An electronic device glass back cover hot bending forming process

Abstract

This invention relates to the field of curved glass processing technology, specifically disclosing a hot bending forming process for electronic device glass back covers that can improve mold indentation on product surfaces, enhance sandblasting effects, and increase the yield of hot bending products. The process includes cutting to obtain a glass sheet; preparing a graphite mold; loading the glass sheet into the graphite mold and sequentially preheating, forming, slow cooling, and rapid cooling; polishing the camera hole of the glass sheet; sandblasting the glass sheet using two different angles; and sequentially performing alkaline etching, chemical hardening, and grinding on the glass sheet. The glass sheet is divided into a pulling area and a non-pulling area, with a camera hole in the pulling area, and the width of the pulling area is greater than the width of the non-pulling area. The lower mold of the graphite mold has a groove composed of a first forming area and a second forming area, the first forming area being lower than the second forming area, and a corresponding clearance groove for the camera hole in the first forming area. The lower mold of the graphite mold also has several micro-holes, protrusions embedded in the groove, and inserts that penetrate the top and bottom of the lower mold and extend from the bottom of the lower mold.

Description

Technical Field

[0001] This invention relates to the field of curved glass processing technology, and in particular to a hot bending forming process for glass back covers of electronic devices. Background Technology

[0002] With the improvement of consumption concepts, users' requirements for the texture, feel, and appearance of smart electronic products (especially iPads and mobile phones) are constantly increasing. 3D curved glass is widely loved and sought after by the younger generation of consumers due to its advantages such as high aesthetics, thinness, transparency, fingerprint resistance, anti-glare, hardness, scratch resistance, and excellent weather resistance. 3D curved glass is a single piece of glass with a 3D structure. Its manufacturing process mainly includes CNC machining of raw materials, hot bending, polishing, hardening, and bonding. Among these, the hot bending process is one of the key steps in 3D glass forming. It belongs to precision forming technology and has significant advantages over mechanical processing of materials, saving time and labor and improving the productivity of curved glass. To improve the yield rate and the feel and appearance of 3D curved glass, the current main method for surface treatment is a combination of wet sandblasting and NaOH etching. Wet sandblasting results in a rougher, more matte finish on the surface of 3D curved glass, while also removing scratches and other imperfections. Compared to traditional methods such as mold masking spraying, chemical gradient etching, and gradient sandblasting, the wet sandblasting and NaOH etching method not only improves production efficiency and reduces production and labor costs, but also offers advantages such as environmental friendliness and energy conservation.

[0003] The 3D curved glass hot bending process is mainly divided into four stages: preheating, forming, slow cooling, and rapid cooling. In the preheating stage, flat glass is placed in a graphite mold and heated to the softening point of the glass. In the forming stage, while maintaining the forming temperature of the glass that has reached the softening point, pressure is applied to the mold according to preset parameters so that the softened glass replicates the shape of the mold cavity. In the slow cooling stage, the glass is slowly cooled at the annealing temperature to eliminate the thermal stress generated by the expansion of the glass due to the temperature rise. In the rapid cooling stage, a cooling plate with cooling water is used to quickly cool the annealed curved glass to obtain the product.

[0004] For the aforementioned processes, due to the use of molds, mold marks are inevitably generated on the edges of the hot-bent glass during the hot bending process. These mold marks will affect the overall appearance quality of the product. Furthermore, in the wet sandblasting stage, the traditional sandblasting angle is 90°, with sand particles striking the horizontal surface of the glass perpendicularly. This prevents the sandblasting of crater designs with sandblasting angles of 0° or 180° and the body of periscope telephoto lenses, thus affecting the sandblasting quality of the product surface. In addition, during the traditional curved glass forming process, the pores on the glass surface form a crater structure after hot bending. Because the crater area needs to be bent and replenished with material from around it, material shortages around the crater can easily occur, affecting the final structure of the formed product and resulting in poor product appearance. Summary of the Invention

[0005] Therefore, it is necessary to provide a hot bending forming process for electronic device glass back covers that can improve the mold indentation on the product surface, enhance the sandblasting effect on the product surface, and increase the yield of hot bending.

[0006] A hot bending forming process for glass back covers of electronic devices includes the following steps:

[0007] S1. Cut the glass sheet to obtain a glass sheet with an wing-shaped structure. The glass sheet is divided into a pulling area and a non-pulling area. A camera hole to be formed into a volcano crater is opened at the edge of the glass sheet in the pulling area. The width of the pulling area is greater than the width of the non-pulling area.

[0008] S2. Prepare a graphite mold, which includes a lower mold and an upper mold snapped together with the lower mold. The lower mold has a groove for accommodating a glass sheet and abutting against the lower surface of the glass sheet. The bottom shape of the groove is adapted to the shape of the glass sheet. The bottom of the groove includes a first forming area corresponding to the pulling area and a second forming area corresponding to the non-pulling area. The first forming area is lower than the second forming area. The first forming area has a clearance groove corresponding to the camera hole of the glass sheet. The lower mold has several micro-holes that communicate with the clearance groove and the external environment to form a heat absorption structure. The bottom surface of the upper mold has a protrusion that abuts against the upper surface of the glass sheet and is embedded in the groove. The upper mold has a through hole that penetrates the top and bottom surfaces of the upper mold and corresponds to the clearance groove. An insert is inserted into the through hole, and the end of the insert extends out from the bottom of the through hole.

[0009] S3. Place the glass sheet into the lower mold of the graphite mold, and cover the upper mold on the top of the glass sheet. Send the closed graphite mold into the hot bending machine for preheating, forming, slow cooling and fast cooling in sequence.

[0010] S4. Remove the heat-bent glass sheet and polish the area around the camera hole of the glass sheet.

[0011] S5. Sandblast the flat surface of the glass sheet using the first sandblasting angle α1, and sandblast the vertical part of the glass sheet using the second sandblasting angle α2. α1 is 90°, 15°≤α2<90°, or 90°<α2≤165°.

[0012] S6. The sandblasted glass sheet is sequentially subjected to alkaline etching, chemical hardening, and grinding to obtain the glass back cover for electronic devices.

[0013] In one embodiment, the graphite mold further includes at least one pair of latches for engaging the upper mold and the lower mold. Each pair of latches is respectively engaged on both sides of the upper mold and the lower mold. One side of the latch is provided with a slot with a vertical cross-section of a parallelogram structure. The slot includes a first surface parallel to the side of the upper mold, a second surface located on one side of the first surface and parallel to each other, and a third surface. The second surface is located above the third surface. A first arc transition portion with a superior arc structure is provided between the second surface and the first surface. The first arc transition portion and the second surface together form a first limiting portion. A second arc transition portion with a inferior arc structure is provided between the third surface and the first surface. The second arc transition portion and the third surface together form the first limiting portion.

[0014] The upper surface edge of the upper mold has a first snap-fit ​​notch that penetrates the side of the upper mold, and the lower surface edge of the lower mold has a second snap-fit ​​notch that penetrates the side of the lower mold. The shape of the upper surface of the first snap-fit ​​notch is adapted to the shape of the first limiting part, and the shape of the lower surface of the second snap-fit ​​notch is adapted to the shape of the second limiting part.

[0015] In one embodiment, the edge of the recessed groove is provided with a radius (R).

[0016] In one embodiment, the through hole is a stepped hole, and the insert is provided with a stepped portion that conforms to the inner contour of the stepped hole; the upper surface of the upper mold has two operating holes communicating with the through hole on both sides of the through hole.

[0017] In one embodiment, the bottom surface of the lower mold is provided with an air intake channel communicating with each of the micropores.

[0018] In one embodiment, the preheating temperature of the graphite mold is between 710°C and 770°C, the molding temperature of the graphite mold is between 670°C and 740°C, the slow cooling temperature of the graphite mold is between 300°C and 600°C, and the rapid cooling temperature of the graphite module is 24°C.

[0019] In one embodiment, in step S4, a polishing rod with a polyurethane polishing pad on its surface is used to locally polish the area around the camera hole of the glass sheet using nano-cerium oxide polishing liquid.

[0020] In one embodiment, α2 is 15° or 165°.

[0021] The hot bending forming process for electronic device glass back covers of this invention involves creating micro-holes in the lower mold to form a heat absorption structure and polishing the area around the camera hole to reduce mold marks caused by excessive pressure on the platform. A second sandblasting angle is used to sandblast the body of the glass sheet, ensuring comprehensive sandblasting of the product surface and improving the sandblasting effect by using two different sandblasting angles to sandblast different parts of the product. The glass sheet is designed with an wing-shaped structure, and the first forming area of ​​the lower mold is lower than the second forming area. During crater forming, the glass sheet pulling area provides the glass raw materials required for crater forming. This ensures that there is no material shortage during crater forming and prevents waste due to excessive material size in non-pulling areas. It ensures smooth crater forming pulling operations, avoids surface defects caused by material shortages, and improves the yield rate of hot bending. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the glass sheet structure in one embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the structure of a graphite mold from one perspective in one embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the graphite mold from another perspective in one embodiment of the present invention;

[0025] Figure 4 This is a schematic cross-sectional view of a graphite mold in one embodiment of the present invention;

[0026] Figure 5 This is an exploded structural diagram of a graphite mold in one embodiment of the present invention;

[0027] Figure 6 This is a front view of the lower mold in one embodiment of the present invention;

[0028] Figure 7 This is a side view of the buckle in one embodiment of the present invention. Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0030] This invention discloses a hot bending forming process for glass back covers of electronic devices that can improve mold indentation on product surfaces, enhance sandblasting effects, and increase the yield of hot bending products. This hot bending forming process optimizes the structure of the glass sheet to be formed and the structure of the graphite mold for hot bending the glass sheet. At the same time, it performs polishing, etching, hardening, and grinding processes on the hot-bent glass sheet, thereby improving the surface quality of curved glass products.

[0031] For specific details, please refer to... Figure 1-6 The hot bending forming process for the glass back cover of the electronic device in this embodiment includes the following steps:

[0032] S1. Cut the original glass sheet to obtain a glass sheet 10 with an wing-shaped structure. The glass sheet is divided into a pulling area 101 and a non-pulling area 102. A camera hole 103 to be formed into a volcano crater is opened at the edge of the glass sheet in the pulling area 101. The width of the pulling area 101 is greater than the width of the non-pulling area 102. In this embodiment, the glass back cover of the electronic device to be processed is a curved glass back cover of an iPad. The glass sheet has an approximately cuboid structure, a thickness of 0.5±0.01mm, a non-pulled area 102 with a length of 246.49±0.01mm, and a width of 177.378±0.01mm. The pulled area 101 is located on one side of the non-pulled area 102, and its width is greater than that of the non-pulled area 102. The side of the pulled area 101 away from the camera hole 103 is flush with the non-pulled area 102. A protrusion is provided on the side of the pulled area 101 facing away from its contact surface with the non-pulled area 102 near the camera hole 103. Preferably, the width difference between the pulled area 101 and the non-pulled area 102 is 4.6mm, and the protruding length of the protrusion is 4.6mm. In this way, the glass sheet can be made 1153.507cm shorter along its long side. 2 Glass saving in the wide-edge direction: 866.5cm 2 This ensures that the crater platform does not lack material during the hot bending process.

[0033] It should be noted that the crater structure in this embodiment refers to the structure in which the camera hole 103 of the formed product has an arc-shaped edge after hot bending during the glass sheet hot bending process, and the whole structure is similar to a volcano. This structure is used to cover the edge of the camera of the electronic product after assembly, so as to achieve the positioning and protection of the camera.

[0034] S2. Prepare a graphite mold. The graphite mold 20 includes a lower mold 201 and an upper mold 202 that is snapped together with the lower mold 201. The lower mold 201 has a groove 203 for accommodating a glass sheet and abutting against the lower surface of the glass sheet. The bottom shape of the groove 203 is adapted to the shape of the glass sheet. The bottom of the groove 203 includes a first forming area corresponding to the pulling area 101 and a second forming area corresponding to the non-pulling area 102. The first forming area is lower than the second forming area, and the first forming area has a corresponding glass sheet forming area. The glass plate camera hole 103 has a relief groove 204. The lower mold 201 has several micro-holes that communicate with the relief groove 204 and the external environment to form a heat absorption structure. The bottom surface of the upper mold 202 has a protrusion 205 that abuts against the upper surface of the glass plate and is embedded in the groove 203. The upper mold 202 has a through hole 206 that penetrates the top and bottom surfaces of the upper mold 202 and corresponds to the relief groove 204. An insert 207 is inserted into the through hole 206, and the end of the insert 207 extends out from the bottom of the through hole 206.

[0035] In this embodiment, graphite material is used to make the mold for hot bending of curved glass because graphite material has advantages such as oxidation resistance, deformation resistance, moderate strength and hardness, and is not prone to reacting or sticking with glass, and has good demolding performance. Furthermore, graphite has excellent thermal conductivity under high temperature conditions, which facilitates the rapid conduction of heat to the glass sheet, thereby improving the heating speed and heating effect of the glass sheet. The precision and surface quality of the graphite forming surface can also meet the requirements of hot bending. In addition, graphite raw materials are abundant and inexpensive, which helps to reduce the production cost of the mold.

[0036] By making the first forming area lower than the second forming area, that is, the height of the upper surface of the first forming area is less than the height of the upper surface of the second forming area, the first forming area of ​​the lower mold 201 (i.e., the area used for pulling the glass sheet) is designed with a stepped structure. This ensures that when the upper mold 202 and the lower mold 201 are closed, the part of the glass sheet corresponding to the first forming area is not compacted. When preheating is completed and the temperature of the glass sheet reaches the softening point Tf, the volcano forming pulling can be carried out smoothly. In other words, this stepped structure provides a clearance for the pulling operation during volcano hot bending forming. Preferably, the height difference between the first forming area and the second forming area is 0.05mm. Thus, when the glass sheet is inserted between the upper mold 202 and the lower mold 201 of the graphite mold 20 and clamped, the non-pulling area 102 of the glass sheet is compacted when the mold is closed, and there is a gap between the pulling area 101 of the glass sheet and the upper surface of the first forming area. During the hot bending process, all the raw materials required for the crater platform (around the camera hole 103) to be formed from the glass sheet are from the pulling area 101 of the glass sheet. This design can prevent the non-pulling area 102 of the glass sheet from deforming due to pulling during the forming of the crater platform, and also avoid defects such as wrinkles and uneven glass thickness caused by pulling during the forming of the crater platform.

[0037] In this embodiment, a clearance groove 204 corresponding to the camera hole 103 of the glass sheet is formed in the first forming area. This clearance groove 204 provides a receiving area for the end of the insert 207, so that the insert 207 can pass through the camera hole 103 of the glass sheet to be heated and bend, and position the crater position of the glass product. In addition, the insert 207 is also made of high-temperature resistant graphite material, which can maintain the shape of the insert 207, extend its service life, and avoid the problem of sticking during material handling. By setting the insert 207, while ensuring that the number of molds is reduced when adjusting product features, the damaged insert 207 can also be replaced separately when it wears out, so as to avoid the mold being scrapped together. This saves mold processing time and avoids unnecessary waste.

[0038] In traditional curved glass hot pressing, the mold is first sent to a preheating workstation for preheating, and then to a forming workstation. The upper mold 202 uses its own weight and pressure to press the glass, thus hot pressing the glass into shape. The heat for softening and deforming the glass mainly comes from the heat conduction effect when the heating plate of the hot bending machine comes into contact with the graphite mold, and a small part comes from the heat convection of the high-temperature nitrogen environment inside the hot bending machine. Because of the gap between the graphite mold and the insert after mold closing, the temperature transferred from the graphite mold to the glass sheet is too high in some areas, resulting in a hazy surface on the glass sheet. Furthermore, the thickness of the camera hole used to form the crater of the glass sheet is not guaranteed to be completely consistent, causing local haziness to appear on the glass sheet due to excessive pressure during hot bending. In addition, the roughness of some areas at the bottom of the insert and inside the clearance hole is too large, which will cause the crater of the formed product to have a hazy surface. Therefore, it is difficult to eliminate the hazy phenomenon on the surface of the glass after hot bending, and polishing is required to remove the hazy surface. The process is complicated and costly. If the pressure applied by the upper mold 202 is simply increased, the glass workpiece will be deformed or uneven in thickness due to excessive pressure, resulting in an unsatisfactory thermoforming effect and a long forming time, which is difficult to meet the process requirements. In this embodiment, by setting micropores to form a heat-absorbing structure on the lower mold 201, when the glass sheet is preheated to soften, the upper mold 202 is subjected to pressure through a cylinder using its own weight and a pressure system. Simultaneously, a corresponding suction force is applied at the crater position (avoidance groove 204) to ensure the softened crater glass completely adheres to the mold, completing the crater forming. This simplifies the forming process, ensures the dimensions of the hot-bending sample platform, reduces or avoids mold marks caused by overpressure, guarantees the quality of the lower surface of the glass sheet, and reduces the draft angle when removing the formed glass product, thus lowering the difficulty of removing the glass product. It should be noted that since the mold in this embodiment is made of graphite material, which is a network structure composed of carbon atoms, the gaps between these network structures constitute the micropores in this embodiment. That is, the micropores on the lower mold used to form the heat-absorbing structure are caused by the material of the lower mold itself, eliminating the need for further CNC machining or other methods to form micropores on the lower mold.

[0039] S3. Place the glass sheet into the lower mold 201 of the graphite mold 20, and cover the upper mold 202 on top of the glass sheet. Send the closed graphite mold 20 into the hot bending machine for preheating, forming, slow cooling, and rapid cooling in sequence to complete the hot bending operation of the glass sheet. Preferably, the preheating temperature of the graphite mold 20 is between 710℃ and 770℃, the forming temperature of the graphite mold 20 is between 670℃ and 740℃, the slow cooling temperature of the graphite mold 20 is between 300℃ and 600℃, and the rapid cooling temperature of the graphite mold is 24℃.

[0040] In this embodiment, the hot bending machine should be selected as one that can absorb heat from the bottom of the graphite mold 20. After the upper mold 202 and the lower mold 201 are closed, they should be fixed with clips to prevent the glass sheet from exceeding the thickness specifications due to expansion during the hot bending process. It can also prevent the glass deformation in the non-pulling area during the volcano forming of the product from causing poor product dimensions.

[0041] S4. Remove the hot-bent glass sheet and polish the area around the camera hole 103. Since mold marks are unavoidable during the hot-bending process, these marks on the edges of the hot-bent glass will affect the overall appearance quality of the glass. To reduce and avoid mold marks on the edges of the hot-bent glass, in step S4, a polishing rod with a polyurethane polishing pad on its surface is used to locally polish the area around the camera hole 103 of the glass sheet with nano-cerium oxide polishing liquid. Because polyurethane polishing pads offer excellent polishing performance and a long service life, the micropores on the surface of the polyurethane polishing pad soften and roughen the surface during polishing, and retain abrasive particles in the polishing fluid, ensuring full contact between the abrasive and the product being polished. The nano-cerium oxide polishing fluid contains abrasives, such as rare earth particles like cerium oxide. During polishing, glass fragments ground off the glass surface are also mixed into the polishing fluid, polishing the glass sheet together with the abrasives in the fluid, forming a fractured layer on the glass surface. This fractured layer can be removed by friction with the polyurethane polishing pad, eliminating mold marks on the glass surface. Thus, while avoiding damage to the glass surface, mold marks are removed, improving the glass surface quality.

[0042] S5. Sandblast the flat surface of the glass sheet using a first sandblasting angle α1, and sandblast the raised portion of the glass sheet using a second sandblasting angle α2. α1 is 90°, 15°≤α2<90°, or 90°<α2≤165°. In this embodiment, both the first and second sandblasting angles are the angles between the ejected sand jet and the tangent direction of the surface to be sandblasted. Preferably, α2 is 15° or 165°. In this embodiment, by using different sandblasting angles for different parts of the formed glass sheet, and sandblasting the flat surface of the glass sheet using a 90° sandblasting angle, the flat surface of the glass sheet can be quickly and evenly sprayed with sand particles, improving sandblasting efficiency. Since the pits on the sandblasted surface are caused by both sand particle cutting and crack propagation, in this embodiment, an inclined sandblasting angle is used to sandblast the raised portion of the glass sheet, resulting in a significant sand particle cutting effect. This solves the difficulty of sandblasting the raised portion of the crater structure of the glass sheet, while making the roughness of the raised portion of the crater comparable to the effect of sand particles vertically striking the horizontal surface of the glass sheet. Furthermore, through extensive experimentation and adjustment of the sandblasting angle at the crater of the glass slide, it was found that the roughness of the sandblasted surface is related to the sandblasting angle as follows: Fr(15°)>Fr(45°)>Fr(90°), where Fr stands for surface roughness. Therefore, in this embodiment, a sandblasting angle of 15° is used to perform sandblasting on the crater portion of the glass slide.

[0043] S6. The sandblasted glass sheet is sequentially subjected to alkaline etching, chemical hardening, and grinding to obtain the glass back cover for electronic devices. Alkaline etching is used to change the surface properties of the sandblasted glass, chemical hardening is used to increase the hardness of the glass and strengthen it, and grinding is used to remove uneven parts of the glass surface, thereby obtaining a smooth glass product.

[0044] Please combine Figure 2-3 as well as Figure 5 and Figure 7In one embodiment, the graphite mold 20 further includes at least one pair of latches 208 for engaging the upper mold 202 and the lower mold 201. Each pair of latches 208 engages the upper mold 202 and the lower mold 201 on opposite sides. One side of each latch 208 has a slot 2081 with a parallelogram-shaped vertical cross-section. The slot 2081 includes a first surface 2082 parallel to the side of the upper mold 202, a second surface 2083 located on one side of the first surface 2082 and parallel to each other, and a third surface. 2084. The second surface 2083 is located above the third surface 2084. A first arc transition portion 2085 with a superior arc structure is provided between the second surface 2083 and the first surface 2082. The first arc transition portion 2085 and the second surface 2083 together form a first limiting portion. A second arc transition portion 2086 with a inferior arc structure is provided between the third surface 2084 and the first surface 2082. The second arc transition portion 2086 and the third surface 2084 together form the first limiting portion. The upper surface edge of the upper mold 202 has a first locking notch 2021 that penetrates the side of the upper mold 202. The lower surface edge of the lower mold 201 has a second locking notch 2011 that penetrates the side of the lower mold 201. The upper surface shape of the first locking notch 2021 is adapted to the shape of the first limiting portion, and the lower surface shape of the second locking notch 2011 is adapted to the shape of the second limiting portion. In this embodiment, by providing a buckle 208 with a parallelogram-shaped slot 2081, when the glass sheet is placed between the upper mold 202 and the lower mold 201 of the graphite mold 20, the upper mold 202 and the lower mold 201 close. The lower surface of the protrusion 205 of the upper mold 202 and the bottom surface of the groove 203 of the lower mold 201 together press against the glass sheet. The circumferential side of the protrusion 205 on the upper mold 202 abuts against the edge of the groove 203. When the buckle 208 is engaged with the edge of the upper mold 202 and the edge of the lower mold 201 respectively, the first limiting part of the buckle 208 engages with the first engaging notch 2021 of the upper mold 202 and limits its position, and the second limiting part of the buckle 208 engages with the second engaging notch 2011 of the lower mold 201 and limits its position. While limiting the upper mold 202 and lower mold 201 along the thickness direction of the graphite mold 20 and preventing the upper mold 202 from falling off the lower mold 201, the buckle 208 is not easy to fall off the upper mold 202 and lower mold 201 under the joint constraint of the first snap-fit ​​notch 2021 and the second snap-fit ​​notch 2011. While improving the connection stability of the upper mold 202 and lower mold 201, it can also prevent the upper mold 202 and lower mold 201 from generating lateral (width direction of graphite mold 20) relative movement. In this way, the upper mold 202 and lower mold 201 are firmly locked together, which can prevent the glass from expanding during the hot bending process and causing the thickness to exceed the specification, and can also prevent the non-pulling area of ​​the glass sheet from deforming during the crater forming, thus improving the hot bending forming quality of the glass sheet.

[0045] In one embodiment, the groove edge of the relief groove 204 is provided with a radius (R-angle). This can prevent the mold from cracking under stress and also prevent the product from cracking due to stress concentration. In addition, the R-angle at the edge of the relief groove 204 facilitates the insertion of the insert 207 during assembly, avoids interference between the insert 207 and the edge of the relief groove 204, and can also prevent adverse phenomena such as mold breakage caused by bumps or improper operation during processing, handling and operation, thus extending the service life of the graphite mold 20.

[0046] Please see Figure 2 In one embodiment, the through hole 206 is a stepped hole, and the insert 207 has a stepped portion that conforms to the inner contour of the stepped hole. Thus, during the assembly of the graphite mold 20, after the upper mold 202 and lower mold 201 are closed, the latch 208 is engaged, and then the insert 207 can be inserted through the through hole 206. The stepped portion on the through hole 206 limits the maximum depth to which the insert 207 can be inserted, thus avoiding difficulties in removal caused by excessive insertion depth. Furthermore, in this embodiment, the upper surface of the upper mold 202 has two operating holes 2061 on both sides of the through hole 206, communicating with the through hole 206. These operating holes 2061 provide insertion holes for fingers or tools when removing or placing the insert 207, allowing the operator to insert their fingers or tools into the operating holes 2061 and grasp the top of the insert 207 to remove it, reducing the difficulty of removing the insert 207. It should be noted that in this embodiment, when the glass sheet is inserted into the graphite mold 20 and the mold is closed, the bottom of the insert 207 is initially inserted into the through hole 206 and abuts against the part of the upper surface of the glass sheet located at the edge of the camera hole. During the preheating process of the glass sheet, the glass sheet continuously softens and deforms, and the insert 207 falls under its own weight. In this way, the glass material at the edge of the camera hole undergoes deformation in a specific direction under the push of the insert 207, so as to achieve the hot bending and shaping of the glass sheet.

[0047] In one embodiment, the bottom surface of the lower mold 201 is provided with suction channels 209 that communicate with each micropore. Furthermore, in this embodiment, since the mold is made of graphite material, the micropores on the lower mold are distributed throughout the bottom surface of the lower mold 201 and communicate with structures such as the grooves 203 and clearance grooves 204 on the top surface of the lower mold 201. Thus, by providing suction channels 209 on the bottom surface of the lower mold 201, an external vacuum device can be connected through the suction channels 209, causing negative pressure to be generated in the entire groove 203 and clearance groove 204 area of ​​the lower mold 201. This allows the softened glass to completely conform to the grooves 203 of the lower mold 201, and the softened crater glass to completely conform to the mold, completing the crater forming. This ensures the size of the hot-bending sample platform and reduces or avoids mold marks caused by overpressure on the platform, while also ensuring the quality of the lower surface of the glass sheet. Simultaneously, it reduces the draft angle when removing the formed glass product, lowering the difficulty of removing the glass product. Furthermore, the distance between the top surface of the suction channel 209 and the bottom surface of the groove 203 is greater than or equal to the thickness of the groove 203, and the ratio of the depth of the suction channel 209 to the depth of the groove 203 is between 2:1 and 5:1. In this embodiment, the depth ratio of the suction channel 209 to the groove 203 is 5:1, and the distance between the top surface of the suction channel 209 and the bottom surface of the groove 203 is equal to the thickness of the groove 203. This avoids the problems of insufficient suction force on the glass sheet and weak heat absorption caused by an excessively large distance between the suction channel 209 and the groove 203, and also avoids the problem of the lower mold 201 breaking due to an excessively small distance between the suction channel 209 and the groove 203 and excessive heat absorption force at the bottom of the lower mold 201. Preferably, the width of the suction channel 209 is 8mm and the depth is 6mm.

[0048] It should be noted that, in order to improve the hot bending quality of the glass sheet, this embodiment also proposes a large number of assumptions to address the current problems of the glass sheet and verifies the results through repeated adjustments, as shown in the table below:

[0049]

[0050] The following examples illustrate the manufacturing process of glass back covers for electronic devices.

[0051] 1) Graphite mold material selection

[0052] In this embodiment, the graphite mold is made of POCO graphite raw material, which has a coefficient of thermal expansion of 7.88 x 10⁻⁶. -6 / ℃, density is 1.77g / cm³ 3 The physical properties are as follows:

[0053] ＜3 ＜5 96 60

[0054] 2) Mold Design

[0055] The mold shape is designed based on the shape of the aforementioned glass sheet. Taking into account the actual dimensions of the finished product, the allowance for subsequent processing, the coefficient of thermal expansion of the hot-bent glass, and other factors, the final mold dimensions are designed. This design allows the glass to be hot-bent without external force or localized heating; simply controlling the temperature and timing is sufficient to complete the forming process.

[0056] 3) CNC machining of molds

[0057] The CNC machining of the mold in this embodiment includes shape machining and forming surface machining.

[0058] The external machining parameters are as follows:

[0059] Diamond electro-hydraulic tools D10R / D3R0 Φ10mm / Φ3mm 24000±500RPM 8000±600mm / min

[0060] The processing parameters for the formed surface are as follows:

[0061] Diamond electro-hydraulic tools D6R3 / D4R2 Φ0.6mm / Φ0.4mm 24000±500RPM 8000±600mm / min

[0062] 4) Polishing of the molding surface

[0063] The forming surface of the CNC-machined mold is manually polished with 7000# sandpaper to remove the graphite powder suspended on the surface of the forming surface, so as to prevent the glass surface from producing defects such as bumps and indentations during hot bending. The standard for judging the quality of the forming surface polishing is Sa<120nm.

[0064] 5) Hot bending forming

[0065] i) Wipe and remove foreign matter from the surface of the graphite mold by vacuum adsorption.

[0066] ii) Manually place the cleaned and qualified airfoil glass sheet into the lower mold of the graphite mold, cover it with the upper mold, and lock the upper and lower molds with the buckle. Send the closed graphite mold to the entrance of the hot bending machine.

[0067] iii) The mold is fed into the hot bending working chamber filled with nitrogen in the hot bending machine workstation via a lever.

[0068] iv) The graphite mold carrying the airfoil glass sheet is sent out of the hot bending machine after passing through preheating, forming, slow cooling and cooling processes in sequence. In this embodiment, the graphite mold passes through 5 preheating stations in sequence during preheating; 3 forming stations in sequence during forming; 4 slow cooling stations in sequence during slow cooling; and 6 cooling stations in sequence during cooling.

[0069] The main factors affecting the hot bending of curved glass include heating temperature, applied pressure, and forming time, but the degree of influence of each process parameter varies greatly, making the hot bending process of glass very complex and non-linear. If the glass temperature inside the mold is too high during forming, the glass will melt, resulting in sticking to the mold after cooling. If the glass heating temperature is too low, cold lines, low precision, or even breakage may occur after hot bending. During the glass cooling stage, if the cooling rate is too fast, it will cause uneven temperature distribution in the glass sheet, especially a large temperature difference in the thickness direction, leading to cracking of the product due to excessive internal thermal stress during forming. To address this problem, this embodiment uses cross-validation and conducts numerous experiments to obtain a set of optimal hot bending parameters for each workstation, as detailed in the table below.

[0070]

[0071]

[0072] As can be seen, the temperature of the graphite mold gradually increases in each preheating station, gradually decreases in each station during the forming stage, gradually decreases in each station during the slow cooling stage, and remains constant in each station during the cooling stage. In this embodiment, the glass hot bending process involves first placing the graphite mold containing the glass sheet onto the heating plate of the heating station, which has already reached the preset temperature. Then, the cylinder on the heating station pushes the upper heating plate of the hot bending machine downward until the upper heating plate contacts the upper surface of the upper mold. In this process, the heating station is isothermal-controlled. By controlling the temperature of the heating plate and the heating time, the glass sheet inside the graphite mold is heated to a viscoelastic state that allows it to be bent and formed. Then, the graphite mold is pushed to the first forming station by a lever device in the forming chamber of the hot bending machine. The dual servo motors on the forming station drive the upper heating plate downward to slowly apply downward pressure to the graphite mold, causing the viscoelastic glass inside the mold to be filled and formed. The lever device then pushes the graphite mold to the second and third forming stations in sequence. The servo motors continue to apply pressure to the graphite mold, so that the glass sheet is held under pressure in the graphite mold for a period of time, which is beneficial for better shaping of the glass. Finally, the graphite mold is pushed to the slow cooling and cooling station to cool down until it reaches room temperature.

[0073] In this embodiment, instead of placing the graphite mold in a single workstation and adjusting its temperature, the graphite mold is moved between adjacent workstations with small temperature differences. This allows the temperature of the graphite mold to change naturally and slowly as it is transferred, thus avoiding rapid changes in the glass sheet's state caused by sudden temperature changes in the graphite mold. This prevents the stress inside the glass sheet from being released in a timely manner, which could negatively impact the glass's performance.

[0074] v) Manually open the graphite mold, use a vacuum cleaner to clean the mold and glass after hot bending, and then check the appearance and size of the formed glass.

[0075] 6) Removal of indentations around the crater platform

[0076] The five-axis polishing equipment is used to polish the indentations around the crater on the glass slide. The parameters of the five-axis polishing equipment are as follows: maximum spindle speed is 5000 RPM; feed rate is 30-800 mm / min; polishing rod material is 3M abrasive wheel wrapped with rubber or sponge, and the Shore hardness of the rubber or sponge is 20-40 HSC; cutting depth is 0.8-0.9 mm, and removal depth is 15-20 μm.

[0077] 7) Sandblasting of user face

[0078] The abrasive used is 3000# green silicon carbide (SIC) with a Mohs hardness of 9.5 and a particle size of approximately 5µm. The glass feeding direction requires the crater protrusion to be at the rear, the glass sheet spacing to be 30mm, the glass conveying speed to be 0.35m / min, the water pressure to be ≥3bar, the cooling water temperature to be 8-12℃, the air pressure to be ≥6bar, the exhaust pressure to be <-200Pa, the abrasive-to-water ratio to be 3.5±0.2%WT, and the distance between the nozzle and the product to be 40mm. The product surface is blasted using a traditional method with a blasting angle of 90°, where the abrasive particles strike the horizontal glass surface perpendicularly. The crater protrusion body uses an angled blasting scheme, with the blasting angle between the protrusion body and the abrasive particles being 15° or 165°. The incident angle of the abrasive blasting on the product protrusion body is 15° or 165°, and the reflection angle is 165° or 15°.

[0079] 8) Alkaline etching

[0080] The consumables use an etching solution of 50% NaOH + 5% NaG, with an etching temperature of 120±5℃ and a removal rate of 0.023-0.026 μm / edge. The NaOH etching system is a vertical chemical processing system; the etching time is 33 min. Quality control parameters are required: roughness: Pitch / Sdq>19.5, Sq:0.6-1.4μm, Sdq:0.39-0.43μm, Ssc<1.43μm; optical performance requirements: sharpness <90, graininess <1.0, gloss (60°) <30.

[0081] 9) Chemical hardening (including two hardening processes)

[0082] First chemical hardening: preheating time is 60±5 min, preheating temperature is 380±10℃, first chemical hardening time is 240±5 min; first chemical hardening temperature is 380±2℃; consumables are 69±2% NaNO3 (WT%) / 31±2% KNO3 (WT%) / 0.5±0.1% HSiO3 (WT%).

[0083] Second chemical hardening: preheating time is 15±1 min, preheating temperature is 380±10℃, second chemical hardening time is 40±1 min; second chemical hardening temperature: 380±2℃; consumables are 5±1% NaNO3 (WT%) / 95±1% KNO3 (WT%) / 0.5±0.1% HSiO3 (WT%).

[0084] The quality control parameters are as follows: CS1 (compressive stress) is 115-150MPa, DOL1 (Depth of layer) is 153-165μm; CS2 is 750-850MPa, and DOL2 is 6.95-8.65μm.

[0085] In this embodiment, two chemical hardening processes are employed to exchange smaller-radius ions (Na+) in the glass surface with larger-radius ions (K+) in the molten salt. The difference in ion volume creates compressive stress on the glass surface. Furthermore, the KNO3 content in the second chemical hardening process is significantly greater than that in the first process, thereby increasing the number of (Na+) ions and the depth of the exchange between (K+) ions and the surface layer, thus improving the impact resistance of the glass.

[0086] 10) Single-sided grinding bottom

[0087] The polishing consumables are white abrasive leather. The upper / lower disc rotation speed of the polishing equipment is 0 / 30±5 rpm, and the batch size is 3 PCS / batch. The disc pressure is 80-120 kg. The polishing slurry is white CeO2 polishing slurry, and the abrasive particle size D50 = 1.48 μm.

[0088] The hot bending forming process for electronic device glass back covers of this invention involves creating micro-holes in the lower mold to form a heat absorption structure and polishing the area around the camera hole to reduce mold marks caused by excessive pressure on the platform. A second sandblasting angle is used to sandblast the body of the glass sheet, ensuring comprehensive sandblasting of the product surface and improving the sandblasting effect by using two different sandblasting angles to sandblast different parts of the product. The glass sheet is designed with an wing-shaped structure, and the first forming area of ​​the lower mold is lower than the second forming area. During crater forming, the glass sheet pulling area provides the glass raw materials required for crater forming. This ensures that there is no material shortage during crater forming and prevents waste due to excessive material size in non-pulling areas. It ensures smooth crater forming pulling operations, avoids surface defects caused by material shortages, and improves the yield rate of hot bending.

[0089] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A hot bending forming process for glass back covers of electronic devices, characterized in that, Includes the following steps: S1. Cut the glass sheet to obtain a glass sheet with an wing-shaped structure. The glass sheet is divided into a pulling area and a non-pulling area. A camera hole to be formed into a volcano crater is opened at the edge of the glass sheet in the pulling area. The width of the pulling area is greater than the width of the non-pulling area. S2. Prepare a graphite mold, which includes a lower mold and an upper mold snapped together with the lower mold. The lower mold has a groove for accommodating a glass sheet and abutting against the lower surface of the glass sheet. The bottom shape of the groove is adapted to the shape of the glass sheet. The bottom of the groove includes a first forming area corresponding to the pulling area and a second forming area corresponding to the non-pulling area. The first forming area is lower than the second forming area. The first forming area has a clearance groove corresponding to the camera hole of the glass sheet. The lower mold has several micro-holes that communicate with the clearance groove and the external environment to form a heat absorption structure. The bottom surface of the upper mold has a protrusion that abuts against the upper surface of the glass sheet and is embedded in the groove. The upper mold has a through hole that penetrates the top and bottom surfaces of the upper mold and corresponds to the clearance groove. An insert is inserted into the through hole, and the end of the insert extends out from the bottom of the through hole. S3. Place the glass sheet into the lower mold of the graphite mold, and cover the upper mold on the top of the glass sheet. Send the closed graphite mold into the hot bending machine for preheating, forming, slow cooling and fast cooling in sequence. S4. Remove the heat-bent glass sheet and polish the area around the camera hole of the glass sheet. S5. Sandblast the flat surface of the glass sheet using a first sandblasting angle α1, and sandblast the upright part of the glass sheet using a second sandblasting angle α2. α1 is 90°, 15°≤α2<90°, or 90°<α2≤165°. The first sandblasting angle α1 and the second sandblasting angle α2 are both the angle between the sprayed sand jet and the tangent direction of the surface to be sandblasted. S6. The sandblasted glass sheet is sequentially subjected to alkaline etching, chemical hardening, and grinding to obtain the glass back cover for electronic devices.

2. The hot bending forming process for the glass back cover of electronic devices according to claim 1, characterized in that, The graphite mold also includes at least one pair of latches for engaging the upper mold and the lower mold. Each pair of latches is respectively engaged on both sides of the upper mold and the lower mold. One side of each latch is provided with a slot with a vertical cross-section of a parallelogram structure. The slot includes a first surface parallel to the side of the upper mold, a second surface located on one side of the first surface and parallel to each other, and a third surface. The second surface is located above the third surface. A first arc transition portion with a superior arc structure is provided between the second surface and the first surface. The first arc transition portion and the second surface together form a first limiting portion. A second arc transition portion with a inferior arc structure is provided between the third surface and the first surface. The second arc transition portion and the third surface together form the first limiting portion. The upper surface edge of the upper mold has a first snap-fit ​​notch that penetrates the side of the upper mold, and the lower surface edge of the lower mold has a second snap-fit ​​notch that penetrates the side of the lower mold. The shape of the upper surface of the first snap-fit ​​notch is adapted to the shape of the first limiting part, and the shape of the lower surface of the second snap-fit ​​notch is adapted to the shape of the second limiting part.

3. The hot bending forming process for the glass back cover of electronic devices according to claim 1, characterized in that, The groove opening edge of the clearance groove is provided with a radius (R).

4. The hot bending forming process for the glass back cover of electronic devices according to claim 1, characterized in that, The through hole is a stepped hole, and the insert has a stepped portion that conforms to the inner contour of the stepped hole; the upper surface of the upper mold has two operating holes on both sides of the through hole that communicate with the through hole.

5. The hot bending forming process for the glass back cover of electronic devices according to claim 1, characterized in that, The bottom surface of the lower mold is provided with an air intake channel that communicates with each of the micropores.

6. The hot bending forming process for the glass back cover of electronic devices according to claim 1, characterized in that, The preheating temperature of the graphite mold is between 710℃ and 770℃, the molding temperature of the graphite mold is between 670℃ and 740℃, the slow cooling temperature of the graphite mold is between 300℃ and 600℃, and the rapid cooling temperature of the graphite module is 24℃.

7. The hot bending forming process for the glass back cover of electronic devices according to claim 1, characterized in that, In step S4, a polishing rod with a polyurethane polishing pad on its surface is used to locally polish the area around the camera hole of the glass slide with nano-cerium oxide polishing liquid.

8. The hot bending forming process for the glass back cover of electronic devices according to claim 1, characterized in that, α2 is 15° or 165°.

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