Fiber composite material thin-wall component and integrally-formed framework and manufacturing method thereof

Abstract

The invention discloses a fiber composite material thin-wall component and an integrated forming method thereof. The thin-wall component comprises a thin-wall layer formed by natural fiber prepreg and an open type grid forming framework formed by co-curing with the back face of the thin-wall layer. The forming framework is of a single-layer grating structure and is composed of a plurality of ribs, opening units are formed among the ribs, and a through type or communicated type mechanical lock key structure is arranged on the side, attached to the thin-wall layer, of the forming framework. In the co-curing process, resin in the prepreg enters the mechanical lock key structure under the action of heating and pressure and is cured, and a resin built-in integrated structure is formed. Structurally-reinforced grating units or framework modules are arranged in edge areas or connecting areas of the thin-wall components, so that the local compressive collapse resistance and the connecting durability are improved. On the premise that the weight is not obviously increased, the buckling resistance of the thin-wall component and the bearing capacity of a connecting area are improved.

Description

Technical Field

[0001] This invention relates to the field of composite material structure design and manufacturing, specifically to a structural reinforcement technology applicable to thin-walled components made of natural fiber reinforced composite materials. More specifically, it relates to an integrated thin-walled sheet, curved component, and its manufacturing method formed by co-curing an open grid skeleton with natural fiber composite materials. This structure can be applied to lightweight thin-walled products such as vehicle exterior panels, sports equipment housings, furniture parts, and equipment panels. Technical Background

[0002] With the development of lightweight, green manufacturing, and sustainable materials technologies, the application of natural fiber reinforced composite materials in transportation, sports equipment, building components, and home furnishings is gradually increasing. Natural fibers (such as flax, ramie, hemp, and bamboo fiber) have advantages such as low density, high specific stiffness, excellent damping performance, and low environmental impact, and can replace glass fiber composite materials in some applications, meeting the dual requirements of weight reduction and environmental protection.

[0003] However, the application of natural fiber composites in thin-walled structures remains significantly limited. Many vehicle exterior panels, sports equipment shells, furniture and equipment housings are typically thin-walled curved structures, with thicknesses generally between 1 and 3 mm. When such structures are subjected to localized concentrated loads (such as screw fastening, clip clamping, edge connections), out-of-plane pressure, or bending loads, natural fiber composites often exhibit localized collapse, buckling instability, and fatigue damage in the joint areas, making it difficult to meet the stiffness and durability requirements for long-term service.

[0004] Therefore, current technology lacks a three-dimensional molded skeleton structure that can be freely arranged inside or on the back of thin-walled natural fiber composite materials, conform to complex curved surfaces, and significantly improve the local load-bearing capacity of screw connection areas and edge regions. Especially in thin-walled components such as vehicle exterior panels and curved shells, how to improve buckling resistance, local compressive strength, and connection durability through a designable skeleton structure without significantly increasing weight remains a pressing technical problem that needs to be solved. Summary of the Invention

[0005] This invention proposes a designable three-dimensional open grid-type molded skeleton and its co-curing structure with fiber composite materials, enabling thin-walled components to achieve local high stiffness, high durability and reliable connection performance without significant weight increase.

[0006] To achieve the above objectives, this invention provides a thin-walled component made of natural fiber composite material and its integrated molding skeleton.

[0007] The thin-walled component comprises a thermosetting resin or thermoplastic resin laminate reinforced with natural fibers such as flax, ramie, hemp, and bamboo fiber. The thickness is generally 1 to 3 mm, and it can be in the form of a planar, curved, or complex geometric shape.

[0008] The thin-walled member has an open grid-like frame on its back side, the frame having:

[0009] 1) Single-layer truss / grid structure (similar to a steel tower structure);

[0010] 2) Rib thickness: 0.8–3 mm;

[0011] 3) Rib width 10–30 mm;

[0012] 4) It has open units inside (such as triangles, rhombuses, honeycomb shapes, etc.), with an opening rate of 40-80%;

[0013] 5) Three-dimensional bonding and shaping with the inner surface of the thin-walled component.

[0014] The skeleton may be composed of one or more of the following materials:

[0015] 1) High-temperature engineering thermoplastic materials: PEI, PPS, PA11, PA12, PPAs and their carbon fiber / glass fiber reinforced composites;

[0016] 2) Lightweight metal materials: Aluminum alloys (such as 6061 and 6082), obtained by CNC machining or metal forming.

[0017] The skeleton can be manufactured by 3D printing (FDM / SLS), injection molding, or CNC machining.

[0018] To improve the interfacial bonding between the skeleton and the natural fiber layer, the skeleton is provided on at least one side:

[0019] 1) Serrated surface structure;

[0020] 2) Or features of mechanical locking keys such as pits, bumps, micropores, and steps.

[0021] During the curing process, the resin can flow into the aforementioned microstructure to form a mechanical bond, thereby improving its peel and shear strength.

[0022] The bonding surfaces of the skeleton can be selectively coated with a thin resin pre-coating (20–50 μm thick) to improve resin flowability, wettability, and interface quality during curing.

[0023] During the molding process, the natural fiber laminate is placed on the surface of the mold, and the skeleton is positioned on its back. Through processes such as vacuum bag molding, hot pressing, RTM, RFI, or autoclave curing, the two are kept in the same shape as the inner surface of the mold. During the curing process, the resin penetrates the key structure of the skeleton to form an integrated solidified structure.

[0024] In the edge areas, screw connection areas, or snap-fit ​​installation locations of thin-walled components, an open frame made of metal materials such as aluminum alloy is preferably provided, enabling it to:

[0025] 1) Bearing screw preload

[0026] 2) Provides high resistance to localized compressive collapse.

[0027] 3) Improve the fatigue durability and structural stability of the connection.

[0028] 4) This structure can be combined with a thermoplastic material skeleton used in the central area to form a hybrid skeleton system.

[0029] Further improvements to the present invention include, but are not limited to:

[0030] 1) The skeleton can be combined from multiple independent modules, which is suitable for the free arrangement of large-sized curved surface components;

[0031] 2) The unit shape of the skeleton can be optimized into a triangular, inverted trapezoidal, honeycomb, V-shaped, or cross-rib structure according to the load path;

[0032] 3) The dimensions of the skeleton unit can be optimized according to the component thickness, curvature, and local load;

[0033] 4) Different materials can be used for different areas of the skeleton (e.g., PA12-CF for the central area and aluminum alloy for the edge area).

[0034] 5) The skeleton can be automatically aligned with the mold through positioning protrusions or guide grooves;

[0035] 6) The skeleton can be fixed to the natural fiber layer before curing by hot melt contact, positioning clamps or removable supports;

[0036] 7) The thin-walled component may be a vehicle exterior cover, a sports equipment shell, an equipment panel, a furniture component, etc.

[0037] Compared with existing technologies, this invention has the following significant advantages: A freely designable three-dimensional skeleton structure: This solves the problem that textile-based thickened ribs cannot be freely arranged or adapted to complex curved surfaces. Significantly improved local compressive collapse resistance: Especially in connection areas such as screws and clips, it enables thin-walled natural fiber components to achieve metal-level local load-bearing capacity. Improved overall buckling and bending stiffness: The grid skeleton forms a medium-scale structural support, significantly increasing the strength of thin-walled components without significantly increasing weight. Enhanced interfacial bonding: The serrated / locking key structure significantly improves interfacial peel and shear strength, making the skeleton and shell an integral structure. Compatibility with multiple processes and material systems: It can be used with thermoplastic 3D printing, metal CNC, or directly integrated into existing natural fiber composite material processes. Improved durability and stability of screw connections: Using a metal skeleton to reinforce edges and installation areas solves the industry pain point of traditional natural fiber boards being unable to reliably install screws. Achievement of lightweight and sustainable design: The natural fiber composite material bears the main out-of-plane shape and damping performance, while the skeleton bears the local high-load areas, achieving material synergy. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the following embodiments are only for illustrating the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or modifications made to the present invention without departing from the technical concept of the present invention should fall within the scope of protection of the present invention.

[0039] Example 1: Integrated molding structure of natural fiber prepreg thin-walled component and unreinforced thermoplastic open grid skeleton

[0040] This embodiment provides a thin-walled fiber composite material component that is co-cured with natural fiber prepreg and a non-reinforced thermoplastic open grid skeleton.

[0041] The thin-walled composite material layer is composed of a natural fiber reinforced resin matrix, wherein the natural fiber is preferably flax fiber, but ramie fiber, hemp fiber, bamboo fiber or a mixture thereof may also be selected.

[0042] In this embodiment, the natural fiber exists in the form of a prepreg, which is a semi-cured material of natural fiber fabric that has been pre-impregnated with a thermosetting resin system and is in the B stage state.

[0043] The resin matrix used in the prepreg is preferably an epoxy resin system, whose gel temperature and curing characteristics are suitable for vacuum bag pressing, hot pressing, or autoclave molding processes. The prepreg is stored at room temperature or low temperature and is taken out and warmed up before use.

[0044] In this embodiment, according to the thickness requirements of the target component, 2 to 4 layers of natural fiber prepreg are laid on the concave surface of the mold to form a preformed layer. The total thickness of the thin-walled composite material layer after molding is preferably 1.2 to 2.5 mm.

[0045] The thin-walled composite material layer serves as the main shaped outer surface of the component, providing the component's shape, overall continuity, and out-of-plane damping performance.

[0046] The open grid forming skeleton is set on the back of the thin-walled composite material layer. It is a single-layer grid structure consisting of multiple interconnected ribs, with multiple opening units formed between the ribs.

[0047] In this embodiment, the molded skeleton is made of a non-fiber reinforced thermoplastic material, preferably one or more of PA11, PA12, PEI or PPS, and does not contain carbon fiber, glass fiber or other reinforcing fiber fillers.

[0048] The molded skeleton can be manufactured by FDM or SLS additive manufacturing, or it can be obtained by injection molding followed by thermosetting to achieve a three-dimensional shape consistent with the curvature of the thin-walled component.

[0049] In this embodiment:

[0050] 1) The rib thickness is 1.2–2.5 mm;

[0051] 2) The rib width is 12–25 mm;

[0052] 3) The opening unit is triangular, rhomboid, or honeycomb-shaped;

[0053] 4) The feature size of the unit is 15–40 mm;

[0054] 5) The overall open area ratio is 50-80%;

[0055] The molded skeleton covers 30-80% of the back of the thin-walled composite material, and the coverage ratio can be designed and adjusted according to the local stiffness and load-bearing requirements of the component.

[0056] To enhance the interfacial bonding strength between the molded skeleton and the thin-walled composite material layer, the molded skeleton is provided with a mechanical locking key structure on the side that is in contact with the thin-walled composite material layer.

[0057] In this embodiment, the mechanical locking key structure includes at least one of the following structural forms, and preferably a combination of multiple structures:

[0058] 1) The serrated structure has a serration height of 0.3–0.8 mm and a serration spacing of 1.5–3.5 mm, and is set along the length of the rib;

[0059] 2) Groove structure, with a groove depth of 0.2–0.6 mm and a groove width of 0.4–1.2 mm;

[0060] 3) The pit structure has a diameter of 0.4 to 1.5 mm and a depth of 0.2 to 0.8 mm.

[0061] All of the above-mentioned mechanical interlocking structures are oriented toward the opening of the thin-walled composite material layer, so that the resin in the prepreg flows under heating and pressure and enters the interior of the interlocking structure, forming a stable mechanical interlocking interface after curing.

[0062] To improve the reliability of the interfacial bonding between the unreinforced thermoplastic skeleton and the prepreg resin, the bonding surface of the molded skeleton is treated before molding.

[0063] The surface treatment method may be selected from one or a combination of the following:

[0064] 1) Plasma treatment, with a treatment power of 200–600 W and a treatment time of 20–60 s;

[0065] 2) Sandblasting roughening treatment, with a sandblasting particle size of 120-220 mesh and a sandblasting pressure of 0.2-0.5 MPa;

[0066] A resin pre-coating layer is applied to the bonding surface of the skeleton. The pre-coating layer is the same as or compatible with the resin system used in the prepreg. The pre-coating layer has a thickness of 20-50 μm and is preheated at 40-60 °C for 10-20 min to make it semi-molten or semi-cured.

[0067] The pre-coating layer flows and cures together with the resin in the prepreg during the molding process, thereby improving interfacial wettability and reducing interfacial porosity.

[0068] In this embodiment, the manufacturing method of the thin-walled component includes the following steps:

[0069] 1) After the natural fiber prepreg is warmed at room temperature, it is laid on the concave surface of the mold to form a preformed layer;

[0070] 2) Place the open grid molding skeleton on the back of the preformed layer;

[0071] 3) Initial alignment is achieved by using the positioning protrusions on the skeleton to align with the mold positioning structure, or by setting several temporary spot bonding structures between the skeleton and the preformed layer to prevent the skeleton from slipping during vacuuming or pressurization.

[0072] 4) Vacuum bag sealing of the layered structure;

[0073] 5) Evacuate to -0.085 to -0.095 MPa and maintain for 10 to 20 minutes;

[0074] 6) Co-curing molding is carried out under heating conditions, so that the resin in the prepreg flows under vacuum pressure difference and / or external pressure and enters the mechanical key structure;

[0075] 7) According to the curing regime of the prepreg resin system, cure at 80-130 ℃ for 1-3 h (hot pressing or autoclave process can be used if necessary).

[0076] 8) After curing, demold and trim the edges of the component.

[0077] In the thin-walled component obtained through the above steps, the open grid molding skeleton and the natural fiber prepreg thin-walled layer form an inseparable integrated solid structure.

[0078] Example 2: Metal skeleton module reinforcement structure for the connection area and edge area of ​​thin-walled components

[0079] In this embodiment, to improve the local load-bearing capacity of thin-walled components in screw connection areas, edge flange areas, or snap-fit ​​installation areas, metal-formed skeleton modules are provided in the aforementioned areas.

[0080] The metal skeleton module is made of aluminum alloy, preferably 6061 or 6082 aluminum alloy. The thickness of the metal skeleton module is 1.0 to 1.8 mm, and its structural form can be a strip structure, an Ω-shaped structure, or a partially ring structure.

[0081] The metal skeleton module has a micro-step structure or groove structure processed on the side that is bonded to the thin-walled composite material. The step height is 0.2 to 0.6 mm and the step width is 0.5 to 2.0 mm, which is used to form a resin embedded structure during the curing process.

[0082] The metal skeleton module is preferably subjected to sandblasting and chemical forming or anodizing treatment before molding to improve the reliability of interface bonding.

[0083] The metal skeleton module and the thin-walled composite material layer form an integrated structure during the co-curing process, which significantly improves the resistance to compressive collapse and the durability of the connection area.

[0084] Example 3: Modular open grid frame structure

[0085] In this embodiment, the open grid forming skeleton is composed of multiple independent skeleton modules, each module having a size of 50 to 150 mm.

[0086] The skeleton modules are positioned together using plug-in structures, alignment slot structures, or temporary fixing structures, forming a continuous structure during co-curing. In areas with significant changes in component curvature, flexible connecting sections are provided at the edges of the skeleton modules, with ribs that are 20-50% thinner than the main ribs, or release slot structures are provided to adapt to local curvature changes.

[0087] Example 4: Comparative Examples and Performance Verification Description

[0088] To verify the technical effectiveness of the present invention, the following comparative embodiments are provided:

[0089] 1) Comparative Group 1: Thin-walled components of natural fiber composite materials without a skeleton;

[0090] 2) Comparison Group 2: Components with a planar frame but without a mechanical locking key structure;

[0091] 3) Implementation Group 1: Install a non-reinforced thermoplastic grid skeleton with a mechanical locking key structure;

[0092] 4) Implementation Group Two: Based on Implementation Group One, a resin pre-coating layer is added;

[0093] 5) Implementation Group 3: Based on Implementation Group 2, a metal frame module is set in the connection area.

[0094] By comparing the components in different groups through local indentation tests, out-of-plane bending tests, and interface peeling or shearing tests in the screw connection area, it can be verified that the present invention can significantly improve the local compressive strength, buckling resistance, and interface bonding reliability of thin-walled components without significantly increasing the weight.

[0095] The above description is only a preferred embodiment of the present invention. Various modifications or substitutions made by those skilled in the art without departing from the technical concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A method of integrated forming of a thin-walled fiber composite component, characterized in that The method comprises the following steps: laying at least two layers of natural fiber prepreg on a mold cavity to form a thin-walled preform layer with a thickness of 1.2-2.5 mm; setting a pre-prepared open single-layer grid forming framework on the back of the thin-walled preform layer, the forming framework being composed of a plurality of ribs, and open cells being formed between the ribs; the forming framework being provided with a communicating mechanical lock structure on the side adhering to the thin-walled preform layer, the communicating mechanical lock structure comprising a sawtooth structure arranged along the length direction of the ribs, and the sawtooth structure being communicated with each other through continuous grooves and / or pit structures, or being communicated with through holes penetrating through the thickness direction of the ribs; under the action of vacuum pressure difference and / or external pressure, the forming framework is adhered to the thin-walled preform layer and three-dimensionally adhered to the mold cavity; the laying structure is co-cured to make the resin in the prepreg flow under heating conditions and enter the communicating mechanical lock structure, and after curing, a continuously distributed resin embedded structure is formed along the rib direction, and / or a resin riveting structure is formed on both sides of the through hole, so that the forming framework and the thin-walled layer form an inseparable integrated structure; wherein, in the screw connection area, edge area or connection area of the thin-walled member, a structured reinforced grid cell or framework module is arranged, and an embedded connection is formed with the thin-walled preform layer in the same co-curing process to improve the local resistance to collapse and connection durability.

2. The method of claim 1, wherein The communicating mechanical lock structure forms a continuously distributed communication network along the length direction of each rib, so that the cured resin forms a continuous and uninterrupted resin embedded band in the rib direction.

3. The integrated molding method according to claim 1 or 2, characterized by, When the communicating mechanical lock structure comprises through holes penetrating through the thickness direction of the ribs, the cured resin forms a resin rivet joint on both sides of the through hole, thereby forming a double-sided mechanical riveting structure on both sides of the rib.

4. The integrated molding method according to any one of claims 1 to 3, characterized by, The height of the sawtooth structure is 0.3-0.8 mm, the depth of the continuous groove is 0.2-0.6 mm, and the sawtooth structure and the continuous groove form a micro-scale mechanical lock network on the rib adhering surface.

5. The integrated molding method according to any one of claims 1 to 4, characterized by, The open grid forming framework is made of a thermoplastic material without fiber reinforced filler, and the thermoplastic material is selected from PA11, PA12, PEI or PPS.

6. The integrated molding method according to any one of claims 1 to 5, characterized by, A metal framework module is arranged in the screw connection area or edge area of the thin-walled member, the metal framework module being provided with a micro-step structure or groove type mechanical lock structure on the side adhering to the thin-walled preform layer, and forming a resin embedded connection with the thin-walled preform layer in the co-curing process.

7. The integrated molding method according to any one of claims 1 to 6, characterized by, The open grid forming framework is composed of a plurality of grid modules, adjacent grid modules being positioned through plug-in structures or alignment structures, and the local curvature change of the thin-walled member being adapted through rib thinning or release grooves in the curvature change area.