A process for molding a chalcogenide glass microlens array by applying multiple loads.

Abstract

This invention discloses a process for molding a chalcogenide glass microlens array using multiple loads. A low-level load is applied before the chalcogenide glass preform is uniformly heated to the molding temperature, causing deformation of the preform and increasing its contact area with the upper and lower molds, thereby accelerating the heating process. As the chalcogenide glass preform continues to deform, the magnitude and type of the applied load are changed to reduce the stress generated in the glass material during molding, thus lowering the residual stress in the finished glass lens. This effectively improves the processing quality and efficiency of the chalcogenide glass microlens array while reducing production costs.

Description

Technical Field

[0001] This invention relates to a process for molding a chalcogenide glass microlens array by applying multiple loads, belonging to the field of ultra-precision machining. Background Technology

[0002] With the development of optical technology, the performance and precision requirements of various optical systems are becoming increasingly stringent. The surface shapes of optical elements have evolved from spherical surfaces to complex surfaces such as aspherical surfaces, diffractive surfaces, freeform surfaces, and array surfaces. Microlens arrays, due to their unique geometric structure, have been widely used in optical communication, optical sensors, and lighting displays. Microlens arrays offer advantages such as a large field of view, large depth of field, and high integration. They hold significant research and application value in miniaturization and integration. Furthermore, the types of optical elements are gradually shifting from plastic optical elements to glass optical elements. Compared to polymer materials, optical glass materials have advantages such as low thermal expansion, low birefringence, high transmittance, good mechanical properties, and chemical stability, enabling them to meet higher precision requirements and withstand harsher operating conditions.

[0003] Common methods for manufacturing microlens arrays include photoresist hot reflow, laser direct writing, focused ion beam etching, and nanoimprint lithography. These methods can be used to fabricate high-performance microlens arrays, but precision is difficult to control, making it difficult to achieve the required uniformity when the formed area is large. Furthermore, these manufacturing methods are limited by material selection and the shape of the processed surface. Ultra-precision machining techniques such as single-point diamond turning are more versatile and flexible in microlens array fabrication, capable of processing more complex surfaces and producing microlenses with better uniformity. However, when the shape of the processed surface is complex, these methods have long processing cycles and high costs, making them less advantageous for mass production of optical components. Precision glass molding technology can efficiently produce optical components with various complex surface shapes, offering advantages in mass production. Simultaneously, a variety of moldable glass materials are available, including oxide glasses for the visible light band and chalcogenide glasses for the infrared band. Chalcogenide glasses, due to their wide infrared transmission range, high refractive index, and high nonlinearity, are increasingly used in fields such as infrared detection. Furthermore, chalcogenide glasses can be easily molded into precision optical devices. However, chalcogenide glasses have low thermal conductivity, resulting in slow heating rates and long processing cycles in the molding process. This problem is particularly pronounced when using low-cost spherical preforms. In addition, spherical preforms have large deformation and generate significant residual stress after molding. Summary of the Invention

[0004] The purpose of this invention is to provide a process for molding chalcogenide glass microlens arrays by applying multiple loads, so as to solve the problems existing in the prior art, reduce the processing time of the molding process of chalcogenide glass microlens arrays, reduce the residual stress of the molded lenses, improve the quality and efficiency of mass production of chalcogenide glass microlens arrays, and reduce production costs.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] This invention provides a process for molding a chalcogenide glass microlens array by applying multiple loads, as shown in the attached figure. Figure 1 As shown, it includes the following steps: Step 1: Place the spherical glass preform into a molding tool with a molding surface, transport the molding tool to the molding chamber of the molding machine, fill the molding chamber with nitrogen gas, and heat the molding tool and the glass preform. Step 2: When the glass preform is heated to a molding temperature higher than the glass transition temperature in the molding chamber of the molding machine, the lower mold in the molding tool closes upward under a specific load, and the glass preform is squeezed by the mold, so that the molding surface of the mold is copied onto the glass preform. The residual stress and surface accuracy are controlled by controlling the magnitude and type of load applied to the lower mold. Step 3: Maintain pressure on the lower mold to hold the glass preform under pressure, and reduce the temperature of the glass preform to below the transition temperature at a low cooling rate; Step 4: Remove the holding pressure, increase the cooling rate, and reduce the temperature of the glass preform to room temperature; Step 5: Remove the molding tool from the molding chamber of the molding machine, and after demolding, obtain a glass lens with a specific surface profile.

[0007] In step one, the molding tool includes an outer sleeve, an inner ring, an upper mold, and a lower mold. The lower mold has a matching groove for accommodating the inner ring. The outer sleeve is located outside the inner ring and has vent holes for purging the molding tool with nitrogen. After assembly, the tool is transported to the molding chamber of the molding machine.

[0008] In step two, after the glass preform is heated to a temperature above its transition temperature, a load is applied to the surface of the lower mold, driving the lower mold to close upwards. The mold closing temperature should ensure that the viscosity of the glass is within 10. 9 -10 7Within the range of dPa·s. Multiple sets of different loads are applied at different times during the molding process, with the first set of loads applied before the internal temperature of the glass preform reaches the optimal molding temperature. After each load application, the system switches to displacement control, maintaining the lower mold displacement unchanged for a certain period of time, thereby reducing the internal stress of the glass preform through the stress relaxation phenomenon of the glass.

[0009] In step three, the holding pressure applied to the lower mold is 0.2-0.5 MPa, and the holding time is 50-100 s. The glass preform is cooled at a low cooling rate to bring its viscosity to 10. 13 dPa·s.

[0010] In steps three and four, the cooling of the glass preform is mainly carried out by convective heat transfer, and the cooling rate is controlled by controlling the flow rate of nitrogen.

[0011] Beneficial effects: This invention not only optimizes the forming method of chalcogenide glass microlens arrays, but also provides an operable solution for industry. By applying different loads at different stages of preform deformation, the residual stress of the formed lenses is reduced and the processing time is effectively shortened while ensuring processing accuracy, demonstrating significant practical value. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of a method for molding chalcogenide glass microlens arrays by applying multiple loads;

[0013] Figure 2 This is a schematic diagram of the forming tool;

[0014] Figure 3 It is the load curve applied to the lower mold 2 during the molding stage;

[0015] Figure 4 The temperature change curve of the glass preform is plotted based on the finite element simulation results of the molding process with multiple loads and the molding process with a single constant load as described in this invention.

[0016] Figure 5 This is the equivalent stress simulation result of the compression molding process with multiple loads applied according to the present invention after the first and second loads have been applied;

[0017] Figure 6 The results are simulation results of residual stress in a compression molding process under a constant load of 0.015 mm / s.

[0018] Figure 7 The results are simulation results of residual stress in a compression molding process under a constant pressure load of 2.5 MPa.

[0019] Figure 8 These are the residual stress simulation results of the compression molding process method with multiple loads applied as described in this invention; Detailed Implementation

[0020] Example 1: A process for molding a chalcogenide glass microlens array by applying multiple loads.

[0021] The technical solutions of the embodiments of the present invention will now be described with reference to the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] like Figure 1 As shown: This embodiment provides a process for molding a chalcogenide glass microlens array by applying multiple loads, including the following steps:

[0023] Step 1: Place the spherical glass preform 5 into a forming tool with a forming surface. The forming tool includes an upper mold 1, a lower mold 2, an inner collar 3, and an outer sleeve 4. Figure 2 As shown, the lower mold 2 is provided with a groove that matches the inner sleeve 3 to accommodate the inner sleeve. The inner sleeve 3 is used to form the vertical surface of the edge of the chalcogenide glass lens and to constrain the radial direction of the chalcogenide glass lens, reducing the lateral flow of the glass material during the molding process and increasing the filling rate of the edge sub-lens. The displacement of the lower mold 2 can be adjusted by controlling the height of the inner sleeve 3. An outer sleeve 4 is provided outside the inner sleeve 3. The outer sleeve 4 plays a guiding role to ensure the coaxiality of the upper mold 1 and the lower mold 2 during the molding process. Air guide holes are designed on the outer sleeve 4 to facilitate nitrogen purging inside the molding tool. The molding tool is transported to the molding chamber of the molding machine and filled with nitrogen to prevent the glass and mold from being oxidized during the heating process. Then, the molding tool and the glass preform are heated by infrared heating lamps inside the molding machine.

[0024] Step 2: The spherical glass preform 5 is heated to a molding temperature above the glass transition temperature in the molding chamber of the molding machine. The corresponding viscosity value of the glass should be maintained at 10. 9 -10 7Within the range of dPa·s, the lower mold 2 closes upward under a specific load, and the spherical glass preform 5 is squeezed by the upper and lower molds, so that the surface shape of the mold is copied onto the preform. The residual stress and surface accuracy are controlled by controlling the magnitude and type of load applied to the lower mold 2. In this embodiment, the molding temperature range of chalcogenide glass is 200℃-236℃. Considering the residual stress and molding time, the molding temperature is set to 230℃. The load curve applied during the molding stage is as follows: Figure 3 As shown, a total of 6 different loads were applied to the lower mold 2. To reduce heating time and improve processing efficiency, the first load was applied when the internal temperature of the spherical glass preform 5 reached 200℃: the lower mold 2 was moved upward by 0.15mm at a molding rate of 0.005mm / s, and then kept stationary. After heating for 370s, the second load was applied: the lower mold 2 was moved upward by 1.16mm at a molding rate of 0.01mm / s, and then kept stationary. After heating for 384s, the spherical glass preform 5 was uniformly heated to 230℃. The third and fourth loads were then applied: at a molding rate of 0.02mm / s... Under the molding rate control, mold 2 moves upward by 2.24 mm, and under the molding rate control of 0.015 mm / s, mold 2 moves upward by 1.95 mm. To prevent the glass material and inner ring 3 from squeezing each other and generating large stress in the later stage of molding, the load type is changed from rate control to pressure control. After the lower mold 2 remains stationary for 20 seconds, the fifth set of loads is applied: a constant pressure of 2.5 MPa is applied to the lower surface of the lower mold 2 and the pressure is maintained for about 40 seconds. The edge vertical surface of the formed glass lens appears. Then the sixth set of loads is applied: a constant pressure of 5 MPa is applied to the lower surface of the lower mold 2 and the displacement reaches the specified value after 60 seconds. The molding stage ends.

[0025] Step 3: Anneal the molded lens. Apply a small pressure to the lower mold 2 to hold the glass preform under pressure of 0.5 MPa for 50 seconds. Simultaneously, reduce the temperature of the preform to below the transition temperature at a low cooling rate, so that the viscosity of the glass material reaches 10. 13 The heat transfer during annealing is mainly through forced convection, so the cooling rate can be controlled by adjusting the flow rate of nitrogen.

[0026] Step 4: Cool the annealed lens. In this step, the holding pressure on the lower mold 2 is removed, and the nitrogen flow rate is increased to increase the cooling rate and reduce the temperature of the lens to 20°C.

[0027] Step 5: Remove the cooled molding tool from the molding chamber of the molding machine, and after demolding, obtain a glass lens with a specific surface profile.

[0028] Spherical chalcogenide glass preforms have low thermal conductivity and a small contact area with the mold, requiring a long heating time and severely impacting processing efficiency. Therefore, in step two, applying a load before the spherical glass preform 5 is uniformly heated to the molding temperature causes deformation in the area where the preform contacts the upper and lower molds, increasing the contact area between the glass and the mold. According to Fourier's law of thermal conductivity, increasing the contact area increases the heat flowing into the glass preform per unit time. Furthermore, after deformation, the distance between the upper and lower molds and the center of the glass preform decreases, further reducing the heating time. Therefore, applying a small load before the glass preform reaches the molding temperature can reduce the heating time without generating significant stress. Figure 4 Temperature simulation results of the process method described in this invention show the advantage of the chalcogenide glass microlens array molding process with multiple loads in shortening the heating time. Figure 5 The stress simulation results show that in the process method described in this invention, applying a load before the internal temperature of the glass preform reaches the molding temperature will not cause a stress surge, and the equivalent stress after the second load application is reduced compared to the equivalent stress after the first load application.

[0029] Towards the end of the molding stage in step two, the deforming glass will come into contact with the inner ring 3. At the initial contact point, the contact area is very small. If the interaction force between the glass and the inner ring 3 is too large at this time, it will generate significant local stress, potentially causing the glass to shatter. Therefore, the type of applied load is changed from a constant rate to a constant pressure to better control the interaction force between the glass and the inner ring 3. Figure 6 , Figure 7 , Figure 8 The simulation results of residual stress from different process methods show that the chalcogenide glass microlens array molding process method with multiple loads described in this invention can achieve a lower residual stress level.

[0030] This specification illustrates the principles and implementation methods of the present invention through specific examples. The descriptions of these embodiments are merely illustrative of the method and core ideas of the present invention. For those skilled in the art, modifications to the specific implementation methods and application scope will be possible based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. This invention provides a process for molding a chalcogenide glass microlens array by applying multiple sets of loads, characterized in that, Includes the following steps: Step 1: Place the spherical glass preform into a molding tool with a molding surface, transport the molding tool to the molding chamber of the molding machine, fill the molding chamber with nitrogen gas, and heat the molding tool and the glass preform. Step 2: When the glass preform is heated to a molding temperature higher than the glass transition temperature in the molding chamber of the molding machine, the lower mold in the molding tool closes upward under a specific load, and the glass preform is squeezed by the mold, so that the molding surface of the mold is copied onto the glass preform. The residual stress and surface accuracy are controlled by controlling the magnitude and type of the load applied to the lower mold. Step 3: Maintain pressure on the lower mold to hold the glass preform under pressure, and reduce the temperature of the glass preform to below the transition temperature at a low cooling rate; Step 4: Remove the holding pressure, increase the cooling rate, and reduce the temperature of the glass preform to room temperature; Step 5: Remove the molding tool from the molding chamber of the molding machine, and after demolding, obtain a glass lens with a specific surface profile.

2. The process for molding a chalcogenide glass microlens array by applying multiple loads according to claim 1, characterized in that: In step one, the molding tool includes an outer sleeve, an inner ring, an upper mold, and a lower mold. The lower mold has a matching groove for accommodating the inner ring. The outer sleeve is located outside the inner ring and has air vents designed on it to purge the molding tool with nitrogen. After assembly, the tool is transported to the molding chamber of the molding machine.

3. The process for molding a chalcogenide glass microlens array by applying multiple loads according to claim 1, characterized in that: In step two, after the glass preform is heated to a temperature above its transition temperature, a load is applied to the surface of the lower mold to drive the lower mold to close upwards. The closing temperature should ensure that the viscosity of the glass is within 10. 9 -10 7 Within the range of dPa·s, multiple sets of different loads are applied at different times during the molding process. The first set of loads is applied before the internal temperature of the glass preform reaches the optimal molding temperature. After each load is applied, the system switches to displacement control to keep the lower mold displacement constant for a certain period of time. This reduces the internal stress of the glass preform through the stress relaxation phenomenon of the glass.

4. The process for molding a chalcogenide glass microlens array by applying multiple loads according to claim 1, characterized in that: In step three, the holding pressure applied to the lower mold is 0.2-0.5 MPa, and the holding time is 50-100 s. The glass preform is cooled at a low cooling rate to bring its viscosity to 10. 13 dPa·s.

5. The process for molding a chalcogenide glass microlens array by applying multiple loads according to claim 1, characterized in that: In steps three and four, the cooling of the glass preform is mainly carried out by convective heat transfer, and the cooling rate is controlled by controlling the flow rate of nitrogen.

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