JPH0659570B2 - Electric discharge machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention, when performing machining by applying a pulsed machining voltage while leaving a pause in a machining gap formed between a tool electrode and a workpiece, The present invention relates to an electric discharge machining apparatus that avoids an abnormality in a machining state by changing a pause time when an abnormality in the machining state is detected.

[Prior Art] FIG. 3 is a schematic diagram showing a conventional electric discharge machining apparatus. In the figure, (1) is an electrode, (2) is a workpiece, (3) is an X cross table, and (4) is Y. A cross table, (5) a machining power supply for supplying a pulsed current to a machining gap formed by the electrode (1) and the workpiece (2), and (6) an actuator for vertically driving the electrode (1), (7) is an actuator for driving the X cross table, (8) is an actuator for driving the Y cross table, (9a), (9b), (9
c) is a servo amplifier that supplies current to the actuators (6), (7), and (8), (10) is a gap voltage detection circuit that detects the voltage of the machining gap, and (11) is a voltage applied A pulse signal corresponding to an elapsed time from when the discharge occurs to the discharge (hereinafter, no-load time Td) is generated. Td pulse generator, (1
2) is a Td measuring device for measuring the pulse width of the Td pulse, (13)
Is a discharge waveform classifier that generates output signals that classify each discharge pulse into three types of immediate discharge (D1), normal discharge (D2), and open (D3) based on the measurement results of the Td measuring device (12), (14) ，
(15) and (16) are counters that count the signals output by the discharge waveform classifier (13) for each of the three types of groups, and (17) is whether the machining status is normal from the count value of immediate discharge (D1). A machining state discriminator for discriminating whether or not there is an abnormality, (18) is an electrode feed control device for performing electrode feed control based on the count numbers of (14), (15) and (16)
Reference numeral (19) is an electric condition control device for controlling the down time and the like based on the result of the processing state discriminator (17).

Next, the operation will be described. The machining power supply (5) supplies a pulse voltage to a machining gap formed by the electrode (1) and the workpiece (2) to generate an electric discharge in the machining gap, and at the same time, the electrode (1) and the workpiece (2). Is performed by changing the relative position of. The vertical movement of the electrode (1) moves the actuator (6), and the movement of the workpiece (2) moves the actuators (7), which drive the X, Y cross tables (3), (4).
(8). The voltage of the machining gap during machining is detected by the inter-electrode voltage detection circuit (10) and the Td pulse generator
(11) generates a pulse signal corresponding to the no-load time Td from the application of voltage to the occurrence of discharge. FIG. 4 schematically shows the waveform between the electrodes and the Td pulse signal.
The Td measuring device (12) measures the pulse width of the Td pulse signal, that is, the no-load time Td of each discharge waveform. From the result, the discharge waveform classifier (13) immediately discharges each discharge pulse (D
Output signals classified into three types of 1), normal discharge (D2) and open (D3) are generated. Here, () D1: 0 <Td <T1 ... When a short circuit occurs or the dielectric strength of the machining gap is not recovered.

() D2: T1 <Td <T2 ... When there is an unloaded voltage for an appropriate time and the contribution to machining is the largest.

() D3: T2 <Td <T3 ... When the no-load voltage application time is relatively long.

Is.

As the voltage waveform in the machining gap, it is desirable to use a discharge generation configuration in which there is a no-load voltage with a time not longer than a certain amount, and the electrode feed control device (18) uses a counter (1
D1, D2, D3 counted by 4), (15) and (16)
The electrode servo feed is performed depending on the frequency.

In addition to the above electrode feed control, in order to prevent a transition to abnormal machining due to an increase in machining sludge concentration between the poles, the machining state determiner (17) determines whether the machining state is normal or abnormal depending on the frequency of D1. Then, the control device (19) avoids abnormal machining by controlling the switching of the down time and the like based on the result.

[Problems to be Solved by the Invention] Since the conventional electric discharge machining apparatus is configured as described above, the abnormal machining state is determined only by the frequency of short circuit / immediate electric discharge, and stable machining to abnormal machining is performed. It was necessary to change the discrimination level when the machining conditions could not be controlled by accurately discriminating and predicting the transition, and the electrode area and machining electrical conditions were different. Also, if the discrimination level is fixed, abnormal machining is not optimally avoided, that is, the machining efficiency decreases due to too early or too late changing of conditions, or damage to the workpiece due to steady arc discharge. There was a problem such as occurrence.

The present invention has been made to solve the above problems, by avoiding abnormal machining by accurately predicting and determining the transition from stable machining to abnormal machining and controlling the machining conditions, It is an object of the present invention to obtain an electric discharge machining device capable of extremely stable and efficient machining.

[Means for Solving Problems] In the electric discharge machining apparatus according to the present invention, the time width of the pulse voltage applied to the machining gap is set to the first division time T1 and the second division time T.
2. Classification means for classifying into the third division time T3, and a ratio D1 of the number D1 of discharge pulses generated in the first division time T1 and the number D2 of discharge pulses generated in the second division time T2 within a predetermined time or a predetermined number of pulses. / D2 for every predetermined time, the current D1 / D2 value and the previous D1 / D2 value
A processing state determination unit that compares a ratio or difference value of values with a reference value and determines the processing state as abnormal when the ratio or difference value exceeds the reference value, and the processing state determination unit determines that the processing state is abnormal. And a control means for controlling so as to increase the pause time when a certain signal is output.

[Operation] In the electric discharge machining device according to the present invention, the time width of the pulse voltage applied to the machining gap is set to the first division time T by the classification means.
The second dividing time T2, the third dividing time T3, and the number of discharge pulses D1 and the second discharging pulse number D1 generated in the first dividing time T1 during a predetermined time or a predetermined pulse number are calculated by the calculating means.
Ratio D1 / D of the number D2 of discharge pulses generated in the division time T2
2 is calculated every predetermined time. Further, the processing state determination means compares the current D1 / D2 value and the previous D1 / D2 value ratio or difference value with the reference value, and when the ratio or difference value exceeds the reference value, the processing state is abnormal. Judge as
Further, the control means controls so as to increase the pause time when the processing state determination means outputs a signal indicating that the processing state is abnormal.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, (1) is an electrode, (2) is a workpiece,
(3) is an X cross table, (4) is a Y cross table, (5) is a machining power supply that supplies a pulsed current to a machining gap formed by the electrode (1) and the workpiece (2), and (6). Is an actuator for vertically driving the electrode (1),
(7) is an actuator for driving the X cross table, (8) is an actuator for driving the Y cross table, and (9a), (9b) and (9c) are the actuators (6), (7) and (8). ), A servo amplifier for supplying a current, (10) an inter-electrode voltage detection circuit for detecting the voltage in the machining gap, and (11) an elapsed time from the application of the voltage to the occurrence of discharge (hereinafter, no-load time). Td pulse generator for generating a pulse signal corresponding to Td), (12) is Td
Td measuring device for measuring pulse width of pulse, (13) is T
d A discharge waveform classifier that is a classifying unit that generates an output signal that classifies each discharge pulse into three types of immediate discharge (D1), normal discharge (D2), and open (D3) based on the measurement result of the measuring device (12), (14), (15), and (16) are counters that count the signals output by the discharge waveform classifier (13) for each of the three types of groups, and (18) is (14), (1
5) and (16), the electrode feed control device that controls the electrode feed from the count number, (20) is (14), (15), (1
6) D1 / D2 (immediate discharge pulse number / normal discharge pulse number) is calculated from the count number of 6), which is a first calculator which is a first calculating means, and (21) temporarily calculates the calculated value of D1 / D2 A memory for storing, (22) calculates a ratio between the latest value of D1 / D2 calculated by the first calculator (20) and the previous value of D1 / D2 stored in the memory (21), A second calculator which is a calculation means, and (27) is a processing state determination means which determines whether the processing state is normal or abnormal from the ratio of D1 / D2 calculated by the second calculator (22). A state discriminator, (28), is a control device which is a control means for switching the pause time from the result of the machining state discriminator (27).

Next, the operation of the embodiment of the present invention will be described.

In FIG. 1, the Td measuring device (12) is T
The pulse width of the d pulse signal, that is, the no-load time Td of each discharge waveform is measured, and the discharge waveform classifier (1
3) generates an output signal in which each discharge pulse is classified into three types: immediate discharge (D1), normal discharge (D2), and open (D3), and the electrode feed control device (18) generates a counter (1
D1, counted by 4), (15), and (16)
The electrode servo feed is performed according to the frequency of D2 and D3.

On the other hand, the first calculator (20) is (14), (15),
From the count numbers D1, D2, D3 of (16) to D1 / D2
Calculate (immediate discharge pulse count / normal discharge pulse count). The second calculator (22) calculates the ratio of the D1 / D2 to the previous D1 / D2 once stored in the memory (21) (hereinafter simply referred to as D
Calculate the ratio ε of 1 / D2). Memory (21)
The data of is updated to new data after the above calculation is finished and used for the next calculation. That is, the second calculator (22) finds the ratio ε = (D1 / D2) _n / (D1 / D2) _{n-1 of} D1 / D2.

FIG. 5 shows changes in the ratio ε of D1 / D2 with respect to the working depth for different electrode feed conditions. As the working depth becomes deeper, the ratio ε of D1 / D2 sharply increases in both cases. You can see that it is rising. This is because as the working depth becomes deeper, the sludge discharge capability between the poles decreases and the sludge concentration increases, resulting in unstable working. Since the change of ε is very large, the discrimination level can be set to be the same even when the electrode feed conditions are different. Further, since ε corresponds to the differential value of D1 / D2, the change in the processing state can be discriminated earlier.

The machining abnormality discriminator (27) discriminates whether the machining is abnormal or normal depending on whether ε exceeds a predetermined level, and when abnormal, issues a signal to the control device (28) which controls the down time,
Automatically switches the pause time. That is, when the machining state is abnormal, well-known downtime control, specifically, the downtime is increased to reduce the amount of sludge generation, thereby avoiding abnormal machining.

FIG. 7 shows the flow of this control.

FIG. 6 shows the relationship between the processing time and the processing depth when the down time is fixed and when the automatic control of the present invention is performed. When the down time is fixed, the shorter the down time is, the faster the machining speed is, but since the sludge generation amount per unit time increases, the machining depth that causes abnormal machining (machining impossible) becomes shallow. On the other hand, the automatic control of the present invention does not cause abnormal machining, and the machining speed is increased by about 15%.

In the above embodiment, the electrode feed control is set to D1, D
Although an example in which the frequency is set to 2 or D3 is shown, as shown in FIG. 2, the average voltage detector between electrodes (23) and the AD converter (2
4) and the like may be provided to control the electrode feed by the average voltage control. Further, the same effect can be obtained even if the control is performed using the difference of D1 / D2 instead of the ratio of D1 / D2. Further, when the frequency of D3 is low, the processing may be performed in two divided times in which D3 is added to D2.

[Effects of the Invention] As described above, according to the present invention, abnormal machining is predicted / determined based on the ratio or difference between the current D1 / D2 value and the previous D1 / D2 value, and the pause time is automatically switched. With this configuration, abnormal machining can be completely avoided, and an electric discharge machining apparatus capable of extremely stable and efficient machining can be obtained.

[Brief description of drawings]

1 is a block diagram showing the structure of an electric discharge machine according to an embodiment of the present invention, FIG. 2 is a block diagram showing the structure of an electric discharge machine according to another embodiment of the present invention, and FIG. 3 is a conventional electric discharge machine. FIG. 4 is a configuration diagram showing the configuration of the apparatus, FIG.
5 is a schematic diagram of a pulse signal, FIG. 5 is a diagram showing changes in the ratio ε of D1 / D2 to the machining depth, and FIG. 6 is a machining time and machining depth when the down time is fixed and when automatic control is performed. 7 is a control flow chart in an embodiment of the present invention. In the figure, (1) is an electrode, (2) is a workpiece, (3) is an X cross table, (4) is a Y cross table, and (5).
Is a processing power source, (6), (7) and (8) are actuators, (9a), (9b) and (9c) are servo amplifiers,
(10) is an inter-electrode voltage detection circuit, (11) is a Td pulse generator, and (12) is Td for measuring the pulse width of the Td pulse.
Measuring instrument, (13) is discharge waveform classifier, (14), (1
5) and (16) are counters, (18) is an electrode feed controller, (20) is a first calculator, (21) is a memory, (2)
2) is the second calculator, (23) is the average voltage detector between poles,
(24) is an A-D converter, (27) is a processing state discriminator,
(28) is a control device. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An electric discharge machining apparatus which performs machining by applying a controlled pulse voltage to a machining gap in which an electrode and a workpiece are opposed to each other to generate an electric discharge in the machining gap and repeatedly supplying a machining radio wave. , A classifying means for classifying the pulse time width into a first segmented time T1, a second segmented time T2, and a third segmented time T3, and a discharge pulse number D1 generated in the first segmented time T1 within a predetermined time or a predetermined pulse number. And the ratio D1 / of the number D2 of discharge pulses generated in the second divided time T2
A calculation means for calculating D2 every predetermined time, and a current D1 /
Processing state determination means for comparing the ratio or difference value of the D2 value and the previous D1 / D2 value and the reference value, and determining the processing state as abnormal when the ratio or difference value exceeds the reference value, and this processing An electric discharge machining apparatus comprising: a control unit that controls to increase a pause time when a signal indicating that the machining state is abnormal is output from the state determination unit.