Manufacturing method for recycling carbon fiber composite longitudinal and transverse reinforced structure

Abstract

The invention discloses a manufacturing method of a recycled carbon fiber composite longitudinal and transverse reinforced structure, and relates to the field of composite manufacturing, the manufacturing method comprises the following steps: preparing a longitudinal and transverse reinforced mold with specific size connection points; carrying out humidification treatment on the continuous recycled carbon fiber large tows so as to endow the continuous recycled carbon fiber large tows with shaping capability and bulkiness; the processed tows are sequentially embedded into longitudinal and transverse rib grooves of a mold, and the height of the tows is reduced by about half at each connecting point through poking loosening and broadening operation, so that the height of the whole reinforced structure is equal, and all fibers are kept continuous and uninterrupted; and finally, carrying out resin impregnation and curing. According to the manufacturing method, surface protrusions of the cross points are eliminated, the smooth structure appearance is guaranteed, meanwhile, a complete fiber force transmission path is constructed, the mechanical property and damage tolerance of the longitudinal and transverse reinforced structure are remarkably improved, and the manufacturing method is particularly suitable for manufacturing of light high-strength components in the fields of aerospace, rail transit and the like.

Description

Technical Field

[0001] This invention belongs to the field of composite material manufacturing technology, specifically a method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material. Background Technology

[0002] Longitudinal and transverse stiffened structures are a type of lightweight, high-strength structure widely used in aerospace, shipbuilding, and high-end equipment industries. They typically consist of interwoven, perpendicular "ribs" (longitudinal stiffeners) and "beams" (transverse stiffeners) on a flat or curved panel, forming a mesh-like skeleton. This skeleton is then co-cured or bonded to the skin, achieving extremely high specific strength and specific stiffness with an extremely light weight. In this field, pre-impregnated carbon fiber tape is commonly used as the primary material for manufacturing stiffened structures. This material possesses high strength and high modulus, and the carbon fibers exhibit excellent mechanical properties along their length. They typically have a fixed width and height (i.e., thickness).

[0003] In manufacturing longitudinally and transversely stiffened structures, the process typically involves first laying stiffeners in one direction (e.g., longitudinally), and then vertically laying stiffeners in another direction (e.g., transversely) on top of them. This inevitably creates connection points, or intersections, between the longitudinal and transverse directions. Because carbon fiber strips have a fixed height that cannot be changed on-site, when one strip is laid on top of another, at the intersection, the total height at that point becomes the sum of the heights of both strips. This results in a noticeable "bulge" or "step" in that localized area, affecting the structural shape and surface quality.

[0004] To address the issue of inconsistent heights at the aforementioned intersections, existing technologies commonly employ a "cutting" process. This involves intentionally severing one direction (usually the later-laid direction) of the carbon fiber strip at the intersection, creating an interruption and bypassing the previously laid stiffeners to maintain consistent height across the entire structure. While this method solves the problem of geometric flatness, it severely sacrifices fiber continuity, leading to a significant deterioration in mechanical properties. Composite materials, especially carbon fiber composites, heavily rely on the complete force transmission path of continuous fibers for their high strength and stiffness. Intentionally cutting fibers means creating an artificial weak point at each intersection. Loads (such as tensile, compressive, and shear forces) cannot be effectively transmitted through continuous fibers when passing through these cut points; they must "bypass" through the matrix resin or interlayer interfaces, greatly reducing the overall stiffness and strength of the structure. Fiber cutting directly makes this a potential failure initiation point. Simultaneously, this "cutting" process disrupts the integrity of the longitudinal and transverse stiffening structure and introduces stress concentration points at the ends of the "cut" fibers. Under cyclic or impact loading, microcracks readily initiate and propagate from the fiber ends, ultimately leading to delamination, cracking, or premature failure of the structure. This significantly reduces the structure's fatigue performance and damage tolerance. Furthermore, the "cutting" operation itself increases the steps and complexity of the manufacturing process, making the fabrication of longitudinally and transversely stiffened structures more complicated and difficult to guarantee consistent quality.

[0005] Due to the aforementioned issues, designers of longitudinally and transversely stiffened structures are forced to compromise on performance due to manufacturing limitations, preventing them from fully utilizing the mechanical potential of carbon fiber materials. To meet safety margins, it may be necessary to increase the density or thickness of the stiffeners, leading to an unnecessary increase in structural weight and contradicting the original intention of using composite materials to achieve lightweighting.

[0006] In summary, existing technologies using fixed-section carbon fiber strips to lay up longitudinally and transversely stiffened structures face a dilemma: either accept inconsistent heights at the intersections, affecting the structural shape and surface quality; or cut the fibers to ensure a smooth shape, but at the cost of sacrificing core mechanical properties and structural integrity. This "cutting" process is a long-standing and unresolved technical challenge in this field. Therefore, there is an urgent need for an innovative material form or laying method that can achieve a smooth transition at the intersections of longitudinally and transversely stiffened structures without interrupting fiber continuity, thereby fundamentally improving the manufacturing quality and structural performance of composite materials. Summary of the Invention

[0007] The technical problem to be solved by this invention is: in view of the technical problems existing in the prior art, this invention provides a method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material, which can maintain and maximize the mechanical properties of carbon fiber while ensuring the quality of the structural shape.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0009] A method for manufacturing a longitudinally and transversely reinforced structure made of recycled carbon fiber composite material includes the following steps:

[0010] Step S1, Mold preparation: A pair of matching longitudinally and transversely reinforced female and male molds are used; the female mold is provided with longitudinally and transversely intersecting rib grooves, and the intersection of the rib grooves forms a connection point; the width of the connection point is greater than the width of the rib grooves at non-intersecting points, forming an enlarged area for accommodating fiber expansion;

[0011] Step S2, Fiber preparation: Continuous recycled carbon fiber bundles are used and humidified to give the recycled carbon fiber bundles the ability to be shaped, fluffy and laterally deformable.

[0012] Step S3, Fiber Laying and Spreading:

[0013] S31. The recycled carbon fiber bundle after humidification treatment in step S2 is embedded and filled into the groove corresponding to the female mold along the first direction.

[0014] S32. At each of the connection points in the rib groove in the first direction, the filled recycled carbon fiber bundle is loosened and laterally widened so that it spreads out in the expanded area of ​​the connection point, while reducing the thickness of the bundle at that point and maintaining the continuity of the fiber in the longitudinal direction.

[0015] S33. Repeat steps S31 and S32 to complete the filling of the second direction groove and the widening and thinning operation at the connection point; the second direction intersects with the first direction;

[0016] S34. Repeat the filling and thinning operation until all longitudinal and transverse rib grooves and their connection points are filled, and the height of all ribs and connection points is basically the same.

[0017] Step S4, Resin Impregnation and Curing: Seal the female mold filled with recycled carbon fiber bundles, inject liquid resin to fully impregnate the fibers; then close the male mold, apply pressure to remove excess resin and compact the fibers; finally, cure the resin, and after demolding, obtain a longitudinally and transversely reinforced structure of recycled carbon fiber composite material.

[0018] Preferably, the maximum width of the connection point is designed to be 1.8 to 2.2 times the width of the groove at the non-intersection point; in step S3, the height of the single-layer filament bundle at the connection point is reduced to 45% to 55% of the original height.

[0019] Preferably, in step S2, the recycled carbon fiber bundle is formed by connecting multiple segments of original recycled carbon fiber bundles of finite length end to end; adjacent segments of original bundles are bonded by end overlap, and the overlap area is thinned so that the linear density of the overlap area is lower than the linear density of the bundle body.

[0020] Preferably, in step S2, the humidification medium used in the humidification treatment is one or more of water, epoxy resin diluent, or an aqueous solution containing flame retardant or toughening agent; the humidification amount is controlled within a range that keeps the filament bundles together without causing inter-filament adhesion.

[0021] Preferably, in steps S32 and S33, the loosening and widening operations are completed in situ during the laying process by manual operation, an arc-shaped prying mechanism, a robotic arm with widening function, or automated laying equipment.

[0022] Preferably, in step S4, the resin impregnation is performed using a resin transfer molding process or a vacuum-assisted resin infusion process.

[0023] Preferably, the linear density of the thinned region is reduced by 30% to 50% compared to the main body.

[0024] The present invention provides a method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material, which has the following advantages compared with the prior art:

[0025] (1) The manufacturing method of the longitudinal and transverse stiffened structure of the recycled carbon fiber composite material of the present invention utilizes the good deformation ability of the continuously recycled carbon fiber bundle after humidification treatment, and with the help of a mold with a specific enlarged connection point, the "in-situ widening and thinning" process is used at the intersection of the longitudinal and transverse stiffeners to replace the traditional "fiber cutting" or "direct stacking" process.

[0026] (2) The manufacturing method of the recycled carbon fiber composite longitudinal and transverse stiffened structure of the present invention treats the intersection by “widening and thinning” rather than “cutting”, ensuring that the carbon fiber bundles in all longitudinal and transverse directions are continuous and uninterrupted, constructing a complete load transfer path, maximizing the reinforcing efficiency of carbon fiber, and significantly improving the overall strength, stiffness and fatigue performance of the structure.

[0027] (3) The manufacturing method of the longitudinal and transverse stiffened structure of the recycled carbon fiber composite material of the present invention achieves the high consistency of the entire longitudinal and transverse stiffened structure by precisely controlling the fiber width and thinning at the connection point, and obtains a flat and smooth structural surface.

[0028] (4) The manufacturing method of the longitudinal and transverse stiffened structure of the recycled carbon fiber composite material of the present invention uses recycled carbon fiber large tow as raw material, which reduces the production cost and realizes the recycling of carbon fiber material, which is in line with the concept of green manufacturing.

[0029] (5) The manufacturing method of the longitudinal and transverse stiffened structure of recycled carbon fiber composite material of the present invention liberates the structural design, allowing designers to focus more on the rib layout and topology optimization from the perspective of optimal mechanics, without being constrained by fiber interruption caused by the manufacturing process. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the longitudinal and transverse stiffening of the present invention.

[0031] Figure 2 This is a schematic diagram of the intersection of the longitudinal and transverse stiffening structure of the present invention. Detailed Implementation

[0032] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0033] Example 1

[0034] like Figure 1 As shown, the method for manufacturing longitudinally and transversely stiffened structures of recycled carbon fiber composite materials according to the present invention, applied in the manufacturing of stiffened wall panels for aerospace structural components, includes the following steps:

[0035] Step S1, Mold Preparation: Use aluminum alloy to make longitudinally and transversely reinforced female and male molds. The width of the ribs Ws is designed to be 5mm, the connection point is designed to be circular, and its maximum diameter is designed to be 10mm (i.e., 2 times Ws).

[0036] Step S2, Fiber Preparation: Select 24K pyrolysis recycled carbon fiber tow. Use a low-viscosity epoxy resin diluent for humidification, controlling the tow weight gain to approximately 0.8%, so that it has suitable shaping ability and fluffiness.

[0037] The humidification process of this invention is not merely a simple pretreatment; its core function lies in utilizing the surface tension and lubrication of the liquid to reduce the coefficient of friction between the recycled carbon fiber monofilaments. This allows tens of thousands of monofilaments to smoothly slide and spread out to both sides during the 'loosening and widening' operation in step S3, rather than breaking or tangling. This is the key process window for achieving 'widening without damage'.

[0038] Step S3, Fiber Laying and Spreading:

[0039] S31. Using semi-automatic equipment, guide the humidified continuous carbon fiber bundles and embed them into all longitudinal (X-direction) grooves of the female mold.

[0040] S32. When the equipment laying head reaches each longitudinal connection point, the built-in arc-shaped paddle automatically extends and gently pushes the filament bundle to both sides, so that it is evenly widened in the connection point area with a diameter of 10mm, while the height is reduced from the initial h to about 0.5h.

[0041] S33. After completing the filling and thinning of all longitudinal ribs, use semi-automatic equipment to complete the filling and thinning of all transverse (Y-direction) ribs and connection points. Ensure that all ribs are at the same height.

[0042] Step S4, Resin Impregnation and Curing: Close the female mold and male mold to form an RTM mold. Inject low-viscosity epoxy resin into the mold cavity under vacuum conditions. After the resin has fully impregnated the fibers, apply a pressure of 0.5 MPa and heat to 120°C for curing. After curing, demold to obtain a recycled carbon fiber reinforced wall panel for aerospace applications.

[0043] like Figure 2 As shown, the present invention discloses a method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material, which follows the principle of volume conservation in its design. Since the intersections need to accommodate bidirectionally stacked fibers, to avoid bulges caused by excessive height stacking (i.e., The local height of unidirectional fibers at the intersection must be reduced. According to the principle of constant cross-sectional area ( When the height is halved, the fiber bundle must be broadened in the width direction. Therefore, the 'enlarged area' at the die connection point is a key geometric feature for achieving equal-height layup while maintaining fiber continuity.

[0044] Example 2

[0045] The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to the present invention, applied to the manufacturing of interior partition panels for rail transit, includes the following steps:

[0046] Step S1, Mold Preparation: Simple female and male molds are made using composite materials. The rib width is 8mm, and the maximum width of the connection point is approximately 16mm.

[0047] Step S2, Fiber Preparation: Low-cost wet-process recycled large-tow carbon fibers are selected. Humidification is achieved using an aqueous solution containing a small amount of flame retardant.

[0048] Step S3, Fiber Laying and Spreading:

[0049] S31. The operator manually inserts the humidified continuous carbon fiber bundle into the transverse groove of the female mold.

[0050] S32. At each transverse connection point, the operator, wearing gloves, pinches and widens the filament bundle with his thumb and forefinger, visually inspecting it to reduce its height by about half.

[0051] S33. After completing the horizontal filling, manually fill the vertical rib grooves in the same way and thin out the connection points. Achieve the final design height by alternating two layers of filling.

[0052] Step S4, Resin Impregnation and Curing: A vacuum-assisted resin infusion process is used. A vacuum bag film is laid on the female mold, a vacuum is drawn, and flame-retardant epoxy resin is injected. After resin impregnation, curing is carried out using a stepped temperature increase process from room temperature to 80°C.

[0053] Example 3

[0054] The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to the present invention, applied to the manufacture of industrial robot arm skeletons, includes the following steps:

[0055] Step S1, Mold Preparation: High-precision CNC steel mold is used. Rib width is 3mm, and the maximum width of the connection point is approximately 6mm.

[0056] Step S2, Fiber Preparation: 12K recycled carbon fiber tow is selected to ensure operational precision in small-scale applications. Humidification is achieved using an epoxy resin diluent containing nano-toughening agents.

[0057] Step S3, Fiber Laying and Spreading:

[0058] S31. An automated fiber laying robot is used for laying. The robot path planning system pre-sets the positions of all connection points.

[0059] S32. During the laying process, when the laying head reaches the connection point, the pressure and posture of the laying rollers are adjusted in real time, and the micro-pulling mechanism is used to precisely control the width and thinning height of the filament bundle to the design value (50% of the original height).

[0060] S33. A spiral laying path is adopted to ensure that the filament bundles in the X and Y directions overlap evenly at the connection point.

[0061] Step S4, Resin Impregnation and Curing: High-pressure RTM process is adopted. After mold closing, fast-curing epoxy resin is injected under high pressure and cured for a short time at high temperature to obtain a final component with high fiber volume fraction and high precision.

[0062] The above embodiments are merely preferred examples of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material, characterized in that, Includes the following steps: Step S1, Mold preparation: A pair of matching longitudinally and transversely reinforced female and male molds are used; the female mold is provided with longitudinally and transversely intersecting rib grooves, and the intersection of the rib grooves forms a connection point; the width of the connection point is greater than the width of the rib grooves at non-intersecting points, forming an enlarged area for accommodating fiber expansion; Step S2, Fiber preparation: Continuous recycling of carbon fiber bundles is used, and they are then humidified. Step S3, Fiber Laying and Spreading: S31. The recycled carbon fiber bundles after humidification treatment in step S2 are embedded and filled into the grooves corresponding to the female mold along the first direction. S32. At each of the connection points in the rib groove in the first direction, the filled recycled carbon fiber bundle is loosened and laterally widened so that it spreads out in the expanded area of ​​the connection point, while reducing the thickness of the bundle at that point and maintaining the continuity of the fiber in the longitudinal direction. S33. Repeat steps S31 and S32 to complete the filling of the second direction groove and the widening and thinning operation at the connection point; the second direction intersects with the first direction; S34. Repeat the filling and thinning operation until all longitudinal and transverse rib grooves and their connection points are filled, and the height of all ribs and connection points is basically the same. Step S4, Resin Impregnation and Curing: Seal the female mold filled with recycled carbon fiber bundles, inject liquid resin to fully impregnate the fibers; then close the male mold, apply pressure to remove excess resin and compact the fibers; finally, cure the resin, and after demolding, obtain a longitudinally and transversely reinforced structure of recycled carbon fiber composite material.

2. The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to claim 1, characterized in that, The maximum width of the connection point is 1.8 to 2.2 times the width of the groove at the non-intersection point; in step S3, the height of the single-layer filament bundle at the connection point is reduced to 45% to 55% of the original height.

3. The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to claim 1, characterized in that: In step S2, the recycled carbon fiber bundle is formed by connecting multiple segments of original recycled carbon fiber bundles of finite length end to end; adjacent segments of original bundles are bonded by end overlap, and the overlap area is thinned, with the linear density of the overlap area being lower than that of the main body of the bundle.

4. The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to claim 3, characterized in that, In step S2, the humidification medium used in the humidification treatment is one or more of water, epoxy resin diluent, or an aqueous solution containing flame retardant or toughening agent.

5. The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to claim 1, characterized in that, In steps S32 and S33, the loosening and widening operations are completed in situ during the laying process by manual operation, an arc-shaped prying mechanism, a robotic arm with widening function, or automated laying equipment.

6. The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to claim 1, characterized in that, In step S4, the resin impregnation is performed using a resin transfer molding process or a vacuum-assisted resin infusion process.

7. The method for manufacturing a longitudinally and transversely reinforced structure of recycled carbon fiber composite material according to claim 1, characterized in that, The linear density of the thinned area is reduced by 30% to 50% compared to the main body.

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