JPS63318210A - Control device for electric discharge machine - Google Patents

Abstract

PURPOSE:To carry out stable machining while improve machining efficiency by operating the ratio of effective discharge pulses to the whole discharge pulses to set an effective discharge pulse rate and varying a machining condition based on the compared value with a previously set reference value. CONSTITUTION:The number of the whole discharge pulses are detected by a whole discharge pulse detecting means 6 at each set time and the voltage between electrodes is compared with a reference voltage value which is previously set in a reference voltage setting means 7 by an effective discharge pulse detecting means 8 to detect the number of effective discharge pulses. And, an effective discharge pulse rate is calculated from the detected number of effective discharge pulses and the number of whole discharge pulses by an effective discharge pulses rate operating means 9 and sent to a comparing means 11, to compare the effective discharge pulse rate with the set reference value of an effective discharge pulse ratio which is previously set in a reference value setting means 10 and which can be judged in an unstable condition. And, based on the compared value, the feeding of a machining electrode 1 in the vertical direction, a discharge stopping time, and an electrode draw-up quantity for a defined time can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for an electric discharge machine, and particularly to stabilization of machining and improvement of machining efficiency.

[Prior Art] In electrical discharge machining, in which the workpiece is machined by applying a pulse voltage to the machining gap where the electrode and the workpiece face each other, a pulse voltage is applied to the machining gap between the electrode and the workpiece. By controlling the length to an appropriate distance depending on the machining situation, the workpiece can be machined while preventing short circuits and arcs. The machining conditions for this machining are the peak value of the discharge current and the pulse application time, which are set according to the machining that is intended for one purpose, and the occurrence of discharge within a unit time is increased to the extent that short circuits do not occur. To determine the time and perform highly efficient machining. In addition, in order to efficiently discharge sludge during processing, various conditions such as the distance for pulling up the electrode at regular intervals are also appropriately determined.

Figure 8 shows an example of the pulse waveform that appears between the electrodes when the gap length between the electrode and the workpiece changes, where (a) is the voltage waveform, and (b) the pulse voltage is the open circuit voltage (V). Discharge voltage (V) at which the signal becomes low and discharge occurs
When , the current waveform shows a high signal. In the figure (
The voltage waveform shown at) is when the gap length between the electrodes is at an appropriate distance. When a voltage is applied between the electrodes, after an open circuit voltage (V) is generated for a certain time width, discharge starts and the discharge voltage (V ), and the machining current (i) flows.

However, if the gap length between the poles becomes shorter than the appropriate distance (a2)
As shown in the figure, the discharge voltage (V 2 ) immediately occurs without an open-circuit voltage (V 2 ), and if machining continues in this state, it will develop into an arc state and cause damage to the electrode or the workpiece.

In addition, if the gap length between the electrodes is longer than the appropriate distance, the open circuit voltage (V) will become extremely long as shown in (a3), the number of discharges per unit time will decrease, and the machining speed will significantly decrease due to the decrease in discharge efficiency. It will drop.

In order to prevent the above-mentioned change in the gap length between the electrodes, the gap length between the electrodes has conventionally been controlled by measuring the average machining voltage between the electrodes. This control method uses a preset voltage value as a reference value, and if the detected average machining voltage value between poles is larger than the reference value, the open circuit voltage (
V ) is long and the inter-electrode gap length is farther than the appropriate distance, a command is given to lower the electrode feed, and conversely, if the average machining voltage value between the inter-electrode is smaller than the reference value, the open circuit voltage (V ) is determined.
is small or absent, and it is determined that the inter-electrode gap length is narrower than the appropriate distance, and a command is issued to increase the electrode feed.

[Problems to be Solved by the Invention] The average machining voltage between the machining poles used to control the gap length between the poles is not only the open voltage (V) and the discharge voltage (V) of 0g, but also the voltage pulse width and the discharge body stop. very affected by time.

The discharge pause time is often set empirically based on the area of the shape of the machining electrode, the machining depth, etc. However, during machining, conditions may become unstable due to the generation of sludge, etc., so if the operator determines that the conditions are unstable, the operator may intentionally extend the discharge pause time sufficiently by manual operation. In many cases, unstable conditions can be avoided by Furthermore, in an electric discharge machine equipped with a gap state detection circuit and a pause control circuit, a method is also adopted in which when an unstable condition is detected, the discharge pause time is made longer than a set value by a certain period of time. Therefore, the discharge pause time during machining can be arbitrarily changed from the set value.

Further, the discharge voltage (V 2 ) changes even under the same processing conditions depending on the material of the electrode or workpiece, or the time after the start of the discharge.

In order to perform stable machining using the average machining voltage between machining poles, which fluctuates due to changes in the discharge pause time, discharge voltage (V), etc., the reference voltage value must be set in response to changes in machining conditions, etc. First, there is a problem in that it is difficult to perform stable processing when processing conditions change.

Furthermore, if the unstable state during machining is determined based on an instantaneous state and the discharge pause time is made longer than a set value, there is a problem that the machining speed becomes slower.

Furthermore, even when setting the fixed electrode lifting distance to efficiently discharge generated sludge, if machining is performed using a setting value that is uniquely set depending on the shape of the machining electrode, etc., the machining depth may become deep. Because machining becomes unstable, the amount of time the electrode is pulled up is sometimes intentionally increased manually during machining, which sometimes slows down the machining speed.

This invention was made to solve such problems, and it is possible to control the gap length between the poles without being affected by the set machining conditions to perform stable machining, and to improve machining efficiency. The object of the present invention is to obtain a control device for an electric discharge machine that can perform the following steps.

[Means for Solving the Problems] A control device for an electric discharge machine according to the present invention includes a total discharge pulse detection means, a reference voltage setting means, an effective discharge pulse detection means,
The apparatus includes an effective discharge pulse rate calculation means, a reference value setting means, a comparison means, and a machining condition control means.

The total discharge pulse detection means detects the total discharge pulse during machining at predetermined time intervals. The reference voltage setting means sets a reference voltage value higher than the discharge voltage of the pulse voltage and lower than the open circuit voltage. The effective discharge pulse detection means compares each discharge pulse voltage during machining with a preset reference voltage value, detects that the open pulse voltage exceeds the reference voltage value, and detects an effective discharge pulse.

The effective discharge pulse rate calculation means calculates the ratio of the total discharge pulse to the effective discharge pulse to calculate the effective discharge pulse rate. The reference value setting means sets one or more reference values of the effective discharge pulse rate. The comparison means compares the effective discharge pulse rate with a preset reference value. The machining condition control means changes the machining conditions based on the comparison value compared by the comparison means.

[Operation] In this invention, the discharge state between the machining machining machines is detected, the ratio of effective discharge pulses for each fixed time period is determined, and the machining conditions are changed based on the change in this ratio.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
In the figure, (1) is the machining electrode, (2) is the machining m h (
1) is the workpiece to be machined, (3) is the power supply that supplies machining power, and (4) is a rectangular pulse by intermittent discharge current flowing through the machining gap between the machining electrode (1) and the workpiece (2). (5) is a voltage detector that detects the voltage between the processing electrode (1) and the workpiece (2); (6) is the processing electrode (1) and the workpiece (2); Total discharge pulse detection means for detecting the total number of discharge pulses applied in between, (7) is a reference voltage setting means for setting the reference voltage value of the pulse voltage applied to the machining gap, and (8) is the voltage applied to the machining gap. The effective discharge pulse detection means detects the number of effective discharge pulses contributing to stable machining from the pulse voltage and the reference voltage value set in the reference voltage setting means (7).

(9) is the ratio of the number of effective discharge pulses to the total number of discharge pulses from the total number of discharge pulses detected by the total discharge pulse detection means (6) and the number of effective discharge pulses detected by the effective discharge pulse detection means (8), that is, Effective discharge pulse rate calculation means for calculating the effective discharge pulse rate, (10) reference value setting means for setting one or more reference values of the effective discharge pulse rate, and (11) preset effective discharge pulse rate. (12) is a comparison means (
This is a machining condition control means that changes the machining gap, discharge pause time, etc. based on the comparison value of 11).

Below, before explaining the operation of this embodiment, the principle of the present invention, which is the determination of effective discharge pulses that contribute to stable machining among the discharge pulses generated during machining, will be explained based on the waveform diagram in Fig. 2. . In Figure 2, (a) shows the machining electrode (
1) and the workpiece (2), (b) shows the voltage waveform of the voltage between the machining electrodes and the workpiece (2), and (b) shows the discharge voltage (V
) is applied and the discharge pulse signal becomes high when g is applied.

Among the discharge pulse signals shown in FIG. 2(b), those that are effective for machining and those that are abnormal are distinguished based on the voltage waveform between the electrodes. This distinction is made by regarding the case where the open-circuit voltage (V) before the occurrence of discharge is extremely small in the interelectrode voltage shown in (a) as abnormal.

That is, the pulse waveform (23) in FIG. 2(a), (
As shown in 24), when the open circuit voltage (V) is extremely low, what is called instant discharge occurs, and more sludge is present between the electrodes than during normal machining.
The distance between the poles is narrower than the appropriate distance. If machining is continued in this state, an arc will eventually develop and damage to the machining electrode (1) or workpiece (2) will occur. Therefore, it is possible to appropriately detect such a state and control the vertical feed of the machining electrode (1) to make the machining gap appropriate, to lengthen the discharge pause time to suppress the amount of sludge generation, or to control the electrode's regular timing. It is necessary to increase the upper volume to discharge the sludge between the poles.

In order to determine whether this is an abnormal discharge pulse or an effective discharge pulse that contributes to stable machining, the voltage between the electrodes during discharge, that is, the discharge voltage (V ) is a certain set reference value (V) lower than o
As the ref threshold, after applying the interelectrode voltage, an open circuit voltage (V) exceeding the threshold (V) is generated and ref is generated.

A case where a discharge occurs is considered to be an effective discharge, and a case where the discharge voltage (V) does not exceed the threshold value (V) after applying the inter-electrode voltage is considered to be an abnormal discharge.For example, in Fig. 2 (a)
), the effective discharge has pulse waveforms (21), (22), and (25), and the effective discharge pulse becomes as shown in FIG. 2(e).

The larger the ratio of effective discharge pulses to the total discharge pulses in a preset set time (T), that is, the value of the effective discharge pulse rate, is considered to be a stable machining state, and conversely, the smaller the value of the effective discharge pulse rate is, the more likely the arc state or It can be considered as an unstable machining state due to arc state.

Therefore, in this embodiment, the total number of discharge pulses and the number of effective discharge pulses during machining are detected at each set time (T), the effective discharge pulse rate is calculated, and based on that value, the machining electrode (1
), the discharge pause time, or the amount of time the electrode is pulled up at a given time.

The operation of this embodiment will be explained below based on the flowchart shown in FIG.

Simultaneously with the start of machining, a predetermined set time (T
), the total discharge pulse detection means (6) detects the total discharge pulse (N
) is detected, and the effective discharge pulse detection means (8) compares the inter-electrode voltage with a reference voltage value (V) set in advance in the reference voltage setting means (7) to calculate the number of effective discharge pulses (n). Detect (step 30)
. The number of detected effective discharge pulses (n) and the total number of discharge pulses (
N), the effective discharge pulse rate calculation means (9) calculates the effective discharge pulse rate n/N and sends it to the comparison means (11). The comparison means (11) compares the effective discharge pulse rate n/N with the set reference value (αl) of the effective discharge pulse rate, which is set in advance in the reference value setting means (lO) and can be judged as an unstable state (step 31). . Here, if the effective discharge pulse rate n
If /N is smaller than the set value (α1), use the machining condition control means (12) to change the electrode feed to one step higher than the currently set feed rate, or change the currently set discharge pause time. Either the time is changed to be one step longer than the current time, or the electrode regular pulling distance is changed to be one step longer than the currently set condition (step 32).

Furthermore, when the effective discharge pulse rate n/N is larger than the set value (αl), the value (α) of the effective discharge pulse rate that can be determined as a sufficiently stable state is set in advance, that is, α2〉αl. Steady state reference value in the relationship (α2)
If it is larger (step 33), the electrode feed is changed one step lower than the current setting value, or the discharge rest time or the electrode regular lifting distance is controlled to be one step smaller than the current setting value. (step 34). Also, if the effective discharge pulse rate n/N is larger than the set reference value (α1) that is determined to be an unstable state, and the stable state reference value (α2
), machining is continued without changing the set values of machining conditions such as machining gap and discharge suspension time.

FIG. 4 shows the total discharge pulse detection means (N) for detecting the total discharge pulse number (N) and the effective discharge pulse number (n) according to the above embodiment.
6) and an example of a specific electric circuit of the effective discharge pulse detection means (8). The operation of the electric circuit shown in the figure will be explained with reference to the waveform diagram shown in FIG. In addition, in FIG. 5, the signals (A) to (G) are the signals (A) to (G) shown in FIG.
shows the signal. As shown in the figure, the comparator (40) compares the input electrode-to-electrode voltage signal (A) with a predetermined threshold (V), and the electrode-to-electrode voltage (A) exceeds the threshold (V). r
When ef' is exceeded, a high signal (C) is output. The signal (C) output from this comparator (40) is sent to the inverting amplifier (41
), and this inverted signal and a pulse signal (B) indicating the timing to apply the voltage between electrodes (A) are input to an AND gate (42) to obtain a full discharge pulse signal (F).

On the other hand, the signal of the falling edge of the pulse signal (B) indicating the timing of applying the voltage between electrodes (^) in the multi-by-break (43), that is, the timing signal (D) every time the application pulse of the voltage between electrodes (A) ends. is generated and input to the flip-flop (45). The flip-flop bus (45) outputs a signal (E) based on this timing signal (D) and a signal output from the comparator (40) and sent through the not gate (44), and this output signal (E) and the total The discharge pulse signal (F) is input to the AND gate (46) to generate an effective discharge pulse signal (G).

The total discharge pulse signal (F) and the effective discharge pulse signal (G) obtained as described above are each counted by a counter (47).

(48) to calculate the total number of discharge pulses (N) and the number of effective discharge pulses (n), and calculate the effective discharge pulse rate calculation means (
9).

In the above embodiment, a case has been described in which a one-stage setting standard value (α1) is set as the setting standard value of the effective discharge pulse rate that can be determined to be an unstable state, which is set in the standard setting means (10). The value of the set standard value (α1) for unstable state judgment is further expanded, and the set standard values (α ), (α1□), which have a relationship of α1□ × α1°, are used as standards, and the machining conditions can be changed depending on the degree of the unstable state. Changes may be made in stages.

Figure 6 shows the unstable state and the set reference value for judgment (α).
, (α1°), and the effective discharge pulse rate calculation means (9) in the flowchart shown in FIG. 3 makes a two-stage determination, and the effective discharge pulse rate n/N is set If it is smaller than the reference value (α11) (step ata), that is, if it is determined that the state is quite unstable, the machining conditions such as the discharge pause time are suddenly changed by two steps (step 32a), and the effective discharge pulse rate n/ N is larger than the set standard value (α), and the set standard value (
If it is smaller than α1□) (step aib), the machining conditions are changed by one step as in the case shown in FIG. 3 (step 32b). As a result, unstable conditions can be detected with higher accuracy, and more efficient machining can be performed. In each of the above embodiments, the effective discharge pulse rate was calculated based on the number of pulses within the set time (T), but it can also be calculated based on the cumulative energization time of the discharge pulses.

In each of the above embodiments, the total number of discharge pulses (N) and the number of effective discharge pulses (n) are detected as the effective discharge pulse rate, and the effective discharge pulse rate n/N is calculated from each number of pulses. However, each number of pulses (N), (
At the same time as the effective discharge pulse rate n/N calculated from n), the time (t
oN) is detected, the ratio of the cumulative time (ToN) to the set time (T) (hereinafter referred to as effective discharge rate) is calculated, and the machining conditions are changed using this effective discharge rate as well. This allows processing to be performed more efficiently. That is, the value T of the effective discharge rate. This is because it is considered that the larger N/T is, the faster the processing speed is.

Below, the effective discharge pulse rate n calculated from the above pulse number
Another embodiment of the present invention in which the effective discharge pulse rate calculated from /N and the time of the effective discharge pulse, that is, the effective discharge rate ToN/T, is calculated, and the machining gap, discharge pause time, etc. are controlled based on these values. This will be explained based on the flowchart in FIG.

Simultaneously with the start of machining, a predetermined set time (T
), the total discharge pulse detection means (6) detects the total discharge pulse (N
) is detected, and at the same time, the number of effective discharge pulses (n) is detected by the effective discharge pulse detection means (8) (step 50). While detecting this effective discharge pulse, each energization time (1) of the effective discharge pulse within the set time (T) is detected, and its integrated value (ToN) N is calculated.

The effective discharge pulse rate calculating means (9) calculates the effective discharge pulse rate n/N from the detected number of effective discharge pulses (n) and the total number of discharge pulses (N), and calculates the time during which the effective discharge pulses are occurring. The effective discharge rate T is calculated from the integrated value (ToN) and the set time (T). Calculate N/T-β and use comparison means (11
). The comparison means (11) first compares the effective discharge pulse rate n/N with a set reference value (α1) preset in the reference value setting means (lO) for determining an unstable state. If the discharge pulse rate n/N is smaller than the set reference value (αl), the machining condition control means (
In step 12), change the electrode feed to one step higher than the currently set feed speed, change the discharge pause time to one step longer than the currently set time, or change the electrode to a fixed periodic pull-up. Change the distance so that it is one step larger than the currently set condition (step 53).Also, if the effective discharge pulse rate n/N is greater than the set reference value (α1), conversely, change the electrode feed to the current one. The current setting value is changed to one step lower, or the discharge pause time or the fixed electrode pulling distance is controlled to be one step smaller than the current setting value (step 54).

In this state, the total number of discharge pulses (N) and the number of effective discharge pulses (n) in the set time (T) are re-detected,
Effective discharge rate T at that time. Calculate N/T Step 5
5) Comparison means (11) compares the effective discharge rate (β) calculated before changing the machining conditions such as electrode feeding and discharge pause time one step lower or smaller (step 5B). Effective discharge rate T calculated using this set time (T). If N/T is smaller than the effective discharge rate (β) calculated from the previous set time (T), either change the electrode feed again to one step higher than the currently set feed rate, or restart the discharge. The pause time is changed to be one step longer than the currently set time, or the electrode regular pulling distance is changed to be one step longer than the currently set condition (step 57). If the effective discharge rate ToN/T is greater than β, machining is continued in that state, and the above operations are repeated at the next set time (T).

According to this embodiment, the effective discharge rate T changes in response to an instantaneous change in the interelectrode state. Since the conditions of electrode feed, discharge pause time, or constant electrode distance can be automatically changed so that N/T is maximized, efficient machining can be performed.

In the above embodiment, a case has been described in which a one-stage setting reference value (α1) is set as the setting value of the effective discharge pulse rate that can be determined to be an unstable state, which is set in the reference setting means (10). By dividing the set reference value into (α) and (α1°) as in the embodiment shown in FIG. 6, an unstable state can be detected with higher accuracy.

[Effects of the Invention] As explained above, the present invention detects the discharge state between the electrodes during machining, determines the ratio of effective discharge pulses at each predetermined time, and adjusts the electrode feed based on the change in this ratio. Since the machining conditions such as the discharge rest time or the constant electrode distance are changed, the optimal machining conditions can be automatically set according to the discharge state during machining, and electrical discharge machining can be performed stably. .

In addition, since electrical discharge machining can always be performed under optimal machining conditions during machining, efficient machining can be achieved.
This has the effect of increasing processing speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 (
a), (b), and (c) are explanatory diagrams showing the operating principle of the present invention, where (a) is a voltage waveform diagram between electrodes, (b) is a discharge pulse waveform diagram, and (c) is an effective discharge pulse waveform diagram. , FIG. 3 is a flowchart showing the operation of the embodiment shown in FIG. 1,
FIG. 4 is an electric circuit diagram showing a specific example of the total discharge pulse detection means and the effective discharge pulse detection means of the embodiment shown in FIG.
FIG. 5 is a waveform diagram showing the waveforms of each part of the electric circuit shown in FIG. 4, FIG. 6 is a flowchart showing the operation of the second embodiment, and FIG. 7 is a flowchart showing the operation of the third embodiment. , FIGS. 8(a) and 8(b) are waveform diagrams showing the operation of the conventional example, in which (a) is a voltage waveform diagram of the pulse voltage, and (b) is a current waveform diagram of the discharge current. (1)...Machining electrode, (2)...Workpiece, (3)
...power supply, (4) ...pulse voltage generation means, (6)
... Total discharge pulse detection means, (7) ... Reference voltage setting means, (8) ... Effective discharge pulse detection means, (9)
... Effective discharge pulse rate calculation means, (10) ... Reference value setting means, (11) ... Comparison means, (12) ...
Processing condition control means. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (7)

[Claims] (1) In electrical discharge machining equipment that processes a workpiece by applying a pulse voltage to a machining gap where an electrode and a workpiece face each other to generate electric discharge, the total discharge during machining is measured at predetermined intervals. A total discharge pulse detection means for detecting the pulse; a reference voltage setting means for setting a reference voltage value higher than the discharge voltage of the pulse voltage and lower than the open circuit voltage; and a reference voltage setting means for each discharge pulse voltage during machining and the reference voltage setting means. an effective discharge pulse detection means that detects an effective discharge pulse by comparing the open pulse voltage with a reference voltage value set in the reference voltage value and detecting that the open pulse voltage exceeds the reference voltage value; effective discharge pulse rate calculation means for calculating an effective discharge pulse rate in a predetermined time from the pulse and the effective discharge pulse detected by the effective discharge pulse detection means; and one or more reference values for the effective discharge pulse rate. a reference value setting means for setting the effective discharge pulse rate, a comparison means for comparing the effective discharge pulse rate calculated by the effective discharge pulse rate calculation means with a reference value set in the reference value setting means, and a comparison value compared by the comparison means. A control device for an electric discharge machine, comprising: a machining condition control means for changing machining conditions by; (2) A control device for an electrical discharge machine according to claim 1, wherein the effective discharge pulse rate detection means calculates the effective discharge pulse rate based on the number of discharge pulses. (3) A control device for an electrical discharge machine according to claim 1, wherein the effective discharge pulse rate detection means calculates the effective discharge pulse rate based on the cumulative time of discharge pulses. (4) A control device for an electrical discharge machine according to claim 1, wherein the effective discharge pulse rate detection means calculates the effective discharge pulse rate based on the number of discharge pulses and the cumulative time of the discharge pulses. (5) A control device for an electric discharge machine according to any one of claims 1 to 4, wherein the machining condition control means changes the machining gap. (6) A control device for an electric discharge machine according to any one of claims 1 to 4, wherein the machining condition control means changes the electric discharge suspension time. (7) A control device for an electrical discharge machine according to any one of claims 1 to 4, wherein the machining condition control means changes the electrode regular pull-up distance.