A method of co-curing a composite structure with a stringer

Abstract

This invention relates to a method for co-curing and molding a composite material structure with longitudinal beams, comprising: designing a molding mold according to the molding contour of the structure and opening a longitudinal beam conformal molding groove on the mold wall to match the outer contour of the longitudinal beam; splitting the molding mold into multiple segmented molds along the axial direction of the structure; designing a flexible expandable core mold according to the inner contour of the longitudinal beam of the structure; performing an integral interwoven layup of the longitudinal beam and inner skin and an outer skin layup based on the molding mold and the flexible expandable core mold; wrapping the longitudinal beam with the outer skin and inner skin to form an integral sandwich preform; covering the preform and vacuum-pressurizing; sending the covered preform into an autoclave and performing integrated co-curing and molding using stepped heating and graded pressurization to obtain a preformed structural component; demolding and trimming the preformed structural component to obtain the final finished structural product. This solution fully and effectively realizes the integrated molding of the longitudinal beam structure and the main structural body.

Description

Technical Field

[0001] This invention relates to the field of composite material mold forming technology, and in particular to a method for co-curing and forming a composite material structure and a longitudinal beam. Background Technology

[0002] In the aerospace and special equipment fields, irregularly shaped curved composite material structures (such as cabins) are widely used due to their unique performance advantages, such as a good strength-to-weight ratio and excellent corrosion resistance. Currently, the mainstream manufacturing process in this field is a combination of split molding and subsequent bonding / riveting processes. The specific steps are as follows: First, the irregularly shaped cabin shell is molded separately by hot pressing and curing; second, the composite material longitudinal beams are also cured and molded separately; finally, the molded cabin and longitudinal beams are assembled by bonding or riveting.

[0003] In the industry, the manufacturing of composite material irregular cabins and longitudinal beams generally follows a combination process of separate preparation and secondary bonding / mechanical connection. That is, the irregular cabin and independent longitudinal beam corner pieces are first laid up and cured separately. After both are completely cured and demolded, they are then combined and connected by structural adhesive bonding, bolt riveting or mechanical assembly of fasteners to form a complete cabin structure.

[0004] However, this existing process solution has many insurmountable technical defects and engineering pain points.

[0005] Firstly, the process of modular molding followed by secondary assembly results in poor overall structural integrity. A distinct interface layer exists between the hull and the longitudinal beams, leading to low interlaminar shear strength and peel strength. Under load-bearing conditions, this interface is highly susceptible to debonding, cracking, and delamination failure, significantly reducing the overall structural load-bearing reliability and service life. For example, in the aerospace field, spacecraft experience enormous external forces during high-speed flight; failure of this interface could damage the hull structure and jeopardize flight safety.

[0006] Secondly, mechanical connections require numerous assembly holes. This not only disrupts the continuity of the composite fiber, causing stress concentration and weakening the structure's mechanical properties, but also adds many processes such as drilling, reinforcement, and assembly. These additional processes complicate the manufacturing process and significantly extend the production cycle. In defense equipment manufacturing, a prolonged production cycle can affect the timely supply of equipment, potentially impacting national defense security.

[0007] Thirdly, secondary bonding places extremely high demands on surface treatment, adhesive layer thickness, curing environment, and assembly position accuracy. Due to significant human factors and process fluctuations, product consistency is poor, resulting in a high scrap rate. This poses a serious obstacle to the high-precision, high-reliability requirements of mass production. For example, in the manufacturing of special equipment, poor consistency in mass-produced products can lead to inconsistent equipment performance, affecting overall combat effectiveness.

[0008] Fourth, modular molding requires the design of two separate molding molds, which not only increases the cost of the molds but also occupies a significant amount of space. Furthermore, the subsequent assembly and testing tooling is extremely complex, keeping manufacturing costs consistently high. For cost-sensitive fields such as aerospace and defense, these high manufacturing costs can limit product development and production scale.

[0009] Fifth, for irregularly shaped cabin structures with large curvature, variable cross-sections, and irregular curved surfaces, controlling the shape matching between the shell and longitudinal beams is extremely difficult. After split molding, alignment deviations and excessive fitting gaps are very likely to occur, requiring extensive subsequent repair and polishing work. This severely restricts the dimensional and shape accuracy of the equipment cabin, affecting the quality and performance of the product. For example, in some aerospace missions with extremely high requirements for cabin shape accuracy, this accuracy problem may lead to the cabin not fitting perfectly with other components, affecting the performance of the entire spacecraft.

[0010] It is evident that existing split-molding and subsequent bonding / riveting processes have numerous drawbacks in manufacturing irregularly shaped curved composite material cabins for aerospace and special equipment, failing to meet current manufacturing demands for high performance, high reliability, low cost, and high efficiency. Therefore, there is an urgent need to develop a new manufacturing process to address the problems of existing processes and drive technological progress in this field. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for co-curing and molding composite material structures and longitudinal beams.

[0012] To achieve the above-mentioned objectives, this invention provides a method for co-curing and molding a composite material structure with a longitudinal beam, comprising the following steps: S1. Design a forming mold for the structural forming contour and open a longitudinal beam conformal forming groove on the mold wall to match the outer contour of the longitudinal beam. The forming mold is divided into multiple segmented molds along the axial direction of the structural body. S2. Design a flexible, expandable core mold based on the inner contour of the longitudinal beam of the structure, which is used to form the laying space of the longitudinal beam between the core mold and the conformal groove of the longitudinal beam. S3. Based on the forming mold and the flexible expandable core mold, the longitudinal beam and inner skin are interwoven and the outer skin is laid up, and the longitudinal beam is wrapped with the outer skin and the inner skin to form an integral sandwich integrated precast blank; S4. Cover the precast blank and apply vacuum pressure; S5. The coated blank is sent into an autoclave and co-cured using stepped heating and graded pressurization to obtain a structural blank. S6. After the structural blank is cooled, it is demolded and then trimmed to obtain the final structural product.

[0013] According to one aspect of the present invention, step S3, which involves integrally interwoven lay-up of the longitudinal beam and inner skin and lay-up of the outer skin based on the molding die and the flexible expandable core mold, includes: S31. A flexible expandable core mold is bonded to the non-paving area within the conformal groove of the longitudinal beam to create the padding space for the longitudinal beam. S32. Pre-cut longitudinal beam prepreg and inner skin prepreg are stacked and laid in the laying space in an alternating stacking manner to a preset number of layers; wherein, the area of ​​the inner skin prepreg is larger than the area of ​​the longitudinal beam prepreg, and part of the inner skin prepreg is laid on the outer surface of the segmented mold. S33. All the ply-laid segmented molds are joined together to form a complete molding mold, and an outer skin is laid on the surface of the molding mold to wrap the longitudinal beams and inner skin to form a precast blank.

[0014] According to one aspect of the present invention, the longitudinal beam comprises: a longitudinal beam body and a longitudinal beam bend; The main body of the longitudinal beam is a plate-like structure with a length greater than its width; The bending portion of the longitudinal beam is located at both ends of the longitudinal beam body along its length, or at both ends of the longitudinal beam body along its length and at one end of the longitudinal beam body along its width.

[0015] According to one aspect of the present invention, in step S32, in the step of stacking and laying pre-cut longitudinal beam prepreg and inner skin prepreg in the laying space to a predetermined number of layers in an alternating stacking manner, the shape and size of the longitudinal beam prepreg are consistent with the longitudinal beam body; wherein, from the inner side to the outer side of the longitudinal beam, multiple layers of longitudinal beam prepreg and single layers of inner skin prepreg are laid alternately to form the longitudinal beam body; The inner skin prepreg is bent at the edge of the longitudinal beam prepreg, and the bent portions of the multiple inner skin prepregs are laid together to form the longitudinal beam bending section.

[0016] According to one aspect of the invention, in the process of alternately laying multi-layer longitudinal beam prepreg and single-layer inner skin prepreg in the direction from the inner side to the outer side of the longitudinal beam, the number of layers of longitudinal beam prepreg closer to the inner side of the longitudinal beam is greater than the number of layers of longitudinal beam prepreg closer to the outer side of the longitudinal beam.

[0017] According to one aspect of the invention, at the junction of the outer surface of the segmented mold and the conformal forming groove of the longitudinal beam, at least a portion of the inner skin prepreg is laid side by side in sequence by cutting it into multiple narrow strips of prepreg. If two adjacent layers of inner skin prepreg are laid side by side in sequence by cutting them into multiple narrow strips of prepreg at the junction, the narrow strips of prepreg in the two adjacent layers of inner skin prepreg are stacked in a staggered manner.

[0018] According to one aspect of the present invention, in step S3, in the step of integrally interwoven layup of longitudinal beams and inner skin and layup of outer skin based on molding die and flexible expandable core mold, low-temperature pre-compaction and degassing are performed once every 3 to 5 layers of prepreg to remove interlayer air bubbles.

[0019] According to one aspect of the present invention, in step S3, in the step of integrally interwoven lay-up of longitudinal beams and inner skin and lay-up of outer skin based on molding die and flexible expandable core mold, the outer skin prepreg, longitudinal beam prepreg, and inner skin prepreg are all made of carbon fiber unidirectional prepreg or fabric prepreg, and their matrix resin is a high-temperature resistant bismaleimide resin system.

[0020] According to one aspect of the present invention, step S3, the step of covering the preform and vacuum-pressuring, includes: Polytetrafluoroethylene release cloth, release film, breathable felt, flow guide net, and vacuum bag film are sequentially laid on the outer surface of the preform. The edges of the vacuum bag membrane are sealed, and a vacuum is drawn to -0.095MPa to -0.1MPa. Pressure testing is performed to ensure no leakage, guaranteeing uniform and pressure application to the irregular curved surfaces of the structure.

[0021] According to one aspect of the present invention, the carbon fiber unidirectional prepreg or fabric prepreg is T700 / T800 carbon fiber unidirectional prepreg and / or fabric prepreg; The width of the narrow strip prepreg is 10 mm.

[0022] According to one aspect of the present invention, this approach achieves continuous integral layup of the main body and axial longitudinal beam fibers in a composite material structure, with no interface breaks. This not only effectively ensures the overall structural strength and reliability but also fully realizes the effect of continuous force transmission, resulting in superior mechanical properties.

[0023] According to one aspect of the present invention, the longitudinal beams are integrally laid with the inner and outer skins, enabling them to be fully embedded in the cabin sandwich structure. The inner and outer skins wrap and anchor the beams, significantly improving their anti-peeling and anti-bending performance.

[0024] According to one aspect of the present invention, this approach effectively solves the problems of difficult demolding and internal cavity deformation of the structure by using a flexible, expandable core mold to adapt to the complex inner contour of the longitudinal beam.

[0025] According to one aspect of the present invention, the longitudinal beam and the main body can be simultaneously cured in a single thermal cycle without secondary assembly and connection, resulting in superior structural stability and reliability.

[0026] According to one aspect of the present invention, this solution effectively eliminates interface delamination, debonding, and porosity defects, and significantly improves the overall stiffness, strength, fatigue life, and sealing reliability of the structure.

[0027] According to one aspect of the present invention, this approach can be conveniently and flexibly adapted to complex irregular curved surface structures with varying curvature, ensuring surface accuracy and dimensional consistency. At the same time, it also significantly simplifies the process flow, reduces the number of tooling fixtures, shortens the production cycle, and lowers manufacturing costs.

[0028] According to one aspect of the present invention, this aspect fully and effectively realizes the integrated sandwich molding of the longitudinal beam structure. The inner skin not only covers the outer surface of the longitudinal beam, but also intersperses and distributes between the layers inside the longitudinal beam, forming a deep interwoven structure of "core within skin and skin within core". At the same time, the longitudinal beam and the skin are tightly connected without interface breakage, realizing continuous fiber force transmission, and significantly improving the overall stiffness, bending resistance and fatigue life of the cabin.

[0029] According to one aspect of the present invention, the longitudinal beam ply arrangement adopts a method where the inner layer has more layers to meet the main load-bearing requirements, while the outer layer is reduced to the necessary number of layers to maintain structural integrity. This avoids excessive redundancy in design and minimizes material usage while ensuring mechanical performance, thus meeting the goal of lightweighting the structure and giving the present invention a wider range of application prospects. Attached Figure Description

[0030] Figure 1 This is a step diagram of the method for co-curing and molding the composite material structure and longitudinal beam of the present invention; Figure 2 This is a schematic diagram of the combination of a segmented mold and a flexible expandable core mold according to one embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of one embodiment of the present invention; Figure 4 This is a structural diagram of a longitudinal beam according to one embodiment of the present invention; Figure 5This is a schematic diagram of the ply structure of a longitudinal beam according to one embodiment of the present invention. Detailed Implementation

[0031] In describing embodiments of the present invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" express orientations or positional relationships based on the orientations or positional relationships shown in the relevant drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on the present invention.

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the embodiments of the present invention are not limited to the following embodiments.

[0033] like Figure 1 As shown, according to one embodiment of the present invention, a method for co-curing and molding a composite material structure with a longitudinal beam includes the following steps: S1. Design a forming mold for the structural forming contour and open a longitudinal beam conformal forming groove on the mold wall to match the outer contour of the longitudinal beam. The forming mold is divided into multiple segmented molds along the axial direction of the structural body. S2. Design a flexible, expandable core mold based on the inner contour of the longitudinal beam of the structure, which is used to form the laying space of the longitudinal beam between the core mold and the conformal groove of the longitudinal beam. S3. Based on the forming mold and the flexible expandable core mold, the longitudinal beam and inner skin are interwoven and the outer skin is laid up, and the longitudinal beam is wrapped with the outer skin and the inner skin to form an integral sandwich integrated precast blank; S3. The precast blank is covered and vacuum pressure is maintained; S4. The coated blank is sent into a hot autoclave and co-cured using stepped heating and graded pressurization to obtain a structural blank. S5. After the structural blank is cooled, it is demolded and then trimmed to obtain the final structural product.

[0034] According to one embodiment of the present invention, in step S1, the step of designing a forming mold for the structural forming contour and opening a longitudinal beam conformal forming groove on the wall of the forming mold to match the outer contour of the longitudinal beam is wherein the wall of the forming mold is set to match the irregular curved surface of the structural body. The structural body may be a cabin, a launch tube body, etc., with an irregularly rotating irregular curved surface. Thus, the forming mold is divided into multiple segmented molds along the axial direction of the structural body, thereby allowing the wall of each segmented mold to accurately match the forming contour of the corresponding position of the structural body. See [link to relevant documentation].Figure 2 In this embodiment, the forming mold in the longitudinal beam area uses the inner side of the longitudinal beam as an asymmetrical mold-separating interface along the thickness direction of the longitudinal beam. The main cavity of the longitudinal beam groove is completely integrated onto a single segmented mold. This mold-separating structure enables rapid and precise assembly of the segmented mold, while also facilitating the laying of the longitudinal beam and the demolding and removal of the formed components. In this embodiment, for the longitudinal beam position, when the forming mold is split into segmented molds, the inner side of the longitudinal beam groove is used as the dividing boundary along the thickness direction of the longitudinal beam. Thus, the main groove portion of the longitudinal beam groove is divided onto a segmented mold, which facilitates the assembly of the segmented mold and the laying and disassembly of the longitudinal beam.

[0035] In this embodiment, the high-temperature release agent needs to be evenly sprayed onto the working surface of the mold to ensure no areas are missed. In particular, for new molds, it is generally necessary to spray the release agent more than 4 times. After each application of the release agent, allow it to dry at room temperature or under heating conditions, then wipe it clean with a clean cloth before applying the next application of the release agent.

[0036] like Figure 2 As shown, according to one embodiment of the present invention, in step S2, the flexible expandable core mold designed according to the inner contour of the longitudinal beam of the structure can be made of expandable silicone rubber. Based on its fit with the conformal molding groove of the longitudinal beam, the shape of both sides of the longitudinal beam is fully restricted. Furthermore, based on the thermal expansion characteristic of the flexible expandable core mold, pressure can be applied to the ply at the longitudinal beam position during the molding stage, achieving excellent longitudinal beam profile molding while also ensuring dense compaction of the longitudinal beam's interior, resulting in superior mechanical properties after molding. Thus, by replacing the traditional rigid core mold with a flexible expandable core mold, the overall manufacturing cost of the molding die is saved, and the performance of the longitudinal beam can be fully and effectively optimized, resulting in a finished product with superior working performance.

[0037] In this embodiment, the expansion rate of the flexible expandable mandrel is set to 3%~5%. During the autoclave curing and heating process, the flexible expandable mandrel expands as a whole due to heat, applying radial pressure to the layup within the conformal groove of the longitudinal beam. This continuously compacts the layup inside the longitudinal beam during curing, thereby reducing the porosity inside the longitudinal beam, increasing the fiber volume content, and enhancing the interlayer bonding strength and overall structural reliability of the longitudinal beam. If the expansion rate is less than 3%, the applied internal pressure is insufficient, the compaction effect is limited, and it is difficult to meet the high reliability requirements after the longitudinal beam structure is formed. If the expansion rate is greater than 5%, the excessive expansion may cause the longitudinal beam's dimensional deviations to exceed tolerances, or cause resin to overflow from the mold segment interface, resulting in local resin loss and thus forming structural defects such as dry spots, pores, and looseness inside the longitudinal beam.

[0038] In this embodiment, the flexible expandable core mold uses a single-sided adhesive structure to connect and position with the segmented mold. This not only stably maintains the pre-set assembly position of the expandable core mold, ensuring installation positioning accuracy and structural robustness, but also reserves expansion space so that the expandable core mold can be compressed into prepreg after thermal expansion, ensuring the internal quality of the longitudinal beam. The mutual fixation is achieved by adhesive bonding to the segmented mold on one side, ensuring the accurate and secure installation of the flexible expandable core mold.

[0039] According to one embodiment of the present invention, step S3, which involves integrally interwoven lay-up of the longitudinal beam and inner skin and lay-up of the outer skin based on the molding die and the flexible expandable core mold, includes: S31. A flexible expandable core mold is bonded to the non-paving area within the conformal groove of the longitudinal beam to create the padding space for the longitudinal beam. S32. Pre-cut longitudinal beam prepreg and inner skin prepreg are stacked and laid in the laying space in an alternating stacking manner to a preset number of layers; wherein, the area of ​​the inner skin prepreg is larger than the area of ​​the longitudinal beam prepreg, and part of the inner skin prepreg is laid on the outer surface of the segmented mold. S33. All the ply-laid segmented molds are joined together to form a complete molding mold, and an outer skin is laid on the surface of the molding mold to wrap the longitudinal beams and inner skin to form a precast blank.

[0040] Combination Figure 3 and Figure 4 As shown, according to one embodiment of the present invention, the longitudinal beam includes: a longitudinal beam body 11 and a longitudinal beam bending portion 12; wherein, the longitudinal beam body 11 is generally a plate-like body with a length greater than its width; specifically, the longitudinal beam bending portion 12 is disposed at both ends of the longitudinal beam body 11 in the length direction, or at both ends of the longitudinal beam body 11 in the length direction and at one end of the longitudinal beam body 11 in the width direction. In this embodiment, the longitudinal beam body 11 is used to achieve its stable supporting function in the length direction, and the longitudinal beam bending portion 12 achieves a fixed connection with the skin, thereby realizing stable force transmission.

[0041] like Figure 5As shown, according to one embodiment of the present invention, in step S32, in the step of stacking and laying pre-cut longitudinal beam prepreg and inner skin prepreg in the laying space to a preset number of layers in an alternating stacking manner, the shape and size of the longitudinal beam prepreg are consistent with the longitudinal beam body 11; wherein, from the inner side to the outer side of the longitudinal beam, multiple layers of longitudinal beam prepreg 1A and single layer of inner skin prepreg 1B are laid alternately to form the longitudinal beam body 11; in this embodiment, the thickness and lay-up angle of the longitudinal beam prepreg 1A at different positions are consistent; the thickness and lay-up angle of the single layer of inner skin prepreg 1B are consistent with the longitudinal beam prepreg 1A, or they can be set to be different from the longitudinal beam prepreg 1A, and can be adjusted in a targeted manner according to the stress requirements.

[0042] The inner skin prepreg 1B is bent at the edge of the longitudinal beam prepreg, and the bent portions of the multiple inner skin prepregs 1B are laid together to form the longitudinal beam bending portion 12.

[0043] like Figure 5 As shown, according to one embodiment of the present invention, during the alternating laying of multiple layers of longitudinal beam prepreg and single-layer inner skin prepreg in the direction from the inside to the outside of the longitudinal beam, the number of layers of longitudinal beam prepreg closer to the inside of the longitudinal beam is greater than the number of layers of longitudinal beam prepreg closer to the outside of the longitudinal beam. In this embodiment, the number of layers of longitudinal beam prepreg laid in the direction from the inside to the outside of the longitudinal beam is first reduced and then kept constant. Thus, the number of layers of longitudinal beam prepreg adjacent to the inside of the longitudinal beam is the largest. Then, after the single-layer inner skin prepreg is laid, the number of layers of longitudinal beam prepreg laid will be reduced accordingly. Thus, by alternating stacking, the number of layers of longitudinal beam prepreg is reduced to a preset number, and then the number of layers of longitudinal beam prepreg in the subsequent laying process remains unchanged at the preset number.

[0044] In this embodiment, during the process of covering and laying the longitudinal beam prepreg with a single-layer inner skin prepreg, the inner skin is bent in a bending manner to cover the sides of the multi-layer longitudinal beam prepreg, so that the multi-layer longitudinal beam prepreg can be stably confined within a fixed space.

[0045] In this embodiment, from the inner side to the outer side of the longitudinal beam, the bent portions of the inner skin prepreg are sequentially laid together, thus completely covering the longitudinal beam prepreg in a circumferential manner to form a sandwich structure. In this embodiment, to facilitate the direct laying of the bent portions of the inner skin prepreg, the width of the longitudinal beam prepreg at different locations can be set differently. Specifically, from the inner side to the outer side of the longitudinal beam, the width of the longitudinal beam prepreg increases sequentially. This ensures the flatness of the side surface after laying, facilitating the overall structural density during molding.

[0046] By employing the above-mentioned method of covering the multi-layer longitudinal beam prepreg with an inner skin, multiple parallel and spaced rigid supports can be formed inside the longitudinal beam after overall curing, making the entire longitudinal beam structure more stable and reliable. In particular, based on the gradient arrangement of different numbers of layers of the multi-layer longitudinal beam prepreg, a continuous stiffness gradient is formed inside the longitudinal beam, avoiding abrupt stiffness changes and interlayer stress concentrations caused by sudden changes in the number of layers. The load is smoothly transferred from the core load-bearing area of ​​the longitudinal beam to the skin, achieving a continuous and abrupt force transmission process.

[0047] Through the above-described configuration, the alternating application of inner skin prepreg and multi-layer longitudinal beam prepreg allows the cured longitudinal beams to achieve interlocking anchorage based on the stacking of the inner skin prepreg and multi-layer longitudinal beam prepreg. This mechanical interlocking of different structural layers significantly improves anti-peeling and anti-delamination capabilities. Furthermore, it substantially increases the interlayer bonding area between the longitudinal beams and the skin, causing cracks to deflect when they encounter the skin fibers during interlayer propagation, thus significantly enhancing crack arrest capability.

[0048] Through the above settings, the bending and wrapping of the multi-layer longitudinal beam prepreg assembly by the inner skin prepreg ensures that the multi-layer longitudinal beam prepreg assembly is fully enclosed and constrained, preventing the longitudinal beams from peeling off from the skin layers after curing, thus ensuring the reliability of the structure. At the same time, the pressure applied by the flexible expandable core mold during the molding process makes the overall interlayer connection denser, making interlayer debonding even more difficult to occur.

[0049] With the above setup, the single-layer inner skin prepreg setting method, due to its thin body and good flexibility, can closely fit the irregular curved surface of the longitudinal beam side; effectively fill the triangular area between the edge of the longitudinal beam and the skin, and eliminate the fiber bridging, wrinkles and other layup defects commonly found in traditional wide material laying at places of abrupt curvature change.

[0050] like Figure 5 As shown, according to one embodiment of the present invention, at the junction of the outer surface of the segmented mold and the conformal forming groove of the longitudinal beam, the inner skin is laid using a normally conformal sheet. In another embodiment, at the junction of the outer surface of the segmented mold and the conformal forming groove of the longitudinal beam, at least a portion of the inner skin prepreg is laid side-by-side sequentially by cutting it into multiple narrow strips of prepreg. If two adjacent layers of inner skin prepreg are both laid side-by-side sequentially by cutting them into multiple narrow strips of prepreg at the junction, the narrow strips of prepreg in the adjacent layers are stacked in a staggered manner. In this embodiment, the width of the narrow strip of prepreg is 10 mm.

[0051] By using the above-mentioned settings, the junction between the outer surface of the segmented mold and the longitudinal beam conformal forming groove is addressed by using narrow strip prepreg for application. This effectively overcomes structural defects such as fiber bridging and wrinkles caused by large corner positions, making the internal structure more compact and reliable.

[0052] In this embodiment, from the inner side to the outer side of the longitudinal beam, the innermost and outermost inner skin prepregs can be laid in a complete manner. The inner skin prepreg between the innermost and outermost layers can be laid at the junction by cutting it into multiple narrow strips. This ensures the integrity and reliability of the inner and outer structures, and the staggered laying method eliminates structural defects such as fiber bridging and wrinkles at corners, making the overall structure more stable and reliable. Of course, during the laying process, the inner skin prepreg can be further controlled to be laid as a whole at a predetermined number of layers, thereby ensuring reliable overall structural forming through interlayer coordination. Of course, in another embodiment, from the inside to the outside of the longitudinal beam, the outermost inner skin prepreg can be laid in a complete manner, while the remaining inner skin prepregs are laid at the junctions by cutting them into multiple narrow strips. This achieves the same effect when the innermost inner skin prepreg is wrapped inside during the subsequent outer skin prepreg laying process, resulting in a smoother outer skin prepreg laying position, which is more beneficial for ensuring the internal compactness of the overall structure. Alternatively, in another embodiment, all inner skin prepregs can be cut into multiple narrow strips and laid at the junctions. As long as the misalignment of adjacent narrow strips is effectively controlled, the stability and reliability of the overall structure can be ensured, effectively eliminating structural defects such as fiber bridging and wrinkles.

[0053] According to one embodiment of the present invention, the outer skin can also be laid side-by-side in the remaining areas with greater curvature by cutting it into multiple narrow strips of prepreg. If adjacent layers of outer skin prepreg are both laid side-by-side in the same manner at their junction, the narrow strips of prepreg in the adjacent layers are stacked in a staggered manner. In this embodiment, the width of the narrow strips of prepreg is 10 mm.

[0054] The above settings effectively overcome structural defects such as fiber bridging and wrinkles caused by large curvature positions, making the surface of the outer skin at large curvature positions smoother, which has a beneficial effect on improving the overall quality of the product.

[0055] According to one embodiment of the present invention, in step S3, during the integral interlacing layup of the longitudinal beams and inner skin and the outer skin based on the molding die and the flexible expandable core mold, a low-temperature pre-compaction degassing process is performed every 3 to 5 layers of prepreg to remove interlayer air bubbles and avoid curing pore defects. In this embodiment, during the low-temperature pre-compaction degassing process, the temperature is controlled within the range of 60 to 80°C, and the pressure is 0.2 MPa to 0.4 MPa (or vacuuming to -0.095 MPa with slight external pressure can ensure the degassing effect without causing deformation of the flexible core mold); the pressure is maintained for 30-60 minutes; after completion, the temperature is lowered to below 40°C before depressurization to prevent "springback" and pore regeneration, thus completing the full removal of interlayer air bubbles. In this embodiment, the preferred temperature control range is 65°C-75°C to avoid the risks of insufficient resin viscosity reduction in the low-temperature stage and pre-curing in the high-temperature stage, ensuring the stable and controllable pre-compaction degassing effect, and improving process stability and batch consistency. In another embodiment, for prepregs with high curing temperature systems, compaction at a temperature range of 100±5℃ for 60 minutes can be used to ensure that the resin is fully impregnated and to remove gas at the same time.

[0056] According to one embodiment of the present invention, in step S3, the step of integrally interwoven lay-up of the outer skin, longitudinal beams, and inner skin based on the molding die and the flexible expandable mandrel, the outer skin prepreg 1C, longitudinal beam prepreg 1A, and inner skin prepreg 1B are all made of carbon fiber unidirectional prepreg or fabric prepreg, and their matrix resin is a high-temperature resistant bismaleimide resin system. In this embodiment, the carbon fiber unidirectional prepreg or fabric prepreg is T700 / T800 carbon fiber unidirectional prepreg and / or fabric prepreg.

[0057] In this embodiment, the prepreg is obtained through pre-preparation. The prepreg removal stage involves taking the prepreg out of cold storage and thawing it at room temperature for at least 8 hours until no condensation remains on the packaging bag before use. The prepreg cutting stage involves designing a prepreg cutting diagram based on the laying location and corresponding laying plan, and using a prepreg cutting machine to cut the prepreg to the required shape and size, thus enabling the aforementioned laying process to be performed.

[0058] According to one embodiment of the present invention, step S4, the step of covering the preform and vacuum-pressuring, includes: Polytetrafluoroethylene release cloth, release film, breathable felt, flow guide net, and vacuum bag film are sequentially laid on the outer surface of the preform. The edges of the vacuum bag membrane are sealed, and a vacuum is drawn to -0.095MPa to -0.1MPa. Pressure testing is performed to ensure no leakage, guaranteeing uniform and pressure application to the irregular curved surfaces of the structure.

[0059] According to one embodiment of the present invention, in step S5, the coated blank is fed into an autoclave and integrally co-cured using stepped heating and graded pressurization to obtain the structural blank. During the curing process, the temperature is increased at a rate of 0.5℃ / min, and after holding at that temperature, the temperature is decreased at a rate of 0.5℃ / min. After cooling to below 50℃, the autoclave door is opened for further cooling. After cooling to room temperature, the subsequent demolding operation is performed. In this embodiment, during the curing process, the pressure is increased to 0.1MPa at room temperature, and the pressure is increased at a rate of 0.5℃ / min. The temperature was increased at a rate of 0.5℃ / min until it reached 110±5℃. Then, the pressure was increased to 0.3 MPa and held for 180 min. At this temperature, the resin viscosity was minimized, exhibiting optimal flowability and wettability, allowing the resin to fully penetrate the fiber bundles and fill the gaps between the longitudinal beams and the skin. This was particularly beneficial for the complete wetting of complex interwoven structures. Next, the temperature was increased again at a rate of 0.5℃ / min to 120±5℃ and held for 120 min. At this temperature, the resin began to partially cross-link, and the viscosity slowly increased. This stage allowed the resin to transition from a fully flowing to a restricted flow state, preventing excessive resin loss and ensuring stable resin content in the structure. Finally, the temperature was increased again at 0.5℃ / min. After heating to 170±5℃ at a rate of 5℃ / min, the pressure was increased to 0.5 MPa and held for 240 min. This long holding time allowed for a slow release of heat during curing, preventing temperature overshoot due to heat accumulation and ensuring reliable completion of the curing process. Then, the temperature was increased to 200±5℃ at a rate of 0.5℃ / min, pressure was increased to 0.6 MPa, and held for 60 min. This consumed any remaining reactive groups from the previous stage, ensuring a smooth progression of crosslinking. Finally, the temperature was increased to 240±5℃ at a rate of 0.5℃ / min and held for 240 min to fully develop the crosslinking network and achieve the final designed performance. After completing the heating operations during curing and holding, a cooling operation was initiated. Once the temperature dropped below 60℃, the pressure was simultaneously released to atmospheric pressure at a rate of 0.1 MPa / min.

[0060] With the above settings, the flexible mandrel (such as silicone rubber) expands uniformly with temperature changes due to a relatively slow heating rate (0.5℃ / min) and a fine temperature plateau, avoiding uneven local expansion of the mandrel caused by rapid heating, thereby ensuring uniform pressure on the prepreg and dimensional accuracy of the final part.

[0061] According to one embodiment of the present invention, in step S6, after cooling and demolding the structural blank, and trimming the structural blank to obtain the final structural product, the molding mold and the structural blank assembly are pushed out of the autoclave after the autoclave temperature drops below 50°C. After cooling to room temperature, demolding begins to obtain the structural blank. Burrs, flash, etc., on the surface of the structural blank are removed with a file. Further, the typical dimensions, weight, and internal quality of the structural blank are inspected to determine if the inspection results are within the design range. If the inspected structure meets the requirements, the final structural product is obtained.

[0062] The above description is merely an example of a specific solution of the present invention. For any devices and structures not described in detail herein, it should be understood that they are implemented using common devices and methods already available in the art.

[0063] The above description is merely one embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for co-curing and molding a composite material structure with a longitudinal beam, characterized in that, Includes the following steps: S1. Design a forming mold for the structural forming contour and open a longitudinal beam conformal forming groove on the mold wall to match the outer contour of the longitudinal beam. The forming mold is divided into multiple segmented molds along the axial direction of the structural body. S2. Design a flexible, expandable core mold based on the inner contour of the longitudinal beam of the structure, which is used to form the laying space of the longitudinal beam between the core mold and the conformal groove of the longitudinal beam. S3. Based on the forming mold and the flexible expandable core mold, the longitudinal beam and inner skin are interwoven and the outer skin is laid up, and the longitudinal beam is wrapped with the outer skin and the inner skin to form an integral sandwich integrated precast blank; S4. Cover the precast blank and apply vacuum pressure; S5. The coated blank is sent into an autoclave and co-cured using stepped heating and graded pressurization to obtain a structural blank. S6. After the structural blank is cooled, it is demolded and then trimmed to obtain the final structural product.

2. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 1, characterized in that, In step S3, the steps of integrally interwoven layup of the longitudinal beam and inner skin and layup of the outer skin based on the forming mold and the flexible expandable core mold include: S31. A flexible expandable core mold is bonded to the non-paving area within the conformal groove of the longitudinal beam to create the padding space for the longitudinal beam. S32. Pre-cut longitudinal beam prepreg and inner skin prepreg are stacked and laid in the laying space in an alternating stacking manner to a preset number of layers; wherein, the area of ​​the inner skin prepreg is larger than the area of ​​the longitudinal beam prepreg, and part of the inner skin prepreg is laid on the outer surface of the segmented mold. S33. All the ply-laid segmented molds are joined together to form a complete molding mold, and an outer skin is laid on the surface of the molding mold to wrap the longitudinal beams and inner skin to form a precast blank.

3. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 2, characterized in that, The longitudinal beam includes: the main body of the longitudinal beam (11) and the bending part of the longitudinal beam (12); The main body of the longitudinal beam (11) is a plate-like body with a length greater than its width; The bending portion (12) of the longitudinal beam is provided at both ends of the longitudinal beam body (11) in the length direction, or at both ends of the longitudinal beam body (11) in the length direction and at one end of the longitudinal beam body (11) in the width direction.

4. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 3, characterized in that, In step S32, the pre-cut longitudinal beam prepreg and inner skin prepreg are stacked and laid in the laying space in an alternating stacking manner to a preset number of layers. The shape and size of the longitudinal beam prepreg are consistent with the longitudinal beam body (11). In the direction from the inside to the outside of the longitudinal beam, multiple layers of longitudinal beam prepreg and single layers of inner skin prepreg are laid alternately to form the longitudinal beam body (11). The inner skin prepreg is bent at the edge of the longitudinal beam prepreg, and the bent portions of the multiple inner skin prepregs are laid together to form the longitudinal beam bending portion (12).

5. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 4, characterized in that, In the process of alternately laying multi-layer longitudinal beam prepreg and single-layer inner skin prepreg from the inside to the outside of the longitudinal beam, the number of layers of longitudinal beam prepreg closer to the inside of the longitudinal beam is greater than the number of layers of longitudinal beam prepreg closer to the outside of the longitudinal beam.

6. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 5, characterized in that, At the junction of the outer surface of the segmented mold and the longitudinal beam conformal forming groove, at least a portion of the inner skin prepreg is laid side by side in sequence by cutting it into multiple narrow strips of prepreg. If two adjacent layers of inner skin prepreg are laid side by side in sequence by cutting them into multiple narrow strips of prepreg at the junction, then the narrow strips of prepreg in the two adjacent layers of inner skin prepreg are stacked in a staggered manner.

7. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 6, characterized in that, In step S3, during the process of laying the longitudinal beam and inner skin together and laying the outer skin on the basis of the molding mold and the flexible expandable core mold, a low-temperature pre-compaction degassing is performed every 3 to 5 layers of prepreg to remove interlayer air bubbles.

8. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 7, characterized in that, In step S3, the process of integrally interwoven layup of longitudinal beams and inner skin and layup of outer skin based on molding die and flexible expandable core mold, the outer skin prepreg, longitudinal beam prepreg, and inner skin prepreg are all made of carbon fiber unidirectional prepreg or fabric prepreg, and the matrix resin is a high-temperature resistant bismaleimide resin system.

9. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 8, characterized in that, Step S4, the step of covering the preform and vacuum-pressuring, includes: Polytetrafluoroethylene release cloth, release film, breathable felt, flow guide net, and vacuum bag film are sequentially laid on the outer surface of the preform. The edges of the vacuum bag membrane are sealed, and a vacuum is drawn to -0.095MPa to -0.1MPa. Pressure testing is performed to ensure no leakage, guaranteeing uniform and pressure application to the irregular curved surfaces of the structure.

10. The method for co-curing and molding the composite material structure and longitudinal beam according to claim 9, characterized in that, The carbon fiber unidirectional prepreg or fabric prepreg is T700 / T800 carbon fiber unidirectional prepreg and / or fabric prepreg; The width of the narrow strip prepreg is 10 mm.

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