JPH0659569B2 - 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 an electrode regular pull-up operation condition 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 the elapsed time from when the discharge occurs to the discharge (hereinafter, the 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 a no-load 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. When a certain signal is output, a control means for controlling so as to increase the electrode regular pull-up amount or the electrode regular pull-up frequency is provided.

[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 electrode regular pull-up amount or the electrode regular pull-up frequency when a signal indicating that the machining state is abnormal is output from the machining state determination means.

[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, and (5) is an electrode (1).
And a machining power supply for supplying a pulsed current to the machining gap formed by the workpiece (2), (6) an actuator for vertically driving the electrode (1), and (7) for driving an X cross table. An actuator, (8) is an actuator that drives the Y cross table, (9a), (9b), and (9c) are servo amplifiers that supply current to the actuators (6), (7), and (8), and (10 )
Is a machining gap voltage detection circuit that detects the voltage in the machining gap, and (11) is a Td pulse that generates a pulse signal corresponding to the elapsed time from the application of voltage to the occurrence of discharge (hereinafter, no-load time Td) Generator, (12) Td measuring instrument for measuring the pulse width of Td pulse, (13) Immediate discharge (D1), normal discharge (D2), open each discharge pulse from the measurement result of Td measuring instrument (12) Generate an output signal classified into three types (D3),
Discharge waveform classifier which is a classifying means, (14), (15) and (16) are counters for counting the signals output by the discharge waveform classifier (13) for each of three groups, and (18) is ( 14), (15), (16)
The electrode feed control device that controls the electrode feed from the count number of (20) is D1 / D from the count number of (14), (15), and (16).
Calculate 2 (immediate discharge pulse number / normal discharge pulse number),
A first calculator which is a first calculation means, (21) is the D1 / D
A memory for temporarily storing the calculated value of 2, (22) is the first calculator
Latest value of D1 / D2 calculated by (20) and memory (21)
A second calculator that is a second calculating means for calculating the ratio with the previous D1 / D2 stored in the second calculator, and (27) is the second calculator.
A machining state discriminator which is a machining state discriminating means for discriminating whether the machining state is normal or abnormal from the ratio of D1 / D2 calculated in (22), and (28) is a result of the machining state discriminator (27). The control device is a control unit that switches the electrode pull-up operation at regular intervals.

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

In FIG. 1, as in the conventional example, 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) measures each discharge pulse individually. Generates output signals that are classified into three types: immediate discharge (D1), normal discharge (D2), and open (D3), and the electrode feed controller (18) uses counters (14), (15), (16) The electrode servo feed is performed according to the counted frequencies of D1, D2 and D3.

On the other hand, the first calculator (20) calculates the count numbers D1, D2 and D3 of (14), (15) and (16) from D1 / D2 (immediate discharge pulse number /
Calculate the number of normal discharge pulses). The second calculator (22) stores the D1 / D2 and the previous D1 / D2 once stored in the memory (21).
A ratio with D2 (hereinafter simply referred to as a ratio D1 / D2 ε) is calculated. The data in the memory (21) is updated to new data after the above calculation is completed, and then used for the 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 if abnormal, sends a signal to the control device (28) which controls the electrode pull-up operation condition. , Automatic switching of electrode pull-up operation is performed. That is, when the processing state is abnormal, the well-known electrode regular pull-up operation control, specifically, the electrode regular pull-up amount, the electrode regular pull-up frequency, etc. are increased to improve the sludge discharge capacity, and abnormal machining is performed. Make frequent.

The electrode regular pull-up operation discharges sludge between the electrodes by periodically moving the electrode (1) up and down independently of the electrode feed control, and is indispensable especially when performing non-jet machining. .

FIG. 7 shows the flow of this control.

FIG. 8 shows changes in the D1 / D2 ratio ε and the JUMP parameter in one machining example in which this control is performed, and it can be seen that the JUMP parameter is sequentially changed as the machining progresses. .

Fig. 6 shows the operating conditions for the electrode pull-up (JUMP parameter)
It shows the relationship between the processing time and the processing depth in the case of fixing and the case of performing the automatic control of the present invention. J
When the UMP parameter is fixed, the smaller the JUMP amount is, the smaller the JUMP time per unit time is, so that the machining speed is high, but the machining depth that causes abnormal machining (incapable of machining) becomes shallow. On the other hand, the automatic control of the present invention does not cause abnormal machining, and the machining speed is about 20.
%It has increased.

In the above embodiment, the electrode feed control is set to D1, D
Although the example is performed by the frequency of 2 and D3, as shown in FIG. 2, the electrode feed by the average voltage control is performed with the configuration in which the inter-electrode average voltage detector (23) and the A-D converter (24) are provided. It may be controlled. Also, instead of the ratio of D1 / D2, D1 / D
The same effect can be obtained by controlling using the difference of 2. 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, the abnormal machining is predicted / determined by the ratio or the difference value between the current D1 / D2 value and the previous D1 / D2 value, and the electrode regular pull-up operation is automatically performed. Since it is configured to switch to, the abnormal machining can be completely avoided, and an electric discharge machining apparatus capable of performing extremely stable and efficient machining can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the constitution of an electric discharge machine in one embodiment of the present invention, FIG. 2 is a constitution diagram showing the constitution of an electric discharge machine in 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 processing apparatus, FIG.
Schematic diagram of d-pulse signal, Fig. 5 shows D1 / D2 for machining depth.
6 is a diagram showing a change in the ratio ε of FIG. 7, FIG. 6 is a diagram showing a relationship between the machining time and the machining depth when the electrode constant pull-up operation condition (JUMP parameter) is fixed and when automatic control is performed, FIG. The figure shows the control flow in one embodiment of the present invention,
FIG. 8 is a diagram showing changes in the D1 / D2 ratio ε and the JUMP parameter in one processing example in which control is performed in one 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, (5) is a machining power supply,
(6), (7) and (8) are actuators, (9a), (9b) and (9c) are servo amplifiers, (10) is a voltage detection circuit between electrodes, (11) is a Td pulse generator, (12) ) Is T for measuring the pulse width of the Td pulse
d measuring instrument, (13) discharge waveform classifier, (14), (15), (16) counter, (18) electrode feed controller, (20) first calculator, (21) A memory, (22) is a second calculator, (23) is an average voltage detector between electrodes, (24) is an AD converter, (27) is a machining state discriminator, and (28) is a controller. . 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 an electrode regular pull-up amount or an electrode regular pull-up frequency when a signal indicating that the machining state is abnormal is output from the state determination unit.