JPH11138610A - Method and apparatus for forecasting shape of finished molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for optimizing the shape of a mold, molding conditions, and others by forecasting the shape of a finished molding produced by injection molding, compression molding, or injection compression molding and an apparatus for the method. SOLUTION: For a molding produced by compression molding are provided a temperature change calculation means 14 for calculating the temperature change of a mold and a molding in a minute time along the history of its production time, a heat strain calculation means 15 for calculating heat strain generated in the mold and the molding corresponding to the temperature change calculated by the means 14, a data storage part 13 for storing stress relaxation data prepared in advance on the basis of a temperature-time conversion rule, an internal stress calculation means 15 for calculating the internal stress of the molding from the stress relaxation data stored in the part 13 and the heat strain calculated by the means 15, and final shape forecasting means 16, 17 for forecasting the final shape of the molding based on the calculation results by the means 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finished shape of a molded product which can optimize a mold shape and molding conditions for a molded product produced by an injection molding method, a compression molding method or an injection compression molding method. The present invention relates to a prediction method and an apparatus therefor.

[0002]

2. Description of the Related Art In injection molding various molding materials into a predetermined shape, it is necessary to perform a deformation analysis in advance of cooling of a molded product processed by the injection molding and to set an optimal mold shape and molding conditions. It is extremely important for obtaining a molded product having good dimensional accuracy.

[0003] In the case of performing a deformation analysis of a molded article due to such cooling, conventionally, the temperature of a predetermined location of the molded article has reached a predetermined temperature such as a flow stop temperature, a solidification temperature, or a glass transition temperature. The temperature distribution in the molded article at the time is set as the initial state, and the deformation amount of the molded article is calculated from the temperature distribution in the initial state, the temperature difference until the molded article is removed from the mold, and the linear expansion coefficient of the molded article. I predict.

In the simulation system proposed in Japanese Patent Publication No. Hei 6-22840, the temperature from the initial state to the time when the molded product is taken out of the mold is subdivided, and the heat in the subdivided minute temperature range is reduced. Calculate the amount of strain based on the coefficient of linear expansion, specific heat, thermal conductivity, and Young's modulus that change corresponding to each minute temperature range,
The amount of thermal strain in each minute temperature range is accumulated, and the accumulated sum is predicted as the final deformation of the molded product.

[0005]

Conventionally, when analyzing the deformation of a molded article caused by cooling, it is based on the premise that the entire molded article is uniformly cooled from an initial state to a final temperature. However, since the concept of aging over time has not been introduced, if the cooling gradient or the molding cycle is significantly different, the amount of deformation of the obtained molded product will actually differ greatly, whereas the calculated result will be There is a contradiction that they become the same.

Further, the temperature distribution of the molded article at the time when a predetermined place of the molded article reaches the flow stop temperature, the solidification temperature, or the glass transition point temperature is set as an initial state. The criteria for setting the location varies depending on the simulation software. Moreover, the molded product does not shrink until the set initial state, and even if the molded product has a temperature higher than the specific temperature, if the predetermined location is lower than the specific temperature, the entire molded product will not be shrunk. It is extremely unnatural because of the idea of shrinking uniformly.

On the other hand, in a simulation system disclosed in Japanese Patent Publication No. Hei 6-22840, thermal strain is calculated from the difference between the temperature of a molded product in an initial state and the temperature of a molded product when it is removed from a mold. Or, after taking out from the mold, the entire molded article has a uniform temperature, for example, as is clear from calculating the thermal strain based on the temperature difference until reaching room temperature, the entire molded article is uniformly cooled. It is assumed that there is. Also, in such a calculation method,
Since the molded product is always cooled uniformly, the temperature distribution in the initial state determines the magnitude of the thermal strain, and only the constant thermal strain is calculated without being affected by the cooling history after the initial state. Will be.

By the way, single-lens reflex cameras and VT
When manufacturing an optical lens such as a photographing lens of an R camera or an imaging lens of a laser beam printer by injection molding, since the shape transfer accuracy of the optical surface is on the submicron order, the local sink on the micron order is:
This is a major problem in optical performance. For this reason, in the analysis method on the premise that the whole contracts uniformly as described above, the deformation amount of the molded product cannot be accurately evaluated. Moreover,
It is well known that even if the initial temperature state is the same as the final temperature state, the final molded product deforms greatly depending on the cooling history such as the length of the cooling time and the magnitude of the cooling gradient and the pressure history. However, the conventional simulation system described above cannot accurately predict the accuracy of the final molded product.

[0009]

An object of the present invention is to optimize a mold shape and molding conditions by predicting a finished shape of a molded product manufactured by an injection molding method, a compression molding method, or an injection compression molding method. It is an object of the present invention to provide a method and an apparatus for obtaining the same.

[0010]

According to a first aspect of the present invention, a molded article manufactured by an injection molding method, a compression molding method, or an injection compression molding method is used in a short time along a history of the manufacturing time. Calculating the temperature change of the mold and the molded article, calculating the amount of thermal strain generated in the mold and the molded article corresponding to the calculated temperature change, and calculating the calculated amount of thermal strain. , Temperature-
A step of calculating an internal stress of the molded article from stress relaxation data created in advance based on a time conversion rule, and a step of predicting a final shape of the molded article based on the calculation result. The feature lies in a method for predicting the finished shape of a molded product.

In a second aspect of the present invention, a mold manufactured by an injection molding method, a compression molding method, or an injection compression molding method for a minute time along a history of the production time and the mold and Temperature change calculating means for calculating a temperature change of a molded article, and thermal distortion amount calculating means for calculating an amount of thermal strain generated in the mold and the molded article in accordance with the temperature change calculated by the temperature change calculating means A data storage unit that stores stress relaxation data created in advance based on a temperature-time conversion rule; the stress relaxation data stored in the data storage unit; and a heat calculated by the thermal strain amount calculation unit. An internal stress calculating means for calculating the internal stress of the molded article from the amount of strain, and predicting a final shape of the molded article based on a calculation result by the internal stress calculating means. In moldings finished shape predicting apparatus being characterized in that comprises a final shape prediction unit.

According to the present invention, for a molded product manufactured by an injection molding method, a compression molding method, or an injection compression molding method, a temperature change of a mold and a molded product in a very short time along a history of the manufacturing time. It is calculated by the temperature change calculating means. The amount of thermal strain generated in the mold and the molded product corresponding to the temperature change calculated by the temperature change calculating means is calculated by the thermal strain amount calculating means. The internal stress of the molded article is calculated by the internal stress calculating means from the thermal strain calculated by the thermal strain calculating means and the stress relaxation data based on the temperature-time conversion rule stored in the data storage unit. Then, based on the calculation result, the final shape of the molded article is predicted by the final shape prediction means.

That is, a viscoelasticity test in a solid phase below the glass transition temperature of the molding material and a viscoelasticity test in a molten phase above the glass transition temperature are performed, and the data of both are joined to form a continuous relaxation elasticity. A coefficient master curve and a temperature shift factor introducing a temperature-time conversion rule are stored in the data storage unit. Then, the thermal strain during the short time is reflected by the aging process of the stress generated by the time, and the history of the temperature and pressure during cooling is integrated by integrating the history over the entire cooling time. I am handling it.

[0014]

In the first and second embodiments of the present invention, the molded article is a lens having a plurality of optical surfaces,
Of these optical surfaces, the optical surface having the largest effective area may be a compression surface over the entire surface, and the outer periphery of the compression surface may coincide with the outer periphery of the molded product. Similarly, the mold is for molding a lens having a plurality of optical surfaces, and among the plurality of optical surfaces, the optical surface having the largest effective area is a compression surface over the entire surface. The outer periphery of the surface may coincide with the outer periphery of the molded product.

In the compression molding method, the amount of compression may be changed based on the weight of the molding material to be molded. In this case, the amount of change in the compression amount is obtained by projecting the product of the difference between the reference molding material weight and the actual molding material weight and the specific gravity of the molding material along the compression direction of the compression surface of the mold. The value may be divided by the area. In this case, the specific gravity of the molding material may be calculated from specific gravity data stored in advance based on the temperature and the pressure.

The weight of the molding material may be measured after the molding material is put into a mold and before the compression step.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an apparatus capable of implementing the method for predicting a finished shape of a molded article according to the present invention is applied to compression molding of an optical lens constituting a taking lens of a VTR camera will be described in detail with reference to FIGS. However, the present invention is not limited to such an embodiment, and can be applied to technologies in other fields that include similar problems.

As shown in FIG. 1 showing a schematic configuration of the present embodiment, an optical lens L to be molded and its mold (see FIG. 2) stored in a first data storage section 12 are provided in a data input section 11. ), Data such as pressure conditions and cooling conditions are input. Data relating to the shape is set in a format that divides the entire optical lens L and the mold into fine regions and can be handled by the finite element method. ing.

However, since the optical lens L is generally a rotationally symmetric body having the optical axis C as a symmetry axis, the optical axis C as shown in FIG. The analysis is performed on an axisymmetric three-dimensional １ ／ model. Also, in order to reduce the number of convergence calculations described below as much as possible and to increase the calculation efficiency, the dimensions of the mold are set slightly larger than the actual design dimensions in view of the shrinkage of the molding material. Specifically, the mold size in the present embodiment is set to, for example, 1.006 times the actual design size of the optical lens L, and this value is set to the first value.
It is stored in the data storage unit 12. In this embodiment, the initial condition is that the molding pressure is 85 MPa, the temperature condition is that the resin injection temperature is 260 ° C., the cooling time with 114 ° C. primary cooling water is 10 minutes, and the cooling time with 80 ° C. secondary cooling water is 10 minutes. 8
When the secondary cooling was completed, the molded optical lens was taken out from the mold at the time of completion of the secondary cooling, and was set to be air-cooled at room temperature (23 ° C.).

Various physical property values such as specific volume data and viscoelasticity data of a molding material are input and stored in a second data storage section 13 as a data storage section according to the present invention. In the present embodiment, PMMA (polymethyl methacrylate) resin is employed as a molding material, and the linear expansion coefficient that greatly affects the calculation of the thermal strain is calculated from PVT data representing the relationship between pressure, volume, and temperature. Approximately converted as a function α _{(P, T)} as shown in FIG. 3 depending on pressure and temperature. Further, the viscoelastic data, processes the data measured by the viscoelasticity tester to create a master curve on mitigation modulus G _(t) as shown in FIG. 4, the temperature shift factor a _{T (T)} is also at each temperature This is stored in the second data storage unit 13. The above-mentioned viscoelasticity data is converted into two kinds of data of a solid property test below the glass transition point temperature and a melt property test above the glass transition point temperature and joined together.
From room temperature to the injection molding temperature, in this embodiment from 20 ° C. to 300
A continuous master curve is created in the range of ° C.

The temperature distribution calculating section 14 corresponds to the temperature change calculating means in the present invention, and the data input section 1
Based on the data relating to the molding shape and the processing conditions from No. 1 and the data relating to the molding material from the second data storage unit 13, a heat conduction analysis of the molding material injected into the molding cavity of the mold is performed, and its temperature distribution is determined. Is calculated.

The thermal strain / stress relaxation calculating section 15 corresponds to the thermal strain amount calculating means and the internal stress calculating means in the present invention, and the temperature of the molding material in the mold calculated by the temperature distribution calculating section 14. Distribution and second data storage unit 1
Based on the viscoelasticity data stored in No. 3 and taking into account stress relaxation, a shrinkage strain due to thermal shrinkage of the molding material in the mold is calculated, and this is output to the calculation result storage unit 16.

The calculation result storage section 16 corresponds to the final shape prediction means according to the present invention, and the shrinkage due to the heat shrinkage of the molding material in the mold calculated by the thermal strain / stress relaxation calculation section 15. The distortion is stored, a shape error between the design shape of the optical lens L input to the data input unit 11 and the optical surface of the optical lens L obtained by molding is calculated, and the data is output to the calculation result display unit 17. .

The operation result display section 17 is provided in the operation result storage section 1.
The surface accuracy of the optical surface of the optical lens L obtained by molding the data stored in 6 is displayed by interference fringes as shown in FIG.

In this case, the shrinkage ratio of the resin to the cavity of the mold does not match under the above-mentioned initial conditions, and distortion occurs in addition to the error in the radius of curvature of the optical surface. There is no problem if the curvature radius error and the distortion amount are within the allowable range.
In order to obtain an optical lens L having a desired design shape, it is necessary to modify molding conditions.

Specifically, based on the shape error with respect to the design shape stored in the calculation result storage unit 16, a change in the initial condition is examined. In this case, the error in the radius of curvature is determined by the amount of shrinkage of the resin, and cannot be dealt with by changing the molding conditions (changes in cavity dimensions and molding material are required). In this embodiment, in order to obtain such molding conditions, the cooling temperature was selected as the parameter, and the parameter was input to the data input unit 11 again, and the above-described processing was repeated. In this case, only the temperature of the primary cooling water was changed to 116 ° C. as initial conditions, and other conditions were set to be the same as the previous initial conditions. The calculation result is displayed on the calculation result display section 17, and the result as shown in FIG. 6 is obtained.

As is apparent from FIG. 6, although the distortion amount of the optical surface is smaller than that under the initial molding conditions, it is not zero. Therefore, in order to find a condition for obtaining a better surface accuracy, the primary cooling water temperature is set to 118 ° C.
And the other conditions are set to be the same as the previous case, and the reprocessing described above is attempted.

FIG. 7 shows the calculation result. Comparing this result with the result of FIG. 6, it can be seen that the distortion amount is smaller under the second molding condition. Therefore, the molding conditions in the present embodiment are as follows: molding pressure 85 MPa, injection temperature 260 ° C.
Cooling for 10 minutes with primary cooling water at 116 ° C, cooling for 8 minutes with secondary cooling water at 80 ° C, take out from the mold when secondary cooling is completed, and air cooling at room temperature (23 ° C) are optimal. Turned out to be.

In the above-described embodiment, the temperature of the primary cooling water is changed. However, other conditions such as the cooling time, the secondary cooling water temperature, and the cooling time may be changed. In any case, it is not necessary to set the initial solidification state as in the related art between the melting temperature range and the solidification region.

FIGS. 8 to 10 show the surface accuracy of the optical surface when the optical lens L is actually molded under the molding conditions of FIGS. 5 to 7 by interference fringes.
FIG. 9 corresponds to FIG. 6, and FIG. 10 corresponds to FIG. As is apparent from these results, it can be recognized that the analysis and evaluation according to the present invention and the actual processing results match. This shows that it is possible to simulate processing accuracy close to actuality by introducing a viscoelastic concept called stress relaxation instead of general thermal strain analysis, and by using the evaluation method according to the present invention, It is also possible to optimize the molding conditions before performing the molding operation using the mold, and to optimize the mold structure such as the optimal water pipe arrangement.

Incidentally, an optical lens made of resin generally has a flange portion having no optical function formed on an outer peripheral portion of an optical surface thereof. Such an optical lens is manufactured by compression molding or injection compression molding. One of the mirror cores for forming a pair of optical surfaces is operated to apply a compressive force to the resin in the cavity. For this reason, in the process of cooling and the resin in the cavity of the mold shrinking, the flange portion discontinuously connected to the optical surface cannot follow the contraction direction of the optical surface,
The contraction is restricted by the mold. As a result, although the accuracy of the optical surface on the side where the compressive force is applied to the flange portion is improved, the accuracy of the optical surface on the side where the compressive force is not applied to the flange portion is deteriorated.

This is remarkable when the thickness of the lens shape in the section perpendicular to the compression direction is large. For example, when the manufactured optical lens is a convex lens whose outer peripheral edge portion is thinner than the optical axis center portion, as shown in FIGS. 11 and 12 showing the temperature distribution of the resin filled in the mold. in, order to proceed cooling from the portion in contact with the mold, faster than the center portion of the flange portion L _F is relatively thick for a thick optical lens L is located in the thin outer peripheral edge portion of the relatively thick The temperature will be lower than the glass transition temperature. As is well known, in a polymer material such as a resin, the elastic modulus near the glass transition point temperature changes exponentially, so that the glass at a temperature higher than the glass transition point temperature is in a flowing state. flanges L _F became transition temperature below becomes a solidified state,
The compressive force of the movable insert 21 for generating the compressive force is intensively received. For this reason, the compressive force from the movable insert 21 is applied to the optical surface L formed by the fixed insert 22 opposite to the movable insert 21.
_The compression force is insufficient in the vicinity of the outer peripheral edge of the optical surface L _O without being transmitted to _O , and the amount of shrinkage is larger than that in the central portion, and FIGS. 13 and 14 showing the final molding state in the mold. As shown in the drawing, as the fixed-side insert 22 and the resin are separated from each other as the resin contracts, the optical lens taken out of the mold becomes a movable-side insert 21 for generating a compressive force.
The outer peripheral edge of the optical surface L _O formed by the fixed insert 22 opposed to the above-mentioned surface insert has a reduced surface accuracy.

[0033] If it is possible to load a compressive force to the flange portion L _F, it is possible to suppress the shrinkage, the movable insert 21 for in order to compress the flange portion L _F is for molding the optical surface And the movable side insert 21
Or move together with the movable-side embracing piece 23 for molding a flange portion L _F and hold, or these must be integrally manufactured, the fabrication of such molded piece is very difficult This is well known.

Next, a mold for manufacturing an optical lens suitable for carrying out the present invention which can solve such a problem will be described with reference to FIG.
This will be described with reference to FIGS.

FIG. 15 shows a cross-sectional structure of a mold for injection-molding a meniscus convex lens. The fixed-side mold 2 is connected to a not-shown molding machine injection cylinder-side platen.
4 and a movable mold 25 which is connected to a mold opening device side platen (not shown) and is separable from the fixed mold 24 at the parting plane PL, and is injection-molded (injection compression molding) therebetween. A molding cavity 26 having a shape corresponding to the meniscus convex lens to be formed is formed.

The fixed mold 24 includes a fixed mounting plate 27.
And a fixed side mold plate 28, a fixed side holding piece 29, and a fixed side insert 22 for forming a convex optical surface of a meniscus convex lens facing the molding cavity 26. Also,
The movable mold 25 includes a movable mounting plate 30, a movable mold plate 31, a movable holding piece 23, a movable receiving plate 32,
A movable-side spacer block 33; a movable-side insert 21 for forming a concave optical surface of the meniscus convex lens facing the molding cavity 26; a movable-side compression cylinder 34 for applying a compressive force to the movable-side insert 21; And a pressure sensor 35 for measurement.

Temperature adjusting flow paths 36 and 37 for flowing a temperature adjusting fluid are provided in the holding pieces 29 and 23, and temperature sensors 38 and 39 are provided in the inserts 22 and 21, respectively.
Are respectively incorporated.

FIG. 16 shows the cross-sectional shape of the meniscus convex lens L manufactured by the apparatus shown in FIG. 15, and specifically has an outer diameter of 40 mm, a center thickness of 8 mm, and an outer peripheral end thickness of 5 mm. , The outer diameter is the maximum effective diameter.

At the start of the molding operation, a temperature control medium (in this embodiment, water) supplied from a temperature controller (not shown) is supplied to the temperature control channels 36 and 37 in the mold, so that a temperature of 90 ° C. It is kept in a steady state. Dies 24, 25 clamped by a clamping device (not shown)
A predetermined amount of PMMA resin in a molten state is injected and filled therein, and the pressure is maintained at 80 MPa for 10 seconds.
Hydraulic oil is sent from the external oil pressure source to the 0 and movable side compression cylinders 34, and a pressure control valve (not shown) is adjusted so that the indicated value of the pressure sensor 35 attached to the movable side insert 21 becomes 20 MPa. And the PM in the molding cavity 26 is
Cooling was performed for about 2 minutes while compressing the MA resin.

The meniscus convex lens L that has been compression-cooled is
When the temperature of the whole becomes lower than the heat deformation temperature (100 ° C. in the case of PMMA), the supply of the hydraulic oil from the hydraulic pressure source to the movable compression cylinder 34 is stopped in a state where the mold is closed before the mold is opened. Then, the relief valve is released and the compression by the movable insert 21 is stopped. Thereafter, the mold is opened by the mold opening device of the injection molding machine, and the mold is taken out of the mold.

Since there is no flange at the outer peripheral edge of the meniscus convex lens L injection-molded in this manner,
Despite compression from one side (concave optical surface side) of the pair of optical surfaces, the movable insert 21 can follow the shrinkage of the resin, and the compressive force is also exerted on the fixed insert 22 side. Insert 2
The transfer of the optical surfaces formed on 1, 22 is performed with high accuracy.

In the above-described example, the meniscus convex lens L having no flange portion has been described. However, a highly accurate meniscus convex lens having a plane portion perpendicular to the optical axis on only one side of a pair of optical surfaces can be obtained. Transfer can be performed.

Another example of such a mold structure is shown in FIG. 17, but members having the same functions as those in the previous example shown in FIG. 15 are denoted by the same reference numerals, and overlapping description is omitted. Shall be. That is, in this example, the outer diameter of the movable side insert 21 is set to be larger than the outer diameter of the fixed side insert 22, and a flat portion corresponding to a flange portion between the movable side insert 21 and the fixed side holding piece 29 is formed. It is formed on the outer peripheral edge of the meniscus convex lens.

FIG. 12 shows a cross-sectional shape of the meniscus convex lens L manufactured by the apparatus shown in FIG. 11, and specifically has an outer diameter of 40 mm, a center thickness of 10 mm, and an outer peripheral end thickness of 6 mm. The effective diameter of the convex optical surface formed by the fixed insert 22 is 34 mm, and the effective diameter of the concave optical surface formed by the movable insert 21 is 40 mm, which is the same as the outer diameter. The flat portion L _P perpendicular ring with respect to the optical axis to the outer peripheral edge of the convex optical surface is formed.

The molding conditions are as follows.
Pressure for 12 seconds, and the indicated value of the pressure sensor 35 is 2
It is the same as the previous case except that the pressure is changed to 5 MPa.

[0046] The outer peripheral edge of the convex optical surface of the meniscus lens L to be injection molded Thus, although there is a ring-shaped flat portion L _P, a concave optical surface for receiving a compression force by the movable-side insert 21 The entire surface is formed by a curved surface having a single radius of curvature, and since these surfaces are uniformly compressed, the movable side insert 21 can follow the shrinkage of the resin despite the compression from one side. Becomes possible,
The compressive force is also effectively transmitted to the convex optical surface side, and the optical surfaces formed on the inserts 21 and 22 are transferred with high accuracy.

In the above-described example, the meniscus convex lens L has been described, but high-precision transfer can also be performed on a biconvex lens.

Another example of such a mold structure is shown in FIG. 19, and members having the same functions as those of the previous two examples shown in FIGS. The description of the operation will be omitted. That is, also in this example, the outer diameter of the movable side insert 21 is set to be larger than the outer diameter of the fixed side insert 22, and the flat portion corresponding to the flange portion between the movable side insert 21 and the fixed side holding piece 29. Is formed on the outer peripheral edge of one convex optical surface of the biconvex lens.

FIG. 20 shows the cross-sectional shape of the biconvex lens L manufactured by the apparatus shown in FIG. 19. Specifically, the outer diameter is 40 mm, the center thickness is 16 mm, and the outer end thickness is 3 mm. The effective diameter of the convex optical surface formed by the fixed-side insert 22 is 36 mm, and the effective diameter of the convex optical surface formed by the movable-side insert 21 is the same as the outer diameter of 40 mm.
mm. The flat portion L _P perpendicular ring with respect to the optical axis to the outer peripheral edge of the convex optical surface which is molded is formed by the fixed-side insert 22.

The molding conditions are as follows: PMMA resin is 95 MPa
Pressure for 20 seconds, and the indicated value of the pressure sensor 35 is 3
It is the same as the previous case except that the compression force was adjusted to be 5 MPa and the cooling time was set to 3 minutes.

[0051] The outer peripheral edge portion of one convex optical surfaces of the biconvex lens L to be injection molded Thus, although there is a ring-shaped flat portion L _P, convex optical receiving a compressive force by the movable-side insert 21 On the surface side, the entire surface is formed by a curved surface having a single radius of curvature. Since the entire surface is uniformly compressed, the movable side insert 21 follows the shrinkage of the resin despite the compression from one side. Thus, the compressive force is also effectively transmitted to the convex optical surface side formed by the fixed insert 22, and the optical surfaces formed on the inserts 21 and 22 are transferred with high accuracy.

Next, such an optical lens manufacturing system will be described below with reference to FIGS. 21 and 22. Here, the optical lens manufacturing system is preliminarily processed into a shape substantially corresponding to the shape of a product optical lens. A case of a compression forming method in which a lens blank is inserted into the above-described mold and subjected to heating, compression, and cooling steps to obtain an optical lens as a product (hereinafter, a product lens) will be described.

In FIG. 21 showing the outline of this system, 41 is an injection molding machine for molding the above-mentioned lens blank, 42 is a compression molding machine schematically shown in FIG.
Is a preheating chamber where the lens blank is heated before molding,
44 is a stocker for stocking the product lens which has been subjected to the compression molding and final processing, and 45 is a space between the injection molding machine 41 and the preheating chamber 43 and between the preheating chamber 43 and the compression molding machine 4.
The lens blanks are transferred between
Further, in order to transfer the product lens between the compression molding machine 42 and the stocker 44, a handling robot 46 for transporting the lens blank and the product lens is connected to the injection molding machine 41 to perform injection for forming the lens blank. A molding die, 47 is a compression molding die incorporated in the compression molding machine 42 to compress the lens blank into a product lens, and 48 is a temperature of the injection molding die 46 and the compression molding die 47. A temperature controller for supplying a temperature control medium to each of the molds 46 and 47 so as to maintain the set temperature;
9 is a pallet for storing the product lens in the stocker 44, 50 is an input port for inputting a lens blank into the preheating chamber 43 by the handling robot 45, 51
Is a takeout port for taking out a lens blank from the preheating chamber 43 by the handling robot 45.

The schematic structure of the above-described compression molding machine 42 is shown in FIG. 22, except that the cartridge heaters 52, 53 are embedded in the holding pieces 29, 23, respectively, as shown in FIGS. Is substantially the same as
Members having the same functions as in the previous example are denoted by the same reference numerals.

When the preparation for compression molding is completed, the lens blank previously processed by injection molding is removed from the preheating chamber 4.
Transfer to 3 and heat to 100 ° C. On the other hand, the compression molding die 47 has the built-in cartridge heaters 52 and 5.
3, the inserts 22 and 21 on the fixed side and the movable side
Is heated to 180 ° C. Each insert 22,2
In the heating of 1, the current flowing to the cartridge heaters 52 and 53 is performed by PID control so as to reach the set temperature in the shortest time while sequentially detecting the temperature by the temperature sensors 38 and 39, and the temperature indicated by the temperature sensors 38 and 39 is reduced. Set temperature 18
When the temperature reaches 0 ° C., a blank input signal is sent to the handling robot 45 and the compression molding machine 42 to maintain the set temperature.

The handling robot 45 that has received the lens blank input signal based on the detection signals from the temperature sensors 38 and 39 transfers the lens blank in the preheating chamber 43 to the compression mold 47. It is monitored and confirmed by a video camera (not shown) installed in the compression molding machine 42 that the lens blank is settled at a predetermined position in the molding cavity 26 of the compression molding die 47. Closes the parting surface PL of the compression molding die 47. At this time, the movable insert 21 is previously retracted to a position where it does not come into contact with the lens blank so that an excessive compressive force is not applied between the inserts 22 and 21 and the lens blank.

When the compression molding die 47 is completely closed, the movable insert 21 is advanced (raised), and the inserts 22 and 21 are brought into contact with the lens blank. 180 ° C
The surface temperature of the lens blank rises due to the contact with the heated inserts 22 and 21, and the temperature of the inserts 22 and 21 is maintained until the softening temperature is reached. In the present embodiment, the depth from the surface of the lens blank to be softened is 0.2 (corresponding to the aspherical amount) with respect to the spherical surface.
mm and hold for one minute. Insert 2
After one minute has passed after the lenses 2 and 21 were brought into contact with the lens blank, the movable side compression cylinder 34 used the movable side compression cylinder 34 until the load measured by the pressure sensor 35 built in the back side of the movable side insert 21 became 250 kg. The insert 21 is advanced. When the indicated value of the pressure sensor 35 incorporated in the movable side insert 21 reaches 250 kg, the position of the movable side insert 21 is maintained, the current output to the cartridge heaters 52 and 53 is cut off, and the temperature is set to 90 ° C. The cooled cooling water flows through the temperature control flow paths 36 and 37 to be cooled.

When the temperature of the compression molding die 47 reaches 90 ° C., the compression molding die 47 is opened and the product lens is taken out from the compression molding die 47.

As described above, in the case of an optical lens having two opposing optical surfaces, the effective diameter of the optical surface having the larger optically effective area is made to coincide with the outer diameter of the optical lens so that the discontinuous portion is formed. By applying a compressive force to the resin held in the molding cavity by the movable side insert that forms the optical surface with the larger optically effective area, the resin held in the molding cavity is compressed by the shrinkage accompanying cooling. Since uniform pressure can be applied to the entire optical surface and the optical surface on the opposite side to the resin that is released from the molding surface,
The movable insert can follow the shrinkage of the resin, and the optical surface formed on the insert can be accurately transferred to the optical surface of the injection-molded optical lens. Then, the finished shape of the product lens may be predicted using such a system.

When the lens blank is formed into a product lens by compression molding as described above, the lens blank is formed into a product lens while giving a predetermined amount of compression to the lens blank.

In this case, the lens blank is manufactured with dimensional accuracy such that it can be inserted into the molding cavity of the compression mold without interference, and can be processed with high precision by a predetermined compression molding process. Also, the lens blank is
Since the lens blank is manufactured with rough shape accuracy so as to reduce the processing cost, there is a certain degree of dimensional variation in the finished dimensions of the lens blank which is limited in cost.

Conventionally, lens blanks having such dimensional variations are uniformly processed under preset compression molding conditions, so that lens blanks having variable dimensions are over-compressed or under-compressed. There is a possibility that a sink occurs in the manufactured product lens, a springback occurs due to overcompression, and a problem that optical surface accuracy is lost occurs.

In order to suppress such molding defects, it is only necessary to reduce the dimensional variation of the lens blank. However, for that purpose, the processing accuracy of the lens blank must be strictly controlled. If the processing accuracy of the lens blank is strictly controlled, the processing cost of the lens blank naturally increases, and the manufacturing cost of the product lens increases.

It is also conceivable that the dimensional accuracy of the lens blank is not strictly controlled, and the dimensional inspection of the lens blank is performed before performing the compression molding process, and a lens blank whose dimensional accuracy is unacceptably shifted is removed. Since the removed lens blank cannot be used as a product lens, it is eventually discarded, and the production cost of the obtained product lens increases.

A compression molding method capable of overcoming such disadvantages will be described below with reference to FIGS. 23 and 24. Members having the same functions as those described above are denoted by the same reference numerals. , Overlapping description will be omitted.

In FIG. 23 showing the concept of the compression molding system in this case, 61 is a frame, 62 is a mold opening cylinder, 63 is a cylinder pressure rod for driving the movable side compression cylinder 34, and 64 is a pressure rod drive Ball screw, 65 is a servo motor for driving a ball screw, 66 is a servo motor control device, 67 is a blank weight measuring device for measuring the weight of a lens blank put into the molding cavity 26 of the compression molding machine 47, and 68 is a blank weight measuring device. This is an arithmetic unit that calculates the amount of compression by comparing the measured weight of the lens blank with a reference blank weight described later.

A lens blank previously molded into a shape corresponding to a substantially product lens by an injection molding machine 41 as shown in FIG. 21 is transferred to a preheating chamber 43 (see FIG. 22).
Heat to 100 ° C. On the other hand, the compression molding die 47
Are fixed and movable inserts 22, 21 by built-in cartridge heaters 52, 53 (see FIG. 22).
Is heated to, for example, 174 ° C. Inserts 22, 21
Is heated by sequentially detecting the temperature by the temperature sensors 38 and 39 (see FIG. 22) and applying a current flowing through the cartridge heaters 52 and 53 to the set temperature in the shortest time by PID.
When the temperature indicated by the temperature sensors 38 and 39 reaches the set temperature of 174 ° C., a blank input signal is sent to the handling robot 45 and the compression molding machine to maintain the set temperature.

The handling robot 45 having received the lens blank input signal goes to the take-out port 51 for taking out the lens blank preheated in the preheating chamber 43. A blank weight measuring device 67 is provided in the outlet 51.
Is provided, and the weight of the lens blank transferred to the handling robot 45 is measured, and the measurement result is transferred to the arithmetic unit 68.

The arithmetic unit 68 includes a weight of a reference lens blank (hereinafter, referred to as a reference blank) set in advance through various molding trials, an optimal compression amount and a cooling gradient for the reference blank. Is stored. The reference step rank weight in this embodiment is 14.65 g.
Is set to

The handling robot 45 conveys the weighed lens blank to the compression molding die 47, and confirms that the lens blank has been set at a predetermined position in the molding cavity 26 of the compression molding die 47. Monitoring and confirmation is performed by a video camera installed at 42, and upon receiving a confirmation signal output, the compression molding machine 42 closes the parting surface of the compression molding die 47.

After one minute has passed since the movable insert 21 was brought into contact with the lens blank, in the case of a reference blank, the movable insert 21 was raised by 0.3 mm and a compressive force was applied to form the product lens. It is designed to be molded. At this time, the value measured by the pressure sensor 35 (see FIG. 22) built in the movable side insert 21 becomes, for example, 60 MPa.

Here, when the weight of the lens blank carried into the compression molding die 47 is 14.42 g, the arithmetic unit 68 calculates the difference between the reference blank weight and the weight of the lens blank (14.65-14.42). ) = 0.23 g is calculated,
The above-mentioned weight difference is converted into a volume difference from the PVT data indicating the relationship between the pressure, the specific volume, and the temperature as shown in FIG. The arithmetic unit 68 stores a weight value of 14.65 g of the reference blank and a volume value under the reference molding conditions.

For example, when the temperature of the lens blank at the time of being preheated and carried into the compression molding die is 96 ° C., the specific volume at that time is 0.857 cm ³ / g, and When the lens blank is compressed at 174 ° C. under the standard molding conditions, the pressure applied to the lens blank is 60 MPa, and the specific volume in this state is 0.1 MPa.
It turns out that it is 864 cm < ³ > / g. So, this 174 ℃
Under a pressure of 60 MPa, the volume of the lens blank that is 0.23 g lighter than the reference blank is calculated to be about 0.2 cm ³ smaller than the volume of the reference blank, and the volume difference is -0.2 cm. Remember ³ Further, the arithmetic unit 68 divides the determined volume difference by the projected area of the movable side insert 21 in the compression direction, and calculates the volume difference as a compression amount difference.

The compression amount difference thus calculated is subtracted from the reference compression amount of 0.3 mm to calculate the current compression amount, calculate the rotation speed of the compression servomotor, and issue a command to the servomotor. In the present embodiment, the difference in compression amount is about 10 μm, and the actual movement amount of the movable side insert 21 is 0.31 mm.
It has become.

After being compressed in this manner, the current output to the cartridge heaters 52 and 53 is shut off, and cooling water set at 90 ° C. is passed through the compression molding die 47 to cool it. When the temperature of the compression mold 47 reaches 90 ° C., the compression mold 47 is opened, the movable insert 21 is lowered by about 1 mm, and the molded product lens is detached from the movable insert 21. Let it. Thereafter, the movable side insert 21 is lifted and released from the compression molding die 47.

As described above, the weight of the lens blank is measured before molding the product lens, and the weight difference between the lens blank and the reference lens blank weight is determined. The volume difference is calculated and the volume difference is calculated from the weight difference. The amount of compression can be calculated from the volume difference calculated and the amount of compression corresponding to each lens blank can be added, making it possible to stabilize product lenses with high precision under constant molding conditions regardless of the manufacturing accuracy of the lens blank. it can. Moreover, it is not necessary to strictly control the processing accuracy of the lens blank, and the processing error can be increased, so that the processing cost of the lens blank can be reduced. Then, the finished shape of the product lens may be predicted using such a system.

[0077]

According to the present invention, it is possible to almost accurately evaluate the processing accuracy of an optical lens to be injection-molded in accordance with the length of cooling time, the level of cooling water, or the level of molding pressure. Even if a molding operation is not actually performed using a mold, it is possible to predict and set optimum molding conditions in the mold. Therefore, it is possible to properly examine the layout of the water pipe, the diameter of the water pipe, the layout of the molding cavity, etc. at the mold design stage, and to manufacture the optimal mold for the target molded product. Can be. In addition, it is possible to confirm the capabilities of the peripheral equipment and to predict the molding time.

As described above, since it is possible to predict the processing accuracy of a molded product and the capacity of equipment before actually manufacturing a metal mold, it is possible to correct the mold, rework the equipment, or replenish the equipment. And the like can be avoided, and a great load can be reduced both economically and temporally.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a device for predicting a finished shape of a molded article according to the present invention.

FIG. 2 is a conceptual diagram showing an analysis model of a mold and an optical lens in the embodiment shown in FIG.

FIG. 3 is a graph showing a relationship between a temperature and a linear expansion coefficient of a molding material used in the example shown in FIG.

FIG. 4 is a graph showing the relationship between time and relaxation modulus of a molding material used in the example shown in FIG.

FIG. 5 is a pattern diagram of interference fringes showing the prediction accuracy of the optical surface of the optical lens when the primary cooling water temperature is set to 114 ° C.

FIG. 6 is a pattern diagram of interference fringes showing the prediction accuracy of the optical surface of the optical lens when the primary cooling water temperature is set to 116 ° C.

FIG. 7 is a pattern diagram of interference fringes showing the prediction accuracy of the optical surface of the optical lens when the primary cooling water temperature is set to 118 ° C.

FIG. 8 is an interference fringe pattern diagram showing the accuracy of the optical surface of an optical lens actually formed when the primary cooling water temperature is set to 114 ° C.

FIG. 9 is a pattern diagram of interference fringes representing the accuracy of the optical surface of the optical lens actually formed when the primary cooling water temperature is set to 116 ° C.

FIG. 10 is a pattern diagram of interference fringes representing the accuracy of the optical surface of the optical lens actually formed when the primary cooling water temperature is set to 118 ° C.

FIG. 11 is a cross-sectional view showing contours of a temperature distribution during cooling when a meniscus convex lens having a flange portion is molded.

FIG. 12 is a cross-sectional view showing, with contour lines, a temperature distribution during cooling when a biconvex lens having a flange portion is molded.

FIG. 13 is an exaggerated cross-sectional view of the contracted state when the meniscus convex lens shown in FIG. 11 is molded by a conventional method.

FIG. 14 is an exaggerated cross-sectional view showing a contracted state when the biconvex lens shown in FIG. 12 is molded by a conventional method.

FIG. 15 is a cross-sectional view illustrating an example of an injection mold used as an object of the present invention.

16 is a cross-sectional view illustrating a shape of a meniscus convex lens formed by the injection mold illustrated in FIG.

FIG. 17 is a cross-sectional view showing another example of the injection mold used in the present invention.

18 is a cross-sectional view illustrating a shape of a meniscus convex lens formed by the injection mold shown in FIG.

FIG. 19 is a cross-sectional view showing another example of the injection mold used in the present invention.

20 is a cross-sectional view illustrating a shape of a biconvex lens formed by the injection molding die illustrated in FIG.

FIG. 21 is a conceptual diagram of a lens manufacturing system that can implement the present invention.

22 is a cross-sectional view illustrating a schematic structure of a compression molding machine in the lens manufacturing system illustrated in FIG.

FIG. 23 is a conceptual diagram illustrating an example of a compression molding system using a compression molding die according to the present invention.

FIG. 24 is a graph showing the relationship between the temperature, specific volume, and pressure of the resin used in the system shown in FIG. 23.

[Explanation of symbols]

11 data input unit 12 first data storage unit L lens C optical axis 13 second data storage unit 14 the temperature distribution calculator 15 thermal distortion, stress relieving operation unit 16 operation result storage unit 17 calculation result display unit L _F flange 21 movable Side insert 22 Fixed side insert L _O optical surface 23 Movable side holding piece 24 Fixed side mold PL Parting surface 25 Movable side mold 26 Molding cavity 27 Fixed side mounting plate 28 Fixed side mold plate 29 Fixed side holding piece 30 Moving side Mounting plate 31 Movable mold plate 32 Movable receiving plate 33 Movable spacer block 34 Movable compression cylinder 35 Pressure sensor 36, 37 Temperature control flow path 38, 39 Temperature sensor 40 Fixed cylinder L _P plane 41 Injection molding machine 42 Compression molding machine 43 Preheating chamber 44 Stocker 45 Handling robot 46 Injection mold 7 Mold for compression molding 48 Temperature controller 49 Pallet 50 Input port 51 Removal port 52, 53 Cartridge heater 61 Frame 62 Mold opening cylinder 63 Cylinder pressure rod 64 Ball screw for driving pressure rod 65 Servo motor for driving ball screw 66 Servo motor control device 67 Blank weight measuring device 68 Computing device

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29C 45/56 B29C 45/56 B29D 11/00 B29D 11/00 G02B 1/04 G02B 1/04 3/00 3/00 Z

Claims (14)

[Claims] 1. A step of calculating a temperature change of a mold and a molded product in a short time according to a history of the production time for a molded product manufactured by an injection molding method, a compression molding method, or an injection compression molding method. Calculating the amount of thermal strain generated in the mold and the molded product in accordance with the calculated temperature change; and the calculated amount of thermal strain and the stress created in advance based on the temperature-time conversion rule. Calculating the internal stress of the molded article from the relaxation data; and predicting the final shape of the molded article based on the calculation result. . 2. The molded article is a lens having a plurality of optical surfaces, and among the plurality of optical surfaces, the optical surface having the largest effective area is a compression surface over the entire surface. 2. The method for predicting a finished shape of a molded product according to claim 1, wherein the outer periphery of the surface coincides with the outer periphery of the molded product. 3. The mold for molding a lens having a plurality of optical surfaces, wherein the optical surface having the largest effective area among the plurality of optical surfaces is a compression surface over the entire surface. 3. The method for predicting a finished shape of a molded product according to claim 1, wherein an outer periphery of the compression surface coincides with an outer periphery of the molded product. 4. The molding method according to claim 1, wherein the compression molding method changes a compression amount based on a weight of a molding material to be the molded article. Product shape prediction method. 5. The change amount of the compression amount is a difference between a reference weight of the molding material and an actual weight of the molding material,
The method according to claim 4, wherein the product of the specific gravity of the molding material and the product is divided by a projection area of the compression surface of the mold along a compression direction. 6. The method according to claim 5, wherein the specific gravity of the molding material is calculated from specific gravity data stored in advance based on temperature and pressure. 7. The method according to claim 4, wherein the weight of the molding material is measured after the molding material is charged into a mold and before a compression process is started. 3. A method for predicting a finished shape of a molded article according to the above. 8. For a molded product manufactured by an injection molding method, a compression molding method, or an injection compression molding method, a temperature at which a temperature change of a mold and a temperature of the molded product in a short time along a history of the manufacturing time is calculated. Change calculating means, thermal strain calculating means for calculating the amount of thermal strain generated in the mold and the molded article in accordance with the temperature change calculated by the temperature change calculating means, and based on a temperature-time conversion rule. A data storage unit for storing stress relaxation data created in advance, and the stress relaxation data stored in the data storage unit;
An internal stress calculating means for calculating an internal stress of the molded article from the thermal strain amount calculated by the thermal strain calculating means; and a final shape of the molded article based on a calculation result by the internal stress calculating means. A finished shape predicting device for a molded article, comprising: a final shape predicting means for predicting the finished shape. 9. The molded article is a lens having a plurality of optical surfaces, and among the plurality of optical surfaces, the optical surface having the largest effective area is a compression surface over the entire surface. 9. The device for predicting a finished shape of a molded product according to claim 8, wherein the outer periphery of the surface coincides with the outer periphery of the molded product. 10. The mold for molding a lens having a plurality of optical surfaces, wherein the optical surface having the largest effective area among the plurality of optical surfaces is a compression surface over the entire surface. 10. The finished shape predicting device for a molded product according to claim 8, wherein an outer periphery of the compression surface coincides with an outer periphery of the molded product. 11. The molding method according to claim 8, wherein the compression molding method changes a compression amount based on a weight of a molding material to be the molded article. Product finish shape prediction device. 12. The amount of change in the amount of compression is obtained by multiplying a product of a difference between a reference weight of the molding material and an actual weight of the molding material and a specific gravity of the molding material by a compression surface of the mold. The finished shape estimating device for a molded product according to claim 11, wherein the value is equal to a value obtained by dividing by a projected area along the compression direction. 13. The apparatus according to claim 12, wherein the specific gravity of the molding material is calculated from specific gravity data stored in advance based on temperature and pressure. 14. The method according to claim 11, wherein the weight of the molding material is measured after the molding material is charged into a mold and before a compression step is started. 3. A device for predicting the finished shape of a molded product according to item 1.