Aluminum-based silicon carbide ultra-thin mirror precision machining method based on gradient polishing

Abstract

The present application relates to the technical field of precision grinding, and particularly relates to a precision processing method of aluminum-based silicon carbide ultra-thin mirror based on gradient grinding, which comprises the following steps: preparing an aluminum-based silicon carbide blank by using silicon carbide and aluminum, eliminating residual stress after annealing for 4 hours, and obtaining a rough-processed aluminum-based silicon carbide blank by machine cutting and chamfering; in a precision surface grinder, the rough-processed aluminum-based silicon carbide blank is ground in stages to obtain an ultra-thin mirror; the ultra-thin mirror is polished in a magneto-rheological polishing machine to obtain an aluminum-based silicon carbide ultra-thin mirror based on gradient grinding; wherein, the composite grinding tool is prepared from a diamond micro-powder surface layer, a cerium oxide nanoparticle / graphene composite intermediate layer and an elastic polymer base; the composite grinding tool is used to absorb vibration through the elastic polymer base, chemical softening and thermal management of the cerium oxide nanoparticle / graphene intermediate layer and gradient structure design, so as to ensure the quality performance of the ultra-thin mirror.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precision grinding, in particular to a precision processing method of aluminum-based silicon carbide ultra-thin mirror based on gradient grinding. BACKGROUND

[0002] As a frontier technology in the field of optics, the development of ultra-thin mirror is closely related to technological innovation. This concept originated from the large-aperture space telescope project of the National Aeronautics and Space Administration (NASA) in the 1960s, aiming to break through the weight and volume limitations of traditional mirrors. At that time, NASA proposed the use of thin film mirror technology to achieve lightweight space optical systems, which quickly sparked a global research frenzy, with research institutions in Russia, Canada, Japan and other countries following suit, driving the diversified development of ultra-thin mirror technology.

[0003] Aluminum-based silicon carbide is a particle-reinforced metal matrix composite material that combines the advantages of aluminum and SiC particles. It uses aluminum as the matrix and SiC particles as the reinforcing body in a certain form, proportion and distribution state to form a multi-phase composite material with distinct interfaces. It has comprehensive superior performance that single metals do not possess, making it suitable for manufacturing electronic device backing materials, heat sinks and other electronic devices. In addition, aluminum-based silicon carbide can also be used to manufacture precision parts for inertial navigation systems, rotating scanning mirrors, infrared observation mirrors, laser mirrors, laser gyroscopes, mirrors, mirror bases and optical instrument brackets, among many other precision and optical instruments.

[0004] High-volume SiC / Al composite materials have high hardness (HV≥25GPa) and high brittleness. Traditional rough machining can easily produce surface micro-cracks and edge chipping. Moreover, ultra-thin structures (thickness≤5mm) are prone to deformation under machining stress, making it difficult to achieve surface roughness≤2nm and face type precision RMS≤1 / 30λ technical specifications. Therefore, we propose a precision processing method for aluminum-based silicon carbide ultra-thin mirrors based on gradient grinding. SUMMARY

[0005] The present application aims to provide a precision processing method for aluminum-based silicon carbide ultra-thin mirrors based on gradient grinding to solve the problems raised in the background art.

[0006] To achieve the above-mentioned purpose, the present application provides a precision processing method for aluminum-based silicon carbide ultra-thin mirrors based on gradient grinding, S1.1, aluminum-based silicon carbide blanks are prepared using 65-67vol% silicon carbide and 33-35vol% aluminum. After annealing to eliminate residual stress and machining and chamfering, a rough machined aluminum-based silicon carbide blank is obtained.

[0007] S1.2, in the precision surface grinder, the rough machined aluminum-based silicon carbide blank is divided into rough grinding stage, semi-fine grinding stage and fine grinding stage for gradient grinding, and the grinding wheel, the grinding wheel particle size, the spindle speed, the feed speed, the axial pressure, the cooling liquid flow and the composite grinding tool are adjusted to obtain the ultra-thin mirror;

[0008] S1.3, in the magnetic flow variable polishing machine, the ultra-thin mirror is polished by polishing liquid to obtain the aluminum-based silicon carbide ultra-thin mirror based on gradient grinding;

[0009] The composite grinding tool is prepared from a diamond micro-powder surface layer, a composite intermediate layer and an elastic polymer base.

[0010] The composite grinding tool is designed by material functionalization layering, the diamond micro-powder surface layer, the cerium oxide nanoparticle / graphene composite intermediate layer and the elastic polymer base. The diamond micro-powder surface layer serves as the main grinding layer and realizes high-efficiency mechanical removal through the high hardness of diamond. In the cerium oxide nanoparticle / graphene composite intermediate layer, the two-dimensional sheet structure of graphene can adsorb cerium oxide nanoparticles, inhibit agglomeration through van der Waals force and π-π interaction, enhance dispersibility, and quickly conduct grinding heat through the extremely high thermal conductivity of graphene, reduce interface temperature, avoid thermal stress cracks caused by local temperature rise, and the extremely high thermal conductivity is also conducive to the interaction of cerium oxide nanoparticles and the surface. In the grinding process, the tetravalent cerium ion in cerium oxide has strong oxidizing properties, which has high chemical activity on the surface of aluminum-based silicon carbide, reducing the fine grinding resistance. The elastic polymer base absorbs processing vibration energy through elastic deformation, reduces the rigid impact between the grinding tool and the workpiece, and inhibits edge chipping.

[0011] The staged gradient grinding process, high speed combined with low feed speed can reduce the single cutting depth, reduce the crack propagation probability of brittle materials, and the neutral pH nano-emulsion has cooling and lubricating functions, reducing thermal stress accumulation;

[0012] In the fine grinding stage, the diamond micro-powder realizes micron-level material removal; the cerium oxide nanoparticles soften the surface layer through chemical mechanical action to reduce scratches; the spiral trajectory avoids stress concentration caused by local repeated processing, and low pressure and temperature control inhibits deformation;

[0013] The asymmetric magnetic field assisted stress compensation polishing, the core idea of which is to dynamically regulate the polishing pressure distribution by using the magnetic rheological effect to offset the deformation of the ultra-thin mirror body due to its own weight. The magnetic rheological fluid is locally hardened under the action of the magnetic field to form a controllable shear force field, which adjusts the polishing pressure in real time. Through closed-loop feedback control, the surface error is dynamically corrected, and finally the nanometer-level surface roughness and sub-micron-level surface accuracy are realized.

[0014] As preferred, in S1.1, the specific steps of the rough machined aluminum-based silicon carbide blank are:

[0015] 65-67 vol% silicon carbide and 33-35 vol% aluminum were ball-milled under argon protection at a ball-to-material ratio of 5:1, a speed of 200-300 rpm, and a time of 4-5 hours. After holding at 200-250 MPa for 5 minutes, the green body was placed in a vacuum furnace for 10 minutes. -3 Under a vacuum of 180 MPa, the aluminum-based silicon carbide preform is heated to 200-300℃ and held for 1-2 hours, then hot-pressed and sintered at 580℃ and 50-55 MPa for 2-3 hours to obtain an aluminum-based silicon carbide preform. After annealing the preform at 550℃ for 4 hours, residual stress is eliminated using a vibration aging device. The preform is then cut to a thickness of 5-5.5 mm using a diamond wire cutter and chamfered at a 45° angle with a W20 diamond wheel, resulting in a rough-machined aluminum-based silicon carbide preform. The powder metallurgy method, performed under a protective atmosphere and at a sintering temperature below the melting point of aluminum, significantly reduces the possibility of interfacial reactions. Powder metallurgy allows for wide control over the size and content of ceramic particles and ensures a more uniform distribution of nanoparticle reinforcements in the matrix, reducing agglomeration and segregation, thereby strengthening the composite material.

[0016] Preferably, the parameters of the vibration aging device are: frequency 75-80Hz, amplitude 0.04-0.05mm, and time 25-30min.

[0017] Preferably, the specific parameters for the coarse grinding stage in S1.2 are as follows:

[0018] The machine uses a metal-bonded diamond grinding wheel with a grit size that gradually decreases from W40 to W20. The spindle speed is 2000-2500 rpm, the feed rate is 0.06-0.08 mm / min, the axial pressure is 13-15 N, and the coolant flow rate is 5-7 L / min.

[0019] Preferably, the specific parameters for the semi-finishing stage in S1.2 are as follows:

[0020] Resin-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W20 to W10. The spindle speed is 3000-3200 rpm, the feed rate is 0.03-0.05 mm / min, the axial pressure is 6-8 N, and the coolant flow rate is 3-5 L / min.

[0021] Preferably, the specific parameters for the fine grinding stage in S1.2 are as follows:

[0022] In an ultra-precision CNC grinding machine, a composite grinding wheel is used for fine grinding. The spindle speed is 3800-4000 rpm, the feed rate is 0.015-0.02 mm / min, and the machining is carried out with a circular helical trajectory. The pitch is 0.1-0.2 mm, the axial pressure is ≤5 N, and nitrogen and -10℃ cold air are used for aerosol cooling. The surface temperature rise is ≤30℃, resulting in an ultra-thin lens.

[0023] Preferably, the specific steps for preparing the ultrathin mirror based on gradient grinding to obtain the aluminum-based silicon carbide ultrathin reflector are as follows:

[0024] Ultrathin mirrors were polished in a magnetorheological polishing machine. An asymmetric magnetic field Halbach permanent magnet array was designed with an edge magnetic field of 0.5T and a center magnetic field of 0.2T to form an asymmetric shear stress field. The polishing parameters were: polishing pad hardness Shore A 50-60, rotation speed 100-200rpm, polishing fluid flow rate 10-15mL / min, and polishing time 30-60min, to obtain an aluminum-based silicon carbide ultrathin reflective mirror based on gradient grinding.

[0025] Preferably, the coolant is a neutral pH nanoemulsion, specifically composed of: 80-85% polyalphaolefin synthetic ester, 3-5% polyoxyethylene ether emulsifier, 0.5-0.8% nano-Al2O3 and SiC mixed particles in a mass ratio of 4:1, 0.3-0.4% benzotriazole, 0.2-0.3% triethanolamine, 0.05-0.1% phosphate buffer, and the balance being deionized water.

[0026] Preferably, in step S1.3, the polishing fluid comprises: 0.8-1.2% nanodiamond abrasive, 2-4% colloidal silica, 0.5-0.8% cerium oxide nanoparticles, 0.2-0.5% benzotriazole, 1-2% ethylenediaminetetraacetic acid, 1-3% hydrogen peroxide, 0.05-0.07% hexagonal boron nitride, 0.5-1.2% sodium dodecylbenzenesulfonate, 0.03-0.05% polyethylene glycol, 1-3% potassium hydroxide pH adjuster, and the remainder being water.

[0027] Preferably, the steps for preparing the composite abrasive are as follows:

[0028] S2.1. Mix the elastic polymer with nanoparticles and solidify them to obtain an elastic polymer substrate;

[0029] S2.2, Cerium oxide nanoparticles, thermally conductive materials and adhesives are mixed and cured on the surface of an elastic polymer substrate to form an intermediate layer;

[0030] S2.3. Acid-treated diamond micropowder is mixed with cerium oxide nanoparticles and binder and cured on the surface of the intermediate layer to obtain a composite abrasive.

[0031] Specifically, in S2.1, polydimethylsiloxane prepolymer is mixed with alumina nanoparticles, ultrasonically dispersed for 25-30 min, then hydrogen-containing siloxane crosslinking agent and platinum catalyst are added, vacuum degassing is performed, and the mixture is cast and cured. The mixture is then cured at 60-80℃ for 2-3 h to obtain a polydimethylsiloxane substrate. This substrate is then placed in an oxygen plasma treatment device with a power of 40-50 W, an oxygen flow rate of 45-50 sccm, and a treatment time of 2-5 min to obtain an activated substrate. The activated substrate is then immersed in an ethanol solution with a volume fraction of 3-5% KH-550 for 30-50 min and dried at 65-75℃ for 1-2 h to obtain an elastic polymer substrate.

[0032] S2.2. Cerium oxide nanoparticles, graphene, and ammonium bicarbonate are dispersed in isopropanol and ultrasonically treated at 200-300W for 1-2 hours. Then, epoxy resin and polyetheramine with a mass ratio of 3.1-3.3:1 are added to obtain a mixed slurry. The mixed slurry is spin-coated onto the surface of an elastic polymer substrate at 2000-3000 rpm for 30-40 seconds to form an intermediate layer with a thickness of 20-30 μm. It is cured at 80-85℃ for 1-1.5 hours and then cured at 150-155℃ for 2-3 hours. After rinsing with deionized water, it is dried at 60-70℃ to obtain a cerium oxide nanoparticle / graphene composite intermediate layer.

[0033] S2.3. Immerse diamond micropowder in a mixed acid solution of concentrated H2SO4 and HNO3 at a volume ratio of 3:1, reflux at 75-80℃ for 2-3 hours, centrifuge and wash until neutral, and dry at 60-70℃ to obtain acid-treated diamond micropowder. Mix the acid-treated diamond micropowder with cerium oxide nanoparticles at a mass ratio of 9:1, and then add epoxy resin and methylhexahydrophthalic anhydride to obtain a mixture. Apply the mixture to the surface of the cerium oxide nanoparticle / graphene composite intermediate layer using a doctor blade to obtain a diamond micropowder surface layer with a coating thickness of 40-50μm. Finally, apply pressure for curing at a pressure of 0.5MPa, a curing temperature of 150-160℃, and a curing time of 3-4 hours to obtain a composite abrasive.

[0034] The mass ratio of polydimethylsiloxane prepolymer to alumina nanoparticles is 10–12:1; the mass ratio of polydimethylsiloxane prepolymer, hydrogen-containing siloxane crosslinking agent, and platinum catalyst is 8–12:1:0.006–0.01; the mass ratio of cerium oxide nanoparticles, graphene, and ammonium bicarbonate is 4–5:2–2.5:1; the mass ratio of cerium oxide nanoparticles to epoxy resin is 4:5–5.5; the mass ratio of acid-treated diamond powder to cerium oxide nanoparticles is 8–9:1; the mass ratio of acid-treated diamond powder to epoxy resin is 9:3.8–4.5; and the mass ratio of epoxy resin to methylhexahydrophthalic anhydride is 4–5:1.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] This precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding employs a gradient grinding strategy to gradually release processing stress and reduce the risk of surface damage through particle size reduction and process parameter optimization. The functional design of the composite abrasive, through a diamond micro powder surface layer, a cerium oxide nanoparticle / graphene composite intermediate layer, and an elastic polymer substrate, achieves "mechanical-chemical" synergistic removal while suppressing thermal damage and edge chipping, meeting the ultra-precision machining requirements of aluminum-based silicon carbide mirrors. Active stress compensation through asymmetric magnetic field-assisted technology improves the surface accuracy of the ultrathin mirror, thereby effectively improving the machining quality of the mirror. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] The present invention provides a precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding.

[0039] S1.1. Prepare an aluminum-based silicon carbide billet using 65-67 vol% silicon carbide and 33-35 vol% aluminum. After annealing to eliminate residual stress, machine chamfer the billet to obtain a rough-machined aluminum-based silicon carbide billet.

[0040] S1.2 In a precision surface grinder, the rough-machined aluminum-based silicon carbide blank is subjected to gradient grinding in three stages: rough grinding, semi-fine grinding, and fine grinding. The grinding wheel, grinding wheel grit size, spindle speed, feed speed, axial pressure, coolant flow rate, and composite grinding tool are adjusted to obtain an ultra-thin lens.

[0041] S1.3 In a magnetorheological polishing machine, the ultrathin lens is polished with polishing fluid to obtain an aluminum-based silicon carbide ultrathin reflective mirror based on gradient grinding.

[0042] The composite abrasive is prepared by a diamond micro powder surface layer, a composite intermediate layer and an elastic polymer substrate;

[0043] The epoxy resin is selected from E-51, the polyetheramine is selected from D230, and the hydrogen-containing siloxane crosslinking agent is selected from HMS-301.

[0044] Example 1: A precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding, comprising the following steps:

[0045] S1.1 65 vol% silicon carbide and 35 vol% aluminum were ball-milled under argon protection at a ball-to-material ratio of 5:1, at 300 rpm for 4 hours. After holding at 200 MPa for 5 minutes, the green body was placed in a vacuum furnace for 10 minutes. -3 Under a vacuum of 100 Pa, the aluminum-based silicon carbide billet was heated to 300℃ and held for 1 hour, and then hot-pressed and sintered at 50 MPa and 580℃ for 2 hours to obtain an aluminum-based silicon carbide billet. After annealing at 550℃ for 4 hours, residual stress was eliminated by a vibration aging device with a frequency of 80 Hz, an amplitude of 0.05 mm, and a time of 30 min. The billet was then cut into 5 mm thick sections using a diamond wire cutter and chamfered at 45° with a W20 diamond grinding wheel, with a chamfer width of 0.3 mm, to obtain the rough-machined aluminum-based silicon carbide billet.

[0046] The coolant is a neutral pH nanoemulsion, specifically composed of: 85% polyalphaolefin synthetic ester, 5% polyoxyethylene ether emulsifier, 0.8% nano-Al2O3 and SiC mixed particles in a mass ratio of 4:1, 0.4% benzotriazole, 0.3% triethanolamine, 0.1% phosphate buffer, and the balance being deionized water.

[0047] The specific components of the polishing fluid are: 1.2% nano-diamond abrasive, 4% colloidal silica, 0.8% cerium oxide nanoparticles, 0.5% benzotriazole, 2% ethylenediaminetetraacetic acid, 3% hydrogen peroxide, 0.07% hexagonal boron nitride, 1.2% sodium dodecylbenzenesulfonate, 0.05% polyethylene glycol, 3% potassium hydroxide pH adjuster, and the remainder is water;

[0048] The composite abrasive is prepared from a diamond micropowder surface layer, a cerium oxide nanoparticle / graphene composite intermediate layer, and an elastic polymer substrate. The mass ratio of polydimethylsiloxane prepolymer to alumina nanoparticles is 10:1; the mass ratio of polydimethylsiloxane prepolymer, hydrogen-containing siloxane crosslinking agent, and platinum catalyst is 8:1:0.006; the mass ratio of cerium oxide nanoparticles, graphene, and ammonium bicarbonate is 4:2:1; the mass ratio of cerium oxide nanoparticles to epoxy resin is 4:5; the mass ratio of acid-treated diamond micropowder to cerium oxide nanoparticles is 9:1; the mass ratio of acid-treated diamond micropowder to epoxy resin is 9:4.5; and the mass ratio of epoxy resin to methylhexahydrophthalic anhydride is 4:1.

[0049] The specific steps for preparing composite abrasives are as follows:

[0050] S2.1. The polydimethylsiloxane prepolymer is mixed with alumina nanoparticles and ultrasonically dispersed for 30 min. Then, a hydrogen-containing siloxane crosslinking agent and a platinum catalyst are added. The mixture is degassed under vacuum and then cast and cured. The mixture is cured at 80℃ for 3 h to obtain a polydimethylsiloxane substrate. The substrate is then placed in an oxygen plasma treatment device with a power of 50 W, an oxygen flow rate of 50 sccm, and a treatment time of 2 min to obtain an activated substrate. The activated substrate is then immersed in a 5% KH-550 ethanol solution for 30 min and dried at 65℃ for 2 h to obtain an elastic polymer substrate.

[0051] S2.2. Cerium oxide nanoparticles, graphene, and ammonium bicarbonate were dispersed in isopropanol and ultrasonically treated at 300W for 2 hours. Then, epoxy resin and polyetheramine with a mass ratio of 3.3:1 were added to obtain a mixed slurry. The mixed slurry was spin-coated onto the surface of an elastic polymer substrate at 3000 rpm for 30 seconds to form an intermediate layer with a thickness of 30 μm. The intermediate layer was cured at 80℃ for 1 hour and then cured at 150℃ for 3 hours. After rinsing with deionized water, the intermediate layer was dried at 60℃ to obtain a cerium oxide nanoparticle / graphene composite intermediate layer.

[0052] S2.3. Immerse diamond micropowder in a mixture of concentrated H2SO4 and HNO3 in a volume ratio of 3:1, reflux at 80°C for 2 hours, centrifuge and wash until neutral, and dry at 70°C to obtain acid-treated diamond micropowder. Mix the acid-treated diamond micropowder with cerium oxide nanoparticles in a mass ratio of 9:1, and then add epoxy resin and methylhexahydrophthalic anhydride to obtain a mixture. Coat the mixture onto the surface of the cerium oxide nanoparticle / graphene composite intermediate layer with a doctor blade to obtain a diamond micropowder surface layer with a coating thickness of 50 μm. Finally, apply pressure to cure the mixture at a pressure of 0.5 MPa, a curing temperature of 160°C, and a curing time of 4 hours to obtain a composite abrasive.

[0053] S1.2 In a precision surface grinder, the rough-machined aluminum-based silicon carbide blank is subjected to staged gradient grinding. The specific parameters are as follows: Rough grinding stage: Metal-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W40 to W20, spindle speed 2500 rpm, feed rate 0.08 mm / min, axial pressure 15 N, and coolant flow rate 5 L / min; Semi-finish grinding stage: Resin-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W20 to W10, spindle speed 3200 rpm, feed rate 0.03 mm / min, axial pressure 8 N, and coolant flow rate 3 L / min; Finish grinding stage: In an ultra-precision CNC grinder, composite grinding tools are used for finish grinding, with a spindle speed of 3800 rpm, feed rate of 0.015 mm / min, machining with a circular helical trajectory, pitch of 0.1 mm, axial pressure ≤5 N, and aerosol cooling using nitrogen and -10℃ cold air, resulting in a surface temperature rise ≤30℃, thus obtaining an ultra-thin lens;

[0054] S1.3. The ultrathin lens was polished in a magnetorheological polishing machine. An asymmetric magnetic field Halbach permanent magnet array was designed with an edge magnetic field of 0.5T and a center magnetic field of 0.2T to form an asymmetric shear stress field. The polishing parameters were: polishing pad hardness Shore A 50, rotation speed of 200rpm, polishing fluid flow rate of 10mL / min, and polishing time of 60min, to obtain an aluminum-based silicon carbide ultrathin reflective mirror based on gradient grinding.

[0055] Example 2: A precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding, comprising the following steps:

[0056] S1.1 65 vol% silicon carbide and 35 vol% aluminum were ball-milled under argon protection at a ball-to-material ratio of 5:1, at 300 rpm for 4 hours. After holding at 200 MPa for 5 minutes, the green body was placed in a vacuum furnace for 10 minutes. -3 Under a vacuum of 100 Pa, the aluminum-based silicon carbide billet was heated to 300℃ and held for 1 hour, and then hot-pressed and sintered at 50 MPa and 580℃ for 2 hours to obtain an aluminum-based silicon carbide billet. After annealing at 550℃ for 4 hours, residual stress was eliminated by a vibration aging device with a frequency of 80 Hz, an amplitude of 0.05 mm, and a time of 30 min. The billet was then cut into 5 mm thick sections using a diamond wire cutter and chamfered at 45° with a W20 diamond grinding wheel, with a chamfer width of 0.3 mm, to obtain the rough-machined aluminum-based silicon carbide billet.

[0057] The coolant is a neutral pH nanoemulsion, specifically composed of: 85% polyalphaolefin synthetic ester, 5% polyoxyethylene ether emulsifier, 0.8% nano-Al2O3 and SiC mixed particles in a mass ratio of 4:1, 0.4% benzotriazole, 0.3% triethanolamine, 0.1% phosphate buffer, and the balance being deionized water.

[0058] The specific components of the polishing fluid are: 1.2% nano-diamond abrasive, 4% colloidal silica, 0.8% cerium oxide nanoparticles, 0.5% benzotriazole, 2% ethylenediaminetetraacetic acid, 3% hydrogen peroxide, 0.07% hexagonal boron nitride, 1.2% sodium dodecylbenzenesulfonate, 0.05% polyethylene glycol, 3% potassium hydroxide pH adjuster, and the remainder is water;

[0059] The composite abrasive is prepared from a diamond micropowder surface layer, a cerium oxide nanoparticle / graphene composite intermediate layer, and an elastic polymer substrate. The mass ratio of polydimethylsiloxane prepolymer to alumina nanoparticles is 11:1; the mass ratio of polydimethylsiloxane prepolymer, hydrogen-containing siloxane crosslinking agent, and platinum catalyst is 8:1:0.006; the mass ratio of cerium oxide nanoparticles, graphene, and ammonium bicarbonate is 4:2:1; the mass ratio of cerium oxide nanoparticles to epoxy resin is 4:5; the mass ratio of acid-treated diamond micropowder to cerium oxide nanoparticles is 9:1; the mass ratio of acid-treated diamond micropowder to epoxy resin is 9:4.5; and the mass ratio of epoxy resin to methylhexahydrophthalic anhydride is 4:1.

[0060] The specific steps for preparing composite abrasives are as follows:

[0061] S2.1. The polydimethylsiloxane prepolymer is mixed with alumina nanoparticles and ultrasonically dispersed for 30 min. Then, a hydrogen-containing siloxane crosslinking agent and a platinum catalyst are added. The mixture is degassed under vacuum and then cast and cured. The mixture is cured at 80℃ for 3 h to obtain a polydimethylsiloxane substrate. The substrate is then placed in an oxygen plasma treatment device with a power of 50 W, an oxygen flow rate of 50 sccm, and a treatment time of 2 min to obtain an activated substrate. The activated substrate is then immersed in a 5% KH-550 ethanol solution for 30 min and dried at 65℃ for 2 h to obtain an elastic polymer substrate.

[0062] S2.2. Cerium oxide nanoparticles, graphene, and ammonium bicarbonate were dispersed in isopropanol and ultrasonically treated at 300W for 2 hours. Then, epoxy resin and polyetheramine with a mass ratio of 3.3:1 were added to obtain a mixed slurry. The mixed slurry was spin-coated onto the surface of an elastic polymer substrate at 3000 rpm for 30 seconds to form an intermediate layer with a thickness of 30 μm. The intermediate layer was cured at 80℃ for 1 hour and then cured at 150℃ for 3 hours. After rinsing with deionized water, the intermediate layer was dried at 60℃ to obtain a cerium oxide nanoparticle / graphene composite intermediate layer.

[0063] S2.3. Immerse diamond micropowder in a mixture of concentrated H2SO4 and HNO3 in a volume ratio of 3:1, reflux at 80°C for 2 hours, centrifuge and wash until neutral, and dry at 70°C to obtain acid-treated diamond micropowder. Mix the acid-treated diamond micropowder with cerium oxide nanoparticles in a mass ratio of 9:1, and then add epoxy resin and methylhexahydrophthalic anhydride to obtain a mixture. Coat the mixture onto the surface of the cerium oxide nanoparticle / graphene composite intermediate layer with a doctor blade to obtain a diamond micropowder surface layer with a coating thickness of 50 μm. Finally, apply pressure to cure the mixture at a pressure of 0.5 MPa, a curing temperature of 160°C, and a curing time of 4 hours to obtain a composite abrasive.

[0064] S1.2 In a precision surface grinder, the rough-machined aluminum-based silicon carbide blank is subjected to staged gradient grinding. The specific parameters are as follows: Rough grinding stage: Metal-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W40 to W20, spindle speed 2500 rpm, feed rate 0.08 mm / min, axial pressure 15 N, and coolant flow rate 5 L / min; Semi-finish grinding stage: Resin-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W20 to W10, spindle speed 3200 rpm, feed rate 0.03 mm / min, axial pressure 8 N, and coolant flow rate 3 L / min; Finish grinding stage: In an ultra-precision CNC grinder, composite grinding tools are used for finish grinding, with a spindle speed of 3800 rpm, feed rate of 0.015 mm / min, machining with a circular helical trajectory, pitch of 0.1 mm, axial pressure ≤5 N, and aerosol cooling using nitrogen and -10℃ cold air, resulting in a surface temperature rise ≤30℃, thus obtaining an ultra-thin lens;

[0065] S1.3. The ultrathin lens was polished in a magnetorheological polishing machine. An asymmetric magnetic field Halbach permanent magnet array was designed with an edge magnetic field of 0.5T and a center magnetic field of 0.2T to form an asymmetric shear stress field. The polishing parameters were: polishing pad hardness Shore A 50, rotation speed of 200rpm, polishing fluid flow rate of 10mL / min, and polishing time of 60min, to obtain an aluminum-based silicon carbide ultrathin reflective mirror based on gradient grinding.

[0066] Example 3: A precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding, comprising the following steps:

[0067] S1.1 65 vol% silicon carbide and 35 vol% aluminum were ball-milled under argon protection at a ball-to-material ratio of 5:1, at 300 rpm for 4 hours. After holding at 200 MPa for 5 minutes, the green body was placed in a vacuum furnace for 10 minutes. -3 Under a vacuum of 100 Pa, the aluminum-based silicon carbide billet was heated to 300℃ and held for 1 hour, and then hot-pressed and sintered at 50 MPa and 580℃ for 2 hours to obtain an aluminum-based silicon carbide billet. After annealing at 550℃ for 4 hours, residual stress was eliminated by a vibration aging device with a frequency of 80 Hz, an amplitude of 0.05 mm, and a time of 30 min. The billet was then cut into 5 mm thick sections using a diamond wire cutter and chamfered at 45° with a W20 diamond grinding wheel, with a chamfer width of 0.3 mm, to obtain the rough-machined aluminum-based silicon carbide billet.

[0068] The coolant is a neutral pH nanoemulsion, specifically composed of: 85% polyalphaolefin synthetic ester, 5% polyoxyethylene ether emulsifier, 0.8% nano-Al2O3 and SiC mixed particles in a mass ratio of 4:1, 0.4% benzotriazole, 0.3% triethanolamine, 0.1% phosphate buffer, and the balance being deionized water.

[0069] The specific components of the polishing fluid are: 1.2% nano-diamond abrasive, 4% colloidal silica, 0.8% cerium oxide nanoparticles, 0.5% benzotriazole, 2% ethylenediaminetetraacetic acid, 3% hydrogen peroxide, 0.07% hexagonal boron nitride, 1.2% sodium dodecylbenzenesulfonate, 0.05% polyethylene glycol, 3% potassium hydroxide pH adjuster, and the remainder is water;

[0070] The composite abrasive is prepared from a diamond micropowder surface layer, a cerium oxide nanoparticle / graphene composite intermediate layer, and an elastic polymer substrate. The mass ratio of polydimethylsiloxane prepolymer to alumina nanoparticles is 12:1; the mass ratio of polydimethylsiloxane prepolymer, hydrogen-containing siloxane crosslinking agent, and platinum catalyst is 8:1:0.006; the mass ratio of cerium oxide nanoparticles, graphene, and ammonium bicarbonate is 4:2:1; the mass ratio of cerium oxide nanoparticles to epoxy resin is 4:5; the mass ratio of acid-treated diamond micropowder to cerium oxide nanoparticles is 9:1; the mass ratio of acid-treated diamond micropowder to epoxy resin is 9:4.5; and the mass ratio of epoxy resin to methylhexahydrophthalic anhydride is 4:1.

[0071] The specific steps for preparing composite abrasives are as follows:

[0072] S2.1. The polydimethylsiloxane prepolymer is mixed with alumina nanoparticles and ultrasonically dispersed for 30 min. Then, a hydrogen-containing siloxane crosslinking agent and a platinum catalyst are added. The mixture is degassed under vacuum and then cast and cured. The mixture is cured at 80℃ for 3 h to obtain a polydimethylsiloxane substrate. The substrate is then placed in an oxygen plasma treatment device with a power of 50 W, an oxygen flow rate of 50 sccm, and a treatment time of 2 min to obtain an activated substrate. The activated substrate is then immersed in a 5% KH-550 ethanol solution for 30 min and dried at 65℃ for 2 h to obtain an elastic polymer substrate.

[0073] S2.2. Cerium oxide nanoparticles, graphene, and ammonium bicarbonate were dispersed in isopropanol and ultrasonically treated at 300W for 2 hours. Then, epoxy resin and polyetheramine with a mass ratio of 3.3:1 were added to obtain a mixed slurry. The mixed slurry was spin-coated onto the surface of an elastic polymer substrate at 3000 rpm for 30 seconds to form an intermediate layer with a thickness of 30 μm. The intermediate layer was cured at 80℃ for 1 hour and then cured at 150℃ for 3 hours. After rinsing with deionized water, the intermediate layer was dried at 60℃ to obtain a cerium oxide nanoparticle / graphene composite intermediate layer.

[0074] S2.3. Immerse diamond micropowder in a mixture of concentrated H2SO4 and HNO3 in a volume ratio of 3:1, reflux at 80°C for 2 hours, centrifuge and wash until neutral, and dry at 70°C to obtain acid-treated diamond micropowder. Mix the acid-treated diamond micropowder with cerium oxide nanoparticles in a mass ratio of 9:1, and then add epoxy resin and methylhexahydrophthalic anhydride to obtain a mixture. Coat the mixture onto the surface of the cerium oxide nanoparticle / graphene composite intermediate layer with a doctor blade to obtain a diamond micropowder surface layer with a coating thickness of 50 μm. Finally, apply pressure to cure the mixture at a pressure of 0.5 MPa, a curing temperature of 160°C, and a curing time of 4 hours to obtain a composite abrasive.

[0075] S1.2 In a precision surface grinder, the rough-machined aluminum-based silicon carbide blank is subjected to staged gradient grinding. The specific parameters are as follows: Rough grinding stage: Metal-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W40 to W20, spindle speed 2500 rpm, feed rate 0.08 mm / min, axial pressure 15 N, and coolant flow rate 5 L / min; Semi-finish grinding stage: Resin-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W20 to W10, spindle speed 3200 rpm, feed rate 0.03 mm / min, axial pressure 8 N, and coolant flow rate 3 L / min; Finish grinding stage: In an ultra-precision CNC grinder, composite grinding tools are used for finish grinding, with a spindle speed of 3800 rpm, feed rate of 0.015 mm / min, machining with a circular helical trajectory, pitch of 0.1 mm, axial pressure ≤5 N, and aerosol cooling using nitrogen and -10℃ cold air, resulting in a surface temperature rise ≤30℃, thus obtaining an ultra-thin lens;

[0076] S1.3. The ultrathin lens was polished in a magnetorheological polishing machine. An asymmetric magnetic field Halbach permanent magnet array was designed with an edge magnetic field of 0.5T and a center magnetic field of 0.2T to form an asymmetric shear stress field. The polishing parameters were: polishing pad hardness Shore A 50, rotation speed of 200rpm, polishing fluid flow rate of 10mL / min, and polishing time of 60min, to obtain an aluminum-based silicon carbide ultrathin reflective mirror based on gradient grinding.

[0077] Example 4: A precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding, comprising the following steps:

[0078] S1.1 65 vol% silicon carbide and 35 vol% aluminum were ball-milled under argon protection at a ball-to-material ratio of 5:1, at 300 rpm for 4 hours. After holding at 200 MPa for 5 minutes, the green body was placed in a vacuum furnace for 10 minutes. -3Under a vacuum of 100 Pa, the aluminum-based silicon carbide billet was heated to 300℃ and held for 1 hour, and then hot-pressed and sintered at 50 MPa and 580℃ for 2 hours to obtain an aluminum-based silicon carbide billet. After annealing at 550℃ for 4 hours, residual stress was eliminated by a vibration aging device with a frequency of 80 Hz, an amplitude of 0.05 mm, and a time of 30 min. The billet was then cut into 5 mm thick sections using a diamond wire cutter and chamfered at 45° with a W20 diamond grinding wheel, with a chamfer width of 0.3 mm, to obtain the rough-machined aluminum-based silicon carbide billet.

[0079] The coolant is a neutral pH nanoemulsion, specifically composed of: 85% polyalphaolefin synthetic ester, 5% polyoxyethylene ether emulsifier, 0.8% nano-Al2O3 and SiC mixed particles in a mass ratio of 4:1, 0.4% benzotriazole, 0.3% triethanolamine, 0.1% phosphate buffer, and the balance being deionized water.

[0080] The specific components of the polishing fluid are: 1.2% nano-diamond abrasive, 4% colloidal silica, 0.8% cerium oxide nanoparticles, 0.5% benzotriazole, 2% ethylenediaminetetraacetic acid, 3% hydrogen peroxide, 0.07% hexagonal boron nitride, 1.2% sodium dodecylbenzenesulfonate, 0.05% polyethylene glycol, 3% potassium hydroxide pH adjuster, and the remainder is water;

[0081] The composite abrasive is prepared from a diamond micropowder surface layer, a cerium oxide nanoparticle / graphene composite intermediate layer, and an elastic polymer substrate. The mass ratio of polydimethylsiloxane prepolymer to alumina nanoparticles is 11:1; the mass ratio of polydimethylsiloxane prepolymer, hydrogen-containing siloxane crosslinking agent, and platinum catalyst is 8:1:0.006; the mass ratio of cerium oxide nanoparticles, graphene, and ammonium bicarbonate is 4.5:2.25:1; the mass ratio of cerium oxide nanoparticles to epoxy resin is 4:5; the mass ratio of acid-treated diamond micropowder to cerium oxide nanoparticles is 9:1; the mass ratio of acid-treated diamond micropowder to epoxy resin is 9:4.5; and the mass ratio of epoxy resin to methylhexahydrophthalic anhydride is 4:1.

[0082] The specific steps for preparing composite abrasives are as follows:

[0083] S2.1. The polydimethylsiloxane prepolymer is mixed with alumina nanoparticles and ultrasonically dispersed for 30 min. Then, a hydrogen-containing siloxane crosslinking agent and a platinum catalyst are added. The mixture is degassed under vacuum and then cast and cured. The mixture is cured at 80℃ for 3 h to obtain a polydimethylsiloxane substrate. The substrate is then placed in an oxygen plasma treatment device with a power of 50 W, an oxygen flow rate of 50 sccm, and a treatment time of 2 min to obtain an activated substrate. The activated substrate is then immersed in a 5% KH-550 ethanol solution for 30 min and dried at 65℃ for 2 h to obtain an elastic polymer substrate.

[0084] S2.2. Cerium oxide nanoparticles, graphene, and ammonium bicarbonate were dispersed in isopropanol and ultrasonically treated at 300W for 2 hours. Then, epoxy resin and polyetheramine with a mass ratio of 3.3:1 were added to obtain a mixed slurry. The mixed slurry was spin-coated onto the surface of an elastic polymer substrate at 3000 rpm for 30 seconds to form an intermediate layer with a thickness of 30 μm. The intermediate layer was cured at 80℃ for 1 hour and then cured at 150℃ for 3 hours. After rinsing with deionized water, the intermediate layer was dried at 60℃ to obtain a cerium oxide nanoparticle / graphene composite intermediate layer.

[0085] S2.3. Immerse diamond micropowder in a mixture of concentrated H2SO4 and HNO3 in a volume ratio of 3:1, reflux at 80°C for 2 hours, centrifuge and wash until neutral, and dry at 70°C to obtain acid-treated diamond micropowder. Mix the acid-treated diamond micropowder with cerium oxide nanoparticles in a mass ratio of 9:1, and then add epoxy resin and methylhexahydrophthalic anhydride to obtain a mixture. Coat the mixture onto the surface of the cerium oxide nanoparticle / graphene composite intermediate layer with a doctor blade to obtain a diamond micropowder surface layer with a coating thickness of 50 μm. Finally, apply pressure to cure the mixture at a pressure of 0.5 MPa, a curing temperature of 160°C, and a curing time of 4 hours to obtain a composite abrasive.

[0086] S1.2 In a precision surface grinder, the rough-machined aluminum-based silicon carbide blank is subjected to staged gradient grinding. The specific parameters are as follows: Rough grinding stage: Metal-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W40 to W20, spindle speed 2500 rpm, feed rate 0.08 mm / min, axial pressure 15 N, and coolant flow rate 5 L / min; Semi-finish grinding stage: Resin-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W20 to W10, spindle speed 3200 rpm, feed rate 0.03 mm / min, axial pressure 8 N, and coolant flow rate 3 L / min; Finish grinding stage: In an ultra-precision CNC grinder, composite grinding tools are used for finish grinding, with a spindle speed of 3800 rpm, feed rate of 0.015 mm / min, machining with a circular helical trajectory, pitch of 0.1 mm, axial pressure ≤5 N, and aerosol cooling using nitrogen and -10℃ cold air, resulting in a surface temperature rise ≤30℃, thus obtaining an ultra-thin lens;

[0087] S1.3. The ultrathin lens was polished in a magnetorheological polishing machine. An asymmetric magnetic field Halbach permanent magnet array was designed with an edge magnetic field of 0.5T and a center magnetic field of 0.2T to form an asymmetric shear stress field. The polishing parameters were: polishing pad hardness Shore A 50, rotation speed of 200rpm, polishing fluid flow rate of 10mL / min, and polishing time of 60min, to obtain an aluminum-based silicon carbide ultrathin reflective mirror based on gradient grinding.

[0088] Example 5: A precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding, comprising the following steps:

[0089] S1.1 65 vol% silicon carbide and 35 vol% aluminum were ball-milled under argon protection at a ball-to-material ratio of 5:1, at 300 rpm for 4 hours. After holding at 200 MPa for 5 minutes, the green body was placed in a vacuum furnace for 10 minutes. -3 Under a vacuum of 100 Pa, the aluminum-based silicon carbide billet was heated to 300℃ and held for 1 hour, and then hot-pressed and sintered at 50 MPa and 580℃ for 2 hours to obtain an aluminum-based silicon carbide billet. After annealing at 550℃ for 4 hours, residual stress was eliminated by a vibration aging device with a frequency of 80 Hz, an amplitude of 0.05 mm, and a time of 30 min. The billet was then cut into 5 mm thick sections using a diamond wire cutter and chamfered at 45° with a W20 diamond grinding wheel, with a chamfer width of 0.3 mm, to obtain the rough-machined aluminum-based silicon carbide billet.

[0090] The coolant is a neutral pH nanoemulsion, specifically composed of: 85% polyalphaolefin synthetic ester, 5% polyoxyethylene ether emulsifier, 0.8% nano-Al2O3 and SiC mixed particles in a mass ratio of 4:1, 0.4% benzotriazole, 0.3% triethanolamine, 0.1% phosphate buffer, and the balance being deionized water.

[0091] The specific components of the polishing fluid are: 1.2% nano-diamond abrasive, 4% colloidal silica, 0.8% cerium oxide nanoparticles, 0.5% benzotriazole, 2% ethylenediaminetetraacetic acid, 3% hydrogen peroxide, 0.07% hexagonal boron nitride, 1.2% sodium dodecylbenzenesulfonate, 0.05% polyethylene glycol, 3% potassium hydroxide pH adjuster, and the remainder is water;

[0092] The composite abrasive is prepared from a diamond micropowder surface layer, a cerium oxide nanoparticle / graphene composite intermediate layer, and an elastic polymer substrate. The mass ratio of polydimethylsiloxane prepolymer to alumina nanoparticles is 11:1; the mass ratio of polydimethylsiloxane prepolymer, hydrogen-containing siloxane crosslinking agent, and platinum catalyst is 8:1:0.006; the mass ratio of cerium oxide nanoparticles, graphene, and ammonium bicarbonate is 5:2.5:1; the mass ratio of cerium oxide nanoparticles to epoxy resin is 4:5; the mass ratio of acid-treated diamond micropowder to cerium oxide nanoparticles is 9:1; the mass ratio of acid-treated diamond micropowder to epoxy resin is 9:4.5; and the mass ratio of epoxy resin to methylhexahydrophthalic anhydride is 4:1.

[0093] The specific steps for preparing composite abrasives are as follows:

[0094] S2.1. The polydimethylsiloxane prepolymer is mixed with alumina nanoparticles and ultrasonically dispersed for 30 min. Then, a hydrogen-containing siloxane crosslinking agent and a platinum catalyst are added. The mixture is degassed under vacuum and then cast and cured. The mixture is cured at 80℃ for 3 h to obtain a polydimethylsiloxane substrate. The substrate is then placed in an oxygen plasma treatment device with a power of 50 W, an oxygen flow rate of 50 sccm, and a treatment time of 2 min to obtain an activated substrate. The activated substrate is then immersed in a 5% KH-550 ethanol solution for 30 min and dried at 65℃ for 2 h to obtain an elastic polymer substrate.

[0095] S2.2. Cerium oxide nanoparticles, graphene, and ammonium bicarbonate were dispersed in isopropanol and ultrasonically treated at 300W for 2 hours. Then, epoxy resin and polyetheramine with a mass ratio of 3.3:1 were added to obtain a mixed slurry. The mixed slurry was spin-coated onto the surface of an elastic polymer substrate at 3000 rpm for 30 seconds to form an intermediate layer with a thickness of 30 μm. The intermediate layer was cured at 80℃ for 1 hour and then cured at 150℃ for 3 hours. After rinsing with deionized water, the intermediate layer was dried at 60℃ to obtain a cerium oxide nanoparticle / graphene composite intermediate layer.

[0096] S2.3. Immerse diamond micropowder in a mixture of concentrated H2SO4 and HNO3 in a volume ratio of 3:1, reflux at 80°C for 2 hours, centrifuge and wash until neutral, and dry at 70°C to obtain acid-treated diamond micropowder. Mix the acid-treated diamond micropowder with cerium oxide nanoparticles in a mass ratio of 9:1, and then add epoxy resin and methylhexahydrophthalic anhydride to obtain a mixture. Coat the mixture onto the surface of the cerium oxide nanoparticle / graphene composite intermediate layer with a doctor blade to obtain a diamond micropowder surface layer with a coating thickness of 50 μm. Finally, apply pressure to cure the mixture at a pressure of 0.5 MPa, a curing temperature of 160°C, and a curing time of 4 hours to obtain a composite abrasive.

[0097] S1.2 In a precision surface grinder, the rough-machined aluminum-based silicon carbide blank is subjected to staged gradient grinding. The specific parameters are as follows: Rough grinding stage: Metal-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W40 to W20, spindle speed 2500 rpm, feed rate 0.08 mm / min, axial pressure 15 N, and coolant flow rate 5 L / min; Semi-finish grinding stage: Resin-bonded diamond grinding wheels are used, with the wheel grit size decreasing from W20 to W10, spindle speed 3200 rpm, feed rate 0.03 mm / min, axial pressure 8 N, and coolant flow rate 3 L / min; Finish grinding stage: In an ultra-precision CNC grinder, composite grinding tools are used for finish grinding, with a spindle speed of 3800 rpm, feed rate of 0.015 mm / min, machining with a circular helical trajectory, pitch of 0.1 mm, axial pressure ≤5 N, and aerosol cooling using nitrogen and -10℃ cold air, resulting in a surface temperature rise ≤30℃, thus obtaining an ultra-thin lens;

[0098] S1.3. The ultrathin lens was polished in a magnetorheological polishing machine. An asymmetric magnetic field Halbach permanent magnet array was designed with an edge magnetic field of 0.5T and a center magnetic field of 0.2T to form an asymmetric shear stress field. The polishing parameters were: polishing pad hardness Shore A 50, rotation speed of 200rpm, polishing fluid flow rate of 10mL / min, and polishing time of 60min, to obtain an aluminum-based silicon carbide ultrathin reflective mirror based on gradient grinding.

[0099] Comparative Example 1: The method of Example 5 was used directly with diamond micron powder.

[0100] Comparative Example 2: The method of Example 5 was used directly with diamond micron powder and cerium oxide nanoparticles, without preparing a multilayer structure through composite preparation.

[0101] Comparative Example 3: The composite abrasive was modified using the method of Example 5 without the addition of graphene.

[0102] Comparative Example 4: The method of Example 5 was used to polish the diamond using MD-W single-crystal polishing slurry.

[0103] Comparative Example 5: Using the method of Example 5, without staged gradient grinding, the grinding wheel directly transitioned from W40 grinding wheel grit size to W10 grinding wheel grit size.

[0104] This invention discloses a precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding using composite abrasives. The performance indicators and testing standards for this method are as follows:

[0105] Surface roughness is a parameter describing the microscopic geometric shape error of a machined surface, reflecting the fineness of the surface texture. Roughness directly affects the efficiency of light scattering and reflection. Excessive surface roughness Ra will cause significant visible light scattering, reducing the clarity of the mirror image. High-roughness surfaces are prone to stress accumulation, which can lead to the propagation of microcracks and reduce the life of the workpiece. By using a white light interferometer, five regions are randomly selected on the mirror surface, with a scanning area of ​​100×100μm², and the Ra value is calculated. Surface shape accuracy is the deviation between the actual machined surface and the ideal geometric shape (such as a plane, sphere, or aspherical surface). Surface shape error will cause wavefront distortion, which directly affects the imaging resolution. By using a laser interferometer, the mirror is placed on an air-bearing vibration isolation platform, and the laser beam is incident perpendicularly. The reflected wavefront deviation is analyzed, and the RMS value is calculated.

[0106] The precision machining methods for aluminum-based silicon carbide ultrathin mirrors prepared in Examples 1-5 and Comparative Examples 1-5 based on gradient grinding were tested using the above standards, and the data obtained are shown in Table 1:

[0107] Table 1 Performance data of Examples 1-5 and Comparative Examples 1-5

[0108]

[0109] The above data fully demonstrates that, compared to Comparative Examples 1-5, Examples 1-5 clearly show the effect of composite abrasives on the surface roughness and surface accuracy of the precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding.

[0110] Because this invention employs a composite grinding tool to prepare a precision machining method for aluminum-based silicon carbide ultrathin mirrors based on gradient grinding, the composite grinding tool effectively improves the surface roughness and surface accuracy of the aluminum-based silicon carbide ultrathin mirrors based on gradient grinding, specifically as follows:

[0111] As can be seen from Examples 1-3, with the continuous increase of polydimethylsiloxane prepolymer content, the surface roughness performance of the aluminum-based silicon carbide ultrathin mirror based on gradient grinding first decreases and then increases. Due to the good elastic effect of the polymer substrate, the elastic modulus of the composite abrasive is optimized with the increase of polymer content, thereby effectively absorbing the vibration generated during fine grinding and reducing the occurrence of grinding chatter. However, when the content of flexible polymer in the polymer substrate is large, the polymer substrate is too soft, resulting in uneven pressure transmission and fluctuations in the diamond abrasive penetration depth, which in turn increases the surface roughness. However, the soft polymer substrate can adapt to the overall curvature change of the lens, making it more in line with the workpiece curvature, thus reducing surface distortion and improving surface accuracy.

[0112] As can be seen from Examples 2, 4 and 5, the surface roughness of the aluminum-based silicon carbide ultrathin mirror based on gradient grinding gradually decreases as the content of cerium oxide nanoparticles and graphene increases. Since cerium oxide nanoparticles can chemically react with the surface of aluminum-based silicon carbide, they can effectively reduce the grinding resistance and reduce brittle fracture. Graphene has good thermal conductivity and can reduce thermal stress deformation. Therefore, the surface roughness gradually decreases as the content of cerium oxide nanoparticles and graphene increases.

[0113] Based on the above test experiments, it can be seen that the precision machining method of aluminum-based silicon carbide ultrathin mirror based on gradient grinding prepared according to Example 5 has the best performance. Therefore, Example 5 is regarded as the best example.

[0114] A comparison of Example 5 with Comparative Examples 1-3 shows that:

[0115] Comparative Example 1 directly uses diamond micron powder. The surface roughness and surface accuracy of the aluminum-based silicon carbide ultrathin mirror based on gradient grinding are poor. Since pure diamond grinding is a purely mechanical removal process, it lacks the chemical softening of cerium oxide, the thermal management of graphene, and the damping effect of the polymer substrate. This leads to an increase in thermal stress cracking, an increase in edge chipping, and rigid impact causing surface distortion. Therefore, the surface roughness and surface accuracy are significantly deteriorated.

[0116] Comparative Example 2 directly used diamond micro powder and cerium oxide nanoparticles without preparing a multilayer structure through composite. The surface roughness of the aluminum-based silicon carbide ultrathin mirror based on gradient grinding was poor. Since the cerium oxide nanoparticles were directly mixed in the diamond layer, they were prone to agglomeration, resulting in uneven distribution of chemically active areas and unstable chemical grinding effect, which led to a decrease in surface roughness.

[0117] Comparative Example 3 modified the composite abrasive without the addition of graphene. The surface roughness of the aluminum-based silicon carbide ultrathin mirror based on gradient grinding was poor. It lacked a graphene interlayer, and the interlayer had low thermal conductivity. The heat generated by grinding gradually accumulated, thermal management failed, the epoxy resin softened, and the diamond abrasive grains were easy to fall off. The resin softening also reduced the abrasive grain bonding force, resulting in a decrease in the grinding efficiency and effect of the material.

[0118] Comparative Example 4 used MD-W single-crystal diamond polishing slurry for polishing. The surface roughness and surface accuracy of the aluminum-based silicon carbide ultrathin mirror based on gradient grinding were poor. Due to the smaller cutting depth of nano-sized diamonds, combined with the lubricating effect of surfactants, cerium oxide chemical polishing of the silicon carbide surface with hydrogen peroxide significantly reduced surface microcracks. In contrast, the micron-sized diamond abrasives in ordinary polishing slurries, due to their larger particle size, easily formed deep scratches on the aluminum-based silicon carbide surface, resulting in poor surface roughness. Furthermore, the uniform dispersion of nano-diamonds and cerium oxide also... It can ensure uniform polishing pressure distribution, reduce local over-cutting or under-cutting, and at the same time, ethylenediaminetetraacetic acid chelates metal ions to prevent them from redepositing and forming protrusions, maintaining surface consistency. Since the aluminum matrix in aluminum-based silicon carbide is relatively soft and the silicon carbide reinforcing phase is relatively hard, there is a hardness difference between the two. Ordinary polishing slurries are prone to over-polishing of the aluminum matrix due to mechanical dominance, while benzotriazole can inhibit aluminum matrix corrosion and reduce surface pitting defects. Cerium oxide and hydrogen peroxide preferentially soften the silicon carbide phase, achieving simultaneous flattening of the two phases and improving surface accuracy. Therefore, the surface accuracy of ordinary polishing slurries is poor.

[0119] Comparative Example 5 did not undergo staged gradient grinding. The surface roughness and surface accuracy of the aluminum-based silicon carbide ultrathin mirror based on gradient grinding were poor. Without staged grinding, the transition from coarse abrasive grains to fine abrasive grains was direct. As a result, the large-sized defects on the material surface were not fully removed in the coarse grinding stage, and it was difficult to completely repair these defects in the fine grinding stage. This significantly increased the surface roughness. Furthermore, the processing stress was applied to the ultrathin mirror at once, resulting in local stress concentration. During the processing, the workpiece underwent irreversible plastic deformation or elastic rebound, and the surface distortion was severe.

[0120] In summary, the elastic vibration absorption of the polydimethylsiloxane substrate suppresses edge chipping and subsurface damage. The chemical softening and thermal management effects of the cerium oxide nanoparticle / graphene interlayer reduce surface roughness and suppress temperature rise during the fine grinding process. Through gradient structure design, the transition from a rigid surface layer to an elastic substrate effectively balances the removal rate and surface accuracy, thereby effectively improving the processing quality of the reflector.

[0121] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A precision machining method of aluminum-based silicon carbide ultra-thin mirror based on gradient lapping, characterized in that: S1.1: an aluminum-based silicon carbide blank is prepared from 65-67 vol% silicon carbide and 33-35 vol% aluminum, residual stress is eliminated after annealing, and the aluminum-based silicon carbide blank is obtained after rough machining and chamfering; S1.2: the rough machined aluminum-based silicon carbide blank is divided into three gradient lapping stages, i.e., a rough lapping stage, a semi-fine lapping stage and a fine lapping stage, in a precision surface grinder, and a super-thin mirror is obtained by adjusting the grinding wheel, the grinding wheel particle size, the spindle speed, the feed speed, the axial pressure, the cooling liquid flow and the composite grinding tool; S1.3: the super-thin mirror is polished in a magnetorheological polishing machine by using a polishing liquid to obtain an aluminum-based silicon carbide ultra-thin mirror based on gradient lapping; The composite grinding tool is prepared from a diamond micro-powder surface layer, a composite intermediate layer and an elastic polymer substrate. The steps for preparing the composite grinding tool are as follows: S2.1: a polydimethylsiloxane prepolymer is mixed with alumina nanoparticles, and after ultrasonic dispersion for 30 min, a siloxane crosslinking agent and a platinum catalyst are added, vacuum degassing is performed, and the mixture is poured and cured to form a polydimethylsiloxane substrate, which is then placed in an oxygen plasma treatment device, set to a power of 50 W, an oxygen flow of 50 sccm and a treatment time of 2 min to obtain an activated substrate, which is then soaked in an ethanol solution containing 5% KH-550 for 30 min and dried at 65°C for 2 h to obtain an elastic polymer substrate; S2.2: cerium oxide nanoparticles, graphene and ammonium bicarbonate are dispersed in isopropyl alcohol, and ultrasonic treatment is performed at 300 W for 2 h, then an epoxy resin and a polyether amine are added in a mass ratio of 3.3:1 to obtain a mixed slurry, which is spin-coated on the surface of the elastic polymer substrate at 3000 rpm for 30 s to form an intermediate layer with a thickness of 30 μm, which is then cured at 80°C for 1 h and at 150°C for 3 h, washed with deionized water and dried at 60°C to obtain a cerium oxide nanoparticle / graphene composite intermediate layer; S2.3: diamond micro-powder is immersed in a mixed acid of concentrated H2SO4 and HNO3 in a volume ratio of 3:1, refluxed at 80°C for 2 h, washed by centrifugation until neutral, and dried at 70°C to obtain acid-treated diamond micro-powder, which is then mixed with cerium oxide nanoparticles at a mass ratio of 9:1, and an epoxy resin and methylhexahydrophthalic anhydride are added to obtain a mixture, which is coated on the surface of the cerium oxide nanoparticle / graphene composite intermediate layer by a doctor blade to obtain a diamond micro-powder surface layer with a coating thickness of 50 μm, and finally cured under pressure at a curing pressure of 0.5 MPa, a curing temperature of 160°C and a curing time of 4 h to obtain the composite grinding tool.

2. The method of claim 1, wherein the method is a gradient-lap-based precision machining method for an aluminum-based SiC ultra-thin mirror. In the S1.1, the specific steps of the rough machined aluminum-based silicon carbide blank are as follows: 65-67 vol% silicon carbide and 33-35 vol% aluminum are mixed by ball milling under argon protection, wherein the ball-to-material ratio is 5:1, the rotation speed is 200-300 rpm, the time is 4-5 h, the green body is placed in a vacuum furnace after being kept at 200-250 MPa for 5 min -3 The green body is heated to 200-300℃ under a vacuum of 10 Pa for 1-2 h, and is hot-pressed and sintered at 50-55 MPa and 580℃ for 2-3 h to obtain an aluminum-based silicon carbide green body. After the aluminum-based silicon carbide green body is annealed at 550℃ for 4 h, residual stress is eliminated by using a vibration aging device. The aluminum-based silicon carbide green body is cut into a thickness of 5-5.5 mm by using a diamond wire cutting machine, is chamfered at 45° by using a diamond grinding wheel with a granularity of W20, and the chamfering width is 0.2-0.3 mm to obtain a rough machined aluminum-based silicon carbide green body.

3. The method of claim 2, wherein the method is a gradient-diamond-milling-based precision machining method for an aluminum-based SiC ultra-thin mirror. The parameters of the vibration aging device are as follows: a frequency of 75-80 Hz, an amplitude of 0.04-0.05 mm and a time of 25-30 min.

4. The method of claim 1, wherein the method is a gradient-lap-based precision machining method for an aluminum-based SiC ultra-thin mirror. In the S1.2, the specific parameters of the rough lapping stage are as follows: Metal bond diamond grinding wheel is used, the grain size of the grinding wheel is W40 decreasing to W20, the spindle speed is 2000-2500 rpm, the feed speed is 0.06-0.08 mm / min, the axial pressure is 13-15 N, and the cooling liquid flow is 5-7 L / min.

5. The method of claim 1, wherein the method is a gradient-lap-based precision machining method for an aluminum-based SiC ultra-thin mirror. In the S1.2, the specific parameters of the semi-finishing stage are as follows: Resin bond diamond grinding wheel is used, the grain size of the grinding wheel is W20 decreasing to W10, the spindle speed is 3000-3200 rpm, the feed speed is 0.03-0.05 mm / min, the axial pressure is 6-8 N, and the cooling liquid flow is 3-5 L / min.

6. The method of claim 1, wherein the method is a gradient-lap-based precision machining method for an aluminum-based SiC ultra-thin mirror. In the S1.2, the specific parameters of the finishing stage are as follows: In the ultra-precision numerical control grinding machine, the ultra-thin mirror is finished by using a composite grinding tool, the spindle speed is 3800-4000 rpm, the feed speed is 0.015-0.02 mm / min, the surface is processed in a ring spiral trajectory, the pitch is 0.1-0.2 mm, the axial pressure is ≤5 N, the surface temperature is raised by ≤30 ℃ through nitrogen gas and -10 ℃ cold air, and the ultra-thin mirror is obtained.

7. The method of claim 1, wherein the method is a gradient-diamond-milling-based precision machining method for an aluminum-based SiC ultra-thin mirror. The specific steps for preparing the aluminum-based silicon carbide ultra-thin mirror based on gradient grinding are as follows: The ultra-thin mirror is polished in a magneto-rheological polishing machine, an asymmetric magnetic field Halbach permanent magnet array is designed, the edge magnetic field is 0.5 T, the center is 0.2 T, an asymmetric shear stress field is formed, the polishing parameters are as follows: the hardness of the polishing pad is Shore A 50-60, the rotation speed is 100-200 rpm, the polishing liquid flow is 10-15 mL / min, and the polishing time is 30-60 min, and the aluminum-based silicon carbide ultra-thin mirror based on gradient grinding is obtained.

8. The method of claim 1, wherein the method is a gradient-diamond-milling-based precision machining method for an aluminum-based SiC ultra-thin mirror. The cooling liquid is a neutral pH nano-emulsified liquid, and the specific components are as follows: poly-alpha-olefin synthetic ester 80-85%, polyoxyethylene ether emulsifier 3-5%, nano-Al2O3 and SiC mixed particles with a mass ratio of 4:1 0.5-0.8%, benzotriazole 0.3-0.4%, triethanolamine 0.2-0.3%, phosphate buffer 0.05-0.1%, and the rest is deionized water.

9. The method of claim 1, wherein the method is a gradient-diamond-milling-based precision machining method for an aluminum-based SiC ultra-thin mirror. The specific components of the polishing liquid in the S1.3 are as follows: nano-diamond abrasive 0.8-1.2%, colloidal silicon dioxide 2-4%, cerium oxide nanoparticles 0.5-0.8%, benzotriazole 0.2-0.5%, ethylenediaminetetraacetic acid 1-2%, hydrogen peroxide 1-3%, hexagonal boron nitride 0.05-0.07%, sodium dodecylbenzenesulfonate 0.5-1.2%, polyethylene glycol 0.03-0.05%, potassium hydroxide pH adjuster 1-3%, and the rest is water.

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