JP2004283972A - Grinding wheel and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grinding wheel that contains aluminum and silica and can work a ground object to provide successful surface roughness while supplying colloidal silica liquid, and its manufacturing method. <P>SOLUTION: Aluminum and silica are contained in a bonding material for bonding abrasive grains, and contents of silica in bonding material to the total weight of aluminum and silica are set less than 15 wt%. Since contents of aluminum are large, much colloidal silica of a reverse electrical characteristic adheres to the grinding wheel, and the ground object can be worked to provide the successful surface roughness. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a grinding wheel used for grinding an optical element such as a lens or a prism made of a brittle material such as glass, and a method of manufacturing the grinding wheel.
[0002]
[Prior art]
As a conventional method of grinding an optical element such as a lens or a prism, a grinding tool (a grinding wheel) containing aluminum and silicon as a bonding material for bonding abrasive grains is used, and processing is performed while supplying colloidal silica liquid during grinding. It is disclosed to do so (for example, see Patent Document 1).
[0003]
In this conventional grinding method, while the aluminum surface layer in the grinding wheel is positively charged, the negatively charged silica ultrafine particles are adsorbed, and a film of gelled silica ultrafine particles adheres to the grinding tool. Is what you do. In addition to performing the grinding process using the diamond abrasive grains of the grinding wheel, the adsorbed silica particles exert a polishing action, so that it is possible to simultaneously perform mirror polishing. As the grinding wheel to be used, since aluminum alone has a high extensibility of the material and cannot secure a grinding wheel structure, silicon containing low ductility is contained in order to secure strength and abrasion resistance as a grinding wheel.
[0004]
[Patent Document 1]
JP, 2001-315061, A
[Problems to be solved by the invention]
As described above, the conventional processing method of simultaneously performing grinding and polishing utilizes the zeta potential of the aluminum used for the grinding wheel and the colloidal silica liquid supplied during the processing. However, the grinding wheel used has the following problems since it contains silicon at a high weight ratio of 35 to 15% in the binder for binding the abrasive grains.
[0006]
With a high silicon content as described above, the amount of elastic deformation of the binder due to the grinding force is reduced, and the cutting depth of diamond abrasive grains given to the workpiece is increased, so that the surface roughness of the workpiece is Worsens. In addition, since the cutting depth of the diamond abrasive grains increases and the surface roughness deteriorates, it becomes difficult to make the surface of the object to be mirror-finished even by polishing with silica fine particles adhering to the grindstone. That is, when the roughness of the ground surface by diamond abrasive grains is poor, it is difficult to obtain high specularity due to the poor initial roughness even if the polishing action by the silica fine particles is added.
[0007]
In particular, since the content of silicon is large, the content of aluminum is relatively reduced, so that a region exhibiting a positive zeta potential, which is a whetstone surface potential, is narrowed, and the adhesion of silica fine particles is reduced. As a result, the polishing action is reduced. That is, the area of aluminum exhibiting a positive zeta potential in the colloidal silica liquid is narrowed, and the amount of silica particles having a negative potential adhering to aluminum is reduced, so that the polishing action is reduced. For this reason, in the above-described conventional method, the roughness remains at the level of Ra of 0.043 μm. At this level, the performance remains close to the level before the polishing step obtained by the existing lapping process. Therefore, when a smaller surface roughness is required, there is a problem that a further polishing step is required.
[0008]
In addition, since small surface roughness is often required in high-mix low-volume production, the addition of such a further polishing step has a disadvantage in production cost in low-volume production.
[0009]
The present invention has been made in consideration of such a conventional problem, and in a process of performing grinding while supplying a colloidal silica liquid using a grinding wheel containing aluminum and silicon, the object to be ground is excellent. It is an object of the present invention to provide a grinding wheel capable of processing to a high surface roughness. Further, another object of the present invention is to provide a manufacturing method capable of favorably manufacturing the grinding wheel.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the grinding wheel according to the first aspect of the present invention mainly includes aluminum and silicon in a binder for binding abrasive grains, and the binder in the binder with respect to the total weight of aluminum and silicon. The silicon content is less than 15% by weight.
[0011]
According to the first aspect of the present invention, since the content of silicon in the binder is less than 15% by weight, the region of aluminum exhibiting a positive zeta potential in the colloidal silica liquid is widened and adheres to aluminum. The amount of silica particles having a negative potential increases, and the polishing action increases. In addition, since the extensibility of aluminum is suppressed due to the silicon content and the elastic deformation of the binder accompanying the grinding force acts effectively, the cutting depth of the abrasive grains in the workpiece can be reduced, and abundant Good surface roughness can be obtained by the polishing action of the silica particles.
[0012]
According to a second aspect of the present invention, there is provided the grinding wheel according to the first aspect, wherein the grinding wheel is formed by sintering a mixed powder of abrasive grains, aluminum powder, and silicon powder.
[0013]
The powder to be combined by sintering is aluminum, and the aluminum powder itself is in a state of being joined by welding only at the contacting portions. The abrasive and silicon are interspersed between the aluminum bonded in this manner. For this reason, the abrasive grains fall off with the wear of the grinding wheel, and new abrasive grains can easily appear. Thereby, excellent grinding efficiency can be obtained. In addition, since it is a powder, it is easy to adjust the mixing ratio according to the object to be ground, and it is easy to cope with the production of various kinds and small quantities.
[0014]
The method for manufacturing a grinding wheel according to the third aspect of the present invention includes a step of mixing abrasive grains, an aluminum powder and a silicon powder, a step of press-forming the mixed powder, and a step of pressing the formed product. And sintering.
[0015]
According to the third aspect of the present invention, by applying pressure during sintering, the aluminum powders come into strong contact with each other, and a physical external force is also applied to the oxide film covering the outer periphery of the aluminum powder in addition to heat. Therefore, the oxide film is easily melted, and the heating temperature can be reduced accordingly. Thereby, the thermal influence on the abrasive grains can be reduced, and a good grinding wheel can be manufactured.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The grinding wheel of the present invention has a composition containing aluminum and silicon as a binder for binding abrasive grains such as diamond abrasive grains. Further, when the object to be ground is ground by the grinding wheel, the processing is performed while supplying the colloidal silica liquid. In the present invention, a mixture of aluminum powder and silicon powder is used as a raw material as a binder holding abrasive grains. In this case, the content of silicon in the binder is based on the total weight of aluminum and silicon. By mixing the two so that the weight ratio is less than 15%, it is possible to exhibit the structure and strength characteristics that can be used as a grindstone while making use of the ductility of aluminum. The silicon content can be appropriately adjusted to any value of less than 15% depending on the purpose of use of the grinding wheel.
[0017]
The grinding wheel in this embodiment is obtained by mixing diamond SD # 600 with abrasive grains at a concentration of 100, and using commercially available aluminum powder and high-purity silicon powder (impurities other than silicon 100 ppm or less) as a binder for supporting the same. Was used. This aluminum powder contains a small amount of silicon (x% by weight) and a small amount of metal impurities (y% by weight) in addition to aluminum.
[0018]
The inventors have determined that the weight ratio of aluminum to silicon in the binder is 99.85: 0.15, 99.5: 0.5, 95: 5, 90:10, 85:15, 80:20. As described above, six types of mixed powders obtained by mixing the above two powders were prepared, and the performance was evaluated by actual grinding.
[0019]
Assuming that the weight of the aluminum powder to be mixed is A and the weight of the silicon powder is B, the weight of aluminum in the binder is (100-xy) A / 100, and the weight of silicon is B + xA / 100. Therefore, to obtain a binder having a weight ratio of aluminum to silicon of, for example, 95: 5, A and B are selected so that (100-xy) A / 100: B + xA / 100 = 95: 5. A mixed powder is produced. However, since the values of x and y are extremely small, there is no problem in actually producing a mixed powder with A: B = 95: 5. Since the aluminum powder used in the present embodiment contains 0.15% by weight of silicon, it is necessary to obtain a binder having a weight ratio of aluminum to silicon of 99.85: 0.15. Only aluminum powder was used without using silicon powder.
[0020]
In mixing the powders, a mixed powder in a powder state different from an alloy produced by melting silicon in aluminum by mixing and mixing at a weight ratio in the powder state was used. The main purpose of using the mixed powder is to improve the surface roughness of the object to be ground in addition to being able to easily adjust the mixing ratio, and it is necessary to further improve the strength of the binder by alloying It is because there is no sex.
[0021]
In the production of the grinding wheel composed of the above-mentioned six types of mixed powder, aluminum and silicon were measured and mixed in respective weight distributions, and further, the diamond abrasive grains of SD # 600 were mixed so as to have a concentration of 100. Then, a mold for obtaining a desired shape was filled and molded. The compacting was performed by sintering a material that had been compression-molded (cold-pressed) at room temperature by a press machine while preventing the powder from being oxidized in a hydrogen reducing atmosphere. During heat sintering in a hydrogen reducing atmosphere, a hot press that applies pressure during sintering was used in order to prevent the diffusion of atoms between powders by the oxide film on the aluminum and silicon surfaces. . As a result, it is possible to apply plastic deformation to the powder, whereby sintering can proceed while destroying the oxide film on the surface of the powder. The sintering temperature was set in a range of about 450 to 550 ° C., and a pressure of about 0.7 to 1.5 t / cm ² was applied for sintering and molding.
[0022]
Next, in order to evaluate the performance of the grinding wheel manufactured under the above-described conditions and procedures, spherical grinding is performed on the optical glass material s-BSL7 that is actually commercially available, and the obtained surface roughness and shape are determined. It was measured by Foam Talysurf (manufactured by Taylor Hobson KK). The surface roughness was evaluated as to whether or not a surface roughness close to the polished surface could be obtained by performing processing while supplying colloidal silica liquid to the prepared grinding wheel. It was used as a criterion for evaluating sex.
[0023]
In order to evaluate the wear resistance of the grinding wheel, it is desirable to measure the amount of wear of the grinding wheel, but the roughness of the grinding wheel surface is severe, making it difficult to measure the dimensions. Therefore, it is difficult to specify the processing action point to be the measurement point, so that the actual change in the shape of the workpiece is substituted. In this case, when the shape change of the object to be ground is small, it can be estimated that the amount of wear of the grinding stone formed by grinding the object is small, and it can be sufficiently inferred that the wear resistance of the grinding stone is high.
[0024]
In the actual processing, a spherical surface having a radius of curvature of about 15 mm was formed on a commercially available optical glass material s-BSL7 having a diameter (φ) of 14 mm using each of six types of grindstones. As for the object to be ground, 100 pieces were continuously ground with one kind of grindstone. The difference between the radii of curvature of the spherical shapes obtained at the first and the 100th workpieces was determined as a change in the radius of curvature, and was used as a substitute value for evaluating the wear resistance of the grinding wheel.
[0025]
The spherical grinding process uses an existing spherical surface generating machine (curve generator; CG machine), the rotational speed of the grinding wheel is 10,000 rpm, the rotational speed of the object to be ground is 10 rpm, and the cutting depth during grinding is 0.5 mm / Min., Spark-out time is about 10 seconds, and a 6% colloidal silica liquid (trade name "Snowtex 30", manufactured by Nissan Chemical Industries, Ltd.) having an average particle size of 15 nm with respect to the processing area at the time of grinding. This was performed while supplying the diluted liquid.
[0026]
FIG. 1 shows the results of the evaluation. FIG. 1 shows the results of grinding using the above-mentioned six types of grinding wheels. The horizontal axis shows the mixing ratio of aluminum and silicon for the six types of grinding wheels, and the characteristic curve T consisting of the left vertical axis and the solid line shows The average surface roughness Ra value obtained from the optical glass material s-BSL7, which is the object to be ground, is represented by the characteristic curve S consisting of the right vertical axis and the broken line, and the radius of curvature of the first and 100th objects to be ground The amount of change as a difference is shown. The silicon content in the grindstone binding material increases toward the right on the horizontal axis in the graph, and the compounding ratio of 99.85: 0.15 on the leftmost side indicates the performance of a grinding wheel using commercially available aluminum powder as it is. The rightmost blending ratio of 80:20 indicates a grinding wheel containing silicon at the maximum of 20%.
[0027]
From the graph change in FIG. 1, the surface roughness Ra (shown by the characteristic curve T) obtained as the silicon content increases increases, and conversely, the shape change amount of the workpiece (shown by the characteristic curve S). Is smaller. Particularly, in the case of a grindstone (99.85% by weight of aluminum, 0.15% by weight of silicon) using a commercially available powder without mixing silicon, the surface roughness Ra becomes the smallest when the surface roughness Ra is 0.02 μm or less, and the high interface property is obtained. Has been demonstrated. However, this whetstone, on the contrary, has the largest change in the shape of the object to be ground at 130 μm or more, indicating that the abrasion resistance is poor. Similarly, in a grindstone having a silicon content of 20% by weight, the change in shape of the object to be ground is as small as just over 50 μm, and the abrasion resistance of the grindstone is high. It is a very large value of 05 μm, and although abrasion resistance can be obtained as in the case of the grinding wheel shown in the prior art, the surface quality is significantly reduced. In particular, in the grinding wheel having a silicon content of 20% by weight, as shown by the characteristic curve S, the amount of change in the radius of curvature of the object to be ground is not so much improved as compared to the grinding wheel having a 15% by weight content. Thus, the obtained surface roughness Ra is greatly increased.
[0028]
The above phenomenon is due to the fact that the low ductility silicon is mixed with aluminum, which is the main component of the binder, to increase the strength of the binder between the particles, and the abrasive grains such as diamond abrasive grains supported by this are firmly held. This is because the amount of cut into the object to be ground increases, and the roughness of the ground surface increases. That is, silicon having low ductility intervenes between aluminum particles having high ductility, while ensuring the ductility of aluminum, silicon acts to suppress the ductility, and the strength as a grinding wheel can be maintained. You can do it. For this reason, the abrasive grains are held more firmly than a grindstone in which the abrasive grains are held only by the bonding material of aluminum, whereby elastic deformation of the abrasive grains sunk into the bonding material due to the grinding force is suppressed, and the cutting depth is accordingly reduced. And the surface roughness increases. In particular, in this embodiment, a mixed powder of aluminum and silicon is used, so that these effects can be easily adjusted by the mixing ratio of the two powders. Furthermore, by performing sintering by hot pressing, a high pressure is applied between the particles in addition to the sintering temperature. I have. As described above, the strength of the binder of the grindstone is increased, the cutting depth of diamond is increased, and the ground surface roughness is increased. Therefore, it is also difficult to make the ground surface of the work to be mirror-finished by the polishing action of silica particles. .
[0029]
When the silicon content increases, the surface area occupied by aluminum in the surface layer of the grindstone decreases, so that the region where the zeta potential, which is the surface potential, of the colloidal silica liquid becomes positive decreases. As a result, the area of the colloidal silica liquid to which the silica particles adhere is reduced, and the polishing effect of the silica particles is also reduced. Here, the aluminum is an aluminum particle having an oxide film observed on the surface layer of the grindstone, and indicates an aluminum particle whose surface is combined with oxygen in the air to form an oxide film. The oxidized aluminum particles exhibit a positive zeta potential in the colloidal silica liquid. Therefore, in order to exert the action of attaching silica particles (fine particles of silicon oxide) exhibiting a negative potential and the polishing action associated therewith, aluminum is preferably used as much as possible. Need to be increased. The silicon powder mixed with aluminum is oxidized and intervenes in the surface layer as silicon oxide. Since this silicon oxide forms a negative surface potential similarly to the silica particles in the colloidal silica liquid, it inhibits the adhesion of the silica particles and reduces the polishing action of the silica particles. However, when the content of aluminum is increased, as described above, the extensibility of the binder is increased and the strength as a grindstone cannot be secured, so that the shape retention (durability) of the workpiece is reduced. For this reason, it is desirable to contain some silicon.
[0030]
From the above, the results shown in FIG. 1 are obtained, and it is understood that it is desirable to adjust the contents of aluminum and silicon according to the usage of the grinding wheel. For example, in the production of lenses, such as digital cameras and optical communication devices, which must be mass-produced, the wear resistance (durability) of the grinding wheel becomes important from the viewpoint of the production cost, in addition to the specularity in the CG process. Therefore, it is desirable to contain silicon at a high ratio as shown in FIG. On the other hand, when special, high-precision and extremely small-volume manufacturing such as microscopes, medical devices, and space development optical devices are required, the polishing process, which is the final process, should be easier than the durability of the grinding wheel in the CG process. In addition, since it is required that an intermediate process requiring dedicated jigs and tools be omitted and high mirror finish is obtained, it is desirable to use a grindstone shown in FIG.
[0031]
In this embodiment, a mixed powder of an aluminum powder and a silicon powder is used as a binder of the grinding wheel, so that each powder is obtained and the mixing of the powder is adjusted according to the purpose of use. This facilitates production of the desired material. Further, a higher effect can be obtained by using a hot press for effectively acting the interparticle bonding during sintering of both powders.
[0032]
It is possible to produce a grindstone containing a small amount of silicon by using not only the mixture of the two powders but also the commercially available aluminum powder as described above. In this case, the durability is inferior, but it can be fully utilized by utilizing it according to the application. Although diamond is used as abrasive grains for grinding optical glass, c-BN (cubic boron nitride) may be used as abrasive grains when the object to be ground is a metal material. .
[0033]
【The invention's effect】
As described above, according to the grinding wheel of the present invention, it is possible to obtain a good surface roughness with respect to an object to be ground, and to have a characteristic flexibly corresponding to the required surface roughness and durability. be able to.
[0034]
ADVANTAGE OF THE INVENTION According to the manufacturing method of the grinding wheel of this invention, the heating temperature of sintering can be reduced, and the thermal influence on an abrasive grain can be reduced.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram of a grinding wheel according to an embodiment of the present invention.

Claims (3)

The bonding material for bonding abrasive grains mainly contains aluminum and silicon, and the content of silicon in the bonding material is less than 15% by weight based on the total weight of aluminum and silicon. Grinding wheel. The grinding wheel according to claim 1, wherein the grinding wheel is formed by sintering a mixed powder of abrasive grains, aluminum powder, and silicon powder. A step of mixing abrasive grains, an aluminum powder and a silicon powder, a step of press-molding the mixed powder, and a step of sintering while pressing the molded product. Manufacturing method of grinding wheel.

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