JPH07106917B2 - Glass lens forming method and apparatus thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for molding a glass lens and an apparatus therefor, and particularly, a molding method suitable for molding a glass lens, a biconcave lens, a meniscus lens, etc. having a large diameter. A method and an apparatus thereof.

[Conventional technology]

In recent years, instead of glass lens processing methods that require polishing finish, pre-measured glass materials (glass gobs)
Attention has been paid to a precision press working method in which the surface is transferred to a glass surface by using an ultraprecision mold after heating and softening.

Many invention proposals have been made so far for this type of glass lens molding method and apparatus, and a lens having a small diameter,
We have already made many achievements in the manufacture of biconvex lenses.

The reason for this has been found out by the inventor to be as follows. That is, when the surface of the ultra-precision mold is transferred to the lens by pressurization and then both the lens and the mold are cooled to a temperature below the transition temperature, in the case of a lens with a small diameter, the difference in the coefficient of thermal expansion between the glass being molded and the mold This is because the difference in the amount of contraction between the two is small, and therefore the deviation of the contact point between the glass and the mold is small, and in the case of a biconvex lens, the mold has a shape that does not prevent the contraction when the lens contracts. Because.

[Problems to be solved by the invention]

However, large-diameter lenses where the contact point between the mold and the lens is large, or biconcave lenses where the contraction of the glass is blocked by the mold,
In the case of molding a meniscus lens, etc., there is a problem that it is difficult to obtain a highly accurate lens by measuring the obtained lens with an interferometer and a curved interference fringe is observed in the center of the lens. It was

In particular, in the case of a biconcave lens, a meniscus lens, etc., a temperature difference occurs between the central portion and the outer peripheral portion of the glass to be molded during slow cooling, and the outer peripheral portion is cooled in order from the outer peripheral portion to the inner portion, so that the outer peripheral portion comes first. As the mold solidifies and the shrinkage inside the glass is blocked by the mold, if the glass is continuously pressed to the transition temperature, cracks will occur, and even if the pressure is weakened, the entire lens will maintain the shape at the time of molding and shrink uniformly. Instead, the interferometer measurement will show the curvature of the interference fringes in the center of the lens. Further, if the extremely slow gradual cooling is performed so as to eliminate this temperature difference, the gradual cooling requires a long time, and the production efficiency is extremely deteriorated, which is not suitable as a production method.

The present invention has been made to eliminate the above problems and drawbacks, and an object thereof is to provide a glass lens molding method and apparatus capable of increasing the shape accuracy even in a large-diameter lens, a biconcave lens, a meniscus lens, and the like. Is to provide.

[Means for solving problems]

In order to achieve this object, the glass lens molding method according to the present invention performs a first pressurization of glass which is placed in a mold and heated to a predetermined temperature, and at that time, after the first pressurization, A pressure margin of more than the amount of shrinkage of the glass generated during the temperature decrease from the temperature to the transition temperature is left, then the pressure is weakened to lower the temperature, and the pressure residual margin is zero near the glass transition temperature. It is characterized in that it is re-pressurized until it becomes, and the applied pressure is weakened and gradually cooled to the transition temperature, and further cooled.

Furthermore, the glass lens success device according to the present invention comprises a mold having an upper mold and a lower mold having a molding surface corresponding to the lens surface of the glass lens, and a pressure mold for the upper mold and the lower mold. Pressure means for pressurizing at least one, a position sensor for detecting displacement of the pressurizing means or the pressurizing die for setting the remaining pressure after the first pressurization, and a signal from this position sensor It is characterized by comprising a control mechanism for controlling the pressurizing means based on the above, and a temperature adjusting means for the glass to be molded and the molding die.

〔Example〕

 Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows the whole glass lens forming apparatus according to an embodiment of the present invention. An upper mold 2 and a lower mold 3 are arranged in a heat molding chamber 1 which is closed by a box 1a, and the upper mold 2 and the lower mold 3 are provided with an upper fixed shaft 4 and a lower part via heat insulating bases 9 and 10, respectively. It is fixed to the tip of the movable shaft 5. The lower movable shaft 5 is connected to a pressurizing cylinder (not shown) and is driven to move upward when pressurizing. Further, in order to detect the operating position of the lower die 3, a detection piece 7 is attached to the lower movable shaft 5, and a position sensor 8 that responds to the detection piece 7 (for example, an eddy current type with a high detection accuracy of a minute position interval). A displacement sensor) is fixedly arranged on the box 1a by means not shown. The signal from the position sensor 8 is supplied to a control mechanism (not shown). The control mechanism includes a sequencer or a computer, and controls the operation of the lower movable shaft 5 based on the signal.

Figure 2a shows the state of the mold with the pressure margin (gap Δt) left after the first press, and Figure 2b shows the state of the mold completely repressed and completely pressed. There is.

The molding die includes upper and lower cavity dies 12, 13 having precision molding surfaces corresponding to the lens surfaces, body dies 11, 15 holding the cavity dies 12, 13 from the periphery, and bases 16, 17. The cavity die 12 and the body die 11 form the upper die 2 shown in FIG. 1, and the cavity die 13 and the body die 15 form the lower die 3. The material of the cavity dies 12 and 13 is, for example, a dense ceramic, and the body dies 11 and 15 and the bases 16 and 17 are, for example, a tungsten alloy having good oxidation resistance. In this case, the relationship of expansion coefficient is ceramics <tungsten alloy << glass. Glass to be molded by the cavity dies 12 and 13 is indicated by numeral 14.

Next, a method of molding a glass lens by the molding device having the above structure will be described.

After the glass to be molded 14 is placed on the cavity die 13 set inside the lower mold 3, the inside of the heat molding chamber 1 is filled with an inert gas (nitrogen gas), and the temperature is raised by heating. Then, after reaching a pressable set temperature and performing soaking, the lower mold 3 is raised by the lower movable shaft 5 connected to a pressure cylinder (not shown), and the fixed upper mold 2 and The first pressure molding is performed between the two. This pressurizing stroke is limited as follows by stopping the pressurizing cylinder by the position sensor 8 and a control mechanism (not shown). That is, the pressure is limited so as to leave a predetermined pressure margin (see Δt in FIG. 2a) for the second pressure molding described later. The predetermined pressure residual amount Δt is the amount of heat shrinkage of the glass that occurs between the time when the first pressurization is finished and the time when the glass is cooled to the transition temperature, that is, the amount of heat shrinkage of the glass after the first time. Is set larger than, for example, 10 to 100 μm
And depends on the shape and size of the lens. The remaining pressure margin Δt is further selected to an appropriate value in consideration of the following two points.

The larger the pressurizing stroke, the better the stretching with a small force during pressing.

However, if the second pressurizing stroke is increased, the elongation of the lens peripheral portion becomes too weak during the first pressing, and the complete shape accuracy cannot be obtained even if the second pressing is performed.

After the first pressure molding, the temperature of the glass is lowered to near the transition temperature to make the temperature uniform, and the second pressure molding is performed. This pressure molding is performed until the pressure residual amount Δt becomes zero,
It is completely pushed down. Next, the lens is taken out from the mold after being gradually cooled to the transition temperature and further cooled.

The glass lens molded in this manner does not cause disturbance such as interference fringe curve. Therefore, even for a lens having a large diameter, a biconcave lens, and a meniscus lens, it is possible to mold a glass lens with sufficiently satisfactory accuracy by adopting the apparatus and method of the present invention.

Next, an actual molding example of the concave meniscus lens will be described. As the glass, Hoya glass type FD5 (heavy flint type glass) with a transition temperature of 430 ° C is used, the cavity dies 12 and 13 are made of silicon carbide having an expansion coefficient of 4 × 10 ^-6 mm / ° C, and the barrel dies 11 and 15 are made of an expansion coefficient of 5 × 10 ^-6 mm / ° C tungsten alloy with an outer diameter of 20 m
m, a radius of curvature R of the upper surface and a lower surface of 20 mm, and a thinnest center wall thickness of 1.2 mm were molded.

The first press was carried out at a temperature of 550 ° C. and a load of 160 kg, leaving a pressure margin Δt of 30 μm. Next, the pressurizing load was switched to a low pressure, and at the same time, the temperature was lowered at 40 ° C / min. The load at this time was set to be large enough to compensate for the contraction of the member (mold, heat insulating material, etc.) accompanying the temperature decrease.

The second press at 480 ° C, which is close to the transition temperature,
Pressing was performed until the remaining pressure was almost zero. The pressure at this time was about 120 kg, which is slightly lower than the previous pressure, and after pressurization, the low pressure was switched again to gradually cool to the transition temperature, and then rapidly cool to take out the lens from the molding die.

As a result of measuring the interference fringes of the lens obtained by the above molding method with a Fizeau interferometer, the interference fringes were not disturbed, and no particular curvature was observed.

As in the above molding example, when pressing was performed at a temperature of 550 ° C. and the temperature was lowered to around the transition temperature (430 ° C.) at which glass solidifies, the gap generated by the difference in expansion coefficient was the third.
In the figure, Δt: 3.4μm, Δt ₁ : 1.5μm, Δt ₂ : 0.1μ
As a result of calculation, Δt> Δ
It becomes t ₁ + Δt ₂ , and it seems that the inaccuracy (curve of stripes) that occurs in the central part of the lens does not occur by continuing to pressurize in the temperature range where viscous flow occurs in the glass.

However, in reality, in the slow cooling process, a temperature difference occurs between the central portion and the outer peripheral portion of the barrel dies 11 and 15, the cavity dies 12 and 13, and the lens 14, and they are sequentially cooled inward from the outer peripheral portion. The contraction of the glass in the radial direction is hindered by the mold, and cracking occurs if pressure is continuously applied to the transition temperature, and even if the pressure is weakened, bending of interference fringes occurs. Further, in the case of carrying out slow cooling so as to eliminate this temperature difference, slow cooling requires a long time, and production efficiency is extremely deteriorated, so that it cannot be adopted as a production system.

Therefore, it is necessary to satisfy Δt> Δt ₁ + Δt ₂ when the second pressing is performed as in the above embodiment.

〔The invention's effect〕

As described above, according to the present invention, the pressurization is performed in two steps, and at the time of the first pressurization, a pressurizing amount equal to or more than the shrinkage amount of the glass that occurs thereafter is left, and then the temperature is reduced and then the temperature is lowered. By applying pressure again near the transition temperature, interference fringes do not occur in lenses with large diameters and lenses of all shapes, and it is possible to obtain a glass lens with high shape accuracy. It plays.

[Brief description of drawings]

FIG. 1 is a schematic view of an entire glass lens molding apparatus according to an embodiment of the present invention, FIG. 2a is a vertical cross-sectional view of a mold showing a state in which a pressure margin after the first pressure is left, and FIG. FIG. 3 is a vertical cross-sectional view of the mold showing a state in which the mold is completely pressed by re-pressurizing.
It is a longitudinal cross-sectional view of a mold showing a state before the second pressurization. 1 ... Heat molding chamber, 1a ... Box, 2 ... Upper mold, 3 ... Lower mold, 4 ... Upper fixed shaft, 5 ... Pressurizing means (lower fixed shaft), 7 ... Detection piece, 8 ... Position sensor, 9,10 ... Insulation base, 11,15 ... Body type, 12,13 ... Cavity die, 14
…… Glass to be molded, 16,17 …… Base, Δt …… Pressure remaining margin, Δt ₁ , Δt ₂ …… Gap between cavity die and glass to be molded

Claims (2)

[Claims] 1. A glass which is placed in a mold and heated to a predetermined temperature for a first pressurization, and at that time, a glass which is generated during a temperature decrease from the temperature after the first pressurization to a transition temperature. Then, the pressure is reduced by lowering the pressure, and the temperature is lowered again near the transition temperature of the glass until the remaining pressure is zero, and the pressure is reduced. A method for molding a glass lens, which comprises gradually cooling to a transition temperature and further cooling. 2. A molding die having an upper die and a lower die having a molding surface corresponding to the lens surface of the glass lens, and for pressurizing at least one of the upper die and the lower die for pressure molding. The pressure applying means, the position sensor for detecting the displacement of the pressure applying means or the pressurizing die for setting the remaining pressure after the first pressure application, and the pressure applying means based on the signal from the position sensor. An apparatus for forming a glass lens, comprising: a control mechanism for controlling; and a means for adjusting the temperature of a glass to be formed and a forming die.