Ultra-precision machining method for large-size polycrystalline diamond optical sheet

Abstract

The invention provides an ultra-precision machining method for a large-size polycrystalline diamond optical sheet, and belongs to the technical field of ultra-hard material precision machining. According to the machining method, the efficient laser machining capacity, the rapid high-precision finishing capacity of double-face mechanical grinding, the rapid smoothing capacity of mechanical polishing and the ultra-precision fixed-point removing capacity of ion beam polishing are effectively combined, and a stepped and combined machining route is formed; the technical problems of the whole system of machining efficiency, precision and cost of the large-size polycrystalline diamond are systematically solved, a large-size double-sided ultra-precision machined polycrystalline diamond optical product with the machining precision meeting the requirements that the planeness is smaller than or equal to 0.5 micron, the parallelism is smaller than or equal to 1 micron and the surface roughness Ra is smaller than or equal to 3 nm is finally obtained, the machining precision is not affected by the size of a diamond piece, and the machining precision is not affected by the size of the diamond piece. The total processing time is not more than 35 hours, and the finally obtained polycrystalline diamond optical sheet can be used for key optical components of high-end equipment such as a high-power laser, a laser weapon, an electron cyclotron, an infrared seeker and the like.

Description

Technical Field

[0001] This invention belongs to the field of diamond precision machining technology, and particularly relates to a high-efficiency, ultra-precision machining method for large-size polycrystalline diamond optical sheets. Background Technology

[0002] Polycrystalline diamond, due to its extremely high hardness, excellent thermal conductivity, good chemical stability, and wide spectral transmittance, has become an ideal material for manufacturing high-end key components such as high-power laser windows, high-precision optical mirrors, and high-power microwave windows. However, when large-size polycrystalline diamond sheets are used as optical window materials, they require extremely high surface accuracy, parallelism, and low roughness to prevent light refraction and scattering during propagation from affecting their optical performance. At the same time, the extremely high hardness, wear resistance, chemical stability, and anisotropy of polycrystalline diamond make efficient and precise machining extremely difficult; traditional machining methods are inefficient or even completely ineffective. Currently, achieving ultra-precise surface profiles (PV < 1 μm) and low surface roughness (Ra < 3 nm) in large-size (diameter ≥ 50 mm) polycrystalline diamond optical products, along with efficient and low-cost machining, remains a significant challenge for the industry.

[0003] In existing technologies, the precision machining of polycrystalline diamond is mainly achieved through methods such as mechanical grinding and polishing (MJP) and chemical mechanical grinding and polishing (CMP). However, these methods reveal inherent limitations when faced with the extreme requirements for surface accuracy and quality in high-end applications. While mechanical grinding achieves high processing efficiency, its unidirectional force characteristics make it difficult to control surface accuracy and roughness, especially for large-sized polycrystalline diamonds with significant anisotropy. CMP, while achieving extremely low surface roughness, suffers from low processing efficiency, high processing costs, and lacks the ability to correct the initial surface shape, making it unsuitable for machining large-sized diamonds. More importantly, these methods are typically performed as isolated processes, lacking a comprehensive surface shape control mechanism. Effectively combining these different processing methods to achieve ultra-precision machining of polycrystalline diamond will face the following core challenges: The first challenge is the design and integration of the process chain. Different processing methods (such as thermal ablation, mechanical grinding, and atomic sputtering) have drastically different material removal mechanisms, scales of action, and forms of damage introduction. Designing a process chain that leverages strengths and avoids weaknesses, ensuring a smooth transition and guaranteeing that the output state of the preceding process (such as surface shape, roughness, and damaged layer) is exactly the optimal input state for the following process, is the primary technical challenge.

[0004] Secondly, there is the challenge of accurately matching and transmitting processing status and indicators. Each process not only needs to achieve its own processing goals (such as removal amount and roughness), but also needs to reserve a reasonable and efficient removal allowance for the next process, and control the secondary damage introduced. If the indicators of any link are out of control (such as excessive roughness or excessively deep damage layer after rough grinding), it will lead to a sharp drop in the efficiency of subsequent processes or even make it impossible to correct, and the entire process chain will fail.

[0005] Finally, there is the challenge of uniformity control brought about by large size and anisotropy: for large-sized polycrystalline diamonds, the differences in grain orientation and hardness lead to different processing responses. The combined process must ensure uniform material removal and surface correction capabilities across the entire workpiece surface to avoid surface errors such as "saddle-shaped" and "bowl-shaped" defects. This places extremely high demands on the equipment precision and process parameter adaptability of each process step.

[0006] Therefore, there is an urgent need in this field for a combined processing technology that can balance processing efficiency and achieve ultra-high processing precision for polycrystalline diamond optical products, systematically solving the overall technical challenges of processing efficiency, precision, and cost of large-size polycrystalline diamond, and realizing industrial application. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned difficulties and provide a method for ultra-precision assembly processing of large-size polycrystalline diamond optical wafers with reasonable process connection, high processing efficiency, excellent precision, and suitability.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An ultra-precision machining method for large-size polycrystalline diamond optical wafers includes: S1: A pulsed laser is used to perform double-sided laser rough grinding on a polycrystalline diamond optical wafer blank to obtain a rough-ground polycrystalline diamond optical wafer. The surface roughness Ra of the rough-ground polycrystalline diamond optical wafer is reduced to below 600 nm, and the flatness and parallelism are reduced to below 30 μm. The polycrystalline diamond optical wafer blank is described in the following text. S2: The coarsely ground polycrystalline diamond optical sheet is subjected to double-sided fine grinding using a high-precision double-end grinding machine to obtain a finely ground polycrystalline diamond optical sheet. The surface roughness Ra of the finely ground polycrystalline diamond optical sheet is reduced to below 200 nm, and the flatness and parallelism are reduced to below 5 μm. S3: The polycrystalline diamond optical sheet is mechanically rough polished using a high-precision diamond polishing machine to obtain a rough polished polycrystalline diamond optical sheet. The surface roughness Ra of the rough polished polycrystalline diamond optical sheet is reduced to below 10 nm, and the flatness and parallelism are reduced to below 2 μm. S4: The coarsely polished polycrystalline diamond optical sheet is subjected to ion beam fine polishing using an ion beam polishing machine to obtain an ultra-precision processed polycrystalline diamond optical sheet. The surface roughness Ra of the ultra-precision processed polycrystalline diamond optical sheet is reduced to below 3nm, the flatness is reduced to below 0.5μm, and the parallelism is reduced to below 1μm.

[0009] Furthermore, in step S1, a near-infrared pulsed fiber laser with a wavelength of 1064 nm is selected, which can easily obtain a high average power of over 100 watts, thereby ensuring processing efficiency.

[0010] Further, step S1 includes: the pulsed laser is a nanosecond pulsed red laser, the laser polishing path adopts parallel line polishing and layer polishing method alternately, the laser power of laser polishing is 50-100W, the frequency is 150-200kHz, the linear speed is 10-20 mm / s, the scanning time is 2-4 h, and the heat-affected layer depth is 10-25 μm.

[0011] Furthermore, the surface roughness Ra of the coarsely ground polycrystalline diamond optical sheet is reduced to 350–600 nm, and the flatness and parallelism are reduced to 20–30 μm.

[0012] Furthermore, in step S2, the high-precision double-sided grinding machine has a sun gear speed of 5-20 rpm, an upper platen speed of 5-20 rpm, a lower platen speed of 10-35 rpm, a grinding pressure of 5-30 kg, and a pressurization time of 5-20 s. The double-sided fine grinding process can achieve directional dressing by controlling the speed ratio between the sun gear and the upper and lower grinding plates. When the planetary gear rotates clockwise and the sun gear rotates counterclockwise, and the speed of the lower platen is greater than the speed of the sun gear, the "concave in the middle and convex around the edges" surface can be dressed into a flat state. When the planetary gear rotates counterclockwise and the sun gear rotates clockwise, and the speed of the lower platen is greater than the speed of the sun gear, the "convex in the middle and concave around the edges" surface can be dressed into a flat state.

[0013] Furthermore, in step S2, the grinding fluid used includes single-crystal diamond micro powder with a particle size of 5-25 μm, pure water, rust inhibitor, and diamond micro powder suspension, wherein the mass ratio of pure water: single-crystal diamond micro powder: rust inhibitor: diamond micro powder suspension is (40-60):(4-6):(1-4):(1-4), and the concentration of the diamond micro powder suspension is 20%-50%. Thus, the surface accuracy, thickness deviation, and parallelism of the polycrystalline diamond during the fine grinding process can be adjusted by changing the rotational speed ratio between the sun wheel and the upper and lower grinding discs.

[0014] Furthermore, the surface roughness Ra of the finely ground polycrystalline diamond optical sheet is reduced to 160–200 nm, and the flatness and parallelism are preferably reduced to 3–5 μm.

[0015] Furthermore, in step S3, the polycrystalline diamond optical wafer is polished using a mechanical polishing method with a grinding wheel. The polishing wheel is a ceramic-bonded diamond wheel with a diamond grit size of 200-400#, a radial runout of <10μm, an end face runout of <5μm, a polishing machine speed of 1500-3000 r / min, and a counterweight of 1-5 Kg.

[0016] Furthermore, the surface roughness Ra of the coarsely polished polycrystalline diamond optical sheet is reduced to 5–10 nm, and the flatness and parallelism are preferably reduced to 1.5–2 μm.

[0017] Furthermore, in step S4, the parameters for the ion beam polishing process are: argon as the ion source gas, an accelerating voltage of 500V to 1500V, and a beam current density of 0.5 to 2 mA / cm². 2 The incident angle is 0° to 45°, and the workpiece stage speed is 1 to 10 rpm.

[0018] Therefore, the core of the ultra-precision machining method for large-size polycrystalline diamond optical wafers provided by this invention lies in constructing an innovative process route of "from rough to fine, multi-energy field synergy, and deterministic control." This method first employs a high-power laser with specific parameters for efficient rough machining, achieving rapid removal through a controllable heat accumulation mechanism; then, double-sided fine grinding is used to simultaneously trim the macroscopic surface shape and remove the heat-affected layer; next, a high-precision polishing machine is used to achieve rapid and smooth polishing of the diamond wafer without compromising its original dimensional accuracy; finally, contactless and stress-free ion beam polishing is used to achieve atomic-scale removal, realizing ultra-high precision machining. Furthermore, the high-quality double-sided ultra-precision machined polycrystalline diamond optical wafers prepared by this method provide key material solutions for optical components in cutting-edge equipment such as laser windows in extreme ultraviolet (EUV) lithography machines, high-power laser weapons, microwave weapon output windows, and electron cyclotron accelerator windows, significantly enhancing my country's core technological competitiveness in the field of ultra-precision manufacturing. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the processing flow according to an embodiment of the present invention; Figure 2 This is a schematic diagram of laser rough grinding processing according to an embodiment of the present invention; Figure 3 This is a schematic diagram of dual-plane fine grinding according to an embodiment of the present invention; Figure 4 This is a schematic diagram of mechanical rough polishing according to an embodiment of the present invention; Figure 5 This is a schematic diagram of ion beam polishing according to an embodiment of the present invention; Figure 6 Flatness test data after polishing in Embodiment 1 of the present invention; Figure 7 Surface roughness detection data after polishing in Example 1 of this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0021] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and unless otherwise specified, such ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0022] Unless otherwise specified, the terminology used in this invention is a common term in the relevant field. Unless otherwise specified, the preparation processes and testing methods used in each embodiment are conventional means well known to those skilled in the art, and the raw materials and equipment used can be obtained from publicly available commercial channels.

[0023] To improve a method for processing polycrystalline diamond optical products with both high efficiency and ultra-high precision on both sides, this invention combines laser double-sided rough grinding, double-sided mechanical grinding, mechanical polishing, and ion beam polishing. It effectively integrates the high efficiency of laser processing, the rapid and high-precision finishing capabilities of double-sided mechanical grinding, the rapid smoothing capabilities of mechanical polishing, and the ultra-precise targeted removal capabilities of ion beam polishing to form a step-by-step, combined processing route. This systematically solves the overall technical challenges of processing efficiency, precision, and cost for large-size polycrystalline diamond, enabling industrial application. Therefore, the innovation and breakthrough of this invention lie in the precise definition and chain-like connection of process functions, rather than a simple accumulation of multiple methods. Based on the material removal mechanism and precision improvement logic, the processing is precisely divided into four functionally distinct and closely connected stages.

[0024] Specifically, the technical solution adopted in this invention is as follows: Please see Figures 1 to 5 A method for ultra-precision machining of large-size polycrystalline diamond optical wafers, comprising: S1: A pulsed laser is used to perform double-sided laser rough grinding on a polycrystalline diamond optical wafer blank to obtain a rough-ground polycrystalline diamond optical wafer. The surface roughness Ra of the rough-ground polycrystalline diamond optical wafer is reduced to below 600 nm, and the flatness and parallelism are reduced to below 30 μm. The polycrystalline diamond optical wafer blank is described in the following text. S2: The coarsely ground polycrystalline diamond optical sheet is subjected to double-sided fine grinding using a high-precision double-end grinding machine to obtain a finely ground polycrystalline diamond optical sheet. The surface roughness Ra of the finely ground polycrystalline diamond optical sheet is reduced to below 200 nm, and the flatness and parallelism are reduced to below 5 μm. S3: The polycrystalline diamond optical sheet is mechanically rough polished using a high-precision diamond polishing machine to obtain a rough polished polycrystalline diamond optical sheet. The surface roughness Ra of the rough polished polycrystalline diamond optical sheet is reduced to below 10 nm, and the flatness and parallelism are reduced to below 2 μm. S4: The coarsely polished polycrystalline diamond optical sheet is subjected to ion beam fine polishing using an ion beam polishing machine to obtain an ultra-precision processed polycrystalline diamond optical sheet. The surface roughness Ra of the ultra-precision processed polycrystalline diamond optical sheet is reduced to below 3nm, the flatness is reduced to below 0.5μm, and the parallelism is reduced to below 1μm.

[0025] The polycrystalline diamond optical wafer blank is preferably a polycrystalline diamond thick film prepared by chemical vapor deposition (CVD), and its typical initial state is: diameter ≥ 50 mm, thickness 1.2~1.8 mm, growth surface roughness Ra 2~5 μm, nucleation surface roughness Ra 10~30 nm, overall flatness ≤ 60 μm, and parallelism ≤ 60 μm.

[0026] Furthermore, the core function of step S1 is high-efficiency integral forming. Utilizing laser technology, most of the excess material is rapidly removed, quickly bringing the original blank from a macroscopically irregular state close to the target size, and providing a relatively flat and uniform reference for subsequent machining. Its output indicators, including a surface roughness Ra ≤ 600 nm and flatness and parallelism ≤ 30 μm, aim to balance efficiency with providing a repairable initial state for process S2. If Ra > 600 nm, it means that there are deep laser scanning grooves or microcracks on the surface, which will be difficult to smooth out in a reasonable time in process S2, and may easily lead to rapid failure of the diamond micropowder. If flatness > 30 μm, process S2 requires a longer finishing time, and may affect the final thickness consistency due to uneven removal. Therefore, after the laser double-sided rough grinding treatment in step S1, the surface roughness Ra of the obtained rough-ground polycrystalline diamond optical sheet is preferably reduced to 350–600 nm, and the flatness and parallelism are preferably reduced to 20–30 μm (output indicators).

[0027] To further realize the core function of step S1, the present invention specifically selects a near-infrared pulsed fiber laser with a wavelength of 1064 nm in step S1, which can easily obtain a high average power of over 100 watts, thereby ensuring processing efficiency.

[0028] Furthermore, in step S1, the laser polishing path adopts parallel line polishing and layer polishing methods. That is, after one layer is scanned and removed, the workpiece is rotated at a specific angle and the next layer is scanned and removed. This process is repeated alternately until the predetermined removal depth is reached, thus avoiding the generation of obvious periodic patterns and stress concentration.

[0029] Furthermore, in step S1, the laser grinding power is 50–100W, the frequency is 150–200kHz, the linear speed is 10–20mm / s, and the scanning time is 2–4 hours. Through rapid, continuous pulsed energy impact, a graphitization phase transition occurs on the diamond surface, achieving a processing efficiency of 200–300 μm / h. This allows for rapid processing of diamond to near-net-shape, while controlling the heat-affected layer depth within the range of 10–25 μm. After laser rough grinding, the surface roughness Ra of the polycrystalline diamond optical wafer is reduced to below 600nm, and the flatness and parallelism are reduced to below 30μm. Controlling the heat-affected layer depth within the range of 10–25 μm represents the optimal balance between quality and cost; if the heat-affected layer depth is too shallow, processing efficiency will drop sharply, and costs will increase significantly; if the heat-affected layer depth is too deep, it will be impossible to connect to the subsequent fine grinding process.

[0030] The core function of step S2 is high-precision surface shaping and damage layer removal. Utilizing the error averaging principle of double-sided grinding, the macroscopic surface shape error generated in S1 is efficiently corrected, and the laser heat-affected layer is removed simultaneously. The establishment of the output indicators for step S2—surface roughness Ra ≤ 200 nm, flatness and parallelism ≤ 5 μm—is to obtain sufficient geometric accuracy to support the polishing process in S3, while refining the surface texture to a scale where mechanical polishing can be effective. Ra needs to be reduced to below 200 nm at this stage because this is the optimal pre-surface state for efficient and stable operation of the mechanical polishing wheel abrasive grains (tens of micrometers in diameter). If Ra is too high, polishing efficiency is low and wheel wear is rapid; flatness ≤ 5 μm is a key prerequisite to ensure that subsequent polishing focuses on reducing roughness rather than correcting the surface shape. Therefore, after the double-sided mechanical grinding process in step S2, the surface roughness Ra of the finely ground polycrystalline diamond optical wafer is preferably reduced to 160–200 nm, and the flatness and parallelism are preferably reduced to 3–5 μm (output indicators).

[0031] To further realize the core function of step S2, preferably, the double-sided fine grinding in step S2 utilizes the error averaging effect of the upper and lower grinding discs in a high-precision double-end grinding machine to eliminate the macroscopic heat-affected layer left in step S1 while achieving precise control of the polycrystalline diamond surface shape and thickness. The sun gear speed is 5–20 rpm, the upper disc speed is 5–20 rpm, the lower disc speed is 10–35 rpm, the grinding pressure is 5–30 kg, and the pressurization time is 5–20 s. The processing can achieve directional dressing by controlling the speed ratio between the sun gear and the upper and lower grinding discs. When the planetary gear rotates clockwise and the sun gear rotates counterclockwise, and the lower disc speed is greater than the sun gear speed, the "concave in the middle and convex around the edges" surface shape can be dressed into a flat state. When the planetary gear rotates counterclockwise and the sun gear rotates clockwise, and the lower disc speed is greater than the sun gear speed, the "convex in the middle and concave around the edges" surface shape can be dressed into a flat state.

[0032] Further, in step S2, the grinding fluid includes single-crystal diamond powder with a particle size of 5-25 μm, pure water, rust inhibitor, and diamond powder suspension. The mass ratio of pure water to single-crystal diamond powder to rust inhibitor to diamond powder suspension is (40-60):(4-6):(1-4):(1-4), preferably (45-50):4:2:(2-4), such as 45:4:2:2, 45:4:2:3, 45:4:2:4, 48:4:2:2, 48:4:2:3, 48:4:2:4, 50:4:2:2, 50:4:2:3, 50:4:2:4, etc. The diamond powder suspension used in this invention is a commercially available product, and its concentration can be 20%-50%, such as 20%, 30%, 40%, 50%, etc.

[0033] The core function of step S3 is rapid surface smoothing. Building upon the excellent surface profile achieved in step S2, it rapidly reduces flatness and surface roughness. The output indicators of step S3—surface roughness Ra ≤ 10 nm, flatness and parallelism ≤ 2 μm—are crucial thresholds for ensuring a smooth transition of the surface microstructure to the atomic-level removal in step S4. At this stage, if the surface roughness is >10 nm, the ion beam will spend a significant amount of time removing microscopic peaks and valleys, resulting in extremely low efficiency and greatly increasing the time and cost of ion beam polishing. If polishing is forcibly pushed to ≤5 nm in this process, aiming for even lower levels, mechanical stress can easily cause the already achieved micron-level surface profile accuracy to deteriorate (flatness rebounds to >2 μm). Therefore, after the double-sided mechanical polishing treatment in step S3, the surface roughness Ra of the obtained coarsely polished polycrystalline diamond optical sheet is preferably reduced to 5–10 nm, and the flatness and parallelism are preferably reduced to 1.5–2 μm (output indicators).

[0034] To further realize the core function of step S3, preferably, the mechanical polishing method in step S3 uses a ceramic-bonded diamond wheel as the polishing medium. Through a controllable processing method of high-speed mechanical grinding, the abrasive grains of the wheel precisely cut and grind the surface of the polycrystalline diamond optical sheet to obtain a smooth, flat, and low-roughness high-quality surface. The diamond polishing wheel has a particle size of 30-60 μm, a concentration of 100%-120%, a polishing machine speed of 1500-3000 r / min, and a counterweight of 1-5 Kg.

[0035] The core function of step S4 is the deterministic convergence of surface features at the atomic scale and the preparation of ultra-smooth surfaces. As the final step, it builds upon the excellent surface features and subsurface quality provided by the previous three steps to achieve the final target of nanoscale roughness and submicron-level surface features.

[0036] To further realize the core function of step S4, the ion beam polishing step S4 employs a low-energy, high-current processing scheme. An argon ion beam is generated using an ion source, accelerated, and then uniformly irradiates the workpiece surface at a certain angle. The ions strip away atoms from the workpiece surface one by one through physical sputtering. After one ion beam polishing cycle, the surface profile is measured online. Based on the surface profile error, a second and third iteration of polishing are performed until the final surface profile and roughness indicators are achieved. Preferably, the ion source gas in step S4 is argon, the accelerating voltage is 500V–1500V, and the beam current density is 0.5–2 mA / cm². 2 The incident angle is 0° to 45°, and the workpiece stage rotation speed is 1 to 10 rpm.

[0037] This invention clearly defines the input prerequisites and output indicators for each process, forming an interconnected "machining tolerance chain." From the initial blank state to the final product, the machining allowance and precision indicators at each stage are precisely calculated and experimentally verified, ensuring the determinism and repeatability of the process. Therefore, compared with the prior art, the main beneficial effects of this invention are as follows: This invention provides an ultra-precision assembly processing method for large-size polycrystalline diamond optical wafers. Its core lies in constructing an innovative process route that is "from roughing to finishing, multi-energy field synergy, and deterministic control." The method first employs a high-power laser with specific parameters for efficient roughing, achieving rapid removal through a controllable heat accumulation mechanism. Next, double-sided fine grinding is used to simultaneously refine the macroscopic surface shape and remove the heat-affected layer. Then, a high-precision polishing machine is used to achieve rapid and smooth polishing of the diamond wafer without compromising its original dimensional accuracy. Finally, contactless and stress-free ion beam polishing is employed to achieve atomic-scale removal, realizing ultra-high precision processing.

[0038] Through the synergistic processing of the aforementioned technology chain, this invention successfully overcomes the technical bottleneck of simultaneously achieving large size, high surface accuracy, and ultra-smooth surface in polycrystalline diamond optical wafers. The final processed product achieves sub-micron level surface accuracy (flatness PV value ≤ 0.5μm) and nano-level surface roughness (Ra < 3nm), with extremely low subsurface damage and maximum preservation of crystal structure integrity. The high-quality, ultra-precision processed polycrystalline diamond optical wafers prepared by this method provide a key material solution for optical components in cutting-edge equipment such as laser windows in extreme ultraviolet (EUV) lithography machines, high-power laser weapons, microwave weapon output windows, and electron cyclotron accelerator windows.

[0039] The technical solution protected by this invention will be further explained and illustrated with the following specific embodiments. Example 1 Taking a CVD polycrystalline diamond billet with initial dimensions of Φ60 mm × 1.8 mm, growth surface Ra≈2μm, nucleation surface Ra≈10nm, and flatness≈60μm as an example.

[0040] This embodiment provides an ultra-precision assembly processing method for large-size polycrystalline diamond optical wafers, including step S1 laser double-sided rough grinding, step S2 double-sided mechanical grinding, step S3 mechanical polishing, and step S4 ion beam polishing. The specific details of each step are as follows: Step S1: Double-sided rough grinding is performed using a near-infrared nanosecond pulsed laser with a wavelength of 1064 nm. A 60 mm diameter vacuum adsorption fixture is used to fix the polycrystalline diamond optical sheet in the cutting cavity. The power is set to 95 W, the pulse frequency to 200 kHz, and the scanning speed to 15 mm / s. Layered laser grinding is performed using these parameters to efficiently thin the blank from 1.8 mm to 1.25–1.28 mm, with the growth surface thinned by 0.4–0.5 mm and the nucleation surface thinned by 0.1–0.15 mm, resulting in a total removal of 0.52 mm. After laser grinding, a coarsely ground polycrystalline diamond optical sheet is obtained. This sheet exhibits a uniform scanning texture on its surface. Measurements show that the heat-affected layer depth is approximately 20 μm, Ra is reduced to 550 nm, and flatness and parallelism are reduced to 28 μm. This improves the surface condition from "micron-level grain undulations" to "submicron-level uniform texture," creating conditions for the subsequent mechanical fine grinding step S2.

[0041] Step S2: Use a high-precision double-end face grinder to perform double-sided fine grinding. The coarsely ground polycrystalline diamond optical sheet obtained in step S1 is placed convex-side down in a blued steel planetary wheel for double-sided fine grinding. The planetary wheel has an opening size of 60.2 mm. The diamond microparticles in the fine grinding slurry have a particle size of 5.7 μm. The mass ratio of pure water, diamond microparticles, rust inhibitor, and 30% diamond suspension is 50:6:3:2. Double-sided fine grinding is performed using a forward rotation process with the lower plate rotating at 35 rpm, the sun wheel rotating at 18 rpm, the upper plate rotating at 25 rpm, the grinding pressure at 35 kg, and the pressurization time at 25 s. This yields a finely ground polycrystalline diamond optical sheet with a uniform scanning pattern on its surface. Measurements show that the surface roughness Ra of the finely ground polycrystalline diamond optical sheet is reduced to 180 nm, and the flatness and parallelism are reduced to 4 μm. This eliminates the macroscopic surface shape error and heat-affected layer of step S1, improving the surface shape accuracy to the micron level and laying the geometric foundation for polishing.

[0042] Step S3: Mechanical rough polishing using a high-precision diamond polishing machine. A ceramic-bonded diamond abrasive wheel with a particle size of 30 μm, a concentration of 100%, and an effective width of 45 mm is used to perform mechanical rough polishing on the finely ground polycrystalline diamond optical sheet obtained in Step S2. The wheel speed is 2500 r / min, the oscillation speed is 10 mm / s, the polishing pressure is 3 kg, each polishing cycle lasts 1 hour, and the total processing time is 10 hours. The final rough-polished polycrystalline diamond optical sheet is obtained. Measurements show that its surface roughness Ra is reduced to 8 nm, and its flatness and parallelism are reduced to 1.8 μm. This achieves a rapid transformation of the surface from a "frosted" to a "mirror-like" finish, reducing the roughness by an order of magnitude. Ra ≤ 10 nm is a prerequisite for entering the high-efficiency region of ion beam polishing.

[0043] Step S4: Fine polishing using an ion beam polisher. The coarsely polished polycrystalline diamond optical wafer obtained in step S3 is transferred to a vacuum chamber, and an argon ion beam is used with an accelerating voltage of 800 V and a beam current density of 1.0 mA / cm². 2 With an incident angle of 30°, atomic-level removal is achieved through ion sputtering to obtain an ultra-smooth surface. The processing time for a single pass is approximately 6 hours, ultimately yielding a double-sided ultra-precision machined polycrystalline diamond optical sheet. Measurements show that the surface roughness Ra of this double-sided ultra-precision machined polycrystalline diamond optical sheet is reduced to 2.18 nm, and the flatness and parallelism converge to 0.484 μm. Thus, this step performs atomic-level micro-removal, ultimately converging the surface profile and achieving an ultra-smooth surface. Ion beam polishing is extremely sensitive to the preceding surface profile. Thanks to the excellent foundation provided by S3, the ion beam can focus on nanoscale surface profile fine-tuning and atomic-level smoothing, ultimately achieving ultra-precision specifications.

[0044] according to Figure 6 and Figure 7It can be seen that by using a stepped and combined ultra-precision machining method, a double-sided ultra-precision machined polycrystalline diamond optical sheet with a specification of 60×1.2 mm was obtained. The flatness of the optical sheet reached 0.484 μm and the surface roughness Ra reached 2.18 nm.

[0045] Comparative Example To verify the necessity of the process chain designed in the embodiments of the present invention and the scientific nature of the setting of indicators for each process, the following comparative examples are designed.

[0046] (1) The impact of processing steps Comparative Examples A through D each provide a method for processing large-size polycrystalline diamond optical wafers, which is basically the same as the processing method provided in Example 1, with the main difference being: Comparative Example A omits step S1, and step S2 starts directly from the rough surface of the original CVD polycrystalline diamond billet; In Comparative Example B, step S2 is omitted, and the coarsely ground polycrystalline diamond optical sheet obtained in step S1 directly enters the coarse polishing stage. In Comparative Example C, step S3 is omitted, and the finely ground polycrystalline diamond optical sheet obtained after step S2 is directly subjected to ion beam polishing. In Comparative Example D, step S4 is omitted, and the finely ground polycrystalline diamond optical sheet obtained after step S2 is polished using only step S3.

[0047] The processing effects of Example 1 and Comparative Examples A to D are shown in Table 1.

[0048] Table 1. Results of the impact of processing steps Group Final processing result (PV / Ra) Total working hours Results Analysis Example 1 0.484 μm / 2.18 nm 28 h Complete process chain, achieving goals efficiently Comparative Example A Three cracks appeared on the edge during the fine grinding process, with a crack length of 1-3 mm. 110h The initial large surface area error could not be corrected, and the grinding time was extremely long, resulting in large cracks. Comparative Example B 12.72 μm / 21.37 nm 75 h Polishing cannot correct flatness, and the heat-affected layer causes subsurface defects on the polished surface, making it difficult to further reduce Ra. Comparative Example C 5 μm / 173 nm 52 h Due to the high initial Ra, ion beam polishing requires the removal of a large amount of material to smooth the surface, which is extremely time-consuming and makes surface convergence difficult. Comparative Example D 1.6 μm / 6nm 20 h Without ion beam polishing, there is a lack of atomic-scale removal, making it difficult to further improve processing precision.

[0049] As can be seen from Table 1, each of the S1 to S4 processes is indispensable. Each process plays an irreplaceable role in connecting the preceding and following steps; omitting any step will cause the processing chain to break, making it impossible to achieve the final accuracy within an acceptable timeframe.

[0050] (2) The influence of output indicators of laser double-sided rough grinding process Comparative Examples E to F each provide a method for processing large-size polycrystalline diamond optical wafers, which are basically the same as the processing method provided in Example 1, with the main difference being: The surface roughness Ra of the coarsely ground polycrystalline diamond optical sheet obtained by comparative example E (excessively poor performance) after double-sided coarse grinding in step S1 was reduced to 700 nm, and the flatness and parallelism Pv were both reduced to 40 μm. The surface roughness Ra of the coarsely ground polycrystalline diamond optical sheet obtained by comparative example F (over-pursuit) after double-sided coarse grinding in step S1 was reduced to 300 nm, and the flatness and parallelism Pv were both reduced to 15 μm.

[0051] The processing effects of Example 1 and Comparative Examples E to F are shown in Table 2.

[0052] Table 2. Results of the Influence of Laser Double-Sided Rough Grinding Process on Output Indicators Group S2 Processing Difficulty and Results Final processing result (PV / Ra) analyze Example 1 S2 easily completes the repair, with normal processing time. 0.484 μm / 2.18 nm The indicators are appropriate, providing the best starting point for subsequent processes. Comparative Example E The S2 grinding pressure needs to be increased, which significantly increases the risk of chip cracking during processing, increases processing time by 50%, and the flatness after finishing is still poor (8μm). 4 μm / 5.8nm The S1 metric went out of control, causing the entire subsequent chain to pay a price to fix its defects, resulting in substandard accuracy. Comparative Example F The S2 machining allowance is insufficient, resulting in a product that is too thin and must be scrapped. Increasing the blank thickness would increase costs. 0.9 μm / 2.3 nm The excessive pursuit of local metrics in S1 sacrificed efficiency and failed to leave sufficient "shaping margin" for S2, thus limiting the overall surface convergence ability. (3) The impact of double-sided fine grinding process on output indicators Comparative Examples G to I each provide a method for processing large-size polycrystalline diamond optical wafers, which are basically the same as the processing method provided in Example 1, with the main difference being: In comparative example G (Ra index poor), the grinding time in step S2 was insufficient in order to improve efficiency, which reduced the surface roughness Ra of the finely ground polycrystalline diamond optical sheet obtained after double-sided fine grinding in step S2 to 300 nm, and the flatness and parallelism Pv were both reduced to 12 μm. Comparative Example H (poor Pv index) had improper grinding parameters in step S2, resulting in insufficient shaping ability. This caused the surface roughness Ra of the finely ground polycrystalline diamond optical sheet obtained after double-sided fine grinding in step S2 to decrease to 190 nm, and the flatness and parallelism Pv to decrease to 8 μm. In Comparative Example I (over-pursuit), step S2 excessively extended the grinding time in pursuit of perfection, resulting in a reduction in the surface roughness Ra of the finely ground polycrystalline diamond optical sheet obtained after double-sided fine grinding in step S2 to 150 nm, and a reduction in both flatness and parallelism Pv to 3 μm.

[0053] The processing effects of Example 1 and Comparative Examples G to I are shown in Table 3.

[0054] Table 3. Results of the Influence of Double-Sided Grinding Process on Output Indicators Group S3 Processing Status and Results Final processing result (PV / Ra) analyze Example 1 Polishing was smooth, took 10 hours, and resulted in a stable surface shape. 0.484 μm / 2.18 nm With optimal performance indicators, Ra≤200nm and Pv<5μm provide an ideal micro-machining substrate for S3. Comparative Example G Polishing was inefficient, taking up to 15 hours, and the resulting roughness was Ra-20nm, with a slight deterioration in the surface texture. 4 μm / 7.4nm An excessively high Ra value in S2 leads to an overburdened S3 process, reduced efficiency, and negatively impacts the final surface accuracy. Comparative Example H Polishing cannot correct surface defects of this magnitude; the flatness remains >3μm after polishing. 1.5 μm / 3.5 nm S2 failed to complete the surface refinement, leaving macroscopic surface errors in subsequent steps, exceeding the correction capabilities of S3 / S4, resulting in a final surface that is unqualified. Comparative Example I The polishing allowance is insufficient, and the material thickness is close to the lower limit, but the surface shape is well maintained. 0.458 μm / 2.1 nm The S2 specification significantly increases processing time, raises overall costs, and imposes stricter requirements on billet thickness. This demonstrates that the S2 specification represents the optimal balance between efficiency and precision; over-optimization is uneconomical. (3) The impact of mechanical rough polishing process on output indicators Comparative Examples J to L each provide a method for processing large-size polycrystalline diamond optical wafers, which is basically the same as the processing method provided in Example 1, with the main difference being: In Comparative Example J (Poor Ra Index), insufficient polishing time or improper parameters in step S3 resulted in a reduction in the surface roughness Ra of the coarsely polished polycrystalline diamond optical sheet obtained after mechanical rough polishing in step S3 to 15 nm, and a reduction in both flatness and parallelism Pv to 2 μm. In Comparative Example K (Sacrificing Ra for Pv), in pursuit of low roughness, excessively high pressure or excessively fine grinding wheels were used in step S3, resulting in local overheating and stress deformation. This caused the surface roughness Ra of the coarsely polished polycrystalline diamond optical wafer obtained after mechanical coarse polishing in step S3 to be reduced to 5 nm, and the flatness and parallelism Pv to be reduced to 3.5 μm. In Comparative Example L (Pv remains the same but Ra is slightly higher), conservative parameters are used in step S3 to ensure the surface shape, so that the surface roughness Ra of the rough-polished polycrystalline diamond optical sheet obtained after mechanical rough polishing in step S3 is reduced to 12 nm, and the flatness and parallelism Pv are both reduced to 1.5 μm.

[0055] The processing effects of Example 1 and Comparative Examples J to L are shown in Table 4.

[0056] Table 4. Results of the impact of mechanical rough polishing process on output indicators Group S4 processing status Final processing result (PV / Ra) analyze Example 1 S4 ion beam polishing for 6 hours to achieve high-efficiency convergent surface shaping 0.484 μm / 2.18 nm The performance indicators are optimal; Ra≤10 nm is an ideal prerequisite for efficient ion beam operation; flatness≤2μm lays a perfect foundation for final refinement. Comparative Example J S4 requires the removal of a significant amount of material to reduce roughness, increasing the time required to 20 hours, and prolonged sputtering may introduce new surface profile errors. 1.11 μm / 5.17 nm The failure of Ra in S3 to meet the standard severely hampered the efficiency of S4 and limited the improvement of the final surface quality. Comparative example K S4 first needs to correct the deteriorated surface shape of S3, and the ion beam reshaping time is >40 hours, which is extremely time-consuming. 1.65 μm / 2.21 nm Ra≤10nm is the optimal value to meet the requirements of subsequent processes. Comparative Example L S4's efficiency falls between that of Example 1 and Comparative Example J, taking approximately 9 hours. 0.48 μm / 3.78 nm Although the result met the target, the total working hours increased; this confirms the scientific validity of the key threshold of Ra≤10nm, as even a value slightly higher than this significantly affects overall efficiency. Based on Tables 2-4, targeted verification of the output indicators for each of processes S1, S2, and S3 clearly demonstrates that the output indicators of each process are a technical prerequisite for the efficient execution of subsequent processes. Deviations from these thresholds will directly lead to decreased processing chain efficiency, increased costs, or final accuracy failure. Furthermore, the optimal indicator value is not the theoretical limit achievable by that process, but rather the globally optimal solution under multiple constraints, including processing efficiency, cost control, conditions created for the next process, and the final product qualification rate. Overly pursuing local optimization of a single process indicator may actually disrupt the overall synergy of the process chain.

[0057] All comparative examples demonstrate, inversely, the necessity, rationality, and innovation of the "step-by-step" process chain and its quantitative indicator system designed in this invention, reflecting the deterministic control capability of the entire process from macroscopic rapid prototyping to atomic-level refinement.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for ultra-precision machining of large-size polycrystalline diamond optical wafers, comprising: S1: The polycrystalline diamond optical wafer blank is subjected to laser double-sided rough grinding using a pulsed laser to obtain a rough-ground polycrystalline diamond optical wafer. The surface roughness Ra of the rough-ground polycrystalline diamond optical wafer is reduced to below 600 nm, and the flatness and parallelism are reduced to below 30 μm. S2: The coarsely ground polycrystalline diamond optical sheet is subjected to double-sided fine grinding using a high-precision double-end grinding machine to obtain a finely ground polycrystalline diamond optical sheet. The surface roughness Ra of the finely ground polycrystalline diamond optical sheet is reduced to below 200 nm, and the flatness and parallelism are reduced to below 5 μm. S3: The polycrystalline diamond optical sheet is mechanically rough polished using a high-precision diamond polishing machine to obtain a rough polished polycrystalline diamond optical sheet. The surface roughness Ra of the rough polished polycrystalline diamond optical sheet is reduced to below 10 nm, and the flatness and parallelism are reduced to below 2 μm. S4: The coarsely polished polycrystalline diamond optical sheet is subjected to ion beam polishing using an ion beam polishing machine to obtain an ultra-precision processed polycrystalline diamond optical sheet. The surface roughness Ra of the ultra-precision processed polycrystalline diamond optical sheet is reduced to below 3 nm, the flatness is reduced to below 0.5 μm, and the parallelism is reduced to below 1 μm.

2. The ultra-precision machining method according to claim 1, characterized in that, In step S1, a near-infrared pulsed fiber laser with a wavelength of 1064 nm is selected.

3. The ultra-precision machining method according to claim 2, characterized in that, Step S1 includes: the pulsed laser is a nanosecond pulsed red laser, the laser polishing path adopts parallel line polishing and layer polishing method alternately, the laser power of laser polishing is 50-100W, the frequency is 150-200kHz, the linear speed is 10-20mm / s, the scanning time is 2-4h, and the heat-affected layer depth is 10-25μm.

4. The ultra-precision machining method according to claim 3, characterized in that, The surface roughness Ra of the coarsely ground polycrystalline diamond optical sheet is reduced to 350–600 nm, and the flatness and parallelism are reduced to 20–30 μm.

5. The ultra-precision machining method according to claim 1 or 4, characterized in that, In step S2, the high-precision double-sided grinding machine has a sun gear speed of 5-20 rpm, an upper platen speed of 5-20 rpm, a lower platen speed of 10-35 rpm, a grinding pressure of 5-30 kg, and a pressurization time of 5-20 s. The double-sided fine grinding process can achieve directional dressing by controlling the speed ratio between the sun gear and the upper and lower grinding plates. When the planetary gear rotates clockwise and the sun gear rotates counterclockwise, and the speed of the lower platen is greater than the speed of the sun gear, the "concave in the middle and convex around the edges" surface can be dressed into a flat state. When the planetary gear rotates counterclockwise and the sun gear rotates clockwise, and the speed of the lower platen is greater than the speed of the sun gear, the "convex in the middle and concave around the edges" surface can be dressed into a flat state.

6. The ultra-precision machining method according to claim 5, characterized in that, In step S2, the grinding fluid used includes single-crystal diamond micro powder with a particle size of 5-25 μm, pure water, rust inhibitor, and diamond micro powder suspension, wherein the mass ratio of pure water: single-crystal diamond micro powder: rust inhibitor: diamond micro powder suspension is (40-60):(4-6):(1-4):(1-4), and the concentration of the diamond micro powder suspension is 20%-50%.

7. The ultra-precision machining method according to claim 6, characterized in that, The surface roughness Ra of the finely ground polycrystalline diamond optical sheet is reduced to 160–200 nm, and the flatness and parallelism are preferably reduced to 3–5 μm.

8. The ultra-precision machining method according to claim 1, characterized in that, Step S3 uses a grinding wheel mechanical polishing method to polish the polycrystalline diamond optical sheet. The polishing wheel is a ceramic bonded diamond wheel with a diamond grit size of 200-400#. The radial runout of the wheel is <10 μm, the end face runout is <5 μm, the polishing machine speed is 1500-3000 r / min, and the counterweight is 1-5 Kg.

9. The ultra-precision machining method according to claim 8, characterized in that, The surface roughness Ra of the coarsely polished polycrystalline diamond optical sheet is reduced to 5–10 nm, and the flatness and parallelism are preferably reduced to 1.5–2 μm.

10. The ultra-precision machining method according to claim 1 or 9, characterized in that, In step S4, the parameters for the ion beam polishing process are: argon as the ion source gas, an accelerating voltage of 500 V to 1500 V, and a beam current density of 0.5–2 mA / cm². 2 The incident angle is 0° to 45°, and the workpiece stage rotation speed is 1 to 10 rpm.

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