JPH08243927A - Grinding tool and its manufacture and grinding device - Google Patents

Abstract

PURPOSE: To form a grinding tool to work a mirror surface having small surface roughness by wire electric discharge machining. CONSTITUTION: A wire electric discharge machine has a wire 56 to be supplied along a wire guide 60. A work 70 of a conductive and highly hard material is placed on a table arranged so as to be opposed to the wire guide 60. The wire 56 performs electric discharge machining on a surface of the work 70 of a conductive highly hard material by discharge. A top part being a cutting edge and a recessed part being a pocket are formed on the surface of the conductive and highly hard material by this electric discharge machining. This work 70 is used as a grinding tool, and a work object can be ground into a mirror surface.

Description

Detailed Description of the Invention

[0001]

[Industrial field of application] This technology is used for precision processing of metal, glass, ceramics, etc. with a small surface roughness in grinding, and for example, manufactures optical parts and dies for pressing and injection molding optical parts. In particular, the present invention relates to a tool for so-called mirror-surface grinding and a method for manufacturing the same, which can perform grinding with extremely small surface roughness and precision.

[0002]

2. Description of the Related Art Various attempts have been made in the past for obtaining a mirror surface by grinding, but basically it is a technique for mastering a grindstone having a small abrasive grain size.
Generally, grinding with a resin-bonded grindstone of # 3000 or more and a metal-bonded grindstone of # 1000 or more is likely to cause clogging, which makes it difficult to use and is not practical. Therefore, a method called so-called in-process electrolytic dressing has been invented in which a metal bond grindstone is used as a grindstone, and during grinding, a material clogged between the abrasive grains is dissolved by an electrolytic action to perform dressing. These are as disclosed in, for example, JP-A-3-196968 or JP-A-4-8476. This method makes it possible to use a grindstone of # 10000 or more, and is an excellent method for obtaining a machined surface having extremely small surface roughness.

Further, a suspension in which fine particle abrasive grains are dispersed, that is, a colloidal solution, is electrophoresed to prepare a grindstone for mirror grinding, as disclosed in JP-A-2-262965 or Japanese Patent Laid-Open No. 2-262965. Kaihei 5-69287
There are techniques disclosed in published patent publications such as Japanese Patent Publication. Alternatively, a technique for polishing by mechanically contacting an aggregate of fine particles obtained by electrophoresing such a colloidal solution with a work piece is described by Sakata and Kurobe et al. Proceedings p521 "Ultra-precision polishing of optical glass by electrophoretic phenomenon (FFF)"
(Third report) -Application to spherical surface polishing- "and the like. These methods are excellent as methods for obtaining a grindstone having an extremely high abrasive grain density.

[0004]

However, the method of electrolytically dressing a metal bond grindstone in-process has the following drawbacks. First, there is a problem that the electrolysis action acts not only on the grinding debris that causes the clogging but also on the metal portion to which the abrasive grains are bonded, and changes the shape of the grindstone during the grinding process. In particular, the action of electrolysis concentrates on the shape where the electric field is likely to concentrate, such as the edge portion of the grindstone or a small convex shape, which makes it particularly difficult to maintain the shape of the grindstone. This is a common problem in the method of dressing the grindstone by utilizing the electrolysis phenomenon.

Although it is possible to use grindstones of # 10000 or more by in-process electrolytic dressing, it is extremely difficult to stably manufacture grindstones of # 10000 or more in practice. The reason for this is that it is difficult to produce a metal powder having a particle diameter corresponding to an extremely small abrasive grain having a diameter of 5 μm or less, and it is extremely difficult to mix the metal powder and the abrasive grain so as to be uniformly dispersed. Because it is difficult. These become particularly serious when trying to manufacture a grindstone of # 8000 or more. A cross-sectional photograph of such a grindstone is shown in FIG. As can be seen from this photograph, the metal powder is 1 for the extremely small abrasive grain size of 1 to 2 μm.
Since it is about 0 μm or more and the dispersion is non-uniform, it is understood that the abrasive grains cannot be expected to be uniformly exposed on the surface of this grindstone.

Not only is it impossible to obtain a surface roughness commensurate with the particle size of the abrasive grains by performing grinding while electrolytically dressing such a stone, but the sparse parts of the abrasive grains cause uneven wear. The shape of the workpiece collapses, deteriorating the shape accuracy of the workpiece. For these reasons, improvement in surface roughness cannot be expected even if the abrasive grain size is reduced. Further, as a grindstone for performing mirror-surface grinding, it is said that a method of increasing the degree of concentration of the abrasive grains instead of reducing the size of the abrasive grains, that is, increasing the density of the abrasive grains contained in the grindstone is also effective. However, since the degree of freedom between the metal particles and the compounding ratio of the abrasive grains necessary for hardening is not great, the density of the abrasive grains cannot be increased unless the abrasive grain size is small.

On the other hand, the method of manufacturing a grindstone by electrophoresis is as follows:
It is easy to produce a uniform whetstone, but because the whetstone is extremely soft and wear occurs extremely easily during processing, it is not suitable for grinding that actively creates a shape, so-called shape creation, This technique is effective only in the polishing process or surface grinding process to improve only the surface roughness. In view of these problems, the present invention has a surface roughness of 0.1 μm Rma.
It is intended to provide a means for realizing precise mirror grinding for achieving a shape accuracy of 1 μm or less at x or less.

[0008]

A conductive high hardness material is subjected to electrical discharge machining to form irregularities on the surface, and this is used as an abrasive grain cutting edge for grinding. Further, the grinding tool is manufactured by this means.

[0009]

According to this grinding tool, the irregularities on the surface corresponding to the number of abrasive grains can be dramatically increased as compared with the grindstone of the conventional manufacturing method, and mirror grinding can be easily performed.
Further, the unevenness of the surface can be increased or decreased according to the electric discharge machining conditions, and various required surface roughness values can be answered. In addition, since the grindstone itself does not elute due to the electrolytic action because it does not have a metal portion as a bulk, it is possible to prevent deterioration of the shape accuracy due to electrolytic dressing. In addition, since the grindstone itself is a high hardness material, the shape does not change due to uniform wear during processing.

[0010]

FIG. 2 is an explanatory view showing the outline of a wire electric discharge grinding apparatus used in the present invention. The wire electric discharge grinding apparatus indicated by reference numeral 1 as a whole has a linear guide rail 12 mounted on a base 10.
The first table 14 is mounted, and the movement of the first table 14 is controlled along an axis (X axis) perpendicular to the paper surface by a servo device (not shown) provided on the base 10. A linear guide rail 16 is mounted on the first table 14,
The second table 20 placed on the linear guide rail 16 is controlled to move along a Y axis orthogonal to the X axis by a servo device (not shown) provided on the first table 14. Therefore, the work table 30 mounted on the second table 20 can position the work (workpiece) 70 fixed by the jig 32 at arbitrary coordinates on the plane formed by the X axis and the Y axis. .

On the other hand, a column 40 which is erected on the base 10
In the vertical axis (Z
It is mounted so that it can move freely along the axis. The wire electric discharge machining head 50 has a wire supply bobbin 52 and a wire winding bobbin 54, and runs a wire 56 along a wire guide 60. A voltage is applied to the wire 56, and the wire 56 reaching the wire guide 60 is discharged to a work 70 made of a conductor, and the work is processed.

By performing electric discharge machining on the workpiece 70 in the workpiece table 30 while supplying the machining liquid 34 from the nozzle 36, it is possible to obtain machining conditions according to the material of the workpiece.

FIGS. 3A and 3B show a state in which the wire electric discharge machine shown in FIG. 2 is used to perform electric discharge machining on the work 70 made of a conductive high hardness material mounted on the work table 30. Show. The traveling wire 56 is a wire guide 60.
A traveling system (not shown) travels along a groove provided in the vehicle at a speed of several mm per minute. The electric discharge machining is performed by generating an electric discharge 80 when the traveling wire reaches the top of the wire guide. The existence of a liquid for generating a good electric discharge is essential for electric discharge machining, and an oil-based machining liquid or an aqueous machining liquid may be used. Alternatively, the processing liquid may be poured over the processed portion. Although not shown in the drawings in this embodiment, an oil-based working liquid was used, and the working was performed by dipping in the working liquid.

FIG. 4 shows details of the workpiece 70 made of the high hardness material thus discharged. Surface 7 of work 70
Reference numeral 2 is a surface where the fine crater-shaped concave portions 74 and the top portions 76, which are scooped out by the discharge, are integrated. This discharge is performed between the work 70 and the wire on the top of the wire guide 60, but the wire 56 is always replaced with a new part as the wire 56 runs, so the problem of electrode consumption inherent to the electric discharge machining is solved. This method is a method disclosed in "Research on high-precision micro-axis machining (first report) -Development of wire electric discharge grinding method" by Masawa, Fujino et al.

This method is disclosed in Japanese Patent Laid-Open No. 4-10 by the inventors.
1724 and the like, the tension during wire traveling, the position of the wire guide and the traveling wire, etc. are stabilized and the accuracy is improved, and these methods are also used in the present invention. By scanning one surface of the work 70 made of a high-hardness material in this manner, the electric discharge machining surface 72 can be formed over the entire surface.

FIG. 5 shows a state in which the workpiece 70, which has been subjected to the electric discharge machining as described above, is used as a machining tool to perform mirror surface machining on the workpiece 90. The top portion 76 formed on the surface of the high hardness material 70 by electric discharge machining functions as a cutting blade having high hardness, and the surface 92 of the workpiece 90 can be processed into a mirror surface having extremely small surface roughness. This Creator 7
The size of 4 and the height of the top portion 76 can be adjusted depending on the electrical discharge machining conditions. Therefore, the electrical discharge machining conditions may be determined according to the material of the high hardness material 70, the material of the workpiece 90, the required surface roughness and the machining speed.

As an example of this, sintered cBN (steric boron nitride) by a micro-electric discharge power source using an RC circuit
FIG. 6 shows an example in which a cutting edge for grinding is attached to the surface of. The processing conditions are a surface processed while operating with a wire discharge electrode of −, a sintered cBN plate of +, a capacitor capacity of 220 pF, a voltage of 110 V, and a pitch interval of 0.05 mm. FIG. 7 shows the surface roughness measured with a laser microscope. According to this, it is understood that fine cutting edges having a diameter of about 2 μm are formed with a height of 3 μm and an average interval of about 5 μm. Sintered cBN plate with such cutting edges produces S
As a result of grinding while pressing a US420J2 flat plate, 0.0
A surface roughness of about 3 to 0.05 μmRmax could be obtained. Such cutting edges can be controlled by selecting electrical discharge machining conditions.

In FIG. 8, as the processing conditions, the wire discharge electrode is −, the sintered cBN plate is +, and the capacitor capacity is 220 p.
It is a surface processed while operating at F, a voltage of 60 V and a pitch interval of 0.05 mm. In such an electric discharge machining state, the electric discharge energy is about 1/3 as compared with the above-mentioned example, a fine cutting edge having a diameter of 1 μm or less can be generated, and the roughness when ground is reduced. Can be improved.

FIG. 9 shows the surface processed while the wire discharge electrode is −, the sintered cBN plate is +, the capacitor capacity is 3300 pF, the voltage is 110 V, and the pitch interval is 0.05 mm. Under such an electric discharge machining condition, the electric discharge energy is about 15 times that of the above-mentioned example, and a cutting edge having a diameter of about 5 μm can be generated.
Although the surface roughness after grinding becomes rough, the processing speed can be improved.

On the other hand, when the electric discharge machining conditions are not appropriate,
Cracks may occur on the surface of the sintered cBN and effective cutting edges may not occur. FIG. 10 shows such an example. The processing conditions are as follows: the wire discharge electrode is −, the sintered cBN plate is +, the capacitor capacity is 1000 pF, and the voltage is 80V.

Next, another embodiment according to the present invention will be described.
As shown in FIG. 11, a tool 100 made of a sintered cBN material as a high hardness material is attached to the rotary shaft 110, and chucking 12
The sintered cBN material tool 100 is rotated by a bearing and a motor (not shown) through 0, and is electric discharge machined by a wire 56 that runs along a wire guide 60. At this time, the wire electric discharge machining head is sintered c
The BN material tool 100 is processed while being rotated, and the positioning is controlled so that the shape of the surface of the sintered cBN material tool 100 becomes a part of a sphere. In this manner, cutting edges are formed by electric discharge machining on the surface of the sintered cBN tool 100 as in the previous embodiment.

Sintered cB having a shape of a sphere in this way
The N material tool 100 is used as a tool for shape creation. As the work piece 150, 13 Cr martensitic stainless steel, more specifically, STAVAX (trade name) manufactured by Woodyholm, Sweden is used.

As shown in FIG. 12, from the machining point 152 on the workpiece 150 to the position away from the radius r of the sintered cBN material tool 100 in the direction normal to the shape of the workpiece 150 to be machined. The tool may be positioned so that the center 102 of the sphere of the tool 100 made of the sintered cBN material comes. The shape can be created by operating the surface of the workpiece 150 while maintaining such a positional relationship. This work piece 150
The surface of can be made to have a very small surface roughness by selecting the electric discharge machining conditions as described in the first embodiment.

When the cutting edge formed on the surface of the tool 100 made of the sintered cBN material is extremely small and clogging occurs during processing, an electrolytic dressing electrode 180 is equipped and electrolytic in-process dressing is performed by an electrolytic power source. I'm fine. In this case, the sintered cBN material tool 100 does not have a metal layer unlike a conventional metal bond grindstone, and cBN particles are directly bonded by a sintering aid,
The dropping phenomenon due to electrolysis is unlikely to occur. Therefore, there is an advantage that, unlike the case where the metal bond grindstone is electrolytically dressed, the problem of scratches due to the falling abrasive grains and the shape collapse of the grindstone does not occur. Further, as a problem peculiar to a grindstone using fine abrasive grains, the problem of deterioration of processing accuracy due to uneven wear due to uneven abrasive grain density does not occur.

Further, in the above-mentioned examples, since a stainless steel-based material was used as the workpiece, sintered cBN was used as the high hardness material. However, when the counterpart material is an electroless Ni-P alloy plated surface, In the case of a toned alloy or the like, the melting of carbon atoms does not occur, so a sintered diamond material may be used. Further, a cemented carbide may be used as the high hardness material.

[0026]

As described above, according to the present invention,
The number of irregularities on the surface corresponding to the number of abrasive grains can be dramatically increased as compared with the conventional grindstone of the manufacturing method, and mirror polishing can be easily performed. Further, the unevenness of the surface can be increased or decreased according to the electrical discharge machining conditions, and various required surface roughness values can be satisfied. In addition, since the grindstone itself does not elute due to the electrolytic action because it does not have a metal portion as a bulk, it is possible to prevent deterioration of the shape accuracy due to electrolytic dressing. In addition, since the grindstone itself is a high hardness material, the shape does not change due to uniform wear during processing.

[Brief description of drawings]

1 is a cross-sectional electron micrograph of a conventional grinding wheel.

FIG. 2 is an explanatory diagram of an electric discharge machine using a wire electric discharge head.

FIG. 3 shows a method of generating an electric discharge and a cutting edge by a wire electric discharge machining head.

FIG. 4 is an explanatory view of grinding / polishing processing by a cutting edge.

FIG. 5 is an explanatory view of grinding / polishing processing by a cutting edge.

FIG. 6 is an electron micrograph of a cutting edge.

FIG. 7 is a chart showing surface irregularities of a cutting edge.

FIG. 8 is an electron microscope photograph under a small cutting edge generation condition.

FIG. 9 is an electron micrograph under a large cutting edge generation condition.

FIG. 10 is an electron micrograph under an inappropriate electrical discharge machining condition.

FIG. 11 is an explanatory view showing a method for manufacturing a spherical grindstone according to the present invention.

FIG. 12 is an explanatory view of a shape generating / grinding device using a spherical grindstone according to the present invention.

[Explanation of reference numerals] 1 wire electric discharge machine, 10 bases, 14, 20
Table, 30 work mounting table, 50 wire electric discharge machining head, 56 wire, 60 wire guide, 70 work (hard material tool), 76 top (cutting edge), 90 workpiece, 100 rotating tool,
150 workpiece, 180 electrolytic in-process dressing device.

Claims (6)

[Claims] 1. Grinding made of a high hardness material, characterized by comprising a cutting edge formed on the surface of the conductive high hardness material by subjecting the surface of the conductive high hardness material to electric discharge machining. tool. 2. A step of forming a conductive high-hardness material into a tool shape, and forming a cutting edge on the surface of the conductive material by performing electric discharge machining on the surface of the conductive material formed into the tool shape. The manufacturing method of the grinding tool characterized by including the process. 3. A grinding machine comprising: a grinding head provided with the grinding tool according to claim 1; and an electrolytic in-process dressing device arranged to face the grinding head. 4. The grinding tool according to claim 1, wherein the conductive high hardness material is a diamond sintered body. 5. The grinding tool according to claim 1, wherein the conductive high hardness material is a cubic boron nitride (cBN) sintered body. 6. The grinding tool according to claim 1, wherein the conductive high hardness material is a tungsten carbide sintered body.