A method for ultra-smooth polishing of large-aperture, high-steepness aspheric quartz glass

Abstract

A method for ultra-smooth polishing of large-diameter, high-steepness aspheric quartz glass includes the following steps: 1) generating a machining program file based on the equation of the aspheric element to be machined; 2) determining parameters such as the polishing path, polishing time, and polishing load; 3) performing rough and fine polishing processes primarily using mechanical action; 4) performing an ultra-smooth pre-polishing process primarily characterized by chemical mechanical action to remove subsurface damage layers; and 5) performing an ultra-smooth machining process to remove atomic-level surface material. The polishing method proposed in this invention simultaneously addresses the key technical issues of deterministic control of low-frequency surface shape accuracy, surface defect control, and ultra-smooth machining of the polished element material surface. In particular, it is unaffected by element size and asphericity, exhibits strong versatility, and is highly stable. The entire process utilizes only robotic polishing equipment, resulting in low cost and high efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-precision processing of optical elements, and specifically relates to a method for ultra-smooth polishing of large-aperture, high-steepness aspheric quartz glass using a robot polishing device. Background Art

[0002] Ultra-smooth processing of optical components is a key area of ​​modern optics, crucial for achieving high-performance optical systems. As optical systems evolve toward higher resolution, higher precision, and higher sensitivity, the impact of surface roughness on system performance becomes increasingly significant. Ultra-smooth surfaces can reduce light scattering, improving imaging quality and light transmission efficiency.

[0003] Quartz glass, with its excellent physical and chemical properties, is a critical substrate material in fields such as laser fusion, laser gyroscopes, and extreme ultraviolet lithography. Its ultra-smooth surface quality is a technical challenge that limits the performance of these high-precision optical systems. With the development of the high-end equipment manufacturing industry, demand for large-aperture aspheric, ultra-smooth optical components continues to grow. However, the processing of large-aperture (typically diameters greater than 200mm) aspheric optical components faces core challenges, including difficult quality control, low processing efficiency, and high requirements for consistent material removal.

[0004] Currently, commonly used ultra-smooth polishing technologies include magnetorheological polishing, ion beam polishing, chemical mechanical polishing, traditional mechanical polishing, etc. The above polishing methods have certain restrictions on the size and asphericity of optical components, and magnetorheological polishing has the problems of high equipment and polishing fluid costs and easy generation of polishing marks; ion beam polishing has the disadvantages of high operating requirements, low efficiency and limitation on component size; the ultra-smooth polishing technology of traditional high-polishing grinding machines, although it can achieve mass production with a roughness of 0.1nm, is powerless for large-diameter and high-steepness aspheric surfaces; chemical mechanical polishing technology combines the synergistic effect of chemical corrosion and mechanical removal to achieve high-precision surface modification and ultra-smooth polishing effects. For different materials, it is necessary to select appropriate polishing fluids and mechanical parameters to obtain the best polishing effect. Summary of the Invention

[0005] In response to the shortcomings of existing technologies and the need for ultra-precision, deterministic, and ultra-smooth polishing of large-aperture aspheric components, this invention provides a method for ultra-smooth polishing of large-aperture, high-steepness aspheric quartz glass. By controlling the polishing liquid composition (e.g., cerium oxide particle size and pH value), polishing pad properties (hardness and groove structure), and process parameters (pressure and rotation speed) in stages, this method achieves full-band error convergence, from rough polishing to atomic-level ultra-smooth polishing. This method offers stable and deterministic processes, achieving simultaneous convergence across the entire frequency range using only small polishing equipment, resulting in low cost and high efficiency.

[0006] The technical solutions adopted by the present invention are as follows:

[0007] A method for ultra-smooth polishing of large-diameter, high-steepness aspheric quartz glass is characterized by comprising the following steps:

[0008] Step 1) Generate a machining program file based on the equation of the aspheric element to be machined;

[0009] Step 2) determining the polishing path, polishing time and polishing load parameters;

[0010] Step 3) performing rough polishing using a cerium oxide polishing liquid having an average particle size of 1 μm to 3 μm and a polyurethane polishing pad having a hardness of 60 to 95 Shore A;

[0011] Step 4) fine polishing is performed using a cerium oxide polishing liquid with an average particle size of 0.3-0.6 μm and an asphalt mixture with a needle penetration of 0.6 mm-1.2 mm;

[0012] Step 5) ultra-smooth pre-polishing is performed using a cerium oxide polishing liquid with an average particle size of 0.1 to 0.3 μm and an asphalt mixture with a needle penetration of 0.15 to 0.5 mm;

[0013] Step 6) A cerium oxide polishing liquid with an average particle size of 20 to 40 nm and a flexible polishing pad with a porosity of 90% to 96% are combined to perform atomic-level ultra-smooth polishing.

[0014] Preferably, in step 3, the cerium oxide polishing solution is diluted with ultrapure water at a mass ratio of 5% to 20%, and the pH of the solution is adjusted to between 5 and 7 by citric acid;

[0015] Preferably, the polyurethane polishing pad in step 3 has a hardness of 60-95 Shore A, a groove structure on the surface, a groove width of 1-3 mm, and a groove spacing of 12-20 mm;

[0016] Preferably, in step 4, the cerium oxide polishing solution is diluted with ultrapure water at a mass ratio of 10% to 20%, and the pH of the solution is adjusted to between 5 and 7 by citric acid.

[0017] Preferably, in step 4, the asphalt mixture has a needle penetration range of 0.6 mm to 1.2 mm, and the surface is grooved with a groove width of 2 to 4 mm and a depth of 2 to 3 mm;

[0018] Preferably, in step 5, the polishing abrasive uses cerium oxide with an average particle size of 0.1 μm-0.3 μm, citric acid is used to adjust the pH to 5-7, the concentration is 5%-15%, and the content of impurities with a particle size greater than 0.3 μm in the polishing liquid is ≤0.01%;

[0019] Preferably, in step 5, the penetration range of the asphalt mixture is limited to 0.15mm-0.5mm, the surface is grooved, the groove width is 2-3mm, and the depth is 1-2mm;

[0020] Preferably, the needle penetration test temperature is 23-25 ​​degrees Celsius in the test container, and the temperature is maintained for more than 5 minutes;

[0021] Preferably, in step 6, the average particle size of the cerium oxide polishing abrasive is 20-40 nm, the concentration is 5%-10%, the content of impurities with a particle size greater than 40 nm in the polishing liquid is ≤0.01%, and H2O2 with a concentration of 6%-7.7% is selected as the oxidant, with a mass fraction of 0.2%-1.2%;

[0022] Preferably, in step 6, the polishing disc uses a flexible polishing medium with an elastic modulus of 0.1 MPa to 1.5 MPa;

[0023] Preferably, in step 6, the small tool polishing equipment used has a rotation speed of 350-450 r / min, a feed speed of 10-20 mm / s, a polishing pressure of 2-2.5 kg, and a polishing liquid dripping rate of 3-6 ml / min.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The present invention is not limited by the surface shape and size of the component. It is particularly advantageous for achieving an ultra-smooth surface with a high-frequency roughness of less than 0.2nm for large-diameter (greater than 200mm) and high-steepness components. It is also suitable for ultra-smooth processing of components with microstructures.

[0026] 2. Traditional methods struggle to achieve both surface accuracy and ultra-smooth surfaces for large-diameter, high-steepness components. This invention achieves full-band error control through a phased polishing process (rough polishing → fine polishing → ultra-smooth pre-polishing → atomic-level polishing) by regulating the polishing fluid, polishing pad, and process parameters.

[0027] 3. Only small tool polishing equipment can achieve high-precision ultra-smooth conformal polishing in the full frequency band, avoiding surface texture problems, simple operation, and at the same time has the advantages of high polishing efficiency and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a basic flow chart of the present invention;

[0029] Figure 2 is the initial surface shape error of the quartz element after milling in the embodiment of the present invention;

[0030] Figure 3 is the surface shape error of the quartz element after rough polishing in the embodiment of the present invention;

[0031] Figure 4This is the mid-frequency roughness morphology of the quartz component after rough polishing in an embodiment of the present invention;

[0032] Figure 5 This is the high-frequency roughness morphology of the quartz component after rough polishing in an embodiment of the present invention;

[0033] Figure 6 is the surface shape error of the quartz component after fine polishing in the embodiment of the present invention;

[0034] Figure 7 This is the mid-frequency roughness morphology of the quartz component after fine polishing in an embodiment of the present invention;

[0035] Figure 8 This is the mid-frequency roughness profile of the ultra-smooth pre-polishing stage of the quartz element in an embodiment of the present invention;

[0036] Figure 9 This is the high-frequency roughness morphology of the quartz element in the ultra-smooth pre-polishing stage in an embodiment of the present invention;

[0037] Figure 10 This is the high-frequency roughness morphology of the quartz element in the ultra-smooth stage in an embodiment of the present invention;

[0038] Figure 11 This is the mid-frequency roughness morphology of the quartz element in the ultra-smooth polishing stage in an embodiment of the present invention;

[0039] Figure 12 It is the surface shape error of the quartz element after ultra-smooth polishing in the embodiment of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below with reference to specific preferred embodiments and the accompanying drawings. It should be understood that this embodiment is only a part of the embodiments of the present invention and not all of the embodiments, and should not limit the scope of protection of the present invention. It should be noted that the technical features of this embodiment and possible embodiments can be combined with each other unless they conflict. The present invention will be described in detail below with reference to the embodiments.

[0041] See also Figure 1 , Figure 1 The flowchart of the ultra-smooth polishing method of large-diameter, high-steepness aspheric quartz glass of the present invention is as shown in the figure. The ultra-smooth polishing method of large-diameter, high-steepness aspheric quartz glass comprises the following steps:

[0042] Step 1) Generate a machining program file based on the equation of the aspheric element to be machined;

[0043] Step 2) determining the polishing path, polishing time and polishing load parameters;

[0044] Step 3) performing rough polishing using a cerium oxide polishing liquid having an average particle size of 1 μm to 3 μm and a polyurethane polishing pad having a hardness of 60 to 95 Shore A;

[0045] Step 4) fine polishing is performed using a cerium oxide polishing liquid with an average particle size of 0.3-0.6 μm and an asphalt mixture with a needle penetration of 0.6 mm-1.2 mm;

[0046] Step 5) ultra-smooth pre-polishing is performed using a cerium oxide polishing liquid with an average particle size of 0.1 to 0.3 μm and an asphalt polishing pad with a needle penetration of 0.15 to 0.5 mm;

[0047] Step 6) A cerium oxide polishing liquid with an average particle size of 20 to 40 nm and a flexible polishing pad with a porosity of 90% to 96% are combined to perform atomic-level ultra-smooth polishing.

[0048] The optical element in this embodiment is a piece of aspheric quartz glass with an aperture of 300 mm×200 mm and an asphericity of 145 μm. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] In step S1 of this embodiment, the initial surface shape error of the quartz element after milling is measured by three-coordinate measurement, such as Figure 2 As shown in the figure, a machining program file is generated based on the aspheric equation.

[0050] Step S2 determines polishing parameters such as the polishing disc size, polishing path, and polishing load according to the initial surface shape error.

[0051] During the rough polishing process of step S3, the average particle size of the cerium oxide is 1μm-3μm. The polishing liquid is diluted with ultrapure water at a mass ratio of 5% to 20%, and the pH of the solution is adjusted to between 5-7 by citric acid. The hardness of the polyurethane polishing pad is 60-95 Shore A, and the surface has a groove structure with a groove width of 1-3mm and a groove spacing of 12-20mm. This embodiment uses a cerium oxide polishing liquid with an average particle size of 1.5μm (concentration 35wt%, pH=8.0), a ratio of ultrapure water to polishing liquid of 5:1, citric acid is used to adjust the solution pH to 6.5, and an FST-110 polishing pad (hardness 78 Shore A) is selected, with a groove width of 2mm and a groove spacing of 15mm. The process controls the pressure to 5KG, the rotation speed to 400rpm, and the polishing liquid droplet acceleration to 15ml / min. After rough polishing, the knife marks produced by milling are evenly removed, and the surface shape error after rough polishing is measured using a ZYGO interferometer, as shown Figure 3 As shown, the surface error RMS = 0.92λ (λ = 632.8nm), the medium frequency roughness after rough polishing is measured using a white light profilometer, as shown Figure 4As shown, the roughness rms = 3.592nm, the high frequency roughness after rough polishing is measured using an atomic force microscope as shown Figure 5 As shown, Rq=5.2nm.

[0052] During the fine polishing process of step S4, the particle size of cerium oxide is 0.3-0.6um. The polishing liquid is diluted with ultrapure water at a mass ratio of 10% to 20%, and the pH of the solution is adjusted to between 5 and 7 by citric acid. The penetration range of the asphalt mixture is 0.6mm-1.2mm, the surface is grooved, the groove width is 2-4mm, and the depth is 2-3mm. This embodiment uses a cerium oxide polishing liquid with an average particle size of 0.4μm (concentration 50%, pH8), and uses citric acid to adjust the pH to 7; the asphalt penetration is selected to be 0.8mm, the surface is grooved, the groove width is 3mm, and the depth is 2mm. After fine polishing, a ZYGO interferometer is used to measure the surface shape error, such as Figure 6 As shown, the surface shape error RMS = 14.559nm, and the medium frequency roughness is measured using a white light profilometer, as shown Figure 7 As shown, the roughness rms = 1.7nm.

[0053] It should be noted that based on the viscoelastic regulation of asphalt penetration, when the penetration is in the range of (60-120) × 0.1mm, on the one hand, the flexible deformation ability of the asphalt molecular chain can achieve micron-level dynamic bonding with the surface of the aspherical substrate (bonding accuracy ≤3μm), effectively compensating for the geometric error of the processed surface; on the other hand, it can effectively suppress the deformation of the entire polishing disc, reduce loss, and increase the life of the polishing disc.

[0054] Step S5 is the ultra-smooth pre-polishing stage. The polishing abrasive uses cerium oxide with an average particle size of 0.1μm-0.3μm. Citric acid is used to adjust the pH to 5-7 and the concentration to 5%~15%. The content of impurities with a particle size greater than 0.3μm in the polishing liquid is ≤0.01%; the penetration range of the asphalt mixture is limited to 0.15mm-0.5mm, the surface is grooved, the groove width is 2-3mm, and the depth is 1-2mm. In this embodiment, the average particle size of the cerium oxide polishing liquid used is 0.1μm (concentration 15wt%, pH=8.0), and citric acid is used to prepare the solution with a pH of 7; the asphalt penetration is 0.25mm, the surface is grooved, the groove width is 2mm, and the depth is 2mm. After ultra-smooth pre-polishing, a white light profilometer is used to test the intermediate frequency roughness, such as Figure 8 As shown, high frequency roughness is measured using Bruker atomic force equipment. Figure 9 shown.

[0055] Step S6 realizes the atomic-level removal ultra-smooth polishing stage. The average particle size of the cerium oxide polishing abrasive is 20-40nm, the concentration is 5%-10%, the content of impurities with a particle size greater than 40nm in the polishing liquid is ≤0.01%, and H2O2 with a concentration of 6%~7.7% is selected as the oxidant, with a mass fraction of 0.2%~1.2%; the polishing disc uses a flexible polishing medium with a porosity of 90%~96% and an elastic modulus of 0.1MPa~1.5MPa; the polishing equipment used has a rotation speed of 350-450r / min, a feed speed of 10-20mm / s, a polishing pressure of 2-2.5Kg, and a polishing liquid dripping rate of 3-6ml / min. In this embodiment, the average particle size of the cerium oxide polishing abrasive is 30 nm, the concentration is 10%, the content of impurities with a particle size greater than 40 nm in the polishing liquid is ≤0.01%, and H2O2 with a concentration of 7.7% is selected as the oxidant, with a mass fraction of 1%; the polishing disc uses a flexible polishing medium with an elastic modulus of 0.2 MPa and a porosity of 95%; the polishing equipment speed is 400 r / min, the feed speed is 15 mm / s, the polishing pressure is 2.5 kg, and the polishing liquid dripping rate is 6 ml / min.

[0056] After processing, the high-frequency roughness was measured using Bruker atomic force equipment. Figure 10 As shown, the results of the white light profilometer measuring the medium frequency roughness are as follows Figure 11 As shown, the ZYGO interferometer measures the surface error as Figure 12 shown.

[0057] The above processing results show that the present invention uses only a small robot tool polishing device and a chemical mechanical polishing method to process large-diameter, high-steepness aspheric components, and can obtain an ultra-smooth processing result with a high-frequency roughness of less than 50pm, and the component surface has the characteristics of low defects and high quality. Comparing the surface shape error distribution of the component before and after ultra-smooth processing, it can be seen that Figure 6 and Figure 12 , rms change of 2.8nm, achieving ultra-smooth conformal processing results.

[0058] The above embodiments are only generally preferred implementation methods of the present invention, but the protection scope of the present invention is not limited by the above embodiments. All technical solutions under the principles and ideas of the present invention belong to the protection scope of the present invention.

Claims

1. A method for ultra-smooth polishing of large-diameter, high-steepness aspheric quartz glass, characterized in that: The following steps are involved: Step 1) Generate a machining program file based on the equation of the aspheric element to be machined; Step 2) determining the polishing path, polishing time and polishing load parameters; Step 3) performing rough polishing using a cerium oxide polishing liquid having an average particle size of 1 μm to 3 μm and a polyurethane polishing pad having a hardness of 60 to 95 Shore A; Step 4) fine polishing is performed using a cerium oxide polishing liquid with an average particle size of 0.3-0.6 μm and an asphalt mixture with a needle penetration of 0.6 mm-1.2 mm; Step 5) ultra-smooth pre-polishing is performed using a cerium oxide polishing liquid with an average particle size of 0.1 to 0.3 μm and an asphalt mixture with a needle penetration of 0.15 to 0.5 mm; Step 6) A cerium oxide polishing liquid with an average particle size of 20 to 40 nm and a flexible polishing medium with a porosity of 90% to 96% are combined to perform atomic-level ultra-smooth polishing.

2. The method for ultra-smooth polishing of large-aperture, high-steepness aspheric quartz glass according to claim 1, characterized in that: In step 3, the cerium oxide polishing liquid is diluted with ultrapure water at a mass ratio of 5% to 20%, and the pH is adjusted to 5-7 with citric acid. The surface of the polyurethane polishing pad is provided with a groove structure with a groove width of 1-3 mm and a groove spacing of 12-20 mm.

3. The method for ultra-smooth polishing of large-diameter, high-steepness aspheric quartz glass according to claim 1, characterized in that: In step 4, the cerium oxide polishing liquid is diluted with ultrapure water at a mass ratio of 10% to 20%, and the pH is adjusted to 5-7 with citric acid.

4. The method for ultra-smooth polishing of large-diameter, high-steepness aspheric quartz glass according to claim 1, characterized in that In step 5, the pH of the cerium oxide polishing liquid is adjusted to 5-7 using citric acid, the ultrapure water dilution concentration is 5%-15%, and the content of impurities with a particle size greater than 0.3 μm in the polishing liquid is ≤0.01%.

5. The method for ultra-smooth polishing of large-aperture, high-steepness aspheric quartz glass according to claim 4, characterized in that: The asphalt mixture penetration test temperature is 23-25 ​​degrees Celsius in the water temperature of the test container, and the temperature is maintained for more than 5 minutes.

6. The method for ultra-smooth polishing of large-aperture, high-steepness aspheric quartz glass according to claim 1, characterized in that: The concentration of the cerium oxide polishing liquid in step 6 is 5%-10%, and the content of impurities with a particle size greater than 40 nm is ≤0.01%. The cerium oxide polishing liquid is added with H2O2 at a concentration of 6%-7.7% as an oxidant, with a mass fraction of 0.2%-1.2%.

7. The method for ultra-smooth polishing of large-aperture, high-steepness aspheric quartz glass according to claim 1, characterized in that: The elastic modulus of the flexible polishing medium in step 6 is 0.1 MPa to 1.5 MPa.

8. The method for ultra-smooth polishing of large-diameter, high-steepness aspheric quartz glass according to claim 1, characterized in that: In the step 6, a small tool polishing device is used with a rotation speed of 350-450 r / min, a feed speed of 10-20 mm / s, a polishing pressure of 2-2.5 kg, and a polishing liquid dripping rate of 3-6 ml / min.

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