High-precision processing method of large-size sapphire optical window

Abstract

The application discloses a high-precision processing method for a large-size sapphire optical window, which comprises the following steps: firstly, using a cast iron disc single-axis grinding machine, rough grinding, semi-precision grinding and precision grinding are sequentially performed on the large-size sapphire optical window; wherein, a size-decreasing boron carbide auxiliary material and a grinding amount are sequentially used; then, using a polyurethane disc single-axis polishing machine, large-coarse polishing rotation speed and large-particle-size diamond liquid auxiliary material are used for coarse polishing, and using a polyurethane disc ring polishing machine, large-precision polishing rotation speed and small-particle-size diamond liquid auxiliary material are used for precision polishing; finally, using an ion beam polishing machine and an RF80 ion source, finishing is performed. The improved grinding and polishing-precision polishing-ion beam finishing process is adopted, the surface shape continuity between processes is improved, the processing requirements of the large-size, high-precision surface sapphire optical window are effectively met on the basis of ensuring the overall processing efficiency of the large-size sapphire optical window, and the application is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of optical cold processing technology, specifically relating to a high-precision processing method for large-size sapphire optical windows. Background Technology

[0002] With the continuous development of science and technology, the requirements for window materials with photoelectric properties and other functions are gradually increasing. The performance of traditional optical glass windows can no longer meet the current practical application standards.

[0003] Synthetic single-crystal sapphire is an oxide crystal with special properties. Its chemical composition is aluminum oxide (Al₂O₃), and it possesses excellent optical, physical, and chemical properties. The characteristics of single-crystal sapphire determine its wide application in defense technologies such as submarines, missiles, satellite space technology, and military infrared devices. With the development of multifunctional, intelligent, and high-speed aircraft, the requirements for optoelectronic and other functional materials are gradually increasing. Traditional optical glass windows are increasingly unable to meet current usage requirements. Sapphire's stable chemical properties and excellent mechanical properties allow it to withstand harsh space environments and maintain high strength under high-speed motion, making it an irreplaceable choice for components such as optoelectronic windows, wave-transmitting windows, fairings, and gyroscopes. Optoelectronic windows made of sapphire exhibit stable chemical properties, resistance to mold, light, rain, and salt spray; high hardness and wear resistance, offering better resistance to sand and gravel erosion compared to traditional optical glass; high transmittance, able to withstand various environmental changes such as temperature rise and aerodynamic load variations; and high structural strength, with a material density approximately half that of steel, providing a significant advantage for weight reduction in aircraft.

[0004] Sapphire has a Mohs hardness of 9, second only to diamond. It is chemically stable and generally insoluble in acids and alkalis. Its excellent mechanical properties, high hardness, and strength make sapphire crystals (especially large sapphire optical windows) difficult to grind and polish, resulting in long processing cycles. Traditional pitch disc polishing methods and RF40 ion source ion beam equipment have low processing efficiency and long polishing times. Prolonged polishing can easily lead to numerous bright spots or even rough surfaces on the surface of large optical windows, making them unsuitable for processing large sapphire optical windows. Summary of the Invention

[0005] The main objective of this invention is to address the problems and shortcomings of existing large-size sapphire window processing methods by providing a high-precision large-size sapphire window processing method. The method employs an improved grinding and polishing-precision polishing-ion beam finishing process, which can effectively improve the surface shape connection between each process. While ensuring the overall processing efficiency of large-size sapphire windows, it effectively meets the processing requirements of large-size, high-precision sapphire windows.

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

[0007] A high-precision processing method for large-size sapphire optical windows includes sequential grinding and polishing-precision polishing processes and ion beam finishing processes, specifically comprising the following steps:

[0008] 1) Grinding and polishing - precision polishing process;

[0009] 1-1) Grinding and polishing;

[0010] A cast iron disc single-axis grinding machine was used to perform rough grinding, semi-finish grinding, and fine grinding on large-size sapphire window profiles in sequence. In this process, boron carbide auxiliary materials and grinding amounts with decreasing size were used in sequence. At the same time, the thickness values ​​of the measurement points were ensured to differ by no more than 0.03 mm.

[0011] 1-2) Precision polishing;

[0012] The rough polishing process involves using a polyurethane disc single-axis polishing machine at high speed and with large-particle diamond slurry to polish the surface until the number of apertures at any point on a flat optical template is less than 5. In existing optical processing, the rough polishing step typically uses a pitch disc single-axis polishing machine at a speed of 30-40 rpm. However, pitch is a fluid, and the disc surface is prone to deformation as polishing time increases, leading to edge collapse and hindering surface accuracy. This invention uses a polyurethane disc combined with high-speed polishing (100-110 rpm). Polyurethane has high hardness and surface roughness, making it less prone to deformation during prolonged polishing, thus ensuring surface accuracy and significantly improving polishing efficiency. Polishing is performed until the number of apertures at any point on the entire surface is less than 5, as measured using a Φ150mm diameter flat optical template. The process can then proceed to the next step.

[0013] The fine polishing process utilizes a polyurethane disc ring polisher, high polishing speed, and small-particle-size diamond liquid auxiliary material to achieve a transmission surface area (PV) better than 3.5λ (λ = 632.8 nm). In existing optical processing, the fine polishing process typically employs an asphalt disc ring polisher with a polishing speed generally between 0.5 and 1 rpm. As the polishing time increases, the disc surface is prone to deformation, leading to edge collapse on the parts. The central area of ​​the part exhibits a high aperture, while the periphery has a low aperture, which is detrimental to improving surface accuracy. This invention employs a polyurethane disc combined with high-speed polishing (5–6 rpm), effectively ensuring the surface accuracy of the parts and significantly improving polishing efficiency. Furthermore, depending on the pressure applied by the stainless steel pressure block on the part surface, it can achieve a low aperture in the central area and a high aperture around the periphery. This surface distribution is more conducive to subsequent ion beam finishing, reducing ion beam finishing time. Parts processed using the above method achieve a transmission surface area (PV) better than 3.5λ (λ = 632.8 nm) and can proceed to the next process.

[0014] 3) Fine finishing; The polished sample obtained in step 2) is finely finished using an ion beam polishing machine; Existing ion beam polishing equipment generally uses an RF40 ion source, while this invention uses an RF80 large-aperture ion source, and combined with optimized ion beam polishing process parameters, which can greatly improve processing efficiency while ensuring the processing requirements of large-size, high-precision sapphire windows.

[0015] In the above scheme, the maximum diagonal length of the large-size sapphire window is 500-700mm.

[0016] In the above scheme, the large-particle-size diamond liquid is a 5μm diamond liquid; the small-particle-size diamond liquid is a 3μm diamond liquid.

[0017] In the above scheme, due to the large size of the parts, it is recommended to set multiple evenly distributed measurement points for thickness measurement, which can better calculate the average thickness. In the rough grinding, semi-fine grinding and fine grinding steps, 6 to 10 evenly distributed thickness measurement points are set around the sapphire window, and the thickness value of each measurement point is processed until the difference does not exceed 0.03mm.

[0018] In the above scheme, the rough grinding step in step 1) uses 40μm boron carbide auxiliary material, and the single-sided grinding amount is 0.05~0.07mm; the semi-fine grinding step uses 28μm boron carbide auxiliary material, and the single-sided grinding amount is 0.03~0.05mm; the fine grinding step uses 14μm boron carbide auxiliary material, and the single-sided grinding amount is 0.02~0.03mm.

[0019] In the above scheme, the process conditions for the rough grinding step include: spindle speed of 90-100 rpm, swing shaft speed of 30-35 rpm, and pressure of 0.25-0.3 MPa; the process conditions for the semi-fine grinding step include: spindle speed of 90-100 rpm, swing shaft speed of 30-35 rpm, and pressure of 0.2-0.25 MPa; the process conditions for the fine grinding step include: spindle speed of 50-60 rpm, swing shaft speed of 30-35 rpm, and pressure of 0.15-0.2 MPa.

[0020] Preferably, during rough grinding, boron carbide additive with a particle size of 40μm is mixed with water at a mass ratio of 1:2 to 3; the thickness difference at 6 to 10 points around the edge is no more than 0.03mm to ensure the thickness difference of the window part. A single-sided grinding amount of 0.05 to 0.07mm is sufficient to remove the lines left by wire cutting on the surface of the blank material, and the sand holes are uniform across the entire surface.

[0021] Preferably, during semi-finish grinding, the 28μm boron carbide auxiliary material is mixed with water at a mass ratio of 1:2 to 3; the thickness difference at 6 to 10 points around the edge is no more than 0.03mm to ensure the thickness variation of the window parts. A single-sided grinding amount of 0.03 to 0.05mm is sufficient to remove the sand holes left on the surface after grinding the 40μm boron carbide auxiliary material in the rough grinding process, and the sand holes are uniform across the entire surface.

[0022] Preferably, during fine grinding, the 14μm boron carbide auxiliary material is mixed with water at a mass ratio of 1:2 to 3; the thickness difference at 6 to 10 points around the edge is no more than 0.03mm to ensure the thickness variation of the window parts. A single-sided grinding amount of 0.02 to 0.03mm is sufficient to remove the sand holes left on the surface after grinding the 28μm boron carbide auxiliary material in the rough grinding process, and the sand holes are uniform across the entire surface.

[0023] In the above scheme, the process conditions for the rough polishing step include: spindle speed of 100-110 rpm, swing shaft speed of 70-80 rpm, and pressure of 0.3-0.35 MPa for polishing; the process conditions for the fine polishing step include: spindle speed of 5-6 rpm, workpiece ring speed of 8-10 rpm, uniform pressure applied by a pressure block, and pressure of 3-5 MPa.

[0024] Furthermore, the pressure block can be made of stainless steel or the like, and several pressure blocks are evenly distributed on the surface of the sapphire window to apply uniform pressure.

[0025] In the above scheme, the rough polishing step uses a 1.2-meter polyurethane disc single-axis polishing machine. The large-size sapphire aperture is placed in the fixture, and the pen on the swing axis applies pressure to drive the fixture to reciprocate. A 5μm diamond liquid auxiliary material is used, which is mixed with water at a mass ratio of 1:30 to 35. The surface is polished until the aperture number of the entire surface is detected by a Φ150mm flat optical template, and the aperture number at any position is less than 5.

[0026] In the above scheme, the fine polishing step uses a 2.5-meter polyurethane disc ring polisher. The large-size sapphire window is removed from the tooling and placed into the workpiece ring of the 2.5-meter polyurethane disc ring polisher. A 3μm diamond liquid additive is used, which is mixed with water at a mass ratio of 1:30 to 35. The spindle speed is 5 to 6 rpm, and the workpiece ring speed is 8 to 10 rpm. Several 10cm×10cm×5cm stainless steel blocks are used to uniformly press the upper surface of the sapphire window. Medical tape is used to cover the surface to protect it and prevent the glass from being scratched when the pressure blocks are applied. The pressure applied by the pressure blocks is 3 to 5 MPa. The transmission surface shape PV of the part is better than 3.5λ (λ=632.8nm) when detected by a laser interferometer.

[0027] In the above scheme, the finishing steps include: using an ion beam polishing machine with an RF80 ion source, mounting a large-size sapphire optical window in the ion beam polishing machine fixture, an Ar gas flow rate of 12-15 sccm, a Beam voltage of 1.5-1.7KV, an accelerating voltage of 180-200V, a neutralizer voltage of 200-220V, an ion source power of 300-350W, and a processing distance of 50-55mm; using the above finishing conditions, the surface convergence rate can reach over 90%, and the transmission surface shape PV of the part detected by a laser interferometer is better than 1.5λ (λ=632.8nm).

[0028] Using the above-mentioned processing method of the present invention, sapphire optical windows with a maximum diagonal of 500-700mm can be processed, meeting the processing requirements of large size and high precision surface shape, and the surface shape accuracy PV is better than 1.5λ (λ=632.8nm).

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1) This invention employs an optimized grinding and polishing-precision polishing process. First, a cast iron disc single-axis grinding machine is used to perform rough grinding, semi-fine grinding, and fine grinding on large-size sapphire window profiles in sequence. Then, a polyurethane disc single-axis polishing machine with high roughing speed and large-particle diamond slurry is used for rough polishing. Finally, a polyurethane disc ring polishing machine with high fine polishing speed and small-particle diamond slurry is used for fine polishing. Compared with traditional processing techniques, this invention combines and integrates the improved surface accuracy of each process, which can effectively ensure the surface accuracy of large-size sapphire parts and significantly improve polishing efficiency.

[0031] 2) Based on the above grinding and polishing-precision polishing process, this invention further combines the ion beam finishing process based on the RF80 large-aperture ion source and optimized process conditions; by connecting the surface shape accuracy of each process, it promotes the realization of high-precision large-size sapphire window high-quality surface shape accuracy processing, improves processing efficiency, and effectively improves the problems that the existing long-time polishing finishing process easily leads to a large number of bright spots or even rough surfaces on the surface. Attached Figure Description

[0032] Figure 1 The surface shape inspection results of the machined parts obtained from the rough polishing process;

[0033] Figure 2 The surface shape inspection results of the parts processed by the semi-finish polishing process;

[0034] Figure 3 The surface shape inspection results of the parts obtained from the fine polishing process;

[0035] Figure 4 The surface shape inspection results of the parts processed by the ion beam finishing process;

[0036] Figure 5 A model diagram of the removal function for the RF40 ion source;

[0037] Figure 6 A model diagram of the removal function of the RF80 ion source; Detailed Implementation

[0038] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. These descriptions are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0039] In the following embodiments, the preparation steps of the polyurethane disc used in the polyurethane disc single-axis polishing machine include: preparation of the polyurethane disc, using a 1.5mm thick adhesive polyurethane polishing pad, first cleaning the polishing disc surface with alcohol, and then drying the disc surface with a hot air gun, peeling off the back protective film of the prepared adhesive polyurethane polishing pad, and evenly attaching it to the polishing disc surface. After 24 hours, the polyurethane polishing pad is completely adhered and can be used.

[0040] Example

[0041] A high-precision machining method for large-size sapphire optical windows includes the following steps:

[0042] For rough grinding, a 1.2-meter cast iron disc single-axis grinding machine was used. A large sapphire window profile (500mm × 400mm × 8mm) was placed in the fixture. The pendulum shaft applied pressure to drive the fixture in a reciprocating motion. Boron carbide with a particle size of 40μm was used as an auxiliary material, mixed with water at a mass ratio of 1:2. The spindle speed was set to 90 rpm, the pendulum shaft speed to 35 rpm, and the pressure to 0.25 MPa. The grinding depth on one side was 0.05mm, and the sand holes were uniform across the entire surface. Eight thickness measurement points were set around the sapphire window to control the edge thickness difference of the part, with the thickness difference not exceeding 0.03mm.

[0043] For semi-finish grinding, a 1.2-meter cast iron disc single-axis grinding machine was used. The large sapphire window was removed from the fixture and placed into the fixture of another 1.2-meter cast iron disc single-axis grinding machine. The pendulum shaft applied pressure to drive the fixture to reciprocate. Boron carbide auxiliary material with a particle size of 28μm was used, mixed with water at a mass ratio of 1:2 to 3. The spindle speed was 90 rpm, the pendulum shaft speed was 35 rpm, and the pressure was 0.2 MPa. The grinding amount on one side was 0.03 mm, and the sand holes were uniform throughout the surface. Eight thickness measurement points were set around the sapphire window to control the thickness difference of the part, with the thickness difference not exceeding 0.03 mm.

[0044] For fine grinding, a 1.2-meter cast iron disc single-axis grinding machine was used. The large sapphire window was removed from the fixture and placed into the fixture of another 1.2-meter cast iron disc single-axis grinding machine. The pendulum shaft applied pressure to drive the fixture to reciprocate. Boron carbide auxiliary material with a particle size of 14μm was used, mixed with water at a mass ratio of 1:2 to 3. The spindle speed was 60 rpm, the pendulum shaft speed was 30 rpm, and the pressure was 0.15 MPa. The grinding amount on one side was 0.02 mm, and the sand holes were uniform throughout the surface. Eight thickness measurement points were set around the sapphire window to control the thickness difference of the part, with the thickness difference not exceeding 0.03 mm.

[0045] For rough polishing, a 1.2-meter polyurethane disc single-axis polishing machine was used. A large sapphire aperture was placed in the fixture, and the pendulum shaft applied pressure to drive the fixture in a reciprocating motion. A 5μm diamond liquid additive was used, mixed with water at a mass ratio of 1:30 to 35. The spindle speed was 110 rpm, the pendulum shaft speed was 80 rpm, and the pressure was 0.3 MPa. A Φ150mm flat optical template was used to check the number of apertures on the entire surface. The number of apertures at any position was less than 5.

[0046] For fine polishing, a 2.5-meter polyurethane disc polisher is used. The large sapphire window is removed from the fixture and placed into the workpiece ring of the 2.5-meter polyurethane disc polisher. A 3μm diamond slurry is used as an auxiliary material, mixed with water at a mass ratio of 1:30. The spindle speed is 5 rpm and the workpiece ring speed is 10 rpm. The upper surface of the sapphire window is uniformly pressurized using a pressure block, and the surface is covered with medical tape for protection to prevent scratching the glass during pressure application. The total weight pressure of the pressure block should be 3-5 MPa. The transmission surface shape PV of the part is measured using a laser interferometer and is better than 3.5λ (λ=632.8nm).

[0047] For fine finishing, an IBF1000 ion beam polishing machine was used. A large sapphire optical window was installed in the ion beam polishing machine fixture. The parameters were set as follows: 80-80-80 aperture grid, Ar gas flow rate 12 sccm, Beam voltage 1.5KV, accelerating voltage 200V, neutralizer voltage 200V, ion source power 350Wr, and processing distance 50mm. Using the above parameters, the surface convergence rate can reach over 90%. The transmission surface shape PV of the part was detected using a laser interferometer and was better than 1.5λ (λ=632.8nm).

[0048] Figure 1 The surface shape inspection results of the parts processed by the rough polishing process; Figure 2 The surface shape inspection results of the parts processed by the semi-finish polishing process; Figure 3 The surface shape inspection results of the parts obtained from the fine polishing process; Figure 4The image shows the surface shape inspection results of the parts processed by the ion beam finishing process. It can be seen that the processing method described in this invention can guarantee the large-size sapphire optical window. Using the above-mentioned processing method of this invention, the surface shape accuracy requirements corresponding to each process can be achieved. Furthermore, the connection of surface shape accuracy between each process helps to reduce the ion beam finishing cycle and ensure high surface shape accuracy.

[0049] Figure 5 The diagram shows the removal function model of the RF40 ion source. It can be seen that the corresponding FWHM full-peak half-width removal rate is 16 mm, and the ion beam spot diameter is 35 mm. Figure 6 The diagram shows the removal function model of the RF80 ion source. It can be seen that the corresponding FWHM full peak half width removal rate is 34 mm, and the ion beam spot diameter is 60 mm. This invention adopts an ion beam refinement process based on the RF80 large-aperture ion source, combined with optimized ion beam polishing process conditions, which significantly improves processing efficiency while ensuring high surface accuracy processing effect.

[0050] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A high-precision machining method for large-size sapphire optical windows, characterized in that, This includes a sequential grinding and polishing-precision polishing process and an ion beam finishing process, specifically comprising the following steps: 1) Grinding and polishing - precision polishing process; 1-1) Grinding and polishing; A cast iron disc single-axis grinding machine was used to perform rough grinding, semi-finish grinding, and fine grinding on large-size sapphire window profiles in sequence. In this process, boron carbide auxiliary materials and grinding amounts with decreasing size were used in sequence. At the same time, the thickness values ​​of the measurement points were ensured to differ by no more than 0.03 mm. 1-2) Precision polishing; Rough polishing is performed using a polyurethane disc single-axis polishing machine, high rough polishing speed, and large-particle-size diamond liquid auxiliary material until the aperture number at any position of the flat optical sample is less than 5. Fine polishing is performed using a polyurethane disc ring polisher, high fine polishing speed, and small-particle-size diamond liquid additives to achieve a transmission surface shape (PV) better than 3.5λ, where λ = 632.8 nm. 2) Ion beam finishing; The polished sample obtained in step 1) is finished using an ion beam polisher and an RF80 large-aperture ion source; The maximum diagonal length of the large-size sapphire window is 500~700mm; The rough polishing step uses the following process conditions: spindle speed of 100~110 rpm, swing shaft speed of 70~80 rpm, and pressure of 0.3~0.35 MPa; the fine polishing step uses the following process conditions: spindle speed of 5~6 rpm, workpiece ring speed of 8~10 rpm, uniform pressure applied by a pressure block, and pressure of 3~5 MPa. The ion beam finishing process includes: using an ion beam polishing machine with an RF80 ion source, mounting a large-size sapphire optical window into the ion beam polishing machine fixture, and setting parameters including: an 80-80-80 aperture grid, an Ar gas flow rate of 12~15 sccm, a beam voltage of 1.5~1.7KV, an accelerating voltage of 180~200V, a neutralizer voltage of 200~220V, an ion source power of 300~350W, and a processing distance of 50~55mm.

2. The high-precision machining method according to claim 1, characterized in that, In the rough grinding, semi-fine grinding, and fine grinding steps, 6 to 10 evenly spaced thickness measurement points are set around the sapphire window.

3. The high-precision machining method according to claim 1, characterized in that, Step 1-1) The rough grinding step uses 40μm boron carbide auxiliary material, with a single-sided grinding amount of 0.05~0.07mm; the semi-fine grinding step uses 28μm boron carbide auxiliary material, with a single-sided grinding amount of 0.03~0.05mm; the fine grinding step uses 14μm boron carbide auxiliary material, with a single-sided grinding amount of 0.02~0.03mm.

4. The high-precision machining method according to claim 1, characterized in that, The process conditions for the rough grinding step in step 1-1) include: spindle speed 90~100 rpm, swing shaft speed 30~35 rpm, and pressure 0.25~0.3 MPa; the process conditions for the semi-fine grinding step include: spindle speed 90~100 rpm, swing shaft speed 30~35 rpm, and pressure 0.2~0.25 MPa; the process conditions for the fine grinding step include: spindle speed 50~60 rpm, swing shaft speed 30~35 rpm, and pressure 0.15~0.2 MPa.

5. The high-precision machining method according to claim 1, characterized in that, The large-diameter diamond solution is a 5μm diamond solution; the small-diameter diamond solution is a 3μm diamond solution.

6. The high-precision machining method according to claim 1, characterized in that, In the rough polishing step, 5μm diamond solution is mixed with water at a mass ratio of 1:30~35, and the rotation speed is 100~110rpm; in the fine polishing step, 3μm diamond solution is mixed with water at a mass ratio of 1:30~35, the spindle speed is 5~6rpm, and the workpiece ring speed is 8~10rpm.

7. The high-precision machining method according to claim 1, characterized in that, Step 2) The surface convergence rate of the large-size sapphire window obtained is over 90%, and the surface accuracy PV is better than 1.5λ, λ=632.8nm.

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