JPH0472646B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a machining method for machining a workpiece using a wire-cut electric discharge machining device.

[Conventional technology]

A wire cut electrical discharge machining device uses a wire electrode that is updated and fed in the axial direction with a predetermined tension applied between a pair of positioning wire guides, and the workpiece is placed at an appropriate machining gap from a direction approximately perpendicular to the wire electrode axis. A machining voltage pulse is applied between the wire electrode and the workpiece with the machining liquid flowing along the wire electrode in the machining gap, and the electric discharge generated at this time is This phenomenon is used to perform non-contact processing.

In this case, each discharge melts or evaporates a small amount of the workpiece and removes it, so the discharge is repeated under appropriate conditions and machining is carried out along the desired machining contour on the workpiece. In order to proceed, machining feed is performed in the tangential direction of the machining contour line in a horizontal plane approximately perpendicular to the wire electrode axis on either one of the two sides, while maintaining a proper machining gap at all times. Machining feed at a constant speed predetermined in consideration of various machining conditions, or detecting the voltage of the machining gap so that the machining state of the machining gap is in the desired normal state, so that the machining gap voltage remains approximately constant. The servo control feed is provided so that the processing feed is performed at a seemingly constant speed while controlling the feed speed etc. so that the feed rate and the like are maintained at a constant speed.

In addition, the wire electrode is held and stretched between the capstan and the pinch roller, and between the brake roller and the pinch roller, and is updated and fed in the axial direction continuously or intermittently during processing.
Appropriate tension is applied, but this tension is set taking into account the diameter and material of the wire electrode, the selected electrical processing conditions, etc., and conventionally it was always kept at a constant value during processing. .

[Problem that the invention seeks to solve]

As mentioned above, strong tension is applied to the wire electrode during processing, and although the wire electrode is continuously or intermittently updated and fed to the processing section, new electrodes are always supplied to the processing section. 0.05 for the electrode
A wire rod with a small diameter of ~0.35 mmφ is used, and since high temperature and high pressure gas is generated at the discharge point due to discharge, the wire electrode is positioned in a pair in the opposite direction to the machining feed direction due to the pressure. There was a problem in that the wire guide was bent in an arcuate manner using the wire guide as a fulcrum, and the wire guides did not form an accurate straight line between the wire guides.

The amount of deflection of the wire electrode includes the dimensions of the wire electrode, the material, the applied tension, the length between the positioning guides,
The properties of the machining fluid, the flow rate, the flow rate, the cooling ability of the machining gap, etc., the electrical machining conditions and the machining feed conditions, which are mainly related to the magnitude of the average machining current, but these conditions are If the adjustment is carried out efficiently, it is impossible to make the wire electrode accurately straight.

For this reason, a phenomenon occurs in which the movement of the wire electrode in the processing section is slightly delayed relative to the relative movement of the pair of positioning wire guides with respect to the workpiece. In the case where a pair of positioning wire guides are accurately traced along the machining contour line, a problem arises in that the delay in movement of the wire electrode causes deterioration in machining accuracy such as so-called sag.

Further, since the workpiece is melted or evaporated and removed by the high temperature associated with the electric discharge, gas, sludge, etc. are generated in the machining gap. For example, a coaxial flow of machining liquid that wraps around the wire electrode in a coaxial manner is injected into the machining gap between the wire electrode and the workpiece, but this machining gap is extremely narrow, so conventionally known methods do not Gas, sludge, etc. are not easily removed from the machining gap, and the machining fluid deteriorates due to these gases and sludge within the machining gap. Therefore, it is not possible to increase the average machining current by, for example, further increasing the discharge repetition frequency. Another problem is that machining accuracy and machining speed are reduced due to secondary discharge caused by machining debris such as sludge.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention applies a tension Tf for normal machining to the wire electrode of the machining part between a pair of positioning wire guides, and applies a tension Tf for normal machining to the wire electrode for a desired distance or time at a normal machining feed rate Vf. The process of machining by applying a machining feed relative to the workpiece, and the process of applying a tension Tm larger than the tension Tf for normal machining to the wire electrode and an average speed Vmean smaller than the normal machining feed rate Vf above. The machining is progressed by repeating the steps of applying a relative machining feed for a predetermined distance or time and continuing the machining.

The changes in machining feed and tension may be given as a function of time that changes smoothly, or may be given in steps.

[Effect]

According to the wire cut electric discharge machining method of the present invention, the wire electrode is repeatedly corrected to a straight state along the straight line between the pair of wire electrode positioning guides during machining, and gas and sludge generated in the machining gap due to the electric discharge are removed. The machining fluid in the machining gap that has been contaminated by these components can be easily and reliably removed.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIGS. 1 to 5 are explanatory diagrams showing an embodiment in which a workpiece is machined into a straight line by the wire cut electrical discharge machining method according to the present invention.

In addition, FIG. 5 shows the relationship between the wire electrode and the workpiece during processing shown in FIGS. 1 to 4.
It is an explanatory view seen from above in the figure.

In Figures 1 to 5, 1 is a wire electrode, 2 is a workpiece, 2a is a machining start hole, and 3 and 3' are a pair of upper and lower wire electrode positioners provided facing each other with the workpiece 2 in between. Guide, 4 is capstan, 5
is a brake roller, and 6 and 7 are pinch rollers.

When starting machining, as shown in FIG.
A pair of wire guides 3 and 3' are arranged opposite to each other with the wire a in between, and the wire electrode 1 supplied from a wire supply drum (not shown) is passed between the brake roller 5 and the pinch roller 7 to the die-shaped wire guide 3. From there, the wire is passed through the machining start hole 2a, stretched to the wire guide 3', passed between the capstan 4 and the pinch roller 6, and routed to a recovery drum (not shown).

With the above configuration, the wire electrode 1 is renewedly fed in the axial direction by driving the capstan 4, and a braking force is applied by the brake roller 5 to provide tension.

After the wire electrode 1 is routed as described above, a tension Tf for normal processing is applied to the wire electrode 1.
While updating continuously or intermittently in the axial direction,
The side surface of this wire electrode 1 is opposed to the side surface of the start hole 2a of the workpiece 2 in one direction with a predetermined machining gap interposed therebetween, and machining fluid injection nozzles are provided on both sides of the workpiece 2 in this machining gap. While supplying machining fluid along the wire electrode 1 from (not shown), intermittent machining voltage pulses are applied between the two to generate electric discharge, and from point A to point B (or for a predetermined period of time). A pair of positioning wire guides 3, 3' are moved relative to the workpiece 2 at a normal machining feed rate Vf to apply machining feed, and machining is carried out in a straight line.

As shown in FIG. 2, when the pair of positioning wire guides 3 and 3' move from point A to point B by a distance α (or a predetermined time) as the machining progresses,
The center of the wire electrode 1 is bent in an arched manner in the opposite direction to the machining feed direction due to discharge pressure or other causes, so at this position (or point in time) the machining feed rate is reduced to the normal machining feed rate. Tf is set smaller than Vf, and the torque applied to the capstan 4 and the braking force applied to the brake roller 5 are increased to create a tension Tf applied to the wire electrode 1 during the above-mentioned normal processing.
Give a tension Tm greater than

It is desirable to set this tension Tm as large as possible within a limit that does not cause wire breakage, taking into account the diameter, material, electrical processing conditions, etc. of the wire electrode 1.

In addition, in this case, the feed rate may be changed gently and continuously within a certain period of time, and the feed rate may be changed slowly and continuously within a certain time, and the
The speed may be rapidly reduced to within a short period of time, and the speed may be maintained for a certain period of time or a predetermined constant machining feed distance. The same applies to tension. In addition, the machining feed speed Vk to be maintained in this case is determined by considering the electrical machining conditions, etc., but it is set to 0, that is, the machining feed is temporarily stopped, or is decelerated and then stopped, and after stopping, The speed may be increased to Vf immediately for processing.

Even during such deceleration or stopping, machining voltage pulses are supplied between the wire electrode 1 and the workpiece 2 to continue electrical discharge machining, but when machining feed is temporarily stopped, The supply of machining voltage pulses may also be controlled to decrease at that position, and the control may be changed until the supply is finally temporarily stopped.

If a temporary deceleration or even a discharge pause period is provided in this way, the machining fluid supplied between the wire electrode 1 and the workpiece 2 during this period will easily flow between the two, and the machining fluid will be reduced by the discharge. Generated gas, sludge, etc. are rapidly removed, and deformed and worn-out wire electrodes are renewed and supplied with new ones to the processing section.

Then, with a tension Tm greater than the tension Tf applied during normal processing applied to the wire electrode 1,
Move the pair of positioning wire guides 3 and 3' from point B to point D relative to the workpiece 2 by a distance 〓 (or a predetermined time) at an average speed Vmean smaller than the normal machining feed rate Vf as described above. move the target. In this process, the arcuate bulge portion of the workpiece 2 is almost selectively processed, and the wire electrode 1 changes from the arched state shown in FIG. 2 to the state shown in FIG. 3. approaching in a straight line,
In the state shown in FIG. 4, it is approximately linear.

Also, during this time, the arcuate bulging part of the workpiece 2 is processed almost selectively, so the processing conditions at this time are such that the frequency of the voltage pulse and the discharge current are higher than those for normal processing feed. It is desirable to reduce the average machining current by sequentially decreasing the amplitude, etc. to a predetermined value or at a predetermined rate, but since machining of this bulging portion is usually completed in a short time, the above machining conditions are not met. Even if the switching is performed, the machining efficiency will not be impaired.

After the wire electrode 1 and the machining surface of the workpiece 2 along the wire electrode 1, that is, the machining gap, are made straight along the straight line connecting the pair of positioning wire guides 3 and 3', the next section is Since the processing is performed, the linearity of the wire electrode 1 increases on average during processing, and processing accuracy and processing speed are improved.

The deceleration or stopping of the machining feed described above can be done by adjusting the value of α (or the corresponding predetermined machining feed time) by adjusting the thickness of the workpiece 2, the material of the wire electrode 1, the purpose of machining, and other selected setting machining conditions. It may be determined in advance in consideration and executed each time the machining progresses by α (or a predetermined time), or it may be configured to be executed periodically every time Δt, which is the average time required to process the above α. However, it is possible to designate the position of the deceleration start point B in the NC program by taking into account the shape of the machining contour, or to detect the amount of deflection of the wire electrode 1 using an appropriate method and make sure that the deflection exceeds a certain value. The deceleration may be started when the vehicle becomes tired.

The value of β (or the machining feed time corresponding to β) is
It is determined by the average machining feed rate Vmean, which is smaller than the normal machining feed rate mentioned above, and the time for machining feed at the average speed Vmean (or by the distance β above), but this time (or distance) ) is the sufficient time (or distance) for the wire electrode to recover the specified linearity, taking into consideration the material of the workpiece, the material and diameter of the wire electrode, and other relevant machining conditions.
Set to .

After the above steps, the pair of wire guides 3,
3' is processed by moving it relative to the workpiece 2 from point D to point E by a distance α (or a predetermined time) at the normal processing feed rate Vf, and then the above steps are performed in the same manner. Repeat processing.

In addition, for machining when the machining contour line includes a corner part, the position of the above point D at the corner part is set to be the direction change point of each corner part, and the machining feed rate and the tension applied to the wire electrode are adjusted. Convert
In the same manner as in the above embodiment, a tension Tm greater than the tension Tf applied during normal machining is applied to the wire electrode, and the average machining speed Vmean is lower than the normal machining feed rate Vf for a certain period of time (or a certain distance).
After moving the machining feed to make the wire electrode and the machining surface along the wire electrode of the workpiece, that is, the machining gap, straight along the straight line between the positioning wire guides, move the positioning wire guide relative to the workpiece. Change the direction and proceed with the next processing.

When machining a corner part using the method of the present invention, when the pair of positioning wire guides come to the direction change point of the corner part, the wire electrode and the machined surface of the workpiece along the wire electrode are between the wire guides. Since it is in a straight state along a straight line and machining in the direction change direction is restarted from this position, so-called sagging at the corner portion can be suppressed to a minimum.

〔Effect of the invention〕

According to the wire cut electric discharge machining method of the present invention, the linearity of the wire electrode during the machining period is increased, and the linearity of the machining gap along the wire electrode is also increased, so that machining speed and machining accuracy can be increased, and
Gas, sludge, etc. generated by electrical discharge are easily and reliably removed from the machining gap periodically, and the liquid properties of the machining fluid present in the machining gap are always maintained at an optimum level, and secondary machining due to machining debris is prevented. Since the material can be peeled off, processing speed and processing accuracy can be increased.

In addition, even if the periodic switching of the machining feed movement in the present invention is performed by setting the feed length,
It may be done by setting the feed time, and in that case, the cycle, that is, the set feed length and time, etc., may be normal or
The size may be changed or controlled depending on machining conditions such as abnormalities, straight portions and corner portions of the machining contour, or relatively small circular arc portions.

[Brief explanation of drawings]

FIGS. 1 to 5 are explanatory diagrams showing one embodiment of machining a workpiece by the wire cut electrical discharge machining method according to the present invention. 1... Wire electrode, 2... Workpiece, α... Distance traveled by machining feed at normal machining feed speed, β...
...Distance traveled by machining feed at an average machining feed speed smaller than the normal machining feed speed, 3, 3'... Positioning wire guide, 4... Capstan, 5... Brake roller, 6, 7... Pinch roller.

Claims (1)

[Scope of Claims] 1. A workpiece is placed opposite a wire electrode that is renewed in the axial direction with a predetermined tension applied to it, with a predetermined machining gap interposed therebetween, and a machining fluid is supplied to the machining gap. Wire-cut electrical discharge machining in which a machining voltage pulse is applied between a wire electrode and a workpiece to generate an electric discharge, and the wire electrode and workpiece are moved relative to each other to cut the workpiece. In the method, a tension Tf for normal processing is applied to the wire electrode, and the wire electrode and the workpiece are moved relative to each other by a desired distance or time at a normal processing feed rate Vf, and processing is performed. process, and a tension greater than the tension Tf for the above normal processing on the above wire electrode.
While giving Tm, the wire electrode and workpiece are moved at an average speed smaller than the normal machining feed rate Vf.
The wire cut electric discharge machining method described above is characterized in that machining progresses by repeating a step of relatively moving the machining feed by a predetermined distance or time at Vmean and continuing machining. 2 The machining feed rate in the process of continuing machining by moving the machining feed for a predetermined distance or time at the average speed Vmean is gradually lowered from the normal machining feed rate Vf to the minimum speed Vmin, and the tension is reduced.
The wire cut electric discharge machining method according to claim 1, wherein the wire cut electric discharge machining method is gradually increased from Tf to Tmax. 3. The wire cut according to claim 1, wherein the machining feed rate in the step of continuing machining by moving the machining feed for a predetermined distance or time at the average speed Vmean is a constant speed Vk, and the tension Tm is a constant value Tk. Electric discharge machining method. 4. The wire cut electric discharge machining method according to claim 3, wherein the constant speed Vk in the step of continuing machining by moving the machining feed for a predetermined distance or time at the average speed Vmean is 0.