JP2593243B2 - Press forming apparatus and forming method for optical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a press forming apparatus for an optical element in which a high precision optical element such as an aspherical lens is formed by press molding.

[0002]

2. Description of the Related Art Recently, there has been proposed a manufacturing method in which a glass lens used for an optical device or the like is formed by one-shot molding without a polishing step. In this method, the glass material is poured into the mold from the molten state and press-molded, which is the most efficient in terms of work efficiency, but it is difficult to control the shrinkage of the glass during cooling, and the molding surface is precisely formed. It is not an appropriate manufacturing method for an optical element that needs to be manufactured. Therefore,
For example, as disclosed in Japanese Patent Application Laid-Open No. 58-84134, a glass material (glass blank) approximating the shape of the final molded product is prepared in advance and used for molding having a required highly accurate molding surface. When housed in a mold member and heated, when the viscosity of the glass material reaches a moldable temperature in the range of 10 ⁸ to 10 ¹² poise, the glass material is pressed with the mold member,
A press molding method of an optical component for obtaining an optical element as a final molded product having a cavity shape, particularly a surface corresponding to a molding surface, has already been proposed. Such Richie
According to the topless molding method, the problem relating to shrinkage of glass can be solved to some extent, and further, post-processing such as grinding and polishing after molding is not required.

However, when manufacturing an optical element such as an aspherical lens which requires a high-precision molding surface, it is necessary that the molding surface of the mold member be reliably transferred to a glass material. For this reason, it is important that the molding surface is in close contact with the glass material during the cooling process after the molding is completed. That is, when transferring the molding surface to the glass material, while the temperature of the glass material drops to a desired temperature beyond the glass transition point in the cooling process, if the glass material is not in close contact with the molding surface, the Due to the viscous flow, the optically functional surface of the formed glass material is deformed. In order to achieve such an object, the following press molding method has been conventionally proposed. here,
Means for applying an urging force to the mold member is shown so that the distance between the upper and lower mold members is reduced in conjunction with the volume shrinkage of the glass material accompanying cooling.

That is, as shown in FIG. 7, a pair of upper and lower mold members 48 and 49 are arranged to press a glass material 51a, which has been heated to a temperature at which molding can be performed beforehand, from above and below. The mold member 48 is suspended by the suspending member 52, is moved downward by the action of the ram 55, and presses the upper surface of the glass material 51a with the molding surface 48a formed on the lower surface thereof, so that the required optical function surface is formed. Form. Further, the lower mold member 49 is slidably fitted to the body mold 50 and is elastically held upward by a compression spring 53 with respect to the base 54, and is formed on the body mold 50. The receiving portion 49b faces the stopper portion 50b thus formed, and in a state before press forming, the receiving portion 49b is in contact with the stopper portion 50b.
7 is held upward so as to contact
(See (a)), when the mold member 48 is lowered, the glass member 51a receives a pressing force from the mold member via the glass material 51a, and the glass member 51 descends against the elastic force of the elastic spring. The molding surface formed on the upper surface of the material 51a is pressed against the lower surface of the material 51a to form a required optical function surface on the lower surface of the glass material (see FIG. 7B). At this time, the mold member 48 comes into contact with the upper end of the body mold 50 and is prevented from descending further, so that the glass material 51a receives only a predetermined pressure corresponding to the spring compression amount.

Thereafter, a cooling process is started, and the mold member, the glass material, and the like are all cooled, but the mold member remains closed. Thereafter, the ram 55 is raised (see FIG. 7C), and then the upper mold member 48 is raised to open the mold (see FIG. 7D). In this case, since the glass material maintains a high coefficient of thermal expansion above the transition point as shown in FIG. 8, the glass material is converted from the softening point to the yield point (press forming temperature).
The shrinkage in the cooling process after passing through the mold member is larger than that of the mold member (due to the coefficient of thermal expansion of the metal is shown by the b line in FIG. 8) and tends to separate from the molding surface. By the action of the spring 53, the lower mold member can be raised so as to absorb the difference in shrinkage ratio, thereby preventing the optical surface of the glass material from peeling.

[0006]

However, in the above conventional example, in the cooling process, the relative distance between the upper and lower mold members always follows the contraction of the glass material, so that the following inconvenience occurs. . That is, the cooling proceeds while the molding surface of the mold member is in close contact with the glass material, and when the glass material is cooled to a temperature equal to or lower than the glass distortion point, a large thermal stress acts on a contact point between the molding surface and the glass material. .
That is, since the glass material maintains its viscoelastic properties above the glass strain point, the above-mentioned thermal stress is alleviated with the passage of time, but its elastic properties are lost below the above strain point. Therefore, distortion occurs due to thermal stress and cracks occur.

[0007]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above circumstances, and it is required that a mold member follow a volumetric shrinkage of a glass material under a specific temperature (a temperature higher than a glass strain point). Restriction, until the glass material reaches a temperature below the glass transition point, while maintaining the shape transferability of the molding surface, and furthermore, it is possible to prevent cracks occurring in the mold member during the subsequent cooling process of the optical element. It is intended to provide a press molding device.

[0008]

Therefore, in the present invention,
A glass material in a softened state is pressed using a molding die member, and a press molding apparatus for an optical element in which an optical functional surface corresponding to the molding surface of the mold member is formed on the glass material. In the subsequent cooling process, the upper and lower mold members are relatively moved in a direction to reduce the distance between the upper and lower mold members in conjunction with the volume shrinkage of the glass material with cooling up to the temperature of the transition point of the glass material, In addition, an interval adjusting member for restricting relative movement so as not to follow the volume shrinkage of the glass material at a temperature below the transition point is arranged in relation to the mold member. Here, a glass material to be processed into an optical element shape is heated to a predetermined softening temperature, a pair of mold members and an adjusting member for adjusting the distance between the mold members are provided, and the glass material is put into the mold members. Pressing, transferring the pressed surface shape of the mold member to the glass material and deforming the glass optical element into an optical element shaped glass optical element, and after the shape deformation step, moving the glass optical element to a cooling step; In accordance with the volume contraction of the glass material, one of the mold members is moved together with the glass material, and the movement of the one mold member is prohibited at a temperature of the glass material equal to or lower than the glass transition temperature. Molding.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically described based on the illustrated embodiments. In FIG. 1, reference numeral 1 denotes a molded glass material (glass blank), which is located between upper and lower mold members 2 and 3. Then, the mold members 2 and 3
Is provided with molding surfaces 2a and 3a on upper and lower opposing surfaces, and has a fitting structure in which the optical axis is aligned in the spacing control member 4 as a body die. I can move. The spacing control member 4 is fixed to the base 5 with bolts or the like. An annular convex portion 2b is provided at the upper end of the upper mold member 2,
An annular protrusion 3b is provided at the lower end of the lower mold member 3 so as to face the upper end 4a of the gap control member 4, and the inner periphery of the lower end of the gap control member 4 is Lower end 3
b, the lower end 3b of the mold member 3
An annular recess 4 having a width larger by the gap 6a
b is provided. Here, the space 6a has a size obtained by subtracting the contraction amount of the interval control member 4 from the sum of the heat contraction amounts of the glass material 1, the mold members 2 and 3 from the pressing temperature to the transition point.

[0010] Such a press forming apparatus is used as follows. First, as shown in FIG. 1A, the upper mold member 2 is lifted using a lifting means (not shown), and the glass material 1 is loaded on the lower mold member 3. The glass material 1 is preheated to a temperature at which it can be pressed or is heated at that point. While the glass material 1 is at or at a required press temperature, the mold member 2 is lowered using a mold operating member 7 such as a ram, and the glass material 1 is moved between the mold members 2 and 3. Press forming, forming surface 2
a and 3a are transferred above and below the glass material 1. The thickness of the glass material is determined when the upper mold member 2 comes into contact with the protrusion 2a with the interval control member 4. The state is shown in FIG.

Thereafter, the glass material 1 is cooled via the mold members 2 and 3 and the space control member 4. At this time, the glass material 1 is compared with the mold members 2 and 3 and the space control member 4. Since the coefficient of thermal expansion is very high, the lower mold member 3 is pressed against the glass material 1 by the adhesive force with the glass material 1.
And contracts, and the gap 6a is reduced to the gap 6b as shown in FIG. 1 (c).

When the mold members 2, 3 and the glass molded product (glass material) reach a predetermined temperature below the transition point (however, an appropriate temperature higher than the glass distortion point), the void 6b is almost eliminated. The relative distance between the two mold members 2 and 3 is restricted by the action of the distance control member 4 (see FIG. 1D).
When the temperature of the glass material and the temperature of the two mold members drop below the transition point, for example, 520 ° C., the glass material continues to shrink, but the relative distance between the mold members 2 and 3 is controlled by the distance control member 4. Due to the difference in the coefficient of thermal expansion, the separating force acts between the upper and lower mold members 2, 3 and the glass material, and overcomes the attraction force acting between the two. The member 3 descends by its own weight, and peels off the glass molded product from the upper mold member 2 (see FIG. 1E). Therefore, no thermal stress is applied to the optically functional surface of the glass molded product. Thereafter, before the temperature reaches the glass strain point, the upper mold member 2 is raised at, for example, about 500 ° C. (see FIG. 1F), and the glass molded product on the lower mold member 3 is taken out. It is. As described above, since the molding surfaces 2a and 3a are kept in close contact with the glass molded product until the deformation due to the variation in the temperature distribution is eliminated, it is possible to prevent the formed optical functional surface from being deformed, and furthermore, to prevent the deformation of the glass molded product No crack is generated on the optical function surface.

FIG. 2 shows another embodiment of the present invention.
The difference from the first embodiment is that the upper mold member 2 is
2 and a gap 16a is formed between the top of the mold member 2 and the inner ceiling of the suspending member 12, while the lower mold member 3 is fixedly secured to the base 5. It is a point that is held. The mold operating member 7 such as a ram applies a pressing force to the mold member via the suspension member 12.

In such a configuration, from the state shown in FIG. 2A, the mold operating member 7 is lowered, the mold member 2 is placed on the glass material 1, and further lowered until the void 16a disappears. The press forming pressure is applied to the glass material 1 by the subsequent descent. Then, as shown in FIG. 2B, the thickness of the glass material is determined when the lower portion of the suspending member 12 hits the upper end of the gap adjusting member 4. The temperature of the mold members 2 and 3 and the gap adjusting member 4 and the temperature of the glass material 1 are:
In the process of dropping to a predetermined temperature below the glass transition point, the upper mold member 2 drops so as to follow the shrinkage of the glass material 1 as shown in FIG. During this time, the glass molded product (glass material) is in close contact with the molding surfaces 2a and 3a of the mold member, and the formed optical functional surface is not deformed due to a variation in temperature distribution. Thereafter, the gap 16b between the convex portion 2b of the upper mold member 2 and the upper end of the gap adjusting member 4 is reduced, but at the predetermined temperature, the gap 16b almost disappears (see FIG. 2D), and the gap control is performed. The relative spacing between the mold members 2 and 3 is restricted by the member 4. Further, when the temperature decreases toward the strain point, the mold member 2 is caused to escape upward due to the difference in the coefficient of thermal expansion (see FIG. 2E). And before the glass loses its viscoelastic properties,
That is, at a desired temperature equal to or higher than the glass distortion point, the upper mold member 2 is lifted by the hanging member 12 (see FIG. 2F). As a result, the optically functional surface of the glass molded product is not subjected to thermal stress distortion, and cracks are avoided.

FIG. 3 shows a third embodiment of the present invention. Here, in addition to the same configuration as the first embodiment,
Sheet piece 9 having a suitable coefficient of thermal expansion as an auxiliary spacing adjusting member
Are arranged between the base member 5 and the lower mold member 3, and serve to adjust the gap 26a. That is, the gap 26a is adjusted to a value obtained by subtracting the shrinkage of the body mold 4 from the sum of the shrinkage of the upper and lower mold members 2 and 3 and the glass material 1 to be formed from the pressing temperature to the transition point temperature. .

FIG. 4 shows a fourth embodiment of the present invention. Here, in addition to the same configuration as the second embodiment,
Sheet piece 9 having a suitable coefficient of thermal expansion as an auxiliary spacing adjusting member
Are arranged between the suspension member 12 and the upper mold member 2, and serve to adjust the gap 36a. That is, the gap 36a is adjusted to a value obtained by subtracting the shrinkage amount of the body mold 4 from the sum of the shrinkage amounts of the upper and lower mold members 2 and 3 and the glass material 1 to be formed from the pressing temperature to the transition point temperature. .

FIG. 5 shows a fifth embodiment of the present invention. Here, a gap 46 is provided between the suspending member 12 and the upper mold member 2 and a gap 46a is provided between the gap adjusting member 4 and the lower mold member 3. The structure is a combination of the first and second embodiments. The sum of the gaps 46 and 46a regulates when the relative movement of the upper and lower mold members 2 and 3 below the transition point is restricted.

FIG. 6 shows a sixth embodiment of the present invention. Here, in the fourth embodiment, the auxiliary interval adjusting member 1 is provided corresponding to the respective gaps 46 and 46a.
Equipped with the above-mentioned gaps 46,
46a is adjusted. Then, the gaps 46 and 4
6a are the upper and lower mold members 2, 3 below the transition point.
When the relative movement is restricted.

[0019]

The present invention has been described in detail above. In the cooling process after pressure molding, the temperature of the glass material rises and falls in conjunction with the volume shrinkage of the glass material accompanying cooling until the temperature falls below the transition point of the glass material. As the mold member moves relatively in a direction to relatively reduce the gap, and at a temperature equal to or lower than the transition point, an interval adjusting member that limits the relative movement so as not to follow the volume contraction of the glass material, Since it is arranged in relation to the above-mentioned mold member, cracks that occur in the mold member during the subsequent cooling process while maintaining the shape transferability of the molding surface until the glass material reaches a temperature below the glass transition point. Can be prevented. As a result, it is possible to improve the shape transferability of the surface of the molding die, and to improve the yield by preventing the occurrence of cracks such as annular shapes on the surface of the product.

[Brief description of the drawings]

FIG. 1 (a) is an operation explanatory diagram for explaining a first embodiment of the present invention.

FIG. 1 (b) is an operation explanatory diagram for describing a first embodiment of the present invention.

FIG. 1 (c) is an operation explanatory diagram for explaining a first embodiment of the present invention.

FIG. 1 (d) is an operation explanatory diagram for describing a first embodiment of the present invention.

FIG. 1 (e) is an operation explanatory diagram for explaining a first embodiment of the present invention.

FIG. 1 (f) is an operation explanatory diagram for describing a first embodiment of the present invention.

FIG. 2 (a) is an operation explanatory diagram for explaining a second embodiment of the present invention.

FIG. 2B is an operation explanatory diagram for explaining a second embodiment of the present invention.

FIG. 2 (c) is an operation explanatory diagram for explaining a second embodiment of the present invention.

FIG. 2 (d) is an operation explanatory diagram for describing a second embodiment of the present invention.

FIG. 2 (e) is an operation explanatory diagram for explaining a second embodiment of the present invention.

FIG. 2 (f) is an operation explanatory diagram for explaining a second embodiment of the present invention.

FIG. 3 is an operation explanatory diagram for explaining a third embodiment of the present invention.

FIG. 4 is an operation explanatory diagram for explaining a fourth embodiment of the present invention.

FIG. 5 is an operation explanatory diagram for explaining a fifth embodiment of the present invention.

FIG. 6 is an operation explanatory diagram for explaining a sixth embodiment of the present invention.

FIG. 7A is an operation explanatory diagram for explaining a conventional example.

FIG. 7 (b) is an operation explanatory diagram for explaining a conventional example.

FIG. 7C is an operation explanatory diagram for explaining a conventional example.

FIG. 7D is an operation explanatory diagram for describing a conventional example.

FIG. 8 is a graph showing the amounts of thermal expansion of glass (a) and mold (b).

FIG. 9A is an explanatory view showing a pressed state of a glass material and a state of cracks of a molded product.

FIG. 9 (b) is an explanatory view showing a pressed state of a glass material and a cracked state of a molded product.

[Explanation of Signs] 1 Glass material 2, 3 Mold member 4 Interval adjusting member (body shape) 5 Base member 6a, 6b Air gap

Claims (2)

(57) [Claims] 1. A press forming apparatus for an optical element, wherein a glass material in a softened state is pressed using a molding die member, and an optical functional surface corresponding to a molding surface of the die member is formed on the glass raw material. In the cooling process after the pressure molding, the upper and lower mold members are relatively moved in a direction in which the distance between the upper and lower mold members is relatively reduced in conjunction with the volume shrinkage of the glass material accompanying the cooling up to the temperature of the transition point of the glass material. Like moving
An optical element press, characterized in that an interval adjusting member for limiting relative movement so as not to follow the volume shrinkage of the glass material at a temperature below the transition point is arranged in relation to the mold member. Molding equipment. 2. A glass material to be processed into an optical element shape is heated to a predetermined softening temperature, and a pair of mold members and an adjusting member for adjusting a distance between the mold members are provided, and the glass material is placed in the mold members. Put and pressurized, the pressed surface shape of the mold member is transferred to the glass material and deformed into a glass optical element having an optical element shape, and after the shape deformation process, the glass optical element is shifted to a cooling step, In the cooling step, one of the mold members is moved together with the glass material in accordance with the volume contraction of the glass material, and the movement of the one mold member is prohibited at a temperature of the glass material equal to or lower than the glass transition temperature. A method for forming a glass material, comprising: forming a glass material.