JP2012192520A - Wire electric discharge machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a machining feed rate, prevent formation of a drum shape in which a machining surface of a workpiece is concave or convex, and improve straightness accuracy which is machining accuracy in a wire traveling direction.
A discharge pulse detection device that detects a discharge pulse generated between a wire electrode and a workpiece, a short-circuit pulse determination device that determines whether or not the detected discharge pulse is a short-circuit pulse, and a discharge pulse generated within a predetermined time Counting device for counting the number of consecutive short-circuit pulses, an arithmetic unit for calculating the average number of short-circuit pulses generated within a predetermined time, a storage device for storing the number of consecutive short-circuit pulses as a reference, and the counted short-circuit pulses A machine that compares the average number of continuous pulses and the number of continuous short-circuit pulses as a reference, and changes the processing feed rate based on the number of continuous short-circuit pulses as a reference and the average number of short-circuit pulses counted It has a feed speed control device.
[Selection] Figure 5

Description

  The present invention relates to increasing the accuracy of a wire electric discharge machining apparatus.

  In wire electric discharge machining equipment, when the workpiece thickness is as thick as 40 mm or more, a drum shape is formed in which the machining surface of the workpiece is concave or convex, and straightness that indicates the shape in the wire running direction Had been worsening. This is thought to be a processing phenomenon peculiar to wire electric discharge machining due to an imbalance between the electric discharge reaction force acting on the wire during machining and electrostatic attraction. For this reason, for example, press die machining (for example, combining a metal plate with a metal plate) In the process of punching, etc., there is a problem that the metal plate cannot be punched accurately due to the deterioration of the accuracy of the mold.

  In Patent Document 1, a ratio between the number of discharge pulses generated between the wire electrode and the workpiece every predetermined time and the number of discharge pulses determined as a reference is obtained, and according to the ratio, the discharge pause time and the amount of coolant are determined. The machining accuracy is improved by controlling the feed amount within a predetermined time. The device configuration includes a pulse number counting device that counts the number of discharge pulses generated between the wire electrode and the workpiece every predetermined time, a reference discharge pulse number storage device, a ratio determination device, a discharge pause time control device, and a liquid amount. It consists of a control device and a feed pulse calculation device.

JP 2006-130656 A

  In Patent Document 1 described above, the number of discharge pulses generated between the wire electrode and the workpiece is counted every predetermined time, and the rest time, the amount of coolant, the processing speed according to the ratio to the number of reference discharge pulses. It is said that machining accuracy will be improved by controlling. However, in the present application, it has been found for the first time that there is no correlation between the number of discharge pulses and the straightness accuracy indicating the processing accuracy in the wire traveling direction. That is, it has been found that straightness accuracy is not improved even if the feed amount is controlled according to the number of discharge pulses.

In the present invention, among the number of discharge pulses, the occurrence of continuous short-circuit pulses as a bundle of consecutive short-circuit pulses that are considered to be particularly related to the drum shape that is the shape of the processed surface of the workpiece The purpose is to improve the straightness accuracy by controlling the machining feed rate.
In the present invention, it is determined whether or not a discharge pulse generated based on a general judgment standard commonly used in electric discharge machining is generated in a short-circuit state. As a determination criterion, for example, it is determined that the no-load time is below a certain level, but other criteria, for example, the voltage during discharge is below a certain level or the voltage of the check pulse applied before the occurrence of discharge is at a certain level The determination may be made based on whether or not the current flowing out is equal to or higher than a certain level, or whether the impedance during the rest time before the occurrence of discharge is equal to or smaller than a certain value.

  In the present invention, the number of consecutive short-circuit pulses refers to a number indicating how many times the short-circuit pulses are generated continuously, and the number of consecutive short-circuit pulses is the number of consecutive short-circuit pulses generated. Is counted as one bundle, and the number of the bundle is said. (See FIG. 1).

  A wire electric discharge machining device according to the present invention includes a discharge pulse detection device that detects a discharge pulse generated between a wire electrode and a workpiece, and a short-circuit pulse determination device that determines whether or not the detected discharge pulse is a short-circuit pulse. , A counting device that counts the continuous number of short-circuited pulses generated within a predetermined time, an arithmetic unit that calculates the average continuous number of short-circuited pulses generated within a predetermined time, and a memory that stores the continuous number of short-circuited pulses serving as a reference Based on the device, the comparison device that compares the average number of short-circuit pulses counted and the number of continuous short-circuit pulses as a reference, and the number of continuous short-circuit pulses as a reference and the average number of short-circuit pulses as counted, It has a machining feed rate control device that changes the machining feed rate or a discharge pause time control device that changes the discharge pause time.

  According to the present invention, since the machining feed rate is changed according to the average number of short-circuit pulses generated within a predetermined time, the drum shape in which the machining surface of the workpiece is concave or convex is improved. Straightness accuracy is improved.

It is a figure which shows the concept of the short circuit pulse continuous number and the frequency | count of continuous short circuit pulse generation | occurrence | production. It is a figure explaining the structure of the wire electric discharge machining apparatus shown in Embodiment 1. FIG. It is a figure which shows the relationship between the frequency | count of continuous short circuit pulse generation | occurrence | production, and a process feed rate. It is a figure which shows an example of the relationship between the frequency | count of continuous short circuit pulse generation | occurrence | production, and the shape of the processed surface of a workpiece. It is a figure explaining the structure of the wire electric discharge machining apparatus shown in Embodiment 2. FIG. It is a figure explaining the structure of the wire electrical discharge machining apparatus shown in Embodiment 3. FIG. It is a figure explaining the structure of the wire electric discharge machining apparatus shown in Embodiment 4. FIG.

Embodiment 1.
2 is a block diagram showing a wire electric discharge machining apparatus according to Embodiment 1 of the present invention. In FIG. 2, a wire electric discharge machining apparatus includes a discharge pulse generator 1 that supplies a discharge pulse between a wire electrode and a workpiece, a wire electrode 2, a discharge pulse detection device 4 that detects the discharge pulse, and whether the discharge pulse is a short-circuit pulse. Short-circuit pulse discriminating device 5 for discriminating whether or not, counting device 6 for counting the number of occurrences of continuous short-circuit pulses generated within a predetermined time, storage device 7 for storing the number of continuous short-circuit pulses generated as a reference, and counting continuous short-circuiting Comparing device 8 for comparing the number of pulse generation times with the number of continuous short-circuit pulse generations as a reference, and a processing feed speed control device 9 for changing the processing feed rate, the workpiece 3 is processed by the wire electric discharge machining device. It is processed into a desired shape.

  In the present invention, the pulse between the wire electrode and the workpiece is detected as a signal by the discharge pulse detection device 4, and the signal output from the discharge pulse detection device 4 is input to the short-circuit pulse determination device 5 and short-circuited. It is determined whether it is a pulse. The short-circuit pulse signal output from the short-circuit pulse discriminating device 5 enters the counting device 6 and the number of occurrences of continuous short-circuit pulses generated within a predetermined time is counted. The signal counted by the counting device 6 enters the comparison device 8. In the comparison device 8, a signal is also input from the storage device 7 in which the reference number of consecutive short-circuit pulses is stored, and these two signals are compared by the comparison device 8. A signal for controlling the machining feed rate output from the comparison device 8 enters the machining feed rate control device 9 and controls the machining feed rate so as to reduce the deviation obtained from the comparison device 8.

  Next, the principle of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing the relationship between the number of consecutive short-circuit pulses and the machining feed rate. The curve in the figure shows, for example, the relationship between the number of continuous short-circuit pulses generated and the machining feed rate when the drum shape does not occur when the thickness of the workpiece is constant. In the figure, the number Nr of continuous short-circuit pulses generated on the horizontal axis is the reference number of continuous short-circuit pulses, and is determined by the plate thickness and material of the workpiece, the taper angle of the wire electrode, the wire diameter, the material, and the like. The slope of this curve also varies depending on the machining feed rate, the workpiece plate thickness, and the machining conditions according to the number of continuous short-circuit pulses.

When the thickness of the workpiece is as thick as 40 mm or more, since the wire tends to bend due to the unbalance of the discharge reaction force and electrostatic attraction acting on the wire during processing, the shape of the processed surface of the workpiece is It becomes a concave shape or a convex shape as shown in the upper part of FIG. In other words, when considering the case where the machining feed rate is a certain value, a concave shape occurs when the number of continuous short-circuit pulses generated is less than Nr, under the condition of ×, and conversely, when it is greater than Nr, Under these conditions, a convex shape occurs. Such a concave or convex drum shape is a barometer indicating the shape accuracy in the wire traveling direction, and the fact that the drum shape is formed indicates that the straightness of the workpiece is not good. .

  Therefore, in order to prevent the drum shape from occurring, the machining feed rate is controlled while monitoring the number of continuous short-circuit pulses generated under a certain machining speed. That is, when the number of consecutive short-circuit pulses is increased from the reference Nr, it is assumed that the number of occurrences is the case of the X mark on the side larger than Nr in the figure, so that it matches the curve in the figure, If the machining feed rate is slowed and conversely the number of consecutive short-circuit pulses is reduced, it is assumed that the x mark is on the side smaller than Nr in the figure. Increase the feed rate. In this way, the machining feed rate is controlled so that the number of continuous short-circuit pulses generated so that the drum shape is not formed on the machining surface of the workpiece.

FIG. 4 shows an example of the result of an experiment conducted by changing the machining feed rate with a constant machining amount.
In this figure, the figure shown in the middle is measured data showing the machining status of the machined surface of the workpiece, and the horizontal axis shows the size of the irregularities on the machined surface on an arbitrary scale. Yes, the vertical axis represents the length of the wire in the wire traveling direction on an arbitrary scale. The lower horizontal axis indicates the number of continuous short-circuit pulses generated per second on an arbitrary scale, where N is the case where the most accurate straight machining can be realized.

If the number of continuous short-circuit pulses is greater than the predetermined number of occurrences, the work surface of the workpiece is convex. Conversely, if the number of continuous short-circuit pulses is less than the predetermined number of occurrences, the work surface of the work piece is It can be seen that has a concave shape.
When the machining feed rate becomes faster than the machining feed rate that is the reference number N of continuous short-circuit pulses, the number of short-circuit pulses increases, and the shape of the processed surface of the workpiece becomes a convex shape. If the machining feed rate becomes N, the short-circuit pulse decreases and the shape of the machined surface of the workpiece becomes concave, so that the straightness accuracy of the workpiece deteriorates.

  Also, at the time of the pre-stage machining (here, the pre-stage machining is a process in the machining step one step before each machining step except for the first machining step. If a disturbance such as a change in the machining amount occurs, the short-circuit pulse tends to occur as the machining amount increases, and this affects the straightness accuracy. I found out. Therefore, it is considered that high-precision straight machining of the workpiece can be realized by setting the machining feed rate in accordance with the number of continuous short-circuit pulses.

  Next, the operation of the present invention will be described with reference to FIG. A discharge pulse is generated between the wire electrode 2 and the workpiece 3 by the discharge pulse generator 1. A discharge pulse generated between the wire electrode 2 and the workpiece 3 is detected by the discharge pulse detection device 4, and it is determined whether or not the detected discharge pulse is a short-circuit pulse by the short-circuit pulse determination device 5. From the determined short-circuit pulses, the counting device 6 counts the number of consecutive short-circuit pulses. The counted number of consecutive short-circuit pulses generated is compared with the reference number of consecutive short-circuit pulses generated in the storage device 7 by the comparison device 8. The machining feed control device 9 changes the machining feed speed so as to reduce the deviation between the number of continuous short-circuit pulses generated as a reference from the comparison result and the counted number of continuous short-circuit pulses. Note that the number of continuous short-circuit pulses generated as a reference is determined from the thickness of the workpiece.

  When a pulse other than a short-circuit pulse is generated, the number of consecutive short-circuit pulses is reset there. However, the continuous number is not limited to two or more, and may be three or more and four or more.

  In the case of a concave shape, the occurrence of short-circuit pulses is reduced, the number of continuous short-circuit pulses generated within a predetermined time is reduced, and is reduced by about 20% from the reference number of continuous short-circuit pulses. On the contrary, in the case of a convex shape, the occurrence of short-circuit pulses increases, the number of continuous short-circuit pulses generated within a predetermined time increases, and increases by about 20% from the reference number of continuous short-circuit pulses generated.

  In the above, the predetermined time to be counted may be every 1 sec or may be averaged by taking a moving average every short time such as 1 msec.

  In addition, the reference number of continuous short-circuit pulses generated varies depending on the wire diameter and taper angle of the wire electrode, the plate thickness of the workpiece, and the material. Therefore, even when processing a workpiece whose plate thickness changes during processing, high straightness processing (highly accurate processing where the accuracy of straightness is not comparable to normal processing. For example, straightness error is about 1 μm. The following processing can be realized.

  Further, the counting by the counting device is not limited to counting the number of continuous short-circuit pulses, but may be the number of short-circuit pulses or the number of consecutive short-circuit pulses.

Embodiment 2.
FIG. 5 shows a wire electric discharge machining apparatus described in the second embodiment of the present invention. The arithmetic device 10 is added to FIG. 2 of the first embodiment. The configuration of the apparatus of the present embodiment is the same as that of the first embodiment, but the signal output from the counting device 6 is not directly input to the comparison device 8, but passes through the arithmetic unit 10. After that, the point of entering the comparison device 8 is different.

  In the wire electric discharge machining apparatus shown in the second embodiment, the number of generated short-circuit pulses is counted. That is, the number of consecutive short-circuit pulses obtained from the short-circuit pulse discriminating device 5 is counted by the counting device 6 every predetermined time as in the first embodiment. From the number of consecutive short-circuit pulses counted by the counting device 6, an average value of the number of consecutive short-circuit pulses is obtained by the arithmetic device 10. The average value obtained by the arithmetic unit 10 and the number of consecutive short-circuit pulses stored in the storage unit 7 and used as a reference determined by the plate thickness are compared by the comparison unit 8 so that the deviation is reduced. The feed rate control device 9 controls the machining feed rate.

For example, the average value per predetermined time of the number of continuous short-circuit pulses is 2 to 3 for the concave shape, but increases to 5 to 6 for the convex shape. The average value per predetermined time is compared with a reference value, and the machining feed speed control device 9 changes the machining feed speed so that the deviation is reduced.

The time for counting the number of consecutive short-circuit pulses is about 300 msec to 1 sec, and the average value of the number of consecutive short-circuit pulses between 300 msec and 1 sec is calculated. However, the counting time is not limited, and an averaging process such as moving average of average values between 1 msec to 50 msec may be performed. The number of continuous short-circuit pulses to be compared varies depending on the wire diameter of the wire electrode, its material, taper angle, plate thickness of the workpiece, its material, and the like, and is not limited to a certain constant.

  As described above, when the processed surface of the workpiece has a drum shape and the number of continuous short-circuit pulses is different from the reference number of continuous short-circuit pulses, the deviation between the counted number of short-circuit pulses and the reference number of continuous short-circuit pulses is calculated. Since the machining feed rate is changed so as to be reduced, high straightness machining without a drum shape on the machining surface of the workpiece can be realized.

Embodiment 3.
FIG. 6 shows a wire electric discharge machining apparatus described in the third embodiment of the present invention. Instead of the machining feed rate control device 9 shown in FIG. 2 of the first embodiment, a discharge pause time control device 11 is provided.

  The principle of the apparatus in the third embodiment will be described below. When the workpiece thickness is as large as 40 mm or more, the wire deflection occurs due to the unbalance between the discharge reaction force and electrostatic attraction acting on the wire being processed, and the processed surface of the workpiece is concave or convex. A drum shape is formed. The formation of the drum shape deteriorates the straightness accuracy indicating the shape accuracy in the wire traveling direction. When the discharge frequency is lowered, the number of continuous short-circuit pulses is reduced and the processed surface of the workpiece is convex. When the discharge frequency is increased, the number of continuous short-circuit pulses is increased and the processed surface of the workpiece is concave. This is also the first time that we learned. Therefore, it is possible to achieve high straightness machining by controlling the discharge pause time and changing the discharge frequency so as to reduce the deviation between the reference number of consecutive short-circuit pulses and the counted number of consecutive short-circuit pulses. it can.

  In the operation of the device in the third embodiment, the discharge pause time is controlled by the discharge pause time control device 11 so as to reduce the deviation obtained from the comparison device 8 as in the first embodiment, and the discharge frequency is changed. Therefore, it is possible to realize high straightness processing in which the processed surface of the workpiece does not have a drum shape.

Embodiment 4 FIG.
FIG. 7 shows a wire electric discharge machining apparatus described in Embodiment 4 of the present invention. Instead of the machining feed rate control device 9 shown in FIG. 5 of the second embodiment, a discharge pause time control device 11 is provided.

  Similar to the second embodiment, the number of consecutive short-circuit pulses generated within a predetermined time is counted, and the average value of the number of consecutive short-circuit pulses counted by the arithmetic unit 10 is calculated. The comparison unit 8 compares the average value obtained by the arithmetic unit 10 with the reference short-circuit pulse number stored in the storage unit 7, and the discharge pause time control unit 11 reduces the discharge pause time so as to reduce the deviation. By controlling the above and changing the discharge frequency, high straightness machining can be realized.

  DESCRIPTION OF SYMBOLS 1 Discharge pulse generator 2 Wire electrode 3 Workpiece 4 Discharge pulse detector 5 Short pulse discriminator 6 Counting device 7 Storage device 8 Comparison device 9 Processing feed rate control device 10 Arithmetic device 11 Discharge pause time control device.

Claims (2)

In a wire electrical discharge machining apparatus that applies a voltage between a wire electrode and a workpiece, generates a discharge pulse, and moves the wire electrode and the workpiece relative to each other while machining the workpiece by discharge,
A discharge pulse detecting device for detecting a discharge pulse generated between the wire electrode and the workpiece;
A short-circuit pulse discriminating device for discriminating whether or not the detected discharge pulse is a short-circuit pulse;
A counting device for counting the continuous number of short-circuit pulses generated within a predetermined time;
An arithmetic unit for calculating the average number of short-circuit pulses generated within a predetermined time; and
A storage device for storing the continuous number of short-circuit pulses as a reference;
A comparison device for comparing the average number of short-circuit pulses counted with the number of continuous short-circuit pulses as a reference;
Based on the reference number of continuous short-circuit pulses and the average number of short-circuit pulses counted, a machining feed rate control device that changes the machining feed rate, or a discharge pause time control device that changes the discharge pause time,
A wire electric discharge machining apparatus comprising:   The continuous number of short-circuit pulses serving as a reference stored in the storage device is determined by the wire diameter, material or taper angle of the wire electrode, or the plate thickness or material of the workpiece. Wire electrical discharge machining equipment.

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