JP2003104740A - Press forming apparatus and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for press forming capable of improving dimensional precision of an optical element by suppressing warpage of a master block, and to provide a method for press forming. SOLUTION: The press forming apparatus 100 is provided with a pair of upper and lower master blocks 102 and 104, where each master block 102 and 104 has four forming faces arranged in a row, and each master block 102 and 104 is constituted so as to satisfy a relationship: L×α×ΔT/t<0.0008 (wherein L is the length, t is the thickness, α is a coefficient of thermal expansion, and ΔT is a temperature difference generated between both ends in the thickness direction at the induction heating), thereby warpage of each master block 102 and 104 is suppressed and dimensional accuracy of the optical element is improved.

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 and a press used in a high precision press capable of obtaining an optical element without polishing by press forming a preformed glass material in a heat-softened state. It relates to a molding method.

[0002]

2. Description of the Related Art Conventionally, in the field of manufacturing optical lenses and the like, a preformed glass material (preform) is prepared in order to obtain a highly accurate lens shape without surface polishing, and this preform is heated and softened. Then, a method of performing press working with a highly accurate molding surface is known (Japanese Patent Laid-Open No. 2001-2001).
10829). In particular, in recent years, in order to mold a plurality of preforms at one time, a long-shaped molding mother die having a plurality of molding surfaces in a line has been used (Japanese Patent Laid-Open No. 11-29333).

[0003]

However, when such a long molding die is used, the molding die is warped due to the temperature difference in the thickness direction, so that a molded product closer to both ends will move up and down. However, there is a problem that the molding surface of the molded article tilts, the molded lens is tilted, and the thickness of the molded product becomes large. In particular, in recent years, rapid heating and rapid cooling have been performed in response to increasing demands for shortening cycle time, and in response to the demand for more multi-cavity production, the mother die has been made longer. As a result, the problem of warping of the mother mold is becoming more serious.

Therefore, an object of the present invention is to provide a press molding apparatus and a press molding method capable of suppressing the warp of a mother die and improving the dimensional accuracy of an optical element.

[0005]

A press molding apparatus according to the present invention is an optical element press molding apparatus that obtains a plurality of optical elements by simultaneously press-molding a plurality of objects to be molded on a plurality of molding surfaces. , A long-sized mother die for holding the plurality of molding surfaces in a line, a heater for heating the mother die, and a support for supporting the mother die so that the upper die and the lower die face each other. A body and a drive shaft that is connected to the support on the upper mold side and / or the lower mold side and that moves in a direction in which the upper mold half and the lower mold half are moved toward and away from each other. As the mother die, the upper die and the lower die heated by the heater are brought close to each other by the drive shaft to press-form the plurality of objects to be formed, in the longitudinal direction. L (mm), thickness t (mm), coefficient of thermal expansion α (/
℃) and the temperature difference ΔT (℃) that occurs at both ends in the thickness direction
, Which has a relationship represented by L · α · ΔT / t <0.0008.

According to this structure, it is possible to suppress the warp of the long-sized mother die, improve the dimensional accuracy of the optical element molded on each molding surface, suppress the tilt, and improve the lens thickness accuracy. Can be improved.

Further, in the present invention, it is preferable that the plurality of molding surfaces are arranged so as to be divided into the plurality of mother dies and arranged in a line.

Further, in the present invention, the heater is
It is preferably one induction heating coil that winds the one or more masters.

The press-molding method according to the present invention is a press-molding method for an optical element, in which a plurality of optical elements are obtained by simultaneously press-molding a plurality of objects to be molded on a plurality of molding surfaces. And a step of preparing a mother die having a long shape which holds the mother die in a line, the upper die and the lower die being supported so as to face each other, and a step of heating the mother die. A step of press-molding the object to be molded by bringing the upper mold and the lower mold close to each other by a drive shaft connected to the support on the upper mold side and / or the lower mold side, as the mother mold. During the press molding step, the length L (mm) in the longitudinal direction, the thickness t (mm), the coefficient of thermal expansion α (/ ° C),
And the temperature difference ΔT (° C) that occurs at both ends in the thickness direction is
The one that satisfies the relationship represented by α · ΔT / t <0.0008 is used.

Further, in the present invention, it is preferable that the plurality of molding surfaces are arranged so as to be in a line by being divided into the plurality of mother dies.

Further, in the present invention, it is preferable that the heating is performed by winding one induction heating coil around the one or more master molds.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on the illustrated embodiments. FIG. 1 is a cross-sectional view showing a main structure of a press molding apparatus according to an embodiment of the present invention. This press molding apparatus 100 press-molds a preform formed by molding a glass material into a flat spherical shape in advance,
An optical lens having a predetermined shape is obtained.

The press molding apparatus 100 comprises an upper mother die 102 and a lower mother die 104 which are vertically opposed to each other. Each of the upper mother die 102 and the lower mother die 104 is made of a tungsten alloy and has a long shape that is long in the left-right direction in the drawing. The upper mother die 102 is provided with four upper die members 112 having a molding surface for pressing the preform in a row. The lower mother die 104 has four lower die members 11 at positions facing the respective upper die members 112 of the upper mother die 102.
4 in a row. The lower surface of the upper mold member 112 and the upper surface of the lower mold member 114 are molding surfaces for pressing the preform. The lower mother die 104 is attached to a lower support 108 that is driven in the vertical direction, and the upper mother die 102 is attached to an upper support 106 that is a fixed member. An induction heating coil 110 for high frequency induction heating surrounds the upper master mold 102 and the lower master mold 104, respectively.
02 and the lower mother die 104 are wound in a substantially elliptical shape substantially along the outer shape thereof.

A sleeve 11 is provided on the outer periphery of the upper mold member 112.
6 is attached. The sleeve 116 fits with the lower mold member 114 with a slight clearance and slides to prevent axial displacement of the upper and lower surfaces of the optical lens. A guide pin 118 is provided so as to project from the upper mother die 102, and a guide hole 120 that engages with the guide pin 118 is formed in the lower mother die 104. Upper mold member 11
2. The lower mold member 114 and the sleeve 116 are formed by forming silicon carbide by CVD on the molding surface of sintered silicon carbide.

FIG. 2 is a view showing the planar shape of the lower mother die 104. The lower mother die 104 has a substantially elliptical shape with rounded ends in the longitudinal direction. 4 molding surfaces A, B, C,
Ds (upper surface of the lower die member 114) are arranged in a row along the longitudinal direction of the lower mother die 104 at equal intervals. Although illustration is omitted, the planar shape of the upper mother die 102 is the same as that of the lower mother die 104.

In this embodiment, for the upper mother die 102, the length L (mm), the thickness t (mm), the coefficient of thermal expansion α (/ ° C.), and the upper mother die 102 during press molding. The relationship expressed by the following equation (1) is established between the temperature difference ΔT (° C.) generated at both ends in the thickness direction. L ・ α ・ ΔT / t <0.0008 (1)

Similarly, for the lower mother die 104, the length L
Also, between the thickness t, the thermal expansion coefficient α, and the temperature difference ΔT that occurs at both ends in the thickness direction of the lower mother die 104 during press molding,
It is configured so that the relationship represented by the above formula (1) is established.

The relationship expressed by the equation (1) is established for each of the upper mother die 102 and the lower mother die 104 because the warpage of the upper mother die 102 and the lower mother die 104 during press molding is performed. This is to suppress it.

FIG. 3 is a schematic view for explaining the effect of suppressing the warp of the upper mother die 102 and the lower mother die 104.
As in the example shown in FIG. 3A, the larger the warp of the upper mother die 202 and the lower mother die 204 is, the molding surfaces located at both longitudinal ends of each mother die (here, the lower die member 114 (Upper surface)
The inclination θ of becomes large. Further, the gap between the upper and lower molding surfaces is slightly widened due to the warp. On the other hand, in the present embodiment,
As shown in FIG. 3B, the upper mother die 102 and the lower mother die 1
By suppressing the warp of No. 04, the inclination θ ′ of the molding surface is minimized. As a result, the dimensional accuracy of the press-molded optical lens can be improved. Therefore,
When a plurality of molding surfaces are arranged in a matrix so as to form a single line, FIG.
If the inclination θ is too large as shown in (A) of FIG. 3, a plurality of mother molds are used so that the inclination θ ′ becomes small as shown in (B) of FIG. By arranging the plurality of mother dies in a line, a large number of simultaneous press moldings can be performed.

As such an example, a modification of the press molding apparatus according to the first embodiment will be described. The press molding apparatus according to the present modification is the upper mother die 102 shown in FIG.
And two sets of the lower mother die 104. FIG. 4 is a plan view showing the arrangement of the lower mother die in the press molding apparatus of this modification. In the press molding apparatus of the present modification, the two lower mother molds 104 have the respective lower mold members 11
4 are arranged in a line. Although not shown, the two upper mother dies 102 are also arranged in the same manner as the lower mother dies 104 (that is, the upper die members 112 are arranged in a line). The heating coil 400 includes two upper mother molds 10.
2 (omitted in FIG. 4) and two lower mother molds 104 are provided so as to orbit, and these are simultaneously heated by high frequency induction heating. According to this modification, a large number of preforms can be press-molded at the same time, and the warp can be suppressed by satisfying the above formula (1) for each of the upper mother die 102 and the lower mother die 104. The upper mother mold 10
Two or more sets including the lower mother die 104 may be provided. By using a plurality of master molds in this way, the warp of the master mold does not increase even if the number of molding surfaces is increased, so that it is possible to simultaneously press-mold a large number of optical elements having good surface accuracy and wall thickness accuracy.

FIG. 5 is a sectional view showing the structure of the main part of the press molding apparatus according to the second embodiment. In the press molding apparatus 300 according to this embodiment, a gap is provided between the upper mother die 102 and the upper support 106, and the spacer 30 is provided in the gap.
2 is inserted. Similarly, the lower mother mold 104 and the lower support 1
08 also has a gap, and the spacer 304 is provided in the gap.
Have been inserted. The reason for providing such a gap is to prevent heat of the upper mother die 102 and the lower mother die 104 from being dissipated through the upper support 106 and the lower support 108. The other configurations of the press molding apparatus 300 are the same as those of the press molding apparatus 100 according to the first embodiment. That is, also in the present embodiment, the above conditional expression (1) is established for each of the upper mother die 102 and the lower mother die 104.

The above modification (FIG. 4) may be applied to the press molding apparatus 300 according to the second embodiment.

[0023]

EXAMPLES Next, examples relating to the above-described respective embodiments will be described. First, as Examples 1 to 4, barium borosilicate glass was pressed using the press molding apparatus 100 (FIG. 1) according to the first embodiment to have a diameter of 6.
A 6 mm biconvex lens was molded. In Examples 1 to 4, Table 1 (described later) shows the length L, the thickness t, the width W, the thermal expansion coefficient α, and the temperature difference ΔT at both ends in the thickness direction of the mother dies 102 and 104 in the press molding apparatus 100. I changed it. In Examples 1 to 3 and Example 4, the mother molds 102 and 104 were made of tungsten alloys having different thermal expansion coefficients.

Barium borosilicate glass (transition point 514
Flat glass-shaped glass preform (weight: 54 mg) at ℃, yield point 545 ° C.) was supplied to four levitation dishes on a support arm (not shown) and supported while supporting the gas while levitation. All the members were placed in a heating chamber (not shown). The heating chamber is kept at 700 ° C. by Pilemax (PX-DS). In the heating chamber, the four glass preforms are batch-heated for a certain period of time according to the molding cycle speed of the optical glass element, and heated to about 596 ° C. (a temperature equivalent to 10 ⁸ poise). It On the other hand, 4 molding surfaces, each molding die
50 ℃ (The above glass preform is 10.2 poise) ±
It was preheated by heating within 3 ° C. After that, the support arms are arranged immediately above the plurality of lower mother molds 104, and the support arms are quickly opened to divide the plurality of floating trays into right and left, and four preforms are respectively associated with the floating trays. Simultaneous transfer was made by dropping them on the molding surface of the lower mold at the same time. Immediately thereafter, the support arm is moved to the lower mother die 104
After retreating from the top, the high frequency power was cut off, the lower master mold was raised and pressed at a pressure of 60 kg / cm ² . Next, the pressure applied to the glass was limited to the upper mold weight, the glass was cooled to 470 ° C., and then the lower mold 104 was lowered to release the mold, which was simultaneously taken out by an adsorption pad (not shown). The cycle time of this press molding process varies depending on the capacity of the high frequency power source and the size (heat capacity) of the mother die, but it is 180 seconds when the mother die having a length of 190 mm is used and when the mother die having a length of 112 mm is used. It was 110 seconds.

The tilt of the optical lens thus press-molded was measured. The measurement was carried out on the optical lens molded on the extreme molding surface (molding surface A or D in FIG. 2) of the four molding surfaces. In addition, tilt is measured by measuring the thickness of the optical lens with a micrometer.
It was calculated from the maximum and minimum values and the lens diameter. Table 1 shows the tilt measurement results.

[0026]

[Table 1]

On the other hand, in Examples 5 to 7, barium borosilicate glass was pressed by the press molding apparatus 300 (FIG. 5) according to the second embodiment to mold a biconvex lens having a diameter of 6.6 mm. . In Examples 5 to 7, the mother die 10
The length L, the thickness t, the width W, the coefficient of thermal expansion α, and the temperature difference ΔT at both ends in the thickness direction of Nos. 2, 104 were changed as shown in Table 1. In Examples 5 to 6 and Example 7, the mother dies 102 and 104 were made of tungsten alloys having different thermal expansion coefficients.
Configured. Specific press molding methods are described in Examples 1 to 4.
Is the same as. The tilt of the optical lens thus obtained by press molding was measured. The measurement results are also shown in Table 1 above. Further, based on the measurement results, L · α · ΔT / t was calculated for each of Examples 1 to 7. FIG. 6 shows the relationship between the value of L · α · ΔT / t and the tilt.

From FIG. 6, it is understood that L · α · ΔT / t and tilt are in a substantially proportional relationship, and the smaller L · α · ΔT / t is, the smaller the tilt can be made. Generally, the allowable range of tilt in the optical lens is within 2 minutes. From Fig. 6, in order to suppress the tilt within 2 minutes, L ・ α ・ ΔT
It is understood that / t should be 0.0008 or less.

Further, it can be seen from Table 1 that the tilts of Examples 5 to 7 are smaller than those of Examples 1 to 4. This is because gaps are provided between the master molds 102 and 104 and the supports 106 and 108, respectively, so that heat dissipation from the master molds 102 and 104 is suppressed and the temperature difference ΔT is suppressed to be small (as a result, L · It is considered that this is because α · ΔT / t can be suppressed to a small value.

As described above, according to the press-forming apparatus according to each of the above-mentioned embodiments, each mother die 102, 10 is formed.
4 is configured such that L · α · ΔT / t is 0.0008 or less, the warp of the mother molds 102 and 104 during induction heating can be suppressed, and thereby the dimensional accuracy of the optical lens can be improved. .

Further, particularly in the press molding apparatus according to the second embodiment, the mother molds 102 and 104 and the supports 106 and 1 are provided.
Since a gap is provided between the mother mold 102 and
The temperature difference ΔT at both ends in the thickness direction of 104 can be reduced to further suppress the warp and further improve the dimensional accuracy of the optical lens.

The embodiments of the present invention have been described above with reference to the drawings. However, it is obvious that the present invention is not limited to the matters shown in the above-mentioned embodiment, and changes and improvements thereof can be made based on the description of the claims. For example,
In the above embodiment, four molding surfaces are arranged in each of the upper mother die 102 and the lower mother die 104, but the number of molding surfaces in each mother die may be any number. Although the upper mother die 102 and the upper die member 112 are separate members in the above embodiment, they may be integrally formed. Similarly, the lower mother die 104 and the lower die member 114 may be integrally formed.

Although the non-isothermal press molding method is used in the above-mentioned embodiment, the present invention may be adopted in an isothermal press molding method in which a preform is put in a molding die and the molding die and the preform are heated. it can. Further, in the above-mentioned embodiment, the mother die which holds a plurality of mold members each having a molding surface is used, but the mother die itself having a plurality of molding surfaces may be used.

[0034]

As described above, according to the present invention, as the mother die, the length L, the thickness t, the coefficient of thermal expansion α, and the temperature difference ΔT occurring at both ends in the thickness direction during press molding are provided. In the meantime, L
Since the one satisfying the relationship represented by α · ΔT / t <0.0008 is used, it is possible to suppress the warp of the mother die, and thereby the dimension of the optical element molded on each molding surface. The accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a main part structure of a press molding apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view showing a planar shape of a lower mother die of the press molding apparatus shown in FIG.

FIG. 3 is a schematic diagram for explaining the effect of suppressing warpage.

FIG. 4 is a plan view showing a modified example of the first embodiment.

FIG. 5 is a cross-sectional view showing a main part structure of a press molding apparatus according to a second embodiment.

FIG. 6 is a graph showing tilt measurement results for Examples 1 to 7.

[Explanation of symbols]

100,300 Press molding equipment 102 upper matrix 104 Lower mother 106 upper support 108 Lower support 110 induction heating coil 112 Upper mold member 114 Lower mold member 116 sleeve 118 guide pin 120 guide holes 122,124 thermocouple 302, 304 spacer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 6/10 331 H05B 6/10 331 (72) Inventor Eiji Tajima 2-7 Nakachuai, Shinjuku-ku, Tokyo No. 5 F-term in Hoya Co., Ltd. (reference) 3K059 CD72 CD77

Claims (6)

[Claims] 1. A press molding apparatus for an optical element, which obtains a plurality of optical elements by simultaneously press-molding a plurality of objects to be molded with a plurality of molding surfaces, wherein the plurality of molding surfaces are held in a line. A long-sized mother die, a heater that heats the mother die, a support that supports the mother die so that the upper die and the lower die face each other, and the upper die side and / or the lower die side An upper mold heated by the heater as a mother mold, which is connected to a support and includes a drive shaft that moves in a direction in which the mother mold on the upper mold side and the mother mold on the lower mold side move toward and away from each other. During the step of press-molding the plurality of objects to be molded by bringing the side mold and the lower mold side close to each other by the drive shaft, the length L (mm) in the longitudinal direction and the thickness t (mm) , Thermal expansion coefficient α (/ ° C), and temperature difference ΔT (° C) that occurs at both ends in the thickness direction are L · α · ΔT / <Press forming apparatus which is characterized by using a satisfy the relationship represented by 0.0008. 2. The press molding apparatus according to claim 1, wherein the plurality of molding surfaces are arranged so as to be in a line by being divided into the plurality of mother molds. 3. The press molding apparatus according to claim 1, wherein the heater is one induction heating coil that winds the one or more mother dies. 4. A method of press-molding an optical element, wherein a plurality of optical elements are obtained by simultaneously press-molding a plurality of objects to be molded with a plurality of molding surfaces, wherein the plurality of molding surfaces are held in a line. And a step of heating the mother die, which is a long-sized mother die in which the upper die and the lower die are supported so as to face each other, and the upper die side and / or Press-molding the molded body by bringing the upper mold and the lower mold close to each other by a drive shaft connected to the support on the lower mold side; and, in the step of press-molding as the mother mold, Length L (mm) in the longitudinal direction, thickness t (mm), coefficient of thermal expansion α (/
℃) and the temperature difference ΔT (℃) that occurs at both ends in the thickness direction
Is used to satisfy the relationship represented by L · α · ΔT / t <0.0008. 5. The press molding method according to claim 4, wherein the plurality of molding surfaces are divided into the plurality of mother molds and arranged in a line. 6. The press molding method according to claim 4, wherein the heating is performed by winding one induction heating coil around the one or a plurality of mother dies.