JP2010208009A - Wire for electric discharge machining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wire for electric discharge machining for realizing a smooth surface by high speed machining without generating electric discharge non-contributing to slit machining and performing unidirectional machining with a small machining width and good yield of a workpiece. <P>SOLUTION: This wire has a wire surface formed by a straight electric discharge region continuous in the longitudinal direction and a non-electric discharge region having higher electric resistance than that in the electric discharge region. By making the non-electric discharge region into an insulating layer, reforming the electric discharge region into a layer with excellent dispersibility or forming a cross-sectional shape of the wire itself into an irregular shape, preferably, a truck shape, improvement of machining speed, reduction of machining surface roughness and reduction of a machining groove width, etc. can be attained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

In wire electric discharge machining, the present invention relates to an electric discharge machining wire that can perform high-speed and high-precision machining particularly in a specific direction.

Wire electric discharge machining is a process of cutting a workpiece by electric discharge energy using a thin wire as an electrode wire. A voltage is applied between the electrode wire and the workpiece (mold, die, etc.) in the working fluid atmosphere while continuously running the electrode wire under tension. Then, a pulsed discharge is repeatedly generated between the workpiece and the electrode wire. The machining liquid is high-purity water or oil, and is supplied to the discharge site or the electric discharge machining is performed in the liquid. Electric discharge machining consists of melting, explosion, scattering, cooling, and sludge removal processes. When the electrode wire and the workpiece are continuously approached, the electric discharge machining is repeatedly performed to process the workpiece into a predetermined shape.

Wire electric discharge machining has been originally used in favor of manufacturing objects having various curved surfaces. However, in recent years, the use of not only complicated shapes but also simple slit processing has been studied due to the improvement of the processing performance. In particular, application to slice processing of hard and brittle materials such as compound semiconductors such as Si and SiC is expected.

Conventional wire electric discharge machining has been used to form complex machining surfaces. In order to obtain such a processed surface, the direction in which the wire advances (hereinafter referred to as the processing direction) changes every moment. At that time, the wire surface facing the processing direction also changes every moment. Accordingly, there has been a demand for uniform processing performance over the entire wire surface.

A conventional concrete electric discharge machining wire is shown in FIG. FIG. 5 shows a vertical cross section (hereinafter simply referred to as a cross section) of the conventional wire in the longitudinal direction. (P) consists only of the base material 12, for example, a brass wire or a tungsten wire. (Q) is a layer formed on the surface of the base material 12 or a modified surface. For example, as in Patent Document 1, there is one having a steel wire as the base material 12 and a brass plating layer as the metal layer 14. . In addition, there is one in which a layer further covering the surface is formed as shown in (r). For example, as disclosed in Patent Document 2, a wire having a non-insulating resistance film (high resistance layer 16) having an electric resistance larger than that of a base material on substantially the entire outermost surface is described.

The wire having the structure as shown in FIG. 5 (r) can stably generate a discharge with a small discharge gap. Further, by using the wire electric discharge machine and optimizing the inter-electrode serve control (control of the servo voltage value), the discharge gap can be reduced and the machined surface can be smoothed. Furthermore, the machining groove width can be reduced, and the number of discharges can be increased to increase the machining speed. In general, it becomes possible to increase the processing efficiency of the fine processing.

JP 2006-136852 A JP 2008-296350 A

As represented by Patent Literature 1 and Patent Literature 2, since the machining direction of conventional electric discharge machining wires is unspecified, the same performance has been required over the entire surface. If the electrical discharge machining performance is uneven at a specific portion of the wire, stable machining cannot be achieved.

However, when the processing direction can be specified (hereinafter referred to as unidirectional processing), it has become clear that having a uniform processing performance on the entire surface of the wire is an adverse effect. FIG. 6 shows a schematic diagram of a conventional electric discharge machining state in the cross-sectional direction. In unidirectional machining, the discharge 20 only needs to be performed in the machining direction (the direction of the single arrow in the figure). However, it has become apparent that the discharge 20a is actually generated not only in the processing direction but also on the lateral surface or the rear side of the wire processing direction. Such a discharge 20a other than the machining direction does not directly contribute to the machining but also causes harm. In other words, the processing surface is roughened by useless discharge.

Further, as apparent from FIG. 6, the machining width 24 (double arrow in the figure) is increased by the electric discharge 20a behind the wire. In the case of multi-processing, it is required to make the machining width 24 as small as possible. This is because the workpiece 22 is melted / exploded / scattered by electric discharge machining. That is, the yield of the workpiece 22 is greatly affected. For example, in the case of performing multi-EDM which slices several tens or hundreds of Si wafers at a time, a slight decrease in yield greatly affects.

From the above, conventional electric discharge machining wires are not suitable for unidirectional machining. Therefore, it does not generate electric discharge that does not contribute to machining, effectively generates electric discharge to achieve high-speed machining, realizes a smooth surface, and specializes in unidirectional machining with a small machining width and good workpiece yield. An object of the present invention is to provide an electric discharge machining wire.

As an electric discharge machining wire that solves the above problems,
The wire surface is composed of a discharge region that is continuous in the wire longitudinal direction at the same peripheral edge of the wire cross-section, and the other region is composed of a non-discharge region having a higher electrical resistance than the discharge region.
It is characterized by that.

Furthermore, the non-discharge area may be an insulating layer.

Furthermore, the discharge area may be a metal layer or a high resistance layer.

The cross-sectional shape of the electric discharge machining wire is preferably a shape superior to unidirectional machining. In particular,
A wire having a shape in which the peripheral edge of the wire cross section has a pair of opposing straight portions, and has a curved portion that bulges outward in at least one of the ends connecting the opposing ends of the pair of straight portions. And it is good for the said one curve part to have the said discharge area in the curved-surface part which continues in a wire longitudinal direction, and for the wire cross section to be a shape long in the linear direction of this linear part.

Furthermore, the shape of the cross section of the wire is a track shape in which the pair of linear portions are the same size and parallel to each other, and the curved portions are provided on both ends of the pair of linear portions connected to each other. More preferably.

Since the portion to be discharged at the peripheral edge of the wire is specified, the discharge can be efficiently generated only in the machining direction. Therefore, a smooth surface can be obtained without roughening the processed surface of the workpiece. Furthermore, since wasteful discharge energy is not consumed, energy saving processing can be performed.

In addition, since the discharge is only in the machining direction, the portion where the workpiece is melted and removed can be minimized, so that the yield is improved.

Schematic diagram of a representative wire of the present invention (a) Cross-sectional view orthogonal to the wire longitudinal direction (b) Side view Sectional view showing an example of the discharge area Sectional view showing examples of cross-sectional shapes Sectional view showing an example of a non-discharge area Cross-sectional view of a typical conventional wire Cross-sectional schematic diagram of conventional EDM state Schematic cross-sectional view of the electrical discharge machining state of the present invention Correlation diagram of discharge performance at discharge area angle based on Example 1

The greatest feature is that a specific discharge area continuous on the wire surface and a non-discharge area where no discharge occurs are provided. FIG. 1 shows a schematic diagram of a representative wire of the present invention. 1A is a cross-sectional view orthogonal to the wire longitudinal direction, and FIG. 1B is a side external view. The electric discharge machining wire 2 has a discharge region 8 continuous in the wire longitudinal direction at the same peripheral edge of the wire core member 4. In addition, the other part has a non-discharge region 10 having a higher electrical resistance than the discharge region 8, for example, formed of the insulating layer 6.

As a method of providing the discharge region 8 and the non-discharge region 10, it can be easily formed by changing the surface state of the wire core material 4. Specifically, a state having a difference in electrical resistance may be formed. If there is a difference in electrical resistance, electricity inevitably flows to the side with the lower resistance. The discharge direction can be specified using this. That is, it is possible to realize a wire that can generate an electric discharge only in the direction in which it is desired to be processed.

The “electric resistance” in the present invention means an electric resistance from the surface of the wire core material 4 to the outermost surface of the wire.

“Insulation” means that electricity is not conducted at a voltage in normal use, specifically at a voltage of 50V to 300V.

Further, the “high resistance” may be anything as long as it can avoid the concentrated discharge and improve the dispersive discharge property at the voltage described above. Specifically, it is an oxide layer (for example, zinc oxide layer) or a resin layer (for example, a layer made of alkyd resin, polyethylene resin, polyester resin, etc., and having a thickness of 0.1 to 5 μm). Anything having an effect similar to these may be used, and is not particularly specified.

Accordingly, it is important that the voltage is set to “discharge” or “do not discharge” at a voltage in normal use. Therefore, the discharge area and the non-discharge area may be the same substance. For example, if a resin such as polyester or polyethylene is thinly formed on the wire surface (for example, 1 μm), a high resistance layer is obtained. However, if it is formed thick (for example, 10 μm or more), it can be an insulating layer.

A specific example of the discharge region is shown in FIG. FIG. 2 is a cross-sectional view showing an example of a discharge region. In FIG. 2C, the base material 12 is exposed. For example, a commonly used tungsten wire has no problem in electric discharge machining because of its high electric conductivity and toughness.

FIG. 2D shows an example in which a metal layer 14 is formed on the base material 12. If the base material 12 is, for example, a steel wire, galvanization or brass plating may be performed to improve wire drawing workability. Further, in terms of electrical conductivity, copper plating, silver plating or gold plating may be applied. The metal layer 14 formed by such metal plating can be used as a discharge region.

FIGS. 2E and 2F are examples in which a high resistance layer 16 is formed on the outer periphery of the metal layer 14 in the discharge region 8. As described above, the high resistance layer 16 may be formed of a resin or the like with a predetermined thickness. At this time, the high resistance layer 16 may be formed on the inner peripheral side of the insulating layer 6 as shown in (e), or may be formed only in the discharge region 8 as shown in (f).

The non-discharge region 10 formed by the insulating layer 6 is effective not only with the resin as described above but also with a very high electrical resistance, such as a rubber-based material, for realizing insulation. What is necessary is not particularly specified.

Further, the machining performance can be further improved by variously changing the cross-sectional shape of the wire. FIG. 3 is a sectional view showing an example of a sectional shape. In FIG. 3, (g) is a circular cross section, (h) is a quadrilateral cross section, (i) is a track shape, (j) is an ellipse, (k) is a hexagon, and (l) is a substantially front-rear circle. belongs to. In any case, the portion where the insulating layer 6 is formed is a non-discharge region, and the other portion is a discharge region. FIG. 3 is an example and is not limited thereto.

Among the above shapes, a preferable cross-sectional shape is a major axis with respect to the processing direction. For example, (i), (j), and (l) in FIG. These are wires having a smaller working width and a strong tensile strength.

Moreover, it is desirable to have the convex curve part 18 as a discharge area. For example, in the case of an arc shape such as (g), (i), (j), or (l) in FIG. 3, uniform discharge is easily performed in the machining direction.

As described above, (i) and (l) are preferable as the cross-sectional shape, and the track shape of (i) in which the cross-section of the wire core material 4 is point-symmetric with no corners is also the best from the wire forming surface. It can be said that.

It should be noted that various changes can also be made in the region forming the non-discharge region. FIG. 4 is a cross-sectional view showing an example of a non-discharge region. As a representative example, the cross section is circular. When the ratio of the discharge area in the circumference is expressed by the circumference angle, it is effective at about 120 ° to 250 °, and more preferably 120 ° to 170 °. In detail, various changes can be made according to the quality required for processing as follows.

Details are shown in FIG. FIG. 7 is a schematic sectional view of the electric discharge machining state of the present invention. (S) is a case where electric discharge machining is performed under the condition that the electric discharge gap is reduced. On the other hand, (t) shows a case where electric discharge machining is performed under the condition that the electric discharge gap is increased.

If it is desired to make the processed surface of the workpiece smoother and more accurately, the process can be performed as shown in (s). That is, it is preferable that the voltage setting of the electric discharge machine is lowered and the discharge region is set to 160 ° to 170 °. In this case, a smoother surface can be finished.

If you want to process quickly, you can increase the voltage setting of the electrical discharge machine. At this time, a larger discharge 20b is generated, and the distance (gap) between the workpiece and the wire also increases. The discharge area should be narrowed under these conditions. Even if the discharge area is narrowed, the machining is performed by a large discharge, so that a machining width 24 sufficient for the wire to travel can be secured. The same applies to the examination of the range of the discharge region in other cross-sectional shapes.

The manufacturing method of the wire which provided the discharge area-non-discharge area is not difficult. For example, there are the following methods for forming an insulating resin layer as a non-discharge region.

Prepare a finely finished wire core. At this time, it is preferable to form a surface layer portion serving as a discharge region by metal plating or the like. The prepared wire core material may be a deformed wire having a non-circular cross section by deformed die drawing or roller rolling. The profile processing may be performed after the non-discharge region is formed. The preparation of the wire core material is not limited to these methods, but may be anything similar.

The wire is immersed in the molten insulating resin layer while running. Further, the molten resin adhering to the region desired to be the discharge region of the wire is peeled off while running. The method for peeling off the resin is not particularly specified. For example, it can be easily peeled off by physically contacting with a die or a roller. The discharge area is determined by the area to be peeled off. Immediately after that, a non-discharge area is determined and formed by drying.

Note that the current technology can be applied only to processing in one direction. However, if the electric discharge machine has control for directing the discharge region of the wire of the present invention in the machining direction, it can also be applied to electric discharge machining in an unspecified direction.

Based on the present invention, several types of wires were manufactured and tested. In any of the examples, a wire core material having brass plating on the periphery of a hard steel wire having a diameter of 0.20 mm was used. A discharge region was prepared in increments of 10 ° from 100 ° to 250 °, and 10 μl of nylon resin was applied as a non-discharge region of each wire to produce various wires. As a workpiece, a plate having a material of SKD11 and a thickness of 10 mm was prepared and subjected to electric discharge machining. The equipment used was an electric discharge machine manufactured by Mitsubishi Electric Corporation (model number PX-05), and the setting voltage was 150 V and the wire traveling speed was 10 m / min.

As evaluation items, (1) time (speed) when cutting 50 mm, (2) surface roughness, and (3) processing width were measured. The results were obtained by relative evaluation when each measured value with a conventional wire without a non-discharge region was set to 1. The result is shown in FIG.

When the discharge area was set to 100 ° and 110 °, the processing width was small, and the wire was disconnected without progressing. However, if the set voltage is increased and the discharge gap is increased, it is presumed that the machining can be performed even if it is smaller than 110 °.

When the discharge area is 250 °, the processing speed (right axis) is almost the same as when no non-discharge area is provided. However, after that, when the discharge area was reduced, the machining speed ratio was proportionally increased, that is, the machining time was shortened. In the case of 120 °, the maximum speed was 2.5 times. With respect to the processed surface roughness (left axis), even when the discharge area was a wide angle of 250 °, there was an effect as compared with the case where there was no non-discharge area. As the discharge area was narrowed, the surface roughness became smoother and improved up to 180 ° in proportion. The best processed surface was obtained around 160 ° to 180 °, and after that, the surface roughness was almost the same, and the conventional roughness was reduced to about 80%. Similarly, with respect to the machining groove width (left axis), the machining groove width becomes narrower as the angle of the discharge region is reduced, and the width is a minimum of 85% compared to the conventional case at 120 ° to 140 °.

Next, the basic conditions were the same as in Example 1, and an experiment for confirming the influence of the cross-sectional shape was performed. As prepared wires, two wires each having a track-shaped cross section were prepared in addition to the circular cross section of Example 1. The track shape was formed by rolling, and the ratio of the major axis a to the minor axis b was a: b = 2: 1. In all cases, the cross-sectional area was adjusted so that the tensile strength was approximately the same. One of each two has a brass plating layer (discharge region) on the entire circumference. The other one having a circular cross section was formed in a range of 180 ° as a discharge region. In the case of a track-shaped cross section, only the surface of one curved portion was a discharge region, and the other surface was a non-discharge region. The results are shown in Table 1.

Compared with the conventional one, the effect of the circular cross section is also clearly improved from the result of Example 1. On the other hand, the wire width is narrower by adopting a track shape. As a result, the machining width can be further narrowed, and the machining speed and the machined surface roughness have been remarkably improved by providing the non-discharge region as compared with the track type having no non-discharge region.

2... Wire for electric discharge machining 4... Wire core material 6... Insulating layer 8. 14... Metal layer 16... High resistance layer 18... Curved portion 20, 20 a, 20 b ... Discharge 22 ... Workpiece 24.

Claims (5)

A wire for electric discharge machining in which a wire surface is composed of a discharge region that is continuous in the longitudinal direction of the wire at the same peripheral portion of the cross section of the wire and a non-discharge region in which the other portion has a higher electrical resistance than the discharge region. The wire for electric discharge machining according to claim 1, wherein the non-discharge area is an insulating layer. The wire for electric discharge machining according to claim 1, wherein the electric discharge area is a metal layer or a high resistance layer. A wire having a shape in which the peripheral edge of the wire cross section has a pair of opposing straight portions, and has a curved portion that bulges outward in at least one of the ends connecting the opposing ends of the pair of straight portions. The one curved portion has the discharge area in a curved surface portion formed continuously in the longitudinal direction of the wire, and the wire section has a shape that is long in the linear direction of the straight portion. The wire for electric discharge machining of any one of Claims 1. The shape of the cross section of the wire is a track shape in which the pair of linear portions are the same size and parallel to each other, and the curved portions are provided on both ends of the ends of the pair of linear portions connected to each other. Item 5. The wire for electric discharge machining according to Item 4.