JPH0558863B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for polishing curved surfaces such as lenses of optical systems and reflecting mirrors, and in particular provides a method for polishing curved surfaces that can be applied to aspherical portions of materials to be polished. <Prior Art> Methods for manufacturing curved surfaces such as lenses and reflecting mirrors of optical systems are classified into deformation processing methods, removal processing methods, and additive processing methods. Among these methods, the removal method is often used to produce precision aspherical surfaces, and the deformation method also uses a mold, so the mold must be processed into an aspherical surface. Various methods have been tried to produce an aspherical surface by the removal method, but the one that is industrially useful is a method using a cam tracing mechanism. This method using a cam tracing mechanism uses various combinations of cams to perform machining while controlling the movement of the tool.Recently, a method of controlling the movement of the tool using an electronic control device has also been put into practical use. A method for polishing curved surfaces such as aspherical surfaces produced in this way is to use a grindstone in which a large number of thin plate-shaped pellets are attached with adhesive etc. to the arcuate surface of a convex or concave rotary plate. well known. <Problems to be Solved by the Invention> However, the removal method in which a large number of pellets are attached to a rotating plate as a grinding wheel and polished with this grinding wheel is extremely labor-intensive and requires a lot of effort. A different grinding wheel must be used for each different radius of curvature of the abrasive material. <Means for Solving the Problems> The present invention has been proposed in view of the above, and includes 30 to 70 vol% of abrasive grains having an average particle diameter of 30 μm or less in a mixture of abrasive grains and a liquid, and The surface of the whetstone is compressed and molded by the adhesive force of the liquid.
forming a mold part corresponding to the curved surface to be processed of the material to be polished, pressing the curved surface to be processed of the material to be polished to the mold part,
The present invention is characterized in that the curved surface of the material to be polished is polished by relative movement between the grindstone and the material to be polished. This whetstone uses the surface tension or adhesive force of the liquid to act as the bonding force between the abrasive grains, so the bonding force is much weaker than that of conventional solid-bonded whetstones. The high machining efficiency at the beginning of polishing is maintained without causing dot-lessing and clogging due to shavings, chips, etc. of the material to be polished. Further, even if the grinding wheel becomes clogged with the material to be polished, the self-dressing action can be promoted by appropriately spraying the mixed liquid to soften the working abrasive grain surface. <Examples> Examples of the present invention will be described below. The grindstone used in the present invention is formed by compressing a mixture of abrasive grains and a liquid and using the adhesive force of the liquid. The above-mentioned abrasive grains include diamond, corundum, emery, garnet, silica, triboli, calcined dolomite, welded alumina, artificial emery, silicon carbide, boron carbide, iron oxide, calcined alumina, chromium oxide, cerium oxide, zirconium oxide, etc. Any abrasive grains that can be used as ordinary abrasive grains may be used. The average particle diameter of the abrasive grains is about 30 μm or less, and the abrasive grains are kept soft by the liquid. On the other hand, the liquid used in the present invention is used to hold the above-mentioned abrasive grains by surface tension or adhesive force, and includes water, alkaline solution, acid solution, aqueous solution of many other salts, oily liquid, magnetic fluid, etc. can be used. Although other types of abrasive grains and liquids are mentioned above, it is desirable to select and use the most effective one depending on the properties of the material to be polished. The above-mentioned abrasive grains and liquid are mixed to form a whetstone, and the abrasive grains in the whetstone are in the range of 30 to 70 vol%, and the optimum ratio for polishing in the present invention is 50 to 70 vol%.
It is 60vol%. Further, when the abrasive grain size is large, the above ratio is preferably increased, and when the abrasive grain diameter is small, it is preferably decreased. Further, when mixing abrasive grains and liquid, the liquid may not be mixed uniformly depending on the types of abrasive grains and liquid and the mixing ratio. If the abrasive grains and liquid are not mixed uniformly, the strength of the grindstone will be uneven, and the grindstone will break starting from the weaker parts, making it impossible to polish stably. Therefore, after mixing the liquid with another liquid (diluent) that is more volatile than the liquid and uniformly mixing it with the abrasive grains, the diluent is removed by reducing pressure or heating.
What is necessary is to uniformly mix the abrasive grains and the liquid in the most desirable state. The diluent mentioned above varies depending on the type of liquid, but examples include low molecular weight hydrocarbons such as hexane and heptane, alcohols such as methanol and ethanol,
Water etc. can be used. As mentioned above, the grindstone used in the present invention is made by filling and mixing abrasive grains and a liquid, and if necessary, a diluent, and then dry or semi-dry molding. It is desirable to compact the abrasive grains by compression molding. Further, in the case of compression molding, pressure may be applied or vibration filling molding may be used supplementarily. The pressure for compression molding is 30Kg/cm2 or ^more , preferably 300Kg/cm2 or more.
Kg/ ^cm2 or more. In the abrasive grains manufactured by compression molding in this way, the adhesive force of the liquid acts as a bond and binds the abrasive grains together, and the abrasive grains are kept soft by the liquid, so the hardness of the abrasive grains is moderate. have When the inventor measured the hardness of a grindstone made by compression molding silicon carbide abrasive grains C#3000 using spindle oil, it was 85 to 85 degrees with a rubber hardness meter and 50 to 80 degrees with a mold hardness meter. . By using the grindstone obtained in this way, the material to be polished can be efficiently polished. In addition, since the abrasive grains of the whetstone are kept soft by the liquid, they are naturally scraped off during processing, resulting in self-dot grinding, which prevents clogging with shavings and swarf of the material to be polished. High processing efficiency is maintained. Further, even if the grinding wheel becomes clogged with the material to be polished, the self-dressing action can be promoted by appropriately spraying the mixed liquid to soften the working abrasive grain surface. In the present invention, a mold portion corresponding to the curved surface of the material to be polished is formed on the surface of the grindstone, which is formed by compressing the mixture of abrasive grains and liquid and molding by the adhesive force of the liquid as described above. This mold part is molded into any shape depending on the shape of the curved surface to be processed. For example, if the curved surface 2 to be processed of the material 1 to be polished is an axially symmetrical arc-shaped convex surface as shown in FIG. 1 or FIG. It is concave. If the whetstone 3 is in the shape of a long flat plate, the mold portion 4 is also made long along the length of the whetstone 3, and if the whetstone 3 is in the shape of a disc, the mold portion 4 is formed in an annular shape. On the other hand, as shown in FIG. 3, if the curved surface 2 to be processed of the material 1 to be polished is a non-axisymmetric arcuate pyramidal convex surface, the mold part 4 of the grinding wheel 3 is also made non-axisymmetric to correspond to the curved surface 2 to be processed. . Further, as shown in FIG. 4, if the curved surface 2 to be processed of the material 1 to be polished is an axially symmetrical arcuate concave surface, the mold portion 4 of the grindstone 3 is also an arcuate convex surface corresponding to the shape. In order to form the mold part 4 of the grinding wheel 3 corresponding to the curved surface 2 of the material to be polished 1 as described above, a mold corresponding to the mold part 4 of the grinding wheel 3 is created in advance, and this mold is used to form the mold part 4 of the grinding wheel 3. There is a press molding method in which the mold portion 4 is formed by pressing the grindstone 3, and a cutting method in which the mold portion 4 is formed by scraping the surface of the grindstone 3 with a diamond cutting tool or the like. The grindstone used in the curved surface polishing method of the present invention compresses a mixture of abrasive grains and liquid and is shaped by the adhesive force of the liquid, so it is soft, easy to press mold, and extremely easy to cut. It is easy and the tools do not wear out. In the curved surface polishing method of the present invention, the material to be polished is pressed against the above-described grindstone, and one or both of the grindstone and the material to be polished are caused to revolve, rotate, or move in a straight line to create a relative movement difference. Polish the material with a whetstone. Specific examples of the present invention will be described below. Diameter 20mmφ, material BK-7, surface curvature radius 18
When a spherical lens that had been ground to a surface roughness of 0.9 μm Rmax using diamond pellets was polished using a grindstone according to the present invention, a finished surface roughness of 0.02 μm Rmax was achieved. Fig. 5 shows the grindstone processing equipment. In FIG. 5, a sample 13 is provided at the tip of the shaft 12 of the pressurizing device 11, and the sample 13 is made to face a grindstone 15 provided on the surface of a rotary disk 14. Before polishing the sample 13, a concave mold portion 15' corresponding to the curved surface 13' of the sample 13 to be processed was formed in an annular shape on the surface of the grindstone 15 using the NC three-dimensional driving device 17 having the diamond cutting tool 16. The whetstone 15 with the annular mold part 15' formed on its surface in this way is rotated at high speed on the rotary disk 14, and
While rotating the sample 13 with the pressurizing device 11,
The curved surface 13' of No. 3 to be treated was pressed against the mold part 15' and polished. In order to improve the efficiency of polishing sample 13 with the grindstone 15', two stages of polishing were performed: primary polishing and secondary polishing. In the primary polishing, a grindstone with cerium oxide abrasive grains with an average grain size of 9 μm is used to improve the surface roughness.
Finished with Rmax of 0.06μm. In the secondary polishing, a grindstone using cerium oxide abrasive grains with an average grain size of 1 μm was used to achieve a surface roughness of 0.02 μm Rmax. The processing conditions and processing efficiency for primary polishing and secondary polishing are shown in the table below.

[Table] <Effects of the Invention> In summary, according to the present invention, since the material to be polished is polished with a grindstone in which abrasive grains are bonded with liquid, the pressure of the material to be polished effectively acts on the abrasive grains. The processing speed is fast due to the high pressure, and the polishing efficiency can be significantly increased. In addition, since the pressure of the polished material acting on each abrasive grain is small, the finished surface has a good roughness, and since there is no elasticity, there is less occurrence of edge sag, making it a method of high practical value for precision final polishing. Further, since the grindstone used in the present invention is soft and has good moldability, the mold part can be molded in a short time, and the tool does not wear out when molding the mold part. Furthermore, since the grinding wheel used in the present invention does not need to be sintered, it can be easily manufactured and provided at low cost.Moreover, it compresses a mixture of abrasive grains and liquid and is shaped by the adhesive force of the liquid. This makes it possible to use high pressure and high speed, and the machining efficiency is high, allowing the material to be polished to be polished with high precision in a short time. Furthermore, since polishing is performed with the surface of the material to be polished and the mold part of the grindstone in surface contact, pressure is applied uniformly to the surface to be polished, and no distortion occurs during polishing, making it practical. It will be of high value.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a molded state of the grindstone used in the present invention, FIG. 2 is a partially cutaway perspective view of the same as above,
FIG. 3 is a perspective view of another embodiment of the grindstone in a molded state;
FIG. 4 is a longitudinal sectional view of another embodiment of the grindstone in a molded state, and FIG. 5 is a schematic diagram of the processing device used in the embodiment.

Claims (1)

[Claims] 1 The average particle size is 30μm in the mixture of abrasive grains and liquid.
The following abrasive grains are contained in an amount of 30 to 70 vol%, the mixture is compressed, and a mold part corresponding to the curved surface of the material to be polished is formed on the surface of the grindstone, which is molded by the adhesive force of the liquid. A method for polishing a curved surface, characterized in that the curved surface to be treated is pressed against the mold part, and the curved surface to be treated of the material to be polished is polished by relative movement between the grindstone and the material to be polished.