Zinc selenide aspherical lens and numerical control polishing process thereof

Abstract

The application relates to the technical field of optical processing, and provides a zinc selenide aspheric lens and a numerical control polishing process thereof, which is carried out by using a numerical control polishing machine, comprises main steps of rough polishing, fine polishing, finishing and the like, and process parameters are adjusted according to the characteristics of zinc selenide, so that the zinc selenide aspheric lens with a diameter of less than 320 mm can be polished, the global surface type PV of the zinc selenide aspheric lens is controlled to be less than 0.3 microns by means of the numerical control polishing machine, white zinc metal particles generated due to heating of the lens surface in the polishing process are avoided, the surface smoothness of the finished product reaches 60 / 40, and the laser level is reached. The application also has reference significance for polishing the surface of zinc selenide with a diameter of more than 320 mm.

Description

Technical Field

[0001] This invention relates to the field of optical processing technology, specifically to a zinc selenide aspherical lens and its CNC polishing process. Background Technology

[0002] Aspherical lenses come in shapes including parabolic, quadratic, cubic, or higher-order curves, and their design must consider correction factors such as phase aberration, chromatic aberration, and spherical aberration. Typically, a single aspherical lens can effectively replace multiple spherical lenses, thereby reducing the number of lenses, improving lens precision and sharpness, enhancing color reproduction, reducing light reflection, and simultaneously reducing lens size. Aspherical lenses are characterized by high zoom, short object distance, and large aperture. High zoom simplifies lens types, short object distance is suitable for close-up photography, and large aperture allows for use in low-light environments, thus their applications are becoming increasingly widespread.

[0003] Zinc selenide is a yellow, transparent polycrystalline material with crystal grains of approximately 70 μm and a transmittance range of 0.5–15 μm. Zinc selenide synthesized via chemical vapor deposition (CVD) exhibits almost no impurity absorption and extremely low scattering loss. Due to its minimal absorption at a wavelength of 10.6 μm, zinc selenide has become the preferred material for optical components in high-power CO2 laser systems. Furthermore, it is widely used in various optical systems across the entire transmittance band. Zinc selenide possesses strong thermal shock resistance, making it an ideal optical material for high-power CO2 lasers. However, its hardness is only 2 / 3 that of multispectral grade ZnS, making it relatively soft and easily scratched. Additionally, its high refractive index necessitates the deposition of a high-hardness antireflective coating on its surface to protect it and improve transmittance. Simultaneously, zinc selenide exhibits very low scattering within the commonly used spectral range. When used in high-power laser devices, strict control of the material's bulk absorption and internal structural defects is required.

[0004] CN1785560A discloses a method for processing aspherical optical elements, mainly used for processing zinc selenide and zinc sulfide aspherical optical elements. Its main technical feature is the use of a computer numerical control lathe and diamond circular arc cutting tools to perform cutting on zinc selenide and zinc sulfide. However, using single-point turning makes it difficult to control the surface finish of zinc selenide aspherical lenses to achieve laser-grade finish. Furthermore, the pitting problem on the polished surface of zinc selenide aspherical lenses has always been a challenge in the infrared industry. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a zinc selenide aspherical lens and its CNC polishing process. This CNC polishing process utilizes a CNC polishing machine to perform aspherical polishing on zinc selenide lenses. It can polish zinc selenide aspherical lenses with a diameter of up to 320mm, reducing the mid-frequency error of the zinc selenide aspherical surface and controlling the global surface area (PV) of the zinc selenide aspherical lens to below 0.3μm, achieving laser-grade surface finish. It also has reference value for polishing zinc selenide surfaces larger than 320mm.

[0006] The technical solution of this invention is:

[0007] A CNC polishing process for zinc selenide aspherical lenses, based on a CNC polishing machine, includes the following steps:

[0008] Step 1: Perform contour scanning on the zinc selenide aspherical lens to obtain the contour model;

[0009] Step 2: Based on the contour model, use a CNC polishing machine to perform rough polishing on the zinc selenide aspherical lens;

[0010] Step 3: Perform contour scanning on the rough-polished zinc selenide aspherical lens to obtain a new contour model;

[0011] Step 4: Based on the contour model obtained in Step 3, the zinc selenide aspherical lens is finely polished using a CNC polishing machine;

[0012] Step 5: Refine and polish to obtain the finished product.

[0013] In practical applications, this application uses polishing to obtain zinc selenide with a surface finish reaching laser level. The setting parameters of the CNC polishing machine are adjusted according to the lens and polishing fluid to avoid damage to the zinc selenide aspherical lens by the CNC polishing machine, which would cause irreparable defects.

[0014] In the above-mentioned CNC polishing process of zinc selenide aspherical lenses, if the surface shape PV of the contour model in step 3 is greater than the drawing requirements, return to step 2; if the surface shape PV is less than the drawing requirements, proceed to step 4.

[0015] In the above-mentioned CNC polishing process of zinc selenide aspherical lenses, the polishing liquid used for rough polishing is a mixed solution of 1-2μm alumina, ammonium dichromate, oily suspending agent and pure water, wherein the ratio of alumina:ammonium dichromate:oily suspending agent:pure water is 40:1:60:299.

[0016] In the above-mentioned CNC polishing process of zinc selenide aspherical lenses, step 5 involves transferring the zinc selenide aspherical lens to a polishing machine, adding ammonium dichromate solution to wet the zinc selenide aspherical lens, rotating the zinc selenide aspherical lens at a speed of 100-200 RPM, and then using a polishing pad to finely repair the zinc selenide aspherical lens at a pressure of 4-6 kPa, with polishing liquid and ammonium dichromate solution continuously dripped in during the process.

[0017] In the above-mentioned CNC polishing process of zinc selenide aspherical lenses, before step 1, a zinc selenide aspherical lens with a surface area PV ≤ 2μm is prepared by milling, and the sharp edges at the edges of the zinc selenide aspherical lens are removed.

[0018] In the above-mentioned CNC polishing process for zinc selenide aspherical lenses, in step 2, the actual indentation diameter is compared with the theoretically calculated indentation size, and the height of the rough polishing fixture is adjusted according to the difference to make the theoretical indentation size equal to the actual indentation size.

[0019] In the above-mentioned CNC polishing process for zinc selenide aspherical lenses, the parameter settings of the CNC polishing machine meet the following conditions:

[0020] Set a) When the polishing slurry particle size is 0.5-1μm and the lens diameter is less than 150mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 800-1000RPM and the downward pressure to 0.5-0.7mm.

[0021] Set b, when the polishing slurry particle size is 0.5-1μm and the lens diameter is greater than 150mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 300-500RPM and the downward pressure to 0.5-0.7mm.

[0022] Set c, when the polishing slurry particle size is 1-2μm and the lens diameter is less than 150mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 300-500RPM and the downward pressure to 0.2-0.4mm.

[0023] Set d: When the polishing fluid particle size is 1-2 μm and the lens diameter is greater than 150 mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 150-300 RPM and the downward pressure to 0.2-0.4 mm.

[0024] In the above-mentioned CNC polishing process for zinc selenide aspherical lenses, the remaining settings of the CNC polishing machine in step 2 are as follows:

[0025] The size of the polishing head is one-third to one-quarter of the set lens diameter;

[0026] The correction setting is -30% to -60%.

[0027] The track-pitch value in the path data is set to one percent of the lens diameter;

[0028] The unit of oscillation-time is seconds, and its value is 3 to 5 times the set lens diameter;

[0029] In extrapolate, the filter width is set to 1 / 100 of the lens diameter, the point distance is set to 1 / 100 of the lens diameter, and the target diameter is the effective aperture plus 5-10mm.

[0030] Perform a smoothing process with a smoothing value of 2–3 μm.

[0031] Adjust the values ​​of removal-coefficient and oscillation-time to set the value of feedmin. to 10 mm / min.

[0032] In the above-mentioned CNC polishing process for zinc selenide aspherical lenses, the settings for the CNC polishing machine in step 4 are as follows:

[0033] The polishing slurry particle size is 0.5–1 μm, the pressure is 0.1–0.2 mm, and the other settings are the same as for coarse polishing.

[0034] In addition, this application also provides a zinc selenide aspherical lens with a diameter of less than 320 mm, which is manufactured by the above-mentioned CNC polishing process for zinc selenide aspherical lenses.

[0035] The polishing process described in this application can polish zinc selenide aspherical lenses with a diameter of less than 320mm. With the help of a CNC polishing machine, the global surface area (PV) before optimization can be reduced to less than 0.3μm, and the surface finish can be 60 / 40, reaching laser grade.

[0036] One of the above-described technical solutions of the present invention has at least one of the following advantages or beneficial effects:

[0037] The polishing process of this invention can polish zinc selenide aspherical lenses with a diameter of less than 320mm. With the help of a CNC polishing machine, the PV of the optimized front profile can be reduced to less than 0.3μm. The white zinc metal particles generated during the polishing process are removed to avoid the heat on the lens surface, so that the surface finish of the finished product reaches 60 / 40, which is laser grade and can be used in lasers.

[0038] Meanwhile, compared to single-point turning, polishing can improve processing efficiency and surface finish when machining zinc selenide aspherical lenses, and also save the cost of frequent tool changes.

[0039] Furthermore, this application can also control the stability of the polished surface more precisely by controlling the amount of downward pressure. Attached Figure Description

[0040] Figure 1 This is an optical surface diagram of the aspherical lens after milling according to Embodiment 1 of the present invention;

[0041] Figure 2 This is an optical surface pattern of the aspherical lens obtained in Embodiment 1 of the present invention;

[0042] Figure 3 This is an optical surface pattern of the aspherical lens obtained in Embodiment 3 of the present invention;

[0043] Figure 4 This is an optical surface diagram of the aspherical lens obtained in Comparative Example 1 of the present invention;

[0044] Figure 5 This is an optical surface diagram of the aspherical lens obtained in Comparative Example 2 of the present invention;

[0045] Figure 6 This is an optical surface diagram of the aspherical lens obtained in Comparative Example 3 of the present invention;

[0046] Figure 7 This is a microscope view of the aspherical lens prepared in Comparative Example 5 of the present invention;

[0047] Figure 8 This is a schematic diagram illustrating the interaction between the polishing head and the lens during the finishing process of this invention.

[0048] Figure 9 This is a schematic diagram of the computational theory of indentation according to the present invention.

[0049] Figure 10 This is a simplified flowchart of the processing flow of the present invention.

[0050] Explanation of reference numerals in the attached figures:

[0051] 1. Polishing head; 2. Lens. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0053] In the following examples, the CNC polishing machine is model Satis Loh SPS-200; the CNC milling machine is model Satis Loh SPM-200; and the profilometer is model LUPHOSCAN 260HD 3D. Furthermore, the drawing requires PV < 5.

[0054] Explanation of the CNC polishing machine parameter settings in the text:

[0055] correction: edge dwell rate; track-pitch value in path data: helix pitch; oscillation-time: time required for one round of polishing; filter width in extrapolate: sampling helix pitch; point distance: distance between sampling points; target diameter: target diameter; smooth: smoothing process; min.Height: removal amount; removal-coefficient: dwell time; feed min.: minimum movement speed of the polishing head.

[0056] Example 1

[0057] refer to Figure 1 , 2 A CNC polishing process for zinc selenide aspherical lenses, in this embodiment, the actual diameter of the zinc selenide aspherical lens is 118 mm, and its composition includes a mixed solution of alumina, ammonium dichromate, oily suspending agent and pure water, prepared in a ratio of 40:1:60:299; Figure 10 As shown, it includes the following steps:

[0058] Milling: A CNC milling machine is used to adjust the surface profile of the zinc selenide aspherical lens to below 2μm. Otherwise, medium-to-high frequency surface profile errors will occur during polishing, making it difficult to control the polished surface profile to below 0.5μm. It is also necessary to chamfer or sandpaper grind the edges to remove sharp edges and prevent damage to the polishing skin. The milled surface profile is as follows: Figure 1 As shown.

[0059] Contour scanning: Contour scanning is performed on zinc selenide aspherical lenses with a face size ≤2μm to obtain the first contour model;

[0060] Rough polishing: Fix the zinc selenide aspherical lens and its tooling inside the CNC polishing machine, import the first contour model into the CNC polishing machine to calculate the rough polishing program and start rough polishing;

[0061] Contour scanning: The contour of the rough-polished zinc selenide aspherical lens is scanned to obtain a second contour model; the subsequent processing flow is determined based on the surface shape of the second contour model. The determination process is as follows:

[0062] When the PV of its surface is less than that required by the drawing, proceed to fine polishing;

[0063] When the PV of its surface is greater than the drawing requirements, first observe whether the outline model has astigmatism. The reason is that the hardness of single crystal silicon has the characteristics of different directions and anisotropy, and the removal efficiency is different in different places, which easily produces astigmatism and deformation.

[0064] If astigmatism exists, astigmatism correction is performed, and contour scanning is performed again after astigmatism correction.

[0065] If no astigmatism exists, the coarse polishing procedure is recalculated using the second contour model, and coarse polishing is performed again.

[0066] Repeat the above judgment process until the surface shape of the zinc selenide aspherical lens is smaller than the drawing requirements, then proceed to fine polishing.

[0067] In this embodiment, the following points need to be explained regarding coarse polishing:

[0068] 1. The settings for the CNC polishing machine used for rough polishing are as follows:

[0069] The selected polishing slurry has a particle size of 1μm, and since the lens diameter is set to be less than 150mm, it meets the requirements of setting a or c. In this embodiment, setting c is adopted, so the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine is set to 400RPM and the rotation direction of the polishing head and the workpiece axis is the same, and the downward pressure is 0.4mm. It should be noted that in actual applications, setting a can also be adopted: the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine is set to 900RPM and the downward pressure is 0.6mm, which can also produce aspherical surfaces with good surface shape, but the processing efficiency is slightly different.

[0070] The lens diameter is set to the actual lens diameter plus 10mm, that is, the lens diameter is set to 128mm. The reason is that the CNC polishing process has an edge collapse phenomenon, and the surface shape of the edge has abrupt changes that cannot be controlled. Therefore, when following the polishing trajectory, the polishing head moves a little further out of the lens, which can reduce the edge collapse phenomenon.

[0071] The polishing head should be one-third the size of the lens diameter, and the polishing pad should be gray GR-35 polyurethane polishing pad. The polishing fluid flow rate should be set to maximum and sprayed towards the center of the lens.

[0072] The correction is set to -30%; the track-pitch value in the path data is one-hundredth of the set lens diameter, i.e., 1.28; the oscillation-time unit is seconds, and its value is 3 to 5 times the set lens diameter, which is set to 500 in this embodiment; the filter width in extrapolate is one-hundredth of the set lens diameter, i.e., 1.28; the point distance is one-hundredth of the set lens diameter, i.e., 1.28; the target diameter is 48mm; a smoothing is performed, with a smoothing value of 2μm; the min.height is set to 0.1μm, and the feed min. value is adjusted to 10mm / min by adjusting the removal-coefficient and oscillation-time values ​​to obtain the final coarse polishing procedure.

[0073] 2. There are two methods for correcting astigmatism during aspheric polishing of monocrystalline silicon. One method is to use the 3D correction software Proact on the CNC polishing machine to extend the dwell time on the protruding parts of the surface to eliminate them, but this method is time-consuming. The other method is manual correction, where the operator polishes the protruding parts of the surface, leaving the concave parts unpolished.

[0074] Fine polishing: The zinc selenide aspherical lens and its fixture are fixed again in the CNC polishing machine, and the second contour model obtained from rough polishing is imported into the CNC polishing machine to calculate the fine polishing program and start fine polishing to obtain a semi-finished product. In actual application, after fine polishing, the zinc selenide aspherical lens is taken out, and while dripping hand soap onto the lens surface, it is rinsed with pure water, then wiped with a damp cotton ball soaked in hand soap, and finally wiped clean of surface dirt and moisture with alcohol and citric acid. Then, the zinc selenide aspherical lens is contour scanned. If the surface shape is larger than the drawing requirements, the fine polishing is repeated with the contour model until the surface shape of the semi-finished product is smaller than the drawing requirements, and then it enters the finishing stage.

[0075] In this embodiment, the following points need to be explained regarding fine polishing:

[0076] 1. The settings for the CNC polishing machine used for fine polishing are as follows:

[0077] The selected polishing slurry has a particle size of 0.5μm; the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine are both set to 250RPM, and the downward pressure is 0.2mm; the lens diameter is set to the actual lens diameter plus 10mm, that is, the set lens diameter value is 128mm; the size of the polishing head is one-third of the set lens diameter, and the polishing skin is orange LP-66 polishing skin.

[0078] The polishing fluid flow rate is set to maximum and sprayed onto the center of the lens; the correction is set to -30%; the track-pitch value in the path data is one-hundredth of the set lens diameter, i.e., 1.28; the oscillation-time is in seconds, and its value is 3 to 5 times the set lens diameter, set to 500 in this embodiment; the filterwidth in extrapolate is one-hundredth of the set lens diameter, i.e., 1.28; the point distance is one-hundredth of the set lens diameter, i.e., 1.28; the target diameter is 123mm; no smoothing is performed; the min.height is set to 0.1μm, and the feed min. value is adjusted to 10mm / min by adjusting the removal-coefficient and oscillation-time values ​​to obtain the final fine polishing procedure.

[0079] Fine finishing: Transfer the semi-finished product to the polishing machine for manual finishing. Rotate the semi-finished product at 150 RPM. First, wet the lens with ammonium dichromate solution, controlling the pressure of the lint-free polishing cloth to 6 kPa on the lens surface. Alternately drip polishing fluid and ammonium dichromate solution (the role of ammonium dichromate solution is to remove the white zinc metal particles generated on the lens surface during polishing, and another role is to increase friction). Manual finish for 5 minutes. The above operation can remove deep scratches and residual white spots on the lens surface. Then, rinse with pure water while dripping hand soap onto the lens surface, then wipe with a damp cotton ball soaked in hand soap, and finally clean the lens with alcohol and citric acid. Observe the surface of the lens for any visible scratches. If scratches are found, repeat the above fine-tuning operation. Then, observe the surface smoothness under a microscope at 14x magnification. If there are no white spots or scratches, the surface smoothness is considered acceptable. If the smoothness does not meet the requirements, repeat the fine-tuning operation. If the surface shape is also acceptable, the zinc selenide aspherical polishing is complete. Apply a protective varnish to the surface to prevent scratches. It should be noted that the workpiece rotation speed during fine-tuning is between 100 and 200 RPM to ensure efficiency and avoid polishing fluid splashing out. The pressure on the lens is between 4 and 6 kPa because zinc selenide is a ceramic material and is soft. Scratches generated during the rough and fine polishing processes are relatively deep, and increased hand-hand pressure is needed to remove them.

[0080] The polishing slurry used in the finishing process is a mixture of 0.25μm diamond powder, aluminum oxide, silica, an oily suspending agent, and pure water in a ratio of 2:1:2:6:29; the concentration of the ammonium dichromate solution used is 1%, and the polishing pad is a lint-free cloth or damping cloth. It is important to note that the area covered by the polishing pad in one revolution of the lens must be larger than the surface area of ​​the lens. Figure 8 As shown.

[0081] In addition, refer to Figure 9 In order to improve the machining accuracy, in practical applications, the theoretical indentation is calculated, and the tooling height in the non-CNC polishing machine is adjusted by the difference between the theoretical indentation and the actual indentation so that the theoretical indentation and the actual indentation are equal in size.

[0082] The theoretical indentation calculation method is as follows:

[0083]

[0084] Where: L0 = bL e L can be obtained e =2R0b-b 2 / 2R e +2R0-2b;

[0085] Combining the two equations above, we get:

[0086]

[0087] Simplifying, we get:

[0088]

[0089] Among them, R e R0 is the radius of the aspherical surface; R0 is the radius of curvature of the polishing head; b is the downward pressure; Y0 s This is the theoretical indentation diameter.

[0090] Example 2

[0091] The process is basically the same as in Example 1, except that the actual lens diameter is 200mm and the polishing fluid particle size is 1μm, which meets the requirements of setting b or d. In this example, setting b is used. It should be noted that in actual applications, setting d is used: setting the rotation speed of both the polishing head and the workpiece axis of the CNC polishing machine to 300RPM and the downward pressure to 0.2mm can also produce aspherical surfaces with good surface shape, but the processing efficiency is slightly different.

[0092] Therefore: In rough polishing, the rotation speed of both the polishing head and the workpiece axis of the CNC polishing machine is set to 400 RPM, and the downward pressure is 0.6 mm; the lens diameter is set to the actual lens diameter plus 10 mm, that is, the set lens diameter value is 210 mm; the track-pitch value in path data is one-hundredth of the set lens diameter, that is, 2.1; the unit of oscillation-time is seconds, and its value is 3 to 5 times the set lens diameter, which is set to 850 in this embodiment; the filter width in extrapolate is one-hundredth of the set lens diameter, that is, 2.1; the point distance is one-hundredth of the set lens diameter, that is, 2.1; the target diameter is 190 mm, and the rest remain unchanged.

[0093] In fine polishing, the track-pitch value in the path data is one-hundredth of the set lens diameter, i.e., 2.1; the oscillation-time is in seconds, and its value is 3 to 5 times the set lens diameter, which is set to 190 in this embodiment; the filter width in extrapolate is one-hundredth of the set lens diameter, i.e., 2.1; the point distance is one-hundredth of the set lens diameter, i.e., 2.1; the target diameter is 190mm, and the rest remain unchanged.

[0094] Example 3

[0095] refer to Figure 3 It is basically the same as Example 1, except that: no smoothing is performed during rough polishing.

[0096] Comparative Example 1

[0097] refer to Figure 4 It is basically the same as Example 1, except that the edges of the lens are not ground or chamfered during milling.

[0098] Comparative Example 2

[0099] refer to Figure 5 It is basically the same as Example 1, and conforms to setting c. The difference is that the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine is set to 800 RPM.

[0100] Comparative Example 3

[0101] refer to Figure 6 It is basically the same as Example 1, conforming to setting c, but the downward pressure is 0.6mm.

[0102] Comparative Example 4

[0103] It is basically the same as Comparative Example 3, but the downward pressure is 0.1mm.

[0104] Comparative Example 5

[0105] refer to Figure 7 It is basically the same as Example 1, and meets the setting c, but ammonium dichromate solution was not added during the finishing process.

[0106] Results analysis:

[0107] refer to Figure 2 Examples 1 and 2 both yielded monocrystalline silicon aspherical lenses with acceptable surface shapes and a surface finish of 60 / 40, differing only in the number of repeated coarse polishing cycles. However, reference... Figure 3 In Example 3, mid-frequency errors occasionally occur because the milled lens surface has many burrs and is relatively rough, resulting in a particularly large waviness in the surface shape. If it is used directly without smoothing, it will cause a particularly serious mid-frequency error in the first round of rough polishing, making subsequent processes impossible. Therefore, in actual production, it is preferable to perform smoothing to reduce defective products.

[0108] refer to Figure 4 The central part of the surface of Comparative Example 1 protrudes, presumably due to the wear of the polished skin caused by the edge of the lens.

[0109] refer to Figure 5 The surface of Comparative Example 2 is concave in the middle because the polishing slurry has a large particle size and the polishing head and working shaft rotate at high speeds.

[0110] refer to Figure 6 Compared to the example 3, the downward pressure is larger. Although the polishing efficiency is high, it brings serious mid-frequency error. Moreover, due to the large downward pressure, the lens does not have sufficient contact with the polishing fluid, and deep scratches and pits will appear on the surface of the lens.

[0111] The efficiency of Comparative Example 4 is too slow because the pressure is small and the polishing time is long. Considering economic benefits, it is not suitable for production activities.

[0112] refer to Figure 7 The surface finish of Comparative Example 5 was not up to standard, and obvious white spots were found when observed under a microscope at 14x magnification.

[0113] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A CNC polishing process for zinc selenide aspherical lenses, based on a CNC polishing machine, characterized in that, Includes the following steps: Step 1: Perform contour scanning on the zinc selenide aspherical lens to obtain the contour model; Step 2: Based on the contour model, use a CNC polishing machine to perform rough polishing on the zinc selenide aspherical lens; Step 3: Perform contour scanning on the rough-polished zinc selenide aspherical lens to obtain a new contour model; Step 4: Based on the contour model obtained in Step 3, the zinc selenide aspherical lens is finely polished using a CNC polishing machine; Step 5: Refine and polish to obtain the finished product; The parameter settings of the CNC polishing machine meet the following conditions: Set a) When the polishing slurry particle size is 0.5~1μm and the lens diameter is less than 150mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 800~1000RPM and the downward pressure to 0.5~0.7mm. Set b, when the polishing slurry particle size is 0.5~1μm and the lens diameter is greater than 150mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 300~500RPM and the downward pressure to 0.5~0.7mm. Set c, when the polishing slurry particle size is 1~2μm and the lens diameter is less than 150mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 300~500RPM and the downward pressure to 0.2~0.4mm; Set d: When the polishing slurry particle size is 1~2μm and the lens diameter is greater than 150mm, set the rotation speed of the polishing head and the workpiece axis of the CNC polishing machine to 150~300RPM and the downward pressure to 0.2~0.4mm.

2. The CNC polishing process for zinc selenide aspherical lenses according to claim 1, characterized in that, If the PV of the contour model in step 3 is greater than the drawing requirement, return to step 2; if the PV is less than the drawing requirement, proceed to step 4.

3. The CNC polishing process for zinc selenide aspherical lenses according to claim 1, characterized in that, The polishing solution used for rough polishing is a mixed solution of 1~2μm alumina, ammonium dichromate, oily suspending agent and pure water, wherein the ratio of alumina:ammonium dichromate:oily suspending agent:pure water is 40:1:60:

299.

4. The CNC polishing process for zinc selenide aspherical lenses according to claim 1, characterized in that, In step 5, the zinc selenide aspherical lens is transferred to a polishing machine. Ammonium dichromate solution is added to wet the zinc selenide aspherical lens, and the zinc selenide aspherical lens is rotated at a speed of 100~200 RPM. Then, a polishing pad is used to refine the zinc selenide aspherical lens at a pressure of 4~6 kPa. Polishing liquid and ammonium dichromate solution are continuously dripped in during the process.

5. The CNC polishing process for zinc selenide aspherical lenses according to claim 1, characterized in that, Before step 1, a zinc selenide aspherical lens with a surface area PV ≤ 2μm is prepared by milling, and the sharp edges at the edges of the zinc selenide aspherical lens are removed.

6. The CNC polishing process for zinc selenide aspherical lenses according to claim 1, characterized in that, In step 2, the actual indentation diameter is compared with the theoretically calculated indentation size, and the height of the rough polishing tool is adjusted according to the difference to make the theoretical indentation size equal to the actual indentation size.

7. The CNC polishing process for zinc selenide aspherical lenses according to claim 1, characterized in that, in, The remaining settings for the CNC polishing machine in step 2 are as follows: The size of the polishing head is one-third to one-quarter of the set lens diameter; The edge dwell rate is set to -30% to -60%; The pitch is one-hundredth of the set lens diameter; The time required for one round of polishing is measured in seconds, and its value is 3 to 5 times the set lens diameter; The sampling pitch is one-hundredth of the set lens diameter, the sampling point distance is one-hundredth of the set lens diameter, and the target diameter is the effective aperture plus 5~10mm; Smoothing is performed, with the smoothing value being 2~3μm; Adjust the dwell time and the time required for one round of polishing to set the minimum movement speed of the polishing head to 10 mm / min.

8. The CNC polishing process for zinc selenide aspherical lenses according to claim 7, characterized in that, The settings for the CNC polishing machine in step 4 are as follows: The polishing slurry has a particle size of 0.5~1μm and a pressure of 0.1~0.2mm. The other settings are the same as for coarse polishing.

9. A zinc selenide aspherical lens, wherein the diameter of the zinc selenide aspherical lens is 320 mm or less, characterized in that, The aspherical lens is made using the CNC polishing process described in any one of claims 1 to 8, with a global surface area (PV) of less than 0.3 μm and a surface finish of 60 / 40, reaching laser grade.

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