JPS63200918A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To restrain occurrence of abnormal discharge so as to aim at stabilizing electrical discharge by providing a discriminating and detecting circuit, a time computing circuit, a computing and logic circuit, a digital-analog converting circuit, a machining gap control device, a servo-motor and the like so as to control the machining gap. CONSTITUTION:A discriminating and detecting circuit 8 and a time computing circuit 9 compute an electric discharge delay time or a time rate of an effective discharge time from an electric discharge wave generating in the machining gap. Then the reference voltage of a machining gap control device 22 is changed, and a computing and logic circuit 20 compares and judges the maximum and minimum values of time rates in a predetermined time or variation ranges of the time rates before and after the variation with each other. Further, in accordance with the result of the comparison, the reference voltage is changed. With the repetition of the above-mentioned steps, the reference voltage is controlled to an optimum value. With this arrangement, it is possible to restrain occurrence of abnormal electric discharge so as to always carry out stable machining with a high degree of accuracy even though the machining condition and the combination of the materials of an electrode 1 and workpiece 2 vary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to electrical discharge machining equipment, and particularly to machining gap control thereof.

[Conventional technology]

To control the machining gap in electric discharge machining, the voltage in the machining gap is generally detected and averaged by a smoothing circuit, and the difference between that value and a reference voltage is amplified and input to the electrode feed servo mechanism, so that the gap length is kept constant. Conventionally, the reference voltage value has been set empirically by the user according to the machining conditions and the combination of the electrode and workpiece material.

On the other hand, in Japanese Patent Application Laid-Open No. 59-205232, the time from the application of voltage to the machining gap to the generation of discharge, that is, the distribution state of the discharge delay time is detected.

The discharge state is determined by comparing the detection result with the standard distribution state that indicates the quality of the discharge state, and if it is determined that the discharge state is poor, the reference voltage used to control the machining gap is changed to maintain the discharge state. It has been proposed to control the gap length so that it recovers to a good condition. This proposal is aimed at preventing abnormal discharge, but if the machining conditions or the combination of electrode and workpiece material change, the reference distribution state will also change, so it is difficult to set the reference distribution state in advance. It was necessary to prepare only the machining conditions and combinations of electrodes and workpiece materials.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional technology, when the machining conditions or the combination of electrode and workpiece material change, the reference voltage value of the machining gap control device or the discharge delay time to change the voltage value is adjusted accordingly. There is the trouble of having to reset the reference distribution state, etc., and depending on these settings, the machining gap length may not always be maintained appropriately.

An object of the present invention is to appropriately control the machining gap length without having to set the reference voltage of the machining gap control device and the standard distribution state of the discharge delay time each time as in the above-mentioned prior art.
An object of the present invention is to provide an electric discharge machining device that can always perform highly efficient and stable machining.

[Means for solving problems]

The above purpose is to perform the above-mentioned processing in an electric discharge machining apparatus equipped with a machining gap control device that compares the voltage of the machining gap between the electrode and the workpiece in electric discharge machining with a reference voltage, and controls the machining gap length according to the difference. a first means for determining and detecting at least one of the discharge delay time during normal discharge and the subsequent effective discharge time from the discharge waveform generated in the gap; A second step that calculates the time rate (percentage of the reference time) of the effective discharge time.
and the output data of the second means for a predetermined period of time, and determine the maximum value, minimum value, or difference between the maximum value and the minimum value of the discharge delay time rate or effective discharge time rate for each predetermined time period. and a third means for outputting the reference voltage, and each output value of the third means before and after the change in the reference voltage is compared and determined, and the reference voltage is changed in the direction of increasing or decreasing according to the determination result. This is achieved by adding a fourth means for controlling the reference voltage so as to approach the optimum value by repeating the operation.

[For production]

Figures 2 and 3 show electrical discharge machining experiments conducted under the following conditions.
By changing the average machining voltage, that is, the average voltage value U^ of the machining gap, the discharge delay time during normal discharge, effective discharge time, sustained arc discharge time during abnormal discharge, and the discharge waveform generated for each voltage value are determined. Each time rate of short circuit time Φ, -1Φ0
, Φ0, Φ, and shows the distribution state of each time rate obtained as a result, A, D, G, I are the maximum values during a predetermined time, B, E are the minimum values, C , F, H, and J are time rate characteristic lines showing average values.

Electrode: Copper workpiece: Steel (SKDII) Pulse current: 3,2A Pulse on time: 50μS Figure 2 shows the case when the voltage pulse frequency is constant, and Figure 3 shows the case when the current pulse width is constant. The standard time when calculating the time rate is 50m5. The predetermined time for determining the maximum value, minimum value, and average value of each time rate is 5 seconds.

The following can be said from the distribution of each time rate shown in FIGS. 2 and 3. In other words, when the occurrence of abnormal discharge is suppressed and machining is stable, (i) In Fig. 2(a) and Fig. 3(a), the maximum value of the discharge delay time rate Φ, - is the minimum value. At the time.

This is also the time when the fluctuation range of the time rate, that is, the difference between the maximum value and the minimum value, is the minimum.

(ii) In FIG. 2(b) and FIG. 3(b).

The minimum value of the effective discharge time rate Φ is the maximum, and the fluctuation range of the time rate is also the minimum.

(in) Figure 2 (c), (d) and Figure 3 (e), (
In d), both the maximum value and the average value of the sustained arc discharge time rate Φ0 and the short circuit time rate Φt5, which represent abnormal discharge, are below a certain level.

The optimum value of the average machining voltage (U^) that satisfies these conditions is around 60V in FIGS. 2 and 3.

Generally, when the machining gap is wide, it is difficult for electric discharge to occur and the average voltage value U^ is high; when the machining gap is narrow, short circuits occur and discharge easily occurs, so the average voltage value UA is low. In other words, since the average voltage value U^ corresponds to the machining gap length, the second
The average voltage value UA plotted on the horizontal axis in FIGS. 3 and 3 can be replaced with a reference voltage value UB for controlling the machining gap.

The distribution state of each time rate does not generally change even if the machining conditions or the combination of electrode and workpiece material changes, and it can be said that the same as (i) to (■) above can be said.

The present invention has been made based on the above recognition,
Calculate each time rate of the discharge delay time or effective discharge time during normal discharge determined and detected from the discharge waveform, and calculate the maximum value, minimum value, or difference between the maximum value and the minimum value of each time rate during a predetermined time. After determining the time rate fluctuation width, compare the maximum value, minimum value, or time rate fluctuation width of each time rate with the respective values determined before the change in the reference voltage to determine the magnitude. By repeatedly performing the operation of increasing or decreasing the reference voltage accordingly, the reference voltage is brought closer to the optimum value, that is, the maximum value, minimum value, or time rate variation width of each time rate is adjusted to the above ( i), (ii)
The control is performed so that the following conditions are satisfied.

If necessary to suppress the occurrence of abnormal discharge, determine the time rates of sustained arc discharge time and short circuit time that represent abnormal discharge, and check whether the maximum value or average value of these time rates during a predetermined period of time is below the standard level. It is also possible to determine whether or not the voltage is the same, and add the determination result to the determination criteria when increasing or decreasing the reference voltage.

By controlling the reference voltage of the machining gap control device as described above, it is possible to suppress the occurrence of abnormal discharge and always perform stable machining with high efficiency. There is no need to set the reference voltage value or the distribution state of the discharge delay time standard each time according to the combination of materials of the object, and the discharge delay time, effective discharge time, etc. can be used as control factors for the reference voltage. By taking the ratio, the present invention can be applied to either a constant voltage pulse frequency or a constant current pulse width power supply control method.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an outline of an electric discharge machining apparatus according to the present invention. In the figure, 1 is a processing electrode, and 2 is a workpiece (not shown).

The electrode 1 and the workpiece 2 are placed facing each other in an insulating working liquid, forming a working gap therebetween. 3 is a processing pulse power supply, and the processing DC power supply 4 is connected to a switching element 5 such as a transistor.
The current limiting resistor 6 is connected to the machining gap via the current limiting resistor 6 in series. Reference numeral 7 denotes a control circuit for performing on/off switching of the switch element 5. 8 determines the discharge waveform of the machining gap based on the voltage of the machining gap and the switching signal of the control circuit 7, and determines the discharge delay time and effective discharge time.

This is a discrimination/detection circuit that outputs a signal with a pulse width corresponding to each of the sustained arc discharge time and the short circuit time, and corresponds to the first means of the present invention. 9 is an AND gate circuit lO~13
, clock pulse oscillator 14, time counters 15 to 18
, a time calculation circuit consisting of a reference counter 19, which corresponds to the second means of the present invention, and calculates the output signal of the discrimination/detection circuit 8 as discharge delay time, effective discharge time, sustained arc discharge time, and short circuit, as will be described later. It is converted into a digital signal representing each time rate and output. 20 is an arithmetic/logic circuit having functions corresponding to the third and fourth means of the present invention.

The maximum and minimum values of each of the above time rates during the specified time period.

Calculate the average value, time rate fluctuation range, etc., memorize these values,
Comparison and judgment are performed, and a digital signal of a reference voltage to be applied to the machining gap control device is output in accordance with the judgment result. This output is converted into a reference voltage by a digital-to-analog conversion circuit 21 and applied to a machining gap control device 22. The machining gap control device 22 controls this reference voltage and the machining gap voltage (
The machining electrode 1 is driven by a servo motor or the like according to the difference, and the machining gap length is controlled.

The configuration and operation of each part of the discrimination/detection circuit 8, time rate calculation circuit 9, and calculation/logic circuit 20 will be explained in detail below.

FIG. 4 is a block diagram showing the internal configuration of the discrimination/detection circuit 8. In the figure, the part 8 surrounded by a dotted line is a discrimination/detection circuit, 23 is a timing pulse generator that generates a timing pulse slave, T2, based on the switching signal of the processing pulse power source 3, and 24, 25, 26 are Comparison amplifier 2
7.28.29 First, second and third level setters giving set voltages E2, E2, E, 30.31.32.33
, 34, 35, 36 are AND gate circuits, 37, 38 are flip-flops, 39, 40, 41, 42 are inverters, 43 is a discharge delay time signal output terminal, 44 is an effective discharge time signal output terminal, 45 is a sustained arc The discharge time signal output terminal 46 is a short circuit time signal output terminal.

If the voltage waveform patterns between the electrode 1 and the workpiece 2 in each discharge state are roughly classified, normal discharge (
a,), sustained arc discharge (a,).

There are four types: short circuit (a,) and no discharge (a,).

Next, the operation of the discrimination/detection circuit 8 in FIG. 4 will be explained in FIGS. 5 and 6.
This will be explained using the waveform diagram shown in the figure.

In Fig. 4, the set voltages E, E3, and E3 are set to the levels shown in Fig. 5(a) using the level setters 24, 25, and 26, and the voltages shown in Figs. 5(b) and (c) are Discrimination and detection of discharge time, etc. in each discharge state is performed by the timing pulse slave T8 shown in FIG.

In other words, the voltage waveform (a□) during normal discharge is used for this discrimination.
When input to the detection circuit 8, the output waveform (6
) is as shown in the figure, and the output waveform (f) of the second comparator amplifier 28 is changed by the setting voltage E2 of the second level setter 25.
becomes as shown.

By inputting signals of these two waveforms (e) and (f), a signal of waveform (g) is obtained at the output of the AND gate circuit 30. On the other hand, due to the set voltage E of the third level setter 26, the output waveform (h) of the third comparator amplifier 29 becomes as shown in the figure. The output of the AND gate circuit 31 has a waveform (i
) signals are obtained.

Set the flip-flop 37 with this signal (i),
By resetting with the timing pulse T2, a signal of waveform (j) is obtained at the output of the flip-flop 37. Then, the signal of waveform (k) is obtained at the output of the AND gate circuit 34 by the input of the signal of waveform (h), the signal of waveform (j), and the signal obtained by inverting the signal of waveform (g) by the inverter 40. The signal of this waveform (k) is a time signal having a pulse width corresponding to the discharge delay time during normal discharge. Also, the signal of waveform (g), the signal of waveform (j), the signal of waveform (h)
A signal having a waveform (Q) is obtained at the output of the AND gate circuit 35 by inverting the signal of the signal by the inverter 41. This waveform (Q) signal is a time signal having a pulse width corresponding to the effective discharge time during normal discharge.

When the voltage waveform (a2) during sustained arc discharge is input, signals of waveforms (e) to (j) corresponding to it are generated, and the signal of waveform (g) and the signal of waveform (j) are combined. A signal of waveform (m) is obtained at the output of the AND gate circuit 36 by two inputs of the signal inverted by the inverter 42 . The signal of this waveform (m) is a time signal having a pulse width corresponding to the sustained arc discharge time.

When the voltage waveform (a,) at the time of a short circuit is input, the signal of the corresponding waveform Ce) is inverted by the inverter 39, and the output signal of this inverter 39 and the timing pulse T
1 to the AND gate circuit 32, and the inverter 39
The output signal and the timing pulse T2 are input to the AND gate circuit 33. Then, by setting the flip-flop 38 with the output signal of the AND gate circuit 32 and resetting it with the output signal of the AND gate circuit 33, a signal of waveform (n) is obtained at the output of the flip-flop 38. This waveform (n) signal is a time signal having a pulse width corresponding to the short circuit time.

In the voltage waveform (a4) during no discharge, the voltage waveform (k) above.

No signal with any of the waveforms (Q), (m), and (n) is generated. In this way, the discharge state of each machining pulse can be determined, and the discharge delay time, effective discharge time, sustained arc discharge time, and short circuit time in each discharge state can be detected.

In the time rate calculation circuit 9, the waveforms (k), (Q
), (m), and (n) and the clock pulse output from the clock pulse oscillator 14, and the output pulse of each AND gate circuit is calculated by the time counter 15.
Count each at ~18. The reference counter 19 is used to determine the reference time when calculating the time rate, and the output signal of the reference counter 19 causes the time counters 15 to 15 to
As a result, the count values of time counters 15 to 18 are sent to the arithmetic/logic circuit 20 as data representing each time rate of the discharge delay time, effective discharge time, sustained arc discharge time, and short circuit time. Output. The reference time is set to about 50 m5, for example, in order to reduce variations in measurement data.

The arithmetic/logic circuit 20 can be configured using a microprocessor or the like. Figures 1 and 4 show an operation flowchart of electrode feed servo system reference voltage control based on discharge time rate when a microprocessor is used in Figure 7.
The figure shows the process of determining both the discharge delay time rate and the effective discharge time rate during normal discharge, but only one of the time rates is sufficient as a control factor for reference voltage control. An example in which the time rate is used in combination with the sustained arc discharge time rate and the short circuit time rate will be explained.

In the first step 101 of the flowchart shown in FIG. 7, the contents of the data memory and various registers of the microprocessor are initialized. In the next step 102, the previously stored time count value is and clear the number of inputs. In the subsequent step 103, the effective discharge time count value (N tel ) from the time counter 16 of FIG.
teM A X ) and the minimum value (NteM I N) are determined and stored. In the subsequent step 104, the sustained arc discharge time count value (N,) from the time counter 17 in FIG. 1 is input and integrated (NtaA V
E), and in the subsequent step 105, the short circuit time count value (N
h*) and integrate it (NtsA V E
).

In the subsequent step 106, each time count value input number (Nt) is compared with a preset reference input number (N). If the result is Nt<N, go back and repeat steps 103, 104, and 105, and Nt
ieM AX , NteM ) N , NtaA
The values of VE, Nt, and AVE are updated, and when a predetermined time corresponding to N clock pulses has passed and Nt≧N, steps 106 to 10 are performed.
Proceed to step 7.

This predetermined time is set to several seconds to several tens of seconds in order to reduce variations in measurement data. In step 107,
Effective discharge time rate fluctuation range (Nt, R=
The six or more steps 103 to 107 for calculating NteMAX-Nt, MIN) correspond to the third means of the present invention.

Effective discharge time rate fluctuation range (Nt
aR) is the stored data (N t
e RM ). And Ntl, R”N
t. If it is RM, proceed to step 110 without updating the above stored data, and N t e R < N t
If it is e RM, the above stored data is updated in step 109 (N t e RM 4 - N t e R), and then the process proceeds to step 110. Value (N,,AV
E) is compared with a preset reference level (NtaTH) in step 110, and Nt-A V E S
If NtaT H, proceed to step 111, average value of short circuit time rate (Nt
sAVE) is compared with a preset reference level (N t *TH) in step 111. Then, if N t# A VE≦N * * T H, proceed to step 112 if N is greater than or equal to 0, R≦Nt, RM, N
taAVE≦Nt, THlN t s A V E≦N
If all the conditions of t*TH are satisfied, step 1
At step 12, the reference voltage (Us) of the electrode feed servo system is decreased by one step. If even one of these conditions is not satisfied, i.e. N *e R> Nte RM, N t
aA V E > N taT Hl or N□A V
If E>NtsTH, the process proceeds to step 113, where the reference voltage (UB) is increased by one step. One cycle of control operation ends when step 112 or 113 is executed, and step 10
Return to step 2 and repeat the same operation.

The above steps 108 to 113 correspond to the fourth means of the present invention.

In FIG. 7, the reference voltage (Us) is increased or decreased by one step (for example, IV) as described above.

The initial value of the effective discharge time rate storage data (N t a RM ) is set to a value equivalent to 100% of the effective discharge time rate, and the sustained arc discharge time rate reference level (N t a T H)
, the short circuit time rate reference level (N□TH) is shown in Fig. 8(b),
Set as shown in (c). Also, the reference voltage (Ua)
The initial value of is set to the maximum value. If you do this,
After the start of control, the reference voltage (U[3) moves in the direction in which the effective discharge time rate variation width becomes smaller, that is, in the direction in which the reference voltage value decreases, as shown in FIG. 8(a), and the effective discharge time rate variation width decreases. When the reference voltage value decreases from the voltage value (Us, ) at which the value becomes the minimum, the reference voltage is controlled in an increasing direction. The same applies when the sustained arc discharge time rate average value or the short circuit time rate average value becomes larger than the reference level. In this way, the reference voltage of the machining gap control device is controlled in the decreasing direction, that is, in the direction in which the machining gap becomes narrower, and as a result, the effective discharge time rate fluctuation range becomes larger than before.
When either the average sustained arc discharge time rate or the average short circuit time rate exceeds the standard level, the standard voltage is controlled to return to its original value, thereby suppressing the occurrence of abnormal discharge.
It is possible to perform highly efficient and stable machining at all times.

The effective discharge time (rate) in Fig. 7 may be replaced by the discharge delay time (rate), and the maximum value of the discharge delay time rate or the minimum value of the effective discharge time rate may be used as a control factor instead of the time rate fluctuation range. It is clear that similar results can be obtained.

〔Effect of the invention〕

According to the present invention, the time rate of the discharge delay time or effective discharge time is determined from the discharge waveform generated in the machining gap, and the reference voltage of the machining gap control device is changed to change the time rate before and after the change. By comparing and determining the maximum value, minimum value, or time rate fluctuation range within a predetermined time, and repeating the operation of increasing or decreasing the reference voltage according to the determination result, the reference voltage is controlled to the optimal value, so that processing can be performed easily. Even if the conditions or the combination of electrode and workpiece material change, abnormal discharge can be suppressed and high efficiency can be maintained without having to set the reference voltage value or discharge delay time standard distribution condition each time. An unprecedented electrical discharge machining device capable of performing stable machining can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an outline of the electrical discharge machining apparatus according to the present invention, and Fig. 2 ((a), (b), (c), (d)) shows the voltage pulse frequency being constant and the average machining voltage being varied. Figure 3 shows the distribution of discharge delay time rate, effective discharge time rate, sustained arc discharge time rate, and short circuit time rate when
a), (b), (c), and (d)) are the discharge delay time rate, effective discharge time rate, sustained arc discharge time rate, and short circuit time rate when the current pulse width is constant and the average machining voltage is varied. FIG. 4 is a block diagram showing the internal configuration of the discrimination/detection circuit in FIG. 1. FIG. 5 is a waveform diagram of the discharge waveform and timing pulse of the machining gap in each discharge state. The figure is a time chart of each part signal for explaining the operation of the discrimination/detection circuit in Fig. 4, Fig. 7 is an operation flowchart of the arithmetic/logic circuit in Fig. 1, and Fig. 8 ((a),
(b) and (C)) are explanatory diagrams of reference voltage control in FIG. 7. 1... Electrode 2... Workpiece 3...
Processing pulse power source 8...Discrimination/detection circuit (first means) 9...Time rate calculation circuit (second means) 20...Arithmetic/logic circuit (third and fourth means) 21. ...Digital-to-analog conversion circuit 22...Machining gap control device 103-107...Steps 108-113 of the control program corresponding to the third means...Steps of the control program corresponding to the fourth means

Claims (1)

[Claims] 1. In an electric discharge machining device equipped with a machining gap control device that compares the voltage of the machining gap between the electrode and the workpiece with a reference voltage in electric discharge machining and controls the machining gap length according to the difference, a first means for determining and detecting at least one of the discharge delay time during normal discharge and the subsequent effective discharge time from the generated discharge waveform; a second means for calculating the time rate (percentage of the reference time); and determining the output data of the second means for a predetermined time;
a third means for outputting the maximum value, the minimum value, or the difference between the maximum value and the minimum value of the discharge delay time rate or the effective discharge time rate for each predetermined time; a fourth means for controlling the reference voltage so as to approach the optimum value by repeatedly performing an operation of comparing and determining the third output value and changing the reference voltage in the direction of increasing or decreasing according to the result of the determination; Electrical discharge machining equipment characterized by the addition of: