Ultra-precision cutting machining method for ultra-smooth surface of glassy carbon mold pressing mold and position control-force control cooperative control ultra-high-temperature mold pressing method

Abstract

The invention belongs to the technical field of ultra-high-temperature compression molding of quartz glass optical elements, and particularly provides an ultra-precise cutting machining method for the ultra-smooth surface of a glassy carbon compression mold and a position control-force control cooperative control ultra-high-temperature compression molding method. The ultra-smooth surface of the mold is obtained by machining high-elasticity and high-brittleness glassy carbon by utilizing an ultra-precision single-point diamond lathe in combination with a PCD (Polycrystalline Diamond) turning tool and a single crystal diamond turning tool, and the mold has nanoscale roughness, submicron surface shape precision and complex curved surface shapes such as an aspheric surface, a spherical surface or a micro-nano structure. When the glassy carbon ultra-smooth surface mold is used for conducting ultra-high-temperature compression molding on quartz glass, when the mold pressure increasing rate of the lower mold exceeds a preset threshold value, the mold pressing assembly controls the upper mold to reduce the moving rate, and when the mold pressure increasing rate of the lower mold is smaller than a set value, the mold pressing assembly controls the upper mold to increase the moving rate; and finally, ultrahigh-temperature compression molding of position control-force control cooperative control is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-high temperature molding of quartz glass optical elements, and specifically provides a method for machining a super-smooth surface of a glassy carbon molding die resistant to ultra-high temperature of 1500 °C and a method for ultra-high temperature molding with coordinated position-control and force-control. Background Art

[0002] Due to excellent optical properties, high temperature resistance, chemical stability and other characteristics, quartz glass is widely used in high-end optical elements, such as laser lenses, optical windows, mirrors, etc. However, the traditional grinding, lapping and polishing processes are complex, inefficient and costly, and can no longer meet the market's demand for mass production of high-quality, high-precision and miniaturized optical elements. In view of this, scholars in various countries have proposed direct molding of quartz glass at ultra-high temperature and high pressure to achieve mass production of high-quality and high-precision quartz glass optical elements. The high temperature resistance of quartz glass requires a high-temperature environment to form a glass melt, reduce the viscosity, and then fill the mold cavity for molding. However, the softening temperature of quartz glass at 1500 °C causes significant softening of conventional high-temperature molding dies, and at the same time, adhesion to the glass occurs, ultimately seriously affecting the mold life, molding quality and efficiency. It can be seen that the ultra-high temperature molding of quartz glass poses strict requirements on mold materials, mold surface quality and molding process control.

[0003] Glassy carbon is a typical amorphous carbon, with material characteristics such as high temperature resistance, chemical inertness, high hardness and low thermal expansion coefficient, and is a material that can meet the requirements for ultra-high temperature molding dies of quartz glass. However, the glassy carbon material has a low Young's modulus, high deformation recovery rate and high brittleness, resulting in extremely difficult machining into a super-smooth surface mold required for high-temperature molding, and there is no mature ultra-precision machining technology for glassy carbon. Machining glassy carbon by conventional grinding or milling methods easily causes defects such as cracks and holes on the mold surface, affecting the subsequent high-temperature molding of high-quality quartz glass optical glass.

[0004] In addition, existing molding equipment generally adopts a single pressure control strategy, and adjusts the forming pressure to ensure uniform flow of the glass material and full filling of the mold cavity. However, when the mold surface roughness is high or there are defects, excessive pressure easily causes deformation or even cracking of the optical element, while insufficient pressure will cause defects such as surface unevenness or voids, ultimately affecting the forming quality of the element. In addition, pure pressure control is difficult to achieve precise control of the mold movement trajectory, and thus cannot guarantee the shape and dimensional accuracy of the optical element, and the rough mold surface will further exacerbate this problem. Summary of the Invention

[0005] To achieve the above object, the present invention provides a processing method for the ultra-smooth surface of a glassy carbon molding die capable of withstanding ultra-high temperature of 1500 °C, as well as an ultra-high temperature molding method using the die in combination with position control-force control collaborative control, to overcome the above problems or at least partially solve the problems of difficult processing of glassy carbon dies and the quartz glass molding method.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] In the first aspect, the present invention provides an ultra-precision cutting processing method for the ultra-smooth surface of a glassy carbon molding die to improve the surface quality of the glassy carbon molding die, including the following steps:

[0008] S1. Ultrasonically clean the glassy carbon die to remove the oil stains and debris left by rough machining on the die surface, and then fix the rough-machined glassy carbon die on the spindle of an ultra-precision single-point diamond lathe by using a vacuum adsorption clamping table;

[0009] S2. Install the PCD polycrystalline diamond tool on the tool holder, adjust the position and angle of the tool, and perform precise tool setting through the machine tool processing numerical control system;

[0010] S3. Slowly rotate the spindle, and adjust the coaxiality of the die and the spindle with the help of a micrometer to ensure that the pointer of the micrometer jumps less than one grid during one revolution of the workpiece;

[0011] S4. Set the cutting parameters for semi-finishing, and use the PCD polycrystalline diamond tool to semi-finish the surface of the glassy carbon die to remove the cutting texture and damage defects left by rough machining on the die surface;

[0012] S5. Replace the single-crystal diamond turning tool, set the cutting parameters for finishing, and start ultra-precision turning of the surface of the glassy carbon die to obtain an ultra-smooth surface;

[0013] S6. Perform surface shape detection on the glassy carbon die with an ultra-smooth surface, construct a free-form surface through surface shape error, generate a machining path file, and perform tool radius compensation using data interpolation;

[0014] S7. Through machining compensation, ultra-precision turn the surface of the glassy carbon die again, and detect the surface shape accuracy of the die surface after machining. If the requirements for a nano-level ultra-smooth surface and sub-micron-level surface shape accuracy are met, subsequent ultra-high temperature molding can be carried out. If the surface shape accuracy does not meet the requirements, steps S5 and S6 need to be repeated again.

[0015] The present invention can eliminate material adhesion on the die surface, accurately control the deformation amount, deformation rate and forming rate of the high-temperature quartz glass melt, and efficiently obtain quartz optical glass components with high surface quality, high surface shape accuracy and low residual stress.

[0016] As a further technical solution, the mold material is amorphous glassy carbon, the surface shape of the mold is a complex curved surface such as an aspherical surface, a spherical surface, a micro-nano structure mold, etc., and the surface quality of the mold is a nanoscale roughness and a sub-micron surface shape accuracy.

[0017] As a further technical solution, when semi-finishing with an ultra-precision single-point diamond lathe in step S4, the front angle of the PCD polycrystalline diamond tool is 35° and the rear angle is 7°, the nose radius is 0.2 - 0.8 mm, the blade thickness is 3 - 5 mm, and there is no visible damage when the tool edge is observed under a 150X objective microscope.

[0018] As a further technical solution, when finishing with a single-crystal diamond tool in step S5, the front angle of the single-crystal diamond tool is 0° and the rear angle is 5°, the tool head radius is 0.3 - 1.5 mm, the tip radius is 250 nm, and there are no visible micro-cracks when the tool edge is observed under a 150X objective microscope.

[0019] As a further technical solution, the cutting parameters in step S4 involve a spindle speed of 100 - 2000 r / min, a depth of cut of 1 - 5 μm, and a feed rate of 1 - 10 μm / r.

[0020] As a further technical solution, the cutting parameters in step S5 involve a spindle speed of 100 - 2000 r / min, a depth of cut of 100 - 500 nm, and a feed rate of 0.1 - 1 μm / r.

[0021] As a further technical solution, the cutting parameters in steps S4 and S5 can be determined by the fracture mechanics model of amorphous hard and brittle materials and depend on the critical depth of cut d c , and its calculation formula is d c = λ(H / E) 1 / 2 (Kc / H) 2 , where λ is the brittle-ductile transition factor of the material, K C is the fracture toughness, H is the hardness, and E is the Young's modulus.

[0022] In a second aspect, the present invention proposes a position-control - force-control collaborative control ultra-high temperature molding method, which combines the ultra-smooth surface glassy carbon mold processed above to improve the surface quality, surface shape accuracy, molding efficiency, and yield rate of the molded quartz glass optical element, and includes the following steps:

[0023] S8. Place the processed glassy carbon ultra-smooth surface molding mold into the molding assembly of the position-control - force-control collaborative control ultra-high temperature molding device;

[0024] S9. Perform surface pretreatment on the quartz glass block formed by high-temperature molding to remove oil stains and contaminants. Place the treated quartz glass block in the inner cavity of the glassy carbon mold, and seal it with the upper cover at the same time.

[0025] S10. Start the vacuum pump to ensure that the heating cavity is under a vacuum of 10 -3 Pa. Then turn off the vacuum pump and turn on the nitrogen gas filling device to ensure that the heating cavity is in an atmosphere protected by pure nitrogen.

[0026] S11. Set the initial threshold of the force control module in the molding assembly to 0.5 N. Then start the molding assembly to drive the upper mold to move rapidly towards the lower mold. When the contact force measured by the force control module reaches the threshold of 0.5 N, the upper mold stops advancing, and set the initial position value of the upper mold in the position control module to 0 μm.

[0027] S12. Set the upper mold to perform molding at a certain rate in the position control module, and at the same time set the threshold of the increase rate of the molding pressure of the lower mold in the force control module. Start the position-control and force-control collaborative control of ultra-high temperature and ultra-precision molding of quartz glass. When the increase rate of the molding pressure exceeds the threshold, the molding assembly controls the upper mold to reduce the molding rate, and when the increase rate of the molding pressure is less than the set value, the molding assembly controls the upper mold to increase the molding rate.

[0028] S13. Set the heat preservation time. After the molding is completed, when the heating cavity cools down to room temperature, open the upper cover of the heating cavity and take out the molded quartz glass optical element.

[0029] S14. Use a complex surface optical profiler, white light interferometer, and field emission scanning electron microscope to measure and analyze the surface shape, surface roughness of the molded quartz glass optical element, and the surface wear of the glassy carbon mold.

[0030] As a further technical solution, the glassy carbon super-smooth surface molding mold described in step S8 is divided into an upper mold and a lower mold, and the shape and size of the mold determine the shape and size of the ultra-high temperature molded quartz glass optical element.

[0031] As a further technical solution, the molding assembly described in step S8 simultaneously includes a pressure sensor with an accuracy of 0.1 N and a displacement sensor with an accuracy of 0.5 μm.

[0032] As a further technical solution, the heating temperature of the heating cavity described in step S10 is in the range of 25 - 1600 °C.

[0033] As a further technical solution, the molding rate of the upper mold described in step S12 is in the range of 1 - 150 μm / s for molding, the threshold of the increase rate of the molding pressure of the lower mold is 2 N / s, and the increase rate of the molding pressure is in the range of 0.2 - 2 N / s.

[0034] The beneficial effects of the present invention are as follows:

[0035] Through the ultra-smooth surface processing method of the vitreous carbon molding die of the present invention, the problem of poor processing quality of vitreous carbon dies is overcome. Through ultra-precision single-point diamond turning, combined with the semi-finishing step of a PCD polycrystalline diamond tool and the finishing step of a single-crystal diamond tool, the defects on the surface of vitreous carbon are effectively removed, an ultra-smooth surface at the nanometer level and a surface shape accuracy at the sub-micron level are obtained, ensuring the ultra-high surface quality of the molding die. At the same time, complex curved surface dies such as aspherical, spherical, and micro-nano structure dies can be processed, meeting the molding requirements of different types of optical elements;

[0036] Combining two control modes of position control and force control can accurately control the deformation amount and forming rate of high-temperature glass melt, avoiding component deformation or defects that may occur under a single pressure control mode, significantly improving the surface quality and surface shape accuracy of the molding of optical glass components. The accurate molding control strategy and the high-quality die surface reduce the rejection rate, optimize the molding process, and improve production efficiency and yield. Through the present invention, the problems of difficult processing of vitreous carbon and poor surface quality, low efficiency, and low yield during the ultra-high temperature molding of quartz glass optical components in the prior art can be effectively solved, realizing the mass production of high-quality and high-precision quartz glass optical components. Description of the Drawings

[0037] The specification drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0038] Figure 1 is a schematic process flow diagram of the present invention;

[0039] Figure 2 is an SEM image of the surface morphology of the ultra-smooth surface vitreous carbon die obtained by processing the present invention;

[0040] Figs. 3(a), 3(b), and 3(c) are SEM images of the surfaces of the vitreous carbon dies after high-temperature molding in the finishing, semi-finishing, and rough machining of the present invention;

[0041] Figs. 4(a) and 4(b) are SEM images of the surface wear after position control-force control collaborative control and single force control molding of the ultra-smooth surface vitreous carbon molding die. Detailed Embodiments

[0042] As explained in the background art, there is currently a lack of a processing method for the ultra-smooth surface of glassy carbon materials. Ordinary processing methods will cause damage to the surface of glassy carbon, resulting in problems such as micro-cracks, pores or uneven surfaces. To solve the above problems, the present invention proposes a processing method for a glassy carbon ultra-smooth surface molding die, which constructs surface parameters by means of single-point diamond turning combined with surface shape detection, generates a machining path function, and at the same time uses data interpolation for tool radius compensation to eliminate the problem of large vibration during the processing of glassy carbon. The position-control and force-control collaborative control method proposed in combination with the present invention can accurately control the pressure and movement trajectory of the die at the same time, and can better control the shape and size of the optical element during the molding process, providing an effective solution for the needs of modern optical systems for high-precision components.

[0043] The words expressing position and direction described in the present invention are all illustrated by taking the drawings as examples, but can also be changed according to needs, and all the changes made are included in the protection scope of the present invention.

[0044] Example 1

[0045] This embodiment provides an ultra-precision cutting processing method for the ultra-smooth surface of a glassy carbon molding die, as follows:

[0046] S1. Ultrasonically clean the glassy carbon die to remove the oil stains and debris left by rough machining on the die surface. Subsequently, use a vacuum adsorption clamping table to fix the rough-machined glassy carbon die on the spindle of an ultra-precision single-point diamond lathe.

[0047] S2. Due to the characteristics of a PCD polycrystalline diamond tool with a large nose radius, low cutting stress, wear resistance, and not easily adhering to glassy carbon chips, select a PCD polycrystalline diamond tool, install the PCD polycrystalline diamond tool on the tool holder, adjust the position and angle of the tool, and perform precise tool setting through the machine tool processing numerical control system. Specific parameters of the PCD polycrystalline diamond tool: the rake angle is 35°, the clearance angle is 7°, the nose radius is 0.2 - 0.8 mm, the blade thickness is 3 - 5 mm, and when the tool edge is observed under a 150X microscope of the objective lens, there is no visible damage.

[0048] S3. Slowly rotate the spindle, and adjust the coaxiality of the die and the spindle with the help of a micrometer to ensure that the pointer of the micrometer jumps less than one grid during one revolution of the workpiece, preventing machining defects caused by machine tool vibration during machining.

[0049] S4. Set the cutting parameters for semi-finishing. Use a PCD (polycrystalline diamond) tool to semi-finish the surface of the glassy carbon mold, removing the cutting texture and damage defects left by rough machining on the mold surface. Determine the critical cutting depth from the nano-scratch experiment and the critical cutting depth calculation formula. The determined cutting parameters include a spindle speed of 100 - 2000 r / min, a cutting depth of 1 - 5 μm, and a feed rate of 1 - 10 μm / r. During semi-finishing, the glassy carbon is controlled within the plastic deformation range, and the surface roughness of the glassy carbon after semi-finishing is equal to 1 μm.

[0050] S5. The single-crystal diamond has a small tip radius, high machining quality, and is not prone to element diffusion. Replace the single-crystal diamond turning tool and start ultra-precision turning of the surface of the glassy carbon mold to obtain a super-smooth surface. The cutting parameters include: a spindle speed of 100 - 2000 r / min, a cutting depth of 100 - 500 nm, and a feed rate of 0.1 - 1 μm / r. The specific parameters of the single-crystal diamond turning tool are: a rake angle of 0°, a clearance angle of 5°, a tool head radius of 0.3 - 1.5 mm, a tip radius of 250 nm, and when the tool edge is observed under a 150X microscope of the objective lens, there are no visible micro-cracks. The finish machining is controlled within the ductile regime machining range to avoid the formation of surface and subsurface cracks and achieve damage-free machining.

[0051] The cutting parameters in steps S4 and S5 can be determined by the fracture mechanics model of amorphous hard and brittle materials and depend on the critical cutting depth d c , and its calculation formula is d c = λ(H / E) 1 / 2 (Kc / H) 2 , where λ is the brittle-ductile transition factor of the material, K C is the fracture toughness, H is the hardness, and E is the Young's modulus.

[0052] S6. Use a white light interferometer to measure the surface shape of the glassy carbon mold with a super-smooth surface. Construct a free-form surface through the surface shape error, generate a machining path file, and perform tool radius compensation using data interpolation.

[0053] S7. Through machining compensation, ultra-precision turn the surface of the glassy carbon mold again and detect the surface shape accuracy of the machined mold surface. If the requirements of a nano-level super-smooth surface and a sub-micron-level surface shape accuracy are met, subsequent ultra-high temperature molding can be carried out. If the surface shape accuracy does not meet the requirements, steps S5 and S6 need to be repeated again. Through this step, micro-cracks and air hole defects in the glassy carbon itself can be avoided, and a super-smooth surface glassy carbon mold that is smooth, hole-free, and crack-free can be obtained. At this time, the surface shape accuracy PV of the glassy carbon surface ≤ 0.3 μm, the surface roughness Ra < 2 nm, and the super-smooth surface is as Figure 2 shown;

[0054] The ultra-smooth surface machining method of the glassy carbon molding die proposed in this embodiment overcomes the problem of poor machining quality of glassy carbon dies. Through ultra-precision single-point diamond turning, combined with semi-finishing using a PCD polycrystalline diamond tool and finishing using a single-crystal diamond tool, defects on the surface of glassy carbon are effectively removed, obtaining a nano-level ultra-smooth surface and a sub-micron-level surface form accuracy, ensuring the ultra-high surface quality of the molding die. At the same time, complex curved surface dies such as aspherical, spherical, and micro-nano structure dies can be machined, meeting the molding requirements of different types of optical components.

[0055] Example 2

[0056] This embodiment discloses a method for position-control and force-control collaborative control of an optical element using the glassy carbon ultra-smooth surface molding die obtained in Example 1, as follows:

[0057] S8. Place the machined glassy carbon ultra-smooth surface molding die into the molding assembly of the ultra-high temperature molding device with position-control and force-control collaborative control; the molding assembly simultaneously includes a pressure sensor with an accuracy of 0.1 N and a displacement sensor with an accuracy of 0.5 μm.

[0058] S9. Perform surface pretreatment on the quartz glass block to be molded at high temperature, remove oil stains and contaminants, place the treated quartz glass block into the inner cavity of the glassy carbon die, and seal the upper end cover at the same time.

[0059] S10. Start the vacuum pump to ensure that the heating chamber is at a vacuum degree of 10 -3 Pa, then close the vacuum pump and turn on the nitrogen filling device to ensure that the heating chamber is in a pure nitrogen protection atmosphere; the heating temperature of the heating chamber is between 25 and 1600 °C.

[0060] S11. Set the initial threshold of the force-control module in the molding assembly to 0.5 N, then turn on the molding assembly to drive the upper die to move quickly towards the lower die. When the contact force measured by the force-control module reaches the threshold of 0.5 N, the upper die stops advancing, and set the initial position value of the upper die in the position-control module to 0 μm.

[0061] S12. Set the upper die in the position-control module to perform molding at a certain rate, and at the same time set the threshold of the increase rate of the molding pressure of the lower die in the force-control module, and start the position-control and force-control collaborative control ultra-high temperature and ultra-precision molding of quartz glass. When the increase rate of the molding pressure exceeds the threshold, the molding assembly controls the upper die to reduce the molding rate, and when the increase rate of the molding pressure is less than the set value, the molding assembly controls the upper die to increase the molding rate; the molding rate of the upper die is between 1 and 150 μm / s for molding, the threshold of the increase rate of the molding pressure of the lower die is 2 N / s, and the increase rate of the molding pressure is between 0.2 and 2 N / s.

[0062] S13. Set the heat preservation time. After the molding is completed, when the heating cavity has cooled down to room temperature, open the upper cover plate of the heating cavity and take out the molded quartz glass optical element.

[0063] S14. Use a complex surface optical profiler, a white light interferometer, and a field emission scanning electron microscope to measure and analyze the surface shape, surface roughness, and surface wear of the glassy carbon mold of the molded quartz glass optical element.

[0064] This embodiment combines two control modes of position control and force control, which can accurately control the deformation amount and forming rate of the high-temperature glass melt, avoid the element deformation or defects that may occur in the single pressure control mode, significantly improve the surface quality and surface shape accuracy of the molded optical glass element, and the accurate molding control strategy and high-quality mold surface reduce the rejection rate, optimize the molding process, and improve the production efficiency and yield. Through the present invention, it can effectively solve the problems of difficult processing of glassy carbon and poor surface quality, low efficiency, and low yield in the ultra-high temperature molding process of quartz glass optical elements in the prior art, and realize the mass production of high-quality and high-precision quartz glass optical elements.

[0065] Embodiment 3

[0066] Based on the above method, this example provides a worn surface after multiple moldings of a glassy carbon mold with different roughnesses obtained at different processing stages, as shown in FIGS. 3(a), 3(b), and 3(c). The specific steps are as follows:

[0067] S1. Ultrasonically clean 3 glassy carbon molds to remove the oil stains and debris left by the rough machining on the mold surface. Then, use a vacuum adsorption clamping table to fix the rough-machined glassy carbon mold on the spindle of an ultra-precision single-point diamond lathe to obtain a rough-machined glassy carbon mold at this time.

[0068] S2. Install a PCD polycrystalline diamond tool on the tool holder, adjust the position and angle of the tool, and perform precise tool setting through the machine tool processing numerical control system. The specific parameters of the PCD polycrystalline diamond tool at this time are: rake angle 35°, clearance angle 7°, nose radius 0.2 mm, and blade thickness 3 mm.

[0069] S3. Slowly rotate the spindle and adjust the coaxiality of the mold and the spindle with the help of a micrometer to keep the pointer from jumping. This operation avoids violent vibration during the turning process.

[0070] S4. Set the cutting parameters for semi-finishing, and use the PCD polycrystalline diamond tool to perform semi-finishing on the surface of the glassy carbon mold. The cutting parameters are: spindle speed 1500 r / min, cutting depth 2 μm, feed rate 1 μm / r. At this time, a semi-finished glassy carbon mold is obtained.

[0071] S5. Replace the single-crystal diamond turning tool. The rake angle of the single-crystal diamond tool used is 0° and the clearance angle is 5°. The tool nose radius is 1 mm and the tip radius is 250 nm. Set the finish machining cutting parameters and start ultra-precision turning of the surface of the glassy carbon mold to obtain an ultra-smooth surface. The cutting parameters are: spindle speed 2000 r / min, depth of cut 200 nm, and feed rate 0.2 μm / r.

[0072] S6. Use a white light interferometer to perform surface shape detection on the glassy carbon mold with an ultra-smooth surface. Construct a free-form surface through the surface shape error, generate a machining path file, and perform tool radius compensation using data interpolation.

[0073] S7. Repeat steps S5 and S6 several times to obtain an ultra-smooth surface glassy carbon mold with a smooth, hole-free, and crack-free precision machining.

[0074] S8. Place the rough-machined, semi-finished, and finished glassy carbon molds into the molding component in the ultra-high temperature molding device with position-control and force-control coordinated control in sequence.

[0075] S9. Perform surface pretreatment on the quartz glass block to be molded at high temperature, remove oil stains and contaminants, place the treated quartz glass block into the inner cavity of the glassy carbon mold, and seal the upper cover at the same time.

[0076] S10. Start the vacuum pump to ensure that the heating cavity is at a vacuum degree of 10 -3 Pa, then close the vacuum pump and turn on the nitrogen gas filling device to ensure that the heating cavity is in a pure nitrogen protection atmosphere.

[0077] S11. Set the initial threshold of the force-control module in the molding component to 0.5 N, then turn on the molding component to drive the upper mold to move quickly towards the lower mold. When the contact force measured by the force-control module reaches the threshold of 0.5 N, the upper mold stops advancing, and set the initial value of the position of the upper mold in the position-control module to 0 μm.

[0078] S12. Set the upper mold to perform molding at a rate of 0.1 mm / min in the position-control module, and at the same time set the threshold of the increase rate of the molding pressure of the lower mold in the force-control module, and start the position-control and force-control coordinated control ultra-high temperature and ultra-precision molding of quartz glass. When the increase rate of the molding pressure exceeds the threshold, the molding component controls the upper mold to reduce the molding rate, and when the increase rate of the molding pressure is less than the set value, the molding component controls the upper mold to increase the molding rate.

[0079] S13. Set the holding time. After the molding is completed, when the heating cavity cools down to room temperature, open the upper cover of the heating cavity and take out the molded quartz glass optical element.

[0080] S14. Use a scanning electron microscope to measure and analyze the surface wear of the glassy carbon mold after multiple molding processes.

[0081] In this embodiment, as shown in FIGS. 3(a), 3(b), and 3(c), after multiple ultra-high temperature hot embossing of three glassy carbon molds with different surface roughnesses against fused silica glass, the wear conditions are different. For the precisely machined glassy carbon mold, after multiple hot embossing, there are only a small number of microcracks and abrasive wear characteristics on the surface, and there is no obvious residual fused silica glass on the mold surface; for the semi-finished glassy carbon mold, after multiple hot embossing, more microcracks and abrasive wear characteristics appear on the surface, and at the same time, there is residual fused silica glass on the surface, which will affect the hot embossing forming of high-quality optical glass; for the rough-machined glassy carbon mold, after multiple hot embossing, a large number of damages and severe abrasive wear characteristics appear on the surface, resulting in large-scale spalling of the fused silica glass, and large-scale deposits are formed on the surface of the glassy carbon mold after abrasive wear during the hot embossing process. Therefore, under the same conditions, using a glassy carbon mold with better surface quality can better hot emboss fused silica glass components with better quality.

[0082] Example 4

[0083] Based on the above method, this example provides a glassy carbon ultra-smooth surface mold position control-force control collaborative control and the worn surface after single position control multiple hot embossing. As shown in FIGS. 4(a) and 4(b), the specific steps are as follows:

[0084] S1. Ultrasonically clean 2 glassy carbon molds to remove the oil stains and debris left by rough machining on the mold surface. Subsequently, use a vacuum adsorption clamping table to fix the rough-machined glassy carbon mold on the spindle of an ultra-precision single-point diamond lathe.

[0085] S2. Install a PCD polycrystalline diamond tool on the tool holder, adjust the position and angle of the tool, and perform precise tool setting through the machine tool processing numerical control system. At this time, the specific parameters of the PCD polycrystalline diamond tool are: rake angle 35°, clearance angle 7°, nose radius 0.2 mm, and blade thickness 3 mm.

[0086] S3. Slowly rotate the spindle, and use a micrometer to adjust the coaxiality between the mold and the spindle to keep the pointer from jumping. This operation avoids severe vibration during turning.

[0087] S4. Set the cutting parameters for semi-finishing, and use the PCD polycrystalline diamond tool to semi-finish the surface of the glassy carbon mold. The cutting parameters are: spindle speed 1500 r / min, cutting depth 2 μm, and feed rate 1 μm / r.

[0088] S5. Replace the single-crystal diamond turning tool. The rake angle of the single-crystal diamond tool used is 0°, the clearance angle is 5°, the tool tip radius is 1 mm, and the tip radius is 250 nm. Set the finish machining cutting parameters and start ultra-precision turning of the surface of the glassy carbon mold to obtain a super-smooth surface. The cutting parameters are as follows: spindle speed 2000 r / min, depth of cut 200 nm, feed rate 0.2 μm / r.

[0089] S6. Use a white light interferometer to perform surface shape detection on the glassy carbon mold with a super-smooth surface. Construct a free-form surface through the surface shape error, generate a machining path file, and perform tool radius compensation using data interpolation.

[0090] S7. Repeat steps S5 and S6 several times to obtain a glassy carbon mold with a super-smooth surface that is smooth, hole-free, and crack-free.

[0091] S8. Place the machined glassy carbon mold into the molding component in the ultra-high temperature molding device with position-control and force-control coordinated control in sequence.

[0092] S9. Perform surface pretreatment on the quartz glass block to be molded at high temperature to remove oil stains and contaminants. Place the treated quartz glass block into the inner cavity of the glassy carbon mold, and seal the upper cover at the same time.

[0093] S10. Start the vacuum pump to ensure that the heating chamber is at a vacuum degree of 10 -3 Pa. Then close the vacuum pump and turn on the nitrogen gas filling device to ensure that the heating chamber is in an atmosphere of pure nitrogen protection.

[0094] S11. Set the initial threshold of the force-control module in the molding component to 0.5 N. Then turn on the molding component to drive the upper mold to move quickly towards the lower mold. When the contact force measured by the force-control module reaches the threshold of 0.5 N, the upper mold stops advancing, and set the initial value of the position of the upper mold in the position-control module to 0 μm.

[0095] S12. Set the upper mold to perform molding at a rate of 0.1 mm / min in the position-control module. At the same time, set the threshold of the increase rate of the molding pressure of the lower mold in the force-control module to 2 N / s or turn off the force-control module, and perform position-control and force-control coordinated control or single-position-control ultra-high temperature and ultra-precision molding of the quartz glass component respectively.

[0096] S13. Set the heat preservation time. After the molding is completed, wait for the heating chamber to cool down to room temperature, then open the upper cover of the heating chamber and take out the molded quartz glass optical element.

[0097] S14. Use a scanning electron microscope to measure and analyze the surface wear of the glassy carbon mold after molding.

[0098] In this embodiment, as shown in FIGS. 4(a) and 4(b), when performing position-control and force-control coordinated control of ultra-high temperature molding based on a glassy carbon ultra-smooth surface mold, it can be found that only some minor plastic grooves and brittle cracks appear on the mold surface after multiple moldings, without material adhesion and brittle spalling, which can effectively ensure the surface quality of the formed quartz glass component; when performing single position-control molding based on a glassy carbon ultra-smooth surface mold, a large amount of material adhesion and fragmentation occur on the mold surface. During the molding process, the fragmentation characteristics will be copied onto the surface of the glass melt, forming surface defects, resulting in a decrease in the light transmittance of the component and an increase in scattered light, while the adhered material will significantly affect the molding quality. In addition, under multiple molding cyclic loads, the fragmentation will rapidly expand, causing large-area spalling, ultimately affecting the service life of the mold. It can be seen that the position-control and force-control coordinated control ultra-high temperature molding method proposed by the present invention has good adaptability and flexibility, precisely controls the molding process of the molded glass, improves the surface shape accuracy of the quartz glass component, reduces surface unevenness or defects, reduces mold wear, extends the mold life, and improves the yield of the molded product.

[0099] The above-mentioned glassy carbon ultra-smooth surface molding mold and the position-control and force-control coordinated control ultra-high temperature molding method specifically provide a glassy carbon ultra-smooth surface molding mold resistant to ultra-high temperature of 1500 °C and an ultra-precision machining method for the mold. This method performs ultra-precision cutting through an ultra-precision single-point diamond lathe combined with a PCD polycrystalline diamond turning tool and a single-crystal diamond turning tool, and can effectively machine a glassy carbon mold with an ultra-smooth surface. At the same time, combined with the position-control and force-control coordinated control ultra-high temperature molding control strategy, it accurately controls the deformation amount and forming rate of the high-temperature glass melt. Compared with the position-control system, it can ensure that the mold maintains a stable and precise geometric shape throughout the forming process, avoid optical errors caused by deformation, improve the surface quality and surface shape accuracy of the molded quartz glass optical component, and improve the molding efficiency and yield. It provides a reliable technical guarantee for the mass production of high-quality and high-precision quartz glass optical components, promotes the development of high-end optical component manufacturing technology, and has broad application prospects.

Claims

1. A method for ultra-precision cutting of the ultra-smooth surface of a glassy carbon molding die, characterized in that, As follows: S1. Perform surface treatment on the glassy carbon mold, and fix the rough-machined glassy carbon mold on the spindle of an ultra-precision single-point diamond lathe; S2. Install the PCD polycrystalline diamond tool on the tool holder, adjust the position and angle of the tool, and perform precise tool setting through the machine tool processing numerical control system; S3. Slowly rotate the spindle and adjust the coaxiality between the mold and the spindle; S4. Set the cutting parameters for semi-finishing, and use the PCD polycrystalline diamond tool to semi-finish the surface of the glassy carbon mold to remove the cutting texture and damage defects left by rough machining on the mold surface; S5. Replace with a single-crystal diamond turning tool, set the cutting parameters for finishing, and start ultra-precision turning of the surface of the glassy carbon mold to obtain an ultra-smooth surface; S6. Perform surface shape detection on the glassy carbon mold with an ultra-smooth surface, construct a free-form surface through surface shape error, generate a machining path file, and perform tool radius compensation using data interpolation; S7. Through machining compensation, ultra-precision turn the surface of the glassy carbon mold again, and detect the surface shape accuracy of the mold after machining. If the requirements of nano-level ultra-smooth surface and sub-micron-level surface shape accuracy are met, subsequent ultra-high temperature hot pressing can be carried out. If the surface shape accuracy does not meet the requirements, steps S5 and S6 need to be repeated again.

2. The ultra-precision cutting method for the ultra-smooth surface of the vitreous carbon molding die as described in claim 1, characterized in that, The mold material is amorphous glassy carbon, the surface shape of the mold is a complex surface such as an aspherical surface, a spherical surface, a micro-nano structure mold, etc., and the surface quality of the mold is nano-level roughness and sub-micron-level surface shape accuracy.

3. The ultra-precision cutting method for the ultra-smooth surface of the glassy carbon compression mold as described in claim 1, characterized in that, In step S4, when the PCD polycrystalline diamond tool is used for semi-finishing on the ultra-precision single-point diamond lathe, the rake angle is 35° and the clearance angle is 7°, the nose radius is 0.2 - 0.8 mm, the blade thickness is 3 - 5 mm, and there is no visible breakage when the tool edge is observed under a microscope with an objective lens of 150X.

4. The ultra-precision cutting method for the ultra-smooth surface of the glassy carbon compression mold as described in claim 1, characterized in that, In step S5, when the single-crystal diamond tool is used for finishing on the ultra-precision single-point diamond lathe, the rake angle is 0° and the clearance angle is 5°, the tool tip radius is 0.3 - 1.5 mm, the tip radius is 250 nm, and there is no visible micro-crack when the tool edge is observed under a microscope with an objective lens of 150X.

5. The ultra-precision cutting method for the ultra-smooth surface of the glassy carbon molding die according to claim 1, characterized in that The cutting parameters in step S4 involve a spindle speed of 100 - 2000 r / min, a depth of cut of 1 - 5 μm, and a feed rate of 1 - 10 μm / r.

6. The ultra-precision cutting method for the ultra-smooth surface of the glassy carbon compression mold as described in claim 1, characterized in that, The cutting parameters in step S5 involve a spindle speed of 100 - 2000 r / min, a depth of cut of 100 - 500 nm, and a feed rate of 0.1 - 1 μm / r.

7. The ultra-precision cutting method for the ultra-smooth surface of the vitreous carbon compression mold as described in claim 1, characterized in that, In the steps S4 and S5, the cutting parameters can be determined by the fracture mechanics model of amorphous hard and brittle materials, depending on the critical cutting depth d c , and its calculation formula is d c =λ(H / E) 1 / 2 (Kc / H) 2 , where λ is the brittle-ductile transition factor of the material, K C is the fracture toughness, H is the hardness, and E is the Young's modulus.

8. A method for ultra-high temperature molding of an optical element by position-control and force-control collaborative control using a molding die obtained by ultra-precision cutting of the ultra-smooth surface of the vitreous carbon molding die according to any one of claims 1-7, characterized in that : S8. Place the processed glassy carbon ultra-smooth surface mold into the molding component in the ultra-high temperature hot pressing forming device with position control - force control coordinated control; S9. Perform surface pretreatment on the quartz glass block to be hot pressed and formed at high temperature, place the treated quartz glass block into the inner cavity of the glassy carbon mold, and seal the upper end cover at the same time; S10. Start the vacuum pump to ensure that the heating chamber is under a vacuum of 10 -3 Pa, then turn off the vacuum pump and turn on the nitrogen filling device to ensure that the heating chamber is under a pure nitrogen protection atmosphere; S11. Set the initial threshold value of the force control module in the molding component to the set value, and then start the molding component to drive the upper mold to move rapidly towards the lower mold. When the contact force measured by the force control module reaches the set value, the upper mold stops advancing, and set the initial value of the position of the upper mold in the position control module to 0 μm; S12. In the position control module, set the upper mold to perform die pressing at a set rate. At the same time, in the force control module, set the threshold value for the increasing rate of the die pressing force of the lower mold. Start the position-force coordinated control of ultra-high temperature and ultra-precision die pressing forming of quartz glass. When the increasing rate of the die pressing force exceeds the threshold value, the die pressing assembly controls the upper mold to reduce the die pressing rate. When the increasing rate of the die pressing force is less than the set value, the die pressing assembly controls the upper mold to increase the die pressing rate; S13. Set the heat preservation time. After die pressing is completed, when the heating cavity cools down to room temperature, open the upper cover plate of the heating cavity and take out the die-pressed quartz glass optical element; S14. Use a complex surface optical profiler, a white light interferometer, and a field emission scanning electron microscope to measure and analyze the surface shape, surface roughness, and surface wear of the glassy carbon mold of the die-pressed quartz glass optical element.

9. The method for ultra-high temperature molding with coordinated position and force control of an optical element according to claim 8, wherein In step S8, the die pressing assembly simultaneously includes a pressure sensor with an accuracy of 0.1 N and a displacement sensor with an accuracy of 0.5 μm.

10. The ultra-high temperature molding method for position-force collaborative control of optical elements as described in claim 8, characterized in that, In step S10, the heating temperature of the heating cavity is in the range of 25 to 1600 °C; In step S12, the die pressing rate of the upper mold is 1 to 150 μm / s for die pressing. The threshold value for the increasing rate of the die pressing force of the lower mold is 2 N / s, and the increasing rate of the die pressing force is 0.2 to 2 N / s.

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