Fused quartz glass lens manufacturing process based on powder room-temperature compression molding

Abstract

The invention discloses a fused quartz glass lens manufacturing process based on powder room-temperature compression molding. The fused quartz glass lens manufacturing process mainly comprises two steps of powder room-temperature compression molding and high-temperature sintering. Firstly, a mold with nanoscale surface roughness is machined through ultra-precision turning, then nano silicon dioxide particles are subjected to dry pressing forming through a press machine at the room temperature to obtain a powder pressing block, and the powder pressing block copies the shape and roughness of the mold; and finally, performing high-temperature sintering on the powder briquettes in a muffle furnace to obtain the transparent and compact fused quartz glass lens. According to the method, nano silicon dioxide particles are deformed and rearranged through external force to form a solid briquette with a certain relative density, so that the addition of organic matters and a long-time degreasing process are avoided, batch production can be realized, and the processing efficiency of the fused quartz glass lens is greatly improved; the difficulty of high-temperature mold pressing of fused quartz glass is overcome through powder dry pressing and subsequent sintering modes, and lens modeling can be completed at the room temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of precision machining of optical elements, and particularly relates to a manufacturing process of fused silica glass lenses based on powder room-temperature molding pressing. Background Art

[0002] Fused silica glass has high light transmittance in the ultraviolet-visible-near infrared band, and has excellent mechanical properties, thermal stability and chemical stability, and is an important material for making optical elements. However, due to the hard and brittle characteristics and high melting point of fused silica glass, its forming and processing pose great challenges. At present, grinding and polishing are the main means for processing fused silica glass lenses, but they are limited to simple axisymmetric shapes, such as small-batch processing of optical lenses with spherical surfaces, aspherical surfaces, etc., with low efficiency and causing a certain degree of subsurface damage. Chemical etching, high-energy particle beam / laser beam / electron beam processing methods can obtain optical surfaces with arbitrarily complex micro-scale shapes, but the processes are complex and the time cost is extremely high. Glass precision molding can achieve the processing of optical lenses with high precision and high efficiency. This method heats the glass to its glass transition point and performs molding when the glass is in a viscoelastic state. However, pressing fused silica glass requires a high temperature of up to 1400 °C, which makes the selection range of mold materials extremely narrow. Usually, only materials with high temperature resistance and high hardness such as glassy carbon or silicon carbide can be selected as molds. Problems such as mold processing difficulty, damage and maintenance directly result in the current difficulty in realizing reliable precision molding of fused silica glass lenses.

[0003] The sol-gel method is a means with high flexibility and mildness for preparing transparent and dense silica glass. This method uses ethanol as a co-solvent, and uses the hydrolysis and condensation reaction of a silica precursor (such as tetraethyl orthosilicate or tetramethyl orthosilicate) and water to generate a silica gel, and then the gel is converted into a transparent and dense glass through sintering. By adjusting the composition of the alkoxide precursor, the preparation of multi-component glass can also be realized by this method, and its heat treatment temperature only needs about 1000 °C. At present, the processing of optical glass elements based on the sol-gel method mainly has two methods: casting and additive manufacturing (3D printing). However, the silica gel prepared by the sol-gel method needs to undergo a long atmospheric pressure and low temperature drying process, and under the action of drying stress, it generates huge and irrecoverable volume shrinkage and warping deformation. This inherent defect makes it difficult for the sol-gel method to realize the production of optical elements with high precision. Although most of the shrinkage and deformation can be avoided by supercritical drying, its operation has great risks.

[0004] Polymer-based nanosilica composites are a new means of researching and preparing fused silica glass in recent years. By uniformly dispersing nanosilica particles in a photocurable or thermocurable polymer and then adding an initiator, solidification and shaping can be completed at room temperature through methods such as 3D printing, mold casting, and injection molding. The obtained silica-polymer nanocomposite can also be further processed by processes such as cutting and hot pressing, with high flexibility. Generally, in order to transform the nanosilica composite into transparent fused silica glass, it is necessary to first degrease at 600 °C and then sinter at a temperature of 1300 °C, slightly higher than the temperature required by the sol-gel method. A large amount of gas is released during the degreasing of this composite material. In order to avoid cracking, a very slow heating rate is often required. In addition, in order to ensure the uniformity of nanosilica particles in the polymer, a large amount of time is required for stirring and dispersion, and a certain amount of dispersant needs to be added if necessary, which to a certain extent reduces the production efficiency of this method. Summary of the Invention

[0005] The purpose of the present invention is to provide a precise and efficient manufacturing process for fused silica glass lenses based on powder room-temperature molding to address the current problems of difficult processing and low production efficiency of complex fused silica glass optical lenses, while simplifying the operation process and ensuring indicators such as the surface roughness, surface shape accuracy, and light transmittance of the lenses.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A fused silica glass lens manufacturing device includes an upper punch, a die sleeve, and a die.

[0008] The die sleeve has a through hole, and the lower end of the upper punch and the upper end of the die can extend into the through hole. The upper end surface of the die forms the shape required for the lens.

[0009] Further, the upper punch is made of die steel, and its lower end surface is polished to a surface roughness Sa < 5 nm.

[0010] Further, the die includes a die body. A nickel-phosphorus alloy coating with a thickness of 500 μm is plated on the upper end surface of the die body by electroless nickel plating. The die body is made of brass, and the phosphorus content in the nickel-phosphorus alloy is 10%.

[0011] Further, the shape of the upper end surface of the die is a single spherical surface, a spherical array, or a sinusoidal surface.

[0012] A manufacturing process for fused silica glass lenses based on powder room-temperature molding. Nano-silica particles are filled into a mold, and after molding at room temperature, the formed silica powder compact is sintered at high temperature to obtain a transparent and dense fused silica glass lens.

[0013] The process for manufacturing a fused silica glass lens using the above-mentioned fused silica glass lens manufacturing device. Through the upper punch and the mold, nano-silica particles are filled into the through-hole of the mold sleeve. Then, the mold sleeve is tapped and vibrated to make the nano-silica particles spread evenly on the upper end face of the lower mold. At room temperature, the upper punch is slowly pressed down. When the predetermined pressure is reached, it stops and holds the pressure for a predetermined time to complete the pressing of the powder. After the molding is completed, the whole device is inverted, the lower mold is taken out, and the mold sleeve is slowly pressed down to expose the powder compact from the through-hole. Finally, the powder compact is sintered at high temperature in a muffle furnace to obtain a dense and transparent optical glass lens.

[0014] Further, the type of the nano-silica particles used is Aerosil OX50, the average particle size is 40 nm, and the purity is ≥99.8%.

[0015] Further, the pressing speed of the upper punch is 0.5 mm / s, the predetermined pressure is 70 MPa, and the holding time for holding the pressure is 1 min.

[0016] Further, the sintering atmosphere of the silica powder compact in the high-temperature muffle furnace is air. First, it is heated to 400 °C at a heating rate of 1 °C / min, then heated to 1300 °C at a heating rate of 0.66 °C / min, held at 1300 °C for 10 min, and finally cooled naturally. After sintering, a transparent and dense fused silica glass lens is obtained.

[0017] The beneficial effects of the present invention are as follows: The present invention can realize the molding of the lens through dry pressing of the powder at room temperature, avoiding conditions such as high temperature and special atmosphere required for similar glass precision molding, greatly improving the processing efficiency; the room-temperature molding of the powder greatly reduces the requirements for the mold, reduces the wear of the mold during the molding process, does not require expensive maintenance, and extends the service life of the mold; the selection range of mold materials is also wider compared to glass precision grinding and molding. Materials such as brass, nickel-phosphorus alloy, and mold steel can all be used as suitable mold materials and are all easy to process; in addition, the only material used is nano-silica particles, and there is no need for a cumbersome material preparation process. Since there is no binder such as organic matter, the powder compact can be directly sintered at high temperature relatively quickly, avoiding a long debinding process.

[0018] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings to further elaborate on the present invention in detail. Description of the Drawings

[0019] Figure 1 are schematic diagrams of the molding device and the operation process;

[0020] Figure 2 is a cross-sectional scanning electron microscope image of the sintered fused silica glass;

[0021] Figure 3 is the transmittance diagram of the sintered fused silica glass in the ultraviolet-visible-near-infrared range.

[0022] Figure 1 In the figure, 1. upper punch, 2. die sleeve, 3. nano-silica particles, 4. die. Specific embodiments

[0023] The specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

[0024] The manufacturing device of the fused silica glass lens of the present invention is as Figure 1 shown. Any desired lens shape with an optically smooth surface is machined on the die 4 using ultra-precision turning. Then, the silica nanoparticles are compression-molded at room temperature on a hydraulic press. Finally, the silica powder compact is sintered at high temperature in a muffle furnace to obtain a transparent and dense fused silica glass lens.

[0025] Specifically, the silica raw material used is only nano-silica particles 3, with the model Aerosil OX50, an average particle size of 40 nm, and a purity of ≥99.8%. The nano-silica particles are directly used for molding without other treatments. The molds used are divided into an upper punch 1 and a mold 4. Among them, the upper punch 1 is made of mold steel, and its surface is polished to a surface roughness Sa < 5 nm; the mold 4 is made of brass electroplated with nickel-phosphorus alloy, and a nickel-phosphorus alloy coating with a thickness of 500 μm is plated on the surface of the brass rod by electroless nickel plating. The phosphorus content in the nickel-phosphorus alloy is 10%. In an ultra-precision machine tool, a natural diamond tool is used to machine the required lens shape with a surface roughness Sa < 5 nm on the surface of the nickel-phosphorus alloy, such as a single spherical surface, a spherical array, a sine surface, etc. Room temperature molding is carried out on a hydraulic press. First, the mold sleeve 2 and the mold 4 are fixed, the nano-silica particles 3 are filled into the mold sleeve 2, and then the mold sleeve 2 is tapped and vibrated to make the nano-silica particles spread evenly on the lower mold 4. Then, the upper punch 1 slowly presses down at a speed of 0.5 mm / s and stops when the pressure reaches 70 MPa, and the pressure is maintained for 1 min to complete the pressing of the powder. After the molding is completed, the whole device is inverted, the mold 4 is taken out, and the mold sleeve 2 is slowly pressed down to extrude the powder compact. The whole process of molding and extrusion takes about 2 min. Finally, the powder compact is sintered at high temperature in a muffle furnace to obtain a dense and transparent optical glass lens. The sintering atmosphere is air, the heating rate is 1 °C / min to 400 °C, 0.66 °C / min to 1300 °C, and after holding at 1300 °C for 10 min, it is naturally cooled to complete the sintering process, and a transparent and dense fused silica glass lens can be obtained.

[0026] The process principle of the present invention mainly involves powder densification controlled by stress during powder dry pressing and the sintering mechanism of nanoparticles. During the downward pressing of the upper punch 1, the nano-silica particles 3 undergo three main processes to form a powder compact with a certain relative density and strength: (1) the relative density of the powder green body increases to form a relatively compact block; (2) the relative density of the powder further increases, and interconnected pores are formed around the nanoparticles; (3) the relative density reaches the maximum value, and the interconnected pores become isolated and closed pores. During the process of powder compaction and densification, the mechanisms controlling its densification include stress-induced particle rearrangement, plastic deformation after particle contact, and particle fragmentation, corresponding to the above three main processes respectively. Under the combined action of these mechanisms, the nanoparticles are bonded together through bridging stress. Sintering is a means of solidifying the powder compact through heat energy, including two basic phenomena: densification and grain growth. The driving force for sintering is the reduction of the total interfacial energy. The nano-silica particles used in the present invention are spherical particles with an average particle size of 40 nm. During the sintering process, a neck is formed in the contact area between two adjacent nanoparticles. As sintering progresses, the total interfacial energy decreases, and the neck region gradually increases until the two nanoparticles are completely fused into one. In the present invention, before the silica powder compact is sintered, it has undergone a pressing at a certain pressure once. Under the action of the pressing stress, the contact area between the nano-silica particles is larger and the connection is tighter, which is more conducive to the fusion and densification between the particles during subsequent sintering.

[0027] The present invention will be compared with two existing preparation methods as follows:

[0028] First of all, compared with the precision glass molding of fused silica lenses, this solution avoids the high temperature required for molding and the high cost of mold manufacturing and maintenance. Different from the precision molding of soda-lime glass and chalcogenide glass, the precision molding of fused silica glass often needs to be carried out at a high temperature of about 1400 °C, which prolongs the molding cycle and reduces the efficiency. In order to increase the cooling rate and prevent the oxidation failure of the mold at high temperature, the molding usually needs to be carried out in an inert gas atmosphere, which also increases the processing cost. In addition, the high temperature of 1400 °C greatly limits the range of available mold materials. At present, the molds commonly used for fused silica molding are basically prepared from materials with extremely high mechanical properties and high temperature resistance such as silicon carbide, glassy carbon, and tungsten carbide. However, the brittle characteristics of these materials make it difficult to manufacture molds through general cutting processing. Although grinding and polishing techniques can be used to process these materials, the time cost and cost of processing are extremely high, and it is basically limited to the processing of simple structures with rotational symmetry such as spherical and aspherical surfaces. It is very difficult to realize the manufacturing of complex microstructures such as lens arrays. In addition to the difficult processing problem of mold materials, the protection and maintenance of the mold also increase the cost of fused silica molding. Taking silicon carbide as an example, relevant research shows that the silicon carbide mold fails after 6 molding processes and has a large area of adhesion with the glass. Although the mold can be protected by plating a platinum-iridium coating or a chromium-aluminum nitride coating on the mold surface, after 6 moldings, the coating changes color and delaminates, and the surface roughness increases significantly. This solution first molds the silica nanoparticles and then completes their transformation into fused silica through subsequent high-temperature sintering. Compared with the high-temperature molding of fused silica, the molding of silica nanoparticles in this solution can be carried out at room temperature, and there is no need for vacuum or inert protective gas. It can be molded in large quantities in a short time, with the characteristics of low cost and high efficiency. A wide range of mold materials can be selected for room-temperature molding. Materials such as brass alloy and nickel-phosphorus alloy that are easy to process and form can be used for mold preparation. The processing and cost are significantly superior to materials such as silicon carbide. In addition, during the room-temperature molding process, due to the absence of temperature influence and the low adhesion degree between the nanoparticles and the mold, the damage to the mold is extremely small, and the same mold can complete a large number of repeated manufacturing processes. Due to the improvement of the processability of the mold material, this solution can also realize the molding of complex structures such as free-form surfaces, microlens arrays, and gratings of fused silica.

[0029] Secondly, compared with the method of preparing fused silica lenses by using nano-silica particle-polymer composites, this solution has the advantage of a simple material preparation process. In recent years, nano-silica particle-polymer composites developed can be used to process complex-curved lens blanks through additive manufacturing, hot pressing, injection molding, cutting molding, etc., and then transformed into fused silica by high-temperature sintering. The processing and molding ability of this composite material depends on the properties and proportions of the polymers in the composite material. To meet the processing requirements, a large amount of research on the types, properties, compatibility, and proportions of polymers is often required. In addition, to improve the dispersion uniformity and bonding of silica nanoparticles in the polymer, a certain amount of dispersant may be added or the silica nanoparticles may be chemically modified when necessary. The dispersion and chemical treatment of silica nanoparticles often take dozens of hours or even days. During the high-temperature heat treatment process of the composite material, due to the presence of organic substances such as polymers, the heat treatment is usually divided into two steps: degreasing and sintering. To avoid damage such as cracks in the lens blank caused by the too-fast removal of organic substances such as polymers during the degreasing process, a relatively low heating rate is usually adopted during the degreasing process, and it usually takes 2 to 3 days to complete the degreasing. In contrast, although this solution also uses silica nanoparticles for lens forming and high-temperature heat treatment to achieve its transformation into fused silica, there are no organic additives such as polymers, and the silica nanoparticles can be directly subjected to room-temperature molding and high-temperature sintering without any chemical treatment and modification, which can greatly shorten the material preparation cycle. At the same time, the long degreasing process is also avoided, and rapid sintering treatment can be directly carried out, greatly shortening the processing cycle.

[0030] In the present invention, an external force is used to make the nano-silica particles undergo deformation and rearrangement to form a solid compact with a certain relative density, avoiding the addition of organic substances and the long degreasing process, and batch production can be achieved, greatly improving the processing efficiency of fused silica glass lenses; the difficulties of high-temperature molding of fused silica glass are overcome by powder dry pressing and subsequent sintering, and the shaping of the lens can be completed at room temperature. Figure 2 It can be seen that the fused silica glass sintered by this method is uniform and dense inside, without defects such as pores; Figure 3 It can be seen that the fused silica glass sintered by this method has a light transmittance equivalent to that of commercial fused silica glass and has excellent optical properties.

[0031] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fused silica glass lens manufacturing apparatus, characterized in that, It includes an upper punch (1), a die sleeve (2) and a die (4). The die sleeve (2) has a through hole, and the lower end of the upper punch (1) and the upper end of the die (4) can extend into the through hole. The upper end surface of the die (4) forms the shape required for the lens.

2. The fused silica glass lens manufacturing device according to claim 1, characterized in that The upper punch (1) is made of die steel, and its lower end surface is polished to a surface roughness Sa < 5 nm.

3. The fused silica glass lens manufacturing device according to claim 1, characterized in that The die (4) includes a die body. A nickel-phosphorus alloy coating with a thickness of 500 μm is plated on the upper end surface of the die body by electroless nickel plating. The die body is made of brass, and the phosphorus content in the nickel-phosphorus alloy is 10%.

4. The fused silica glass lens manufacturing device according to claim 1, characterized in that The shape of the upper end surface of the die (4) is a single spherical surface, a spherical array or a sine surface.

5. A manufacturing process for a fused silica glass lens based on powder room-temperature molding, characterized in that Nano-silica particles are filled into the die, and then after molding at room temperature, the molded silica powder compact is sintered at high temperature to obtain a transparent and dense fused silica glass lens.

6. The process for manufacturing a fused silica glass lens using the fused silica glass lens manufacturing device according to any one of claims 1-4, characterized in that Through the upper punch (1) and the die (4), nano-silica particles (3) are filled into the through hole of the die sleeve (2), and then the die sleeve (2) is tapped and vibrated to make the nano-silica particles spread evenly on the upper end surface of the lower die (4). At room temperature, the upper punch (1) is slowly pressed down. When the predetermined pressure is reached, it stops and is held at the pressure for a predetermined time to complete the pressing of the powder. After the molding is completed, the device is inverted as a whole, the lower die (4) is taken out, the die sleeve (2) is slowly pressed down to expose the powder compact from the through hole, and finally the powder compact is sintered in a muffle furnace at high temperature to obtain a dense and transparent optical glass lens.

7. The process for manufacturing a fused silica glass lens according to claim 6, characterized in that, The nano-silica particles (3) used are of the type Aerosil OX50, with an average particle size of 40 nm and a purity ≥ 99.8%.

8. The process for manufacturing a fused silica glass lens according to claim 6, characterized in that, The pressing speed of the upper punch (1) is 0.5 mm / s, the predetermined pressure is 70 MPa, and the holding time at the pressure is 1 min.

9. The process for manufacturing a fused silica glass lens according to claim 6, characterized in that, The sintering atmosphere of the silica powder compact in the high-temperature muffle furnace is air. First, it is heated to 400 °C at a heating rate of 1 °C / min, then heated to 1300 °C at a heating rate of 0.66 °C / min, held at 1300 °C for 10 min, and finally cooled naturally. After sintering, a transparent and dense fused silica glass lens is obtained.

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