Immersed polishing method for processing concave cambered surface of 3D sapphire cover plate

Abstract

The invention relates to the technical field of sapphire cover plate machining, and discloses an immersion type polishing method for machining a concave cambered surface of a 3D sapphire cover plate, and the immersion type polishing method is used for locally and precisely immersing a workpiece, ensuring the polishing effect and reducing the polishing cost and comprises the following steps that S1, the cover plate of a concave structure formed through material reduction is fixed to a water return jig, and the cover plate of the concave structure is fixed to the water return jig; the concave structure of the cover plate faces upwards; the water return jig is provided with a containing groove used for containing the cover plate and a funnel-shaped channel located above the containing groove and communicated with the containing groove, the containing groove is communicated with an external vacuum device to adsorb the cover plate in a vacuum mode, and a water return slope is formed on the inner side face of the funnel-shaped channel. S2, a polishing solution is injected into the inwards-concave structure of the cover plate till the inwards-concave structure is completely immersed in the polishing solution; and S3, rough polishing and fine polishing are sequentially conducted on the concave structure through a polishing head.

Description

Technical Field

[0001] This invention relates to the field of sapphire cover plate processing technology, and in particular to an immersion polishing method for processing the concave arc surface of 3D sapphire cover plates. Background Technology

[0002] Sapphire glass, due to its high hardness, high wear resistance, and excellent optical properties, is widely used in glass protective covers for electronic products. With the upgrading of product design, the demand for 3D sapphire covers with concave curved surfaces is increasing, and the polishing requirements for 3D sapphire covers are also becoming more stringent. Chinese invention patent application (CN105014520A) discloses an immersion chemical mechanical polishing method for sapphire substrates. This method involves completely immersing a hard ceramic disc with a sapphire substrate attached and a polishing pad in a mixed polishing slurry for overall immersion polishing, thereby reducing scratches on the sapphire substrate surface and lowering the polishing pad temperature to extend its lifespan. However, in practical applications, the entire workpiece and polishing head are completely immersed in a large amount of polishing slurry, resulting in huge slurry consumption and high operating costs. Furthermore, a large-sized liquid tank is required to accommodate the workpiece immersion, and the increased size of the liquid tank increases the difficulty and cost of managing the uniformity of the polishing slurry and treating waste liquid. Summary of the Invention

[0003] Therefore, it is necessary to address the above-mentioned shortcomings by providing an immersion polishing method for machining the concave arc surface of 3D sapphire cover plates, which allows for precise local immersion of the workpiece, ensures polishing effect, and reduces polishing cost.

[0004] An immersion polishing method for machining the concave arc surface of 3D sapphire cover plates includes the following steps: S1. Fix the cover plate with a concave structure formed by subtractive processing onto the water return fixture, with the concave structure of the cover plate facing upwards; the water return fixture has a receiving groove for receiving the cover plate and a funnel-shaped channel located above the receiving groove and connected to the receiving groove; the receiving groove is connected to an external vacuum device to vacuum adsorb the cover plate; the inner side of the funnel-shaped channel forms a water return slope. S2. Inject polishing liquid into the concave structure of the cover plate until the polishing liquid completely submerges the concave structure; S3. The concave structure is coarsely polished and then finely polished using a polishing head.

[0005] In one embodiment, the inner contour shape of the receiving groove is adapted to the outer contour shape of the cover plate, and the bottom of the receiving groove is provided with at least one adsorption hole communicating with an external vacuum device.

[0006] In one embodiment, the angle between the backwater slope and the vertical direction is 30°-60°.

[0007] In one embodiment, the concave structure is a rectangular groove, and the concave structure has a first corner portion, a second corner portion, a third corner portion and a fourth corner portion arranged in a clockwise direction. The first corner portion and the third corner portion are diagonally arranged, and the second corner portion and the fourth corner portion are diagonally arranged.

[0008] In one embodiment, step S3, the coarse polishing includes: S311. Starting from the first corner, polish the first number of revolutions clockwise. S312. Starting from the third corner, polish the first number of turns counterclockwise. In step S3, the fine polishing includes: S321. Starting from the second corner, polish the second number of revolutions clockwise. S322. Starting from the fourth corner, polish the second circle counterclockwise.

[0009] In one embodiment, in step S3, the angle between the axis of the polishing head and the normal to the workpiece surface is 1.5°, and the combined pressure of the polishing head in the vertical and horizontal directions is 10-15N.

[0010] In one embodiment, the polishing head includes a rigid support rod for connection to a machine tool spindle, a buffer layer fixed to the bottom end of the rigid support rod, an elastic intermediate layer fixed to the bottom end of the buffer layer, and a polishing layer fixed to the bottom end of the elastic intermediate layer and partially surrounding the elastic intermediate layer, the polishing layer being made of at least polyurethane material.

[0011] In one embodiment, the polishing layer of the polishing head for coarse polishing further includes cerium oxide abrasive, the polishing layer of the polishing head for fine polishing further includes fibers, and the hardness of the polishing head for coarse polishing is greater than that of the polishing head for fine polishing.

[0012] In one embodiment, both the polishing head for coarse polishing and the polishing head for fine polishing are cylindrical structures with a tapered bottom, the tapered bottom of the polishing head being 3°; the buffer layer is a silicone rod or silicone bushing, and the elastic intermediate layer is a polyurethane sheet.

[0013] In one embodiment, the immersion polishing method further includes: S4. After polishing, release the vacuum adsorption, remove the cover plate, and clean and dry it.

[0014] The immersion polishing method for machining the concave arc surface of 3D sapphire cover plates, as described in this invention, uses a return water fixture with a return water slope to position the cover plate to be polished, ensuring that the polishing fluid completely immerses the concave structure of the cover plate. This achieves precise local immersion of the cover plate, requiring only a small amount of polishing fluid to cover the area to be processed on the cover plate. The processed area receives continuous and uniform lubrication and cooling from the polishing fluid, completely avoiding dry grinding and improving the uniformity of the polished surface to ensure polishing effect. The centrifugal force generated by the polishing head agitating the polishing fluid during polishing creates an efficient directional reflux of the polishing fluid on the return water slope, ensuring that the polishing fluid is continuously and precisely replenished to the processed surface of the cover plate, reducing or even eliminating polishing fluid loss. While ensuring polishing effect, only a small amount of polishing fluid is needed to polish the cover plate, eliminating the need for a large liquid pool for workpiece immersion, greatly reducing consumable usage, consumable costs, and environmental impact. The reduced amount of polishing fluid makes it easy to mix the polishing fluid using centrifugal force, reducing the difficulty of managing the uniformity of the polishing fluid. Attached Figure Description

[0015] Figure 1 This is a flowchart of an immersion polishing method in one embodiment of the present invention; Figure 2 This is a side view of a water return fixture in one embodiment of the present invention; Figure 3 This is a top view of a water return fixture in one embodiment of the present invention; Figure 4 This is a schematic diagram of the polishing head in one embodiment of the present invention; Figure 5 This is an enlarged view of the bottom of the polishing head in one embodiment of the present invention; Figure 6 This is a schematic diagram of the steps of an immersion polishing method in one embodiment of the present invention; Figure 7 This is a schematic diagram of the polishing head's path in one embodiment of the present invention. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0017] Please combine Figure 1-2 as well as Figure 6This invention discloses an immersion polishing method for machining the concave arc surface of a 3D sapphire cover plate, which precisely immerses the workpiece locally, ensures polishing effect, and reduces polishing cost. The immersion polishing method includes the following steps: S1. The cover plate with a concave structure formed by subtractive processing is fixed on the return water fixture 100, with the concave structure of the cover plate facing upwards. The return water fixture 100 has a receiving groove 110 for receiving the cover plate and a funnel-shaped channel 120 located above and communicating with the receiving groove 110. The receiving groove 110 is connected to an external vacuum device to vacuum-adsorb the cover plate. The inner side of the funnel-shaped channel 120 forms a return water slope 130. The concave prototype is processed into the 3D sapphire cover plate by subtractive processing to provide a processing surface for polishing operations. In this way, most of the material on the cover plate used to form the concave arc surface is removed, which reduces the amount of work during polishing and improves polishing efficiency. The subtractive processing of the 3D sapphire cover plate can be completed by CNC engraving or laser engraving. By setting the concave structure of the cover plate upwards, it is convenient for the polishing head mounted on the machine tool spindle to be inserted into the concave structure from top to bottom for polishing. On the other hand, the upward-facing concave structure can be used as a container for holding polishing fluid. In this way, there is no need to set up an additional liquid pool for holding polishing fluid, which simplifies the structure of the cover plate polishing equipment.

[0018] In this embodiment, the return water fixture 100 serves as a positioning structure for the cover plate to be polished, and cooperates with the concave structure of the cover plate itself to limit the flow range of the polishing liquid. Of course, when the liquid level is higher than the concave structure of the cover plate after the polishing liquid is added, the return water slope 130 of the return water fixture 100 also serves as a polishing liquid container together with the concave structure of the cover plate. By setting a funnel-shaped channel 120 above the receiving tank 110, a return water slope 130 can be formed on the upper side of the cover plate in the receiving tank 110. This effectively captures and guides the polishing liquid that is thrown out by centrifugal force during the polishing process back into the concave structure of the cover plate, ensuring that the processing area on the cover plate can continuously receive lubrication, cooling and chemical action of the polishing liquid. This fundamentally solves the core problem of the liquid being thrown dry in immersion polishing of small curved surfaces, avoids scratches and thermal damage to the workpiece (cover plate) surface caused by dry grinding, ensures polishing quality, and the concave structure of the cover plate also has water retention capacity, making it more suitable for immersion polishing. Furthermore, the return water fixture 100 achieves self-circulation and automatic replenishment of the polishing slurry, eliminating the need for complex external polishing slurry spraying devices (including pumps, pipelines, nozzles, etc.), simplifying the system structure involved in polishing, reducing initial equipment costs, maintenance points, and failure rates. Directly recycling and reusing polishing slurry that would otherwise be wasted eliminates the need for a recycling device, improving the effective utilization rate of the polishing slurry and aligning with the conservation principles of green manufacturing. A stable and continuous supply of polishing slurry to the workpiece means a more stable polishing environment (chemical environment, coefficient of friction), contributing to improved stability and repeatability of the entire polishing process. Additionally, the funnel-shaped channel 120 creates a top-wide, bottom-narrow insertion opening within the return water fixture 100, guiding the cover plate and reducing the difficulty of inserting it into the receiving groove 110.

[0019] For further details, please refer to Figure 2-3 as well as Figure 6The inner contour of the receiving groove 110 is adapted to the outer contour of the cover plate, and at least one adsorption hole 140 communicating with an external vacuum device is provided at the bottom of the receiving groove 110. In this way, when the adsorption hole 140 is connected to the external vacuum device (such as a vacuum generator), a negative pressure is generated in the receiving groove 110. The cover plate entering the receiving groove 110 will fit against the inner surface of the receiving groove 110 under the action of negative pressure, and the gap between the outer surface of the cover plate and the inner surface of the receiving groove 110 will be completely sealed. While ensuring that the cover plate is stably positioned in the receiving groove 110, it can prevent polishing liquid from entering the receiving groove 110 from the concave structure and the upper part of the cover plate, thereby preventing the loss of polishing liquid and the problem of liquid entering the external vacuum device, so as to facilitate the effective polishing operation. In addition, the return water fixture 100 is fixed to the machine base with screws. For example, multiple screw holes 150 are provided on the upper part of the return water slope 130 or on the upper surface of the return water fixture 100. The return water fixture 100 is fixed to the machine base by multiple screws passing through each screw hole 150 to ensure the stability of the installation of the return water fixture 100. The installation position of the screw holes on the return water slope 130 should preferably be higher than the maximum rotational upward position of the polishing liquid in the funnel-shaped channel 120.

[0020] In one embodiment, the angle between the return slope 130 and the vertical direction is 30°-60°. More preferably, the angle between the return slope 130 and the vertical direction is 45°. In this way, while ensuring that the polishing liquid can quickly flow back into the concave structure after rotating and moving upward, the problem of polishing liquid splashing outward due to the funnel-shaped channel 120 being too low can be avoided. It can also avoid the problem of the polishing head being unable to reach into the concave structure for polishing due to the funnel-shaped channel 120 being too high. In addition, the size of the return fixture 100 in the horizontal plane can be controlled to reduce the area occupied by the return fixture 100 on the machine. In addition, in this embodiment, the return water fixture 100 also includes a limiting channel 160 formed above and communicating with the funnel-shaped channel 120. The limiting channel 160 has the same width at all points along its height direction. The width of the lower part of the limiting channel 160 is the same as the width of the upper part of the funnel-shaped channel 120. The inner side of the limiting channel 160 is a vertical plane, which is used to limit the polishing liquid that may splash from the return water slope 130 into the limiting channel 160, so as to avoid the waste of raw materials caused by the polishing liquid splashing outward.

[0021] S2. Inject polishing fluid into the concave structure of the cover plate until the polishing fluid completely submerges the concave structure. In this embodiment, the amount of polishing fluid injected is such that the liquid level just completely submerges the concave structure to be polished. This achieves the goal of significantly reducing the amount of polishing fluid used while satisfying the requirements of wet grinding of the cover plate, reducing the temperature of the polished part on the cover plate during polishing, and ensuring the polishing effect. During the polishing process, the polishing fluid thrown out by centrifugal force impacts the return water slope 130 and is blocked and flows back into the concave structure of the cover plate, realizing the self-circulation and automatic replenishment of the polishing fluid.

[0022] S3. Use a polishing head to perform rough polishing and fine polishing on the concave structure in sequence.

[0023] In this embodiment, the concave structure is a rectangular groove, and the concave structure has first corner portions arranged sequentially in a clockwise direction (i.e., Figure 7 R1 in the middle), the second corner (i.e. Figure 7 R2 in the middle), the third corner (i.e. Figure 7 R3 in the middle) and the fourth corner (i.e. Figure 7 (R4 in the diagram), the first corner and the third corner are set diagonally, and the second corner and the fourth corner are set diagonally.

[0024] Please see Figure 4 and Figure 5The polishing head 200 includes a rigid support rod 210 for connection to a machine tool spindle, a buffer layer 220 fixed to the bottom end of the rigid support rod 210, an elastic intermediate layer 230 fixed to the bottom end of the buffer layer 220, and a polishing layer 240 fixed to the bottom end of the elastic intermediate layer 230 and partially surrounding it. The polishing layer 240 is made of at least polyurethane material. The rigid support rod 210, buffer layer 220, elastic intermediate layer 230, and polishing layer 240 are connected sequentially in a concave-convex fit to improve the stability of the entire polishing head 200 structure. In this embodiment, the rigid support rod 210 is a bakelite rod, which serves as the main support structure of the entire polishing head 200. It is fixedly connected to the machine tool spindle via a connecting rod so that it can rotate under the drive of the machine tool spindle, thereby polishing the concave structure of the cover plate. The buffer layer 220 is a silicone rod or silicone bushing. As the core buffer and vibration damping element of the polishing head 200, it effectively absorbs and disperses high-frequency vibrations and impact loads generated during polishing. This is crucial for hard and brittle materials such as sapphire, significantly reducing the risk of edge chipping and overall breakage, lowering fragmentation and edge breakage rates, and directly improving production yield. Furthermore, in this design, the buffer layer 220 is integrated into the rigid support rod 210, resulting in a compact structure and longer lifespan. Additionally, the buffer layer 220 ensures that the contact between the polishing head 200 and the cover plate to be polished is no longer a "hard-on-hard" contact, allowing for uniform pressure distribution. This results in more even wear on the polishing head 200, maintaining stable polishing performance throughout its lifespan and ensuring consistent workpiece surface quality during batch processing. The elastic intermediate layer 230 is a polyurethane sheet used in conjunction with the buffer layer 220 to provide vibration damping protection for the polishing head 200, reducing the risk of edge chipping and fragmentation of the sapphire workpiece.

[0025] Further preferably, the polishing layer 240 of the polishing head 200 used for rough polishing further includes cerium oxide abrasive, and the polishing layer 240 of the polishing head 200 used for fine polishing further includes fibers, and the hardness of the polishing head 200 used for rough polishing is greater than that of the polishing head 200 used for fine polishing. That is, a two-stage polishing strategy of "hard first, soft later" is adopted for the concave structure of the cover plate. The first stage of rough polishing uses a hard polishing head containing cerium oxide, which can achieve efficient material removal and preliminary shaping; the second stage of fine polishing uses a soft polishing head containing fibers, which can refine and reduce surface roughness, effectively balancing efficiency and final surface finish, and obtaining a polished surface with better consistency. Preferably, the fibers can be plastic retainers or plant fibers.

[0026] Furthermore, both the polishing head 200 for rough polishing and the polishing head 200 for fine polishing are cylindrical structures with a tapered bottom, the tapering of which is 3°. The rigid support rod 210 is connected to the spindle of the five-axis polishing equipment via a connecting rod. By designing the bottom of the polishing head 200 as a cylindrical structure with a tapered bottom, it can simultaneously adapt to and polish the root (R-angle or corner) and the side wall slope of the concave arc structure in one go. This completely changes the step-by-step polishing mode of the traditional process, which involves polishing the root first and then the wall or vice versa, significantly reducing clamping and processing time and greatly improving production efficiency.

[0027] Furthermore, in this scheme, in step S3, the angle between the axis of the polishing head 200 and the normal to the workpiece surface is 1.5°, and the combined pressure of the polishing head 200 in the vertical and horizontal directions is 10-15N. That is to say, whether in the rough polishing process or the fine polishing process, the polishing head 200 is in contact with the concave structure of the cover plate at an angle. Thus, through precise force control and angle setting, a constant pressure of 10-15N can be applied to the surface of the concave structure using a device with force control function. Combined with a small angle of inclination (1.5°), the stability of the contact force during polishing is ensured, avoiding over-polishing or under-polishing caused by pressure fluctuations, improving process repeatability, stabilizing the polishing process, and ultimately increasing the yield of the cover plate polishing.

[0028] In step S3, the rough polishing includes: S311, polishing clockwise for the first number of revolutions starting from the first corner; S312, polishing counterclockwise for the first number of revolutions starting from the third corner. In step S3, the fine polishing includes: S321, polishing clockwise for the second number of revolutions starting from the second corner; S322, polishing counterclockwise for the second number of revolutions starting from the fourth corner. Of course, during both rough and fine polishing, the rotation can be counterclockwise first, then clockwise, ensuring the two polishing directions are opposite. In other words, whether in rough or fine polishing, the process starts with one corner of the concave structure and rotates clockwise, then starts with another corner diagonally opposite that corner and rotates counterclockwise, employing a symmetrical polishing path. This breaks the periodic repetition of the motion by polishing in both directions from a symmetrical point, making the polishing trajectory more evenly distributed across the entire concave structure, avoiding localized over-polishing or polishing marks, and significantly improving polishing uniformity. Furthermore, the symmetrical starting point polishing path design forcibly alters the flow direction of the polishing slurry, optimizing its distribution and enabling more effective delivery of fresh slurry to the entire processing area, evenly removing heat and debris. Additionally, polishing methods involving either forward rotation followed by reverse rotation, or vice versa, help eliminate the directional texture issues that may arise from unidirectional polishing, resulting in more uniform material removal and improved polishing performance.

[0029] In this embodiment, the amount of polishing wire cut during rough polishing is 10-20µm, and the amount of wire cut is determined based on the depth of the damage layer caused by the previous subtraction process; the amount of polishing wire cut during fine polishing is 7-8µm for the first polishing stage; and the amount of polishing wire cut during the second polishing stage is approximately 10µm.

[0030] In one embodiment, the immersion polishing method further includes: S4. After polishing, release the vacuum adsorption, remove the cover plate and clean and dry it to obtain a 3D sapphire cover plate with a preset concave arc surface.

[0031] The following example illustrates the specific process of the immersion polishing method used for machining the concave curved surface of 3D sapphire cover plates.

[0032] First, the sapphire cover plate (workpiece), whose concave arc surface prototype (i.e., concave structure) has been CNC sculpted, is placed in the receiving tank 110 of the return water fixture 100. An external vacuum pump is activated, creating a negative pressure around the adsorption holes 140 in the receiving tank 110, which firmly adsorbs the workpiece into the receiving tank 110. Then, using a metering injection device, diamond powder polishing liquid with a pH value of approximately 7 (neutral) is injected into the concave structure of the workpiece until the liquid level just submerges the entire concave structure to be polished. Start the five-axis polishing equipment and install the polishing head 200 (hard polyurethane damping polishing head) containing cerium oxide in the polishing layer 240 on the machine tool spindle of the five-axis polishing equipment. Control the angle (tilt angle) between the axis of the polishing head 200 and the normal of the workpiece surface to be 1.5°. Under the combined pressure of 12N along the Y / Z direction (vertical and horizontal direction), the polishing head 200 moves along the preset concave arc surface contour in the concave structure. First, starting from the first corner R1, it rotates 6 times clockwise, and then starting from the third corner R3, it rotates 6 times counterclockwise. Control the polishing wire feed to be 15um. After completion, replace the polishing head 200 with a polishing head 200 containing fibers in the polishing layer 240 (soft polyurethane vibration-damping polishing head). Keeping the tilt angle at 1.5° and the pressure at 12N constant, repeat the above-mentioned forward and reverse polishing path for 6 turns, starting from the second corner R2 and the fourth corner R4 respectively. The wire feed for one polishing pass is 7-8µm, and the wire feed for the second polishing pass is approximately 10µm. After polishing, release the vacuum and remove the workpiece. Ultrasonically clean the workpiece with deionized water and blow it dry to obtain a 3D sapphire cover plate with a concave arc surface.

[0033] The immersion polishing method for machining the concave arc surface of 3D sapphire cover plates according to the present invention uses a return water fixture 100 with a return water slope 130 to position the cover plate to be polished, and to completely immerse the concave structure of the cover plate with polishing fluid. This achieves precise local immersion of the cover plate, and only a small amount of polishing fluid is needed to cover the area to be processed on the cover plate. The processing area is continuously and uniformly lubricated and cooled by polishing fluid, completely avoiding dry grinding, which helps to improve the uniformity of the polished surface and ensure the polishing effect. The polishing head 200 agitates the polishing fluid during polishing, and the centrifugal force generated by the polishing fluid causes the polishing fluid to form an efficient directional return flow on the return water slope 130. This ensures that the polishing fluid is continuously and precisely replenished to the processing surface of the cover plate, reducing or even avoiding the loss of polishing fluid. While ensuring the polishing effect, only a small amount of polishing fluid is needed to polish the cover plate. There is no need to set up a large liquid pool to immerse the workpiece, which greatly reduces the amount of consumables used, consumable costs, and environmental impact. The reduction in the amount of polishing fluid used makes it easy to mix the polishing fluid by centrifugal force, which reduces the difficulty of managing the uniformity of the polishing fluid.

[0034] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0035] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An immersion polishing method for machining the concave arc surface of a 3D sapphire cover plate, characterized in that, Includes the following steps: S1. Fix the cover plate with a concave structure formed by subtractive processing onto the water return fixture, with the concave structure of the cover plate facing upwards; the water return fixture has a receiving groove for receiving the cover plate and a funnel-shaped channel located above the receiving groove and connected to the receiving groove; the receiving groove is connected to an external vacuum device to vacuum adsorb the cover plate; the inner side of the funnel-shaped channel forms a water return slope. S2. Inject polishing liquid into the concave structure of the cover plate until the polishing liquid completely submerges the concave structure; S3. The concave structure is coarsely polished and then finely polished using a polishing head.

2. The immersion polishing method according to claim 1, characterized in that, The inner contour shape of the receiving groove is adapted to the outer contour shape of the cover plate, and at least one adsorption hole communicating with an external vacuum device is provided at the bottom of the receiving groove.

3. The immersion polishing method according to claim 1, characterized in that, The angle between the backwater slope and the vertical direction is 30°-60°.

4. The immersion polishing method according to claim 1, characterized in that, The concave structure is a rectangular groove, and the concave structure has a first corner section, a second corner section, a third corner section and a fourth corner section arranged in a clockwise direction. The first corner section and the third corner section are diagonally arranged, and the second corner section and the fourth corner section are diagonally arranged.

5. The immersion polishing method according to claim 4, characterized in that, In step S3, the coarse polishing includes: S311. Starting from the first corner, polish the first number of revolutions clockwise. S312. Starting from the third corner, polish the first number of turns counterclockwise. In step S3, the fine polishing includes: S321. Starting from the second corner, polish the second number of revolutions clockwise. S322. Starting from the fourth corner, polish the second circle counterclockwise.

6. The immersion polishing method according to claim 1, characterized in that, In step S3, the angle between the axis of the polishing head and the normal to the workpiece surface is 1.5°, and the combined pressure of the polishing head in the vertical and horizontal directions is 10-15N.

7. The immersion polishing method according to claim 1, characterized in that, The polishing head includes a rigid support rod for connection to a machine tool spindle, a buffer layer fixed to the bottom end of the rigid support rod, an elastic intermediate layer fixed to the bottom end of the buffer layer, and a polishing layer fixed to the bottom end of the elastic intermediate layer and partially surrounding the elastic intermediate layer, wherein the polishing layer is made of at least polyurethane material.

8. The immersion polishing method according to claim 7, characterized in that, The polishing layer of the polishing head used for rough polishing also includes cerium oxide abrasive, and the polishing layer of the polishing head used for fine polishing also includes fibers, and the hardness of the polishing head used for rough polishing is greater than that of the polishing head used for fine polishing.

9. The immersion polishing method according to claim 7, characterized in that, Both the polishing head for coarse polishing and the polishing head for fine polishing are cylindrical structures with a tapered bottom, the tapered bottom of the polishing head being 3°; the buffer layer is a silicone rod or silicone bushing, and the elastic intermediate layer is a polyurethane sheet.

10. The immersion polishing method according to claim 1, characterized in that, Immersion polishing methods also include: S4. After polishing, release the vacuum adsorption, remove the cover plate, and clean and dry it.

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