Curved glass forming method for HUD technology

Abstract

The invention relates to the technical field of automobile part manufacturing and special glass processing, and discloses a curved glass forming method for an HUD technology, and the curved glass forming method comprises the following steps: placing a sheet glass raw sheet in a preheating chamber for preheating; glass is heated through a heating lamp set in the preheating chamber, and first-order deformation occurs under the gravity of the glass; the glass is moved to a forming chamber, the glass is subjected to i-order deformation by reducing the mold closing gap between the upper mold and the lower mold in a stepped mode, and i is larger than or equal to 2; after the ith-order deformation, a negative pressure device is started, suction force is applied to the glass, and the glass is subjected to (i + 1) th-order deformation; and the negative pressure device is closed, so that the upper die and the lower die are completely closed, and gradient cooling annealing is carried out. According to the method, the glass deformation process is precisely regulated and controlled, the surface shape precision of the curved glass is improved, and common surface indentation, microcracks and other apparent defects in a traditional hot bending process can be avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of automobile parts manufacturing and special glass processing, and particularly relates to a high-precision forming method for a curved glass component of an automobile head-up display system. BACKGROUND

[0002] With the continuous improvement of the intelligent level of automobiles, as a key component for improving driving safety and interactive experience, the manufacturing process of the core optical element of the head-up display system is increasingly valued. As an important optical component in the system, the free-form surface mirror is usually made of glass material and formed by a heat bending process to meet the requirements of dimensional stability and weather resistance under complex working conditions. However, in the process of realizing the glass curved surface modeling, the traditional heat bending forming process often fails to balance the surface quality and shape precision, which easily leads to problems such as uneven deformation, contour deviation or surface micro-defects of the product. In order to meet the optical use standard, subsequent grinding and polishing processes are usually required for correction, which not only increases the manufacturing cost and process complexity, but also may introduce secondary damage, affecting the reliability and service life of the element.

[0003] Therefore, how to realize high-precision and high-surface-quality curved glass manufacturing in one forming process has become a technical bottleneck that needs to be broken through in this field. SUMMARY

[0004] The application aims to provide a curved glass forming method for HUD technology to solve the problems of uneven deformation, contour deviation or surface micro-defects of the product, and to realize the effects of high precision and high surface quality.

[0005] According to the above idea, the technical solution adopted by the application is as follows: According to the first aspect of the embodiment of the application, a curved glass forming method for HUD technology is provided, comprising the following steps: S1, placing a flat glass original piece in a preheating chamber for preheating; S2, heating the glass in the preheating chamber by a heating lamp group, and causing the first-order deformation of the glass under its own gravity and the preliminary curved surface guidance of the lower mold; S3, moving the glass to a forming chamber, and causing the glass to undergo a total of i-order deformation by gradually reducing the gap between the upper mold and the lower mold, where i is greater than or equal to 2; S4, after the i-order deformation, opening a negative pressure device to apply suction to the glass to cause the i+1-order deformation of the glass; S5, closing the negative pressure device, completely closing the upper mold and the lower mold, and performing gradient annealing.

[0006] In some embodiments, the temperature for preheating in the step S1 is 400-500 DEG C.

[0007] In some embodiments, the deformation amount of the first-order deformation in step S2 accounts for 70% or more of the total deformation amount.

[0008] In some embodiments, the deformation amount of the i-order deformation in step S3 accounts for 90% or more of the total deformation amount.

[0009] In some embodiments, the lower mold temperature in step S3 is 560-590℃, and the upper mold temperature is 5-30℃ lower than the lower mold temperature.

[0010] In some embodiments, the opening time of the negative pressure in step S4 is 10-600S, and the mold temperature is 10-30℃ higher than that in the i-order deformation.

[0011] In some embodiments, a small space is formed between the glass and the lower mold in step S4, and the negative pressure device provides a downward suction force to achieve uniform stress deformation of the glass.

[0012] In some embodiments, the gradient annealing in step S5 includes multiple stages of temperature reduction, wherein the first-stage annealing temperature is 550-570℃, and the annealing time is 180-600 seconds; and the last-stage annealing temperature is 400℃, and the annealing time is 180-600 seconds.

[0013] In some embodiments, after step S5, the method further includes step S6: after the mold is opened and lowered to room temperature, the glass sheet is taken out.

[0014] According to a second aspect of the embodiments of the present application, the curved glass is used as a free-form surface mirror in an automotive head-up display system, and the face shape precision PV value of the formed curved glass is less than 50μm, and the optical use requirement can be met without polishing.

[0015] The present application has the following advantages: 1. The present application realizes precise control of the glass deformation process through the multi-stage synergistic process of "preheating-constrained deformation-negative pressure fine forming-gradient annealing". This method can improve the face shape precision of the curved glass, and can also avoid the surface defects such as surface indentation and micro-cracks commonly seen in traditional hot bending process, so that the surface of the formed glass can directly meet the optical use requirement, and the subsequent secondary processing procedures such as grinding and polishing are saved.

[0016] 2. While ensuring high precision and high apparent quality, the present application simplifies the process flow, shortens the production cycle, and reduces the yield loss and production cost caused by multiple processing. The prepared curved glass can be directly used as a high-reliability optical element in an automotive head-up display system, which helps to promote the development of HUD technology towards higher performance and lower cost. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a flow chart of the forming method of the present application; Figure 2 is a physical map of the curved glass of the present application. DETAILED DESCRIPTION

[0018] The exemplary embodiments will be described in detail herein with reference to the attached drawings. In the following description, like reference numerals refer to like elements, unless the context clearly dictates otherwise. The following exemplary embodiments are described in detail with reference to the attached drawings, which are not necessarily drawn to scale. The following exemplary embodiments are not intended to represent all embodiments in accordance with the present application. Rather, they are merely examples of apparatus and methods in accordance with some aspects of the present application, as detailed in the appended claims.

[0019] The terminology used in this application, is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Unless otherwise defined, technical terms or scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The use of the "a" or "an" to describe the disclosure is merely taken to refer to "one or more" unless otherwise indicated. The term "or" as used herein is used to associate at least one of the items linked by the term, for example, A or B means any of the A or B. The terms "comprise", "comprising", "include", "including", "contain", "containing" or variants thereof are not intended to be limiting, unless otherwise defined. The term "connected" or "coupled" as used herein is used to denote any connection or coupling, either direct or indirect, between two or more elements. The terms "top", "bottom", "front", "back", "leading", "trailing", and the like as used herein are used for description and do not present or imply one position or spatial orientation as limiting. The singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0020] The technical concept of the present application comprises: The bottleneck problem existing in the prior hot bending forming process is that it is difficult to simultaneously consider shape accuracy and surface quality during high-temperature deformation of the glass. The traditional method needs to rely on subsequent grinding, polishing and other processes for remediation, resulting in a complex process, increased cost, and easy introduction of secondary damage. Therefore, there is an urgent need for a curved glass preparation method capable of realizing high precision and high apparent quality in one forming.

[0021] To solve the above problems, the application provides a forming process in stages and in multiple mechanisms. The process realizes the grading and fine control of the deformation process by sequentially adopting constraint deformation and negative pressure assisted fine deformation after preheating and softening the glass. The method not only effectively avoids surface defects caused by direct contact of the mold, but also makes the glass uniformly adhere to the forming surface through negative pressure adsorption, significantly improves the surface accuracy and eliminates surface defects such as micro-cracks and indentation, so that the surface of the formed glass can meet the optical use requirements without secondary polishing.

[0022] Based on the above design, the application simplifies the production process, shortens the cycle and reduces the comprehensive cost under the premise of ensuring the optical performance, forms a high-precision curved glass forming solution suitable for industrial application, and is especially suitable for the manufacture of the free curved mirror of the automotive head-up display system.

[0023] The application provides a curved glass forming method for HUD technology, comprising the following steps: S1, placing a flat glass original piece in a preheating chamber for preheating; S2, heating the glass in the preheating chamber by a heating lamp group, and causing the first-order deformation of the glass under its own gravity and the preliminary curved surface guidance of the lower mold; S3, moving the glass to a forming chamber, and causing the glass to deform by i-order (wherein i≥2) through the stepwise reduction of the gap between the upper mold and the lower mold; S4, after the i-order deformation, opening the negative pressure device to apply suction to the glass to cause the i+1-order deformation of the glass; S5, closing the negative pressure device, completely closing the upper mold and the lower mold, and performing gradient annealing.

[0024] The application realizes the precise regulation and control of the glass deformation process through the multi-stage collaborative process of "preheating-constraint deformation-negative pressure fine forming-gradient annealing". The method not only improves the surface accuracy of the curved glass (the PV value can be controlled below 50 μm, and the slope error is less than 2 mrad), but also avoids the surface defects such as indentation and micro-cracks in the traditional hot bending process, so that the surface of the formed glass can directly meet the optical use requirements, and the subsequent grinding and polishing secondary processing procedures are saved. While ensuring high precision and high surface quality, the process flow is simplified, the production cycle is shortened, and the yield loss and production cost caused by multiple processing are reduced. The prepared curved glass can be directly used as a high-reliability optical element for the automotive head-up display system, and helps to promote the development of the HUD technology in the direction of higher performance and lower cost.

[0025] In this embodiment, sodium calcium silicate glass meeting the optical standards for automotive applications is chosen as the substrate, with a thickness of 2.0 mm. First, according to the 3D mathematical model of the target free-form surface, the large glass plate is cut into a square blank with the desired profile by a computer numerical control (CNC) cutting machine. After cutting, a multi-stage cleaning process including neutral detergent, deionized water ultrasonic cleaning, and high-pressure spraying is used to completely remove the cutting residue, grease, and dust. The cleaned glass sheet is dried in a clean and dry oven at 120°C for 30 minutes to obtain a clean and dry flat glass sheet.

[0026] In this embodiment, the dried glass sheet is placed in a preheating chamber. The lower mold of the preheating chamber has been preheated and stabilized at 400°C. This temperature is intended to uniformly soften the entire glass, achieving sufficient plastic flowability while maintaining a certain shape retention ability to avoid uncontrollable deformation due to overheating. The glass is placed on the lower mold and preheated for 5 minutes to ensure that the overall temperature of the glass is uniformly raised to near the mold temperature.

[0027] In this embodiment, after preheating is complete, the IR (infrared) lamp set suspended above the glass is started. The lamp set is composed of multiple short-wave infrared lamp tubes arranged in parallel, and its overall mounting frame has a servo lifting function. In this embodiment, the distance between the lower surface of the lamp set and the upper surface of the glass is adjusted to 30 mm. The power of all lamp tubes is uniformly set to 50% of the rated power. A uniform and not overly intense radiation heating field is formed on the glass surface to avoid local overheating. IR irradiation lasts for 6 minutes. During this process, under the radiation heating, a small temperature gradient is formed between the upper and lower surfaces of the glass (the upper surface is slightly higher than the lower surface), and combined with the fact that the glass has been uniformly softened, the glass begins to slowly bend and deform from top to bottom, i.e., the first-order deformation, and the deformation amount of the first-order deformation accounts for 70% or more of the total deformation amount. This large pre-deformation is achieved through non-contact radiation heating, and the glass surface does not slide against the mold with strong friction, fundamentally avoiding scratches.

[0028] In this embodiment, the glass sheet that has completed the pre-bending is transferred to the adjacent forming chamber. The lower mold temperature of the forming chamber is set to 570°C, and the upper mold temperature is set to 550°C. The upper mold temperature is set to be 5-30°C lower than the lower mold, for example, in this embodiment, a temperature difference of 20°C is maintained, which can form a temperature gradient from top to bottom. When the upper mold starts to descend and contact the glass, the lower surface of the glass, which is at a higher temperature, has better flowability and is easier to fit with the lower mold; while the upper surface of the glass, which is at a relatively lower temperature, has a slightly higher viscosity, which can reduce adhesion to the upper mold and generate beneficial shear stress during the pressing process, promoting the flow of materials inside the glass to the surrounding, which helps to eliminate local thickness unevenness.

[0029] In this embodiment, the upper mold is first rapidly lowered to just contact the upper surface of the glass. Subsequently, it is slowly pressed down at an extremely low speed of 0.01 mm / s. The glass is allowed to flow in a near-creep manner at high temperature to fully fill every detail of the mold cavity while giving sufficient time for internal stress to relax. Depending on the complexity of the curved surface, it can be divided into 2-4 small stages, with a slight pause (e.g. 10-30 seconds) after each stage of pressing down a certain distance, and a stepwise reduction of the closing gap between the upper and lower molds, with observation of the pressure feedback or fine-tuning. In this embodiment, the upper mold is finally stopped at a position 0.5 mm away from the fully closed lower mold. At this point, the glass has completed further shaping through the contact pressure of the mold, with a cumulative deformation reaching about 95% of the total target amount.

[0030] In this embodiment, the temperature of the upper and lower molds is simultaneously raised to 580°C while maintaining the mold position unchanged. The slightly higher temperature further reduces the viscosity of the glass and enhances its flowability. After the temperature is stabilized, the negative pressure system connected to the internal micro-porous channels of the lower mold is turned on. The lower mold surface is densely covered with micron-sized air holes, which are connected to a common vacuum chamber. After the negative pressure system is started, adsorption forces are generated at multiple small gaps between the glass and the lower mold surface, which originally exist due to microscopic unevenness.

[0031] In this embodiment, a negative pressure of 30 seconds is applied. During this period, atmospheric pressure uniformly acts on the upper surface of the glass, "pushing" it towards the lower mold surface, while the negative pressure "pulls" the glass from below. This process is uniformly stressed and does not produce indentations, and can improve the surface accuracy (PV value) of the glass to below 50 μm, with a slope error controlled within 2 mrad.

[0032] In this embodiment, after the negative pressure action is completed, the negative pressure system is turned off. The temperature of the upper and lower molds is simultaneously adjusted to 570°C, and at this temperature, the upper mold is instructed to slowly descend the last 0.5 mm stroke to reach the fully closed mold state, to perform the final shaping constraint on the glass.

[0033] Subsequently, a strictly controlled gradient annealing program is started: First-stage annealing: reduce the temperature from 570°C to 550°C at a rate of about 5°C / min, and maintain at 550°C for 3 minutes. This temperature is near the annealing point of the glass, aiming to maximize the elimination of thermal stress accumulated in the glass due to rapid deformation.

[0034] Second-stage annealing: continue to reduce the temperature to 520°C and maintain for 5 minutes.

[0035] Third-stage annealing: reduce the temperature to 500°C and maintain for 5 minutes.

[0036] Fourth-stage annealing: reduce the temperature to 480°C and maintain for 3 minutes.

[0037] After that, the heating can be turned off, and the mold and the glass are naturally cooled in the furnace or are programmed to cool at a slower rate to near room temperature. The purpose of the staged cooling is to control the cooling rate, so that the various parts of the glass shrink uniformly, preventing burst or new deformation due to temperature difference stress.

[0038] Finally, the shaped curved glass is transferred back to the preheating chamber or a dedicated picking area, and the vacuum chuck or edge clamping tool is used to pick the glass after the mold is opened. The obtained curved glass component has a smooth surface and does not require any polishing treatment. The face shape precision is detected to be 42 μm PV value and 1.5 mrad slope error, which fully meets the optical assembly requirements of the HUD free curved mirror.

[0039] Based on the core idea proposed in the present application, those skilled in the art can understand that the protection scope of the curved glass staged forming method is not limited to the specific process parameters, equipment models or material specifications described in the foregoing embodiments. As long as a technical solution adopts the core logic of "preheating softening-non-contact pre-deformation-contact constraint deformation-negative pressure assisted precise fitting-gradient relaxation annealing" for one-time forming of high precision and high apparent quality, the technical solution falls within the protection scope of the present application.

[0040] No matter whether the preheating method is using IR lamp group, laser scanning, hot air circulation or other radiation or convection heating means; no matter how the specific number of deformation stages (the value of i) is divided and combined; no matter whether the negative pressure device is formed by the mold micro-holes, the peripheral sealing air extraction or other ways of adsorption; no matter whether the mold structure is integral type, segmented type or with active cooling channel; no matter whether the temperature control is using PID closed loop, fuzzy logic or other intelligent algorithm; and no matter whether the formed glass material is soda lime glass, borosilicate glass, aluminum silicon glass or other optical glass, for example, replacing the IR lamp group with a programmable focused infrared laser array for scanning preheating, or replacing the lower mold micro-hole adsorption with a "air pressure forming" method of applying positive pressure on the upper surface of the glass, all of which belong to the equivalent transformation or simple expansion of the core process logic of the present application. Such design decouples "shape shaping" and "surface shaping", and finally relies on uniform pressure difference to complete precise fitting, further ensuring the optical face shape precision and surface integrity of the product. Any implementation applying this design concept should be covered by the patent range of the present application.

[0041] Specific implementation principles: The application provides a curved glass forming method for HUD technology, which is characterized in that through a synergistic process chain of "preheating softening-multi-stage progressive deformation-negative pressure auxiliary precise fitting-gradient relaxation annealing", the precision and flexibility control of the glass heat bending process are realized. In the traditional heat bending process, due to one-time excessive force or uneven temperature field, the internal stress of the glass is concentrated, the surface and the mold are hard scratched or indented, and it is difficult to completely fit the complex curved surface, so that the product precision is insufficient and subsequent polishing is required. The application decomposes the deformation process and introduces non-contact pre-deformation and negative pressure adsorption final forming, which effectively decouples the contradiction between "shape shaping" and "surface shape preserving".

[0042] The overall process follows the following logical path: first, the glass is uniformly preheated to enter the viscous flow state, providing a uniform plastic basis for subsequent deformation. Second, in the preheating stage, the glass is selectively heated by an adjustable IR lamp group, so that it occurs free pre-bending of large curvature (1st order deformation) under the preliminary guidance of the mold. This stage aims to achieve most of the deformation, avoiding surface damage that may occur when immediately performing hard mold pressing at high temperature. Then, the pre-deformed glass is transferred to the precise forming chamber, and the upper and lower molds with temperature gradient are used to perform step-by-step gap reduction (i-th order deformation), gradually correcting the glass to approach the final shape. This stage focuses on contour refinement and stress uniformization. Next, when the mold is close but not completely closed, the negative pressure system is started, and the softened glass is gently and uniformly adsorbed to the lower mold surface (i+1-th order deformation) using the atmospheric pressure difference. This step can effectively fill the micro-gaps caused by mold processing errors or local stiffness differences of the glass, and is the key to achieving high surface shape precision and excellent appearance quality. Finally, gradient cooling annealing is performed in the fully closed state to release the internal thermal stress of the glass in a controllable manner, preventing bursting and stabilizing its shape memory.

[0043] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the application cover any and all variations of the application that come within the scope of the general inventive concepts and including the preferred embodiments described herein. It is intended that the specification and examples be considered exemplary only, with the true scope and spirit of the application indicated by the following claims.

[0044] It is understood that the application is not limited to the precise construction disclosed and as illustrated in the accompanying drawings, and that various modifications and changes can be effected therein by those skilled in the art without departing from the scope of the application. The scope of the application is limited only by the claims appended hereto.

Claims

1. A method for forming a curved glass for HUD technology, characterized in that, The method comprises the following steps: S1, placing a flat glass original piece in a preheating chamber for preheating; S2, heating the glass in the preheating chamber by a heating lamp group, and causing the first-stage deformation of the glass under its own gravity and the preliminary curved surface guidance of a lower mold; S3, moving the glass to a forming chamber, causing the glass to undergo a total of i-stage deformation by gradually reducing the mold gap of the upper mold and the lower mold, where i≥2; S4, after the i-stage deformation, opening a negative pressure device to apply suction force to the glass to cause the i+1-stage deformation of the glass; S5, closing the negative pressure device, completely closing the upper mold and the lower mold, and performing gradient temperature reduction annealing.

2. A method of forming a curved glass for HUD technology according to claim 1, wherein, The preheating temperature in the step S1 is 400-500℃.

3. A method of forming a curved glass for HUD technology according to claim 1, wherein, The deformation amount of the first-stage deformation in the step S2 accounts for 70% or more of the total deformation amount.

4. The method of claim 1, wherein the glass is a curved glass for HUD technology. The deformation amount of the i-stage deformation in the step S3 accounts for 90% or more of the total deformation amount.

5. The method of claim 1, wherein the glass forming process is a curved surface glass forming process for HUD technology. The temperature of the lower mold in the step S3 is 560-590℃, and the temperature of the upper mold is 5-30℃ lower than that of the lower mold.

6. A method of forming a curved glass for HUD technology according to claim 1, wherein, The negative pressure opening time of the i+1-stage deformation in the step S4 is 10-600S, and the mold temperature is 10-30℃ higher than that of the i-stage deformation.

7. A method of forming a curved glass for HUD technology according to claim 1, wherein, A small space closed chamber is formed between the glass and the lower mold in the step S4, and the negative pressure device provides downward suction force to realize uniform stress deformation of the glass.

8. The method of claim 1, wherein the glass is a curved glass for HUD technology. The gradient temperature reduction annealing in the step S5 comprises multiple stages of temperature reduction, where the first-stage annealing temperature is 550-570℃, and the annealing time is 180-600s; and the last-stage annealing temperature is 400℃, and the annealing time is 180-600s.

9. The method of claim 1, wherein the glass is a curved glass for HUD technology. The step S5 further comprises: S6, after the mold is opened and lowered to room temperature, the glass is taken out.

10. Use of a curved glass prepared according to the method of claims 1-9, characterized in that, The curved glass is used as a free curved surface mirror in an automotive head-up display system, the surface shape precision PV value of the formed curved glass is less than 50μm, and the polished process is not required to meet the optical use requirements.

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