JP2006055961A - Method and apparatus for machining axially symmetric aspheric surface by surface grinding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for machining an axially symmetric aspheric surface of a die for press-forming glass by means of a surface grinding machine, wherein the die highly precisely and efficiently manufactures a large size axially symmetrical aspheric lens not smaller than 50 mm in diameter, and an apparatus therefor. <P>SOLUTION: In this method, the axially symmetric aspheric surface is ground by means of a surface grinding machine by turning a resinoid bond diamond grinding wheel 2 about a horizontal axis. The rotation of a workpiece W for producing the axially symmetric surface is carried out by turning a rotary table 4 arranged on the work table 3 of the surface grinding machine about a vertical rotation axis. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  Axisymmetric aspherical surface machining by a surface grinding machine capable of machining an axisymmetric aspherical lens, a mirror, or a mold for manufacturing the same, which is expected to be developed as an optical component, with high accuracy and high efficiency. The present invention relates to a method and an apparatus.

  Axisymmetric aspherical lenses or mirrors have recently been expected to be developed as optical components because of their absence of aberrations. The current axisymmetric aspherical lens is mainly made of plastic using a ground metal mold, rather than directly grinding glass. This is because a soft metal that can be easily processed as a mold material can be used, and a wide range of lenses having a diameter of 0.1 mm to 100 mm or more can be easily mass-produced by injection molding. However, plastic lenses have weak points such as large thermal deformation, large deterioration due to environment and aging, and easy wrinkling.

  Therefore, a glass lens excellent in heat resistance and durability is required as a highly accurate optical component. There is a glass press molding method using a mold to mass-produce a glass axisymmetric aspherical lens. However, since molding is performed by heating hard glass to a high temperature, the mold material is heat resistant and resistant like cemented carbide and ceramics. A material having both wear characteristics is required. However, since such materials cannot be processed by ordinary cutting because of their high hardness, various grinding methods have been tried.

  For example, in Patent Document 1, although the type of the grindstone is not specified, it is described that the grinding streak is reduced by controlling the feeding direction of the rotating grindstone, and the accuracy degradation due to mirror finishing such as polishing is suppressed. ing.

  By the way, generally, the shape accuracy required for the glass lens is 1 μm or less, and the surface roughness is 10 nm Rz or less. In the above glass press molding, the surface state is transferred to the lens as it is, so that the mold must have the same shape accuracy as the lens. In glass press molding, deformation occurs due to thermal contraction when a glass lens molded by heating is cooled. Accordingly, it is necessary to design and manufacture the lens mold taking this deformation into consideration, and the processing accuracy is required to be one digit lower than the lens shape accuracy, that is, 0.1 μm.

However, because the mold material is a high hardness material as described above,
a) A conventional axially symmetric aspherical surface processing machine can only deal with small workpieces, and cannot perform high-precision processing of a large axisymmetric aspherical surface having a diameter of 50 mm or more, for example.
b) In general grinding processing, the surface roughness required for the lens cannot be obtained, and a polishing process using loose abrasive grains such as lapping with a polishing liquid is required. Increases significantly. This becomes more conspicuous as the mold size increases.
There are problems such as.

  Therefore, most of the axisymmetric aspherical lenses that are currently commercialized by glass press molding have a diameter of 5 mm or less, and the processing process of a large axisymmetric aspherical lens mold or a glass of a large axisymmetric aspherical lens. Manufacture and mass production by press molding have not been realized. For this reason, the current large-scale axisymmetric aspherical lens is not a glass press molding but a method that directly grinds and polishes glass one by one, so it requires a lot of equipment for mass production, and many It takes time and money.

  The large-scale axisymmetric aspherical processing technology for high-hardness materials leads to the production of not only lens molds but also axisymmetric aspherical mirrors, so it is a technology that is also desired from the optical equipment of reflective optics. From the above problems, those having a diameter of 50 mm or more have not been put into practical use.

The present inventors previously proposed a grinding method for non-axisymmetric aspherical surfaces and disclosed in Patent Document 2. However, machining of an axially symmetric aspherical surface is possible by this machining method. However, due to differences in positioning accuracy between the horizontal and longitudinal directions of the surface grinder and differences in rigidity between the longitudinal and lateral directions of the surface grinder itself and the grindstone, it is not possible to make the workpiece completely axisymmetric. It was difficult.
Japanese Patent No. 3236876 JP 2003-260646 A

  The present invention eliminates the above-mentioned problems and enables the production of a large axisymmetric aspherical lens having a diameter of 50 mm or more, which is capable of producing an axisymmetric aspherical surface by a surface grinder of a high-precision and high-efficiency glass press molding die. It aims at realizing the processing method and apparatus.

  The present invention relates to an axisymmetric aspherical surface processing method using a surface grinder that rotates a resinoid bond diamond grindstone around a horizontal axis to grind an axially asymmetric aspheric surface. A method of processing an axially symmetric aspherical surface by a surface grinder, wherein the rotating table provided on the table of the surface grinder is rotated around a rotation axis in the vertical direction, preferably the rotating table A method of processing an axisymmetric aspherical surface by the surface grinder having a rotation speed of 50 to 500 revolutions per minute, or by the surface grinder having a rotation axis of the rotary table inclined with respect to the vertical direction. An axisymmetric aspherical processing method, wherein the resinoid bond diamond grindstone is orthogonal to or parallel to the rotational direction of the rotary table on which the workpiece is mounted. That the feed direction, and a vertical incision is moved in the direction the axisymmetric aspherical surface processing method by a plane grinder performed.

  Further, the present invention provides a surface grinder characterized in that a rotary table is provided on a table of a surface grinder having a resinoid bond diamond grindstone mounted on a horizontal axis and the workpiece is mounted and rotated about a vertical rotation axis. An axisymmetric aspherical processing device according to the above, preferably an axially symmetric aspherical processing device by the above-mentioned surface grinding machine in which the rotary table is rotatably supported by a precision bearing such as a hydrostatic fluid bearing or the like. It is an axisymmetric aspherical surface processing apparatus using the above-mentioned surface grinder having an inclination mechanism for inclining the rotation axis of the rotary table with respect to the vertical direction.

  According to the present invention, a high-precision, high-efficiency large-size axisymmetric aspherical surface of a high-hardness material is ground using a surface grinder, and as a result, for large-sized glass press molding with excellent optical performance. Molds, glass lenses, and mirrors can be mass-produced at low cost, and the excellent effect is achieved in that cost reduction and high performance of optical devices are realized.

  Most conventional axisymmetric aspherical processing machines rotate a small-diameter grindstone at a high speed, so that the rigidity of the processing machine is low and the influence of wear on the grindstone is large.

  In addition, the conventional axisymmetric aspherical processing machines are mostly lathe types in which the rotation axis of the workpiece is perpendicular to the gravity, that is, the horizontal direction, and even a slight eccentricity on the rotary table (chuck) on which the workpiece is mounted. If there is, fluctuations in rotational power occur when the center of gravity moves up and down, which increases rotational runout. This phenomenon is more prominent when a heavy object such as a large mold is attached.

In the present invention, these problems are addressed by the following means, and a large-scale axisymmetric aspherical surface processing is made possible.
a) A surface grinder is used as a processing machine. The surface grinder has a high rigidity of the main body and can sufficiently handle grinding of large workpieces. In the case of a conventional axisymmetric aspherical processing machine, the diameter of the grinding wheel used was about 1 to 60 mm in diameter, but in the surface grinding machine, it is as large as 100 to 1000 mm, and the grinding stone surface area is more than 100 times different. The influence of wear is extremely small.
b) On a normal table of a surface grinder, a rotary table that rotates around a vertical rotation axis is provided. Since the direction of gravity and the direction of the rotation axis of the rotary table are substantially parallel, the above-described rotational shake is unlikely to occur.

  Further, since this rotary table can be attached to a normal table with a fixing means for fixing the workpiece, it can be easily attached and detached, and a rotary table having different specifications can be selected and used according to the processing content.

  For this reason, the present invention is particularly effective for large-scale axisymmetric aspherical processing, and of course it can be used in a diameter range of 10 to 50 mm. Suitable for mold processing.

  Further, the difference in machining accuracy and rigidity depending on the direction which has been a problem when the axisymmetric aspherical machining is performed by the machining method in the above-mentioned Patent Document 2, the rotation of the workpiece to be axisymmetric is performed on a conventional table. The problem was solved by using the rotary table provided in, and a complete axisymmetric shape was obtained.

  Furthermore, by using a resinoid bond diamond grindstone that is easy to obtain a mirror surface as a grindstone, the polishing process that occupies much of the processing time and processing cost in the conventional processing method can be omitted or greatly reduced, The efficiency of large-scale axisymmetric aspherical machining can be greatly improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a conceptual diagram showing a surface grinding machine according to the present invention. If the left-right direction is the X-axis, the front-rear direction is the Y-axis, and the vertical direction is the Z-axis, 1 is the column, 2 is the Z direction along the column 1 3 is a table, W is a workpiece attached to the upper surface of the table 3.

  The table 3 can be moved in both X and Y directions. Parallel grinding is used when the table 3 is moved in the Y direction while keeping the X direction constant. The case where the table 3 is moved in the X direction and the grinding wheel is cut in the Z direction at the same time to perform grinding is referred to as cross grinding. Incidentally, the Z direction is the vertical direction of the grindstone.

  FIG. 2 is an explanatory view showing a main part of the axially symmetric aspherical surface processing apparatus of the present invention, and 4 is a rotary table provided on the table 3. a is the rotational direction of the grindstone 2, and b is the rotational direction of the rotary table 4. Although not specifically shown, the position of the rotation axis of the grindstone 2 is controlled in the Z direction and the position of the table 3 is controlled in both the X and Y directions by a numerical control device built in the surface grinder. The number of rotations of 4 is controlled to perform grinding.

  In the present invention, the grindstone 2 is rotated around a horizontal axis parallel to the Y axis, like a normal surface grinder. As the grindstone 2, a resinoid bond diamond grindstone is used. The reason is that when the workpiece is a cemented carbide mold, it cannot be ground with a general grindstone. The resinoid bond diamond grindstone may be used with coarse and finish grinding using a particle size number smaller than # 1000, but may be finer than # 1000 only for finish grinding. Further, the resinoid bond diamond grindstone may be a porous resinoid bond diamond grindstone having pores in the bond or a non-porous resinoid bond diamond grindstone.

  For the truing dressing of the grindstone 2, for example, a stainless roll method may be used, and a stainless steel roll 5 may be used to form the outer periphery in an arc shape as shown in FIG. P1 is the locus of the grindstone 2 during dressing.

  FIG. 4 is an explanatory diagram when grinding is performed using the grindstone 2 of FIG. 3. When the grinding wheel 2 is moved as shown by the path P2, if the outer peripheral profile is circular, the cusp remaining at the boundary of the grinding groove does not protrude and mirror processing is easy, and a large area on the side surface of the grinding wheel is ground. Efficient because it is used for

  In the present invention, the workpiece is rotated in order to make the machining surface axially symmetric by rotating the rotary table 4 provided on the table 3 around the vertical rotation axis. The rotation of the rotary table by a rotation mechanism such as a motor (not shown) is 50 to 500 rotations per minute. The range of the number of rotations was determined by experiments under various processing conditions. Below 50 rotations, the effect of rotating does not appear. Further, when the rotation is 500 rotations or more, the rotation becomes unstable and the processing accuracy cannot be obtained.

  As described above, the surface accuracy of the lens or mold is on the order of 1 μm or less or 0.1 μm, and it is difficult to maintain this accuracy with a general rotating mechanism. Alternatively, it is desirable to use a precision bearing such as a liquid hydrostatic bearing or a precision ball bearing.

  FIG. 5 is an explanatory view showing parallel grinding, in which (a) is a plan view and (b) is a side view. Grinding is performed while moving the table 3 in the Y direction with the X direction being constant, and then sequentially feeding in the X direction for grinding. FIG. 6 is an explanatory view showing cross grinding, where (a) is a plan view and (b) is a front view. Grinding is performed while moving the table 3 in the X direction while keeping the Y direction constant, and the grinding is performed in the Y direction.

In either case, the movement trajectory of the grindstone 2 is an expression representing the target axisymmetric aspheric surface.
f (x, y, z) = 0
To determine the coordinate value at each point of the machining symmetric cross-section passing through the center of the workpiece W, then determine the tool (grindstone) position coordinate value for each point, and then arrange the tool position coordinate values according to the machining direction, The position control is performed using these processing data.

  The rotation axis of the rotary table 4 is most preferably parallel to the Z direction on the rotary mechanism, but by providing a tilting mechanism 6 between the table 3 and the rotary table 4 as shown in FIG. The rotary table 4 can also be inclined by an angle θ with respect to the Z direction. By inclining, chips discharged by grinding and cooling water are smoothly discharged from the grinding grooves, and the processing efficiency is improved. Further, by performing the inclination in the middle of processing, the side surface of the grindstone 2 that has not been used so far comes into contact with the workpiece W, and the grindstone 2 can be effectively used. For this purpose, θ is at most within 45 °.

  Next, specific examples of the present invention will be described.

  Based on the contents of the present invention, a CNC (computer numerical control) forming surface grinder is used, the rotary table is mounted on the table, the rotation axis thereof is parallel to the cutting direction (Z direction) of the grindstone, and parallel to the direction of gravity. A concave axisymmetric aspherical shape was ground while controlling the grinding wheel position and the table position with a numerical control device.

  The workpiece was a cemented carbide consisting of tungsten carbide fine particles with an outer diameter of 66 mm and a small amount of cobalt, and was fixed on a rotary table with wax.

  The grindstone is a rough and final grind using a porous resinoid bond diamond grindstone with an outer diameter of 200 mm, width of 20 mm, and particle size number # 1500. It was arcuate. Table 1 shows the truing dressing conditions.

  Table 2 shows rough grinding conditions, and Table 3 shows finish grinding conditions.

  The method of feeding the grindstone is cross-grinding that feeds the grindstone from the outer periphery of the rotating workpiece toward the center of the rotation axis of the workpiece in the horizontal direction of the table (X direction), or the grindstone from the outer periphery of the workpiece to the rotation axis of the workpiece. Parallel grinding is sent in the front-rear direction (Y direction) toward the center, and the movement in the left-right direction (X) and the up-down direction (Z) is numerically controlled so that the contact point between the grindstone and the workpiece draws the target aspheric shape went. The wobbling and rotation speed of the grindstone were constantly monitored, and truing dressing was performed by the stainless roll method every time the grinding resistance increased due to clogging of the grindstone. Chemical solution type grinding fluid was supplied for lubrication and cooling during truing and dressing and during grinding.

  The results of the above axially symmetric aspherical processing are as shown in Table 4.

  In Table 4, the shape accuracy of the processed surface is the cross-sectional shape from the processed outer periphery of the axisymmetric aspherical surface to the outer periphery of the processed surface of the body surface using the non-contact type three-dimensional shape measuring device. It shows the deviation in the height direction from the target shape. The surface roughness of the processed surface is an average of the maximum height roughness measured at any five locations on the workpiece with a non-contact three-dimensional surface roughness meter. The shape accuracy was less than 1 μm, and the surface roughness was 50 nm Rz or less. According to the present invention, an axisymmetric aspherical surface having high accuracy and an excellent mirror surface could be easily obtained. The processing time was 16 hours or less for a grinding amount of 100 μm, and a large axisymmetric aspheric shape could be processed with high efficiency.

 As shown in the tables, 800m / min and 1300m / min are optimum for the peripheral speed of the grindstone in truing dressing and in the grinding process, but both are in the range of 800-1300m / min. Is preferable.

It is a conceptual diagram which shows the surface grinder concerning this invention. It is explanatory drawing which shows the principal part of the axially symmetric aspherical surface processing apparatus of this invention. It is explanatory drawing which shows the truing dressing of the grindstone in this invention. It is explanatory drawing in the case of grinding using the grindstone of FIG. It is explanatory drawing which shows the parallel grinding in this invention, (a) is a top view, (b) is a side view. It is explanatory drawing which shows the cross grinding in this invention, (a) is a top view, (b) is a front view. It is explanatory drawing of the principal part which shows the example which inclines a rotary table in this invention.

Explanation of symbols

1 Column 2 Grindstone (Resinoid Bond Diamond Grindstone)
3 Table 4 Rotary table 5 Stainless steel roll 6 Inclination mechanism W Workpiece P1, P2 Grinding wheel trajectory

Claims (7)

  A method of processing an axisymmetric aspheric surface by a surface grinder that rotates a resinoid bond diamond grindstone about a horizontal axis to grind an axisymmetric aspheric surface, wherein the surface grinder rotates the workpiece to be axisymmetric A method of processing an axisymmetric aspherical surface by a surface grinder, wherein the rotating table provided on the table is rotated around a vertical rotation axis.   The method of processing an axisymmetric aspherical surface by a surface grinder according to claim 1, wherein the rotation of the rotary table is 50 to 500 rotations per minute.   The method of processing an axisymmetric aspherical surface by a surface grinder according to claim 1 or 2, wherein a rotation axis of the rotary table is inclined with respect to a vertical direction.   The surface grinding machine according to any one of claims 1 to 3, wherein the resinoid bond diamond grindstone is moved by being moved in a feed direction orthogonal to or parallel to a horizontal direction of a table to which a rotary table is attached, and in a vertical cutting direction. Axisymmetric aspherical processing method.   A rotary table (4) for attaching a workpiece (W) and rotating it around a vertical rotation axis on a table (3) of a surface grinder with a resinoid bond diamond grinding wheel (2) attached to a horizontal axis An axisymmetric aspherical surface processing apparatus using a surface grinder characterized by   6. An axisymmetric aspherical surface processing apparatus using a surface grinder according to claim 5, wherein the rotary table (4) is rotatably supported by a precision bearing such as a hydrostatic fluid bearing.   The axisymmetric aspherical surface processing apparatus by a surface grinder according to claim 5 or 6, further comprising an inclination mechanism (6) for inclining a rotation axis of the rotary table (4) with respect to a vertical direction.

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