JP2007105853A - Control method and device for moving of electrical insulator in electric discharge machining method using electrical insulator sheathed electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method for appropriately automatically maintaining an exposure area of a tool electrode tip end to thereby improve the machining operationality and shorten a machining time in an electric discharge machining method using an electrical insulator sheathed electrode. <P>SOLUTION: The control device always measures the feeding rate to a workpiece of the tool electrode closely related to the exposure area of the tool electrode tip end. An automatic control system for setting the feeding rate within a certain constant range by moving the electrical insulator is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

In the present invention, an electrode having a bottom surface facing a workpiece and having an arbitrary shape is covered with an electrical insulator such as a side surface where discharge is not desired, and between the electrode and the electrical insulator, Alternatively, in a device that realizes electrical discharge machining by flowing the machining fluid into the hollow electrode, the electrical insulator is automatically moved by the tool electrode consumption length to maintain the tool electrode tip exposed area appropriately. The present invention relates to a technique for improving the processing operability and processing speed.

The electric discharge machining method is generally used as a precision machining method for high hardness materials. When machining with a high aspect ratio such as deep holes is performed on high-hardness materials by the conventional electrical discharge machining method using solid metal electrodes, due to machining scraps produced by machining or electrode runout in the transverse direction to the machining direction, etc. Unnecessary discharge occurs on the electrode side surface.

Since these side surface discharges cause a reduction in machining efficiency and machining accuracy, a complicated and precise mechanism is required to drive the electrodes in the machining direction.

In order to prevent a reduction in machining efficiency and machining accuracy due to side discharge, an electric discharge machining method is claimed in which the periphery of the electrode is covered with an electrical insulator and a machining fluid is caused to flow between the electrode and the electrical insulator.
UK Patent GB 2177644 Japanese Patent Laid-Open No. 2005-224887

If an electric discharge machining method using an electric insulator covering electrode is used, a complicated and precise electrode drive mechanism is not required, and machining with a high aspect ratio such as a deep hole can be realized.

In the electric discharge machining method using the electric insulator covering electrode, when the tool electrode is consumed as the machining progresses, it is necessary to move the electric insulator by the consumed length to maintain the tool electrode tip exposed region.

If the tool electrode tip exposed area becomes very narrow, the discharge area also becomes narrow, and the discharge does not spread over the entire bottom surface of the processed part.

Therefore, the cross-sectional area of the machined part is reduced, but the amount of machined waste is not reduced, so the machined waste is delayed. Especially when an aqueous machining fluid is used, an oxide electrical insulation layer is formed on the bottom of the excavated part. And processing may not be continued.

On the other hand, if the electric insulator is excessively moved and the tool electrode exposed area becomes too wide, the discharge area becomes wide and the processing cross-sectional area increases, so that the cross-sectional shape becomes non-uniform and the processing speed also decreases.

Although it is the most reliable method to actually measure the tool electrode consumption length at regular intervals and maintain the tool electrode exposure area appropriately, the machining operability is lowered.

The consumption rate of the tool electrode is never constant, and the electric insulator movement control method assuming that the consumption rate of the tool electrode is constant is not effective.

The present invention provides an electric insulator automatic movement control method for properly maintaining a tool electrode tip exposed region in an electric discharge machining method using an electric insulator covering electrode, and improves the machining operability and machining. It solves the problem of time reduction.

In the electrical discharge machining method using an electrical insulator-covered electrode, the tool electrode is brought close to the work piece, the discharge is continued and the excavation is continued, and the tool electrode is applied to the work piece by the consumption length and machining depth. And a second axis for moving the electrical insulator covering the tool electrode to adjust the tool electrode tip exposed region on the same axis as the first axis feed mechanism. A feed mechanism is provided.

As the machining progresses, the tool electrode is fed to the workpiece by the first axial feed mechanism, and the tool electrode tip exposed area gradually narrows due to the consumption of the tool electrode tip by electric discharge.

The feed mechanism of the tool electrode in the first axis feed mechanism is a feedback control based on two signals of the workpiece and the tool electrode voltage and a predetermined threshold voltage, which is a known technique. It is independent of the movement control system of the electrical insulator that is the shaft feed mechanism.

In the second axial feed mechanism, when the electric insulator is held without being moved, the electric discharge is not diffused by the narrowed tool electrode tip exposed region, and the processing proceeds with a small cross-sectional area.

Since the amount of excavation does not change and only the cross-sectional area of machining decreases, the feed rate of the tool electrode to the workpiece gradually increases.

If the cross-sectional area of processing becomes too small, the processing waste will be discharged, and an electric insulation layer will be formed on the bottom surface of the processing, or the electric insulator will contact the bottom surface of the processing portion, making it impossible to continue processing .

Therefore, before the feed rate of the tool electrode is increased too much, in the second axial feed mechanism, when the electrical insulator is moved a predetermined length in the exposure direction and the tool electrode tip exposed region is expanded, the discharge region is dispersed again. Then, the cross-sectional area of processing is restored to the original.

The higher the threshold feed rate that determines the movement of the electrical insulator, the shorter the machining time will be.However, the machining stop will be stopped for each machining condition such as the type of workpiece and the cross-sectional area of the machining hole. Set the maximum value so as not to reach.

If the feed rate of the tool electrode does not decrease to an appropriate level even after moving the electrical insulator of a predetermined length, the tool electrode is further extended by moving the electrical insulator to expand the tool electrode tip exposed area. Reduce the feed rate.

On the other hand, if the electric insulator is moved excessively and the tool electrode tip exposed region is excessively expanded, the discharge region is excessively widened and the processing cross-sectional area becomes larger than desired.

This leads to a decrease in machining speed and non-uniformity in the cross-sectional shape. Therefore, by moving the electrical insulator in the electrode covering direction and narrowing the exposed area of the tool electrode tip, the machining cross section and machining speed are restored. Can be made.

The threshold feed rate that determines the movement of the electrical insulator in the electrode covering direction is also closer to the threshold feed rate in the electrode exposure direction, leading to a reduction in processing time.

However, if the two threshold feed rates are too close, overshooting of the tool electrode feed rate is likely to occur, and the possibility of machining stop increases, so appropriate values are preliminarily set according to each machining condition. It is necessary to decide.

In the first axial feed mechanism, a position detecting device for detecting the position of the tool electrode and the tool electrode feed speed are calculated thereby, and the speed is used as a signal source, and the second axial feed mechanism has a predetermined length in the electrode exposure direction. An NC control device or a computer control device for moving the electric insulator or moving the electric insulator in the electrode covering direction is provided.

These control devices are programmed to acquire the feed rate of the tool electrode, to move the electrical insulator, and to set the conditions for issuing the movement.

By operating the above machining apparatus, control system, and program, automatic maintenance of the tool electrode tip exposed area is realized in the electric discharge machining method using the electrical insulator covering electrode.

If necessary, according to the above method, the tool electrode can be scanned in a plane perpendicular to the axis thereof.

By the above method, the tool electrode tip exposed region is automatically properly maintained, and the problems of improving the machining operability and shortening the machining time in the electric discharge machining using the electric insulator covering electrode are solved.

In the electric discharge machining method using the electric insulator covering electrode, when the tool electrode is consumed as the machining progresses, it is necessary to move the electric insulator by the consumed length to maintain the tool electrode tip exposed region.

Tool electrode wear does not always progress at a constant speed, so it is the most reliable method to measure the tool electrode wear length at regular intervals by hand and move the electrical insulator. The time required for processing decreases.

The present invention provides an electric insulator automatic movement control method for properly maintaining a tool electrode tip exposed region in an electric discharge machining method using an electric insulator covering electrode, and improves the machining operability and machining. It solves the problem of time reduction.

A principle example of the embodiment of the method of the present invention will be described with reference to FIGS. 1, 2, 3 and 4. FIG.

In FIG. 1, 1 is a workpiece, and its position is fixed. Reference numeral 2 denotes a tool electrode, which is connected to the workpiece via a discharge power source 3, and the workpiece is excavated and processed by electric discharge. A capacitor 4 is connected as necessary to activate discharge. Although a round bar is used as a tool electrode in FIG. 1, an electrode having an arbitrary shape such as a thin wire or a square bar may be used.

The tool electrode 2 is rotated by a tool electrode rotating mechanism 6 via a tool electrode attaching / detaching chuck 5. The position of the tool electrode feed mechanism 7 is fixed, and movement of the tool electrode to the workpiece is controlled to move in the forward direction 8 and the reverse direction 9 to continuously generate discharge. This movement control uses a feedback control based on two signals of a workpiece and a tool electrode voltage and a predetermined threshold voltage, which are known techniques. Details regarding these known techniques are omitted.

The tool electrode 2 is covered and covered with 10 electrical insulators in areas where discharge is not desired. The electrical insulator 10 is connected to 12 machining fluid introduction portions at 11 electrical insulator connection portions. The machining fluid 13 flows between the tool electrode 2 and the electrical insulator 10 from the machining fluid introduction unit 12, passes through the vicinity of the exposed region of the tool electrode 14 where discharge excavation is performed, and is discharged outside the excavation unit. In the case of using a tool electrode having a hollow, the machining fluid may also flow inside the hollow electrode. By flowing the machining liquid into the hollow space, machining waste discharge near the center of the bottom surface of the electrode is promoted, and machining stability and machining speed are improved.

The electric insulator 10 moves in the direction of 16 tool electrode exposures and in the direction of 17 tool electrode covering by the electric insulator moving mechanism 15.

The 18 NC control devices are provided with 19 storage units, 20 programs, a data input unit, and 21 display units, and acquire 22 tool electrode feed speed information sent from the tool electrode feed mechanism 7. Further, the exposure threshold tool electrode feed rate for instructing the movement of the electrical insulator in the tool electrode exposure direction 16 is determined and programmed in the NC controller 18. Also, an enveloping threshold tool electrode feed rate for instructing movement of the electrical insulator in the tool electrode enveloping direction 17 is determined and programmed into the NC controller 18.

When the tool electrode feed speed 22 exceeds the exposed threshold tool electrode feed speed, an electrical insulator movement command 23 is output to the electrical insulator movement mechanism 15 to electrically insulate the tool electrode tip exposed region 14 in the direction 16. The body 10 is moved at a predetermined distance and speed. On the other hand, when the tool electrode feed speed of 22 becomes smaller than the exposed threshold tool electrode feed speed, the electric insulator movement command 23 is output to the electric insulator movement mechanism 15 to narrow the tool electrode tip exposed area 14. 17, the electric insulator 10 is moved at a predetermined distance and speed. Programming for realizing such operation and control is performed on the NC controller 18. The NC control device may be replaced with another control device such as a computer. The configuration shown in FIG. 1 is a limited example, and there are various forms other than these diagrams.

When the processing apparatus and the control system are operated, the tool electrode tip is less consumed in the initial stage of processing. FIG. 2 is a diagram showing a machining situation when the tool electrode tip exposed region 14 is appropriate. In such a situation, a desired machining cross-sectional area and a machining speed in the depth direction are realized by the occurrence of a discharge having a stable and appropriate generation region 24a. It is known that the machining cross-sectional area and the machining speed in the depth direction can be changed under various machining conditions such as the type of machining liquid, capacitor capacity, and type of tool electrode. In the present control system and control device, the tool electrode tip exposed area where the tool electrode protrudes 7 mm from the tip of the electrical insulator is optimal, and stable machining is possible while obtaining a high speed.

As machining in the depth direction progresses, the tip of the tool electrode is consumed. FIG. 3 is a diagram showing a machining situation when the electric insulator 10 is not sufficiently moved and the tool electrode tip exposed region 17 is narrow. Due to the narrow discharge in the 24b generation region, the processing cross-sectional area tends to be reduced. Since the amount of excavation does not change, the processing speed in the depth direction increases. Therefore, the tool electrode feed speed 22 gradually increases.

When this tool electrode feed rate 22 exceeds the exposure threshold tool electrode feed rate for instructing movement of the electrical insulator in the tool electrode exposure direction 16, the electrical control unit 23 sends an electrical insulator movement command 23 from the NC controller 18. Output to the mechanism 15 to move the electrical insulator in the tool electrode exposure direction 16. At this time, setting the exposed threshold tool electrode feed speed to about 1.5 times the tool electrode feed speed in an appropriate machining situation as shown in FIG. 2 leads to the most stable machining. The acquisition of the tool electrode feed rate 22 and the electrical insulator movement command 23 of the NC controller 18 are efficient once every 10 seconds and stabilize the control. The electrical insulator 10 is moved at a speed of 1 mm per second, and a moving length of 1 mm is optimal.

Due to the movement of the electrical insulator 10 in the tool electrode exposure direction 16, the tool electrode tip region is properly maintained as shown in FIG. 2. The machining cross-sectional area returns to an appropriate value again, and the tool electrode feed rate 22 becomes a value smaller than the exposed threshold tool electrode feed rate, and the machining is stabilized.

When the tool electrode feed rate 22 exceeds the exposed threshold tool electrode feed rate, the processing in the stable depth direction is realized by repeating the above control.

Due to stagnation at the bottom surface of the processing waste or non-uniformity of the electrode consumption of the tool electrode, the tool electrode may be moved excessively in the tool electrode exposure direction 16 and the tool electrode tip exposed region 17 may become too wide. . FIG. 4 is a diagram showing a machining situation when the electric insulator is excessively moved and the tool electrode tip exposed region is wide.

In this case, the machining cross-sectional area becomes larger than the appropriate value due to the electric discharge 24c in which the generation region is widened, and the machining speed is lowered accordingly. In many cases, the tool electrode feed speed 22 naturally rises to an appropriate value due to wear of the tip of the tool electrode, but the tool electrode feed speed 22 may be smaller than the covering threshold tool electrode feed speed. In this case, the electric insulator movement command 23 is output to the electric insulator movement mechanism 15 to move the electric insulator 10 in the direction of narrowing the tool electrode tip exposed region 14. For this movement, a movement length of 1 mm is optimal at a speed of 1 mm per second. As a result, when the tool electrode feed rate is excessively lowered, the machining cross-sectional shape is disturbed and the return delay to the proper tool electrode feed rate is prevented. At this time, setting the wrapping threshold tool electrode feed speed to about 0.7 times the tool electrode feed speed in an appropriate machining situation as shown in FIG. 2 leads to the most stable machining.

With the above control principle, the control device can maintain the tool electrode tip exposed region 17 at an appropriate value without directly measuring it. In the electric discharge machining method using the electric insulator-covered electrode, Improve machining operability and reduce machining time.

In an electrical discharge machining apparatus using an electrical insulator-covered electrode equipped with an automatic tool electrode feed mechanism, machining is stopped every 5 minutes, and the distance between the tool electrode tip and the electrical insulator tip is visually observed in the tool electrode tip region. Manual control to adjust to 7 mm, proper tool electrode feed rate 0.06 mm per second, exposed threshold tool electrode feed rate 0.08 mm per second, covering threshold tool electrode feed rate 0.04 mm per second, electrical insulation We compared the processing operability and the total time required for processing in the automatic control where the body movement was 1 mm at a speed of 1 mm per second. The other machining setting conditions are the same, and the machining conditions and results are shown.

Machining conditions Machining object: Circular deep hole Work material: Structural carbon steel Electrode: Tungsten round rod with diameter 0.30mm Electrical insulator: Fluorine resin tube with outer diameter 0.55mm, inner diameter 0.40mm Processing liquid: Sodium chloride in tap water Dissolution. Conductivity is 150μS / cm
Discharge power supply: Pulsed discharge power supply (pulse waveform, 40 μsec on / 100 μsec off)
Capacitor: 7.8μF
Tool electrode movement control: Diameter of hole circle machined by tool electrode movement by automatic discharge voltage feedback control: 0.8mm
Processed hole circle depth: 150mm

Processing result 1
Total time required for processing in automatic control: Total time required for processing in manual control = 178 minutes: 241 minutes

Processing result 2
Number of manual movements of electrical insulators in automatic control: Number of manual movements of electrical insulators in manual control = 0 times: 40 times (average takes 1 minute each time)

It is a figure which shows the concept of the electrical discharge machining apparatus and electric insulator movement control method concerning this invention. It is a figure which shows the processing condition in case a tool electrode front-end | tip exposure area | region is appropriate. It is a figure which shows the processing condition in case a movement of an electrical insulator is inadequate and a tool electrode front-end | tip exposure area | region is narrow. It is a figure which shows the processing condition in case a movement of an electrical insulator is excessive and a tool electrode front-end | tip exposure area | region is wide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Workpiece 2 ... Tool electrode 3 ... Discharge power supply 4 ... Capacitor 5 ... Tool electrode attachment / detachment chuck 6 ... Tool electrode rotation mechanism 7 ... Tool electrode feed mechanism 8 ..Tool electrode feed direction 9 ... Tool electrode feed reverse direction 10 ... Electric insulator 11 ... Electric insulator connection part 12 ... Working fluid introduction part 13 ... Working liquid 14 ... Tool Electrode tip exposed area 15 ... Electric insulator moving mechanism 16 ... Tool electrode exposure direction 17 ... Tool electrode covering direction 18 ... NC controller 19 ... Storage unit 20 ... Program, data Input unit 21 ... Display unit 22 ... Tool electrode feed rate information 23 ... Electrical insulator movement command and movement detailed information 24a · · Discharge 24b · · Discharge 24c · · Discharge

Claims (5)

In the electric discharge machining method, the tool electrode having a bottom face that faces the workpiece and has an arbitrary shape is covered with an electrical insulator around a portion where discharge is not desired, such as the side surface, and the workpiece is machined by electric discharge. By automatically moving the electrical insulator by the tool electrode wear length and maintaining the tool electrode exposure area appropriately, it is possible to generate a stable discharge and improve the machining operability and machining speed. Movement control method. The electric insulator movement control method in the electric discharge machining method according to claim 1, wherein a machining fluid is used. In Claims 1 and 2, when one or more cavities exist in an electrode having a bottom face that faces the workpiece and has an arbitrary shape, the machining fluid is caused to flow into the cavities. A method for controlling the movement of an electrical insulator in an electrical discharge machining method. The electric insulator movement in the electric discharge machining method according to any one of claims 1 to 3, wherein a discharge power source in which a capacitor of 0.01 µF to 100 µF is connected in parallel to the gap between the electrode and the workpiece is used. Control method. The method of controlling movement of an electrical insulator in a processing method according to claim 1, wherein the electrode is scanned while being scanned in a plane orthogonal to the axis thereof.