JPS63151632A - Mold for forming glass lens - Google Patents

Abstract

PURPOSE:To reduce chipping of mold and to prolong mold life, by setting a curved processed part at a chamfered interfacial part and a flat processed part positioned at the outside of the curved processed part on at least one opposing face of a first and a second mold. CONSTITUTION:At least one opposing face of a first and a second molds 11 and 12 are provided with a curved processed part 14 and a flat processed part 15 positioned at the outside of the processed part 14. An interfacial part between the processed parts 14 and 15 are chamfered and a slant face 6 having theta deg. angle from the processed part 15 is formed. A preform 17 is placed on the bottom mold 11, a guide mold 13 is set and the whole molds are heated to soften the preform 17. Then the top mold 12 is lowered and the preform is press molded. Consequently, stress concentration at part to be transferred to the interfacial part is relaxed and occurrence of cracks is prevented to give glass lenses having high optical precision.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a press molding die used for molding a glass lens such as a lens for an optical device such as a camera or a pickup lens for a compact disc.

[Conventional technology]

In recent years, glass lens forming methods have been widely used that eliminate the need for subsequent cold grinding and polishing by directly press-molding glass (for example, Japanese Patent Laid-Open No. 60-1
71233, JP-A-60-171236)
.

FIG. 7 shows an example of such a press forming apparatus. A softened glass material 10 is supplied to the lower mold 1, and the upper mold 2 is placed therein.
is lowered along the guide mold 3 and pressed under pressure to form a glass lens of a predetermined shape.

Next, the upper mold 2 is raised and a glass lens 4 as shown in FIG. 8 is taken out.

[Problem that the invention seeks to solve]

The glass lens 4 formed in this manner has a spherical or aspherical curved surface portion 5 that is effective as a lens, and a flat portion 6 made of surplus glass material located outside of the curved surface portion 5. Cracks 7 are likely to occur in the portion, which causes a drop in optical accuracy. The curved surface portion 5 is shaped according to the shape of the boundary between the curved surface processed portion γ and the flat surface processed portion 8 of the lower mold 1.
This is thought to be due to the fact that large stress was concentrated in this part during molding because the plane part 6 and the part 6 were formed at a relatively small angle α, and the mold itself was also prone to breakage at the boundary part. .

[Means for solving problems]

In the present invention, the boundary between the curved surface processed portion of the mold and the flat surface processed portion located outside the curved surface processed portion is chamfered.

Chamfering may be performed on either a flat surface or a curved surface.

[Effect]

Because there are no sharp corners between the curved surface and flat surface,
The mold itself is not easily damaged, and such corners are not transferred to the glass lens to be molded, so that no significant stress concentration occurs.

〔Example〕

Figure 1 (-) is a sectional view showing one embodiment of the present invention;
b) is a partially enlarged view. The mold of this embodiment is composed of a lower mold 11, an upper mold 12, and a guide mold 13. Down W! The molding surface 11 consists of a spherical curved surface processed part 14 and a flat processed part 15 that constitutes the outer edge, but the boundary between the two is chamfered, and the flat processed part 15 has a chamfer. A sloped surface 16 having an inclination of θ=306 is formed.

Note that the curved surface processing portion 14 may be an aspherical surface depending on the desired lens surface. Upper mold 11, lower mold 12 and guide mold 1
3 is made of tungsten carbide (WC).

In the above configuration, after the preform 17 is placed on the lower mold 11 and the guide mold 13 is set, the entire mold is heated to soften the preform 17. In this state, the shed 12 is lowered and press-formed as shown in FIG. 2. As the upper mold 12 descends, the softened preform 17 is transferred to the lower mold 1.
According to the shape of the molding surface 1, surfaces are formed in this order: a curved surface section 18 made of a spherical surface effective as a lens, an inclined surface 19, and a horizontal section 20, thereby obtaining the shape of a glass lens.

FIG. 3 shows a glass lens 21 formed in this manner. Dimensions of each part are outer diameter, D I = 6.5 ml
s.

The effective diameter of the curved surface portion 18, that is, the diameter of the effective portion through which light passes, is D2 = 4.6 m, and the radius of curvature of the curved surface portion 18 is R1 = &7.
sm, center wall thickness t 1 = Z5 III %, wall thickness difference between outer edge and center t2 = 1.211 m, θ = 30' for flat part 20 (m
It has 2. As a glass material, heavy flint optical glass 5F6 (manufactured by HOYA Corporation; transition temperature 435
°C) was used.

With respect to the angle α where the surfaces tangent to both the curved surface portion 18 and the flat portion 200 intersect, the angle β where the liquid planes of the curved surface portion 18 and the sloped surface 19 intersect, and the angle r where the surfaces tangent to both the sloped surface 19 and the flat portion 200 intersect. (=1806-0) are both larger. Therefore, stress concentration is alleviated compared to a lens molded with a conventional mold in which the curved surface portion 18 and the flat surface portion 20 directly intersect. This also applies to the mold itself, and by chamfering this part, damage such as chipping is less likely to occur. As the radius of curvature of the curved surface processed portion 14 is smaller, the curved surface processed portion 14 and the flat surface processed portion 15 intersect at a sharper angle, so the effectiveness of chamfering increases.

The inclination θ of the sloped surface 14 is not limited to 30°, and is appropriately set depending on the radius of curvature of the curved surface processing portion 12 in particular. For example, when the radius of curvature is small, the slope surface 1
It is desirable to increase the slope of 4 K.

Moreover, chamfering is not limited to chamfering on a flat surface such as the sloped surface 14. Figure 4 shows the curvature radius R2 design 1. O
A lower mold 11A having a spherical surface 23 of fi is shown. In this case, the curved surface processing section 14 and the spherical surface 23, and the spherical surface 23 and the flat processing section 1
The angles formed by the tangential planes of No. 5 are all 180°, which is the maximum, and the effect of alleviating stress concentration is the best. The rest of the structure is the same as that shown in FIG. 1, and a glass lens can be formed that differs only in the shape of the built-up portion 22 in FIG. 3.

Although the above description has been made using a mold for a plano-convex lens as an example, it goes without saying that the present invention can also be applied to a mold for a biconvex lens. Similarly, by combining an upper mold 12B having a convex spherical molding surface 24 as shown in FIG. 5 with a lower mold as described above, a meniscus-shaped glass as shown in FIG. Lens 21B can also be molded.

Further, the glass material is not limited to those mentioned above, and the present invention can be similarly applied to molding of a glass lens using a glass material having other components.

Furthermore, in addition to the above-mentioned tungsten carbide, the constituent materials of the mold include, for example, silicon carbide (STC), zirconium oxide (ZRO), stainless steel, cermet, silicon nitride (SlsN4), etc. depending on the relationship with the glass material to be formed. , may be selected appropriately.

〔Effect of the invention〕

According to the present invention, since the boundary portion between the curved surface processed portion and the planar processed portion is chamfered, this portion is resistant to impact, resulting in chipping and K<. Molding for glass lenses is generally expensive, but the present invention can extend the life of the mold. In addition, for the glass lens to be molded, stress concentration in the portion where the boundary portion is transferred is alleviated,
The generation of cracks is prevented, and a glass lens with high optical precision can be obtained.

[Brief explanation of the drawing]

Figure 1 (-) is a sectional view showing one embodiment of the present invention;
b) is a partially enlarged view, FIG. 2 is a sectional view showing the press-molded state, FIG. 3 is a sectional view of the lens to be molded, and FIG. 4 is a sectional view of main parts showing another embodiment of the present invention. , FIG. 5 is a sectional view showing still another embodiment of the present invention, FIG. 6 is a sectional view of a lens to be molded, FIG. 7 is a sectional view of a conventional example, and FIG. 8 is a sectional view of a lens to be molded. It is. 11, IIA...lower mold, 14...curved surface processing section, 15.self-uniplane processing section, 16...gradient surface (chamfered section), 23...spherical surface (chamfered section) .

Claims (1)

[Claims] Pressing the glass to be formed with the opposing surfaces of the first and second molds,
In a glass lens mold that transfers the surface shape of each opposing surface to both principal surfaces of a glass lens to be molded, at least one of the opposing surfaces of the first and second molds has a curved surface processed portion and an outer surface of the curved surface processed portion. 1. A glass lens molding die comprising a flat processed part located at , and a boundary between the curved processed part and the flat processed part is chamfered.