A manufacturing method, system and application of heat-free bending 3D cover plate glass

Abstract

The application relates to the technical field of glass, in particular to a manufacturing method, system and application of heat-bending-free 3D cover plate glass. The method utilizes laser to construct an induced prestress field on a glass substrate to release 50%-85% of target strain; then, single-side polishing fine adjustment is carried out, the polishing surface to be polished is divided into a center, an edge and a corner area, and stepped pressure is applied to compensate for the removal rate difference; a pressure buffer zone is dynamically generated at the junction of the areas, and the pressure is adjusted based on a smoothing algorithm to ensure that the first and second derivatives are continuous and the step mutation is eliminated. Through light-mechanical coupling stress regulation and dynamic continuous control, the application completely eliminates edge collapse and vibration marks, realizes micron-level curvature shaping, improves the glass surface type precision, optical uniformity and structural strength, and efficiently manufactures high-quality 3D cover plates without high-temperature heat bending.

Description

Technical Field

[0001] This invention relates to the field of glass technology, and in particular to a method, system and application for manufacturing heat-free bending 3D cover glass. Background Technology

[0002] In today's era of rapid development in electronic devices, consumers have increasingly higher demands for the appearance and performance of electronic devices. As a crucial component of electronic devices, the cover glass's performance and appearance directly impact the user experience. The flat design of 2D cover glass makes the appearance of electronic devices relatively monotonous, failing to meet consumers' pursuit of personalization and style. The emergence of 3D cover glass effectively overcomes these shortcomings of 2D cover glass. 3D cover glass features curved shapes, allowing it to better integrate with the body of electronic devices, achieving smoother and more natural lines, and greatly enhancing the overall aesthetics and style of electronic devices.

[0003] In the conventional manufacturing process of 3D cover glass, hot bending is the core step in forming the 3D curved surface. This involves heating the cut glass to its softening point in a high-temperature furnace and then using a mold to bend it into the desired 3D shape. After hot bending, grinding and polishing are performed to eliminate imperfections generated during the process and improve the flatness and smoothness of the glass surface.

[0004] In the current field of 3D cover glass processing, hot bending is a common method for manufacturing 3D glass. However, hot bending has many drawbacks that cannot be ignored. In terms of processing precision, the state of the glass during heating and softening is difficult to control, and even small factors can cause forming deviations, making it difficult to achieve high precision requirements. In terms of energy consumption, a large amount of thermal energy is required to maintain a specific state throughout the heating and cooling process, resulting in huge energy consumption and high costs. In terms of process difficulty, the parameter settings for each step are complex, the operation is difficult, and the requirements for personnel's skills and experience are extremely high, resulting in poor quality stability. In terms of mold costs, due to the requirements for high precision, high temperature resistance, and wear resistance, the materials and manufacturing processes are complex, the costs are high, and the molds have short lifespans and need to be replaced frequently. In terms of production capacity, heating, forming, and cooling take a long time, the production pace is slow, and equipment maintenance is frequent, which seriously limits the increase in production capacity and makes it difficult to meet the needs of large-scale markets.

[0005] Patent CN108455829A proposes a heat-free bending method that utilizes stress difference by thinning the reinforcing layer. However, chemical etching for thinning the reinforcing layer suffers from issues such as low curvature control precision, difficulty in accurately shaping complex curved surfaces, and low process tolerance. Furthermore, the lack of differentiated processing for geometric features easily leads to edge collapse, corner warping, and microscopic surface defects, failing to meet the high surface precision requirements of high-end cover plates. Summary of the Invention (a) Technical problems to be solved In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a manufacturing method, system and application of heat-free bending 3D cover glass, which solves the technical problems of high energy consumption, high mold cost and low yield of traditional hot bending process, as well as edge collapse, corner warping and difficulty in forming large curvature due to uneven stress distribution in existing cold bending technology, and surface fluid turbulence marks and poor surface accuracy caused by pressure step change.

[0006] (II) Technical Solution To achieve the above objectives, the main technical solutions adopted by the present invention include: In a first aspect, this application provides a method for manufacturing heat-free bent 3D cover glass, comprising the following steps: Step S1: Cutting the glass sheet into blanks slightly larger than the final product size; Step S2: CNC precision carving, performing fine edge processing on the blank to form the target outline; Step S3: Cleaning to remove residual dirt and waste residue from the surface of the billet; Step S4, strengthening: chemically strengthen the cleaned blank to form an initial surface compressive stress layer on both sides of the glass. Step S5: Laser-induced prestressing. A laser beam is used to locally scan the surface of the strengthened glass substrate to be bent. The laser-induced thermal effect causes local annealing in the scanned area, reducing the surface compressive stress in the area and creating a non-uniform prestress distribution field inside the glass, causing the glass to undergo pre-bending deformation to achieve 70%-90% of the target curvature. Step S6: Single-sided polishing and fine-tuning. The glass that has been laser-treated is subjected to single-sided material removal processing to further reduce the compressive stress layer strength of the surface, correct the curvature accuracy and eliminate the trace surface roughness generated by laser scanning, so that the two sides of the glass form the final compressive stress strength difference and obtain the target curvature. Step S7: Final wash. The polished glass cover is cleaned to obtain the final product. The target curvature is R600-R1000, and the manufacturing process eliminates the need for high-temperature hot bending of the glass.

[0007] Based on the size requirements of the target C-type 3D glass, select a high-quality glass sheet of appropriate thickness (preferably 0.5~2mm, depending on the final product thickness). Use high-precision cutting equipment, such as a laser cutter or diamond cutter, to cut the glass sheet into blanks slightly larger than the final product size. During the cutting process, strictly control the cutting speed and power to ensure clean cut edges without defects such as chipping or cracks. The glass sheet can be cut into blanks that are 5-10mm larger in length and width than the design size for subsequent processing.

[0008] CNC (Computer Numerical Control) machining involves fixing the cut glass blank onto a CNC machining center and using tools such as milling cutters to perform precision machining according to a pre-programmed machining program. By precisely controlling the parameters of the CNC equipment, such as the cutter speed and feed rate, the edges of the glass blank are chamfered and ground to initially form a contour close to the target shape. During the machining process, it is important to clean up glass debris promptly to prevent scratches on the glass surface. The edges of the glass blank can also be chamfered at specific angles as needed to meet subsequent assembly requirements.

[0009] The cleaning process involves placing the CNC-machined glass into a cleaning device. Depending on the product's size, an ultrasonic cleaner or a flatbed cleaner is selected, along with a specialized glass cleaner, to remove residual debris, oil, and impurities generated during processing. The cleaning solution temperature is controlled between 30-50℃, and the cleaning time is 10-20 minutes. After cleaning, the glass is rinsed multiple times with industrial pure water to ensure no cleaning agent residue remains on the surface. Finally, the glass is thoroughly dried using hot air drying or vacuum drying to prevent water stains.

[0010] In a further embodiment, the laser beam wavelength used in step S5 for constructing the laser-induced prestress is located within the absorption band of the glass substrate, preferably 1064nm, 1070nm, or 532nm; the laser power density is controlled between 50 and 200 W / cm². 2 The spot diameter is set to 0.5~2mm; the laser scanning speed is controlled at 200~500mm / s; the scanning path is planned according to the curvature shape of the target, and is selected from parallel reciprocating scanning along the long axis or short axis, surrounding scanning along the glass perimeter, gridded partition scanning, or local densified scanning for corner areas; through the control of the above process parameters, the stress release amount induced by the laser accounts for 50%~85% of the total stress release amount, and the remaining stress release amount is completed by the single-sided polishing fine adjustment described in step S6.

[0011] By controlling the laser power density, spot diameter, and scanning speed, micro-melting or annealing occurs in specific areas of the glass surface, creating high-stress-release zones. Conversely, higher initial compressive stress is retained in unscanned or low-energy scanned areas, forming low-stress zones. This constructed stress gradient difference creates discrete stress-release centers within the glass, driving non-uniform bending moments. When employing locally intensified scanning, for regions with specific stiffness, such as the ends of narrow, long glass panes or the center of large-sized glass panes, abrupt stress-release interfaces are created at these geometric locations by altering the scan line spacing. This breaks the material's original uniform stress field, utilizing the cumulative effect of local stress differences to compensate for the uneven stiffness caused by the geometry, enabling the glass to overcome physical constraints and produce the desired pre-bending deformation in the region.

[0012] By setting these stress release discontinuities or gradient change zones, the problem of non-uniform deformation, such as bending in the middle, straight at both ends, or concave in the center, which traditional uniform scanning cannot handle, is solved. For narrow and long smart wearable glass, the encrypted scanning at both ends overcomes the high stiffness caused by boundary constraints, ensuring the consistency of curvature along the entire length; for large-size flat glass, the supplementary scanning at the center eliminates the wavy lines caused by residual stress. This mechanism based on local stress regulation allows laser preprocessing to undertake most of the forming task, and the resulting pre-bent surface closely matches the target model, reducing the burden of subsequent polishing and fine-tuning corrections.

[0013] In a further embodiment, the single-sided polishing fine-tuning in step S6 is a light polishing process, with the polishing removal depth controlled at 1~3μm; the contact pressure controlled at 0.05~0.1MPa; the polishing speed at 200~500 rpm; and the polishing time controlled at 3~5min.

[0014] During the polishing process, the temperature and composition of the polishing slurry are continuously monitored to ensure uniform polishing results. The temperature of the polishing slurry is controlled within the range of 25℃±2℃ using a temperature sensor, and the pH value is kept stable at 10.0±0.5 and the abrasive solid content fluctuation does not exceed ±5% by real-time monitoring using an online pH meter and concentration meter.

[0015] Under controlled low pressure, low rotation speed, and short removal depth, polishing only acts on the outermost layer after laser pretreatment. By removing trace amounts of material, it further releases residual compressive stress, thereby precisely fine-tuning the curvature from the pre-bending state to the target value, while simultaneously eliminating the microscopic roughness left by laser scanning. Real-time monitoring of the polishing solution's temperature, pH value, and solids content ensures a high degree of uniformity in the chemical mechanical polishing reaction rate, avoiding localized over-polishing or uneven removal rates caused by environmental fluctuations.

[0016] The shallow removal depth avoids damage to the chemically strengthened layer, preserving the high surface compressive stress and deep stress layer of the glass core, ensuring the mechanical strength of the finished product. A stable polishing environment eliminates random surface errors, achieving curvature accuracy at the micrometer level, with no fluid turbulence marks or microscopic scratches on the surface, resulting in high light transmittance and extremely low haze. This fine-tuning shortens the processing cycle and solves the problems of surface distortion and strength reduction caused by traditional repolishing.

[0017] In a further embodiment, during single-sided polishing in step S6, differentiated pressure control is employed, dividing the glass surface to be polished into four independent main control areas: the center area, the long edge area, the short edge area, and the corner area. A reference contact pressure is set for each of the four main control areas, satisfying a stepwise decreasing relationship: the reference contact pressure of the center area > the reference contact pressure of the edge area > the reference contact pressure of the corner area. This stepwise distribution is used to compensate for edge effects, linear velocity differences, and corner stress concentration caused by geometric differences in the rectangular glass during polishing. At the boundary between two adjacent main control areas, a pressure buffer transition zone is dynamically generated; When the polishing head crosses the boundary, the control system adjusts the output pressure in real time based on a preset smooth transition algorithm, so that the first and second derivatives of the pressure value with respect to position remain continuous during the process of crossing the boundary. By eliminating abrupt changes in the pressure signal, the turbulence of the polishing fluid and mechanical vibration are suppressed, ensuring the surface accuracy of the glass and the uniformity of the residual stress distribution.

[0018] To address the inconsistent material removal rates caused by uneven support stiffness, differences in edge linear velocity, and corner stress concentration during rectangular glass polishing, this method divides the polishing surface into four regions: the center, long side, short side, and corners. A stepped pressure is applied, with higher pressure at the center, lower at the edges, and lowest at the corners, actively compensating for edge effects and ensuring uniform material removal across the entire surface. A dynamic pressure buffer zone is introduced at the region boundaries, and a fifth-order polynomial algorithm is used to control the continuity of the first and second derivatives of pressure changes, transforming the traditional step-like pressure switching into a smooth S-shaped soft transition. This control eliminates mechanical impact and the resulting turbulence in the polishing fluid at its physical source.

[0019] The stepped pressure distribution suppresses the edge collapse and corner warping phenomena that have long plagued rectangular glass processing, ensuring a high degree of consistency in the curvature of the 3D surface. Meanwhile, the smooth transition algorithm eliminates rectangular frame marks, periodic ripples, and micro-vibration marks caused by abrupt pressure changes, achieving optical-grade flatness on the glass surface without fluid turbulence marks. The uniform pressure field ensures the continuity of residual stress distribution, avoiding the risk of microcracks caused by localized stress concentration, and improving the product's optical performance and structural reliability.

[0020] In a further embodiment, the single-sided polishing fine-tuning in step S6 employs differentiated pressure control. A Cartesian coordinate system is established with the geometric center of the glass cover as the origin, the X-axis along the length of the glass, and the Y-axis along the width of the glass, dividing the surface to be polished into four functional areas: The central region is located in the core rectangular area at the geometric center of the glass, and its range is -0.4L≤x≤0.4L and -0.4W≤y≤0.4W, where L is the effective polishing length of the glass and W is the effective polishing width of the glass. The long-side edge region is distributed in two symmetrical rectangular strip regions on both sides of the long side of the central region, with a range of -0.4L≤x≤0.4L, and the y coordinate is between 0.4W and 0.5W and between -0.5W and -0.4W; The short-side edge region is distributed in two symmetrical rectangular strip regions on both sides of the short side of the central region, with the x-coordinate between 0.4L and 0.5L and between -0.5L and -0.4L, and -0.4W≤y≤0.4W; The corner area is located at the four apex corners of the glass, that is, the four rectangular areas where |x|>0.4L and |y|>0.4W.

[0021] To address the large aspect ratio of C-type glass, the long side, short side, and corners are independently divided. This allows for the application of less polishing pressure or shorter processing time to corner and edge areas prone to edge collapse during subsequent polishing steps, while applying standard pressure to the central area. This compensates for differences in material removal rates at different locations and ensures the consistency of the overall curvature.

[0022] In a further embodiment, during the polishing process, different levels of contact pressure are applied to the area, employing a gradient distribution strategy with high pressure at the center, low pressure at the edges, and lowest pressure at the corners, to compensate for edge effects and linear velocity differences during the polishing process. The pressure level relationship is: pressure in the center area > pressure in the transition area > pressure in the edge area > pressure in the corner area. The pressure value range is: the contact pressure in the center area is controlled at 0.08~0.12MPa; the contact pressure in the transition area is controlled at 0.06~0.09MPa; the contact pressure in the long and short edge areas is controlled at 0.04~0.07MPa; and the contact pressure in the corner area is controlled at 0.03~0.05MPa.

[0023] Step 3: At the boundary between adjacent functional areas, a pressure buffer zone is set; the physical width of the pressure buffer zone is a proportional function of the effective glass size. For the boundary along the Y-axis, the buffer band width By = ky × W, where the proportionality coefficient ky ranges from 0.002 to 0.01 (i.e., 0.2% to 1.5% of the glass width). For the boundary along the X-axis, the buffer band width Bx = kx × L, where the proportionality coefficient kx ranges from 0.002 to 0.01 (i.e., 0.2% to 1.5% of the glass length). The starting boundary of the pressure buffer zone coincides with the theoretical geometric boundary line between two adjacent functional areas; the extension direction is a unidirectional extension from the theoretical boundary line into the target entry area (i.e., the new area where the pressure is about to change); the termination boundary is a parallel line at a normal distance B from the theoretical boundary line. Zone affiliation refers to the fact that within the buffer zone, the space is regarded as an independent pressure transition zone, and its pressure value is not fixed to the set value of the original zone or the new zone, but is dynamically determined by the smoothing function; only when the polishing head crosses the termination boundary is it considered to have fully entered the new zone.

[0024] When the polishing operation enters the buffer zone, the control system dynamically adjusts the output pressure of the loading mechanism using an S-shaped pressure gradient curve based on a fifth-order polynomial. This ensures that the first derivative (rate of change) and second derivative (acceleration) of the pressure value P change with position are both continuously and smoothly transitioned, eliminating pressure jumps. The control system ensures that the pressure response frequency of the loading mechanism is not lower than 50Hz, and strictly controls the tracking lag error of the actual pressure to the target curve within ±0.005MPa. This completely eliminates the turbulence and mechanical vibration of the polishing fluid caused by sudden pressure changes, ensuring that there are no rectangular or corner-shaped polishing marks on the glass surface, and that the residual stress distribution across the entire surface is smooth and continuous.

[0025] To completely eliminate the mechanical shock and fluid turbulence caused by pressure jumps during cross-regional polishing head operation, this study proposes a pressure smoothing transition control strategy based on fifth-order polynomial interpolation. The core of this strategy lies in constructing a pressure smoothing transition control strategy that satisfies C in all three dimensions: position, velocity, and acceleration. 2 The continuous pressure-spatiotemporal trajectory enables true soft start and soft stop, ensuring that the glass surface is free of concentric polishing marks and that the residual stress distribution is smooth and continuous.

[0026] At the mathematical modeling level, the first step is to define normalized spatial coordinates. d represents the real-time normal distance from the center point of the polishing head to the boundary line of the current area. When the polishing head is within the original area, d ≤ 0; when the polishing head crosses the boundary and enters the buffer zone, d > 0. B is the preset buffer zone width, determined by B = k × L or B = k × W in step 2. ∈[0,1] maps the entire transition region. The dimensionless progress factor represents the percentage of the buffer zone that has been traversed. The real-time target pressure P(r) within the transition zone is given by the formula... Dynamically determined The core smoothing weight function is responsible for adjusting the pressure from the initial value P. low Seamless transition to target value P high .

[0027] To achieve shock-free soft start and soft stop, the system sets six boundary constraints: position constraint (ensuring pressure pairing at the start and end points), velocity constraint (ensuring no abrupt changes during start and stop), and acceleration constraint (ensuring smooth acceleration and deceleration).

[0028] The starting point of the position constraint represents the period before the pressure changes, with a weight of 0 and S(0)=0; the ending point of the position constraint represents the period after the pressure changes completely, with a weight of 1 and S(1)=1, ensuring accurate connection of the starting and ending pressures.

[0029] Velocity constraints, first derivative (ξ) represents the rate of change of pressure (velocity). If the velocity is not zero at the start, the pressure will jump momentarily, so the velocity must be zero at the start and end. (0) = 0 (starting from a standstill), (1) = 0 (stopped and at rest).

[0030] Acceleration constraints. Second derivative. (ξ) represents the acceleration due to pressure change. If the acceleration is not zero at the start, it means that the speed is built up instantaneously, which will still produce slight mechanical vibrations. For a smooth start, the acceleration at the start and end should also be zero. (0)=0, no acceleration impact at start-up. (1)=0, stop the impact without deceleration.

[0031] According to polynomial interpolation theory, an nth-degree polynomial has n+1 coefficients (degrees of freedom). To solve for the curve, the number of coefficients needed must equal the number of constraints. A polynomial with 6 coefficients has a maximum degree of 5. General formula for a polynomial: We need to solve for the six unknowns a0 to a5. Using... The condition at =0, =0, a0=0; differentiate once. =0, a1=0; differentiate twice =0, a2=0; using Given the condition at point =1, S(1) = 1. (1) = 0, (1) = 0, coefficients a3 = 10, a4 = 15, a5=6, derive the formula .

[0032] The control system acquires the (x, y) coordinates of the polishing head in real time. Based on the region division logic in step 1, it dynamically calculates the current region and the normal distance d from the boundary, and then calculates ξ and the target pressure P in real time. This ensures that the pressure value P changes smoothly and continuously throughout the entire process with position, without any abrupt changes in the first or second derivative. The system mandates that the pressure response frequency of the control loading mechanism be no less than 50Hz, and strictly controls the tracking lag error of the actual pressure to the target curve within ±0.005MPa through high-precision closed-loop feedback. These measures effectively eliminate the turbulence and mechanical vibration of the polishing fluid caused by pressure steps, improving the consistency of the processed surface quality.

[0033] In a further embodiment, the chemical strengthening process in step S4 uses a potassium nitrate strengthening solution immersion method; the immersion temperature is controlled at 400~450℃; the immersion time is set to 2~4 hours according to the glass thickness; a surface compressive stress layer is formed through ion exchange between potassium ions and sodium ions on the glass surface; the initial compressive stress value of the glass surface after strengthening is ≥800MPa.

[0034] Secondly, this application discloses a glass cold bending forming system for realizing the above-mentioned method for manufacturing heat-free bending 3D cover glass, comprising: The laser preprocessing module is equipped with a laser emitter and a multi-axis motion platform. It plans the laser scanning path according to the preset curvature model to construct an induced prestress field on the glass substrate. The polishing execution module includes an adjustable pressure polishing head, a spindle drive mechanism, and a polishing fluid supply system, which performs single-sided polishing and fine-tuning on laser-pretreated glass. It also includes an intelligent control module, which is connected to the laser pretreatment module, the polishing execution module and the online detection module respectively. The control logic of the intelligent control module includes stress distribution strategy, zoned pressure modeling, dynamic buffer generation, smooth trajectory planning and closed-loop feedback adjustment.

[0035] The stress distribution strategy is based on the target curvature to calculate the total stress release and dynamically allocate the laser-induced release ratio, preferably 50%~85% and the polishing-induced release ratio. Partition pressure modeling involves dividing the glass surface to be polished into multiple main control areas and setting a reference contact pressure based on the geometric characteristics of each area. Dynamic buffer generation involves dynamically calculating and generating a pressure buffer transition zone at the boundary between adjacent main control areas, rather than dividing it into fixed areas. Smooth trajectory planning involves controlling the polishing head as it crosses the boundary, adjusting the pressure output based on a smooth transition algorithm to ensure the continuity of the first and second derivatives of the pressure signal, thereby eliminating pressure abrupt changes.

[0036] The system transforms traditional thermoplastic deformation into stress-induced elastic deformation through an intelligent control module. Based on the total strain energy required for inverse calculation of the target curvature, it dynamically balances the contribution ratio of non-contact laser heating / modification and contact polishing surface removal. A non-uniform prestress field is constructed within the glass using laser as coarse adjustment, while stress redistribution induced by polishing to remove trace amounts of material serves as fine adjustment. These two methods complement each other to minimize heat input and maximize deformation controllability. Partitioned pressure modeling and dynamic buffer generation address the stiffness nonlinearity problem in the processing of rectangular thin plates. The system no longer treats the glass as a homogeneous body but discretizes the surface into control units of different stiffnesses based on geometric characteristics. A virtual pressure compliance layer is generated in real-time at the unit boundaries using an algorithm, eliminating abrupt stiffness changes caused by physical boundaries. Smooth trajectory planning introduces high-order kinematic constraints, forcing the rate of change of the pressure signal and the second-order acceleration derivative to be continuous. This eliminates step responses from a control theory perspective, ensuring that the mechanical actuator achieves a soft landing without impact when crossing regional boundaries.

[0037] The system overcomes the common problems of uncontrollable springback and edge collapse in traditional cold bending processes. It achieves micron-level curvature shaping through optomechanics and eliminates residual thermal stress without high-temperature annealing. The dynamic buffering and smooth transition mechanism completely suppresses fluid turbulence marks, periodic vibration marks, and micro-scratches caused by sudden pressure changes, resulting in optical-grade flatness on the finished product surface and reducing yield losses in subsequent polishing or coating processes. By avoiding localized stress concentration and thermal shock, the microcrack initiation rate of the glass substrate is reduced, and the impact resistance and bending fatigue life of the finished product are improved.

[0038] Thirdly, this application provides an application of heat-free bending 3D cover glass, wherein the glass substrate prepared by the above manufacturing method, or the glass finished product processed by the above cold bending forming system, is used as a protective or structural component of a display terminal.

[0039] The finished glass does not require the traditional high-temperature hot bending furnace heating and softening process. Instead, it maintains a stable three-dimensional curved surface shape at room temperature by relying on the internally pre-placed non-uniform induced prestress field and the micro-stress release effect of surface polishing. Applications include front cover glass for smartphones and tablets: utilizing the high edge curvature adaptability of the glass to achieve frameless or waterfall screen designs; curved screens for automotive center consoles and dashboards: utilizing the complex double curvature forming capability of the glass to match irregular interior shapes; curved watch covers for smart wearable devices: utilizing the thinness and impact resistance of the glass to conform to the wrist curve; and decorative curved panels for smart home and commercial displays.

[0040] (III) Beneficial Effects The present invention provides a heat-free bending method, system, and application for manufacturing 3D cover glass. Compared with traditional high-temperature hot bending processes and existing cold bending technologies, this invention eliminates the energy-intensive and costly high-temperature hot bending step. Through laser-induced prestressing and single-sided polishing fine-tuning, it achieves precise three-dimensional curved surface forming of glass at room temperature. The method utilizes laser selective release of surface compressive stress, undertaking most of the curvature forming task, reducing dependence on material removal, and thus fully preserving the deep compressive stress layer and high surface compressive stress value formed by chemical strengthening. This results in a final product that not only possesses excellent 3D curved surface morphology but also maintains excellent mechanical strength close to that of the original sheet. It exhibits good impact resistance and bending resistance in drop ball tests and four-point bending strength tests, solving the problem of strength reduction caused by excessive polishing in traditional cold bending processes.

[0041] This invention introduces a differentiated pressure control strategy and dynamic buffer transition mechanism based on geometric features, overcoming common technical bottlenecks in the cold bending of rectangular glass, such as edge collapse, corner warping, and poor surface accuracy. By dividing the polished surface into four independent regions—the center, long side, short side, and corners—and applying progressively decreasing contact pressure, it compensates for the uneven material removal rate caused by differences in linear velocity and support conditions at different geometric locations. An S-shaped smooth transition algorithm based on a fifth-order polynomial is used at the region boundaries to ensure that the pressure signal remains continuous and without abrupt changes in position, velocity, and acceleration. This soft-start and soft-stop control logic completely eliminates mechanical vibration and polishing fluid turbulence caused by pressure steps, preventing microscopic defects such as rectangular frame marks, periodic ripples, and concentric spiral marks on the surface. This improves the surface accuracy of the product, resulting in high light transmittance, extremely low haze, and no optical distortion points, meeting the optical performance requirements of high-end display terminals.

[0042] This invention, through flexible adjustment of the laser scanning path and polishing parameters, can be widely adapted to glass products with various specifications and curvature requirements, ranging from ultra-thin and narrow smart wearable devices to large-size tablets, solving the problems of difficult and inconsistent forming of complex curved surfaces. Because laser preforming reduces the polishing burden, the processing cycle per piece is shortened, the relative energy consumption index is reduced, and the high dependence on molds and frequent mold replacement costs associated with high-temperature hot bending are avoided. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a diagram showing the process implementation steps. Detailed Implementation

[0045] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application. This application can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0046] These embodiments are provided to make the application thorough and complete, and to fully express the scope of the application to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​illustrated in these embodiments should be interpreted as merely exemplary and not as limiting.

[0047] This invention offers exceptional flexibility and design freedom in selecting the thickness of the glass substrate, breaking free from the constraints of traditional preset specifications or standard dimensions. It can achieve a high degree of customization based on the specific needs of the end application scenario. Its typical thickness covers the range of 0.5~2mm, which can precisely adapt to the differentiated balance requirements of various electronic devices for the thinness and high structural strength of the cover glass.

[0048] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0049] In this application, percentages unless otherwise specified refer to mass percentages.

[0050] Example 1 This embodiment is for a 0.8mm thick, R800 curvature cover glass for general-purpose smartphones or mid-to-high-end mobile terminals.

[0051] Step S1 involves cutting a glass sheet with a thickness of 0.8mm. The sheet is then cut into rectangular blanks that are 6mm larger in length and width than the final design dimensions using a laser cutting device. The cutting power and speed are controlled to ensure that there are no micro-cracks on the edges.

[0052] Step S2 CNC precision carving: The blank is fixed on the CNC machining center, and the glass edge is chamfered and contoured according to the preset program using a diamond end mill to form the final geometric shape of the product, and the machining debris is cleaned up.

[0053] Proceed to step S3, cleaning, where the finely sculpted blank is placed in a 40°C ultrasonic cleaner and treated with a special cleaning agent for 15 minutes. Then, it is rinsed multiple times with industrial pure water and dried with hot air to thoroughly remove surface oil, dust, and processing residues.

[0054] Step S4, chemical strengthening, involves immersing the cleaned billet in a potassium nitrate molten salt solution at a constant temperature of 420°C for 3 hours. The surface compressive stress value is then tested through an ion exchange reaction at high temperature to provide stress reserves for subsequent cold bending forming.

[0055] The core forming stage is step S5, laser-induced prestressing, which uses a 1064nm fiber laser to scan the glass surface to be bent; the process parameters are set as follows: laser power density 120W / cm². 2 The laser spot diameter is 1.0 mm, the scanning speed is 350 mm / s, and the scanning path is planned as a parallel reciprocating line scan along the long axis of the glass with a line spacing of 1.5 mm. Within this critical energy window, the laser energy is efficiently coupled to the glass surface, inducing extremely shallow-depth micro-melting and resolidification or viscous flow annealing in the scanned area. This selectively releases the surface compressive stress in the area while ensuring that the integrity of the glass matrix remains intact and that no microcracks are generated. This process constructs a smooth, non-uniform prestress distribution field inside the glass, driving the glass to produce pre-bending deformation. At this point, the glass curvature has reached 80% of the target value R800.

[0056] Step S6, single-sided polishing and fine-tuning, not only removes the minute surface roughness generated by laser scanning but also further releases stress through material removal, precisely correcting the curvature from the pre-bent state to the target R800. A Cartesian coordinate system is established with the glass geometric center as the origin. The effective polishing length L = 140mm and the width W = 70mm. The surface to be polished is dynamically divided into four functional areas, with the central area... ≤56mm, ≤28mm, long edge area ≤56mm, 28mm< ≤35mm, short side edge area 56mm< ≤70mm, ≤28mm and corner areas >56mm, >28mm. The four zones are designed with progressively decreasing reference contact pressures: a high pressure of 0.10MPa is applied to the center zone to ensure the removal rate of the center material; the pressure is reduced to 0.05MPa at the long and short edge zones to suppress edge collapse; and the pressure is further reduced to 0.035MPa at the corner zones to eliminate the risk of corner warping.

[0057] To completely eliminate mechanical shock during zone switching, the system dynamically generates a 1.0mm wide pressure buffer transition zone at the boundary between adjacent zones. When the polishing head crosses the boundary and enters the buffer zone, the intelligent control system uses a fifth-order polynomial algorithm. Real-time calculation of pressure weights ensures that the output pressure satisfies the C-value requirement for continuous position, velocity, and acceleration in spatial variations. 2The smoothing characteristics completely eliminate pressure abrupt changes. The system employs closed-loop feedback control with a high response frequency of 60Hz, strictly locking the tracking error of the actual pressure to the target curve within ±0.004MPa. Under this refined control, the polishing removal depth is precisely controlled at 2.0μm, the spindle speed is 300 rpm, and the process takes 4 minutes, successfully obtaining an R800 surface with high surface accuracy, no fluid turbulence marks, and uniform residual stress distribution.

[0058] Step S7 final washing is performed to clean the finished product with pure water and vacuum drying, resulting in R8003D cover glass that does not require high-temperature bending, has a perfect appearance, and excellent mechanical properties.

[0059] Example 2 The R800 cover is designed for narrow, elongated, and ultra-thin smart wearable devices.

[0060] This embodiment focuses on 0.5mm ultra-thin glass, applied to the curved cover of smartwatches or smart bands. These products are characterized by a large aspect ratio, thinness, high requirements for fit to the R800 curvature, and the need to avoid corner warping.

[0061] Step S1 involves material preparation. A high-strength aluminosilicate glass sheet with a thickness of 0.5mm is selected. It is then cut into rectangular blanks measuring 45mm × 85mm using a UV laser cutter, each 5mm larger than the final product in both length and width. Due to the thinness of the glass, the cutting power is set to a low-energy, high-frequency mode to ensure a smooth cut free of microcracks.

[0062] Step S2 CNC precision carving: The blank is fixed on a precision CNC machining center, and the contour is machined using a 0.3mm diameter micro diamond end mill. The four corners are rounded with a small radius of 0.2mm to reduce subsequent stress concentration, and debris is cleaned up after machining.

[0063] Step S3 cleaning uses a low-temperature 30℃ ultrasonic cleaning process with a neutral cleaning agent for 10 minutes, followed by rinsing with deionized water and hot air drying to prevent the ultra-thin glass from deforming due to thermal shock during cleaning.

[0064] Step S4 involves chemical strengthening, immersing the billet in molten potassium nitrate at 400°C for 2 hours. For 0.5mm thin glass, the temperature and time should be appropriately reduced to prevent stress oversaturation that could lead to spontaneous breakage.

[0065] Step S5 uses laser-induced prestressing, employing a 532nm green laser with a power density set to 150W / cm². 2 The spot diameter is 0.6 mm, and the scanning speed is 400 mm / s.

[0066] For narrow and long structures, a parallel reciprocating scan is used along the short axis, that is, the width direction, with the scan line spacing set to 0.8mm.

[0067] To address the issue of insufficient curvature at the ends of narrow and long glass, localized high-density scanning is performed within a 5mm radius from the edges of both ends, reducing the line spacing to 0.5mm and increasing stress release in the area.

[0068] After laser treatment, the glass is pre-bent, with a curvature reaching 82% of the target R800.

[0069] Step S6: Single-sided polishing and fine-tuning. Establish a coordinate system with an effective polishing area of ​​L=80mm and W=40mm, and a central area of: ≤32mm, ≤16mm; Long edge area: ≤32mm, 16mm< ≤20mm; Short edge area: 32mm< ≤40mm, ≤16mm corner area: >32mm, >16mm; Central area: 0.09MPa, long edge area: 0.05MPa, short edge area: 0.035MPa, corner area: 0.025MPa.

[0070] The buffer band width is set to 0.6 mm. The control system responds at a frequency of 70 Hz and uses a fifth-order polynomial algorithm to smoothly transition the pressure, with the tracking error controlled within ±0.003 MPa.

[0071] Polishing removes 1.2μm at a speed of 450 rpm for 3 minutes, correcting the curvature to R800, eliminating laser scanning marks, and ensuring the four corners are flat and warped, conforming to the wrist curve.

[0072] Step S7 final washing: rinse with pure water and vacuum dry to obtain the R800 ultra-thin 3D cover plate suitable for smart wearable devices.

[0073] Example 3 This embodiment is for R800 cover plates for large-size, medium-thickness tablet computers.

[0074] This embodiment focuses on 1.1mm thick glass for the front cover of a large-size tablet. Such products have a large area and relatively high rigidity, requiring a greater total stress release to achieve an R800 curvature and address issues like central depressions or edge undulations on a large flat surface.

[0075] Step S1: Cut the glass sheet. Select a glass sheet with a thickness of 1.1mm. Cut it into a rectangular blank with dimensions of 220mm × 160mm, leaving an 8mm machining allowance.

[0076] Step S2 involves CNC precision carving, using CNC equipment to shape the outline, machining the four corners into large rounded corners of R5mm, and chamfering the edges with C0.3mm. During the machining process, attention is paid to chip removal to avoid scratching the large glass surface.

[0077] Step S3 cleaning uses a combination of spraying and ultrasonic cleaning at 40°C for 15 minutes to ensure that contaminants on a large surface area are completely removed.

[0078] Step S4 involves chemical strengthening by immersion in molten potassium nitrate at 430°C for 3 hours. Thicker glass requires more thorough ion exchange to build up sufficient stress reserve.

[0079] Step S5 uses laser-induced prestressing, employing a 1064nm fiber laser with a power density set to 100W / cm². 2 The spot diameter is 1.2 mm, and the scanning speed is 300 mm / s. A grid-based, partitioned scanning method combined with parallel reciprocating scanning along the long axis is employed. The overall scanning uses parallel scanning with a spacing of 1.5 mm.

[0080] To address the issue of insufficient curvature caused by residual stress in the central area of ​​large-size glass, a secondary cleaning is performed in the central 50% area to increase the stress release in the central area and promote the overall bending towards R800.

[0081] After laser treatment, the pre-bending curvature of the glass reaches 75% of the target R800. Due to the thickness and large area of ​​the glass, a significant amount of stress release is retained for fine adjustment in subsequent polishing steps.

[0082] Step S6: Single-sided polishing and fine-tuning, effective polishing area L=210mm, W=150mm.

[0083] Central area: ≤84mm, ≤60mm; Long edge region, ≤84mm, and 60mm < ≤75mm, short side edge area 84mm ≤105mm, and ≤60mm, corner area, 84mm< ≤105mm and 60mm< ≤75mm.

[0084] Central region: 0.11 MPa, Transition region: 0.08 MPa Long side / short side edge region: 0.05MPa Corner area: 0.035MPa.

[0085] For buffer transition control, considering the inertia of the large polishing head, the buffer band width is appropriately increased to 1.5mm. The control system has a response frequency of 55Hz, follows a fifth-order polynomial smooth curve, and controls the tracking error within ±0.004MPa, eliminating fluid patterns caused by pressure surges during large stroke movements.

[0086] Polishing removal depth 2.8μm, rotation speed 280 rpm, time 5 minutes. By removing a large amount of material, residual stress is precisely released, and the curvature is finely adjusted from the pre-bending state to the standard R800. The surface profile accuracy is better than 0.05mm, with no macroscopic wavy lines.

[0087] Step S7 final washing involves a final high-purity water wash and dust-free drying to produce a large-size R800 heat-free bending 3D cover suitable for tablet computers.

[0088] Comparative Example 1 This comparative example is the same as Example 1, except that step S5 is omitted. Since there is no laser scanning to release 50%-85% of the stress and build up pre-bending deformation, in order to achieve the target curvature of R800, this comparative example had to significantly increase the polishing removal depth in step S6 from 2.0 μm in Example 1 to 12 μm, relying solely on the stress difference generated by single-sided material removal to bend the glass, and the polishing time was correspondingly extended to 20 minutes. Excessive material removal directly cut through most of the chemically strengthened layer, causing the surface compressive stress to plummet from the expected 700 MPa or more to 450 MPa, leaving a stress layer depth of only 15 μm. This resulted in severely insufficient mechanical strength in the finished product, failing to meet the usage requirements.

[0089] Comparative Example 2 This comparative example is the same as Example 2, except that the difference lies in the pressure in step S6. This comparative example eliminates the region division and does not use the gradient pressure at the center as in Example 2. Instead, a uniform constant pressure of 0.06 MPa is applied to the entire 0.5 mm ultrathin glass surface without a buffer transition zone. Due to the lack of adaptive adjustment for the deformation differences between the center and edges, excessive material removal occurs in the central region of the glass while insufficient removal occurs at the edges, disrupting the originally uniform stress distribution field. This uneven stress release leads to severe macroscopic surface defects, manifested as edge collapse and corner warping, with the surface accuracy PV value exceeding the acceptable range and a surge in the number of optical distortion points.

[0090] Comparative Example 3 This comparative example is the same as Example 2, except for the pressure transition method at the boundary between regions. This comparative example does not have a pressure buffer transition zone. When the polishing head crosses from the center region to the edge region, or from the edge region to the corner region, the control system directly and instantly jumps the pressure from the set value of the previous region to the set value of the next region, instead of using the S-shaped smooth transition algorithm based on a fifth-order polynomial as in Example 3. This abrupt change in pressure leaves visible rectangular frame marks and periodic ripples on the glass surface, leading to localized stress concentration. In subsequent inspections, these marks become high-incidence areas of optical distortion and are easily induced to propagate microcracks under slight external forces, resulting in a significant decrease in product yield.

[0091] Comparative Example 4 This comparative example is the same as Example 1, except for the laser power density in step S5. In this comparative example, the laser power density is reduced from 120 W / cm² in Example 1 to 40 W / cm². 2 Due to insufficient energy density, the laser cannot effectively micro-melt or anneal the glass surface, resulting in low stress release, accounting for only 10% of the total release, and the pre-bending curvature only reaching 20% ​​of the target value.

[0092] This difference leads to an excessive burden on the subsequent polishing fine-tuning step S6. Even if the polishing depth is increased to 8μm, it is still difficult to correct to R800. Furthermore, because the laser scanning fails to form a smooth prestress field, local stress concentration points appear on the glass surface, resulting in poor curvature uniformity of the final product and spontaneous cracking.

[0093] Comparative Example 5 This comparative example is the same as Example 2, except for the laser scanning path planning in step S5. The localized, intensified scanning of the 5mm edge region at both ends is eliminated; instead, a uniform 0.8mm line spacing is used for parallel reciprocating scanning along the entire line. For narrow, elongated glass, this uniform scanning results in insufficient stress release at both ends, failing to compensate for the stiffness effect at the ends. This difference leads to a non-uniform curvature state after pre-bending the glass, with a curved middle and straight ends. Even with differentiated pressure polishing in subsequent step S6, it is difficult to correct the curvature deviation at both ends, resulting in poor adhesion at both ends of the finished product, which cannot meet the high-fit requirements of smart wearable devices.

[0094] Comparative Example 6 This comparative example is the same as Example 3, except for the chemical strengthening temperature in step S4. In this comparative example, the potassium nitrate molten salt immersion temperature was reduced from 430°C in Example 3 to 350°C. The lower temperature resulted in a significant decrease in the exchange efficiency between potassium and sodium ions, leading to an initial compressive stress of only 600 MPa on the glass surface and insufficient stress layer depth.

[0095] Comparative Example 7 This comparative example is the same as Example 1, except for the control of the polishing removal depth in step S6. The removal depth is set to 8 μm. This results in excessive destruction of the fine prestress distribution field originally constructed by the laser, not only removing the surface roughness generated by the laser but also cutting through the critical stress gradient layer. As a result, the glass curvature exceeds the target value, and the excessive removal leads to uneven overall glass thickness, excessive thickness difference between the center and the edge, severe optical distortion, and the finished product is scrapped.

[0096] Comparative Example 8 This comparative example is the same as Example 2, except for the physical width of the pressure buffer transition zone. Although this comparative example uses a smoothing algorithm, the buffer zone width is forcibly set to 0mm, and the smoothing curve is calculated directly from the theoretical boundary line, but there is no spatial transition zone. This results in a drastic pressure change from high to low pressure within an extremely short displacement, effectively equivalent to a quasi-step change, exceeding the response limit of the mechanical system. This difference prevents the control system from achieving true C within zero width. 2 Continuous pressure oscillations still occurred during actual operation. Fine but dense ripples were left on the 0.5mm ultrathin glass surface, and due to the lag in pressure response, the actual pressure curve deviated significantly from the target curve.

[0097] Comparative Example 9 The difference between this comparative example and Example 3 lies in the polishing spindle speed in step S6. This comparative example increases the speed from 280 rpm in Example 3 to 800 rpm, improving efficiency through higher speed. This results in severe centrifugal splashing of the polishing slurry at high speeds, leading to insufficient slurry supply to the glass edge area and a decreased removal rate. Simultaneously, the hydrodynamic pressure effect caused by high speed alters the contact mechanics model, rendering the preset gradient pressure strategy ineffective. The final product surface exhibits concentric spiral marks, and edge curvature correction fails, resulting in severely substandard surface accuracy.

[0098] Data analysis was performed on the examples and comparative examples.

[0099] Surface compressive stress and stress layer depth are detected after step S7. Surface accuracy is checked after single-sided polishing and fine-tuning in step S6. A high-precision three-dimensional profilometer is used to scan the entire glass surface, calculating the difference between the highest and lowest points to determine the presence of macroscopic surface defects such as edge collapse, corner warping, or rectangular frame marks. Transmittance, haze, and optical distortion point detection are performed after final washing in step S7. Transmittance and haze percentage are measured using an integrating sphere haze meter; optical distortion points are typically detected using projection or fringe reflection methods, observing the degree of deformation of the projected grid to count the number of distortion points per unit area, ensuring no visual interference. Mechanical strength testing is performed after finished product output in step S7. A steel ball of specified mass is dropped freely from different heights until breakage, and the critical height is recorded. Four-point bending strength is determined according to GB / T6552 or ASTM C158 standards on a universal testing machine using a four-point loading method to measure the glass's modulus of rupture. The processing cycle per piece, relative energy consumption index, and estimated yield are statistically analyzed for the entire production data from steps S1 to S7. The processing cycle is obtained by recording the total time taken for a single piece of glass from cutting to final washing and discharge, reflecting the efficiency improvement brought about by the optimization of polishing time in step S6; the relative energy consumption index is calculated based on the total power consumption of the equipment per unit output; the estimated yield is calculated by statistically analyzing the proportion of qualified products that pass all the above performance tests in the batch production, in order to compare the differences in quality stability between the traditional hot bending process and the heat-free bending process of this invention.

[0100]

[0101] Example 1 achieves a balance between stress release and material removal through a combination of laser-induced and differentiated polishing. Laser pretreatment handles the primary curvature shaping, allowing subsequent polishing to achieve precise finishing with only minimal removal, thus fully preserving the deep compressive stress layer formed by chemical strengthening. Combined with a stepped pressure distribution and smooth transition algorithm, edge effects and mechanical impacts are eliminated, ensuring the stability of surface hydrodynamics. This process combination maintains high surface compressive stress and a deep stress layer while achieving high surface accuracy and optical transparency, eliminating optical distortion, and enabling the glass to exhibit good impact resistance and flexural modulus. Ultimately, it achieves high-yield production with high efficiency and low energy consumption.

[0102] Example 2 utilizes localized, intensified scanning of the laser path to specifically release stress in the confined areas at both ends, overcoming the physical characteristic of narrow, elongated glass being difficult to bend at both ends. A low-pressure corner strategy and highly sensitive pressure buffer control prevent corner warping caused by stress concentration in the ultra-thin glass. This stress regulation, while ensuring sufficient stress layer depth to maintain strength, corrects surface deviations caused by complex geometry, achieving a high degree of fit with zero optical distortion, and ensuring the reliability and yield of wearable devices under stringent mechanical testing.

[0103] Example 3 utilizes a gridded laser scanning and center-filling strategy to construct a wide-area uniform prestressed field, resolving the issues of central depressions or wavy lines that easily occur on large flat surfaces. The widened dynamic buffer zone design adapts to the motion inertia of large-size processing, ensuring the continuity and stability of pressure changes over long strokes and avoiding fluid turbulence. This not only maintains a uniform stress layer depth and high surface compressive stress over a large area but also achieves excellent surface accuracy and optical quality. This results in large-size cover plates exhibiting high structural strength in drop ball tests and four-point bending tests, while maintaining good production efficiency and yield.

[0104] Comparative Example 1, lacking a laser-induced pre-bending step, relied entirely on the stress difference generated by single-sided polishing for its forming. To achieve the target curvature, the process was forced to significantly increase the material removal depth, which cut through the surface compressive stress layer, resulting in a drastic decrease in the stress layer depth and a reduction in the surface compressive stress value. The destruction of the strengthening layer caused the glass to lose its core strength barrier, leading to a decline in impact and bending resistance. Excessive material removal caused severe surface distortion and optical scattering, increased haze, and generated numerous optical distortion points, ultimately resulting in extremely low yield and a surge in energy consumption.

[0105] In Comparative Example 2, after eliminating the differentiated pressure for different zones, constant pressure polishing could not compensate for the geometric effects and linear velocity differences at the edges and corners of the rectangular glass. This one-size-fits-all pressure distribution led to an imbalance in material removal rates between the center and edges, disrupting the uniformity of the internal prestress field and causing stress distribution disorder. Although the stress layer depth remained, the distortion of the surface shape altered the light refraction path, creating optical distortion points, reducing optical performance, and causing stress concentration, strength reduction, and yield loss during mechanical testing due to the irregular shape.

[0106] In Comparative Example 3, the lack of a pressure buffer transition zone caused a sudden pressure jump in the polishing head when crossing regions. This instantaneous mechanical impact excited high-frequency turbulence and mechanical vibration in the polishing fluid, leaving periodic ripple marks on the glass surface. These microscopic surface defects not only increased light scattering leading to increased haze and became sources of stress concentration, but also generated numerous optical distortion points. Although the overall stress layer was not cut through, the surface discontinuities and localized stress concentrations weakened the overall structural integrity of the glass, resulting in decreased mechanical strength, and the surface defects directly reduced product yield.

[0107] In Comparative Example 4, insufficient laser power density prevented energy from being effectively coupled to the glass surface, hindering the triggering of micro-melting or annealing mechanisms and resulting in low stress release efficiency. A non-uniform prestress field to drive bending could not be formed within the glass, and pre-bending deformation occurred almost entirely. This condition meant that subsequent processes, regardless of adjustments, could not compensate for the lack of curvature, and the unreleased localized high stress points were highly susceptible to spontaneous glass breakage during processing. Consequently, the process path resulted in products failing to form or shattering instantly, making mechanical property testing impossible and yielding a zero yield.

[0108] Comparative Example 5 illustrates the mismatch between the spatial distribution of laser stress release and the stiffness distribution of the glass structure. For narrow, elongated glass with a large aspect ratio, the ends are constrained by boundaries, resulting in higher structural stiffness than the middle region. This necessitates a greater amount of stress release to produce the same bending deformation. Using a uniform scanning path along the entire length leads to insufficient stress release at the ends, while the middle region experiences relatively excessive release. This longitudinal non-uniformity in stress release prevents the prestressed field built within the glass from driving a uniform curvature, resulting in a non-uniform shape with greater curvature in the middle and flatter ends. This macroscopic curvature inconsistency is difficult to correct with subsequent single-sided polishing fine-tuning, as polishing primarily adjusts the overall radius of curvature rather than correcting the longitudinal curvature gradient. Ultimately, this leads to the finished product failing to achieve the target fit at both ends, exceeding the surface accuracy limit along the long axis, causing optical distortion, and stress concentration due to warping at both ends during assembly, reducing overall mechanical reliability and significantly lowering product yield.

[0109] In Comparative Example 6, the excessively low chemical strengthening temperature inhibited the kinetics of the ion exchange reaction, resulting in low efficiency of potassium ion replacement of sodium ions. This prevented the formation of an initial compressive stress layer of sufficient magnitude and depth on the glass surface. Since cold bending relies on the release of the stress difference between the two sides, the weakness of the initial stress directly limits the surface compressive stress level and stress layer depth of the final product. This inherent strength defect causes the glass to perform poorly in drop ball and bending tests, making it extremely brittle. Furthermore, the shallow stress layer also affects the stability of the surface shape, leading to a decrease in yield.

[0110] In Comparative Example 7, excessive polishing depth disrupted the surface stress gradient distribution of the laser. The polishing process not only removed surface roughness but also excised the stress layer that undertook critical curvature control, leading to distortion of the remaining stress distribution field and uncontrolled curvature. This excessive removal caused uneven glass thickness, resulting in severe optical distortion and high haze. The loss of the strengthening layer caused a sharp drop in surface compressive stress, and the stress layer depth became extremely shallow, leading to insufficient mechanical strength of the glass. This resulted in poor performance in mechanical testing and ultimately, the glass was scrapped due to its inability to meet performance specifications, resulting in a low yield.

[0111] Comparative Example 8 sets the buffer band width to zero, depriving the smooth transition algorithm of physical execution space. The mechanical system cannot complete the pressure change within zero displacement, resulting in high-frequency pressure oscillations and quasi-step impacts during actual execution. This high-frequency vibration leaves fine, dense grooves on the glass surface, disrupting the surface's microscopic smoothness and increasing haze and optical distortion points. Although the stress layer depth is not significantly affected, the microscopic damage to the surface and the small fluctuations in stress distribution weaken the overall strength, leading to a decrease in mechanical properties, and surface defects reduce product yield.

[0112] In Comparative Example 9, the excessively high polishing speed altered the hydrodynamic environment between the polishing head and the glass. The centrifugal force generated by high-speed rotation led to a shortage of polishing fluid supply at the edges. The resulting hydrodynamic film lifted the polishing head, preventing the effective transmission of the preset contact pressure and causing the gradient pressure strategy to fail. This resulted in abnormal material removal rates in the edge area, failure of curvature correction, and deterioration of surface accuracy. Fluid instability produced concentric spiral marks, increasing haze and optical distortion. This imbalance in the contact mechanics model led to a decrease in both surface shape and strength, ultimately affecting product yield and production efficiency.

[0113] While specific embodiments of this application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of this application. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any manner.

Claims

1. A method for manufacturing a heat-free bending 3D cover glass, characterized in that, Includes the following steps: Step S1: Cutting the glass sheet into blanks slightly larger than the final product size; Step S2: CNC precision carving, performing fine edge processing on the blank to form the target outline; Step S3: Cleaning to remove residual dirt and waste residue from the surface of the billet; Step S4, strengthening: chemically strengthen the cleaned blank to form an initial surface compressive stress layer on both sides of the glass. Step S5: Laser-induced prestressing. A laser beam is used to locally scan the surface of the strengthened glass substrate to be bent. The laser-induced thermal effect causes local annealing in the scanned area, reducing the surface compressive stress in the area and creating a non-uniform prestress distribution field inside the glass, causing the glass to undergo pre-bending deformation to achieve 70%-90% of the target curvature. Step S6: Single-sided polishing and fine-tuning. The glass that has been laser-treated is subjected to single-sided material removal processing to further reduce the compressive stress layer strength, correct the curvature accuracy and eliminate the trace surface roughness generated by laser scanning, so that the two sides of the glass form the final compressive stress strength difference and obtain the target curvature. Step S7: Final wash. The polished glass cover is cleaned to obtain the final product. The target curvature is R600-R1000, and the manufacturing process eliminates the need for high-temperature hot bending of the glass.

2. The manufacturing method according to claim 1, characterized in that, The laser beam wavelength used in step S5 for constructing the laser-induced prestress is located within the absorption band of the glass substrate, preferably 1064 nm, 1070 nm, or 532 nm; the laser power density is controlled between 50 and 200 W / cm². 2 The spot diameter is set to 0.5~2mm; the laser scanning speed is controlled at 200~500mm / s; the scanning path is planned according to the curvature shape of the target, and can be selected from parallel reciprocating scanning along the long axis or short axis, surrounding scanning along the glass perimeter, gridded partition scanning, or local densified scanning for corner areas.

3. The manufacturing method according to claim 1, characterized in that, The single-sided polishing fine-tuning described in step S6 is a light polishing process, with the polishing removal depth controlled at 1~3μm; The contact pressure is controlled at 0.05~0.1MPa; the polishing speed is 200~500 rpm; Polishing time should be controlled within 3 to 5 minutes.

4. The manufacturing method according to claim 1, characterized in that, In step S6, during single-sided polishing, differentiated pressure control is used to divide the glass surface to be polished into four independent main control areas: the center area, the long edge area, the short edge area, and the corner area. A reference contact pressure is set for each of the four main control areas, satisfying a stepwise decreasing relationship: the reference contact pressure of the center area > the reference contact pressure of the edge area > the reference contact pressure of the corner area. This stepwise distribution is used to compensate for edge effects, linear velocity differences, and corner stress concentration caused by geometric differences in rectangular glass during the polishing process. At the boundary between two adjacent main control areas, a pressure buffer transition zone is dynamically generated; When the polishing head crosses the boundary, the control system adjusts the output pressure in real time based on a preset smooth transition algorithm, so that the first and second derivatives of the pressure value with respect to position remain continuous during the process of crossing the boundary.

5. The manufacturing method according to claim 4, characterized in that, The single-sided polishing fine-tuning described in step S6 employs differentiated pressure control. A rectangular coordinate system is established with the geometric center of the glass cover as the origin, the X-axis along the length of the glass, and the Y-axis along the width of the glass, dividing the surface to be polished into four functional areas: The central region is located in the core rectangular area at the geometric center of the glass, and its range is -0.4L≤x≤0.4L and -0.4W≤y≤0.4W, where L is the effective polishing length of the glass and W is the effective polishing width of the glass. The long-side edge region is distributed in two symmetrical rectangular strip regions on both sides of the long side of the central region, with a range of -0.4L≤x≤0.4L, and the y coordinate is between 0.4W and 0.5W and between -0.5W and -0.4W; The short-side edge region is distributed in two symmetrical rectangular strip regions on both sides of the short side of the central region, with the x-coordinate between 0.4L and 0.5L and between -0.5L and -0.4L, and -0.4W≤y≤0.4W; The corner area is located at the four apex corners of the glass, that is, the four rectangular areas where |x|>0.4L and |y|>0.4W.

6. The manufacturing method according to claim 4, characterized in that, During the polishing process, different levels of contact pressure are applied to the area, using a gradient distribution with high pressure at the center, low pressure at the edges, and lowest pressure at the corners to compensate for edge effects and differences in linear velocity during polishing. The pressure level relationship is: center area pressure > transition area pressure > edge area pressure > corner area pressure. The pressure range is as follows: contact pressure in the center area is controlled at 0.08~0.12MPa; contact pressure in the transition area is controlled at 0.06~0.09MPa; contact pressure in the long and short edge areas is controlled at 0.04~0.07MPa; and contact pressure in the corner area is controlled at 0.03~0.05MPa.

7. The manufacturing method according to claim 4, characterized in that, At the boundary between two adjacent main control areas, a pressure buffer zone is set; the physical width of the pressure buffer zone is a proportional function of the effective size of the glass. When the polishing operation enters the buffer zone, the control system uses an S-shaped pressure gradient curve based on a fifth-order polynomial to dynamically adjust the output pressure of the loading mechanism, so that the first and second derivatives of the pressure value P change with position are continuous and smooth, eliminating pressure steps.

8. The manufacturing method according to claim 1, characterized in that, In step S4, the chemical strengthening process uses potassium nitrate strengthening solution immersion; the immersion temperature is controlled at 400~450℃; and the immersion time is set to 2~4 hours according to the glass thickness.

9. A glass cold bending forming system for manufacturing the heat-free bending 3D cover glass according to any one of claims 1 to 8, characterized in that, include: The laser preprocessing module is equipped with a laser emitter and a multi-axis motion platform. It plans the laser scanning path according to the preset curvature model to construct an induced prestress field on the glass substrate. The polishing execution module includes an adjustable pressure polishing head, a spindle drive mechanism, and a polishing fluid supply system, which performs single-sided polishing and fine-tuning on laser-pretreated glass.

10. An application of a heat-free bending 3D cover glass, characterized in that, The application uses the glass substrate prepared by the manufacturing method of claim 1 as a protective or structural component of a display terminal.

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