JP2007099591A - Method and apparatus for press forming optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for press forming optical elements, by which precision optical elements each having a prescribed thickness can be manufactured even when there is variation in the volume or the shape of blanks. <P>SOLUTION: The method for press forming the optical elements comprises using a mold having an upper mold and a lower mold. The interval between the upper mold and the lower mold is measured during press-forming, and press-forming is finished or continued according to the measured value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a press molding method and a press molding apparatus for molding an optical element such as a high-precision glass lens used in an optical apparatus.

  The performance of an optical element typified by a glass lens is mainly determined by the surface shape of the optical surface and the thickness of the optical element. In particular, in recent years, a high-performance optical element has been required, and in order to maintain the performance, only an error of about a submicron in the optical surface shape and a few microns in thickness can be allowed. In addition, since the demand for optical elements is increasing in recent years, it is desired to manufacture such high-performance optical elements in large quantities with stable performance.

  As a typical method for manufacturing such an optical element, there is press molding as shown in, for example, Patent Document 1. According to this, since a process such as polishing can be omitted, it is implemented as a manufacturing method capable of mass production. Yes. Among them, the reheat press method has been widely practiced in recent years. This is done by placing a glass material of a predetermined shape and size at room temperature in a mold having an upper mold and a lower mold, softening the glass material by heating the mold, press molding, and molding This is a method of cooling later. According to this method, it is known that the transfer of the optical surface of the molded product is stable and high-performance optical elements can be mass-produced.

  In press molding, usually, molding conditions consisting of a combination of temperature during pressing, pressing force, and pressing time are set according to the shape of the molded product and the molding material. Depending on the shape of the molded product, there may be a plurality of molding processes, and the pressing temperature and pressing force may be different from each other. Usually, the molding conditions are set by pairing the pressing force and the pressing time. Further, the molding conditions are determined in consideration of mold transfer accuracy, mold durability, molding cycle time, and the like. In the conventional general press molding method, the heating, press molding, and cooling steps are repeated according to certain molding conditions set in this way.

  However, when an optical element is molded by such a reheat press method, the thickness of the molded product and the shape of the optical transfer surface may vary even if the molding conditions including the molding temperature, pressing force, and pressing time are constant. . One of the causes is variation in the volume and shape of the glass material.

  If the volume of the glass material is varied, the heat capacity of the glass material is varied, and if the shape is varied, the heat input state to the glass material is different and the temperature distribution of the glass material is not uniform. In other words, if there is a variation in volume or shape in the glass material, the heating state will be different for each glass material. As a result, if molding is performed under certain molding conditions, the thickness of the molded product and the variation in the shape of the optical transfer surface will occur. It will be.

  Therefore, in order to manufacture a large amount of glass optical elements having stable performance, it is preferable to use a glass material with as little variation in volume and shape as possible. Generally, in a glass material used for press molding of an optical element, an allowable variation is said to be about 0.5% of a target value as a volume variation and within 10 μm of a target value as a shape variation.

  However, strictly controlling the volume and shape of the glass material and reducing the allowable tolerance raises the cost for manufacturing the glass material. In addition, even within the tolerance of the volume and shape variations of the glass material as described above, it is inevitable that variations occur in the molded product, and in order to manufacture a precise optical element under certain molding conditions, It is necessary to further reduce the tolerance of the material size, which further increases the cost.

In addition to the factors due to the volume and shape of the glass material, the thickness of the molded product may vary due to errors in temperature and pressing pressure during molding.
JP 2000-327346 A

  The present invention has been made in consideration of the above prior art, and press molding of an optical element capable of producing a precise optical element having a predetermined thickness even if there are variations in the volume or shape of the material. It is an object to provide a method and a press device.

  The invention of claim 1 is a method of press-molding an optical element using a mold having an upper mold and a lower mold, wherein the distance between the upper mold and the lower mold is measured during the press molding, and the measured value is obtained. Accordingly, there is provided a press molding method of an optical element characterized in that press molding is terminated or continued in response.

  The invention of claim 2 is the invention of claim 1, in which molding conditions are set in advance for temperature, pressure, and time, and after the press starts under the molding conditions, the interval is a thickness tolerance of the molded product. When the value corresponding to the lower limit is reached, press molding is terminated.If the value corresponding to the lower limit is not reached, press molding is continued, and when the set time is reached, the interval is equal to the thickness tolerance of the molded product. If the value corresponding to the upper limit is reached, press molding is terminated, and if the value corresponding to the upper limit is not reached, press molding is extended to the maximum extension time.

  According to a third aspect of the present invention, in the press molding apparatus for carrying out the first or second aspect of the present invention, a measuring device for measuring the distance between the upper mold and the lower mold is provided.

  According to the invention of claim 1, by performing press molding while measuring the distance between the upper mold and the lower mold, a molded product having a predetermined thickness can be obtained accurately even if the dimensions of the material vary. Yield is improved and production efficiency is improved. Furthermore, since the tolerance for variation in the volume and shape of the material can be increased, the cost for manufacturing the material can be kept low.

  According to the invention of claim 2, when the value corresponding to the lower limit of the thickness tolerance of the molded product is reached before the preset set time elapses, the press molding is terminated at that point, so that the molded product has the thickness tolerance. It can prevent becoming thinner than the lower limit. If the value corresponding to the upper limit of the thickness tolerance is not reached even after the set time has been reached, it can be easily handled by detecting it during press molding in a heated state and continuing press molding. The thickness of the molded product can be adjusted. Furthermore, by setting the maximum extension time, it is possible to prevent the process from being delayed due to excessively extending the press time.

  According to the invention of claim 3, the invention of claims 1 and 2 can be realized with a simple configuration by providing the measuring device for measuring the distance between the upper mold and the lower mold.

  FIG. 1 shows an outline of a mold peripheral portion of a press molding apparatus of the present invention.

  The mold 2 includes a cylindrical body mold 23, a lower mold 22 fitted in the body mold 23, and an upper mold 21 that can slide inside the body mold 23. The lower surface of the upper mold 21 and the upper surface of the lower mold 22 are molding surfaces, and the material 3 is placed and pressed between them to form an optical element.

  Plate members 11 and 12 are disposed above and below the mold 2, and the upper die 21 is pressed by the press rod 4 fixed to the plate 5 from above the upper plate member 11 to press the material 3. A contact-type position sensor 6 is attached above the plate 5. The position sensor 6 is connected to a control unit (not shown), measures the sliding position of the upper mold 21, and sends the measured value to the control unit. This sliding position corresponds to the distance between the molding surface (lower surface) of the upper mold 21 and the molding surface (upper surface) of the lower mold 22. The control unit compares the measured value with a preset value of the upper mold sliding position, and controls the pressing force and pressing time by the plate 5. Since the position sensor 6 is used for collecting data for controlling the thickness accuracy of the molded product, the position sensor 6 requires a disassembly capability according to the thickness accuracy of the molded product. The position sensor 6 may be a non-contact type.

In such a molding apparatus, molding conditions including a molding temperature, a pressing force F, and a pressing time T are set in advance and stored in the control unit. Further, as control information related to the sliding position of the upper mold 21, the sliding position t ₀ of the upper mold 21 corresponding to the case where a molded product having a reference thickness is obtained, the tolerance d with respect to the reference thickness, the maximum extension time Tex of the press. Etc. are set.

  FIG. 2 is a flowchart showing the press molding procedure of the present invention. Hereinafter, the press molding method will be described with reference to FIG.

Step S1: An n-stage press from the first molding to the n-th molding is started under the standard molding conditions stored in advance in the press molding apparatus. The molding conditions consist of three conditions of temperature (for example, 600 ° C.), pressing force F (for example, 100 N), and time T (for example, 50 seconds). For example, after heating to 600 ° C., pressurizing at 100 N for 50 seconds, It is a process of entering a cooling process. This standard molding condition is set by a combination that allows the thickness of the molded product to be obtained to a desired dimension. When the pressing force F and the pressing time T are paired, for example, when there are a plurality of molding stages. Is set by different pressing forces F _{1 to} Fn and times T _{1 to} Tn for each molding stage from the first molding to the n-th molding.

  Step S2: At the same time as Step S1 starts, the measurement of the sliding position of the upper mold, that is, the upper and lower mold intervals is started.

Step S3: Mold sliding position td when the mold interval is a lower limit of the allowable thickness, that is, mold sliding when the molded product has a dimension smaller by a tolerance d than the reference value. It is determined whether or not the position (td = t ₀ −d) has been reached. This tolerance d is set in advance, and for example, a tolerance d = 0.005 mm is set with respect to a reference thickness of 3 mm for the molded product. If the molded product has reached the lower limit thickness at this point, even if the scheduled press time has not elapsed, no further pressing is performed, and the process proceeds to step S10 to end the pressing.

  Step S4: If the mold sliding position has not reached td in step S3, the pressing is continued.

  Step S5: It is determined whether or not the preset total press time Ts has been reached. If Ts has not been reached, the process returns to step S2.

Step S6: In step S5, when the press time Ts has been reached, the mold sliding position tu when obtaining the molded product whose mold interval is the upper limit of the allowable thickness, that is, the molded product is set to the reference value. On the other hand, it is determined whether or not the mold sliding position (tu = t ₀ + d) when the dimension is larger by the tolerance d is reached. If the mold sliding position has reached tu, the process proceeds to step S10 and the press is terminated.

  Step S7: If the mold sliding position has not reached tu in step S6, the press time is extended.

  Step S8: At the same time as the extension in step S7 is started, it is determined whether or not the mold sliding position has reached tu. When the mold sliding position reaches tu, the process proceeds to step S10 and the press is finished.

  Step S9: In step S8, if the mold sliding position has not reached tu, it is determined whether or not the preset maximum extension time Tex has been reached. When the maximum extension time Tex is reached, even if the mold sliding position does not reach the predetermined tolerance, the process proceeds to step S10 and the press is terminated. When the maximum extension time Tex has not been reached, the process returns to step S7 to further extend the press.

  Step S11: After reaching Step S10 by the above procedure, if there is another material, the process returns to Step S1 and press molding for another material is performed in the same manner as described above. If there is no other material, the work is finished.

  FIG. 3 is an example of molding by the press molding method of FIG. 2, and shows an example in which a molded product having a reference thickness is obtained under preset standard molding conditions. The horizontal axis shows the passage of time, and is a graph showing the temperature, pressing force, and mold sliding position in order from the top.

When the material is set in the mold, the mold is first heated to a predetermined temperature. Thereafter, during the total pressing time Ts, three-stage pressing is performed in which the pressing force gradually decreases from the first molding to the third molding. When the third molding press is completed and the time Ts has elapsed (time point T ₁ ), the distance between the upper mold and the lower mold is the position where a molded product with a reference thickness is obtained, that is, the mold sliding position is t ₀ is reached. Thereby, the molded product according to the reference value is molded, and then the cooling process is started.

  FIG. 4 is a different example of molding by the press molding method of FIG. 2, and shows an example in which pressing is completed in a time shorter than the total press time Ts of preset standard molding conditions. The items indicated by the vertical axis and the horizontal axis of each graph are the same as those in FIG. 3, and the thick dotted line indicates a molding process under standard molding conditions.

Among the preset three-stage presses, during the second molding (time point T ₂ ), the mold sliding position has reached td, that is, the thickness of the molded product has reached the lower limit of tolerance. If detected, the press is terminated at this stage without waiting for the scheduled total press time Ts to elapse, and the process proceeds to the cooling process. In this case, the conventional molding method produces a product having a thickness that is insufficient with respect to the standard of the molded product, but according to the present invention, a molded product having a minimum dimension within an allowable range can be obtained.

  FIG. 5 is a further different example of the molding by the press molding method of FIG. 2, and shows an example in which pressing is performed by extending the total pressing time Ts of standard molding conditions set in advance. The items indicated by the vertical axis and the horizontal axis of each graph are the same as those in FIG. 3, and the thick dotted line indicates a molding process under standard molding conditions.

After the total press time Ts has elapsed after performing the preset three-stage press, if the mold sliding position does not reach tu, that is, the thickness of the molded product is still thicker than the upper limit of the tolerance. When detected, the press is extended with a pre-specified pressing force. In the case of FIG. 5, the press is extended with the pressing force at the time of the final third molding in the standard pressing process. When it is detected that the mold sliding position has reached tu, the press is terminated (time T ₃ ), and the process proceeds to the cooling process. In this case, in the conventional molding method, a product whose thickness exceeds the standard of the molded product is produced, but according to the present invention, a molded product having a maximum dimension within an allowable range can be obtained.

  As shown in FIG. 4 and FIG. 5, by measuring the mold interval and adjusting the press time according to the measured value, it is easy even if the molded product within the tolerance cannot be obtained by the conventional standard pressing process. It is possible to produce molded products within tolerances. If the temperature and pressing force during pressing are changed, the thickness of the molded product will change too much or little, making fine adjustment difficult, but the method of increasing or decreasing the press time makes the thickness of the molded product easy and precise. You can adjust the height.

  FIG. 6 shows still another example of molding by the press molding method of FIG. The items indicated by the vertical axis and the horizontal axis of each graph are the same as those in FIG. 3, and the thick dotted line indicates a molding process under standard molding conditions.

After the preset three-stage press is performed and the total press time Ts has elapsed, when it is detected that the mold sliding position has not reached tu, the press time is extended. If the mold sliding position does not reach tu even when the press is extended to the maximum extension time Tex, the press is terminated without further pressing (time T ₄ ). In this case, the process proceeds to the cooling process when the maximum extension time Tex has elapsed, but a molded product having a size within an allowable range cannot be obtained. In this way, if it is impossible to obtain a molded product within the tolerance of the reference value due to, for example, the volume of the material being too large or foreign matter mixed in the mold, the press will continue indefinitely. The maximum extension time Tex is set so that the process is not delayed, and the press is not performed for a longer time.

  An embodiment in which a biconvex lens having a thickness of 2 mm was molded by the press molding apparatus shown in FIG. 1 according to the press molding method shown in FIG. 2 will be described.

  The dimensions of the spherical glass material placed in the mold were 5.94 mm, 2.97 mm, 3.0 mm, 3.03 mm, and 3.06 mm. These dimensional tolerances are ± 0.005 mm.

  First, a glass material having a diameter of 3.0 mm was selected from these and placed in a mold, and the mold was heated by an infrared lamp. The molding conditions were a molding temperature of 580 ° C., a pressing force of 100 N, and a pressing time of 60 seconds. It was confirmed that the thickness of the molded product obtained under these conditions was 2.0 ± 0.005 mm, and this was used as the standard molding condition. At this time, the indicated value of the position sensor indicating the mold sliding position was 7.150 ± 0.005. Based on this, the mold position when the molded product was the thickest was set to 7.155, the mold position when the molded product was the thinnest was set to 7.145, and the maximum extension time of the press was set to 90 seconds. The press force when the press was extended was 100 N.

  Under such conditions, press molding was performed 50 times for each of the above five types of glass materials. The results are shown in Table 1. Regardless of the size of the glass material, the thickness of the molded product was within the range of 2.000 mm ± 0.005 mm.

  The present invention can be applied to a press molding method and a molding apparatus for manufacturing a molded product having steps of heating, press molding, and cooling.

The schematic of the metal mold | die peripheral part of the press molding apparatus of this invention. The flowchart of the press molding method of this invention. Explanatory drawing which shows the standard example of the press molding by this invention. Explanatory drawing which shows the example from which the press molding by this invention differs. Explanatory drawing which shows the further different example of press molding by this invention. Explanatory drawing which shows the further different example of press molding by this invention.

Explanation of symbols

2: mold, 3: material, 4: press rod, 5: plate, 6: position sensor, 11, 12: plate material, 21: upper mold, 22: lower mold, 23: trunk mold.

Claims (3)

A method of press-molding an optical element using a mold having an upper mold and a lower mold,
A method for press molding an optical element, comprising measuring an interval between the upper mold and the lower mold during the press molding and ending or continuing the press molding according to the measured value.   The molding conditions are set in advance for temperature, pressure, and time, and the press is started when the interval reaches a value corresponding to the lower limit of the thickness tolerance of the molded product before the set time elapses after the press starts under the molding conditions. When the molding is finished and the value corresponding to the lower limit is not reached, press molding is continued, and when the set time is reached, the interval may reach a value corresponding to the upper limit of the thickness tolerance of the molded product. The press molding method for an optical element according to claim 1, wherein the press molding is terminated and the press molding is extended to a maximum extension time if the value corresponding to the upper limit is not reached. The press molding apparatus for implementing the press molding method of the optical element according to claim 1 or 2, further comprising a measuring device for measuring a distance between the upper mold and the lower mold.

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