JP2003306336A - Metal mold for forming optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for processing the lens press surface of a hard metal alloy mold for forming a lens with a large diameter in a short period of time and at a low cost, for which mirror surface finishing with high precision is required. <P>SOLUTION: An optical cutting film is formed on the base of the hard metal alloy mold, where a buffer film is laid between the base of the hard metal alloy mold and the optical cutting film to mitigate thermal expansion stress for eliminating the formation of cracks. The high-precision mold for forming a lens is speedily manufactured by precisely grinding the optical cutting film. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical element molding die.

[0002]

2. Description of the Related Art Generally, as a base material of a glass lens molding die, a material having a hardness that does not deform even when a large press pressure is applied in the vicinity of a glass softening temperature (600 ° C.) is used. In a general alloy steel, when the glass softening point temperature is reached, the hardness decreases, and when a large press pressure is applied, it plastically deforms with a small amount. In view of the shape accuracy required for the optical lens, this minute amount of plastic deformation may reach an unacceptable level. Therefore, in many cases, cemented carbide produced by sintering is used as a mold material for molding glass lenses. Cemented carbide maintains the required hardness even under the high temperature environment where glass is formed, and satisfies the required specifications. However, it is hard from the point of view of machining, so it cannot be cut with a diamond or carbide tool. Therefore, most of the processing is grinding and polishing with a grindstone.

Particularly, the shape accuracy of the lens press surface needs to be finished to a processing accuracy of submicron, and the surface roughness of the surface is required to be a mirror surface state. The diameter of the molded lens is φ
In the case of a large molding die of more than 50 mm, it takes a lot of time and processing cost to finish the pressed surface state as described above from the rough shape of the cemented carbide after sintering.

[0004]

As described above, processing a cemented carbide die requires a great deal of time and cost. Especially, the shape accuracy of the lens press surface is submicron accuracy (± 0.
Up to 1 μm or less), an ultra-high precision curved surface processing machine is occupied for a long time for grinding and polishing, which requires the most processing time and processing cost.

In view of the above points, the present invention provides a method for processing a lens press surface of a large-diameter lens molding die in a short time and at low cost.

[0006]

[Means for Solving the Problems] An optical cutting film which can be machined and has a mirror surface by polishing after the machining is formed on a lens press surface of a cemented carbide die base material by plating or sputtering. The film thickness is preferably in the range of 10 to 100 μm. It may be stacked thicker if necessary. After the film formation, this optical cutting film is turned by diamond turning or the like within the range of the film thickness to finish the target spherical or aspherical shape.

The lens press surface of the cemented carbide die base material before forming the optical cutting film need not be mirror finished. A matte finish without matte finish is also acceptable. Further, the surface shape accuracy may be finished within a range of about ± 10 μm with respect to the target shape. As long as it is processed to such a degree of finishing accuracy and quality, it can be carried out in a relatively short time even with cemented carbide.

In order to finish the surface shape with high precision, the optical cutting film formed by the above-mentioned plating or sputtering is used.
If turning (diamond turning is desirable) within a very small amount and within the range of film thickness, it is possible to perform processing with extremely high precision and speed.

Now, the glass molding die is heated to near the glass molding temperature of 600 ° C. and cooled to near room temperature after molding. This molding temperature cycle is repeated many times. If the optical cutting film is formed directly on the cemented carbide base material, if the difference in the coefficient of thermal expansion between the cemented carbide base material and the optical cutting film is large, the optical cutting film can be finely divided by repeating the molding temperature cycle. Cracks occur. If a crack occurs, it cannot be used as a molding die. Therefore, the present invention, by interposing a thin film of a soft metal between the cemented carbide base material and the cutting film for optics, absorbs and relaxes a slight difference in expansion and contraction caused by the difference in the coefficient of thermal expansion between the two, thereby cutting the It is designed to prevent cracks occurring in the film.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a general lens molding die unit. 1 is a barrel type, 2 is a lower punch type, and 3 is an upper punch type. Reference numeral 4 is a mold cavity space, and a glass material 5 to be a molded glass lens in this space.
Is placed.

FIG. 2 shows a sectional view of a molding die when an optical cutting film 7 is formed on a cemented carbide base material 6. Although the thickness of the optical cutting film 7 is exaggerated in FIG. 2 for the sake of explanation, the actual thickness is about 10 to 100 μm.

The cemented carbide base material 6 of the die is made of a sintered alloy containing tungsten carbide as a main component. Then, as the optical cutting film 7, electroless plating of nickel-phosphorus is applied. The electroless plating layer is subjected to ultra-precision turning by a very small amount to finish the target surface shape. After turning, polish with diamond paste or the like to give a mirror finish.

The temperature of this cemented carbide base material is from room temperature to 600 ° C.
The average coefficient of thermal expansion is 6 × 10^-6/ ° C, nickel-phosphorus
The average thermal expansion coefficient of electroless plating of (Ni-P) is 12x.
10 ^-6/ ° C.

As shown in FIG. 2, when an optical cutting film 7 (electroless plating of nickel-phosphorus) is directly formed on the cemented carbide base material 6, the above-mentioned difference in the coefficient of thermal expansion causes the difference. When the molding temperature cycle is repeated, cracks occur in the optical cutting film 7.

Due to such a difficult problem, an optical cutting film has been formed on a large-diameter cemented carbide die by plating or the like, and then finished by ultraprecision turning to press an optical lens. The method of making a transfer surface has not been put to practical use.

In view of the above points, in the present invention, as shown in FIG. 3, between the cemented carbide base material 8 and the optical cutting film 9,
A buffer film 10 that relaxes and absorbs the difference in thermal expansion and contraction between the two is interposed. As a material of the buffer film 10, a material softer than a cemented carbide or an optical cutting film is used. For example, nickel (Hv: 96) and copper (Hv: 46) are preferable.

As another method (see FIG. 3),
As the material of the buffer film 10, a material having a higher coefficient of thermal expansion than the cemented carbide base material 8 and the optical cutting film 9 is used. With this structure, when the temperature of the mold rises, the cemented carbide base material 8,
Although the buffer film 10 also thermally expands, the buffer film 1 having a larger expansion coefficient than the cemented carbide base material 8 because they are in close contact with each other at the interface.
0 cannot be expanded freely and is restricted by the base material 8 having a small expansion coefficient. Therefore, the expansion amount is smaller than the original expansion amount. This expansion amount is close to the expansion amount of the optical cutting film 9, and the expansion amounts of the buffer film 10 and the optical cutting film 9 are almost the same, so that the thermal expansion stress generated between them is extremely small, and the optical cutting film 9 is very small. It is possible to eliminate the occurrence of cracks. The material of the buffer film is copper (expansion rate: 17 × 10 ⁻⁶ /
cm) is considered.

[0019]

As described above, in order to reduce the cost of a large-diameter glass lens molding die using cemented carbide as a base material, it is necessary to shorten the processing time. Most of the processing cost is required to process the lens press surface with high accuracy and a mirror surface. Therefore, in order to shorten the processing time (= reduce the cost of the mold), the processing of this lens press surface must be made efficient.

Therefore, in the present invention, an optical cutting film that can be cut is applied to a cemented carbide base material by a method such as plating, and the cutting film is turned with a diamond tool or the like, thereby dramatically reducing the processing time. It is possible to achieve high-precision finish as well. However, if the optical cutting film is formed directly on the cemented carbide base material, cracks occur in the optical cutting film due to thermal expansion stress caused by the difference in expansion coefficient between the two. Therefore, in the present invention, a buffer film is provided between the cemented carbide base material and the optical cutting film so that thermal expansion stress is not generated and cracks are eliminated.

As described above, according to the present invention, it is possible to manufacture a large-diameter lens molding die using a cemented carbide as a base material at a significantly lower cost than conventional ones.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a general lens molding die unit.

FIG. 2 is a sectional view showing a state in which an optical cutting film is formed on a cemented carbide base material.

FIG. 3 is a cross-sectional view showing a state in which a buffer film and an optical cutting film are laminated and formed on a cemented carbide base material.

[Explanation of symbols]

1 body type 2 Lower punch type 3 Upper punch type 4 Mold cavity space 5 glass material 6 Cemented Carbide Base Material 7 Optical cutting film 8 Cemented Carbide Base Material 9 Optical cutting film 10 buffer film

Claims (6)

[Claims] 1. A base material having heat resistance equal to or higher than a glass softening point and capable of withstanding press molding, and a first functional layer is formed on a press surface of the base material and a peripheral area thereof by plating, sputtering, or the like. Further, plating is performed so as to cover the first functional layer,
In the optical element molding die in which the second functional layer is formed by sputtering or the like, the first functional layer is a single metal material softer than the die base material and the second functional layer, or a metal alloy material, or An optical element molding die, which is formed of a mixture of a plurality of metal materials. 2. A base material having heat resistance equal to or higher than the glass softening point and capable of withstanding press molding, and a first functional layer is formed on the press surface of the base material and its peripheral region by plating, sputtering, or the like. Further, plating is performed so as to cover the first functional layer,
In the optical element molding die in which the second functional layer is formed by sputtering or the like, the first functional layer has a metal material or a metal alloy material having a thermal expansion coefficient higher than those of the die base material and the second functional layer. Or a mixture of a plurality of metal materials, an optical element molding die. 3. A base material having heat resistance equal to or higher than the glass softening point and capable of withstanding press molding, and a first functional layer is formed on the press surface of the base material and its peripheral area by plating, sputtering, or the like. Further, plating is performed so as to cover the first functional layer,
In an optical element molding die in which a second functional layer is formed by sputtering or the like, the first functional layer is a single metal material that is softer than the die base material and the second functional layer and has a large coefficient of thermal expansion. Alternatively, an optical element molding die formed of a metal alloy material or a mixture of a plurality of metal materials. 4. A base material of a press-molding die is a cemented carbide containing tungsten carbide (WC) as a main component, titanium carbide (TiC) or titanium nitride (Ti).
The optical element molding die according to claim 1, which is a material selected from a cermet containing N) as a main component or a WC sintered body. 5. A base material of a press-molding die is cemented carbide containing tungsten carbide (WC) as a main component, titanium carbide (TiC) or titanium nitride (Ti).
The optical element molding die according to claim 2, which is a material selected from cermet containing N) as a main component or a WC sintered body. 6. A base material of a press-molding die is a cemented carbide containing tungsten carbide (WC) as a main component, titanium carbide (TiC) or titanium nitride (Ti).
The optical element molding die according to claim 3, which is a material selected from a cermet containing N) as a main component or a WC sintered body.