A fairing and a method of making the same

Abstract

The application discloses a fairing and a preparation method thereof. First, a mold is prepared, and then an intermediate layer is prepared as a honeycomb-like structure, which is composed of a plurality of small blocks connected to form the honeycomb-like structure; then, according to different regions of the fairing, an outer skin is laid, metal parts are pre-buried, and a composite core material is laid; the outer skin is reversely wrapped, and at the same time, an inner skin is laid on the composite core material and the metal parts; after covering the mold and heating and curing, the product is cooled and demolded. The preparation method is integrally formed, avoids the limitation of the product being constrained by the size of the tank body, is more easy to prepare large special-shaped product, reduces the weight and increases the effective load, and shortens the manufacturing cycle.

Description

Technical Field

[0001] This invention relates to the field of fairing manufacturing, and more particularly to a fairing and its preparation method. Background Technology

[0002] Composite materials play a vital role in the development of modern science and technology, and are widely used in aerospace, shipbuilding, rail transportation, and launch vehicle fairings. Composite material fairing structures consist of high-strength, high-modulus panels and lower-strength sandwich materials. Carbon / epoxy composite sandwich structures have attracted considerable attention, with core materials primarily including aluminum honeycomb and aramid paper honeycomb. Composite material fairings are often manufactured using a step-by-step autoclave curing process. The process involves separately curing the upper and lower carbon fiber skins, then applying epoxy structural adhesive to the core material and bonding the upper and lower skins together before autoclaving. While this process is very mature, it still has the following problems: 1. Due to the limited plasticity of honeycomb materials, this process is difficult to apply to curved or irregularly shaped structures. 2. The structural strength and precision of the composite fairing are prone to instability due to variations in adhesives and bonding processes. 3. Manufacturing large-sized composite fairings requires extensive splicing of the honeycomb core, which can easily lead to deviations in the bonding angle of the honeycomb. Furthermore, the probability of overlap between the honeycomb splices and the thickened or filled areas of the panel increases, indirectly leading to more seams and a higher risk of delamination at the seams. 4. The autoclave curing process is complex and cumbersome, and the high cost of autoclaves limits its application. Summary of the Invention

[0003] The purpose of this invention is to provide a method for manufacturing a fairing that is integrally molded, low in cost, and easy to operate, and the fairing obtained is lightweight and high in strength.

[0004] To achieve the above objectives, the present invention provides a method for preparing a fairing, characterized in that the steps include:

[0005] S1: Design and manufacture molds, embed heating pipes inside the molds, the molds include lower molds and upper molds for integral molding of composite material covers and molds for core material molding, and then clean the molds.

[0006] S2: Calculate the core material usage based on the product volume, use a core material mold with a grid baffle coated with polytetrafluoroethylene, place unfoamed core material into each grid of the core material mold, and then heat it to fill each grid with foamed core material to obtain pre-made core material. Process the pre-made core material to make it smooth and free of burrs, and then wrap the processed pre-made core material with carbon yarn or fiber cloth to make a composite core material; preferably, the fiber cloth is at least one of glass yarn or Kevlar;

[0007] S3: Based on the structural dimensions of the fairing end, front cone section, cylindrical section, and inverted cone section, cut the inner and outer skins and lay the outer skins on the lower mold of the mold. The outermost layer is 3K carbon cloth. The overall layering sequence is 3K / 45° / 45° / 0° / 90° / 45°. The number of layers and angles are determined according to specific requirements. Avoid bridging and bulging during the layering process.

[0008] S4: After the outer skin is laid, place the embedded metal parts of the riveting structure and fix them on the mold to ensure that they do not shift during molding. At the same time, lay the composite core material on the lower outer skin according to the design.

[0009] S5: The outer skin is reversed and the inner skin is laid on the composite core and metal parts at the same time. The inner skin is laid in the same way as the outer skin.

[0010] S6: After all the yarn is laid, cover with the upper mold and lock it in place. Heat and cure to form the desired shape. Preferably, the curing procedure is as follows: heat to 120-140℃ at a heating rate of 0.5-3℃ / min, and hold at 120-140℃ for 30-50 minutes; after holding at 120-140℃, heat to 140-180℃ at a heating rate of 0.5-3℃ / min, and hold at 140-180℃ for 90-240 minutes.

[0011] S7: Cool down to below 60°C at a cooling rate of no more than 3°C / min, demold, remove the product, and clean the residual resin at the parting line.

[0012] Furthermore, in step S1, the mold is made of high-quality mold steel, and the mold surface is designed and matched according to the standards for butt joint and riveting structures.

[0013] Furthermore, in step S1, the further cleaning of the mold involves first blowing away dust and debris from the surface of the fairing mold with an air gun, then wiping away residual oil stains with a cotton cloth soaked in alcohol; and then applying a release agent evenly to the surface of the mold with a cotton cloth.

[0014] Furthermore, in step S1, the mold is cleaned by first blowing away dust and debris from the surface of the fairing mold with an air gun, then wiping away residual oil stains with a cotton cloth dipped in alcohol, preferably repeating this process 3 times; then applying a release agent evenly to the surface of the mold with a cotton cloth and letting it stand until the release agent adheres to the mold, repeating this step; preferably, letting it stand for 10 minutes, repeating this process 3 times.

[0015] Furthermore, in step S2, the material coated with polytetrafluoroethylene is iron sheet or plastic;

[0016] The thickness of the carbon yarn or fiber cloth is optional, ranging from 0.1 to 1 mm; choose the thickness according to the actual situation, for example, 0.2 mm.

[0017] Furthermore, in step S2, the composite board has a three-layer structure: upper, middle, and lower. The upper and lower layers are respectively the upper skin and the lower skin, and the middle layer has a honeycomb-like structure, which is composed of multiple small blocks connected together. The shape of the small blocks is not limited. Each small block has a foamed core material in the middle and is wrapped with a layer of carbon yarn. The foamed core material and the carbon yarn or fiber cloth are tightly bonded together by heat pressing.

[0018] Furthermore, the shape of the small block is polygonal and / or irregular; preferably, the polygon is a triangle, quadrilateral, pentagon and / or hexagon; the irregular shape is not limited to hemispherical or U-shaped.

[0019] Furthermore, in step S3, the material of the upper and lower skins is carbon fiber prepreg; preferably, the thickness of a single layer of carbon fiber prepreg is 0.1-1mm; the thickness can be selected according to the actual situation, for example, 0.2mm.

[0020] Furthermore, in step S4, the fixing method is screw locking or pin locking.

[0021] Further, step S6 involves covering the upper mold and locking it after all the yarns are laid out, then heating and curing it. The curing procedure is as follows: heating to 140°C at a rate of 0.5–3°C / min, and holding at 140°C for 40 minutes; after holding at 140°C, heating to 170°C–180°C at a rate of 0.5–3°C / min, and holding at 170°C–180°C for 90–240 minutes.

[0022] The composite board is divided into multiple grids according to the mold design. The grid size varies depending on the mechanical performance requirements; for example, it can be a square grid; 10*10mm, 20*20mm, 30*30mm, etc.

[0023] The middle layer of the composite material in the fairing has a honeycomb-like structure. While a honeycomb structure is generally considered to be formed by multiple interconnected hexagons, the honeycomb-like structure of this invention refers to a structure formed by multiple interconnected small blocks. These small blocks are not necessarily hexagonal; they can be any shape, such as triangles, quadrilaterals, pentagons, and / or more polygonal shapes like hexagons, and can also be irregular shapes, including but not limited to hemispherical and U-shaped irregular shapes. The multiple small blocks can be of the same shape or different shapes.

[0024] Each small section has a foamed core material in the center, wrapped with a layer of carbon fiber, and the foamed core material and carbon fiber are tightly bonded together by heat pressing. The foamed core material ensures its lightweight and high strength characteristics. The outer layer of carbon fiber further enhances the strength of the composite board. Because the foamed core material can be cut and combined arbitrarily, it is particularly advantageous for large, complex, and irregularly shaped components. Furthermore, due to the integral molding process, the risks of detachment at the joints caused by adhesive or bonding differences, which are common in existing aluminum honeycomb composite panel bonding processes, are eliminated.

[0025] The advantages of this invention are as follows:

[0026] 1. Compared with traditional sandwich materials, the sandwich structure of this invention has a lower design density, which significantly reduces the weight of the product while maintaining the same external dimensions, and further increases the effective load.

[0027] 2. Compared with the traditional autoclave step-by-step curing molding process, the present invention's integral molding does not require the step-by-step preparation of the upper skin, lower skin, and subsequent adhesive bonding process, which simplifies the overall manufacturing process and shortens the manufacturing cycle.

[0028] 3. The non-autoclave stepwise curing molding process of this invention avoids the limitations imposed by the size of the autoclave, making it easier to manufacture large, irregularly shaped parts. At the same time, it eliminates the need for large molds, significantly reducing costs.

[0029] 4. The present invention uses a composite core material as the sandwich material. In the mold environment, during the heat forming process, the foamed core material expands due to heat and then solidifies and sets. During this process, the outward expansion force generated by the heat compresses the fiber prepreg fabric of each outer layer, which can effectively squeeze out the micro air bubbles between the layers, improve the interlayer bonding force inside the fiber composite material, and thus improve the mechanical properties of the product. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. These embodiments are intended to explain the present invention and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0031] The carbon fiber prepreg and foamed core material in the following examples are not limited to any particular type or category. For example, the FAW of the carbon fiber prepreg can be 200 g / m³. 2 RC is 37%; you can also choose RC as 40%, etc.

[0032] The FAW of the foamed core material can be 200g / m². 2For example, HR-313-6, HR-313-8, and HR-313-10 from Xiamen Haoer New Materials Co., Ltd.

[0033] Example 1:

[0034] A method for preparing a fairing, characterized in that the steps include:

[0035] S1: Design and manufacture molds with embedded heating pipes. The molds can be heated by heat transfer oil, electric heating wires, heating rods, etc. The molds include lower and upper molds for integral molding of composite material covers and molds for core material molding. After the molds are manufactured, they are cleaned.

[0036] Preferably, the mold is made of high-quality mold steel such as 45#, 718, and Q235, and the mold surface is designed and matched according to the standards of butt joint and riveting structure.

[0037] The subsequent cleaning of the mold involves first blowing away dust and debris from the surface of the fairing mold with an air gun, then wiping away residual oil stains with a cotton cloth soaked in alcohol; and then applying a release agent evenly to the surface of the mold with a cotton cloth.

[0038] More preferably, the mold is cleaned by first blowing away dust and debris from the surface of the fairing mold with an air gun, then wiping away residual oil stains with a cotton cloth dipped in alcohol, preferably repeating this process 3 times; then applying a release agent evenly to the surface of the mold with a cotton cloth and letting it stand for 10 minutes to allow the release agent to adhere to the mold, and repeating this step; preferably, letting it stand for 10 minutes and repeating this process 3 times.

[0039] S2: Calculate the core material usage based on the product volume, and use a core material mold with a PTFE-coated material (such as iron sheet, plastic, etc.) as the grid baffle. Place unfoamed core material into each grid of the core material mold, and then heat it to fill each grid with foamed core material to obtain pre-made core material. Process the pre-made core material to make it smooth and free of burrs, and then wrap the processed pre-made core material with carbon yarn or fiber cloth to make a composite core material; preferably, the fiber cloth is at least one of glass yarn or Kevlar;

[0040] Preferably, the thickness of the carbon yarn or fiber cloth is 0.1-1mm; the thickness can be selected according to the actual situation, for example, 0.2mm.

[0041] The composite board has a three-layer structure: upper, middle, and lower. The upper and lower layers are respectively the upper skin and the lower skin, and the middle layer has a honeycomb-like structure, which is composed of multiple small blocks connected together. The shape of the small blocks is not limited. Each small block has a foamed core material in the middle and is wrapped with a layer of carbon yarn on the outside. The foamed core material and the carbon yarn or fiber cloth are tightly bonded together by heat pressing.

[0042] More preferably, the shape of the small block is polygonal and / or irregular; preferably, the polygon is triangular, quadrilateral, pentagonal or hexagonal;

[0043] Preferably, the polygon is a triangle, quadrilateral, pentagon, and / or hexagon, or other more polygonal shapes; it can also be irregular in shape, including but not limited to hemispheres and U-shapes. The multiple small blocks can be of the same shape or different shapes.

[0044] S3: Based on the structural dimensions of the fairing end, front cone section, cylindrical section, and inverted cone section, cut the inner and outer skins and lay the outer skins on the lower mold of the mold. The outermost layer is 3K carbon cloth. The overall layering sequence is 3K / 45° / 45° / 0° / 90° / 45°. The number of layers and angles are determined according to specific requirements. Avoid bridging and bulging during the layering process.

[0045] Preferably, the material for the upper and lower skins is carbon fiber prepreg; the thickness of a single layer is 0.1-1mm; the thickness can be selected according to the actual situation, for example, 0.2mm.

[0046] S4: After the lower skin is laid, place the embedded metal parts of the riveting structure and fix them on the mold to ensure that they do not shift during molding. At the same time, lay the composite core material on the lower skin according to the design.

[0047] Preferably, the fixing method is screw locking or pin locking.

[0048] S5: The outer skin is reversed and the inner skin is laid on the composite core and metal parts at the same time. The inner skin is laid in the same way as the outer skin.

[0049] S6: After all the yarn is laid, cover with the upper mold and lock it in place. Heat and cure to form the desired shape. Preferably, the curing procedure is as follows: heat to 120-140℃ at a heating rate of 0.5-3℃ / min, and hold at 120-140℃ for 30-50 minutes; after holding at 120-140℃, heat to 140-180℃ at a heating rate of 0.5-3℃ / min, and hold at 140-180℃ for 90-240 minutes.

[0050] More preferably, step S6 is as follows: after all the yarns are laid, cover the upper mold and lock it in place, then heat and cure it. The curing procedure is as follows: heat up to 140°C at a heating rate of 0.5 to 3°C / min, and hold at 140°C for 40 minutes. After holding at 140°C, heat up to 170°C-180°C at a heating rate of 0.5 to 3°C / min, and hold at 170°C-180°C for 90 to 240 minutes.

[0051] S7: Cool down to below 60°C at a cooling rate of no more than 3°C / min, demold, remove the product, and clean the residual resin at the parting line.

[0052] The fairing with a diameter of 4.2m and a length of 12m prepared by the above method has an overall weight of approximately 1000Kg, while the fairing manufactured using a similar method with aluminum honeycomb has an overall weight of approximately 1500Kg.

[0053] Example 2: Performance testing of composite sheet material used for fairing:

[0054] 1. Based on the structural dimensions of the composite board (180*360*26mm), and the thickness of the top and bottom skin panels and side walls (1.2mm), prepare the carbon fiber prepreg and foam core material by cutting.

[0055] 2. Based on the composite board mold of 180*360*26mm, design and divide it into square grids of, for example, 20*20mm. Use a material sprayed with polytetrafluoroethylene (such as iron sheet or plastic sheet) as grid baffle. Put unfoamed core material into each grid and heat it to form a full grid. Heat at 130℃ for 15 minutes to form the prefabricated core material.

[0056] 3. Remove the burrs from the precast core material (20*20mm) obtained above and roughen the surface with coarse sandpaper to make it smooth; after the treatment, wrap the precast core material with 0.2mm thick 45° carbon yarn (size 26*82mm) (it can wrap the four sides of the precast core material, or wrap the five or six sides of the precast core material). When wrapping the four sides of the precast core material, leave about 3mm of carbon yarn on the top and bottom and wrap it in reverse to make a composite core material;

[0057] 4. Lay the lower skin, i.e., carbon fiber prepreg, in the lower mold of the composite board;

[0058] 5. Each composite core material prepared above is evenly and densely laid in the lower mold. After all the materials are laid, the upper skin is laid on the composite core material and wrapped over the upper mold cover, and then locked with screws.

[0059] 6. Turn on the heating device of the above mold, the temperature is 150℃, the molding time is 1.5h. During the heating and conduction process, the foamed core material of the sandwich layer expands due to heat, causing the carbon fiber prepreg on its periphery to be squeezed and fill the mold cavity. At the same time, the epoxy resin in the carbon fiber prepreg is cured and formed during the heating process.

[0060] 7. Once the mold has solidified and formed, transfer it to the cooling table;

[0061] 8. Cool to the mold-opening temperature, which is 40℃, for 30 minutes. Open the mold and remove the part to obtain the rough blank.

[0062] 9. Perform finishing and other operations on the appearance of the above-mentioned rough blank to obtain a new type of lightweight and high-strength composite board.

[0063] The obtained composite boards were tested according to the parameters in Table 1, referring to GB / T1452-2018 Test Method for Tensile Strength of Sandwich Structures; GB / T1453-2005 Test Method for Compressive Strength of Sandwich Structures or Cores; and GB / T1455-2005-t Test Method for Shear Strength of Sandwich Structures or Cores.

[0064] The aluminum honeycomb composite panel has an inscribed circle diameter of 6.35 mm and an aluminum foil thickness of 0.06 mm; its density is 64 kg / m³. 3 The paper honeycomb composite board has an inscribed circle diameter of 4.8 mm, an aramid paper wall thickness of 0.05 mm, and a density of 64 kg / m³. 3 .

[0065] Table 1 Comparison of the effects of the composite panels obtained in Example 2

[0066]

[0067] As can be seen from Table 1, compared with aluminum honeycomb composite panels and paper honeycomb composite panels, the composite material for fairing prepared according to the method of the present invention meets the mechanical performance requirements but is lighter in weight, highlighting the characteristics of lightweight and high strength.

[0068] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a fairing, characterized in that the steps include... include: S1: Design and manufacture molds, embed heating pipes inside the molds, the molds include lower molds and upper molds for integral molding of composite material covers and molds for core material molding, and then clean the molds. S2: Calculate the core material usage based on the product volume, use a core material mold with a grid baffle coated with polytetrafluoroethylene, put unfoamed core material into each grid of the core material mold, then heat it to make the foamed core material fill each grid to obtain pre-made core material, process the pre-made core material to make it smooth and burr-free, and then wrap the processed pre-made core material with carbon yarn or fiber cloth to make a composite core material. The middle layer has a honeycomb-like structure, which is composed of multiple small blocks connected together. The shape of the small blocks is not restricted. Each small block has a foamed core material in the middle, and is wrapped with a layer of carbon yarn or fiber cloth. The foamed core material and the carbon yarn or fiber cloth are tightly bonded together by heat pressing. S3: Based on the structural dimensions of the fairing end, front cone section, cylindrical section, and inverted cone section, cut the inner and outer skins and lay the outer skins on the lower mold of the mold. The outermost layer is 3K carbon cloth. The overall layering sequence is 3K / 45° / 45° / 0° / 90° / 45°. The number of layers and angles are determined according to specific requirements. Avoid bridging and bulging during the layering process. S4: After the outer skin is laid, place the embedded metal parts of the riveting structure and fix them on the mold to ensure that they do not shift during molding. At the same time, lay the composite core material on the lower outer skin according to the design. S5: The outer skin is reversed and the inner skin is laid on the composite core and metal parts at the same time. The inner skin is laid in the same way as the outer skin. S6: After all the yarn is laid, cover with the upper mold, lock it, and heat to cure and shape. S7: Cool down to below 60°C at a cooling rate of no more than 3°C / min, demold, remove the product, and clean the residual resin at the parting line.

2. The method for preparing the fairing as described in claim 1, characterized in that, In step S1, the mold is made of high-quality mold steel, and the mold surface is designed and matched according to the standards for butt joint and riveting structures.

3. The method for preparing the fairing as described in claim 1, characterized in that, In step S1, the further cleaning of the mold involves first blowing away dust and debris from the surface of the fairing mold with an air gun, then wiping away residual oil stains with a cotton cloth soaked in alcohol, and then applying a release agent evenly to the surface of the mold with a cotton cloth.

4. The method for preparing the fairing as described in claim 3, characterized in that, In step S1, the mold is cleaned by first blowing away dust and debris from the surface of the fairing mold with an air gun, then wiping away residual oil stains with a cotton cloth dipped in alcohol, repeating 1-4 times; then applying release agent evenly to the mold surface with a cotton cloth and letting it stand until the release agent adheres to the mold, repeating this step.

5. The method for preparing the fairing as described in claim 4, characterized in that, Wipe away residual oil stains with a cotton cloth soaked in alcohol, repeat 3 times; apply release agent evenly to the mold surface with a cotton cloth and let it stand for 10 minutes after the release agent adheres to the mold, repeat 3 times.

6. The method for preparing the fairing as described in claim 1, characterized in that, In step S2, the material coated with polytetrafluoroethylene is iron sheet, high-temperature resistant engineering plastic, aluminum alloy, or stainless steel.

7. The method for preparing the fairing as described in claim 1, characterized in that, In step S2, the thickness of the carbon yarn or fiber cloth is 0.1-1 mm.

8. The method for preparing the fairing as described in claim 1, characterized in that, In step S2, the shape of the small block is polygonal and / or irregular.

9. The method for preparing the fairing as described in claim 8, characterized in that, The polygon is a triangle, quadrilateral, pentagon and / or hexagon; the irregular shape is not limited to hemisphere or U-shape.

10. The method for preparing the fairing as described in claim 1, characterized in that, In step S2, the fiber cloth is at least one of glass yarn or Kevlar.

11. The method for preparing the fairing as described in claim 1, characterized in that, In step S4, the fixing method is screw locking or pin locking.

12. The method for preparing the fairing as described in claim 1, characterized in that, The curing process is as follows: heat to 120-140℃ at a heating rate of 0.5~3℃ / min, and hold at 120-140℃ for 30-50 minutes; after holding at 120-140℃, heat to 140-180℃ at a heating rate of 0.5~3℃ / min, and hold at 140-180℃ for 90-240 minutes.

13. The method for preparing the fairing as described in claim 12, characterized in that, The curing process is as follows: heat to 140℃ at a heating rate of 0.5~3℃ / min, and hold at 140℃ for 40min; after holding at 140℃, heat to 170℃-180℃ at a heating rate of 0.5~3℃ / min, and hold at 170℃-180℃ for 90-240min.

14. The fairing prepared by any of the preparation methods described in claims 1-13.

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