Honeycomb core suitable for special-shaped molded surface and preparation method thereof

Abstract

The invention provides a honeycomb core suitable for a special-shaped profile and a preparation method of the honeycomb core, and relates to the technical field of aerospace materials. The honeycomb core comprises a core body, an upper skin and a lower skin, wherein the upper skin and the lower skin are laid on the upper surface and the lower surface of the core body respectively, and the core body is provided with a special-shaped molded surface capable of being completely attached to the surface of a special-shaped tool. The preparation process of the core body comprises the steps that a cut semi-cured honeycomb core is laid and attached to the surface of a special-shaped tool mold with a specific molded surface, a vacuum bag film is used for coating, the vacuum bag film is vacuumized, and a laid part is obtained; and after curing treatment is conducted on the laid part, the vacuum bag film is removed, and demolding is conducted. By means of the method, the core body has complete hole lattice nodes and can be completely attached to the tool profile, the core is of the structure that honeycomb hole lattices are distributed perpendicular to the normal direction, and when the core is subjected to impact or pressure, stress can be effectively dispersed, and the overall strength and rigidity of materials can be enhanced.

Description

Technical Field

[0001] This invention relates to the field of aerospace materials technology, and in particular to a honeycomb core suitable for irregularly shaped surfaces and its preparation method. Background Technology

[0002] Honeycomb materials, due to their lightweight, high specific strength, and high specific stiffness, have been widely used in the aerospace field, often in the manufacture of sandwich components in aircraft structures. When applied to irregularly shaped surfaces with complex curvatures, traditional processes typically involve cutting and splicing the honeycomb core material to achieve initial bonding with the target surface. However, this cutting method can lead to localized fractures in the honeycomb lattice structure, damage to node integrity, and the creation of gaps and stress concentration points within the core material, thus reducing overall mechanical properties. Furthermore, the cut honeycomb is difficult to completely fit the tooling surface, making it prone to localized failure under stress, affecting the structure's impact resistance and stability.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a honeycomb core suitable for irregularly shaped surfaces and a method for preparing the same.

[0005] According to a first aspect of the present invention, a honeycomb core suitable for irregular surfaces is provided, comprising a core body and an upper skin and a lower skin respectively applied to the upper and lower surfaces of the core body, wherein the core body has an irregular surface capable of completely conforming to the surface of an irregular tooling.

[0006] In an exemplary embodiment of the present invention, the core fabrication step includes: S1, Obtain a core block with a honeycomb grid; S2, the core block is impregnated in the glue tank of the impregnation machine, and then pre-cured. This process is repeated multiple times to obtain a semi-cured honeycomb core. During the impregnation process, the axial direction of the honeycomb lattice of the core block remains perpendicular to the horizontal plane. S3, cut the semi-cured honeycomb core to a preset size; S4, the cut semi-cured honeycomb core is laid on the surface of the irregular tooling mold with a specific shape, and then covered with a vacuum bag film. The vacuum bag film is vacuumed to make the semi-cured honeycomb core completely adhere to the surface of the irregular tooling mold to obtain the laid part. S5, the laying component is cured, and after curing, the vacuum bag film is removed and the core is demolded.

[0007] In an exemplary embodiment of the present invention, in step S2, the pre-curing temperature is 70~100°C and the time is 50~80 min.

[0008] In an exemplary embodiment of the present invention, in step S4, before laying, the irregular tooling mold is cleaned and a release agent is sprayed; sealing strips are pasted around the irregular tooling mold, and the vacuum bag film is bonded to the sealing strips so that the vacuum bag film is fully covered; an air guide tube is installed on the vacuum bag film, and the air guide tube is connected to a vacuum pump.

[0009] In an exemplary embodiment of the present invention, in step S4, before covering the vacuum bag film, a release cloth and a breathable felt are pre-covered on the surface of the semi-cured honeycomb core; the negative pressure of the vacuum treatment is 0.015MPa~0.04MPa.

[0010] In an exemplary embodiment of the present invention, in step S5, the curing temperature is 150~200℃, the curing time is 5~8h, and the heating rate is 2~5℃ / min.

[0011] In an exemplary embodiment of the present invention, in step S2, the impregnation mixture used for the impregnation treatment includes a resin, silica powder, and an organic solvent, wherein the resin is selected from one or more of epoxy resin, silicone resin, and phenolic resin, the resin has a mass fraction of 30-60% in the impregnation mixture, and the silica powder is coated with carbon quantum dots, and its mass fraction in the impregnation mixture is 0.1-3%.

[0012] According to a second aspect of the present invention, a method for preparing a honeycomb core suitable for irregular shapes as described in any of the above claims is provided, comprising: sequentially stacking a lower skin, an adhesive film, a core, an adhesive film, and an upper skin, and then curing them to obtain the honeycomb core; wherein the upper skin and the lower skin are respectively adapted to the shapes of the upper surface and the lower surface of the core.

[0013] In an exemplary embodiment of the present invention, the preparation steps of the upper skin and the lower skin include: Coating: Organic polyborosilazane and dicumyl peroxide are added to DMF and stirred to obtain a coating solution; the coating solution is coated onto carbon fiber cloth and dried to obtain a prepreg; Hot pressing curing: The prepreg is placed in a mold and hot pressing curing is performed to obtain a layered blank that matches the shape of the core surface after curing; Pyrolysis: The layered blank is placed in a pyrolysis furnace, a protective gas is introduced, and high-temperature pyrolysis is carried out; the above coating, hot pressing curing and pyrolysis steps are repeated once or multiple times to obtain the upper skin / lower skin.

[0014] In an exemplary embodiment of the present invention, the pyrolysis process includes: heating to 600-800°C at a heating rate of 3-5°C / min, holding at that temperature for 0.5-1h, and then heating to 1000-1200°C at a heating rate of 1-2°C / min, holding at that temperature for 1-2h.

[0015] The beneficial effects of the honeycomb core with irregular surface shape and its preparation method according to the embodiments of the present invention are: The honeycomb core of this invention is obtained by laying a semi-cured honeycomb core onto a shaped tooling mold, forming it using vacuum bag pressing, and then curing it. This effectively improves the deformability of the honeycomb surface, allowing it to be formed together with the tooling of the shaped surface, thus presenting a structure in which the honeycomb cells are distributed perpendicular to the normal. This structure gives the shaped honeycomb surface superior compressive strength and load-bearing capacity compared to milled honeycomb structures under the same density conditions. The honeycomb cells of this shaped honeycomb core are perpendicular to the normal of the deformed surface. This perpendicular honeycomb structure can effectively disperse stress under impact or pressure, enhancing the overall strength and stiffness of the material. This honeycomb core method is applicable to shaped surfaces with different design requirements, has the ability to fit complex curved surfaces, and can be better applied in the aerospace field.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of honeycomb pores with different aperture ratios in an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the structure of the vacuum bag film in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the core and the irregular tooling mold in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] This invention provides a honeycomb core suitable for irregularly shaped surfaces. The honeycomb core includes a core body and an upper skin and a lower skin respectively attached to the upper and lower surfaces of the core body. The core body has an irregularly shaped surface that can completely conform to the surface of an irregularly shaped tooling.

[0023] Specifically, in one embodiment, the core fabrication steps include: S1. Obtain a core block with a honeycomb grid. Specifically, a honeycomb core block made of para-aramid paper can be selected. For example, obtain multiple sheets of para-aramid paper and apply adhesive to each sheet to form spaced adhesive strips. The adhesive-coated para-aramid papers are then stacked in an alternating pattern to obtain a stack. The adhesive strips on adjacent sheets of para-aramid paper are arranged at equal intervals and staggered. Specifically, epoxy resin adhesives, such as commercially available high-temperature modified epoxy adhesives, can be used for the adhesive strips. The stack is then cut into blocks, hot-pressed, and then stretched and shaped to obtain a core with a honeycomb grid. The stretching and shaping temperature is 180~250℃, and the shaping time is 3~6 hours. It should be noted that the pore size ratio of the honeycomb grid can be changed during stretching to obtain honeycomb grids with different pore size ratios, such as... Figure 1 As shown.

[0024] S2, the core block is impregnated in the glue tank of the impregnation machine, and then pre-cured. This process is repeated multiple times to obtain a semi-cured honeycomb core. During the impregnation process, the axial direction of the honeycomb lattice of the core block remains perpendicular to the horizontal plane.

[0025] Specifically, in one embodiment, in step S2, the pre-curing temperature is 70~100℃ and the time is 50~80min.

[0026] Specifically, in one embodiment, in step S2, the impregnation mixture used for the impregnation treatment includes a resin, silica powder, and an organic solvent. The resin is selected from one or more of epoxy resin, silicone resin, and phenolic resin, and the organic solvent is selected from one or more of anhydrous ethanol, toluene, and petroleum ether.

[0027] More preferably, the resin in the impregnation mixture has a mass fraction of 30-60%, the silica powder is coated with carbon quantum dots, and its mass fraction in the impregnation mixture is 0.1-3%.

[0028] In one embodiment, the method for preparing silica powder coated with carbon quantum dots is as follows: 8g of carbon quantum dots (CQDs) are dispersed in 100mL of water to obtain a CQDs solution; 100g of SiO2 powder and the CQDs solution are mixed, 0.5g of silane coupling agent KH-550 is added, and the mixture is heated to 60°C in a water bath; the mixture is shaken and reacted for 2 hours, and then spray-dried to obtain silica powder coated with carbon quantum dots.

[0029] In this step, by adding silica powder with carbon quantum dots coated on the surface to the resin liquid, the initiation and propagation of microcracks in the resin matrix can be effectively suppressed, thereby significantly improving the fatigue resistance and long-term durability of the honeycomb core material. In particular, during the subsequent vacuum bagging process, the pore structure of the core can be maintained to avoid deformation.

[0030] S3, cut the semi-cured honeycomb core to the preset size. The semi-cured honeycomb core is cut according to the actual required thickness design.

[0031] S4. The cut semi-cured honeycomb core is laid on the surface of a special-shaped tooling mold with a specific shape, and then covered with a vacuum bag film. The vacuum bag film is vacuumed to make the semi-cured honeycomb core completely adhere to the surface of the special-shaped tooling mold, thus obtaining the laid part.

[0032] Specifically, in one embodiment, in step S4, before laying the material, the irregular-shaped tooling mold is cleaned and a release agent is sprayed on it. Spraying the release agent separates the material from the mold; any commercially available release agent can be used.

[0033] Sealing strips are affixed around the perimeter of the irregularly shaped tooling mold, and a vacuum bag film is then bonded to the sealing strips to complete the vacuum bag film coverage. An air guide tube is installed on the vacuum bag film, and the air guide tube is connected to a vacuum pump. Further, the sealing strip is preferably a high-temperature resistant sealing strip.

[0034] In an exemplary embodiment of the present invention, in step S4, before covering the vacuum bag film, a release cloth and a breathable felt are pre-covered on the surface of the semi-cured honeycomb core; the negative pressure of the vacuum treatment is 0.015MPa~0.04MPa.

[0035] S5, the laying component is cured, and after curing, the vacuum bag film is removed and the core is demolded.

[0036] Specifically, in one embodiment, in step S5, the curing temperature is 150~200℃, the curing time is 5~8h, and the heating rate is 2~5℃ / min.

[0037] The present invention also provides a method for preparing a honeycomb core suitable for irregular shapes, comprising: sequentially stacking a lower skin, a film, a core, a film and an upper skin, and then curing them to obtain the honeycomb core; wherein the upper skin and the lower skin are respectively adapted to the shapes of the upper surface and the lower surface of the core.

[0038] In an exemplary embodiment of the present invention, the preparation steps of the upper skin and the lower skin include: Coating: Organic polyborosilazane and diisopropylbenzene peroxide are added to DMF and stirred to obtain a coating solution; the coating solution is coated onto carbon fiber cloth and dried to obtain a prepreg.

[0039] Hot pressing curing: The prepreg is placed in a mold and hot pressing curing is performed to obtain a layered blank that matches the shape of the core surface after curing; Pyrolysis: The layered blank is placed in a pyrolysis furnace, a protective gas is introduced, and high-temperature pyrolysis is carried out; the above coating, hot pressing curing and pyrolysis steps are repeated once or multiple times to obtain the upper skin / lower skin.

[0040] Specifically, in one embodiment, the pyrolysis process includes: heating to 600-800°C at a heating rate of 3-5°C / min, holding at that temperature for 0.5-1h, and then heating to 1000-1200°C at a heating rate of 1-2°C / min, holding at that temperature for 1-2h.

[0041] This embodiment employs the aforementioned methods for preparing the upper and lower skins, using a process path of impregnation with an organoborosilicate coating solution, hot-press curing, and high-temperature pyrolysis to transform carbon fiber prepreg into a ceramic matrix composite skin. This allows for compatibility with irregularly shaped cores, exhibits excellent high-temperature stability and creep resistance, and better meets the specific requirements of aerospace vehicles.

[0042] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0043] Example 1: This example provides a core with an irregular surface shape, which is prepared according to the following steps: (1) Prepare multiple sheets of para-aramid paper, apply glue to each sheet of para-aramid paper to form spaced adhesive strips, and then stack the para-aramid papers in an alternating manner to obtain a stack, wherein the adhesive strips on two adjacent sheets of para-aramid paper are arranged at equal intervals and staggered.

[0044] (2) Hot-press the stack obtained in step (1); (3) After the hot-pressed stack in step (2) is stretched by a stretching machine, it is placed in an oven and shaped at 220°C for 5 hours to obtain a core with honeycomb pores.

[0045] (4) The core obtained in step (3) is impregnated in the glue tank of the impregnation machine. After impregnation, it is pre-cured at 80°C for 60 minutes, and this process is repeated 3 times to obtain a semi-cured honeycomb core. During the impregnation process, the axial direction of the honeycomb lattice of the core block is kept perpendicular to the horizontal plane. The resin liquid used for impregnation includes 30wt% epoxy resin, 2wt% SiO2 powder with carbon quantum dots on the surface, and anhydrous ethanol.

[0046] (5) Cut the semi-cured honeycomb core obtained in step (3) to the preset size.

[0047] (6) Clean the surface of the irregular tooling mold with a specific shape and apply a release agent. Then, wrap the semi-cured honeycomb core 2 obtained in step (5) with the release cloth 6. After wrapping, place the honeycomb core on the surface of the irregular tooling mold, and then wrap it with the breathable felt 5. Apply a layer of high-temperature resistant sealing strip 3 around the irregular tooling mold, bond the vacuum bag film 4 to the sealing strip 3, and install the high-temperature resistant air duct 7. The air duct 7 is connected to the vacuum pump (not shown in the figure). Figure 2 As shown.

[0048] (7) After installation, turn on the vacuum pump (the vacuum negative pressure is about 0.03MPa) and use the vacuum bag pressing method to make the semi-cured honeycomb core completely fit the surface of the special tooling mold to obtain the laying part.

[0049] (8) Place the laying part obtained in step (7) in a curing oven and heat it to 180°C at 3°C / min for 6 hours.

[0050] (9) Remove the cured installation parts, and remove the vacuum bag film, etc. Figure 3 As shown, the core is then demolded.

[0051] Example 2: This example provides a honeycomb core with an irregular surface, prepared according to the following steps: (1) The lower skin, epoxy film, core (prepared in Example 1), epoxy film and upper skin are stacked in sequence to obtain the composite part.

[0052] (2) Place the composite in a vacuum hot press, set the curing temperature to 160°C and the pressure to 0.5 MPa, and cure for 3 hours to obtain a honeycomb core for irregular surfaces.

[0053] The upper and lower skins were prepared according to the following steps: 70g of organoborosilicate and 1g of dicumyl peroxide were added to 30g of DMF and stirred to obtain a mixture. The mixture was coated onto carbon fiber cloth and dried to obtain a prepreg. The prepreg was placed in a mold (the mold has the same irregular shape as in Example 1) for hot-press curing at 150°C, 0.3MPa, and 5h, resulting in a layered preform that matched the surface shape of the core in Example 1. The layered preform was placed in a pyrolysis furnace, and N2 was introduced for high-temperature pyrolysis. The pyrolysis procedure was as follows: the temperature was increased to 650°C at 3°C / min and held for 0.5h, then increased to 1200°C at 1~2°C / min and held for 1.5h. The coating, hot-press curing, and pyrolysis steps were repeated twice to obtain the upper and lower skins.

[0054] Example 3: This example provides a honeycomb core with an irregular surface, prepared according to the following steps: (1) The lower skin, epoxy film, core (prepared in Example 1), epoxy film and upper skin are stacked in sequence to obtain the composite part.

[0055] (2) Place the composite in a vacuum hot press, set the curing temperature to 160°C and the pressure to 0.5 MPa, and cure for 3 hours to obtain a honeycomb core for irregular surfaces.

[0056] The upper and lower skins are made of carbon fiber cloth and epoxy resin prepreg.

[0057] Example 4: This example provides a honeycomb core with an irregular shape. The difference between this example and Example 1 is that the impregnation process of the core is different. Specifically, the resin liquid used for impregnation includes 30wt% epoxy resin and anhydrous ethanol.

[0058] Test case The honeycomb cores obtained in Examples 2-4 were made into 76mm×150mm×12.7mm pieces, and their mechanical properties were tested using an Instron 5967 universal testing machine. The test results are shown in Table 1.

[0059] Table 1

[0060] The above description does not cover all embodiments. The detailed description of embodiments in this disclosure is not intended to limit the scope of the claimed disclosure, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this disclosure without inventive effort are within the scope of protection of this disclosure.

Claims

1. A honeycomb core suitable for irregularly shaped surfaces, characterized in that, It includes a core and an upper skin and a lower skin respectively applied to the upper and lower surfaces of the core. The core has an irregular shape that can completely fit the surface of the irregular tooling.

2. The honeycomb core suitable for irregularly shaped surfaces according to claim 1, characterized in that, The core preparation steps include: S1, Obtain a core block with a honeycomb grid; S2, the core block is impregnated in the glue tank of the impregnation machine, and then pre-cured. This process is repeated multiple times to obtain a semi-cured honeycomb core. During the impregnation process, the axial direction of the honeycomb lattice of the core block remains perpendicular to the horizontal plane. S3, cut the semi-cured honeycomb core to a preset size; S4, the cut semi-cured honeycomb core is laid on the surface of the irregular tooling mold with a specific shape, and then covered with a vacuum bag film. The vacuum bag film is vacuumed to make the semi-cured honeycomb core completely adhere to the surface of the irregular tooling mold to obtain the laid part. S5, the laying component is cured, and after curing, the vacuum bag film is removed and the core is demolded.

3. The honeycomb core suitable for irregularly shaped surfaces according to claim 2, characterized in that, In step S2, the pre-curing temperature is 70~100℃ and the time is 50~80min.

4. The honeycomb core suitable for irregularly shaped surfaces according to claim 2, characterized in that, In step S4, before laying, the irregular tooling mold is cleaned and a release agent is sprayed; sealing strips are pasted around the irregular tooling mold, and the vacuum bag film is bonded to the sealing strips so that the vacuum bag film is completely covered; an air guide tube is installed on the vacuum bag film, and the air guide tube is connected to a vacuum pump.

5. The honeycomb core suitable for irregularly shaped surfaces according to claim 2, characterized in that, In step S4, before covering the vacuum bag film, a release cloth and a breathable felt are pre-covered on the surface of the semi-cured honeycomb core; the negative pressure of the vacuum treatment is 0.015MPa~0.04MPa.

6. The honeycomb core suitable for irregularly shaped surfaces according to claim 2, characterized in that, In step S5, the curing temperature is 150~200℃, the curing time is 5~8h, and the heating rate is 2~5℃ / min.

7. The honeycomb core suitable for irregularly shaped surfaces according to claim 2, characterized in that, In step S2, the impregnation mixture used for the impregnation treatment includes resin, silica powder and organic solvent. The resin is selected from one or more of epoxy resin, silicone resin and phenolic resin. The mass fraction of the resin in the impregnation mixture is 30-60%. The silica powder is coated with carbon quantum dots and has a mass fraction of 0.1-3% in the impregnation mixture.

8. A method for preparing a honeycomb core suitable for irregularly shaped surfaces as described in any one of claims 1 to 7, characterized in that, include: The lower skin, adhesive film, core, adhesive film and upper skin are stacked in sequence and then cured to form the honeycomb core; wherein the upper skin and lower skin are respectively adapted to the shape of the upper surface and lower surface of the core.

9. The method for preparing a honeycomb core with an irregular shape according to claim 8, characterized in that, The preparation steps of the upper skin and the lower skin include: Coating: Organic polyborosilazane and dicumyl peroxide are added to DMF and stirred to obtain a coating solution; the coating solution is coated onto carbon fiber cloth and dried to obtain a prepreg; Hot pressing curing: The prepreg is placed in a mold and hot pressing curing is performed to obtain a layered blank that matches the shape of the core surface after curing; Pyrolysis: The layered blank is placed in a pyrolysis furnace, a protective gas is introduced, and high-temperature pyrolysis is carried out; the above coating, hot pressing curing and pyrolysis steps are repeated once or multiple times to obtain the upper skin / lower skin.

10. The method for preparing a honeycomb core with an irregular shape according to claim 9, characterized in that, The pyrolysis process includes: heating to 600-800℃ at a heating rate of 3-5℃ / min, holding at that temperature for 0.5-1h, and then heating to 1000-1200℃ at a heating rate of 1-2℃ / min, holding at that temperature for 1-2h.

Images