time has elapsed (S8), and the switching element 16 is kept in the OFF state and stands by until the predetermined sampling time elapses. In the meantime, the state of the machining gap G changes, for example, the machining waste in the machining gap G is removed by the supplied machining liquid, and the state in which the concentration of arc discharge or the short-circuit state hardly occurs, that is, the insulating state is recovered.

Then, when the predetermined sampling time has elapsed, the processes of S3 and thereafter are repeated, and the drive circuit 22 again controls the switching element 16 to be turned on / off in accordance with the applied pulse to apply the pulse voltage to the machining gap G. Apply and repeat electrical discharge machining. In this embodiment, the switching element 16 is turned off by the process of S7 until the predetermined sampling time elapses. However, the present invention is not limited to this, and the discharge cycle can be lengthened, the discharge energy can be reduced, or the wire electrode can be reduced. It suffices that the processing condition is changed so as to suppress the electric discharge, such as changing the feed rate of 1 and the wire tension, or increasing the supply amount of the processing liquid. Also, S4
Execution of the processes of to S8 works as the suppression control means M6.

As described above, in the wire-cut electric discharge machine of this embodiment, when the integrated value exceeds the reference value within the predetermined sampling time, the switching element 16 is turned off until the predetermined sampling time elapses and the electric discharge is performed. Suppress. Therefore, before the predetermined sampling time elapses,
When the integrated value exceeds the reference value, the application of the voltage to the machining gap G is immediately stopped, so that the occurrence of abnormal discharge can be predicted quickly and the occurrence thereof can be prevented, and the wire electrode 1 can be disconnected due to abnormal discharge. To prevent. Therefore, the number of breaks in the wire electrode 1 is reduced, and the processing speed is also improved.

Further, since the discharge is suppressed until the predetermined sampling time elapses, if the time until the integrated value exceeds the reference value is short, the discharge suppression period in which the switching element 16 is in the OFF state becomes long. On the contrary, if the time until the integrated value exceeds the reference value is long, the discharge suppression period becomes short. Therefore, the length of the discharge suppression period changes depending on the degree of the state in which the discharge is likely to occur. The discharge suppression period is longer when the discharge is more likely to occur, and conversely, when the discharge is less likely to occur, the machining speed is improved. ..

The present invention is not limited to such embodiments as described above, and can be carried out in various modes without departing from the scope of the present invention.

[0028]

As described above in detail, in the wire cut electric discharge machine of the present invention, if the integrated value exceeds the reference value before the predetermined sampling time elapses, the machining conditions are immediately controlled to the side that suppresses the electric discharge. However, the occurrence of abnormal discharge is promptly predicted to prevent it from occurring. Therefore, it is possible to prevent disconnection of the wire electrode due to abnormal discharge, reduce the number of occurrences of disconnection of the wire electrode, and improve the processing speed.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a basic configuration of a wire cut electric discharge machine according to the present invention.

FIG. 2 is a schematic configuration diagram of a wire cut electric discharge machine according to the present embodiment.

FIG. 3 is an electric circuit diagram showing a pause detection circuit and a pause time integration circuit of this embodiment.

FIG. 4 is a flowchart showing a disconnection prevention control process performed by the electronic control unit of the present embodiment.

FIG. 5 is an enlarged time chart showing an applied pulse, a machining gap voltage, and a discharge current in this embodiment.

FIG. 6 is a time chart showing an applied pulse, a predetermined sampling time, an integrated value, and a discharge suppression period in this embodiment.

[Explanation of symbols]

M1,1 ... Wire electrode M2, 6 ... Workpiece
M3 ... Machining means M4 ... Pause detecting means M5 ... Pause time integrating means M6 ... Suppression control means 16 ... Switching element 22 ... Drive circuit
24 ... Electronic control unit 34 ... Rest time integration circuit 44 ... Rest detection circuit
56 ... Counter

Claims (1)

[Claims] 1. A wire-cut electric discharge machine having a machining means for applying a predetermined pulse voltage to a machining gap in which a wire electrode and a workpiece face each other, and performing pulse discharge repeatedly while controlling to a predetermined machining condition. In the above, the pause detecting means for detecting the discharge pause from the end of the discharge for each pulse by the machining means to the start of the application of the next voltage, and the pause times during the plurality of the discharge pauses are sequentially integrated within a predetermined sampling time. And comparing the integrated value with a predetermined reference value, and when the integrated value exceeds the reference value within the predetermined sampling time, the predetermined sampling time elapses. And a suppression control means for controlling the machining conditions by the machining means thereafter to the electric discharge suppressing side.