Processing method of special-shaped plane optical element

Abstract

The invention provides a machining method for a special-shaped plane optical element. The machining method comprises the steps that firstly, a circular blank meeting the high-precision machining process requirement is selected according to a special-shaped element; secondly, the two faces of the circular blank are sequentially ground, roughly polished and finely polished through different machining devices, the machining process is periodically detected, and device parameters are adjusted till corresponding requirements are met; thirdly, rough forming machining is conducted through a sand line machine, the feeding speed is set according to different materials, and rough machining of the shape of the special-shaped element is completed on the basis that the fine polishing face is protected; and 4, a three-axis numerical control machine tool is used for being matched with the part bonding tool and the bonding glass flat plate to fix the appearance rough machining element, and the appearance rough machining element is milled and ground for multiple times to finish shape finish machining of the special-shaped plane optical element. According to the special-shaped plane optical element based on the combination of traditional cold machining and the numerical control technology, efficient and high-precision machining is achieved, and the requirement for batch production is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical cold processing, and particularly relates to a processing method of a special-shaped plane optical element. BACKGROUND

[0002] The plane optical element is an important component of an optoelectronic system. With the increasingly high imaging precision requirement of an optical system and the increasingly complex shape design of an optoelectronic detection assembly, the surface shape precision requirement of the plane optical element is also increasingly high, and the shape of the plane optical element is usually irregular, the glass side edge is designed with a wedge angle for easy installation, and the size of the plane optical element is large.

[0003] The large-aperture plane optical element ultra-precision processing technology disclosed by the National Science and Technology Library Center uses online electrolytic technology (ELID) grinding instead of traditional milling and initial polishing processes, and uses numerical control polishing to polish the workpiece to the final surface shape precision, which can improve production efficiency and reduce edge effects. However, this processing technology uses continuous polishing as the final processing process, although the surface roughness and waviness of the processed workpiece can meet the engineering requirements, but it inevitably leads to installation errors, which in turn causes the processed workpiece to fail to meet the design requirements or use requirements.

[0004] The shape processing quality of a large-aperture optical element is one of the key problems in the entire system, which can improve the beam quality of the entire system. The patent document with the publication number CN110394601B discloses a numerical control processing method for a multi-dimensional optical window part. The two polished surfaces of the part are protected by coating protective paint and adhesive tape, and the part is attached to a special tooling after being attached to the tooling by a rounding adhesive, and then installed on the machine tool mounting surface. The numerical control five-axis grinding processing method can complete the high-precision and lossless forming processing of the part through one clamping and multiple milling and grinding processing. The patent document can achieve high-precision and lossless processing of the part by protecting the two surfaces of the polished part, one clamping, and controlling the single milling and grinding processing amount, which meets the process requirements of batch processing.

[0005] The patent document with the publication number CN114871902B discloses a large-aperture ultra-diameter-thickness-ratio special-shaped plane optical part flexible polishing disc. The subsequent processing of the special-shaped structure can discard the matching shape polishing disc required in the special-shaped part polishing process, and only a circular part processing polishing disc is needed, which includes a special-shaped part to be processed and a special-shaped adhesive mold. The special-shaped part to be processed is attached to the special-shaped adhesive mold by adhesive before polishing processing, which significantly improves the surface quality of batch processing of high special-shaped plane optical elements and reduces the difficulty of batch processing.

[0006] With Figure 1Taking a planar optical element as an example (420mm diagonal), its shape is dodecagonal, and its surface accuracy (RMS ≤ λ / 20 for transmitted wavefront, λ = 632.8nm) makes it difficult to manufacture. The traditional method is to first shape the part, then grind and polish it. This method is inefficient, time-consuming, and difficult to guarantee accuracy, making it unsuitable for mass production. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies that cannot guarantee processing accuracy and are difficult to mass-produce. Instead, it provides a processing method for irregularly shaped planar optical elements. By combining traditional cold working and CNC technology, it meets the needs for precision processing of various types of irregularly shaped planar optical elements. The processing scheme that sequentially transfers the accuracy of each process achieves efficient and high-precision processing of irregularly shaped planar optical elements, thereby meeting the requirements for mass production.

[0008] To achieve the above objectives, the technical solution provided by this invention is:

[0009] A method for fabricating an irregularly shaped planar optical element, comprising:

[0010] Step 1: Select a round blank that meets the high-precision machining requirements based on the irregularly shaped component;

[0011] Step 2: Grind, rough polish, and fine polish the two sides of the circular blank in sequence on different processing equipment until the surface shape processing accuracy required for the two sides of the optical element is achieved. Periodically check the processing process and adjust the polishing equipment parameters until the surface shape and surface quality of the processed parts meet the corresponding requirements.

[0012] Step 3: Use a wire sander for rough forming. Set the feed speed according to the material to complete the rough forming of the irregular component while protecting the polished surface.

[0013] Step 4: Using a three-axis CNC machine tool, along with a parts bonding fixture and a glass plate bonding fixture, the rough-machined components are milled multiple times until the shape of the irregular planar optical components is finished, thus achieving the precision forming of the irregular planar optical components.

[0014] As a further limitation of the present invention, step one specifically includes:

[0015] The size of the circular blank is determined to be 40 mm - 50 mm larger than its outer envelope based on the outer envelope of the irregular component. After most of the outer shape allowance is cut off by the sanding machine, the remaining outer shape allowance is less than 2 mm. It is then milled in at least two cycles by a three-axis CNC machine tool until its shape meets the precision of fine grinding.

[0016] As a further limitation of the present invention, step two specifically includes:

[0017] The circular blank is ground on both sides using diamond abrasive on a grinding machine. The surface shape, surface sand holes and parallelism of the blank part are checked using a flatness measuring fixture, magnifying glass and micrometer. This process is repeated until the circular blank meets the accuracy requirements of flatness, sand holes and parallelism for rough polishing.

[0018] The circular components are rough polished on both sides using an asphalt mold and polishing powder on a polishing machine. The asphalt mold is made according to the size of the part. The surface shape, parallelism, thickness and surface defects of the part are detected by a laser plane interferometer, a comparative goniometer, a micrometer and a magnifying glass.

[0019] The circular parts are finely polished on both sides on a ring polishing machine. A laser interferometer is used to inspect the surface shape of the circular optical element, and the machine parameters are adjusted according to the inspection results. A digital laser interferometer, magnifying glass, comparative goniometer and micrometer are used to inspect the surface shape, surface quality, parallelism and thickness of the circular optical element. If the surface shape and surface quality do not meet the requirements of the drawing, the above process is returned to repeat the fine polishing.

[0020] As a further limitation of the present invention, the process of surface shaping using a grinding machine, a polishing machine, and a ring polishing machine in step two also includes:

[0021] The process of grinding both sides of a round blank on a grinding machine and checking its surface shape using a traditional inspection instrument is repeated alternately until the rough polishing accuracy requirements are met.

[0022] The asphalt mold was designed based on the polishing machine. The designed asphalt mold was 20% larger than the rough polishing parts. The polishing machine was used to check the parts every 1-2 hours during the rough polishing process. The machine parameters were adjusted according to the test results until all indicators met the requirements of the ring polishing accuracy.

[0023] The tooling is designed according to the size of the circular optical element. The surface shape of the asphalt base is trimmed using the correction disc on the machine tool. The circular element is placed in the separator and the circular optical element is rough polished and fine polished using a ring polisher. The surface shape of the circular optical element is detected by a laser interferometer. The fine polishing process is checked every 2-3 hours. The machine tool parameters are adjusted according to the detection results.

[0024] As a further limitation of the present invention, step three includes:

[0025] The circular part is subjected to micro-stress rough forming on the sanding machine. The rough forming model is designed according to the part model and imported into the machine tool. The rough forming model is required to be 2mm larger on one side than the part model. The circular optical element is clamped on the machine tool to ensure that the sanding feed direction is consistent with the direction of the machine tool software. The feed speed is set according to the material during the rough forming process.

[0026] As a further limitation of the present invention, the protection of the polished surface in step three specifically refers to:

[0027] Protect the two polished surfaces of the round parts with protective paint and adhesive tape to ensure that the shape of the parts is rough-formed and fine-formed on a sanding machine and a three-axis CNC machine tool, respectively.

[0028] As a further limitation of the present invention, step four includes:

[0029] In a three-axis CNC machine tool, irregular planar optical elements are precision shaped. According to the size of the element, a bonding fixture and a bonding glass plate are designed. The rough-shaped optical element and the float glass plate are bonded to the bonding fixture. The fixture is fixed on the machine tool mounting surface with a pressure plate. Then, the irregular optical element is leveled and the side of the optical element is milled with a bullnose grinding wheel. The shape of the optical element is inspected until the shape of the irregular planar optical element is finished.

[0030] As a further limitation of the present invention, in step four, during the milling and grinding process on a three-axis CNC machine tool, the machine tool first mills one round, leaving a margin of 0.5mm-1mm; then it mills one round, leaving a margin of 0mm-0.1mm; then it uses a three-coordinate measuring machine to inspect the shape of the irregular planar optical element; finally, it mills one round again based on the measurement results to complete the finishing of the irregular shape.

[0031] The advantages of this invention are:

[0032] 1. This invention is a processing method for irregularly shaped planar optical elements based on a combination of traditional cold working and CNC technology. It combines the advantages of various processing methods such as grinding, polishing, wire cutting, and three-axis milling, with reasonable precision transfer between each process. It solves the problem of difficult surface shape control for large-size irregularly shaped planar optical elements and is suitable for mass production requirements. Engineering practice has proven that this invention achieves efficient and high-precision processing of irregularly shaped planar optical elements, with a 100% pass rate and a 30% increase in processing efficiency.

[0033] 2. This invention first determines the size of the circular blank based on the envelope of the irregularly shaped component, then grinds, rough polishes, and ring polishes the circular blank to meet the drawing requirements. After that, the part is subjected to micro-stress rough forming and fine forming. The processing technology of this invention first uses ordinary processing equipment to control the grinding and polishing process based on the polished surface shape of the circular part, avoiding the difficulty in controlling the surface processing accuracy of irregularly shaped components during the surface processing. Then, ordinary processing equipment is used to effectively protect the polished surface of the part that has reached the polishing accuracy before irregular micro-stress forming is performed. This solves the problem of difficult surface shape control for large-size irregularly shaped planar optical components and is suitable for mass production needs.

[0034] 3. This invention uses a three-axis CNC machine tool instead of a five-axis machining center to perform precision forming of large-size planar optical components. This ensures high-precision milling and grinding of parts in both planar and irregular shapes, while also controlling milling variables, number of milling cycles, and machining feed parameters to improve processing efficiency. Furthermore, using a conventional CNC machine tool can reduce the expensive equipment cost of a five-axis machining center.

[0035] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0037] Figure 1 This invention provides a flowchart of a method for fabricating irregularly shaped planar optical elements;

[0038] Figure 2 : Flowchart of the fabrication process of the irregular planar optical element provided by the present invention;

[0039] Figure 3 Two-dimensional diagram of the irregular planar optical element provided by this invention;

[0040] Figure 4 The present invention provides a circular blank size diagram derived from the outer envelope of the component.

[0041] Figure 5 The two-dimensional diagram of the planar element of the flatness measuring fixture provided by this invention;

[0042] Figure 6 The present invention provides a two-dimensional rough forming diagram of an irregular planar element;

[0043] Figure 7 : Two-dimensional drawing of the special tooling for bonding parts provided by the present invention. Detailed Implementation

[0044] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0045] See Figure 1 This invention provides a method for fabricating irregularly shaped planar optical elements, in order to... Figure 2 The processing procedure shown is as follows: Figure 3 The irregularly shaped component shown is the object to be processed. The processing method includes the following steps:

[0046] Step 1: Determine the dimensions of the circular blank based on the outer envelope of the irregularly shaped part. The dimensions of the circular blank should be 40mm-50mm larger than the outer envelope of the irregularly shaped part (e.g., ...). Figure 4 As shown, after both sides are finely polished and qualified, the component is first cut off most of the outer shape allowance by a sanding machine. The remaining outer shape allowance is less than 2mm, and then milled by a three-axis CNC machine tool in at least two cycles until the shape of the part meets the precision of fine grinding of irregular shape. The outer diameter of the circular blank of the irregular shape component is preferably 465mm.

[0047] Step 2: Grind, rough polish, and fine polish both sides of the circular blank in sequence on different processing equipment until the surface shape processing accuracy requirements of the irregular planar optical element are met. Periodically check the processing process and adjust the polishing equipment parameters until the surface shape and surface quality of the irregular element meet the corresponding requirements. Specifically: (1) Use 303# diamond abrasive to grind both sides of the round blank on a grinding machine. The grinding amount on one side is about 0.03mm. Use a flatness measuring fixture, a 6x magnifying glass and a micrometer to check the surface shape, surface sand holes and parallelism of the blank part. Repeat this process, allowing the grinding on both sides and the various checks to be repeated alternately until the round blank meets the accuracy requirements of flatness, sand holes and parallelism for rough polishing. The grinding disc is made of cast iron, and the surface of the cast iron disc is provided with concentric circular grooves to facilitate abrasive storage and full grinding of the components; (2) Use asphalt mold and polishing powder to design the asphalt mold on a polishing machine. The designed asphalt mold is 20% larger than the rough polished part. Make the corresponding asphalt mold according to the size of the part; Use asphalt mold and polishing powder to rough polish both sides of the round component on a polishing machine. Make the corresponding asphalt mold according to the size of the irregular part. The diameter of the asphalt mold is about 560mm, which is about 20% larger than the irregular part. The surface shape, parallelism, thickness and surface defects of the parts were inspected using a laser plane interferometer, a comparative goniometer, a micrometer and a 6x magnifying glass. The polishing machine was used to inspect the parts every 1-2 hours during the rough polishing process. The machine tool parameters were adjusted according to the inspection results until the various indicators of the circular element met the technical requirements of ring polishing. (3) The above process was repeated until the inspection was qualified. Then the two sides of the circular element were finely polished on the ring polishing machine. The tooling fixture was designed according to the size of the circular optical element. The material was polytetrafluoroethylene. Then the surface shape of the asphalt base was trimmed using the correction disc on the machine tool. The circular element was placed in the separator and the ring polishing machine was used to rough polish the circular element. For the fine polishing of the circular optical element, a laser interferometer is used to inspect the surface shape of the part. The fine polishing process is carried out every 2-3 hours. The machine tool parameters are adjusted according to the inspection results until the various indicators of the circular element meet the corresponding technical requirements. (4) After the above processing is completed, the surface shape accuracy is inspected. A digital laser interferometer, a 6x magnifying glass, a comparative angle measuring instrument and a micrometer are used to inspect the surface shape, surface quality, parallelism difference and thickness of the circular optical element. If the surface shape and surface quality do not meet the requirements of the drawing, the above process is returned to repeat the fine polishing. When the surface shape and surface quality meet the requirements, the process is transferred to the next process to process the shape.

[0048] The flatness measuring fixture and ring polishing fixture in step two of this embodiment of the invention, and the bonding glass plate and part bonding fixture in step four, all need to be specially designed according to the part dimensions. The flatness measuring fixture is illustrated in the diagram for inspecting the planar optical element under test. Figure 5 It is suitable for surface shape inspection of optical components in mass production processes. Figure 5The flatness measuring fixture is designed with a pull rod, which can measure the flatness of different diameters, with specifications of Φ100 mm - Φ250 mm and Φ250 mm - Φ500 mm. Similarly, in step four of this embodiment, the bonded glass plate used is 20 mm - 30 mm larger on one side than the part, and the parallelism difference between the two surfaces is required to be ≤0.005. Figure 7 The bonding fixture shown is 20mm-30mm larger on one side than the glass surface to be bonded, and the parallelism difference between the bonding surface and the mounting surface must be ≤0.005. In the embodiment of the invention, the ring polishing fixture used in step two is 0.5mm-1mm larger on one side than the part being processed, and 1mm-1.5mm smaller in height. Furthermore, the bullnose grinding wheel used in step four of the embodiment of the invention needs to be specially designed and processed according to the size and characteristics of the part, and a through hole is provided in the center of the grinding wheel to ensure a significant cooling effect during processing.

[0049] Step 3: Perform micro-stress rough forming on a wire abrasive machine. Use protective varnish and adhesive tape to protect the two polished surfaces of the part. Design a rough forming model based on the part model and import it into the machine tool. The rough forming model should be 2mm larger on each side than the part model. Clamp the circular optical element onto the machine tool, ensuring that the wire abrasive feed direction is consistent with the machine tool software direction. During the rough forming process, set the feed rate according to the material (preferably 0.05mm / min). Complete the rough forming of the irregularly shaped element while protecting the polished surfaces. The shape of the circular optical element completed by micro-stress rough forming is as follows: Figure 6 As shown. Preferably, protective paint and adhesive tape are used to protect the two polished surfaces of the circular part, ensuring that the irregular planar component is precision-formed on a sanding machine and a three-axis CNC machine tool respectively. Preferably, rough forming and fine forming are performed according to the shape of the part.

[0050] The wire cutting machine described in this embodiment of the invention is a type of wire EDM, which uses wire as the cutting medium. The three-axis CNC machine tool described in this embodiment can process complex curved surfaces of parts. Wire EDM in this embodiment is typically used for high-hardness materials, offering high processing accuracy. Combining wire EDM and grinding, it is suitable for roughing, removing a large amount of material. Simultaneously, because the wire EDM process generates less heat, it may reduce thermal stress, making it suitable for micro-stress forming, reducing residual stress and deformation, and providing a better foundation for subsequent three-axis precision machining. The three-axis CNC machine tool is more flexible and suitable for grinding complex shapes. To avoid generating grinding force or heat during processing, this embodiment of the invention designs the grinding amount to be less than 2mm, while ensuring the shape accuracy during five-axis machining and the surface accuracy of the finished product. It eliminates the need for rework to correct the surface shape after the required shape accuracy is met, making it suitable for batch processing of irregularly shaped planar optical components, ensuring the accuracy and quality of the final workpiece.

[0051] Step 4: Using a three-axis CNC machine tool with a part bonding fixture and a bonding glass plate to fix the rough-machined component, perform multiple milling operations until the shape of the irregular planar optical component is finished. During the precision forming process of the irregular planar optical component on the three-axis CNC machine tool, design the bonding glass plate and bonding fixture according to the component size. The bonding glass plate is made of float glass, and the bonding fixture is made of hard aluminum. Glue the rough-formed part and float glass plate to the bonding fixture, and fix the fixture on the machine tool mounting surface with a pressure plate. Then, level the irregular optical component and mill the side of the optical component with a bullnose grinding wheel. Preferably, during the milling process, mill one turn first, leaving a 0.5mm-1mm allowance; then mill one turn again, leaving a 0mm-0.1mm allowance. Then, a coordinate measuring machine (CMM) is used to inspect the shape of the optical element. Finally, based on the measurement results, milling is performed again to complete the fine machining of the irregular planar optical element. This embodiment of the invention uses a three-axis CNC machine tool in conjunction with part bonding fixtures and bonding glass plates to ensure high-precision surface accuracy of the element while performing milling and fine machining. This ensures that the surface accuracy and shape machining accuracy meet the inspection requirements, achieving the precision forming of the irregular planar optical element. This embodiment of the invention is a processing method for irregular planar optical elements based on a combination of traditional cold working and CNC technology. It takes into account the advantages of various processing methods such as grinding, polishing, wire cutting, and three-axis milling, and the accuracy transfer of each process is reasonable and suitable for batch processing. Engineering practice has proved that this embodiment of the invention achieves efficient and high-precision machining of irregular planar optical elements, with a processing pass rate of 100% and a 30% increase in processing efficiency. This invention first determines the size of a circular blank based on the envelope of the irregularly shaped component. Then, the circular blank is ground, rough polished, and circumferentially polished to meet the drawing requirements. Afterward, the part undergoes micro-stress rough forming and precision forming. The processing technology of this invention allows for controlled grinding and polishing using ordinary machining equipment based on the polished surface shape of the circular part, avoiding the difficulty in controlling the surface machining accuracy of irregularly shaped components. Then, after achieving the polished accuracy, ordinary machining equipment is used to effectively protect the polished surface before performing irregularly shaped micro-stress forming. This solves the problem of difficult surface shape control for large-size irregularly shaped planar optical components and is suitable for mass production. In this embodiment, a three-axis CNC machine tool replaces a five-axis machining center for precision forming of large-size planar optical components, ensuring machining accuracy, improving machining efficiency, and reducing the expensive equipment cost of five-axis machining centers.

[0052] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for fabricating an irregularly shaped planar optical element, characterized in that, include: Step 1: Select a round blank that meets the high-precision machining requirements based on the irregularly shaped component; Step 2: Grind, rough polish, and fine polish the two sides of the circular blank in sequence on different processing equipment until the surface shape processing accuracy required for the two sides of the optical element is achieved. Periodically check the processing process and adjust the polishing equipment parameters until the surface shape and surface quality of the processed parts meet the corresponding requirements. Step 3: Use a wire sander for rough forming. Set the feed speed according to the material to complete the rough forming of the irregular part while protecting the polished surface. Step 4: Using a three-axis CNC machine tool, along with a parts bonding fixture and a glass plate bonding fixture, the rough-machined components are milled multiple times until the shape of the irregular planar optical components is finished, thus achieving the precision forming of the irregular planar optical components.

2. The method for fabricating an irregularly shaped planar optical element according to claim 1, characterized in that, Step one specifically involves: The size of the circular blank is determined to be 40mm-50mm larger than its outer envelope based on the outer envelope of the irregular component. After the subsequent processing, most of the outer shape allowance is cut off by the sanding machine, and the remaining outer shape allowance is less than 2mm. It is then milled by a three-axis CNC machine tool in at least two cycles until its shape meets the precision of fine grinding.

3. The method for fabricating an irregularly shaped planar optical element according to claim 1, characterized in that, Step two specifically involves: The two sides of the circular blank are ground separately on a grinding machine using diamond abrasive. The surface shape, surface sand holes and parallelism of the blank part are checked using a flatness measuring fixture, magnifying glass and micrometer. This process is repeated until the circular blank meets the accuracy requirements of flatness, sand holes and parallelism for rough polishing. The two sides of the circular part are coarsely polished sequentially on a polishing machine using asphalt mold and polishing powder. The asphalt mold is made according to the size of the part. The surface shape, parallelism, thickness and surface defects of the part are detected by laser plane interferometer, comparative goniometer, micrometer and magnifying glass. The circular parts are finely polished on both sides on a ring polishing machine. A laser interferometer is used to inspect the surface shape of the circular optical element, and the machine parameters are adjusted according to the inspection results. A digital laser interferometer, magnifying glass, comparative goniometer and micrometer are used to inspect the surface shape, surface quality, parallelism and thickness of the circular optical element. If the surface shape and surface quality do not meet the requirements of the drawing, the above process is returned to repeat the fine polishing.

4. The method for fabricating an irregularly shaped planar optical element according to claim 1, characterized in that, Step two, the process of surface shaping using a grinding machine, polishing machine, and ring polisher, also includes: The process of grinding both sides of the round blank with a grinding machine and checking its surface shape with a traditional measuring instrument was repeated alternately until the rough polishing accuracy requirements were met. The asphalt mold was designed based on the polishing machine. The designed asphalt mold was 20% larger than the rough polishing parts. The polishing machine was used to check the parts every 1-2 hours during the rough polishing process. The machine parameters were adjusted according to the test results until all indicators met the requirements of the ring polishing accuracy. The tooling is designed according to the size of the circular optical element. The surface shape of the asphalt base is trimmed using the correction disc on the machine tool. The circular element is placed in the separator and the circular optical element is rough polished and fine polished using a ring polisher. The surface shape of the circular optical element is detected by a laser interferometer. The fine polishing process is checked every 2-3 hours. The machine tool parameters are adjusted according to the detection results.

5. The method for fabricating an irregularly shaped planar optical element according to claim 1, characterized in that, Step three includes: The circular optical element is subjected to micro-stress rough forming on a sanding machine. A rough forming model is designed based on the part model and imported into the machine tool. The rough forming model is required to be 2mm larger on one side than the part model. The circular optical element is clamped onto the machine tool to ensure that the sanding feed direction is consistent with the direction of the machine tool software. During the rough forming process, the feed speed is set according to the different materials.

6. The method for fabricating an irregularly shaped planar optical element according to claim 1, characterized in that, The protection of the polished surface in step three specifically involves: Protect the two polished surfaces of the round parts with protective paint and adhesive tape to ensure that the shape of the parts is rough-formed and fine-formed on a sanding machine and a three-axis CNC machine tool, respectively.

7. The method for fabricating an irregularly shaped planar optical element according to claim 1, characterized in that, Step four includes: On a three-axis CNC machine tool, irregular planar optical elements are precision shaped. According to the size of the element, a bonding fixture and a bonding glass plate are designed. The rough-shaped optical element and the float glass plate are bonded to the bonding fixture. The fixture is fixed on the machine tool mounting surface with a pressure plate. Then, the irregular optical element is leveled and the side of the optical element is milled with a bullnose grinding wheel. The shape of the optical element is inspected until the shape of the irregular planar optical element is finished.

8. The method for fabricating an irregularly shaped planar optical element according to claim 7, characterized in that, In step four, during the milling process on a three-axis CNC machine tool, the machine first mills one round, leaving a margin of 0.5mm-1mm; then it mills another round, leaving a margin of 0mm-0.1mm; then it uses a coordinate measuring machine to inspect the shape of the irregular planar optical element; finally, it mills one more round based on the measurement results to complete the finishing of the irregular shape.

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