JP2005231933A - Mold for optical element and method for molding optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the clearance between a shaping die and a drum die at a high temperature during molding to reduce the deviation of the optical axis of an optical element; and to secure the minimum clearance between the shaping die and the drum die and necessary for sliding before and after molding. <P>SOLUTION: A mold for an optical element is composed of a pair of shaping dies 1 and 2 and a drum die 3 into which the shaping dies are inserted. While an optical element raw material 4 arranged between the shaping dies is being heated, one of the shaping dies slides in the drum die to apply pressure to the optical element raw material, thus transferring optically effective faces formed on the inside surfaces of the shaping dies to the optical element raw material. The thermal expansion coefficient α1 of the raw material of the shaping die 1 which slides in the drum die in molding, the thermal expansion coefficient α2 of the raw material of the shaping die 2 which does not slide in the drum die in molding and receives pressure via the optical element raw material, and the thermal expansion coefficient α3 of the material of the drum die 3 are set so as to have the relation: α2>α1≥α3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element molding die for molding an optical element used in an optical apparatus by a precision glass molding method, and an optical element molding method using the molding die.

  In recent years, many attempts have been made to mold an optical element by one-shot molding without a polishing step. The method of casting a glass material from a molten state into a mold and performing pressure molding is the most efficient, but it is difficult to control glass shrinkage during cooling, and is not suitable for precise optical element molding. Accordingly, it is a general molding method to supply an optical element material preliminarily processed into a certain shape between the upper and lower molds, heat, and press molding. (For example, refer to Patent Document 1).

Such a conventional molding method will be described with reference to FIG. FIG. 2 shows a cross section of the molding die and the optical element in a state where the optical surface is formed by pressing the optical element material. Reference numerals 11 and 12 denote a pair of molds, which are attached to press heads 15 and 16 of the molding apparatus. The pair of molds 11 and 12 are mounted in the body mold 13. The optical element 14 is molded in the space formed by the pair of molding dies 11 and 12 and the barrel die 13. The optical element material before being pressed and molded into the optical element 14 is uniformly heated to a temperature near the softening point of the glass using an appropriate heating means, and then pressed by the molding surfaces of the molds 11 and 12. Is done. The barrel mold 13 is used to eliminate the centering step after molding, and at the same time, the barrel mold 13 aligns the optical axes of the two optical surfaces formed by the molding dies 11 and 12.
JP 58-84134 A

  However, in the method as described above, the following difficulties arise in order to mold an ultraprecision aspherical optical element. That is, since aspherical optical elements are generally difficult to center, a one-shot molding using a barrel mold is necessary. In addition, in an ultra-precision aspherical optical element used for an optical pickup, for example, high accuracy is required such that the optical axis deviation between the two optical surfaces is 10 μm or less.

  On the other hand, processing with an accuracy of a clearance of 10 μm becomes difficult from the surface of fitting between the pair of molds and the barrel mold. Furthermore, since it must be molded at a high temperature, it is difficult to maintain accuracy over the long term. Further, if the material of the mold and the body is the same, the variation in the coefficient of thermal expansion is the same at the normal temperature and at the high temperature, so that the clearance of the processing dimension difference is maintained. Therefore, the processing accuracy of the inner diameter of the body mold and the outer diameter of the mold is reflected in the optical axis deviation, and as a result, the optical performance is affected.

  The present invention reduces the clearance between the molding die and the barrel die at a high temperature during molding, reduces the deviation of the optical axis of the optical element, and slides between the molding die and the barrel die before and after molding. It is an object of the present invention to provide a molding die for optical elements capable of ensuring a necessary minimum clearance.

  The molding die for optical elements of the present invention comprises a pair of molding dies, a barrel die into which the molding dies are inserted, and an optical element material disposed between the molding dies, while heating the molding die. One side is slid in the body mold and a pressing force is applied to the optical element material by the molding die to transfer the optically effective surface processed on the inner surface of the molding die to the optical element material, thereby This is a molding die for manufacturing. Of the pair of molding dies, the coefficient of thermal expansion of the sliding mold material that slides in the barrel mold during molding is α1, and the sliding force is not slid in the cylinder mold during molding, and the pressing force is the sliding molding. When the coefficient of thermal expansion of the mold and the material of the non-sliding mold received through the optical element material is α2, and the coefficient of thermal expansion of the material of the body mold is α3, α2> α1 ≧ α3. Further, the thermal expansion coefficient of each material is set.

  According to the method for molding an optical element of the present invention, the mold is heated while heating a pair of molds, a barrel mold into which the mold is inserted, and an optical element material disposed between the molds. The optical effective surface processed on the inner surface of the molding die is transferred to the optical element material by sliding one of the members in the body mold and applying a pressing force to the optical element material by the molding die. Is made. Of the pair of molding dies, the coefficient of thermal expansion of the material of the sliding mold that slides in the barrel mold during molding is α1, and the pressing force is not slid in the cylinder mold during molding. When the coefficient of thermal expansion of the dynamic mold and the material of the non-sliding mold received via the optical element material is α2, and the coefficient of thermal expansion of the body mold material is α3, α2> α1 ≧ α3 Thus, a molding die in which the coefficient of thermal expansion of each material is set is used.

  By using the molding die for optical elements having the above configuration, the thermal expansion coefficient of the molding die is set to be larger than the thermal expansion coefficient of the barrel mold, thereby reducing the clearance between the molding die and the barrel mold at a high temperature during molding. Thus, the deviation of the optical axis of the optical element can be reduced. In addition, the sliding mold can ensure the minimum clearance required for sliding by using a material having a smaller coefficient of thermal expansion than the non-sliding mold.

  In the molding die for optical elements of the present invention, each of the molding dies is formed using a material mainly composed of tungsten carbide (WC), and the binder content of the tungsten carbide (WC) is slid. The relationship of molding die> non-sliding molding die> trunk die can be established. Thereby, the coefficient of thermal expansion can be easily adjusted.

  In the optical element molding method of the present invention, preferably, the relationship between the thermal expansion coefficients α1 and α3 so that the clearance between the barrel mold and the non-sliding mold at a high temperature for molding is substantially zero. Set. Thereby, the deviation of the optical axis can be further reduced. Further, the optical element material can be molded using the pair of molds and the barrel mold by a molding apparatus for performing the preheating step, the pressing step, and the cooling step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view showing a state before molding when molding is performed without fixing a molding die to a press head of a molding apparatus. Although not shown, the press heads 5 and 6 of the molding apparatus are provided with a heating unit. A non-sliding mold 2 on which a body mold 3 and a sliding mold 1 are inserted is placed on a press head 6. An optical element material 4 is set between the non-sliding mold 2 and the sliding mold 1. The non-sliding mold 2, the sliding mold 1, the body mold 3 and the optical element material 4 are heated to about 600 ° C. by the press head 6, and the press head 5 is lowered to press the sliding mold 1. The pressed optical element material 4 is deformed to mold the optical element.

The outer diameters of the fitting portions 1a and 2a inserted into the body mold 3 in the non-sliding mold 2 and the sliding mold 1 are set to 6.000 mm, and the inner diameter of the body mold 3 is set to 6.008 mm. That is, the clearance between the non-sliding mold 2 at normal temperature and the fitting portion between the sliding mold 1 and the body mold 3 is 8 μm, respectively, and an optical axis deviation within a maximum of 16 μm occurs. As a material for the sliding mold 1, the non-sliding mold 2, and the body mold 3, for example, a tungsten carbide material is used. The non-sliding mold 2 has a binder content of 12% and a thermal expansion coefficient α2 of 6.98 × 10 ⁻⁶ / ° C. The sliding mold 1 has a binder content of 7% and a thermal expansion coefficient α1 of 6.23 × 10 ⁻⁶ / ° C., which is smaller than the non-sliding mold 2. The body mold 3 is a material having a binder content of 5% and a thermal expansion coefficient α3 of 5.07 × 10 ⁻⁶ / ° C., which is smaller than the molds 1 and 2.

  At the molding temperature at which these are heated to about 600 ° C., the clearance between the sliding mold 1 and the body mold 3 is as small as 4 μm, and the clearance between the non-sliding mold 2 and the body mold 3 is as small as 1 μm. Accordingly, the maximum optical axis deviation between the optical surfaces of the sliding mold 1 and the non-sliding mold 2 is within 5 μm, which is smaller than the clearance of 11 μm at room temperature.

  Furthermore, if the outer diameter of the non-sliding mold 2 is set to 6.001 mm, the clearance of the fitting portion at the molding temperature is substantially zero. Accordingly, the clearance of the sliding mold 1 is only 4 μm, and the optical axis deviation is as small as 4 μm at the maximum.

  If the clearance between the body mold 3 and the sliding mold 1 is reduced, the optical axis deviation is further reduced. However, considering the machining accuracy and molding temperature stability of the body mold 2 and the mold, it is stable at a high temperature during molding. In order to enable such sliding, a clearance of about 4 μm is required.

  In general, since the coefficient of thermal expansion varies with temperature, it is necessary to estimate the actual degree of expansion according to the molding temperature. In this case, it is desirable to perform fine adjustment in combination with the outer dimensions of the mold.

  If a material having a large difference in thermal expansion coefficient is used, it is possible to loosen the processing accuracy of the outer diameter of the mold, particularly the inner diameter of the body mold. Furthermore, it is possible to reduce the clearance without individually changing the outer diameter of the mold, which facilitates processing. In addition, since the clearance is large at room temperature, it is easy to insert the mold into the body mold, so that the effect of reducing the accuracy of the automatic mold disassembly and assembly apparatus can be obtained.

  According to the molding die for optical elements of the present invention, the clearance between the molding die and the body die at a high temperature during molding is reduced, the optical axis shift of the optical element is reduced, and the molding die before and after molding. The minimum clearance required for sliding can be ensured between the body mold and the body mold. Therefore, a high-precision optical element can be easily manufactured, which is useful for manufacturing an ultra-precise aspherical optical element used for an optical pickup.

Sectional drawing which shows the state before shaping | molding of the shaping die in this invention, and a shaping | molding method Sectional drawing which shows the molding state of the optical element in this invention and a prior art example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sliding shaping | molding die 2 Non-sliding shaping | molding die 3, 13 Body type | mold 4 Optical element material 5, 6, 15, 16 Press head 11, 12 Molding die 14 Optical element material

Claims (5)

While heating a pair of molds, a barrel mold into which the mold is inserted, and an optical element material disposed between the molds, one of the molds is slid in the barrel mold. In a molding die for an optical element for producing an optical element by applying a pressing force to the optical element material by the molding die to transfer an optically effective surface processed on the inner surface of the molding die to the optical element material. ,
Of the pair of molding dies, the coefficient of thermal expansion of the sliding mold material that slides in the barrel mold during molding is α1, and the sliding force is not slid in the cylinder mold during molding, and the pressing force is the sliding molding. When the coefficient of thermal expansion of the material of the non-sliding mold received through the mold and the optical element material is α2, and the coefficient of thermal expansion of the material of the barrel mold is α3,
A molding die for optical elements, wherein the thermal expansion coefficient of each material is set so as to satisfy the relationship of α2> α1 ≧ α3.   Each mold is formed using a material mainly composed of tungsten carbide (WC), and the binder content of the tungsten carbide (WC) is sliding mold> non-sliding mold> body mold. The molding die for optical elements according to claim 1, wherein: While heating a pair of molds, a barrel mold into which the mold is inserted, and an optical element material disposed between the molds, one of the molds is slid in the barrel mold. In the molding method of an optical element for producing an optical element by transferring an optical effective surface processed on the inner surface of the molding die to the optical element material by applying a pressing force to the optical element material by the molding die,
Of the pair of molding dies, the coefficient of thermal expansion of the sliding mold material that slides in the barrel mold during molding is α1, and the sliding force is not slid in the cylinder mold during molding, and the pressing force is the sliding molding. When the coefficient of thermal expansion of the material of the non-sliding mold received through the mold and the optical element material is α2, and the coefficient of thermal expansion of the material of the barrel mold is α3,
A molding method of an optical element, wherein a molding die in which a coefficient of thermal expansion of each material is set so as to satisfy a relationship of α2> α1 ≧ α3.   4. The method for molding an optical element according to claim 3, wherein the relationship between the thermal expansion coefficients α1 and α3 is set so that the clearance between the body mold and the non-sliding mold at a high temperature for molding is substantially zero. . The optical element molding method according to claim 3, wherein the optical element material is molded using the pair of molds and the barrel mold by a molding apparatus for performing a preheating step, a pressing step, and a cooling step.

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