Foam sandwich structure composite airfoil and integral forming method thereof

Abstract

The invention discloses a foam sandwich structure composite airfoil and a forming method thereof, and belongs to the technical field of composite design and forming. In order to solve the problems that in the forming process of a traditional composite airfoil, the foam unloading forming pressure is insufficient, volatile matter cannot be discharged and the like, a mold pressing co-curing forming process is mainly adopted, and a glue flowing hole with a specific structure is designed in a foam core material so as to optimize resin fluidity and gas emission. The overall quality of the composite airfoil can be effectively improved, the defects of lack of glue, bubbles, layering and the like are avoided, and uniform distribution of resin in the curing process is ensured, so that the compactness, uniformity and structural stability of the composite are improved, and the resistance performance and durability of a product are enhanced.

Description

Technical Field

[0001] The invention provides a foam sandwich structure composite material wing surface and an integral forming method thereof, belonging to the technical field of composite material design and forming. Background Art

[0002] There is a close correlation between the weight of an aircraft and its performance and economic benefits. In the process of aircraft research and development, reducing its structural weight is one of the core goals. Composite wing surfaces have been widely used in the aerospace field due to their excellent mechanical properties, such as high specific stiffness and specific strength, as well as excellent fatigue resistance and corrosion resistance. In the field of composite materials, foam sandwich structures are widely used in the manufacture of aerospace structural parts due to their light weight and high strength. However, in the traditional co-curing molding process, the foam sandwich structure usually cannot provide sufficient internal pressure to ensure that the volatiles inside the prepreg are completely discharged during the curing process, resulting in defects such as bubbles or delamination inside the resin-based composite material. Debonding and delamination inside the composite wing surface during the molding process has a significant impact on the mechanical properties of the main load-bearing beam components of the composite material. This will cause discontinuous stress transfer inside the material, thereby affecting its overall mechanical properties. Debonding and delamination may lead to problems such as decreased stiffness, reduced strength, reduced fatigue life, decreased impact performance, and decreased stability.

[0003] Therefore, how to improve the internal quality of the foam sandwich composite wing surface and reduce the risk of delamination and debonding during the co-curing molding process has become a technical problem that needs to be solved in composite design and manufacturing. Therefore, in order to ensure the flight safety and performance of the aircraft, it is necessary to prevent and detect the debonding and delamination phenomenon inside the composite material through strict quality control and testing methods, and to improve the reliability of the main load-bearing beam components through design optimization and manufacturing process improvement. Summary of the invention

[0004] The purpose of the present invention is to provide a foam sandwich structure composite wing surface and its overall forming method. Through the reasonable design of the foam core material, it has an appropriate glue flow hole structure, which can enhance the internal pressure during the curing process, thereby effectively removing volatiles in the prepreg, reducing the occurrence of bubbles and delamination, and thus improving the structural performance of the wing surface product.

[0005] The technical solution adopted by the present invention to achieve its purpose is as follows:

[0006] In a first aspect, the present invention provides a foam sandwich composite wing surface, comprising a skin and an internal support structure;

[0007] The internal support structure includes metal joints, foam core and multiple stiffeners;

[0008] The foam core material comprises an upper wing surface and a lower wing surface, and is provided with a plurality of glue flow holes;

[0009] The embedded end of the metal joint is butted against the foam core material to form the main structure of the internal support structure;

[0010] The reinforcing rib structure is formed by stacking multiple layers of fiber prepreg, which are distributed at intervals on the foam core material and connect the foam core material and the skin.

[0011] Preferably, at least one of the reinforcing rib structures is wrapped around the outside of the joint between the metal joint and the foam.

[0012] Preferably, the outer surface of the foam core material is also covered with a layer of adhesive film.

[0013] Preferably, the glue flow holes are through holes or blind holes that penetrate the foam core material.

[0014] Preferably, the shape of the glue flow hole is square, circular, triangular or long strip.

[0015] Preferably, the bottom angle of the glue flow hole is a positive bevel angle, a negative bevel angle or a rounded angle.

[0016] In a second aspect, the present invention provides a method for integrally forming a foam sandwich structure composite wing surface, comprising the following steps:

[0017] 1) Design the array density, depth and aperture of the glue flow holes according to the number of layers and glue content of the foam outer layer prepreg;

[0018] 2) machining the foam core material to form glue flow holes;

[0019] 3) Clean the surface debris of the foam core material and dry the foam;

[0020] 4) The metal joint is sandblasted, coated with glue, and then connected to the foam core material, and then covered with a glue film to fix it; and then the fiber prepreg of the reinforcing rib structure is laid on the foam core material to form an internal support structure;

[0021] 5) Laying the fiber prepreg of the skin on the outside of the internal support structure to obtain the wing structure to be cured;

[0022] 6) The wing surface structure to be cured is placed in a mold for hot pressing and curing, and demoulding is performed after cooling to obtain a foam sandwich structure composite wing surface.

[0023] Preferably, in step 1), the resin volume to be removed is calculated according to the area and the number of prepreg layers, at 6% to 10% of the prepreg weight, to determine the total volume of the glue flow holes; and the density and pore size of the glue flow holes are adjusted in combination with the resin fluidity.

[0024] Preferably, in step 1), the diameter and density of the glue flow holes are determined by finite element analysis simulation or experimental molding test.

[0025] Preferably, the depth of the glue flow hole in step 1) is 1 to 3 times the total thickness of the fiber prepreg of the skin and reinforcing rib structure, and the hole area is 0.2 to 1 cm 2 The hole spacing is 50 to 200 mm.

[0026] Preferably, the drying method in step 3) is: placing the foam core material in an oven, drying it at 80±5°C for 1 hour, and then heating it to 130±5°C and drying it for 3 hours.

[0027] Preferably, in step 4), the plying direction of the fiber prepreg of the reinforcing rib structure is [0 / +45 / 0 / 0 / -45 / 0].

[0028] Preferably, in step 5), the plying direction of the fiber prepreg of the skin is [45, 0, -45, 0, 0, 0, 90, 0, 45, 0, -45, 0] s.

[0029] The beneficial effects achieved by the present invention are as follows:

[0030] 1. The present invention designs the array density, depth and aperture of the glue flow holes according to the number of layers and glue content of the foam outer layer prepreg. The more prepreg layers and the higher the glue content, the more glue flow holes are designed to ensure that the resin can flow smoothly into the foam. The volume of the resin to be removed is estimated by multiplying the area and the number of prepreg layers by 6% to 10% of the prepreg weight, and the total volume requirement of the glue flow holes is determined. The density and aperture of the glue flow holes are adjusted in combination with the resin fluidity, so that the design of the glue flow holes is more accurate and reasonable.

[0031] 2. The present invention provides glue flow holes in the foam core material to guide the molding volatiles into the foam during the resin curing process, thereby avoiding the retention of volatiles and providing an exhaust channel, effectively reducing bubbles and delamination defects, improving the density and uniformity of the composite material, and ensuring structural stability and durability.

[0032] 3. The present invention ensures smooth exhaust of resin during the curing process by reasonably designing the glue flow holes, so that the resin can fully infiltrate the fibers in the composite material, reduce glue deficiency and delamination inside the skin, improve the resistance and durability of the composite wing surface, and make the appearance more precise without glue deficiency.

[0033] 4. The internal support structure of the present invention can be integrally molded by coating with adhesive film and laying reinforcing rib prepreg, without the need to bond the upper and lower wing surfaces, thus simplifying the manufacturing process, reducing production costs, improving production efficiency, and saving energy.

[0034] 5. The design of the glue flow holes of the present invention is flexible and diverse. The number of glue flow holes and the array density can be adjusted according to the prepreg resin content, layer thickness and rheological properties. The shape of the glue flow holes can be square, circular, triangular or long strip, and the hole mouth can be set with a positive bevel, a reverse bevel or a rounded corner to optimize the amount of glue stored and reduce the appearance defects caused by the hole area.

[0035] 6. The present invention can utilize simulation tools such as finite element analysis (FEA) to simulate the design of the glue flow hole, or verify through molding tests of experimental samples whether the design of the glue flow hole meets the resin flow and exhaust requirements, thereby ensuring the quality of wing surface molding. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the composite wing surface of the sandwich foam structure with circular blind glue flow holes in Example 1;

[0037] Figure 2 It is a schematic diagram of the composite wing surface of the sandwich foam structure with circular through-hole glue flow holes in Example 2;

[0038] Figure 3 It is a schematic diagram of the composite wing surface of the sandwich foam structure with long chamfered glue flow holes in Example 3;

[0039] Figure 4 Schematic diagram for measuring the size of a single defect. DETAILED DESCRIPTION

[0040] In order to make the various technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and easy to understand, they are described in detail below with reference to the accompanying drawings.

[0041] Example 1

[0042] This embodiment provides a foam sandwich composite wing surface, such as Figure 1 As shown, it includes a skin 11 and an internal support structure. The skin 11 is located on the outer layer of the overall structure and serves as the main surface of the composite wing. In order to facilitate the presentation of the internal support structure, Figure 1 The skin 11 is displayed in perspective. The internal support structure includes a metal joint 12, a rib structure 13, a foam core material 14 and an adhesive film layer (not shown). The metal joint 12 is used to connect to the aircraft deployment mechanism, and its embedded end is connected to the foam core material 14 to form the main frame of the internal support structure of the wing surface. The rib structure 13 is stacked by multiple layers of prepreg and is wrapped around the outside of the joint between the metal joint 12 and the foam core material 14 to provide the necessary mechanical strength. The foam core material 14 plays a role in reducing weight and improving thermal insulation performance. The adhesive film layer covers the outer surface of the foam core material 14 to increase the quality stability and sealing between the internal support structure and the skin 11. There are circular glue flow holes 15 in an array on the foam core material 14, which are blind holes.

[0043] The foam sandwich composite wing surface adopts a co-curing molding process, and the specific implementation process is as follows:

[0044] 1) Design of glue flow holes: Based on the number of prepreg layers (22 layers) in the thickest area of ​​the outer skin of the wing surface, the glue content of the prepreg (38%), and the curing properties of the resin (80℃ for half an hour and pressurization, 120℃ for 2 hours), and considering the rheological properties of the resin (the minimum viscosity at 80℃ is 5Pa·s), the foam material is designed to be polymethacrylimide (foam pore size 0.2-0.4mm). The glue flow holes are selected as round blind holes with a hole diameter of The hole depth and hole spacing are square arrays of 50 mm.

[0045] 2) Foam machining: Use a CNC engraving machine to shape the foam core material and process glue flow holes on the foam.

[0046] 3) Foam drying: clean the debris on the foam surface and dry it; preferably, the drying step is to dry the foam in an oven at 80±5°C for 1 hour, and then heat it to 130±5°C and dry it for 3 hours.

[0047] 4) Surface treatment and assembly: After sandblasting, the metal joints are treated with J-47B glue on the designed and processed foam. The joints are butted and glued to the foam. After ensuring that there is no obvious gap on the mating surface, the whole is covered with J-47A glue film for fixation. Then, the prepreg of the reinforcement structure is laid, and the ply order is [0 / +45 / 90 / -45]s to form the internal support structure of the composite wing surface.

[0048] 5) Laying the skin: Lay CCF800S / 3068 skin prepreg on the outer layer of the above-mentioned internal support structure with the laying sequence of [45,0,-45,0,0,0,90,0,45,0,-45,0]s to obtain a laid wing surface.

[0049] 6) Curing and molding: Remove residual glue and impurities on the mold surface to ensure that the mold surface is smooth and free of oil stains. After applying 2720 mold release agent, install the wing surface into the mold and complete the mold loading. Push it into the press for curing:

[0050] Stage 1: Heat to 80°C, temperature difference 5°C, keep warm for 30 minutes;

[0051] The second stage: After removing the limit gasket, pressurize the press to 10MPa, heat up to 125℃, keep warm for 120 minutes with a temperature difference of 5℃. Remove the mold from the press, place it on the mold cart, cool it down to below 50℃ naturally or by fan, and finally demold it to get the product.

[0052] Example 2

[0053] This embodiment provides a foam sandwich composite wing surface, the structure of which is substantially the same as that of the wing surface in Example 1, such as Figure 2 As shown, it includes a skin 21 and an internal support structure, the internal support structure includes a metal joint 22, a reinforcing rib structure 23, a foam core material 24 and a film layer (not shown), and the foam core material 24 is provided with circular glue flow holes 25 arranged in an array, which are through holes. The skin 21 is located at the outer layer of the overall structure, in order to facilitate the presentation of the internal support structure, Figure 2 The skin 21 is shown in perspective.

[0054] The foam sandwich composite wing surface adopts a co-curing molding process, and the specific implementation process is as follows:

[0055] 1) Design of glue flow holes: Based on the number of prepreg layers (22 layers) in the thickest area of ​​the outer skin of the wing, the glue content of the prepreg (36%), and the curing properties of the resin (80℃ for half an hour and pressurization, 120℃ for 2 hours), and considering the rheological properties of the resin (the minimum viscosity at 80℃ is 12Pa·s), the foam material is designed to be polymethacrylimide (the foam pore size is 0.1mm). The glue flow holes are selected as circular through-hole structures with a pore size of A square array with a hole depth of 5mm and a hole spacing of 50mm.

[0056] 2) Foam machining: The foam core material is processed into shape by a CNC engraving machine, and glue flow holes are processed on the foam.

[0057] 3) Foam drying: clean the debris on the foam surface and dry it; preferably, the drying step is to dry the foam in an oven at 80±5°C for 1 hour, then heat it to 130±5°C and dry it for 3 hours.

[0058] 4) Surface treatment and assembly: After sandblasting, the metal joints are treated with J-47B glue on the designed and processed foam. The joints are butted and glued to the foam. After ensuring that there is no obvious gap on the mating surface, the whole is covered with J-47A glue film for fixation. Then, the prepreg of the reinforcement structure is laid, and the ply order is [0 / +45 / 90 / -45]s to form the internal support structure of the composite wing surface.

[0059] 5) Laying the skin: Lay CCF800S / 3068 skin prepreg on the outer layer of the above-mentioned internal support structure with the laying sequence of [45,0,-45,0,0,0,90,0,45,0,-45,0]s to obtain a laid wing surface.

[0060] 6) Curing and molding: Remove residual glue and impurities on the mold surface to ensure that the mold surface is smooth and free of oil stains. After applying 2720 mold release agent, install the wing surface into the mold and complete the mold loading. Push it into the press for curing:

[0061] Stage 1: Heat to 80°C, temperature difference 5°C, keep warm for 30 minutes;

[0062] The second stage: After removing the limit gasket, pressurize the press to 10MPa, heat up to 125℃, keep warm for 120 minutes with a temperature difference of 5℃. Remove the mold from the press, place it on the mold cart, cool it down to below 50℃ naturally or by fan, and finally demold it to get the product.

[0063] Example 3

[0064] This embodiment provides a foam sandwich composite wing surface, the structure of which is substantially the same as that of the wing surface in Example 1, such as Figure 3 As shown, it includes a skin 31 and an internal support structure, the internal support structure includes a metal joint 32, a reinforcing rib structure 33, a foam core material 34 and a film layer (not shown), and an array of long chamfered glue flow holes 35 are distributed on the foam core material 34, which are blind holes. The skin 31 is located on the outer layer of the overall structure, in order to facilitate the presentation of the internal support structure, Figure 3 The skin 31 is shown in perspective.

[0065] The foam sandwich composite wing surface adopts a co-curing molding process, and the specific implementation process is as follows:

[0066] 1) Design of glue flow holes: Based on the number of prepreg layers (26 layers) in the thickest area of ​​the outer skin of the wing, the glue content of the prepreg (38%), and the curing properties of the resin (80℃ for half an hour of heat preservation and pressurization, 120℃ for 2 hours), and considering the rheological properties of the resin (the minimum viscosity value at 80℃ is 25Pa·s), the foam material is designed to be polymethylamine (the foam pore diameter is 0.2-0.4mm). The foam core is designed to have a square array of long chamfered glue flow holes with a size of 3mm×5mm, a hole depth of 3mm, and a hole spacing of 50mm.

[0067] 2) Foam machining: The foam core material is processed into shape by a CNC engraving machine, and glue flow holes are processed on the foam.

[0068] 3) Foam drying: clean the debris on the foam surface and dry it; preferably, the drying step is to dry the foam in an oven at 80±5°C for 1 hour, then heat it to 130±5°C and dry it for 3 hours.

[0069] 4) Surface treatment and assembly: After sandblasting, the metal joints are treated with J-47B glue on the designed and processed foam. The joints are butted and glued to the foam. After ensuring that there is no obvious gap on the mating surface, the whole is covered with J-47A glue film for fixation. Then, the prepreg of the reinforcement structure is laid, and the ply order is [0 / +45 / 90 / -45]s to form the internal support structure of the composite wing surface.

[0070] 5) Laying the skin: Lay CCF800S / 3068 skin prepreg on the outer layer of the above-mentioned internal support structure with the laying sequence of [0,45,0,-45,0,0,90,90,0,45,0,-45,0]s to obtain a laid wing surface.

[0071] 6) Curing and molding: Remove residual glue and impurities on the mold surface to ensure that the mold surface is smooth and free of oil stains. After applying 2720 mold release agent, install the wing surface into the mold and complete the mold loading. Push it into the press for curing:

[0072] Stage 1: Heat to 80°C, temperature difference 5°C, keep warm for 30 minutes;

[0073] The second stage: After removing the limit gasket, pressurize the press to 25MPa, heat up to 125℃, keep warm for 120 minutes with a temperature difference of 5℃. Remove the mold from the press, place it on the mold cart, cool it down to below 50℃ naturally or by fan, and finally demold it to get the product.

[0074] Foam sandwich composite wing test:

[0075] Ultrasonic nondestructive testing was performed on the foam sandwich composite wing surface formed in the embodiment to detect delamination defects. The specific detection indicators are as follows:

[0076] Single defect size: Z ≤ 30 mm, where Z is the average size of the defect, defined as Z = (X + Y) / 2, X is the defect projection length measured perpendicular to Y, and Y is the minimum projection width of the defect.

[0077] Distance between adjacent defects: d≥200mm, that is, the distance between two defects should be greater than or equal to 200mm.

[0078] like Figure 4 As shown in the figure, the test results show that after ultrasonic testing, the foam sandwich composite wing meets the above requirements, and the test indicators are similar to the skin defects of the prepreg skin independently molded under the same conditions. Through this test, it can be seen that the problem of insufficient pressure on the wing skin caused by insufficient foam unloading molding pressure has been successfully solved, avoiding the defect that volatiles cannot be effectively squeezed out, thereby ensuring the overall quality and performance of the product.

[0079] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0080] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions of the technical solutions of the present invention made by ordinary technicians in the field should all be included in the protection scope of the present invention. The protection scope of the present invention shall be based on what is defined in the claims.

Claims

1. A foam sandwich composite wing surface, characterized in that: Includes skin and internal support structure; The internal support structure includes metal joints, foam core and multiple stiffeners; The foam core material comprises an upper wing surface and a lower wing surface, and is provided with a plurality of glue flow holes; The embedded end of the metal joint is butted against the foam core material to form the main structure of the internal support structure; The reinforcing rib structure is formed by stacking multiple layers of fiber prepreg, which are distributed at intervals on the foam core material and connect the foam core material and the skin.

2. The foam sandwich composite wing surface according to claim 1, characterized in that: At least one of the reinforcing rib structures is wrapped around the outside of the joint between the metal joint and the foam.

3. The foam sandwich composite wing surface according to claim 1, characterized in that: The outer surface of the foam core material is also covered with a layer of adhesive film.

4. The foam sandwich composite wing surface according to claim 1, characterized in that: The glue flow hole is a through hole or a blind hole that penetrates the foam core material; the shape of the glue flow hole is square, round, triangular or long strip; the bottom angle of the glue flow hole is a positive bevel angle, a negative bevel angle or a rounded angle.

5. An integral molding method of a foam sandwich composite wing surface according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) Design the array density, depth and aperture of the glue flow holes according to the number of layers and glue content of the foam outer layer prepreg; 2) machining the foam core material to form glue flow holes; 3) Clean the surface debris of the foam core material and dry the foam; 4) The metal joint is sandblasted, coated with glue, and then connected to the foam core material, and then covered with a glue film to fix it; and then the fiber prepreg of the reinforcing rib structure is laid on the foam core material to form an internal support structure; 5) Laying the fiber prepreg of the skin on the outside of the internal support structure to obtain the wing structure to be cured; 6) The wing surface structure to be cured is placed in a mold for hot pressing and curing, and demoulding is performed after cooling to obtain a foam sandwich structure composite wing surface.

6. The method according to claim 5, characterized in that In step 1), the resin volume to be removed is calculated according to the area and the number of prepreg layers, at 6% to 10% of the weight of the prepreg, to determine the total volume of the glue flow holes; the density and pore size of the glue flow holes are adjusted in combination with the resin fluidity; the pore size and pore density of the glue flow holes are determined by finite element analysis simulation or experimental molding test.

7. The method according to claim 5, characterized in that The depth of the glue flow hole in step 1) is 1 to 3 times the total thickness of the fiber prepreg of the skin and reinforcement structure, and the hole area is 0.2 to 1 cm 2 The hole spacing is 50 to 200 mm.

8. The method according to claim 5, characterized in that The drying method in step 3) is: placing the foam core material in an oven, drying it at 80±5°C for 1 hour, and then heating it to 130±5°C and drying it for 3 hours.

9. The method according to claim 5, characterized in that In step 4), the laying direction of the fiber prepreg of the reinforcing rib structure is [0 / +45 / 0 / 0 / -45 / 0].

10. The method according to claim 5, characterized in that In step 5), the laying direction of the fiber prepreg of the skin is [45,0,-45,0,0,0,90,0,45,0,-45,0]s.

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