JP2006089296A - Forming die of optical element and forming machine provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming die of an optical element not only capable of forming a high quality and highly reliable optical element but also capable of manufacturing the die body easily and in high precision. <P>SOLUTION: This forming die of an optical element is for forming an optical element by pressing an optical material, and the die body is constituted of a tungsten carbide sintered body obtained by sintering tungsten carbide without adding a metallic binder, where the particle diameter of the tungsten carbide is set to ≤100 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical element molding die for molding high-precision optical elements such as lenses, prisms, and gratings used in optical equipment, and a molding machine including the same.

Molded products such as optical parts that require high molding accuracy, such as lenses, prisms, and gratings, require extremely high surface shape accuracy and finishing accuracy.
Particularly in recent years, aspherical lenses, free-form surface prisms, holographic gratings, and the like have been used as optical components for the purpose of improving optical performance.
As the precision of these optical components has increased, glass materials are increasingly being selected as moldings rather than plastics. This is because plastic is easily deformed by environmental changes such as temperature and humidity, and plastic has limited material properties such as refractive index.

Conventionally, as a mold for molding these glass optical elements, tungsten carbide having an average particle size of 0.3 to 2.0 μm is used, and a discharge activated pressure sintering is performed with a theoretical density ratio of 99.9% or more. The thing using the tungsten carbide sintered compact obtained by sintering by this method is known (for example, refer patent document 1).
Japanese Patent No. 3149330

  However, since polycrystalline bodies such as tungsten carbide sintered bodies have different crystal orientations, the required amount of processing differs when machining such as grinding, polishing, and cutting is performed. Therefore, the actual processed surface has a surface roughness corresponding to the crystal grain size of the tungsten carbide sintered body, and the use of the tungsten carbide crystal described in Patent Document 1 has the following problems.

  That is, for example, when molding an optical element for visible light, it is necessary to have a surface roughness that is sufficiently negligible when viewed from the visible light wavelength of 0.4 to 0.7 μm. When using tungsten carbide having a diameter of 0.3 to 2.0 μm, the crystal grain size of those sintered bodies is not small enough to be ignored from the wavelength of visible light. The roughness of the surface to be affected adversely affects the optical performance of the molded optical element.

  In addition, since the crystal orientation is different, when tungsten carbide having an average grain size of 0.3 to 2.0 μm as described above is used, it is applied to a processing part such as a grindstone or a blade during processing such as grinding, polishing, and cutting. There is also a problem that a great load is applied in a plurality of directions, making it difficult to perform precision machining. Therefore, it takes a long time for processing, and the mold cost becomes very high. In particular, in a complicated shape such as a free-form surface prism, the grinding wheel is deformed due to wear during processing, so that the machining allowance of the grinding wheel changes during processing, and the shape accuracy is 0.1 μm or less and the dimensional accuracy is 1 μm. Processing was very difficult.

  The present invention has been made to solve such a problem, and not only can a high-quality and highly reliable optical element be molded, but also a mold body can be manufactured with high accuracy and ease. An object of the present invention is to provide an optical element molding die and a molding machine including the same.

In order to solve the above problems, the present invention provides the following means.
The invention according to claim 1 is an optical element molding die for molding an optical element by pressing an optical material, wherein tungsten carbide is sintered without adding a metal binder, and this firing is performed. A die body is constituted by the bonded tungsten carbide sintered body, and the particle size of the tungsten carbide is set to 100 nm or less.

According to the mold for molding an optical element according to the present invention, a tungsten carbide sintered body is obtained by sintering tungsten carbide having a particle size of 100 nm or less without adding a metal binder, and this tungsten carbide is obtained. The sintered body is configured as a mold body.
As a result, the crystal grain size of the tungsten carbide sintered body obtained by sintering can be reduced, and the processed surface after processing can be made to have good surface roughness, as well as the crystal orientation during processing. The load on the machined part due to the difference can be reduced.

The invention according to claim 2 is the mold for molding an optical element according to claim 1, wherein at least one of chromium carbide and vanadium carbide is added to the tungsten carbide, and the sintering is performed after the addition. It is characterized by that.
According to the mold for molding an optical element according to the present invention, at least one of chromium carbide and vanadium carbide is added to tungsten carbide, and then the sintering is performed. Therefore, grain growth during sintering is suppressed, and the crystal grain size of the tungsten carbide sintered body is further miniaturized.
As a result, even better surface roughness can be obtained, and the load on the processed portion due to the difference in crystal orientation during processing can be further reduced.

The invention according to claim 3 is the optical element molding die according to claim 1 or 2, characterized in that the sintering is discharge plasma sintering.
According to the mold for molding an optical element according to the present invention, tungsten carbide is sintered by a discharge plasma sintering method.
Thereby, the grain growth of tungsten carbide can be controlled, and a dense sintered body can be obtained in a short time.

According to a fourth aspect of the present invention, in the mold for molding an optical element according to any one of the first to third aspects, a press surface for pressing the optical material is provided on the mold body. The press surface is formed by ultra-precision cutting.
According to the molding die for optical elements according to the present invention, the press surface is formed on the die body by ultra-precise cutting.
Here, it is known that a hard and brittle material can be mirror-cut by setting the rake angle of the cutting tool to a negative value. In the present invention, the crystal grain size of the tungsten carbide sintered body is miniaturized. The damage to the cutting edge during processing due to the difference in crystal orientation is reduced.
As a result, it is possible to obtain a good press surface with a surface roughness of 0.1 μm or less simply by performing ultra-precise cutting, thereby shortening the processing time and the processing cost.

According to a fifth aspect of the present invention, in the mold for molding an optical element according to any one of the first to fourth aspects, the crystal grain size of the tungsten carbide sintered body is set to 100 nm or less. Features.
According to the molding die for an optical element according to the present invention, the crystal grain size of the tungsten carbide sintered body is set to 100 nm or less.
Thereby, favorable surface roughness can be obtained, and the load on the processed part due to the difference in crystal orientation during processing can be reliably reduced.

The invention according to claim 6 is characterized in that the molding machine includes the molding die for optical element according to any one of claims 1 to 5 as a molding machine.
Thereby, there can exist an effect similar to the above.

  According to the present invention, since the surface roughness can be improved, a high-quality optical element can be molded. In addition, since the load on the processed portion due to the difference in crystal orientation that occurs during processing can be reduced, the mold body can be manufactured with high accuracy and ease. As a result, the work burden associated with mold manufacture can be greatly reduced and costs can be reduced.

Example 1
Hereinafter, a molding machine according to a first embodiment of the present invention will be described with reference to the drawings.
In this embodiment, a case where the present invention is applied to a glass molding machine will be described as an example.
In FIG. 1, reference numeral 1 denotes a glass forming machine.
The glass molding machine 1 includes a lower shaft 4 that supports a lower mold (molding mold) 2 to be described later, and an upper shaft 5 that supports an upper mold (molding mold) 3. And the upper shaft 5 are arranged to face each other. The upper shaft 5 is connected to a drive unit (not shown). When the drive unit is driven, the upper shaft 5 moves up and down with respect to the lower shaft 4.
The lower shaft 4 and the upper shaft 5 are configured such that a plurality of rectangular metal blocks such as stainless steel having excellent heat resistance are joined. In addition, substantially U-shaped cooling water flow paths 4a and 5a are formed inside the lower shaft 4 and the upper shaft 5, respectively. Cooling water flows in from one opening end of these cooling water flow paths 4a and 5a, and flows out from the other opening end.

  The open ends of the cooling water flow paths 4 a and 5 a are connected to a cooling water cooling and circulation device 7 through a water distribution pipe 6. Then, the cooling water supplied from the cooling water cooling / circulation device 7 passes through the water distribution pipe 6 and flows into the cooling water flow paths 4a and 5a from one opening end, and cools the lower shaft 4 and the upper shaft 5 by heat exchange action. After that, it is discharged from the other opening end, returns to the cooling water cooling / circulation device 7 again through the water distribution pipe 6, is cooled here, and is circulated.

The lower mold 2 is supported by being directed upward by the lower shaft 4, and the upper mold 3 is supported by being directed downward by the upper shaft 5 at a position facing the lower mold 2. And when the drive part connected with the upper axis | shaft 5 is driven, the upper mold | type 3 will raise / lower with respect to the lower mold | type 2, being supported by the upper axis | shaft 5. FIG.
Furthermore, the lower mold 2 and the upper mold 3 in the present embodiment are respectively provided with main body portions (mold main bodies) 2a and 3a. These main body portions 2a and 3a are made of tungsten carbide and metal binder as will be described later. It is comprised by the tungsten carbide sintered compact obtained by sintering by a discharge plasma sintering method, without adding. The particle size of tungsten carbide is set to 80 nm. Furthermore, the crystal grain size of the tungsten carbide sintered body is set in the range of 80 to 100 nm. And the press surfaces 2b and 3b for pressing the glass forming raw material W are provided in the surface which these main-body parts 2a and 3a oppose, respectively. These press surfaces 2b and 3b are formed by grinding and polishing.

Next, the usage method of the glass molding machine 1 comprised in this way is demonstrated.
First, the glass molding machine 1 is placed in a vacuum chamber (not shown). Then, after heating the solid glass molding material W until the softening temperature reaches around 600 ° C., the softened glass molding material W is placed at a predetermined position of the lower mold 2. Then, the drive unit is driven, and the upper mold 3 is lowered by the upper shaft 5. As a result, as shown in FIG. 2, the soft glass forming material W is subjected to precision pressing from above and below by the lower mold 2 and the upper mold 3. After a predetermined time in this state, the cooling water cooling / circulation device 7 is driven to supply cooling water to the cooling water flow paths 4a and 5a.

  This cooling water flows through the distribution pipe 6 and flows into the inside from one opening end of the cooling water flow paths 4a and 5a, and is exhausted from the other opening end around the whole. And it returns to the cooling water cooling circulation apparatus 7 again, it cools and this is circulated. During this time, the lower shaft 4 and the upper shaft 5 are cooled by the heat exchange effect of the cooling water, and the lower mold 2 and the upper mold 3 are cooled via the lower shaft 4 and the upper shaft 5. Therefore, the glass molding material W pressed between the lower mold 2 and the upper mold 3 is cooled. Then, by driving the drive unit again, the upper mold 3 is raised and the molded lens is taken out. Thus, the softened glass molding material W is shape | molded and processed directly into the aspherical lens of the last use shape.

Although a high quality and highly reliable aspherical lens is formed by the above-described series of processing, the lower mold 2 and the upper mold 3 in this embodiment are easily manufactured as follows.
The lower mold 2 and the upper mold 3 are manufactured by a processing machine 11 as shown in FIG.
The processing machine 11 includes an upper die punch 12 and a lower die punch 13 for pressing a workpiece, and the upper die punch 12 and the lower die punch 13 approach and separate from each other in a hollow portion of the cylindrical die 15. To move in the direction you want. Thereby, the upper die punch 12 and the lower die punch 13 press the workpiece set in the cavity from above and below. Further, the upper die punch 12 and the lower die punch 13 are electrically connected to a pulse energizing power source 16.

Under such a configuration, the processing machine 11 is placed in a vacuum chamber (not shown), and the workpiece is filled into the hollow portion of the cylindrical mold 15. This workpiece is made of a dry powder of tungsten carbide, and the particle size of the powder 18 made of tungsten carbide is set to 80 nm. At this time, a metal binder is not added to tungsten carbide. In this state, after evacuating the vacuum chamber to 3.0 × 10 ⁻³ Pa, a punch driving unit (not shown) is driven. Then, the upper die punch 12 and the lower die punch 13 are moved so as to approach each other, and the powder 18 filled in the cavity is pressed from above and below with a pressure of 20 MPa.

  At the same time, pulse energization is performed by applying a pulse voltage of a predetermined frequency between the upper die punch 12 and the lower die punch 13 by the pulse energizing power source 16. At this time, a discharge is generated in the gap between the powders 18 to heat the powders 18. The oxide film, impurities, dirt, etc. formed on the surface of the powder 18 are evaporated and scattered, and the surface of the powder 18 is microscopically dissolved. Since pressure is applied to the powder 18, the powder 18 is in a state where strain energy is accumulated. Then, the surface of the powder 18 is plastically deformed due to the effects of thermal energy and strain energy, and the gap disappears, and the powders 18 are joined together. Then, when the surface of the powder 18 reaches a predetermined temperature, the pressurization and pulse energization are stopped.

  Then, the punch driving unit is driven, and the upper die punch 12 and the lower die punch 13 are moved away from each other to take out tungsten carbide from the cavity. Thereby, a tungsten carbide sintered body is obtained. The crystal grain size of the tungsten carbide sintered body is a minute size within the range of 80 nm to 100 nm. Therefore, processing such as grinding and polishing becomes easy. The tungsten carbide sintered body is used as the main body portions 2a and 3a of the lower die 2 and the upper die 3, and press surfaces 2b and 3b are formed on one surface of the main body portions 2a and 3a by grinding and polishing. The

From the above, according to the glass molding machine 1 in this example, the tungsten carbide sintered body constituting the lower mold 2 and the upper mold 3 has a crystal grain size as small as 80 to 100 nm. The surface roughness of the press surfaces 2b and 3b can be set satisfactorily. Therefore, a high-quality and highly reliable aspheric lens can be molded.
In addition, since the tungsten carbide sintered body has a small crystal grain size, the load on the grinding blade and the grindstone caused by the difference in crystal orientation during grinding and polishing can be reduced, so that the main body portions 2a and 3a can be reduced. In addition, the press surfaces 2b and 3b can be processed with high accuracy and ease. Therefore, it is possible to significantly reduce the work burden associated with the production of the lower mold 2 and the upper mold 3 and to reduce the cost.

  Furthermore, since the discharge plasma sintering method is adopted as the sintering method, the grain growth of the powder 18 can be controlled, a dense sintered body can be obtained in a short time, and space saving can be achieved. Energy saving can be achieved.

Moreover, since the tungsten carbide sintered body does not contain a metal binder, not only the hardness of the entire tungsten carbide sintered body can be improved, but also the hardness can be made uniform. Therefore, it is possible to prevent a reduction in surface accuracy due to a difference in workability between materials when processing by grinding or the like.
Furthermore, since the metal binder is not included as described above, the oxidation resistance of the tungsten carbide sintered body can be improved. Therefore, for example, when the press surfaces 2b and 3b are processed, it is possible to prevent the sintered body from being oxidized by being exposed to a high-temperature oxidizing atmosphere. Therefore, the surface accuracy of the press surfaces 2b and 3b is improved by the volume change due to oxidation. Deterioration can be prevented.

(Example 2)
Subsequently, a second embodiment of the present invention will be described.
This embodiment and the first embodiment have the same basic configuration, and differ only in the following points. That is, in the molding machine 1 in the present example, the tungsten carbide sintered body was obtained by adding a total of 1% or less chromium carbide and vanadium carbide to tungsten carbide, and sintering after these additions. It is. And these sintering are based on HIP method (hot isostatic pressing method). That is, the powder 18 made of the added tungsten carbide is sintered under a high temperature and high gas pressure using an inert gas such as argon or nitrogen gas as a pressure medium.

  Furthermore, the molding machine 1 in the present embodiment is one in which the press surfaces 2b and 3b are formed by ultraprecision cutting. That is, processing was performed using a diamond tool whose rake angle was set to a negative value of −10 ° to −70 °.

From the above, since chromium carbide and vanadium carbide are added before sintering tungsten carbide, grain growth during sintering is suppressed, and the crystal grain size of the tungsten carbide sintered body can be further miniaturized. it can.
Further, since the press surfaces 2b and 3b are provided by ultra-precision cutting, the processing time can be shortened and the processing cost can be reduced.

In the first and second embodiments, the particle size of tungsten carbide is set to 80 nm. However, the present invention is not limited to this, and can be appropriately changed as long as it is 100 nm or less. For example, it may be within a range of 60 nm to 100 nm. In particular, by setting within the range of 60 nm to 80 nm, the crystal grain size of the tungsten carbide sintered body can be reliably set to 100 nm or less.
The crystal grain size of the tungsten carbide sintered body is set within the range of 80 to 100 nm, but can be appropriately changed as long as it is 100 nm or less. For example, it may be within a range of 60 nm to 100 nm, and particularly preferably set within a range of 60 nm to 80 nm.

  Furthermore, although the aspherical lens is formed by the glass molding machine 1, the present invention is not limited to this, and various high-precision optical elements such as a spherical lens, a prism, and a grating can be obtained by changing the press surfaces 2b and 3b. Can be molded. In particular, high-precision and fine groove shapes such as gratings could not be realized by grinding, and the mold itself could not be manufactured in the past, but the tungsten carbide sintered body in this example has a crystal grain size By miniaturization, high-precision cutting can be performed, and a grating mold can be easily manufactured.

  Further, the case where the molding machine according to the present invention is applied to the glass molding machine 1 has been described as an example. However, the present invention is not limited to this, and an optical element made of a synthetic resin or an optical element that molds a synthetic resin on glass. Needless to say, the present invention can also be applied to an element molding machine. However, since the glass molding machine is placed in a higher temperature environment, the strength and corrosion resistance are better when applied to the glass molding machine 1 due to the heat resistance and mechanical strength of the tungsten carbide sintered body. Can be demonstrated.

Further, the glass molding material W is heated and softened in advance, and then installed in the lower mold 2. However, the present invention is not limited to this, and by providing a heater or the like in the lower mold 2, the solid glass molding material W can be changed. After the installation, the glass forming material W may be heated via the lower mold 2.
Note that the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

It is a figure which shows the example which applied the molding machine which concerns on this invention to the glass molding machine as a present Example, Comprising: It is a schematic block diagram which shows a mode that the lower mold | type and the upper mold | type were spaced apart from each other. FIG. 2 is a schematic configuration diagram illustrating a state where the lower mold and the upper mold are clamped in the glass molding machine of FIG. 1. It is a schematic block diagram which shows a mode that the tungsten carbide sintered compact which comprises the main body part of a lower mold | type or an upper mold | type is manufactured.

Explanation of symbols

1 Glass molding machine (molding machine)
2 Lower mold (molding mold)
2a Body (mold body)
2b Press surface 3 Upper die (molding die)
3a Body (mold body)
3b Press surface W Glass molding material (optical material)

Claims (6)

An optical element molding die for molding an optical element by pressing an optical material,
Tungsten carbide is sintered without adding a metal binder, and a mold body is constituted by the sintered tungsten carbide sintered body.
A mold for molding an optical element, wherein a particle size of the tungsten carbide is set to 100 nm or less.   2. The mold for molding an optical element according to claim 1, wherein at least one of chromium carbide and vanadium carbide is added to the tungsten carbide, and the sintering is performed after the addition.   3. The mold for molding an optical element according to claim 1, wherein the sintering is spark plasma sintering. The mold body is provided with a pressing surface for pressing the optical material,
The mold for molding an optical element according to any one of claims 1 to 3, wherein the press surface is formed by ultra-precision cutting.   The mold for molding an optical element according to any one of claims 1 to 4, wherein a crystal grain size of the tungsten carbide sintered body is set to 100 nm or less. A molding machine comprising the mold for molding an optical element according to any one of claims 1 to 5.

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