A foam sandwich structure and its manufacturing method

Abstract

This application provides a foam sandwich structure and its manufacturing method. The composite foam sandwich structure consists of an upper panel, a lower panel, and an internally encapsulated foam core. Based on the curing deformation trends of the upper and lower panels, different segmented foam combination layouts are designed to obtain different foam creep deformation trends. The deformation trends of the two panels cancel each other out, thereby controlling the overall curing deformation of the product. A design theory for compressive creep compensation of mixed foam is established to offset the large compressive creep of low-density foam, ensuring that the product surface is flat and free of depressions. This invention can improve the overall performance of the foam core assembly, making the product both lightweight and high-strength. By reducing curing deformation, assembly accuracy and efficiency can be improved, while achieving product lightweighting.

Description

Technical Field

[0001] This application belongs to the field of composite material manufacturing technology, and in particular relates to a design and manufacturing method for controlling the curing deformation of a foam sandwich structure. Background Technology

[0002] With the rapid development of the aerospace industry, the application of composite products is becoming increasingly widespread, and the requirements for molding precision and lightweighting of composite products are becoming increasingly stringent. Composite foam sandwich structures are a common type of lightweight structure. The core material used is a cross-linked foam material with a high closed-cell rate, characterized by low moisture absorption and isotropy. However, a single foam core cannot meet the requirements of load-bearing structures, and it is usually necessary to bond it with carbon fiber materials to form a composite foam sandwich structure to meet the needs of load-bearing components.

[0003] Traditional single-component low-density foam sandwich structures suffer from severe deformation after curing, affecting subsequent assembly requirements. While single-component high-density foam sandwich structures offer some improvement in deformation, they result in excessive weight gain, making it difficult to meet the development needs of lightweight components. Using mixed-density foam cores for splicing can overcome the shortcomings of single-component foam cores, but depressions will occur at the seams of the segmented foam cores on the surface of the component after molding. Summary of the Invention

[0004] Purpose of the invention: How to achieve precise manufacturing of composite foam sandwich structures, further control deformation, and achieve product lightweighting has become an urgent problem to be solved in the field of composite material manufacturing.

[0005] In a first aspect, this application provides a method for manufacturing a foam sandwich structure, the method comprising:

[0006] Define foam core blocks; wherein, the foam core blocks include blocks of foam with different densities;

[0007] Milling the splicing surfaces of the foam core;

[0008] Splicing foam cores and processing component profiles;

[0009] Substrate installation and curing;

[0010] Component installation and curing.

[0011] Preferably, the process of dividing the foam core into sections includes:

[0012] Based on the product's structural characteristics, the foam core is divided into segmented layout structures. Then, based on the required foam creep deformation trend, the foam density combination method for different segments is determined, the theoretical thickness of the foam core is determined, and the thickness compensation amount for low-density foam is calculated.

[0013] Preferably, the milled foam core splicing surface includes:

[0014] Based on the modular foam arrangement and the thickness compensation of low-density foam, the foam is shaped and the splicing surfaces are milled.

[0015] Preferably, the spliced ​​foam core and the surface of the processed components include:

[0016] The segmented foam cores, whose splicing surfaces have been milled, are then spliced ​​together, and the foam core component surface is then machined.

[0017] Preferably, the lower panel installation and curing includes:

[0018] Take the carbon fiber prepreg for the lower panel and complete the laying and curing of the lower panel on the mold.

[0019] Preferably, the component installation and curing includes:

[0020] A film is laid on the surface of the cured lower panel, the pre-processed foam core assembly is placed on it, a film is laid on the upper surface of the foam core, the upper panel prepreg is then laid on it, and finally the assembly is packaged into a bag and sent into an autoclave for curing.

[0021] Secondly, this application also provides a foam sandwich structure, which consists of an upper panel, a lower panel, and an internally encased foam core;

[0022] The upper and lower panels are made of carbon fiber prepreg, which undergoes curing deformation during the curing process, resulting in warping.

[0023] Preferably, the foam core is composed of segments of foam with different densities spliced ​​together. Under the high temperature and high pressure environment during the curing process, the foam will undergo creep deformation. According to the curing deformation trend of the upper and lower panels, different combinations of segmented foam are designed to obtain different foam creep deformation trends. The deformation trends of the two cancel each other out, thereby controlling the overall curing deformation of the product.

[0024] The advantages and application effects of this invention are as follows:

[0025] 1. Establish a design theory for the compression creep compensation of mixed foam. This design theory reveals the law of compression creep of foam core. Based on the theoretical thickness of foam core, the thickness compensation of low-density foam can be calculated to offset the large compression creep of low-density foam.

[0026] 2. By using foam cores of different densities and developing a modular foam combination layout, the weight reduction effect of low-density foam cores and the high strength and high rigidity of high-density foam cores can be fully combined to improve the overall performance of the foam core components, making the product both lightweight and high-strength.

[0027] 3. Compared with single-component foam sandwich structures, foam sandwich structures made with mixed-density foam can effectively control the curing deformation of composite foam sandwich structures, and improve assembly accuracy and efficiency. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the deformation control principle provided in the embodiments of this application;

[0029] Figure 2 This is a schematic diagram of the low-density foam thickness compensation amount provided in the embodiments of this application;

[0030] Figure 3 This is a schematic diagram of the composite material foam sandwich structure provided in the embodiments of this application;

[0031] Figure 4 This is a schematic diagram of the mixed-density foam "U"-shaped nested structure provided in the embodiments of this application.

[0032] Figure 5 This is a flowchart illustrating the processing of the composite material foam sandwich structure provided in the embodiments of this application.

[0033] Figure 6 This is a schematic diagram of curing deformation measurement provided in an embodiment of this application.

[0034] Among them: 1. Top panel; 2. Bottom panel; 3. Peripheral ring-shaped high-density foam core; 3-1 First high-density foam core block; 3-2 Second high-density foam core block; 3-3 Third high-density foam core block; 3-4 Fourth high-density foam core block; 4. Internal low-density foam core; 5. Foam core assembly; These are the measurement points for product curing deformation. Detailed Implementation

[0035] This invention provides a design and manufacturing method for controlling the curing deformation of a foam sandwich structure. The specific design concept is as follows:

[0036] The composite foam sandwich structure provided in this application consists of an upper panel, a lower panel, and an internally encased foam core.

[0037] The upper and lower panels are laminated boards made of carbon fiber prepreg. Due to the mismatch in thermal expansion coefficients between the prepreg and the mold, the prepreg near the molded surface is under tension in the fiber direction during curing, generating tensile stress. After demolding, the tensile stress is released, resulting in curing deformation and panel warping. To control curing deformation and ensure product lightweighting, different density segmented foam arrangement layouts are designed based on the curing deformation trends of the upper and lower panels and the product's geometry. These layouts include, but are not limited to, nested "U" shapes, S-shapes, and triangles. Different combinations of shapes can produce different creep trends. The creep deformation trend generated by the foam cancels out the curing deformation trend of the panels, thereby controlling the overall deformation of the product.

[0038] High-density foam has a low core content and high structural strength, resulting in strong resistance to compressive creep; while low-density foam has a high core content and weak structural strength, resulting in weak resistance to compressive creep. Under the same thickness, low-density foam exhibits greater compressive creep than high-density foam, with the high-density foam area being higher than the low-density foam area. This causes indentation deformation in the upper panel at the joints between the foam core sections.

[0039] Among them, the experiment found that under the high temperature and high pressure environment during the curing process in the autoclave, the foam core undergoes compression creep, and the compression rate in the thickness direction is related to the foam core density, foam core thickness and curing pressure.

[0040] Among them, under the same curing pressure, there exists a fitting formula for the compressibility θ of foam cores with different densities in the thickness direction relative to the thickness t:

[0041]

[0042] In this context, the superscript of the compression ratio θ indicates the curing pressure P, in MPa; the subscript of the compression ratio θ indicates the foam core density ρ, in kg / m³. 3 Foam core thickness t, unit: mm. The analysis here is based on a curing pressure of 0.25 MPa; similar relationships exist under other curing pressure conditions.

[0043] To ensure the smooth surface of the foam assembly after compression creep, a low-density foam thickness compensation amount is designed to offset the large compression creep of the low-density foam. Its expression is as follows:

[0044] Δt=t low -t high (2)

[0045] Where Δt represents the thickness compensation amount of the low-density foam, t low Indicates the thickness of low-density foam, t high Indicates the thickness of high-density foam, t highIt is also used as a theoretical design thickness.

[0046] According to equation (1), it can be found that the compressibility θ in the thickness direction of the foam core is negatively correlated with the thickness t, and the relationship of the thickness compensation amount Δt of low-density foam can be derived:

[0047]

[0048] Where, θ low θ represents the compressibility in the thickness direction of low-density foam. high δ represents the compressibility in the thickness direction of high-density foam. low δ represents the compressive creep of low-density foam. high This represents the compression creep variable of high-density foam.

[0049] From equations (2) and (3), we can obtain:

[0050]

[0051] At theoretical thickness t high Under certain conditions, θ can be calculated from equation (1) and similar relationships. low and θ high Δt can be calculated from equation (4) and used as the design basis for the thickness compensation of low-density foam.

[0052] In other embodiments of this application, a method for manufacturing a composite foam sandwich structure is also provided, comprising the following steps:

[0053] 1. Develop a foam core segmentation plan: Based on the product's structural characteristics, divide the foam core into segmented layout structures, and then, based on the required foam creep deformation trend, determine the foam density combination method for different segments, determine the theoretical thickness of the foam core, and calculate the thickness compensation amount for low-density foam.

[0054] 2. Milling the splicing surface of the foam core: Based on the layout of the segmented foam and the thickness compensation of the low-density foam, the foam is shaped and the splicing surface is milled.

[0055] 3. Splicing foam cores and processing component surfaces: Splice the segmented foam cores that have been milled to complete the splicing surface, and then process the foam core component surfaces after splicing.

[0056] 4. Lower panel installation and curing: Obtain the carbon fiber prepreg for the lower panel and complete the installation and curing of the lower panel on the mold;

[0057] 5. Component installation and curing: Lay an adhesive film on the surface of the cured lower panel, place the processed foam core component, lay an adhesive film on the upper surface of the foam core, then lay the upper panel prepreg, and finally seal the assembly into a bag and send it into an autoclave for curing.

[0058] In other embodiments of this application, a foam sandwich structure and its manufacturing method are provided. The composite foam sandwich structure consists of an upper panel, a lower panel, and an internally encapsulated foam core. Based on the curing deformation trends of the upper and lower panels, different segmented foam combination layouts are designed to obtain different foam creep deformation trends. The deformation trends of the two panels cancel each other out, thereby controlling the overall curing deformation of the product. A design theory for the compression creep compensation of mixed foam is established to offset the large compression creep of low-density foam, ensuring that the product surface is flat and free of depressions. This invention can improve the overall performance of the foam core assembly, making the product both lightweight and high-strength. By reducing curing deformation, assembly accuracy and efficiency can be improved, while achieving product lightweighting.

[0059] High-density foam has a lower core content and higher structural strength, resulting in stronger resistance to compressive creep. Conversely, low-density foam has a higher core content and weaker structural strength, leading to weaker resistance to compressive creep. At the same thickness, low-density foam exhibits greater compressive creep than high-density foam, with the high-density foam area being higher than the low-density foam area. This causes indentation deformation in the upper panel at the joints between foam core sections. By designing a thickness compensation amount for low-density foam, the larger compressive creep of low-density foam can be offset.

[0060] Among them, the thickness compensation amount of low-density foam is designed, and there is a fitting formula between the compression ratio θ and the thickness t of foam cores of different densities in the thickness direction:

[0061]

[0062] In this context, the superscript of the compression ratio θ indicates the curing pressure P, in MPa; the subscript of the compression ratio θ indicates the foam core density ρ, in kg / m³. 3 Foam core thickness t, unit: mm. The analysis here is based on a curing pressure of 0.25 MPa; similar relationships exist under other curing pressure conditions.

[0063] The expression for the thickness compensation of low-density foam is as follows:

[0064] Δt=t low -t high (2)

[0065] Where Δt represents the thickness compensation amount of the low-density foam, t low Indicates the thickness of low-density foam, t high Indicates the thickness of high-density foam, t high It also serves as the theoretical design thickness.

[0066] The relationship between the low-density foam thickness compensation amount Δt and the following is provided:

[0067]

[0068] Where, θ low θ represents the compressibility in the thickness direction of low-density foam. high δ represents the compressibility in the thickness direction of high-density foam. low δ represents the compressive creep of low-density foam. high This represents the compression creep variable of high-density foam.

[0069] From the above formula, we can obtain:

[0070]

[0071] At theoretical thickness t high Under certain conditions, θ can be calculated from equation (1) and similar relationships. low and θ high Δt can be calculated from equation (4) and used as the design basis for the thickness compensation of low-density foam.

[0072] For other embodiments in this application, please refer to Figures 1-6 The invention will be described in further detail below.

[0073] Three composite foam sandwich structures, each measuring 2m × 1.5m, were manufactured. The foam core material was polymethacrylamide closed-cell rigid foam (PMI foam), and the high-density foam core used was 75kg / m³. 3 The low-density foam core uses 52kg / m³ 3 Both types of foam cores have a theoretical thickness of 30mm and a curing pressure of 0.25MPa. T800 grade carbon fiber prepreg and J-375 adhesive film are used. The density specifications of the three products are 52kg / m³. 3 75kg / m² around the perimeter 3 Internal nesting 52kg / m 3 75kg / m 3 The manufacturing processes are completely identical.

[0074] The specific preparation steps for the mixed-density nested foam structure are as follows:

[0075] 1. Develop a foam core segmentation plan: Based on the rectangular shape of the product, divide the foam core into a nested "U"-shaped segment layout, selecting 30mm thick 75kg / m³ foam core. 3 and 52kg / m 3 Two types of PMI foam cores, with volume percentages of 15% and 85% respectively, are used in a ring-shaped arrangement of 75 kg / m³. 3 The foam core is divided into four parts, 52kg / m³ 3 The foam core is a single piece, such as Figure 5As shown. Based on a theoretical thickness of 30mm and a curing pressure of 0.25MPa, substituting these values ​​into the compression ratio calculation formula:

[0076]

[0077] get:

[0078]

[0079] Then substitute it into the formula for calculating the compensation amount of low-density foam:

[0080]

[0081] We obtain: Δt = 0.9746, from which we determine 52 kg / m³. 3 The foam thickness compensation is 0.9746 mm.

[0082] 2. Milling the splicing surface of the foam core: Based on the block foam assembly layout and 52kg / m 3 Foam thickness compensation amount, for 75kg / m 3 and 52kg / m 3 Two types of foam cores with different densities are shaped and the splicing surfaces are milled.

[0083] 3. Assembling the foam core and processing the component surfaces: Assemble the segmented foam cores according to the foam core segmentation plan. Place J-375 adhesive film on the spliced ​​surfaces, seal and bag them, then place them in an autoclave for curing. Curing conditions are as follows: vacuum throughout the process, curing temperature 180℃±5℃, curing time 150min. After curing, use a milling machine to process the foam core component surfaces.

[0084] 4. Lay the lower panel carbon fiber prepreg layer by layer on the mold, seal and bag it, and send it into an autoclave for curing. The curing conditions are as follows: curing pressure is 0.65MPa, curing temperature is 185℃±5℃, and curing time is 180min.

[0085] 5. Place the cured bottom panel, lay J-375 adhesive film on its surface, position the processed foam core assembly on the bottom panel surface, lay J-375 adhesive film on the upper surface of the foam core, and then lay the top panel prepreg layer by layer. Finally, seal the assembly into a bag and send it into an autoclave for curing. The curing conditions are as follows: curing pressure is 0.25MPa, curing temperature is 185℃±5℃, and curing time is 180min.

[0086] 6. After curing, measure the product weight and surface deformation. Figure 6 As shown.

[0087] Comparing the surface deformation and weight of the three composite foam sandwich structure products, their density specifications are 52 kg / m³.3 75kg / m² around the perimeter 3 Internal nesting 52kg / m 3 75kg / m 3 The maximum deformation of the products is 2.35mm, 1.45mm, and 1.05mm, respectively, and the weights are 15.73kg, 16.03kg, and 16.94kg, respectively.

[0088] The data above shows that using a circumferential ring-shaped 75kg / m²... 3 Nested 52kg / m 3 The mixed-density foam sandwich structure can significantly reduce the curing deformation of the parts and achieve lightweighting, proving the feasibility of the present invention.

Claims

1. A method for manufacturing a foam sandwich structure, characterized in that, The method includes: Define foam core blocks; wherein, the foam core blocks include blocks of foam with different densities; Milling the splicing surfaces of the foam core; Splicing foam cores and processing component profiles; Substrate installation and curing; Component installation and curing; The process of dividing the foam core into blocks includes: Based on the product's structural characteristics, the foam core is divided into blocks. Then, based on the required foam creep deformation trend, the foam density combination of different blocks is determined, the theoretical thickness of the foam core is determined, and the thickness compensation of low-density foam is calculated. Among them, under the same curing pressure, there exists a fitting formula for the compressibility θ of foam cores with different densities in the thickness direction relative to the thickness t: In equation (1), the superscript of the compression ratio θ represents the curing pressure P, in MPa; the subscript of the compression ratio θ represents the foam core density ρ, in kg / m³. 3 Foam core thickness t, unit: mm; To ensure the smooth surface of the foam assembly after compression creep, a low-density foam thickness compensation amount is designed to offset the large compression creep of the low-density foam. Its expression is as follows: Δt=t low -t high (2) In equation (2), Δt represents the thickness compensation amount of the low-density foam, t low Indicates the thickness of low-density foam, t high Indicates the thickness of high-density foam, t high It also serves as the theoretical design thickness; According to equation (1), the compressibility θ in the thickness direction of the foam core is negatively correlated with the thickness t, and the relationship of the thickness compensation Δt of low-density foam is derived: In equation (3), θ low θ represents the compressibility in the thickness direction of low-density foam. high δ represents the compressibility in the thickness direction of high-density foam. low δ represents the compressive creep of low-density foam. high This represents the compression creep variable of high-density foam; From equations (2) and (3), we can obtain: At theoretical thickness t high Under certain conditions, θ can be calculated from equation (1) and similar relationships. low and θ high Δt is calculated from equation (4) and used as the design basis for the thickness compensation of low-density foam.

2. The method according to claim 1, characterized in that, The milling of the foam core splicing surface includes: processing the foam surface according to the block foam combination layout and the low-density foam thickness compensation amount, and milling the splicing surface.

3. The method according to claim 1, characterized in that, The spliced ​​foam core and processed component profiles include: The segmented foam cores, whose splicing surfaces have been milled, are then spliced ​​together, and the foam core component surface is then machined.

4. The method according to claim 1, characterized in that, The lower panel laying and curing process includes: receiving the lower panel carbon fiber prepreg and laying and curing the lower panel on the mold.

5. The method according to claim 1, characterized in that, The component installation and curing include: A film is laid on the surface of the cured lower panel, the pre-processed foam core assembly is placed on it, a film is laid on the upper surface of the foam core, the upper panel prepreg is then laid on it, and finally the assembly is packaged into a bag and sent into an autoclave for curing.

6. A foam sandwich structure manufactured according to the method of claim 1, characterized in that, The foam sandwich structure consists of an upper panel, a lower panel, and an internally encased foam core; The upper and lower panels are made of carbon fiber prepreg, which undergoes curing deformation during the curing process, resulting in warping.

7. The foam sandwich structure according to claim 6, characterized in that, The foam core is composed of segments of foam of different densities spliced ​​together. Under the high temperature and high pressure environment during the curing process, the foam will undergo creep deformation. Based on the curing deformation trends of the upper and lower panels, different segmented foam combination layouts are designed to obtain different foam creep deformation trends. The deformation trends of the two cancel each other out, thereby controlling the overall curing deformation of the product.

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