JPH0616968B2 - Electric discharge machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric discharge machining apparatus for machining by applying a pulsed voltage to a machining gap where a machining electrode and a workpiece face each other, and in particular, control of a machining gap length. It is about.

[Prior Art] Electric discharge machining includes rough machining and finish machining. Further, generally, in the case of rough machining, it is easy to discharge machining chips, and machining speed is a problem.

This is because, during rough machining, the discharge energy per discharge is large, and the shape of the discharge mark is accordingly large, so that the distance between the electrodes is large and the machining waste is easily discharged. Therefore, it is sufficient to consider only the processing speed.

Then, in order to increase the processing speed, it is sufficient to increase the discharge energy applied to the gap, and to shorten the no-load time in the voltage application pulse. That is, by shortening the no-load time, the number of pulse applications increases and the discharge time as a whole also increases by the amount that the no-load time becomes shorter.

As described above, in rough machining, control is required to shorten the no-load time in order to increase the machining speed.

On the other hand, in the case of finishing, since the discharge energy per discharge is small, the shape of the discharge mark is also small at this time. Therefore, if electric discharge is performed with a small distance between the electrodes, it is difficult for the machining waste to be discharged.

Therefore, in order to enhance the effect of discharging the processing waste, it is necessary to increase the inter-electrode distance. However, if the distance between the electrodes is increased, it becomes difficult for the electric discharge to occur and the processing speed becomes slow.

Therefore, in the case of finish machining, it is required to control the distance between the electrodes so as to speed up the machining speed while considering the discharge of machining chips.

FIG. 2 is a block diagram showing machining gap length control of a conventional electric discharge machining apparatus. As shown in FIG. 2, a machining electrode (1) and a workpiece (2) are provided with a DC power supply (3), a switching transistor (4). ), A resistor (5) is connected in series, the signal of the pulse generator (6) is input to the switching transistor (4) through the pulse amplifier (7), and a pulsed voltage is applied to the machining gap. In the machining gap state, the voltage of the machining interval is divided by voltage dividing resistors (8a) and (8b), and the output of the reference voltage circuit (11) and the comparator (16) are passed through the comparator (9) and the discrimination circuit A (10). Is added and amplified by the servo amplifier (12), and then the servo motor (13) is driven and controlled.

Next, the operation will be described.

In FIG. 2, the machining gap voltage is the voltage dividing resistance (8a), (8
It is divided by b). FIG. 3 is a circuit diagram of the comparator (9) and the discrimination circuit A (10).
The reference voltage (9b) is connected to the non-inverting input of C (9a). The reference voltage (9b) corresponds to the middle point between the no-load voltage in the machining gap and the arc voltage during discharge. That is, the output of the comparator IC (9a) becomes L level when the machining gap has no load voltage, and becomes H level during discharge, short circuit and rest time.

In the discrimination circuit A (10), the operational amplifier IC (10a) and the input resistance (10b) are connected to the output of the comparator, and the feedback resistance (10c) adjusts to a predetermined gain. The resistor (10d) is for adjusting the offset. In this circuit example, the machining gap is +10 when the no-load voltage is applied.
V, -10 V is set during discharge, during short circuit, and during rest time. The output of the discrimination circuit A (10) is added to the set voltage of the reference voltage circuit (11), and the servo amplifier (12)
Drives the motor (13).

The machining gap length is controlled so that the machining electrode (1) is lowered when the machining gap voltage is high, and conversely when the machining gap voltage is low, the machining gap length is controlled so as to raise the machining electrode (1). The average voltage of the output is controlled to be equal to that of the reference voltage circuit (11).

In the conventional example of FIG. 2 described above, the distance between the poles can be changed by changing the down time. In such a case, the control is performed so as to obtain a predetermined machining gap length in consideration of the effect of discharging machining chips. Since the unloaded time is long, the processing speed is slower by that much, but it is generally suitable for finishing where it is difficult to discharge the processing chips. However, it is not suitable for roughing which requires a high processing speed and finishing which allows easy discharge of processing chips.

Further, FIG. 4 is a block diagram showing another machining gap length control of the conventional electric discharge machining apparatus, and the discrimination circuit A (1
0) instead of the timing circuit (14) and the discrimination circuit (1
5) is provided.

In the conventional example shown in FIG. 4, the pulse generator (6)
Is output to the timing circuit (14) as the signal (I1). This signal (I1) corresponds to the voltage pulse in the machining gap.

FIG. 5 is an input / output waveform diagram of the timing circuit (14), and the signal (I1) is represented at H level when the voltage pulse is applied. The output (O1) outputs a pulse when a predetermined time has elapsed from the rise of the signal (I1). Also output (O2)
Outputs a pulse after a predetermined time which is further delayed from the output (O1). The delay time of each output (O1), (O2) is set as a constant value or as a function of the pulse width of the signal (I1).

FIG. 6 shows a circuit example of the discrimination circuit B (15). Signal (I
Similarly to the output of the comparator IC (9a) in FIG. 3, 2) becomes L level when the machining gap is at no-load voltage, and becomes H level in other cases. The first flip-flop (15a) receives the AND signal of the signal (I2) and the output (O1) at the S (set) input, and negates (I2) the signal (I2) and outputs (O2).
The AND signal of 1) is connected to the R (reset) input.

With this configuration, at the output (O1) timing, the first flip-flop (15
a) is reset, its output Q1 becomes L level,
It becomes H level during discharge or short circuit. In the second flip-flop (15b), like the first flip-flop (15a), at the timing of the output (O2), the output Q2 becomes L level when there is no load voltage, and H when discharge or short circuit occurs. Become a level.

Therefore, if a discharge or short circuit occurs from the rise of the voltage pulse to the timing output (O1),
The outputs Q1 and Q2 of each flip-flop both become H level. (Discharge state I). Also, timing output (O1)
When a discharge or a short circuit occurs from the time point to the next timing output (O2), the output Q1 of each flip-flop becomes L level and Q2 becomes H level (discharge state II). When a discharge or a short circuit occurs after the timing output (O2), the outputs Q1 and Q2 of each flip-flop are both L level.
Level (discharge state III). In addition, at the time of rest, the above-mentioned discharge or the output issued at the time of short circuit is held.

The output of each flip-flop is an operational amplifier IC (15c)
Is connected to the input resistors (15d) and (15e), and is adjusted to a predetermined gain by the feedback resistor (15f). The resistor (15 g) is for adjusting the offset, and in this circuit example, -10 V in the discharge state I.
To 0V in discharge state II and +10 in discharge state III
It is set to V.

The output of the discrimination circuit B (15) is added to the set voltage of the reference voltage circuit (11), and the machining gap length is controlled as in the conventional example of FIG.

Therefore, the machining gap length is controlled so that the discharge start timing is always focused between the timing outputs (O1) and (O2). Since the control in this case is generally set so as to be short when there is no load voltage, the ratio of the total discharge time to the total voltage pulse application time is high, and the machining speed is faster than in the conventional example of FIG. Therefore, it is suitable for roughing which requires a high machining speed and finishing which has an electrode shape in which machining waste can be easily discharged. However, it is not suitable for finishing where it is difficult to discharge the processing waste.

In addition, even when the dwell time is lengthened, an almost constant no-load time width is obtained regardless of the dwell time width, and the total discharge time ratio to the total voltage pulse application time is still kept high. Also has the advantage of high processing speed.

[Problems to be Solved by the Invention] The conventional electric discharge machine is configured as described above, and in the conventional example of FIG. 2, the output of the discrimination circuit A (10) is evaluated to be −10 V in the pause time width. Therefore, when the dwell time is extended with respect to the same set value of the reference voltage circuit (11), the machining gap length is expanded correspondingly, the no-load time is also increased on average, and the total voltage is increased. The ratio of the total discharge time to the pulse application time is low, and the machining speed is slower than in the case of the previous dwell time.On the other hand, in the finishing machining of the electrode shape where it is difficult to discharge machining waste, the machining gap length increases. By doing so, it has the advantage that the discharge of machining waste is improved and the occurrence of concentrated discharge marks can be prevented.

Further, in the conventional example of FIG. 4, the no-discharge time does not change even if the down time is lengthened, and the machining gap length does not increase, so that it is difficult to discharge the machining chips, so that the concentrated discharge is performed in the finishing machining of the electrode shape. While there is a high possibility of generation of scratches, on the other hand, in the finishing process of the electrode shape where rough machining and discharge of machining scraps are easy, the total discharge time ratio to the total voltage pulse application time is still kept high, It has the advantage of high processing speed.

In general machining, progress of machining depth, switching from rough machining of electrical machining conditions to finishing machining, and change of machining contents by electrode replacement are required in one machining process, and one of the conventional examples is fixed. However, the above-mentioned problems occur when the setting is made manually.

The present invention has been made in order to solve such a problem, and by making it possible to select a processing gap state determining means suited to the processing content, it is faster than when any one of the conventional examples is fixedly set. An object of the present invention is to obtain an electric discharge machining apparatus capable of obtaining a good machining surface at a machining speed without a concentrated electric discharge mark.

[Means for Solving the Problems] In the electric discharge machining apparatus of the present invention, in order to control the machining gap length, the machining electrode, which is moved up and down by the servomotor, and the workpiece are opposed to each other, and the pulse signal of the pulse generator is generated. In an electric discharge machining device that applies a pulsed voltage generated based on the machining gap to a machining gap to perform machining, the voltage of the machining gap is compared with a reference voltage at no-load voltage and other discharges,
A comparator for discriminating between a short circuit and a rest, and when the comparator discriminates that there is no load voltage, outputs a signal to lower the machining electrode, and when the comparator discriminates other than during no load voltage, the machining A first discriminating circuit that outputs a signal to raise the working electrode; a timing circuit that outputs first and second timing signals that are sequentially delayed from the pulse signal of the pulse generator; a rising edge of the pulse signal; When the comparator determines that there is a discharge or a short circuit at a time other than a pause during one timing signal, a signal is output to raise the machining electrode,
When the comparator determines that there is a discharge or a short circuit at a time other than a pause between the first timing output signal and the second timing output signal, a signal for maintaining the machining electrode as it is is output, A signal from either of the second discriminating circuit and a second discriminating circuit that outputs a signal to lower the machining electrode when the comparator discriminates discharge or short-circuit at a time other than the timing output signal other than the pause. Switching means for selecting whether to output, a comparator for comparing the output signal of the discrimination circuit selected by the switching means and the reference set value of the reference voltage circuit, and the servomotor based on the result of the comparator. And a servo amplifier which outputs a drive control signal.

[Operation] In the present invention, the comparator compares the voltage in the machining gap with the reference voltage to determine whether there is no load voltage or when there is any other discharge, short circuit, or rest, and the first determination circuit determines when the comparator has no load voltage. Controls the machining gap length by receiving a discrimination signal and outputting a signal to lower the machining electrode, and receiving a discrimination signal when the comparator is at a time other than when there is no load voltage to output a signal to raise the machining electrode. Therefore, when the pause time is increased, the machining gap length correspondingly increases and the no-load time also increases on average, and the total discharge time ratio to the total voltage pulse application time becomes low, and the machining speed becomes slow. However, due to the expansion of the machining gap length, it is possible to improve the discharge of machining chips in the finishing process of the electrode shape, which is difficult to discharge.
It is also possible to prevent the generation of concentrated discharge marks.

In addition, the second discriminating circuit receives the discriminating signal indicating that the comparator is discharging or short-circuiting at a time other than the pause between the rise of the pulse signal of the pulse generator and the first timing signal of the timing circuit, and raises the machining electrode. To output a signal,
The second timing signal is output by receiving a signal for discriminating discharge and short circuit of the comparator at a time other than a pause between the first timing signal and the second timing signal of the timing circuit and for maintaining the machining electrode as it is. Output a signal to lower the machining electrode in response to the discrimination signal indicating discharge and short circuit of the comparator at times other than the rest,
Since the machining gap length is controlled so that the discharge start period is always focused between the first timing signal and the second timing signal, the average no-load time does not change even if the pause time is increased. In the finishing process in which the machining chips can be easily discharged, the ratio of the total discharge time to the total voltage pulse application time is still kept high, so that the processing speed is high.

Therefore, by selecting the discriminating circuit by the switching means according to the machining progress condition, electromachining condition, working electrode shape, etc., the first discriminating circuit having a slow machining speed in finishing machining in which the discharge of machining chips is poor Prevent concentrated discharge marks by using
In the roughing process or the finishing process in which the discharge of the machining waste is good, the second discriminating circuit having a high machining speed is used to enable high-speed machining, and the optimal machining process can be obtained by making the most of the advantages of each discriminating circuit.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
(1) to (16) are the same as those of the conventional example shown in FIGS. 2 to 6, and the discrimination circuit A in which the machining gap length increases
(10) and the discrimination circuit B (15) where the machining gap length does not increase
Are provided in parallel. (17) is the discrimination circuit A (1
0) or the discrimination signal of the discrimination circuit B (15).

In the electric discharge machine configured as described above, the operation when the changeover switch (17) is selected to the discriminating circuit A (10) side is the same as that of the conventional example shown in FIG. 2 and FIG. On the other hand, when the changeover switch (17) is selected to the discriminating circuit B (15) side, the operation is the same as that of the conventional example shown in FIGS.

The changeover switch (17) is set manually or by an NC code, and the difficulty level of discharging the machining waste is assumed in advance according to the progress of the machining depth, the electrical machining conditions, the electrode shape used, etc. Machining state determination circuit (10),
The advantage of using (15) is obtained.

Although the changeover switch (17) is set manually or by the NC code in the above-described embodiment, it is combined with the control for detecting the arc precursor phenomenon in the machining gap and changing the down time, depending on the occurrence status of the arc precursor phenomenon. The same effect can be obtained even if the discrimination circuit is automatically switched.

[Effects of the Invention] As described above, according to the present invention, the pause time is increased based on the discrimination signal of the comparator by the switching means according to the processing conditions such as the progress status of machining, the electromachining condition, the electrode shape used and the like. At the same time, the machining gap length expands to improve the discharge of machining chips, and the first determination circuit that controls to prevent the occurrence of concentrated discharge marks, and the no-load time does not change even if the pause time is increased. Since the second discriminating circuit for controlling so as to maintain the high speed is selected, the first discriminating circuit is used to detect the machining debris even if the machining speed is slightly slower in finish machining in which the discharge of the machining debris is poor. Controls the gap while considering the discharge, and enables high-speed machining by using the second discrimination circuit, which has a fast machining speed, for rough machining and finishing machining with good machining waste discharge. Optimizing the advantages of each discrimination circuit. Processing process It has the effect that can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional electric discharge machine, and FIG.
FIG. 4 is a partial circuit diagram of the block diagram shown in FIG. 4, FIG. 4 is a block diagram showing another conventional electric discharge machine, FIG. 5 is an input / output waveform diagram of the timing circuit of FIG. 4, and FIG. 6 is FIG. 4 is a partial circuit diagram of the block diagram shown in FIG. In the figure, (1) is a processing electrode, (2) is a workpiece,
(3) is a DC power supply, (4) is a switching transistor, (5) is a resistor, (6) is a pulse generator, (7) is a pulse amplifier, (8a) and (8b) are voltage dividing resistors, and (9) )
Is a comparator, (10) is a discrimination circuit A, (11) is a reference voltage circuit, (12) is a servo amplifier, (13) is a servomotor, (14) is a timing circuit, and (15) is a discrimination circuit B, (16). ) Is a comparator, and (17) is a changeover switch. In the drawings, the same reference numerals denote the same parts.

Claims (1)

[Claims] 1. Machining is performed by causing a machining electrode, which is moved up and down by a servomotor, to face a workpiece, and applying a pulsed voltage generated based on a pulse signal of a pulse generator to a machining gap. In an electric discharge machine, a comparator that compares the voltage in the machining gap with a reference voltage to determine whether there is no load voltage or when there is a discharge, a short circuit, or a rest time, and when the comparator determines that there is no load voltage A first discriminating circuit that outputs a signal to lower the machining electrode, and outputs a signal to raise the machining electrode when the comparator discriminates a time other than when there is no load voltage; and a pulse signal of the pulse generator. A timing circuit that outputs first and second timing signals that are sequentially delayed, and other than during a pause between the rising edge of the pulse signal and the first timing signal And outputs a signal to raise the working electrode when it is determined that the comparator is in discharge and short circuit, and the comparator is in a state other than a pause between the first timing output signal and the second timing output signal. Outputs a signal for maintaining the machining electrode as it is when it is determined to be discharged and short-circuited, and outputs the signal when the comparator determines to be discharged and short-circuited at a time other than a pause after the second timing output signal. A second discriminating circuit that outputs a signal to lower the processing electrode, a switching unit that selects which of the two discriminating circuits outputs the signal, and an output signal of the discriminating circuit that is selected by the switching unit. And a comparator for comparing the reference set value of the reference voltage circuit,
An electric discharge machining apparatus comprising: a servo amplifier that outputs a drive control signal to a servo motor based on a result of the comparator.