JPH0657372B2 - Wire cut electric discharge machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses wire-cut electric discharge machining in which a wire electrode is used, and a machining liquid is supplied to a machining gap facing a workpiece with a minute gap and a voltage pulse is applied to perform electric discharge machining. Regarding the device.

The wire electrode is wound while being pulled from one supply drum to the other winding drum, and a work gap is formed by facing a workpiece to the moving wire electrode in a direction substantially perpendicular to the wire electrode axis. A machining liquid such as water or kerosene is supplied to this machining gap and an intermittent voltage pulse is applied to generate a discharge pulse to perform electric discharge machining.
In this state, the work is cut by giving the work feed to the work, but at this time, the discharge is concentrated on a specific point not only on the work surface but also on the wire electrode surface. It should not happen. When electric discharge is intensively generated at a specific point on the surface of the wire electrode, arc marks are formed at the concentrated point, and not only a groove is formed on the surface to be processed but also the discharge becomes a steady arc or short circuit. Accidents such as disconnection will occur.

Focusing on this problem, for example, Japanese Patent Publication No. 53-26720
JP-A-54-71496, etc., is provided with a device for optically detecting the worn wire diameter and the surface condition of the wire portion moving and passing after electric discharge machining, and moving the wire by the detection signal. It has been proposed to control a device or a processing power source so that the wear and surface condition of a wire electrode can be made substantially constant as desired. However, in such a conventional technique, in order to constantly monitor the surface state of the surface of the wire electrode in the machining advancing direction, it is necessary to control the rotation of the detection device according to the change in the machining advancing direction. The structure of is complicated and requires complicated control. Further, since the pulse discharge is generated not only on the surface of the wire electrode in the machining direction, but also on the surface of the substantially half circumference on the side in the machining direction, the detection device is controlled to rotate according to the change in the machining direction. However, the surface condition (wear condition) of the wire electrode cannot be accurately detected. Further, the detector is reciprocally rotated about the machining direction by a predetermined angle (for example, 90 ° on one side), or the circumference of the wire electrode is rotated by 360 ° so that the discharge generation site or the entire peripheral surface of the wire electrode surface is rotated. Even if it is configured to monitor, it is still possible to accurately detect the wear state of the wire electrode because at each time point, only the information on the surface condition of a part around the wire electrode is obtained. However, it is difficult to accurately determine the wear state of the wire electrode and to appropriately control the processing conditions.

The present invention has been made to solve the above problems, and an object thereof is to reliably detect abnormal wear or local wear of the wire electrode, or its precursor phenomenon, and set the processing conditions. An object of the present invention is to provide a wire-cut electric discharge machining device capable of preventing concentrated discharge, short circuit, disconnection accident, and the like by appropriately switching, and performing highly accurate machining efficiently.

In order to achieve this object, the wire-cut electric discharge machining apparatus of the present invention is arranged such that a wire electrode that travels in the axial direction between a pair of positioning guides arranged at intervals has a minute machining gap and a workpiece to be machined. And the machining liquid is supplied to the machining gap, an intermittent machining voltage pulse is applied between the wire electrode and the workpiece to repeatedly generate a discharge pulse, and the axis of the wire electrode on the workpiece. In a wire-cut electric discharge machine that applies a relative machining feed in a direction substantially perpendicular to the direction, to machine the desired contour shape, the surface state of the wire electrode traveling in the axial direction is detected as a vibration signal by a stylus. A plurality of pickup devices are provided at predetermined angular intervals around the wire electrode that has passed through the processing portion facing the workpiece, and each of the plurality of pickup devices detects each of them. Detecting a frequency spectrum of the frequency spectrum and the low frequency component of the high frequency components from the motion signal, characterized by comprising providing a device for determining the quality of the machining state from the output level of both frequency spectrum.

It is generally recommended that at least four pickup devices be arranged around the wire electrode at 90-degree intervals.

Hereinafter, the details of the present invention will be specifically described with reference to the drawings.

FIG. 1 is an explanatory view showing a main part of an embodiment of a wire-cut electric discharge machine according to the present invention, FIG. 2 is an enlarged sectional view of an embodiment of the pickup device shown in FIG. 1, and FIG. Block diagram of a control circuit that controls the processing conditions so that the surface condition of the wire electrode surface roughness etc. becomes a predetermined state, Fig. 4 is a partial detailed view of the control circuit, and Fig. 5 is the frequency and voltage of the pickup output. It is a graph which shows the relationship of.

In FIG. 1, 1 is a wire electrode, 2 is a work piece, 3 is a wire electrode supply drum, 4 is the winding drum, 5 and 6 are guide rollers, 7 is a capstan, 8 is a pinch roller, and 9 and 10.
Is a brake roller, 11 and 12 are boat-shaped guides, 13 is a working fluid supply nozzle, 14-1, 14-2, 14-3 and 14-4 are pickup devices, and 15 is a predetermined surface condition such as surface roughness of wire electrodes. It is a control device that controls the processing conditions so that the above state is achieved.

In the enlarged sectional view of the pickup device 14-1 of FIG. 2, 16 is a wire electrode holder, 17 is a stylus holder, 18 is a coil holder,
19 is a stylus to which a permanent magnet 20 is attached, 21 is a plate,
22 is a spring, 23 is a pickup coil, 24 is a spacer,
25 is a set screw.

The wire electrode 1 is continuously supplied from the wire electrode supply drum 3 so that the brake rollers 9 and 10 are interposed between the guide rollers 5 and 6.
It is pulled by the capstan 7 and the pinch roller 8 against the braking force given by, and moves along the linear path defined by the boat-shaped guides 11 and 12 while maintaining a predetermined tension, and is wound around the winding drum 4. Taken.

The workpiece 2 is attached to a machining table on a cross slide table (not shown) by a clamp or the like, and relative machining feed between the wire electrode 1 and the workpiece 2 is not shown in the cross slide table according to a predetermined program. It is provided by being driven and controlled by the NC device.

Further, a machining voltage pulse is applied to the opposing machining gap between the wire electrode 1 and the workpiece 2 by a machining pulse power source (not shown), electrical discharge machining is performed, and the workpiece 2 is cut into a target shape.

The pickups 14-1, 14-2, 14-3, and 14-4 are all configured as shown in FIG. 2, and are in contact with the wire electrode 1 from four directions at 90 ° division, and the surface of the surface is The surface condition is detected in accordance with the movement of the wire electrode 1 so that the record needle is used to detect the mechanical unevenness state cut in the groove of the recording, the recording, or the record, for example.

The stylus 19 is slidably supported by a stylus holder 17, and a spring 22 is provided through a plate 21 to a wire electrode holder.
The tip of the wire electrode 1 inserted into 16 is pressed against the surface thereof.

When the wire electrode 1 moves, the stylus 19 vibrates in the axial direction corresponding to the roughness of the surface of the wire electrode 1, so that a high-frequency alternating current is generated in the pickup coil 23 by the magnetic field of the permanent magnet 20. Since this alternating current has a frequency spectrum as shown in FIG. 5 when the processing is proceeding normally, this output signal is analyzed and the state of the shape of the surface unevenness due to the consumption of the wire electrode 1 is analyzed. , And the quality of the surface wear state such as the distribution state around the wire electrode and in the axial direction in that state.

In FIG. 3, 26-1 to 26-4 are pickup devices 14 respectively.
-1 to 14-4 are corresponding wear state determination circuits, 27 is an abnormality determination circuit, 28 is an OR circuit, and 38 is a buzzer. Since the consumption state determination circuits 26-1 to 26-4 have the same configuration, only the same 26-1 will be described here.

As shown in FIG. 4, the consumption state determination circuit 26-1 includes an amplifier
29, semi-divided circuits 30, 31, 32 and 33 whose band is F ₁ , F ₂ , F ₃ and F ₄ , respectively, matching circuits 34 and 35, and OR circuit 3
6. It consists of input negators 37-1 to 37-4.

In addition, in the usual wire cut electric discharge machining that processes a ferrous material with a brass wire electrode (diameter 0.2 mm) at a tension of about 1.5 kg and a machining speed of about 50 to 80 mm ² / min, frequencies _F 1 of FIG. _5, F 2, _{F 3} and _{F 4,} for example _{F 1}
≈ 10 KHz, F ₂ ≈ 20 KHz, F ₃ ≈ 30 KHz,
It is a value of about F ₄ ≈ 40 Hz.

Therefore, since the strength determination circuits 30 to 33 have the same configuration except that the band and the triggering level are different, only the same 30 will be described here.

The strength determination circuit 30 is a band filter whose normal band is F _1.
30-1, a detection circuit 30-2 and Schmitt trigger circuits 30-3 and 30-4.

The triggering levels of the Schmitt trigger circuits 30-3 and 30-4 are set equal to the allowable upper and lower limits of the output voltage of the detection circuit 30-2 when the state of the wire electrode 1 is normal. Therefore, when the output of the pickup device 14-1 is within the normal range, the output of the Schmitt trigger circuit 30-3 becomes the state 0 and the output of the same 30-4 becomes the state 1.

When the output of the bandpass filter 30-1 having the pass band frequency F ₁ becomes higher than normal, the output of the Schmitt trigger circuit 30-3 becomes the state 1, and when the output is low, the output of the Schmitt trigger circuit 30-4. Becomes the state 0, and the buzzer 38 sounds via the OR circuit 36 in any case.

When all the strength discriminating circuits 30 to 33 detect an abnormality at once, the output of the coincidence circuit 34 or 35 becomes the state 1, and the output is transmitted to the abnormality discriminating circuit 27 as shown in FIG.

The abnormality determination circuit 27 refers to NC control steps,
The degree of the abnormality and its persistence and developability are analyzed, an appropriate control signal is transmitted according to the seriousness of the abnormality, and the operation of a known control circuit (not shown) is controlled. When the abnormality is serious, for example, the electric discharge machining is suspended, the wire electrode is updated and the machining condition, for example, the off time of the voltage pulse is switched to a longer value, and in some cases, the machining fluid injection pressure is changed. To be enhanced.

Since the portion of the wire electrode 1 that is consumed varies depending on the direction of processing, the pickup devices 14-1 to F14-4 are arranged in the same shape in four directions. As shown in FIG. -1 to 14-4, the output side of the consumption state determination circuits 26-1 to 26-4 is connected to the buzzer 38 via the OR circuit 28, so that the abnormal consumption of the wire electrode 1 occurs at the location. Depending on which pickup device 14
-1 to 14-4. In some cases, the coincidence circuits 34 and 35 may be omitted, and the outputs of all the strength determination circuits 30 to 33 may be input to the abnormality determination circuit 27, and the abnormality determination circuit 27 may determine the altitude.

Thus, electric discharge machining is performed by electric discharge in liquid based on a pressurizing voltage pulse that is intermittently applied with a pause between the electrode and the object to be machined with the machining liquid. This does not change even in the case of wire-cut electric discharge machining, in which the electrode is wire-shaped and is constantly renewed in the axial direction.

Although the wire electrode depends on the set processing conditions and the like, under normal processing conditions, it is highly probable that the wire electrode will break if several or more discharge pulses occur at substantially the same location on the line. And
By each discharge pulse that is intermittently repeated, craters are formed on the wire electrode surface in a complicated manner such as axially spaced or partially or entirely overlapped, as in the case of the surface of the workpiece. Each crater portion differs in a complicated manner depending on the property of the generated discharge pulse according to various gap states, the overlapping state between craters, and the like. That is, depending on the properties of the discharge pulse, the surface of each part such as the crater and its peripheral part during a normal discharge pulse has a state of remarkably fine and complicated irregularities as compared with that during an abnormal discharge pulse. Therefore, the vibration signal detected by the stylus is discriminated by the frequency spectrum into low-frequency vibrations based on craters and high-frequency vibrations based on fine irregularities on the craters. Can be detected more directly and accurately, and the processing state can be accurately determined.

As described above, according to the present invention, the consumption state of the wire electrode can be accurately discriminated. Therefore, the discrimination signal is used for machining the wire electrode moving speed, the machining feed speed, or the machining voltage pulse off time by the machining power source. By controlling the conditions, it is possible to properly control the processing conditions and prevent a wire electrode disconnection accident due to a concentrated discharge or a short circuit.

Further, according to the present invention, since the roughness of the surface of the wire electrode moving and passing after the electric discharge machining is always constant, machining accuracy such as punching and cutting can be improved. Further, since a part of the wire electrode is not consumed excessively, there is also an effect that the safety factor is lowered, that is, a thinner one can be used for high-speed processing.

The configuration of the present invention is not limited to the above embodiment. That is, the number of pickup devices, control devices, etc., configuration, arrangement, processing conditions to be controlled, control method thereof, etc. can be freely designed and changed within the scope of the object of the present invention. It is one that includes all.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a main part of an embodiment of a wire-cut electric discharge machining apparatus according to the present invention, FIG. 2 is an enlarged sectional view of the pickup device shown in FIG. 1, and FIG. 3 is a surface of a wire electrode. FIG. 4 is a block diagram of a control circuit for controlling the processing conditions so that the roughness is constant, FIG. 4 is a partial detailed view of the control circuit, and FIG. 5 is a graph showing the relationship between the frequency and voltage of the pickup output. 1 ... Wire electrode 2 ... Workpiece 3 ... Supply drum 4 ... Winding drum 5,6 ... Guide roller 7 ... Capstan 8 ... Pinch roller 9, 10 ... Brake roller 11, 12 ... … Ship-shaped guide 13 …… Processing fluid supply nozzle 14-1, 14-2, 14-3, 14-4 …… Pickup device 15 …… Control device 16 …… Wire electrode holder 17 …… Stylus holder 18 …… Coil Holder 19… Stylus 20 …… Permanent magnet 21 …… Plate 22 …… Spring 23 …… Pickup coil 24 …… Spacer 25 …… Set screw 26-1, 26-2, 26-3, 26-4… … Consumption state discrimination circuit 29 …… Amplifier 30, 31, 32, 33 …… Strength discrimination circuit 30-1 …… Band filter 30-2 …… Detection circuit 30-3, 30-4 …… Schmidt trigger circuit 34,35 …… Match circuit 27 …… Abnormality discrimination circuit 28, 36 …… OR circuit 37-1, 37-2, 37-3, 37-4 …… Input negator 38 …… Buzzer

Claims (1)

[Claims] 1. A state in which a workpiece is disposed opposite to a wire electrode that travels in the axial direction between a pair of positioning guides arranged at intervals with a minute machining gap, and a machining liquid is supplied to the machining gap. Then, intermittent machining voltage pulses are applied between the wire electrode and the work piece to repeatedly generate electric discharge pulses, and the work piece is fed with a relative machining feed in a direction substantially perpendicular to the axial direction of the wire electrode. In a wire-cut electric discharge machine for machining a desired contour shape, a pick-up device that detects the surface condition of the wire electrode traveling in the axial direction as a vibration signal with a stylus moves the machining part facing the workpiece. A plurality of wire electrodes are provided around the passed wire electrode at a predetermined angular interval, and the frequency spectrum of the high frequency component and the frequency of the low frequency component are detected from the vibration signals detected by the plurality of pickup devices. Detects the number spectrum, a wire cut electric discharge machining apparatus characterized by comprising providing a device for determining the quality of the machining state from the output level of both frequency spectrum.