JP2767897B2 - Method for producing composite diamond abrasive grains for precision polishing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a precision polishing composite diamond abrasive grain used for finish-polishing precision mechanical parts and optical parts with extremely high precision.

[Conventional technology]

2. Description of the Related Art Conventionally, diamond abrasive grains for polishing have been used as free abrasive grains or whetstones for lapping, for precision polishing of precision machine parts and optical parts.

Most of such diamond abrasive grains are synthesized by the ultra-high pressure method, but the diamond synthesized by the ultra-high pressure method reaches a size of several tens to several hundreds μm, and is crushed and classified to several tens μm or less. Are used as diamond abrasive grains for polishing.

However, recently, with the increase in precision of precision machine parts and optical parts, higher processing accuracy has been required for diamond abrasive grains.

In order to improve the processing accuracy with diamond abrasive grains,
It is only necessary to repeat the grinding of diamond synthesized by the ultra-high pressure method to make finer abrasive grains, but the finer the diamond abrasive grains, the more difficult it is to handle and the worse the dispersibility when making it as a whetstone Come out. In addition, diamond abrasive grains made by grinding have a sharp pointed edge, so there has been a problem that scratches are easily given to the workpiece, but as the abrasive grains become finer, This problem also becomes significant.

In recent years, attempts have been made to synthesize a new type of diamond abrasive grains by a vapor phase synthesis method (CVD method). These attempts are, for example, NEW DIAMOND vol4, No.4,
As disclosed in P.28-29 (1988) and International Publication WO88 / 07599, it is an object of the present invention to provide a composite diamond abrasive in which the surface of a base particle is coated with polycrystalline diamond.

However, although the composite diamond abrasive grains themselves are known from each of the above-mentioned documents, the conditions that the composite diamond abrasive grains should have in order to achieve high processing accuracy for precision polishing, which is recently required, are completely unknown. unknown.

Further, according to the methods described in each of the above-mentioned documents, since the base particles are allowed to stand on the substrate and coated with diamond, the amount obtained at one time is extremely small, which is a major obstacle to industrialization. Further, in the above method, since the surface of the base particles in contact with the substrate remains without being coated with diamond, if the composite diamond particles are used as abrasive grains, the surface of the base particles is not covered with diamond. However, there is a drawback that desired processing performance cannot be obtained due to easy peeling.

As a method for synthesizing a composite diamond which solves these disadvantages of the above method, Japanese Patent Publication No. 62-57568 and Japanese Patent Application
No. 270394 discloses a method of depositing and coating diamond by a gas phase synthesis method while vibrating or flowing substrate particles. However, according to this method, although large-scale processing and continuous processing are possible, the finer the base particles are, the easier it is to agglomerate. Particles are generated, and there is a drawback that many large particles are mixed even when obtaining fine composite diamond abrasive grains.

[Problems to be solved by the invention]

The present invention has been made in view of the above circumstances, to provide a composite diamond abrasive having conditions capable of sufficiently functioning as an abrasive for precision polishing, and to provide a method for producing such a composite diamond abrasive. I do.

[Means for Solving the Problems] In order to achieve the above object, a composite diamond abrasive for precision polishing provided by the present invention is a composite for precision polishing in which the entire surface of heat-resistant base particles is coated with polycrystalline diamond. Diamond abrasive grains having a grain size of 0.1 to 10
μm and the aspect ratio are 1-3, and the layer thickness of the polycrystalline diamond covering the abrasive grains is 0.1 mm of the diameter of the base particles.
The thickness of the polycrystalline diamond is from 1 to 10 times and the ratio of the thickest part to the thinnest part thereof is 1 to 2 and the crystal grain size of the polycrystalline diamond is 2 μm or less.

In order to obtain the above-mentioned composite diamond abrasive grains for precision polishing, the method for producing composite diamond abrasive grains for precision polishing according to the present invention uses a ceramics or a heat-resistant metal when coating the surface of the base particles with polycrystalline diamond by a vapor phase synthesis method. The present invention is characterized in that agglomeration preventing particles having a larger particle diameter than the base particles are mixed in a smaller amount with the base particles, and the surface of the base particles is coated with polycrystalline diamond while moving the base particles.

Since the vapor phase synthesis method of diamond is known from the above-mentioned documents and the like, it will not be described in detail.

[Action]

As a composite diamond abrasive grain for precision polishing, even if any one of the above conditions is missing, a sufficient function cannot be achieved.

That is, if the particle diameter of the composite diamond abrasive grains is less than 0.1 μm, it is extremely difficult to handle as abrasive grains, and if it exceeds 10 μm, the material to be polished tends to be scratched by the abrasive grains and is unsuitable for precision polishing. It is. If the composite diamond abrasive has an aspect ratio (major axis / minor axis ratio) of more than 3, stress concentration will occur during polishing, and the polycrystalline diamond layer will be easily damaged or peeled off. It is easy to be scratched.

In order to reduce the aspect ratio of the abrasive grains to 3 or less as described above, it is necessary that the particles be manufactured using the method of the present invention and that the aspect ratio of the base particles be 1 to 4, preferably 1 to 3.

If the layer thickness of the polycrystalline diamond covering the base particles is less than 0.1 times the diameter of the base particles, the properties as diamond cannot be exhibited. There is no particular upper limit on the layer thickness, but if the layer thickness is too large, it is difficult to manufacture and individual particles tend to be large. Also, the ratio of the thickest part / thintest part of the layer thickness of the polycrystalline diamond is set to 1 to 2 when the ratio exceeds 2, polishing is performed in the same manner as when the aspect ratio of the composite diamond abrasive exceeds 3. This is because stress concentration sometimes occurs, causing breakage or peeling of the polycrystalline diamond layer and scratching the material to be polished.

The method of the present invention is particularly effective for limiting the ratio of the thickest part / thintest part of the layer thickness of polycrystalline diamond to the above range.

The individual crystal grain size of the polycrystalline diamond coated with the base particles is set to 2 μm or less, because if the crystal grain size exceeds 2 μm, a good processed surface cannot be obtained. The processing accuracy largely depends on the diameter of each unit particle constituting the polycrystalline diamond.

Such control of the crystal grain size can be performed by the methods described in Japanese Patent Application Nos. 63-139143 and 63-148631, etc. In addition, as a base particle, a single crystal of diamond or cubic boron nitride is used. It is desirable not to use crystals. On these substrate particles, one large diamond single crystal grows due to epitaxial growth, or the number of nuclei generated is small even if it does not become one large single crystal, and individual diamond particles are likely to grow large. It is. Therefore,
Preferred substrate particles include ceramics or heat-resistant metals such as Mo, W, Si, WC, SiC, Si ₃ N ₄ , and Al ₂ O ₃ .

In addition, according to the method of the present invention, diamond is deposited and coated while moving the base particles together with particles much larger than the base particles. Since the individual base particles are separated into individual base particles, the surfaces of the individual base particles can be uniformly coated with diamond, and composite diamond abrasive grains satisfying the above-mentioned conditions are produced.

In the present method, as a method of moving the base particles together with the aggregation preventing particles, in addition to the method of vibrating the particle container described in the above-mentioned publication, the substrate particles were put in the particle container 3 in the reaction container 2 as shown in FIG. A method of stirring the base particles 1 with the stirring blade 4,
As shown in FIG. 2, there are a method of rotating the reaction vessel 2 itself containing the base particles 1, and a method of flowing the base particles 1 with a raw material gas blown into the reaction vessel 2 as shown in FIG.

〔Example〕

Example 1 A particle container 3 having a diameter of 50 mm was prepared using the manufacturing apparatus shown in FIG.
Then, 1 g of spherical SiC having an average particle diameter of 2 μm as base particles 1 and 0.2 g of SiC having a particle diameter of 100 μm as particles for preventing aggregation were added, and the stirring blade 4 was rotated at 12 rpm. In this state, H ₂ : CH
The pressure in the reaction vessel 2 was maintained at 100 torr while the raw material gas obtained by mixing ₄ in a volume ratio of 100: 2 at 200 SCCM, and the temperature of the W filament 5 was maintained at 2200 ° C. for 100 hours.

As a result, composite diamond particles were obtained in which all the surfaces of all the base particles 1 were covered with polycrystalline diamond.

The particle size of the composite diamond particles was 3.0 to 3.5 μm (3.2 μm on average), and the aspect ratio was 1 to 1.4.
The layer thickness of the polycrystalline diamond is an average of the base particle diameter of 0.3.
Times, and the ratio of the thickest part / thinnest part of the layer thickness is 1.2 or less,
The crystal grain sizes of the polycrystalline diamonds were all about 0.5 μm or less.

The resulting composite diamond particles were used as abrasive grains, and when SKD11 copper as a material to be polished was polished, a surface roughness of 0.003 μmRmax was obtained. For precision polishing using commercially available # 5000 diamond abrasive grains (particle size 0 to 3 μm) performed for comparison, surface roughness
It was 0.01 μm Rmax. The polishing was performed by a loose abrasive method.

Example 2 Using the manufacturing apparatus shown in FIG.
5 g of W powder base particles 1 having an average particle diameter of 0.6 μm and W
0.5 g of the particles were placed. From below, H ₂ : C ₂ H ₅ OH: Ar was passed through a gas dispersion plate 7 fixed to the lower part of the reaction vessel 2 to give a volume ratio of 100: 2:
The raw material gas mixed at 50 was flowed at 200 SCCM, the pressure in the reaction vessel 2 was kept at 50 torr, and the microwave generator 6 was kept for 100 hours while giving a microwave of frequency 2.45 MHz at a power of 300 W. Note that a high frequency generator may be used instead of the microwave generator 6.

As a result, composite diamond particles were obtained in which all the surfaces of all the base particles 1 were covered with polycrystalline diamond.
The particle diameter of the composite diamond particles was 0.73 to 0.77 μm (average 0.74 μm), and the aspect ratio was 1 to 2.
The layer thickness of the polycrystalline diamond is 0.12 on average of the base particle diameter.
Times, and the ratio of the thickest part / thinnest part of the layer thickness is 1.2 or less,
The crystal grain sizes of the polycrystalline diamonds were all about 0.2 μm or less.

Using the obtained composite diamond particles as abrasive grains, 18Ni marage copper as a material to be polished was polished in the same manner as in Example 1 to obtain a surface roughness of 0.002 μmRmax.

〔The invention's effect〕

According to the present invention, it is possible to provide a composite diamond abrasive grain having a condition capable of sufficiently functioning as an abrasive grain for precision polishing of a precision machine component, an optical component, or the like, which has increasingly severe processing accuracy.

[Brief description of the drawings]

1 to 3 are schematic diagrams each showing a specific example of an apparatus for performing the method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Base particle 2 ... Reaction container 3 ... Particle container 4 ... Stirring blade 5 ... Filament 6 ... Microwave or high frequency generator 7 ... Gas dispersion plate

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Claims (2)

(57) [Claims] 1. A method for producing composite diamond abrasive grains for precision polishing, wherein polycrystalline diamond is coated on the surface of heat-resistant base particles by a vapor phase synthesis method, wherein the base particles made of ceramics or heat-resistant metal have a particle size A method for producing a composite diamond abrasive grain for precision polishing as described above, wherein a small amount of agglomeration preventing particles larger than the base particles is mixed with the base particles, and the surface is coated with polycrystalline diamond while moving the base particles. . 2. The obtained composite diamond abrasive grains for precision polishing have a particle size of 0.1 to 10 μm and an aspect ratio of 1 to 3, and the thickness of the polycrystalline diamond coating the abrasive grains is 0.1% of the diameter of the base particles. 2. The polycrystalline diamond according to claim 1, wherein the ratio of the thickest part / the thinnest part of the layer thickness is from 1 to 10 times and the thickness of each layer of the polycrystalline diamond is 2 μm or less. A method for producing composite diamond abrasive grains for precision polishing.