Foam sandwich structure and manufacturing method thereof

Abstract

The invention provides a foam sandwich structure and a manufacturing method thereof.The composite material foam sandwich structure is composed of an upper panel, a lower panel and a foam core wrapped inside, different block foam combination layout modes are designed according to the curing deformation trend of the upper panel and the lower panel, and different foam creep deformation trends are obtained; the deformation trends of the two are counteracted, so that the curing deformation of the whole product is controlled; a mixed foam compression creep compensation amount design theory is established, the large compression creep amount of low-density foam is counteracted, and it is guaranteed that the surface of a product is smooth and free of pits; the overall performance of the foam core assembly can be improved, the product has the characteristics of light weight and high strength, the assembly precision and efficiency can be improved by reducing curing deformation, and meanwhile the product is light in weight.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material manufacturing, and in particular to a design and manufacturing method for controlling the curing deformation of a foam sandwich structure. Background Art

[0002] With the rapid development of the aerospace field, composite products are being used more and more widely, and the requirements for the molding accuracy and lightweight of composite products are becoming higher and higher. Composite foam sandwich structure is a common lightweight structure. The sandwich material used is a cross-linked foam material with a high closed-cell rate, low moisture absorption and isotropy. However, a single foam core cannot meet the requirements of load-bearing structures. It usually needs to be glued together with carbon fiber materials to form a composite foam sandwich structure to meet the needs of load-bearing parts.

[0003] The traditional single-component low-density foam sandwich structure has serious deformation problems after curing, which affects the subsequent assembly requirements; and although the single-component high-density foam sandwich structure has improved in deformation, the product weight is too large to meet the development needs of lightweight parts; using mixed-density foam cores for splicing can overcome the shortcomings of single-component foam cores, but after molding, depressions will appear at the joints of the divided foam cores on the surface of the component. 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, the present application provides a method for manufacturing a foam sandwich structure, the method comprising:

[0006] Formulate foam core blocks; wherein the foam core blocks include block foams of different densities;

[0007] Milling foam core joints;

[0008] Splicing foam cores and machining component profiles;

[0009] Lower panel laying and curing;

[0010] Component laying and curing.

[0011] Preferably, the foam core blocks are formulated, including:

[0012] According to the product structure characteristics, the foam core is divided into block layout structures, and then according to 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 low-density foam thickness compensation is calculated.

[0013] Preferably, the milled foam core joint surface comprises:

[0014] According to the block foam combination layout and the low-density foam thickness compensation, the foam is profiled and the joint surface is milled.

[0015] Preferably, the spliced ​​foam core and processed component profile include:

[0016] The foam core blocks with completed joint surface milling are spliced ​​together, and after the splicing is completed, the foam core component surface is processed.

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

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

[0019] Preferably, the assembly laying and curing includes:

[0020] Lay adhesive film on the surface of the cured lower panel, place the processed foam core assembly, lay adhesive film on the upper surface of the foam core, and then lay the upper panel prepreg. Finally, package the assembly into bags and send it into an autoclave for curing and molding.

[0021] In a second aspect, the present application also provides a foam sandwich structure, which is composed of an upper panel, a lower panel and an internally wrapped foam core;

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

[0023] Preferably, the foam core is composed of block foams of different densities. Under the high temperature and high pressure environment during the curing process, the foam will produce creep deformation. According to the curing deformation trends of the upper and lower panels, different block foam combination layouts are designed to obtain different foam creep deformation trends. The deformation trends of the two offset each other, thereby achieving control of the overall curing deformation of the product.

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

[0025] 1. Establish the design theory of the compression creep compensation of mixed foam. This design theory reveals the law of compression creep of foam core. According to 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 formulating a block foam combination layout, the weight reduction effect of the low-density foam core and the high strength and high stiffness of the high-density foam core can be fully combined to improve the overall performance of the foam core assembly, making the product both light and strong;

[0027] 3. Compared with the single-component foam sandwich structure, the foam sandwich structure prepared with mixed density foam can effectively control the curing deformation of the composite foam sandwich structure and improve the assembly accuracy and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of the deformation control principle provided in an embodiment of the present application;

[0029] Figure 2 is a schematic diagram of the low-density foam thickness compensation amount provided in an embodiment of the present application;

[0030] Figure 3 It is a schematic diagram of the composite foam sandwich structure provided in the embodiment of the present application;

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

[0032] Figure 5 This is a processing flow chart of the composite foam sandwich structure provided in the embodiment of the present application

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

[0034] Wherein: 1 upper panel; 2 lower panel; 3 circumferential annular 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; It is the measurement point for product curing deformation. DETAILED DESCRIPTION

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

[0036] The composite foam sandwich structure provided by the present application consists of an upper panel, a lower panel and an internally wrapped foam core.

[0037] Among them, the upper and lower panels are laminated panels made of carbon fiber prepreg. Due to the mismatch in thermal expansion coefficients between the prepreg and the mold, during the curing process, the prepreg close to the mold surface is in a tensile state in the fiber direction, generating tensile stress. After the product is demolded, the tensile stress is released, resulting in curing deformation and warping of the panel. In order to control the curing deformation and ensure the lightweight of the product, a combination layout of block foams of different densities is designed according to the curing deformation trend of the upper and lower panels and the geometric structure of the product, including but not limited to "U"-shaped nesting, S-shaped, and triangle. Combinations of different shapes can produce different creep trends. The creep deformation trend generated by the foam offsets the curing deformation trend of the panel, thereby controlling the overall deformation of the product.

[0038] Among them, the high-density foam has a small core cell content and high structural strength, and its anti-compression creep performance is strong; while the low-density foam has a large core cell content and weak structural strength, and its anti-compression creep performance is weak. Under the condition of equal thickness, the compression creep of low-density foam is greater than that of high-density foam, showing that the high-density foam area is higher than the low-density foam area, resulting in concave deformation of the upper panel at the joints of the foam core blocks.

[0039] Among them, it was found through experiments that under the high temperature and high pressure environment during the autoclave curing process, the foam core produces 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 conditions, there is a fitting formula for the compression rate θ and thickness t of the foam core with different densities in the thickness direction:

[0041]

[0042] The superscript of the compression rate θ represents the curing pressure P, unit: MPa; the subscript of the compression rate θ represents the foam core density ρ, unit: kg / m 3 ; Foam core thickness t, unit: mm. Here, the analysis is performed with a curing pressure of 0.25 MPa. Similar relationships exist under other curing pressure conditions.

[0043] Among them, in order to ensure the smooth surface of the foam component after compression creep, the low-density foam thickness compensation is designed to offset the large compression creep of the low-density foam. The expression is:

[0044] Δt=t low -t high (2)

[0045] Where Δt represents the low-density foam thickness compensation, t low Indicates the thickness of low-density foam, t high Indicates the thickness of high-density foam, t highAlso used as the theoretical design thickness.

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

[0047]

[0048] Among them, θ low represents the compression rate of low-density foam in the thickness direction, θ high Indicates the compression rate of high-density foam in the thickness direction, δ low represents the amount of compression creep of low-density foam, δ high Represents the amount of compression creep of high-density foam.

[0049] From formula (2) and formula (3), we can get:

[0050]

[0051] In the theoretical thickness t high Under certain conditions, θ can be calculated by formula (1) and similar formulas. low and θ high , Δt can be calculated by formula (4) as the design basis for the low-density foam thickness compensation.

[0052] In another embodiment of the present application, a method for manufacturing a composite foam sandwich structure is provided, comprising the following steps:

[0053] 1. Formulate a foam core block plan: divide the foam core block layout structure according to the product structure characteristics, and then determine the foam density combination of different blocks according to the required foam creep deformation trend, determine the theoretical thickness of the foam core, and calculate the low-density foam thickness compensation;

[0054] 2. Milling the splicing surface of the foam core: According to the combination layout of the block foam and the thickness compensation of the low-density foam, the foam is profiled and the splicing surface is milled;

[0055] 3. Splice the foam core and process the component surface: Splice the foam core blocks that have completed the milling of the splicing surface, and then process the foam core component surface;

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

[0057] 5. Component laying and curing: Lay the adhesive film on the cured lower panel surface, place the processed foam core component, lay the adhesive film on the upper surface of the foam core, and then lay the upper panel prepreg. Finally, package the assembly into bags and send it into the autoclave for curing and molding.

[0058] In other embodiments of the present application, the present application provides a foam sandwich structure and a manufacturing method thereof. The composite foam sandwich structure consists of an upper panel, a lower panel and an internally coated foam core. According to the curing deformation trends of the upper and lower panels, different block foam combination layouts are designed to obtain different foam creep deformation trends. The deformation trends of the two offset each other, thereby achieving control of the overall curing deformation of the product; a design theory of mixed foam compression creep compensation is established to offset the larger compression creep of low-density foam and ensure that the product surface is smooth and without depressions; the invention can improve the overall performance of the foam core assembly, so that the product has the characteristics of light weight and high strength, and by reducing the curing deformation, it can improve the assembly accuracy and efficiency, while achieving product lightweighting.

[0059] Among them, the core cell content in high-density foam is small, the structural strength is high, and its anti-compression creep performance is strong; while the core cell content in low-density foam is large, the structural strength is weak, and its anti-compression creep performance is weak. Under the condition of equal thickness, the compression creep of low-density foam is greater than that of high-density foam, showing that the high-density foam area is higher than the low-density foam area, resulting in concave deformation of the upper panel at the joints of the foam core blocks. By designing the low-density foam thickness compensation, the larger compression creep of low-density foam can be offset.

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

[0061]

[0062] The superscript of the compression rate θ represents the curing pressure P, unit: MPa; the subscript of the compression rate θ represents the foam core density ρ, unit: kg / m 3 ; Foam core thickness t, unit: mm. Here, the analysis is performed with a curing pressure of 0.25 MPa. Similar relationships exist under other curing pressure conditions.

[0063] Among them, the expression of low-density foam thickness compensation is:

[0064] Δt=t low -t high (2)

[0065] Where Δt represents the low-density foam thickness compensation, t low Indicates the thickness of low-density foam, t high Indicates the thickness of high-density foam, t high Also used as the theoretical design thickness.

[0066] Among them, the existence relationship of the low-density foam thickness compensation amount Δt is:

[0067]

[0068] Among them, θ low represents the compression rate of low-density foam in the thickness direction, θ high Indicates the compression rate of high-density foam in the thickness direction, δ low represents the compression creep of low-density foam, δ high Represents the amount of compression creep of high-density foam.

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

[0070]

[0071] In the theoretical thickness t high Under certain conditions, θ can be calculated by formula (1) and similar formulas. low and θ high , Δt can be calculated by formula (4) as the design basis for the low-density foam thickness compensation.

[0072] In other embodiments of this application, please refer to Figure 1-Figure 6 , the invention is further described in detail.

[0073] Three composite foam sandwich structures with a size of 2m×1.5m were manufactured. The foam core material was polymethacrylimide closed-cell rigid foam plastic (PMI foam plastic), and the high-density foam core was 75kg / m 3 , low-density foam core is 52kg / m 3 The theoretical thickness of both foam cores is 30mm, and the curing pressure is 0.25MPa. T800 grade carbon fiber prepreg and J-375 adhesive film are selected. The density specifications of the three products are 52kg / m 3 , circumferential ring 75kg / m 3 Internal nesting 52kg / m 3 , 75kg / m 3 , the manufacturing process is exactly the same.

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

[0075] 1. Formulate a foam core block plan: According to the rectangular shape of the product, the foam core is divided into a "return" type nested block layout, and a 30mm thick 75kg / m 3 and 52kg / m 3 Two density PMI foam cores, the volume proportion of the two density foam cores is 15% and 85% respectively, and the 75kg / m 3 The foam core is divided into four parts, 52kg / m 3 The foam core is a piece, such as Figure 5As shown. Based on the theoretical thickness of 30mm and the curing pressure of 0.25MPa, substitute the compression rate calculation formula:

[0076]

[0077] get:

[0078]

[0079] Substitute into the low-density foam compensation calculation formula:

[0080]

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

[0082] 2. Milling foam core splicing surface: According to the block foam combination layout and 52kg / m 3 Foam thickness compensation, for 75kg / m 3 and 52kg / m 3 Two density foam cores are profiled and the joint surfaces are milled.

[0083] 3. Splice the foam core and process the component surface: Splice the foam core according to the foam core block plan, place J-375 film on the splicing surface, package and bag, and then send it into the autoclave for curing. The curing conditions are as follows: vacuum the whole process, the curing temperature is 180℃±5℃, and the curing time is 150min. After curing, use a milling tool to complete the foam core component surface processing.

[0084] 4. Lay the carbon fiber prepreg of the lower panel layer by layer on the mold, package it into bags and send it into the 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 lower panel, lay J-375 film on its surface, position the processed foam core assembly on the lower panel surface, lay J-375 film on the upper surface of the foam core, and then lay the upper panel prepreg layer by layer, and finally package the assembly into a bag and send it into the 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 the curing deformation of the mold surface. Figure 6 shown.

[0087] Comparison of the deformation and weight of three composite foam sandwich structure products, the density specifications of the three are 52kg / m3 , circumferential ring 75kg / m 3 Internal nesting 52kg / m 3 , 75kg / m 3 The maximum deformation of the products are 2.35mm, 1.45mm, and 1.05mm, and the weights are 15.73kg, 16.03kg, and 16.94kg, respectively.

[0088] From the above data, it can be seen that the circumferential ring 75kg / m 3 Nesting 52kg / m 3 The mixed density foam sandwich structure can significantly reduce the curing deformation of the parts while achieving lightweight, which proves the feasibility of the present invention.

Claims

1. A method for manufacturing a foam sandwich structure, characterized in that: The method comprises: Formulate foam core blocks; wherein the foam core blocks include block foams of different densities; Milling foam core joints; Splicing foam cores and machining component profiles; Lower panel laying and curing; Component laying and curing.

2. The method according to claim 1, characterized in that The foam core blocks are formulated, including: According to the product structure characteristics, the foam core is divided into block layout structures, and then according to 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 low-density foam thickness compensation is calculated.

3. The method according to claim 1, characterized in that: The milled foam core joint surface comprises: According to the block foam combination layout and the low-density foam thickness compensation, the foam is profiled and the joint surface is milled.

4. The method according to claim 1, characterized in that The spliced ​​foam core and processed component profile include: The foam core blocks with completed joint surface milling are spliced ​​together, and after the splicing is completed, the foam core component surface is processed.

5. The method according to claim 1, characterized in that The lower panel paving and curing includes: Receive the carbon fiber prepreg for the lower panel and complete the laying and curing of the lower panel on the mold.

6. The method according to claim 1, characterized in that The component laying and curing includes: Lay adhesive film on the surface of the cured lower panel, place the processed foam core assembly, lay adhesive film on the upper surface of the foam core, and then lay the upper panel prepreg. Finally, package the assembly into bags and send it into an autoclave for curing and molding.

7. A foam sandwich structure, characterized in that: The foam sandwich structure is composed of an upper panel, a lower panel and an internally wrapped foam core; Among them, the upper and lower panels are made of carbon fiber prepreg, which undergoes curing deformation and warping during the curing process.

8. The foam sandwich structure according to claim 7, characterized in that: The foam core is composed of block foams of different densities. Under the high temperature and high pressure environment during the curing process, the foam will produce creep deformation. According to the curing deformation trends of the upper and lower panels, different block foam combination layouts are designed to obtain different foam creep deformation trends. The deformation trends of the two offset each other, thereby achieving control of the overall curing deformation of the product.

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