Forming methods, molding dies, and ceramics for large-size thin-sheet ceramics

Abstract

This invention relates to a method for forming large-size thin-plate ceramics, a forming mold, and the ceramic itself, belonging to the field of ceramic material forming technology. The method includes: filling, floating film floating, pressurization, depressurization-demolding-depressurization, and isostatic pressing steps. The depressurization-demolding-depressurization step includes: gradually depressurizing the upper pressure head while retaining a pre-set pressure; demolding, keeping the sample clamped between the upper and lower pressure heads, and lowering the floating mold until the sample is completely removed; and secondary depressurization: slowly reducing the pre-set pressure to zero, and retracting the upper pressure head to its initial position after leaving the sample. This invention effectively solves the problems of easy cracking, uneven density, difficult demolding, and easy deformation and damage during isostatic pressing of large-size thin-plate ceramics during the forming process, thereby enabling the preparation of high-quality, high-density, and uniform large-size thin-plate ceramic products.

Description

Technical Field

[0001] This invention relates to the field of ceramic material forming technology, and in particular to a method for forming large-size thin-sheet ceramics, a forming mold, and the ceramic itself. Background Technology

[0002] Dry pressing is a common method for preparing ceramic green bodies. In this method, granulated ceramic powder is filled into a mold cavity, and pressure is applied by a press head to densify the powder and form a green body. To improve the density uniformity of the green body, cold isostatic pressing is often used as a secondary densification method. This technique applies isotropic pressure to the green body through a liquid medium, which can eliminate the density gradient within the green body.

[0003] However, the aforementioned technologies face numerous challenges in producing large-size, thin-sheet ceramics. First, insufficient smoothness of the mold's inner wall or the presence of microscopic sharp corners can lead to stress concentration during demolding, easily causing scratches or brittle fracture of the blank. Second, the friction between the thin-sheet blank and the mold's inner wall is significant during demolding, and conventional ejection methods can easily cause cracking. Third, dry pressing can lead to uneven density distribution and pressure gradients within the blank due to friction between powder particles and between the powder and the mold wall. Fourth, thin sheets have a large surface area to volume ratio and small thickness; even minor inhomogeneities can be amplified, leading to defects such as cracking, delamination, and deformation. Furthermore, dry-pressed ceramic sheet blanks have low inherent strength and high brittleness. When directly subjected to cold isostatic pressing, the sheet blanks are prone to breakage due to improper handling during bagging, vacuuming, and pressure application. During isostatic pressing, without external support, the sheet itself may bend or deform, or be damaged by pressure loading. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a molding method, molding die, and ceramic for large-size thin-sheet ceramics. By optimizing the filling material, segmented pressurization, depressurization-demolding-depressurization process, and isostatic pressing treatment with a bearing plate, the problems of easy cracking, uneven density, difficult demolding, and easy deformation and damage during isostatic pressing of large-size thin-sheet ceramics during molding are effectively solved, thereby enabling the preparation of high-quality, high-density, and uniform large-size thin-sheet ceramic products.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] In a first aspect, the present invention provides a method for forming large-size thin-sheet ceramics, which adopts the following technical solution: A method for forming large-size thin-sheet ceramics includes the following steps: Filler: The granulated powder is fed into the mold cavity through a feeding device, and the filler amount is adjusted by controlling the height of the mold cavity; the granulated powder is spray-granulated powder, which meets the requirements of an angle of repose of less than 30° and a loose packing density of 0.75–0.80 g / cm³. 3 The powder has a solid spherical shape with a particle size range of 20–120 μm and a water content of 0.20–0.25 wt%. The feeding device has a long strip-shaped discharge port that spans the entire mold cavity in the length direction and has a gap of 5–10 mm in the width direction to ensure that the powder is evenly distributed in the mold cavity. Pressurization: First, the upper pressure head moves rapidly downward at a speed of 10–30 mm / s, and when it approaches the powder, the speed is reduced to a slow speed of 0.1–0.5 mm / s; when the pressure display shows 1–2 bar, hold the pressure for 1–5 seconds; when the pressure reaches 10 bar, hold the pressure again for 1–5 seconds; then continue to pressurize at a speed of 0.1–0.5 mm / s to 40–50 MPa, and hold the pressure for 10–30 seconds; Depressurization-demolding-depressurization includes: 1. First, depressurize the upper pressure head to 30–40 MPa and hold for 1–5 seconds; then continue to depressurize to 10–20 MPa and hold for 1–5 seconds; finally, retain 0.5–1.0% of the highest pressure as a reserve pressure. 2. Demolding: Keep the sample clamped between the upper and lower pressure heads, and move the floating mold downwards at a speed of 1–5 mm / s until the sample is completely removed; 3. Secondary depressurization: Slowly release the reserved pressure to 0MPa at a speed of 0.1–0.5mm / s; after the upper pressure head leaves the sample, retract to the initial position at a speed of 10–30mm / s; Isostatic pressure: Pressurize to 180-200MPa at a rate of 5–10MPa / min and hold for 5–10min; depressurize to 120-150MPa and hold for 5min; finally depressurize to zero at a rate of 5–10MPa / min.

[0007] Furthermore, in the above method, after the filling step and before the pressurization step begins, the floating mold floats up 2–5 mm.

[0008] Furthermore, in the above method, the isostatic pressing step includes: transferring the ceramic sheet onto a pressure plate, placing the ceramic sheet together with the pressure plate into a plastic sealing film for vacuum sealing, and then performing cold isostatic pressing treatment.

[0009] Furthermore, in the above method, the pressure plate satisfies at least one of the following characteristics: The flatness error shall not exceed 0.01mm; Surface roughness Ra is not greater than 0.2 μm; The material is selected from silicon carbide, aluminum oxide, metal plate or tempered glass plate; The size is greater than or equal to the size of the ceramic sheet blank to be processed; All four sides are rounded.

[0010] Furthermore, in the above method, the sealing film is a co-extruded film with a thickness of 0.2–0.5 mm; and the vacuum sealing is performed after the vacuum degree reaches -0.6–0.8 MPa.

[0011] Furthermore, in the above method, the forming dimensions of the large-size thin-film ceramic are a length of not less than 280mm, a width of not less than 195mm, and a thickness of less than 1mm.

[0012] Secondly, the present invention provides a method for forming large-size thin-sheet ceramics, using a forming mold for implementing the forming method described in any one of the first aspects above, and employing the following technical solution: feeding device; Upload template; Download template; The upper pressure head is connected to the upper template; The lower pressure head connected to the lower template; Floating mode; and A mold cavity connected to the floating mold and located between the upper pressure head and the lower pressure head; The upper pressure head, the lower pressure head, and the mold cavity are fitted together to achieve pressing and forming. The floating mold is configured to move up and down during the pressing process. The feeding device is located above the mold cavity and is configured to feed the granulated powder into the mold cavity.

[0013] Furthermore, in the above-mentioned molding die, the molding die satisfies at least one of the following characteristics: The parallelism error between the upper template, the lower template, and the floating mold shall not exceed 0.03 mm; The single-sided gap between the upper pressure head, the lower pressure head and the mold cavity is 0.01–0.02 mm; The chamfer radius of the mold cavity is R3–5mm; The height deviation of the mold cavity shall not exceed 0.03 mm; The inner corners of the mold are rounded with a radius of 2–3 mm. The surface of the mold that contacts the sample is mirror-finished, with a surface roughness Ra≤0.05μm.

[0014] Furthermore, in the above-mentioned molding die, the gap between the bottom of the feeding device and the working surface of the floating mold is 0.01–0.02 mm, and the working surface of the floating mold is polished with a surface roughness Ra≤0.1 μm.

[0015] Thirdly, the present invention provides a large-size thin-plate ceramic, which adopts the following technical solution: The large-size thin-film ceramic is prepared by the molding method described in any one of the first aspects above, and the thickness of the large-size thin-film ceramic is 0.3–20 mm.

[0016] In summary, compared with the prior art, the present invention has at least one of the following beneficial technical effects: This invention proposes a composite molding method for large-sized thin-sheet ceramics. First, a spray-granulated powder with specific flowability, bulk density, particle size distribution, and water content is used. This powder is then uniformly filled through a long, narrow feed inlet that spans the entire mold cavity in the length direction and has a 5–10 mm gap in the width direction. Subsequently, a segmented pressurization process—"rapid downward movement—slow contact—low-pressure holding—medium-pressure holding—high-pressure holding"—gradually degasses, rearranges, and densifies the powder. After pressing, the pressure is not immediately and completely released or topped out. Instead of demolding, the upper pressure head is first depressurized in stages to 30–40 MPa, 10–20 MPa and held, and then a reserve pressure of 0.5–1.0% of the highest pressure is retained. While the sample is still held by the upper and lower pressure heads, the floating mold is moved down at 1–5 mm / s until the sample is completely demolded. Then the reserve pressure is slowly released to 0 MPa at 0.1–0.5 mm / s. Finally, the ceramic sheet is further densified by staged cold isostatic pressing, holding and depressurizing.

[0017] Compared with existing conventional dry pressing or ordinary cold isostatic pressing processes, this invention improves the uniformity of large-area thin-layer powder spreading in the mold cavity by controlling the characteristics of spray-granulated powder and using a long strip-shaped feeding port, reducing density differences caused by local accumulation, height differences, and uneven filler. Through segmented low-speed pressurization and multiple pressure holding, the powder particles can be gradually rearranged and the gas can be fully discharged, reducing the risk of gas encapsulation, internal cracks, and local low density caused by rapid pressing. The pressurized demolding method of "segmented pressure relief - reserved pressure clamping demolding - secondary slow pressure relief" can avoid free rebound, edge scraping, edge chipping, and cracking of the green body when the pressure drops suddenly or is directly ejected, which is especially beneficial to maintaining the overall stability of large-size thin sheet green bodies during the demolding process. Through subsequent staged cold isostatic pressing, the density and density uniformity of the green body can be further improved while avoiding damage from sudden pressure changes. Overall, this invention does not simply improve a single process parameter, but rather reduces the probability of cracking, chipping, warping, uneven density, and demolding damage in large-size thin-sheet ceramics during the molding process by continuously combining "uniform filling, slow segmented densification, clamping-type pressure demolding, and staged isostatic pressing," thereby improving the integrity of the green body and the yield. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0019] Figure 1 A flowchart of the method for forming large-size thin-sheet ceramics according to the present invention is shown.

[0020] Figure 2 A schematic diagram of the press mold for forming large-size thin-sheet ceramics according to the present invention is shown.

[0021] Figure 3 The image shown is a sample of the ceramic sheet of the present invention before it is encapsulated.

[0022] Figure 4 The image shows a sample of the ceramic sheet of the present invention after it has been encapsulated.

[0023] Figure 5 A sample image of the ceramic sheet sample in Comparative Example 1 of the present invention is shown.

[0024] Figure 6 A sample image of the ceramic sheet sample in Comparative Example 2 of the present invention is shown.

[0025] Figure 7 A sample image of the ceramic sheet sample in Comparative Example 3 of the present invention is shown.

[0026] Figure 8 A sample image of the ceramic sheet sample in Comparative Example 4 of the present invention is shown. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0028] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments of this application. Furthermore, the descriptions of each embodiment in the following embodiments have their own emphasis; for parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0029] The method steps described in this embodiment of the invention can be executed in the order described in the specific implementation, or the execution order of each step can be adjusted according to actual needs, provided that the technical problem can be solved. These are not listed one by one here.

[0030] The present invention will be further described in detail below with reference to the accompanying drawings.

[0031] Reference Figure 1 The present invention provides a method for forming large-size thin-film ceramics by combining hydraulic molding with cold isostatic pressing to prepare ceramic thin films with high uniformity and high reliability.

[0032] The molding method includes the following steps: achieving uniform distribution of powder in the mold cavity through optimized feeding device and mold structure; using segmented pressurization process to gradually densify the powder and expel gas, thereby avoiding the generation of pores and cracks inside the green body; maintaining the sample clamping during demolding through a three-step process of depressurization-demolding-depressurization, thereby avoiding stress concentration and damage to the green body during demolding; placing the ceramic sheet on a pressure plate for plastic sealing and then performing cold isostatic pressing to provide rigid support for the sheet and prevent bending deformation or breakage of the sheet during isostatic pressing.

[0033] The above-described forming method can produce large-sized thin-film ceramics with uniform density and no crack defects. This method is suitable for the large-scale production of high-quality ceramic sheets with a thickness of 0.3–20 mm, with a yield of no less than 95%.

[0034] This molding method is particularly suitable for producing high-power electronic module substrates, such as AlN and Si3N4 ceramic substrates. It is also applicable to the preparation of high-end ceramic products such as fuel cell electrolyte sheets, laser ceramics, and transparent ceramics.

[0035] Reference Figure 2 The present invention also provides a molding die for forming large-size thin-sheet ceramics, including a feeding device 1, an upper template 2, a floating mold 3, a lower template 4, an upper pressure head 5, a mold cavity 6, and a lower pressure head 7.

[0036] The upper pressure head 5 is connected to the upper template 2 and is located above the mold cavity 6, used to apply pressure to the powder. The lower pressure head 7 is connected to the lower template 4 and is located below the mold cavity 6, cooperating with the upper pressure head 5 to complete the pressing action. The mold cavity 6 is connected to the floating mold 3 and is located in the center of the equipment, serving as the space to accommodate ceramic powder and perform pressing and shaping. The floating mold 3 is located in the middle of the equipment and moves up and down during the pressing process. The feeding device 1 is located above the mold and is used to evenly feed the granulated powder into the mold cavity 6.

[0037] This press employs a symmetrical structural design, with the upper pressure head 5, lower pressure head 7, and mold cavity 6 achieving pressing and forming through precise fit. The parallelism error between the upper template 2, lower template 4, and floating mold 3 is controlled within 0.03mm to ensure the uniformity and quality of the formed ceramic sheets. The single-sided gap between the upper pressure head 5, lower pressure head 7, and mold cavity 6 is 0.01–0.02mm. The chamfer radius of mold cavity 6 is R3–5mm. The height deviation of mold cavity 6 does not exceed 0.03mm to ensure precise control of the filler amount. The inner corners of the mold are rounded with R2–3mm to reduce demolding resistance and stress concentration. All surfaces of the mold that come into contact with the sample are mirror-finished, with a surface roughness Ra≤0.05μm.

[0038] The gap between the bottom of the feeding device 1 and the upper worktable surface of the floating mold 3 is 0.01–0.02 mm. The upper worktable surface of the floating mold 3 is polished, with a surface roughness Ra≤0.1μm. The design of the floating mold 3 allows it to float during the pressing process, preventing powder from overflowing from the mold's perimeter when the upper pressure head 5 presses down.

[0039] Furthermore, the powder used for molding is a spray-granulated powder. The characteristics of the spray-granulated powder have a direct impact on achieving uniform filling and high-quality molding.

[0040] In some embodiments, the angle of repose of the spray-granulated powder is less than 30° to ensure good powder flowability. Powder with good flowability can be evenly distributed within the mold cavity during the filling process, reducing density differences caused by uneven powder accumulation.

[0041] In some embodiments, the bulk density of the spray-granulated powder is 0.75–0.80 g / cm³.3 This loose packing density range is beneficial for the uniform accumulation of powder in the mold cavity and densification during subsequent pressing.

[0042] In some embodiments, the spray-granulated powder has a solid spherical morphology with a particle size range of 20–120 μm. The solid spherical powder morphology helps to improve the flowability and filling uniformity of the powder, while this particle size range is beneficial for the rearrangement and densification of the powder during the pressing process.

[0043] In some embodiments, the water content of the spray-granulated powder is 0.20–0.25 wt%. This water content range prevents the powder from sticking to the pressure plate while ensuring good powder flowability. If the powder has too high a water content, it will affect the flowability of the powder, causing it to fail to quickly fill gaps during the pressing process, resulting in uneven density.

[0044] Furthermore, in the filling step, the granulated powder is fed into the mold cavity via a feeding device, and the filling amount is adjusted by controlling the height of the mold cavity. As described above, the feeding device 1 is located above the mold and is used to uniformly feed the granulated powder into the mold cavity 6. The height deviation of the mold cavity 6 does not exceed 0.03 mm to ensure precise control of the filling amount.

[0045] In some embodiments, the feed inlet of the feeding device is elongated, spanning the entire mold cavity in its length direction, with a width gap of 5–10 mm. This elongated feed inlet structure ensures that the powder is evenly distributed along the length of the mold cavity when it is fed into the mold cavity, avoiding density differences caused by local accumulation of powder within the mold cavity.

[0046] In some implementations, the floating mold rises 2–5 mm before the pressurization step begins to prevent the upper pressure head from squeezing the powder and causing it to overflow. When the upper pressure head 5 contacts the powder and applies pressure, the gas in the powder is expelled. If the floating mold 3 does not rise, the gas expulsion will cause the powder to overflow from around the mold, resulting in lower density in the four corner areas of the formed ceramic sheet, leading to edge chipping and breakage during demolding or subsequent processing.

[0047] During the pressurization step, the upper pressure head moves downward rapidly, switching to slow pressurization as it approaches the powder. After segmented pressure holding, pressurization continues until the predetermined pressure is reached and held. This segmented pressurization process gradually densifies the powder and expels gas, thereby preventing the formation of pores and cracks inside the green body.

[0048] In some implementations, the upper pressure head moves rapidly downward at a speed of 10–30 mm / s, then switches to a slower pressurization speed of 0.1–0.5 mm / s as it approaches the powder. The rapid downward movement shortens the idle travel time and improves production efficiency; the slow pressurization stage allows sufficient time for powder particles to rearrange and densify, while also allowing gas in the powder to gradually escape.

[0049] In some implementations, the pressure is held for 1–2 bar for 1–5 seconds, and then held again for 1–5 seconds when the pressure reaches 10 bar. Subsequently, the pressure is increased at a rate of 0.1–0.5 mm / s to 40–50 MPa and held for 10–30 seconds. The holding pressure in the low-pressure stage (1–2 bar) allows for initial rearrangement of the powder particles and the expulsion of most of the gas; the holding pressure in the medium-pressure stage (10 bar) further densifies the powder and expels residual gas; and the holding pressure in the high-pressure stage (40–50 MPa) brings the powder to the predetermined density. This segmented holding pressure process avoids gas encapsulation and internal defects in the green body caused by rapid pressurization.

[0050] Furthermore, in the depressurization-demolding-depressurization step, the upper pressure head is gradually depressurized, retaining a reserve pressure. In some embodiments, the upper pressure head is depressurized to 30–40 MPa and held for 1–5 seconds, then depressurized further to 10–20 MPa and held for 1–5 seconds, finally retaining 0.5–1.0% of the final molding pressure as a reserve pressure. This segmented depressurization process allows the internal stress of the billet to be released gradually, avoiding damage to the billet caused by a sudden drop in pressure.

[0051] During the demolding process, the sample is held between the upper and lower pressure heads while the floating mold moves downwards until the sample is completely ejected. In some embodiments, the floating mold moves downwards at a speed of 1–5 mm / s until the sample is completely ejected. During demolding, the upper and lower pressure heads continuously apply clamping forces to the sample, ensuring that the sample remains under stable stress as it exits the mold cavity.

[0052] In the secondary depressurization step, the reserved pressure is slowly reduced to zero, and the upper pressure head retracts to the initial position after leaving the sample. In some embodiments, the reserved pressure is slowly reduced to 0 MPa at a speed of 0.1–0.5 mm / s, and the upper pressure head retracts to the initial position at a speed of 10–30 mm / s after leaving the sample.

[0053] The aforementioned three-step process of depressurization-demolding-depressurization reduces direct scraping between the blank edge and the mold through pressurized demolding. The reserved pressure continuously applies a slight lateral restraint force to the blank during demolding, offsetting some of the springback stress and protecting the blank edge from mold scratches during demolding. This process also suppresses the expansion and edge breakage phenomenon caused by the sudden disappearance of lateral force and loss of support during demolding, effectively reducing the breakage rate during demolding.

[0054] Furthermore, Figure 3 and Figure 4 The image shows the state of the ceramic sheet sample during the isostatic pressing process. In the isostatic pressing process, the ceramic sheet is transferred to a pressure plate, and the ceramic sheet and the pressure plate are then encapsulated together before cold isostatic pressing.

[0055] The pressure plate provides rigid support for the ceramic sheet green body. The flatness error of the pressure plate does not exceed 0.01 mm to ensure uniform support of the bottom surface of the green body. The surface roughness Ra of the pressure plate is not greater than 0.2 μm. The material of the pressure plate is selected from silicon carbide, alumina, or metal plate. In some embodiments, the material of the pressure plate is silicon carbide. In some embodiments, the material of the pressure plate is tempered glass. The size of the pressure plate is greater than or equal to the size of the ceramic sheet green body to be processed to ensure that the entire bottom surface of the ceramic sheet green body is supported. The four edges of the pressure plate are rounded to avoid damage to the sealing film during molding and isostatic pressing.

[0056] During the encapsulation process, the pressure plate containing the ceramic sheet preform is placed entirely into the encapsulation film for vacuum sealing. In some embodiments, the encapsulation film is a co-extruded film with a thickness of 0.2–0.5 mm. In some embodiments, heat sealing is performed after the vacuum degree reaches -0.6–0.8 MPa during vacuum sealing. The encapsulation film tightly wraps around the pressure plate and the ceramic sheet preform, ensuring that during the subsequent cold isostatic pressing process, the high-pressure liquid medium is evenly transmitted to the ceramic sheet and the pressure plate through the flexible encapsulation film, while preventing the liquid medium from directly contacting the preform.

[0057] In the cold isostatic pressing process, the sealed whole is placed in a cold isostatic press for secondary pressurization and densification. In some embodiments, the pressure is increased to 180–200 MPa at a rate of 5–10 MPa / min and held for 5–10 min, then depressurized to 120–150 MPa and held for 5 min, and finally depressurized to zero at a rate of 5–10 MPa / min. This segmented pressurization and depressurization process allows the ceramic sheet preform to gradually densify during isostatic pressing, while avoiding damage to the preform caused by sudden pressure changes.

[0058] A high-rigidity bearing plate provides rigid support for the green body, effectively preventing the thin sheets from bending and deforming under high pressure. During cold isostatic pressing, high pressure is uniformly transferred to the ceramic thin sheets and the bearing plate through a flexible medium and a plastic sealant. The bearing plate, acting as a rigid support backing, ensures that the pressure is applied evenly to the green body from a single plane, thereby improving densification efficiency and uniformity. After isostatic pressing, the bearing plate is removed, and the plastic sealant is peeled off, yielding the densified ceramic thin sheet green body.

[0059] Figures 5 to 8 A sample image of a ceramic sheet from the comparative example is shown to illustrate the defects caused by improper process parameters.

[0060] Comparative Example 1 In Comparative Example 1, the feeding device, pressurization, depressurization, and molding pressure are the same as in the specific implementation method described above, except that the mold with a chamfered radius of 3mm is replaced with a mold with a radius of 0.5mm. Figure 5Warping was observed at the corners of the samples. This warping was caused by stress concentration at the sharp corners, where the force was greater. When pressing ceramic sheets with dimensions of 280mm × 195mm and a thickness of less than 1mm, the yield was below 40%.

[0061] Comparative Example 2 In Comparative Example 2, the feeding device, pressurization, depressurization, and molding pressure conditions were the same as in the specific implementation method described above, but the powder moisture content was too high (above 0.25 wt%). Figure 6 It was observed that the samples adhered to the support plate and were difficult to separate, leading to sample rejection. This adhesion was caused by the presence of a binder in the powder, which bonded to the support plate after cold isostatic pressing. Excessive moisture content in the powder also affected its flowability, preventing it from quickly filling gaps during pressing and resulting in uneven density. When pressing ceramic sheets with dimensions of 280mm × 195mm and a thickness of less than 1mm, the yield was below 60%.

[0062] Comparative Example 3 In Comparative Example 3, the conditions for pressurization, depressurization, and molding pressure were the same as in the specific implementation method described above, but the material distribution by the feeding device was uneven. Figure 7 Cracking was observed in the samples. This cracking was caused by the powder filling cavity height being only about 1.5 mm. If there is a height difference in the material, the higher areas are compressed first, while the lower areas are not compressed or are compressed less, leading to cracking in the low-density areas of the sample, or breakage during sample transfer. When pressing ceramic sheets with dimensions of 280 mm × 195 mm and a thickness of less than 1 mm, the yield was below 30%.

[0063] Comparative Example 4 In Comparative Example 4, the feeding device, pressurization, depressurization, and molding pressure conditions are the same as in the specific implementation method described above, and the floating mold does not float during filling. Figure 8 During testing, chipping and breaking were observed on the four sides of the unglazed ceramic blank, with severe powder overflow leading to cracking of the sample. This defect was caused by a large amount of gas escaping when the upper pressure head first contacted the powder. Because the floating mold did not move upwards, the powder overflowed from around the mold, resulting in lower density in the corner areas after molding. When pressing ceramic sheets with dimensions of 280mm × 195mm and a thickness of less than 1mm, the yield was below 70%.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for forming large-size thin-sheet ceramic, characterized in that, The forming process employs a molding die, which includes a feeding device, an upper mold plate, a lower mold plate, an upper pressure head connected to the upper mold plate, a lower pressure head connected to the lower mold plate, a floating mold, and a mold cavity connected to the floating mold and located between the upper and lower pressure heads; wherein the chamfer radius of the mold cavity is R3–5mm, and the inner corners of the mold are rounded with R2–3mm, and the process includes the following steps: Filler: The granulated powder is fed into the mold cavity through a feeding device, and the amount of filler is adjusted by controlling the height of the mold cavity; the granulated powder is spray-granulated powder, which meets the following requirements: angle of repose less than 30°, loose density of 0.75–0.80 g / cm³, solid spherical morphology with a particle size range of 20–120 μm, and water content of 0.20–0.25 wt%; the discharge port of the feeding device is elongated, spanning the entire mold cavity in the length direction, with a gap of 5–10 mm in the width direction to ensure uniform distribution of powder in the mold cavity; Floating mold rises: The floating mold rises 2–5 mm to prevent powder from overflowing from the mold sides when the upper pressure head squeezes the powder. Pressurization: First, the upper pressure head moves rapidly downward at a speed of 10–30 mm / s, and when it approaches the powder, the speed is reduced to a slow speed of 0.1–0.5 mm / s; when the pressure display shows 1–2 bar, hold the pressure for 1–5 seconds; when the pressure reaches 10 bar, hold the pressure again for 1–5 seconds; then continue to pressurize at a speed of 0.1–0.5 mm / s to 40–50 MPa, and hold the pressure for 10–30 seconds; Depressurization-demolding-depressurization includes:

1. First, depressurize the upper pressure head to 30–40 MPa and hold for 1–5 seconds; then continue to depressurize to 10–20 MPa and hold for 1–5 seconds; finally, retain 0.5–1.0% of the highest pressure as a reserve pressure.

2. Demolding: Keep the sample clamped between the upper and lower pressure heads, and move the floating mold downwards at a speed of 1–5 mm / s until the sample is completely removed; 3. Secondary depressurization: Slowly release the reserved pressure to 0MPa at a speed of 0.1–0.5mm / s; after the upper pressure head leaves the sample, retract to the initial position at a speed of 10–30mm / s; Isostatic pressure: Pressurize to 180-200MPa at a rate of 5–10MPa / min and hold for 5–10min; depressurize to 120-150MPa and hold for 5min; finally depressurize to zero at a rate of 5–10MPa / min.

2. The molding method according to claim 1, characterized in that, The isostatic pressing step includes: transferring the ceramic sheet onto the pressure plate, placing the ceramic sheet together with the pressure plate into a plastic sealing film for vacuum sealing, and then performing cold isostatic pressing.

3. The molding method according to claim 2, characterized in that, The pressure plate satisfies at least one of the following characteristics: The flatness error shall not exceed 0.01mm; Surface roughness Ra is not greater than 0.2 μm; The material is selected from silicon carbide, aluminum oxide, metal plate or tempered glass plate; The size is greater than or equal to the size of the ceramic sheet blank to be processed; All four sides are rounded.

4. The molding method according to claim 3, characterized in that, The sealing film is a co-extruded film with a thickness of 0.2–0.5 mm; and the vacuum sealing is performed after the vacuum degree reaches -0.6–0.8 MPa.

5. The molding method according to claim 4, characterized in that, The large-size thin-film ceramic has a forming size of not less than 280mm in length, not less than 195mm in width, and a thickness of less than 1mm.

6. A molding die for implementing the molding method according to any one of claims 1 to 5, characterized in that, include: feeding device; Upload template; Download template; The upper pressure head is connected to the upper template; The lower pressure head connected to the lower template; Floating mode; as well as A mold cavity connected to the floating mold and located between the upper pressure head and the lower pressure head; The upper pressure head, the lower pressure head, and the mold cavity are fitted together to achieve pressing and forming. The floating mold is configured to move up and down during the pressing process. The feeding device is located above the mold cavity and is configured to feed the granulated powder into the mold cavity.

7. The molding die according to claim 6, characterized in that, The molding die satisfies at least one of the following characteristics: The parallelism error between the upper template, the lower template, and the floating mold shall not exceed 0.03 mm; The single-sided gap between the upper pressure head, the lower pressure head and the mold cavity is 0.01–0.02 mm; The chamfer radius of the mold cavity is R3–5mm; The height deviation of the mold cavity shall not exceed 0.03 mm; The inner corners of the mold are rounded with a radius of 2–3 mm. The surface of the mold that contacts the sample is mirror-finished, with a surface roughness Ra≤0.05μm.

8. The molding die according to claim 7, characterized in that, The gap between the bottom of the feeding device and the working surface of the floating mold is 0.01–0.02 mm. The working surface of the floating mold is polished and has a surface roughness Ra≤0.1 μm.

9. A large-size, thin-film ceramic, characterized in that, The large-size thin-film ceramic is prepared by the molding method according to any one of claims 1 to 5, and the thickness of the large-size thin-film ceramic is 0.3–20 mm.

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