A low-cost soft mold manufacturing method applicable to T-stiffener reinforced skin structure

Abstract

The application discloses a low-cost soft mold manufacturing method applicable to a T-shaped rib reinforced skin structure, and comprises the following steps: adopting an isolation film and a vacuum bag to integrally encapsulate a laminated plate skin blank body, a T-shaped rib blank body and a T-shaped soft mold on a forming tool; adopting a hot press tank to perform co-curing forming of a "wet" state laminated plate skin and a "wet" state T-shaped rib according to the curing requirements allowed by the material specification of carbon fiber prepreg, and obtaining the T-shaped rib reinforced skin structure; the application has the beneficial effects that: through the structure splitting of step S1, the customization of special tooling (a forming tool, a T-shaped rib pre-compaction tool and a soft mold forming tool), the accurate positioning and cooperation of step S4 and the co-curing forming of the "wet" state laminated plate skin and the "wet" state T-shaped rib of step S6, the defects of poor adaptability of the T-shaped rib to the skin, easy interference of R angles, easy wrinkling of edges and the need of post-grinding in the traditional gluing process are effectively solved.

Description

Technical Field

[0001] This invention relates to a low-cost soft mold manufacturing method applicable to T-rib reinforced skin structures. Background Technology

[0002] Composite materials, with their core advantages of low specific gravity, high specific strength, and high specific modulus, are widely used in aerospace, automotive, chemical, and other fields. Especially in aviation equipment such as drones, the replacement of metal materials with composite materials has become a mainstream trend for reducing overall weight, improving carrying efficiency, and enhancing operational safety. Among these, T-shaped stiffener-reinforced skin structures, as an important form of plate-like thin-walled stiffened structures, are widely used in main load-bearing components such as aircraft wings and rocket shells due to their superior tensile strength, bending shear strength, and stability under the same material weight. This effectively improves structural stiffness and strength while controlling weight, meeting the core requirements of lightweight and high-strength high-end equipment.

[0003] Currently, the molding processes for T-rib reinforced skin structures mainly include secondary bonding and co-curing. In the traditional secondary bonding process, the skin and T-ribs need to be molded separately before being bonded and assembled. The high hardness of metal or cured T-ribs makes it difficult to adapt to the deformation of the wall panels in variable curvature spatial structures such as the central wing. This can easily lead to problems such as R-angle interference and poor fit at characteristic inflection points, resulting not only in potential product quality issues but also requiring additional post-processing grinding and reducing production efficiency.

[0004] For small-sized, high aspect ratio panel skin structures, solid T-ribs offer greater structural stability compared to hollow girder structures. However, while the integrated co-curing molding of such structures offers potential advantages such as short manufacturing cycles, low costs, and high connection strength, it faces technical bottlenecks due to complex molding processes. In traditional co-curing processes, unreasonable tooling design leads to uneven pressure transmission and significant thermal hysteresis, easily causing problems such as edge wrinkles and internal defects in parts. Furthermore, it relies heavily on imported materials and complex tooling, further increasing manufacturing costs and failing to meet the demands of actual production for high precision, low cost, and high efficiency. In summary, existing molding processes for T-rib reinforced skin structures suffer from poor adaptability, complex processes, high costs, and unstable molding quality, failing to fully meet the application requirements of high-end equipment such as those in the aerospace field. Therefore, this invention proposes a low-cost soft mold manufacturing method applicable to T-rib reinforced skin structures to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A low-cost soft mold manufacturing method applicable to T-rib reinforced skin structures includes the following steps:

[0008] Step S1:

[0009] Based on the part model of the T-rib reinforced skin structure, the reinforced rib wall panel structure is divided into two parts: laminate skin and T-rib. A forming tooling for forming the laminate skin, a T-rib pre-compacting tooling for pre-compacting the T-rib, and a soft mold forming tooling for soft mold forming are designed respectively.

[0010] Step S2:

[0011] According to the exported drawing of the flexible tooling reinforcement material, rubber and reinforcement material are laid on the flexible mold forming tooling. After the laying is completed, the flexible mold forming tooling is sealed with a release film, breathable felt and vacuum bag. The sealed flexible mold forming tooling is sent into a thermostatic jar and cured under the curing conditions of the reinforcement material. After curing, a release cloth is laid on the forming surface of the flexible mold to obtain a T-shaped flexible mold.

[0012] Step S3:

[0013] Carbon fiber prepreg is laid on the molding fixture to form a laminate skin blank. During the laying process, a release film, breathable felt and vacuum bag are used to pre-compact the laminate skin blank.

[0014] Simultaneously, carbon fiber prepreg is laid on the T-shaped rib pre-compacting fixture. The T-shaped rib is formed by two L-shaped molds. After the molds are closed, a base plate is laid on the bottom of the two L-shaped structures to form the T-shaped rib blank. Then, the T-shaped rib blank is pre-compacted using a release film, breathable felt and vacuum bag.

[0015] Step S4:

[0016] Remove the pre-compacted T-rib blank from the T-rib pre-compacting fixture and transfer it to the forming fixture where the pre-compacted laminate skin blank is located to position the T-rib blank.

[0017] Step S5:

[0018] The T-shaped soft mold obtained in step S2 is positioned and fitted with the positioned T-shaped rib blank.

[0019] Step S6:

[0020] The laminate skin blank, T-rib blank, and T-shaped soft mold on the molding tooling are encapsulated by an isolation film and a vacuum bag. According to the curing requirements allowed by the material specifications of carbon fiber prepreg, the "wet" laminate skin and "wet" T-rib are co-cured and molded in an autoclave to obtain a T-rib reinforced skin structure.

[0021] As an improvement to the above technical solution, in step S1, the T-shaped rib pre-compacting fixture includes two L-shaped parting molds, one of which is fixedly connected to the fixture surface as a whole, and the other L-shaped parting mold is a movable parting mold that can move relative to the fixed L-shaped parting mold.

[0022] As an improvement to the above technical solution, in step S2, the rubber is domestic PAD rubber, and the reinforcing material is carbon fiber; and the T-shaped pressure pad base plate area of ​​the T-shaped soft mold is not covered with reinforcing material, this area is two layers of pure domestic PAD rubber, the R-corner area of ​​the T-shaped pressure pad is covered with a 5-10mm thick domestic PAD rubber strip, the domestic PAD rubber strip is sandwiched between the two layers of pure domestic PAD rubber, the width of the pure domestic PAD rubber in the T-shaped pressure pad base plate area is 20mm, and it forms a slope shape under the curing pressure in step S2.

[0023] As an improvement to the above technical solution, in step S2, when laying the reinforcing material, the reinforcing material is broken at the top of the T-shaped soft mold, and the break is filled with thin strips of domestic PAD rubber.

[0024] As an improvement to the above technical solution, in step S3, the blanking diagram of the flexible tooling reinforcement material is exported using Fibersim simulation software.

[0025] The laminate skin blank is laid on the forming fixture by projection positioning, and the T-rib blank is laid on the T-rib pre-compacting fixture by engraving on the surface of the fixture.

[0026] As an improvement to the above technical solution, in step S3, a "screw + pin hole" positioning method is used to achieve precise mold closing when the two L-shaped molds are separated and closed.

[0027] As an improvement to the above technical solution, in step S4, the T-shaped rib blank is positioned by laser projection of net dimensions. The positioning outline of the T-shaped rib is projected onto the surface of the laminate skin blank by laser projection. The T-shaped rib blank is then attached to the positioning outline, and a hot air gun is used to assist heating so that the T-shaped rib blank is bonded to the surface of the laminate skin blank.

[0028] As an improvement to the above technical solution, in step S6, breathable felt is not used during encapsulation, and a pressure pad is set in the encapsulation area corresponding to the T-shaped rib blank, while a vacuum bag is directly attached to the encapsulation area corresponding to the laminate skin blank.

[0029] As an improvement to the above technical solution, in step S3, if the thickness of the laminate skin blank is greater than the preset thickness or the number of reinforcing layers is greater than the preset number of layers, a low-temperature high-pressure hot compaction process is adopted for the laminate skin blank. During hot compaction and encapsulation, a thin glass fiber cover plate is set in the curvature change inflection point area of ​​the laminate skin blank to prevent uneven stress accumulation of carbon fiber prepreg from causing wrinkles.

[0030] As an improvement to the above technical solution, after step S5 and before step S6, a covering layer laying step is also included:

[0031] Twisted wires are used to fill the contact surface between the bottom plate of the T-shaped rib blank and the laminate skin blank, turning the right-angle stepped structure of the contact surface into a gentle slope structure. Then, the outermost covering layer is laid, and a peelable fabric is laid in the bonding area between the laminate skin blank and the central wing beam rib.

[0032] In step S2, the domestically produced PAD rubber is a flexible, high-temperature resistant silicone rubber with a minimum temperature resistance of ≥190℃ and an elongation of ≥300%.

[0033] The number of reinforcing material layers is set to 2 or 5 layers of carbon fiber, depending on the inner and outer positions of the T-shaped soft mold, the thickness of the laminate skin, and the conformal requirements.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] By structural disassembly in step S1 and customization of special tooling (forming tooling, T-rib pre-compacting tooling, soft mold forming tooling), precise positioning and matching in step S4, and co-curing and molding of "wet" laminate skin and "wet" T-ribs in step S6, the defects of poor compatibility between T-ribs and skin, easy interference of R-angles, easy wrinkling of edges and the need for post-grinding in traditional adhesive bonding processes are effectively solved.

[0036] The T-shaped soft mold prepared in step S2 adopts a composite structure of domestic PAD rubber and carbon fiber reinforced material. It not only uses the flexibility of rubber to achieve uniform pressure transmission of the complex contour of the T-shaped rib (R angle, bottom plate step), but also uses the reinforcing material to ensure the rigidity of the soft mold to control the surface accuracy and dimensional tolerance of the part, thus avoiding the shortcomings of purely flexible or rigid tooling.

[0037] The simultaneous pre-pressing design of the skin blank and T-rib blank in step S3 reduces the waiting time for the process. The simplified encapsulation and co-curing process of step S6, which abandons the breathable felt, greatly shortens the production cycle. Moreover, the tooling design of domestic materials and bonding requirements significantly reduces the manufacturing cost.

[0038] Meanwhile, the "wet-wet" co-curing process creates an integrated interface between the T-ribs and the skin, significantly improving the connection strength, overall load-bearing capacity, and fatigue resistance. The pre-compaction process in step S3, the thin fiberglass cover plate protection design at the curvature inflection point, and the high-temperature resistance (≥190℃) of the soft mold in step S2 effectively avoid internal defects caused by prepreg accumulation and thermal hysteresis, ensuring the stability of mass production. Ultimately, it can accurately adapt to small-sized, high aspect ratio T-rib reinforced skin structures, meeting the core requirements of the aerospace field for lightweight, high-strength, and high-precision parts, and broadening the molding application range of composite thin-walled reinforced structures. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the soft mold forming process for the T-shaped rib reinforced skin structure of the present invention;

[0040] Figure 2 This is a schematic diagram of the T-shaped rib reinforced skin structure forming of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example:

[0043] like Figure 1-2 As shown, this embodiment proposes a low-cost soft mold manufacturing method applicable to T-rib reinforced skin structures, including the following steps:

[0044] Step S1:

[0045] Based on the part model of the T-rib reinforced skin structure, the reinforced rib wall panel structure is divided into two parts: laminate skin and T-rib. A forming tooling for forming the laminate skin, a T-rib pre-compacting tooling for pre-compacting the T-rib, and a soft mold forming tooling for soft mold forming are designed respectively.

[0046] Step S2:

[0047] According to the exported drawing of the flexible tooling reinforcement material, rubber and reinforcement material are laid on the flexible mold forming tooling. After the laying is completed, the flexible mold forming tooling is sealed with a release film, breathable felt and vacuum bag. The sealed flexible mold forming tooling is sent into a thermostatic jar and cured under the curing conditions of the reinforcement material. After curing, a release cloth is laid on the forming surface of the flexible mold to obtain a T-shaped flexible mold.

[0048] Step S3:

[0049] Carbon fiber prepreg is laid on the molding fixture to form a laminate skin blank. During the laying process, a release film, breathable felt and vacuum bag are used to pre-compact the laminate skin blank.

[0050] Simultaneously, carbon fiber prepreg is laid on the T-shaped rib pre-compacting fixture. The T-shaped rib is formed by two L-shaped molds. After the molds are closed, a base plate is laid on the bottom of the two L-shaped structures to form the T-shaped rib blank. Then, the T-shaped rib blank is pre-compacted using a release film, breathable felt and vacuum bag.

[0051] Step S4:

[0052] Remove the pre-compacted T-rib blank from the T-rib pre-compacting fixture and transfer it to the forming fixture where the pre-compacted laminate skin blank is located to position the T-rib blank.

[0053] Step S5:

[0054] The T-shaped soft mold obtained in step S2 is positioned and fitted with the positioned T-shaped rib blank.

[0055] Step S6:

[0056] The laminate skin blank, T-rib blank, and T-shaped soft mold on the molding tooling are encapsulated by an isolation film and a vacuum bag. According to the curing requirements allowed by the material specifications of carbon fiber prepreg, the "wet" laminate skin and "wet" T-rib are co-cured and molded in an autoclave to obtain a T-rib reinforced skin structure.

[0057] In this embodiment, the structural disassembly in step S1 and the customization of special tooling (forming tooling, T-shaped rib pre-compacting tooling, soft mold forming tooling), the precise positioning and matching in step S4, and the co-curing and molding of the "wet" state laminate skin and the "wet" state T-shaped rib in step S6 effectively solve the defects of poor compatibility between T-shaped rib and skin, easy interference of R-angle, easy wrinkling of edges, and the need for post-grinding in traditional adhesive bonding processes.

[0058] The T-shaped soft mold prepared in step S2 adopts a composite structure of domestic PAD rubber and carbon fiber reinforced material. It not only uses the flexibility of rubber to achieve uniform pressure transmission of the complex contour of the T-shaped rib (R angle, bottom plate step), but also uses the reinforcing material to ensure the rigidity of the soft mold to control the surface accuracy and dimensional tolerance of the part, thus avoiding the shortcomings of purely flexible or rigid tooling.

[0059] The simultaneous pre-pressing design of the skin blank and T-rib blank in step S3 reduces the waiting time for the process. The simplified encapsulation and co-curing process of step S6, which abandons the breathable felt, greatly shortens the production cycle. Moreover, the tooling design of domestic materials and bonding requirements significantly reduces the manufacturing cost.

[0060] Meanwhile, the "wet-wet" co-curing process creates an integrated interface between the T-ribs and the skin, significantly improving the connection strength, overall load-bearing capacity, and fatigue resistance. The pre-compaction process in step S3, the thin fiberglass cover plate protection design at the curvature inflection point, and the high-temperature resistance (≥190℃) of the soft mold in step S2 effectively avoid internal defects caused by prepreg accumulation and thermal hysteresis, ensuring the stability of mass production. Ultimately, it can accurately adapt to small-sized, high aspect ratio T-rib reinforced skin structures, meeting the core requirements of the aerospace field for lightweight, high-strength, and high-precision parts, and broadening the molding application range of composite thin-walled reinforced structures.

[0061] Specifically, in step S1, the T-shaped rib pre-compacting fixture includes two L-shaped parting molds, one of which is fixedly connected to the fixture surface as a whole, and the other L-shaped parting mold is a movable parting mold that can move relative to the fixed L-shaped parting mold.

[0062] In this embodiment, the movable L-shaped parting mold can be moved away from the fixed L-shaped parting mold when laying carbon fiber prepreg, providing ample working space for operators and avoiding the inconvenience of laying operations caused by the limited internal space of traditional integrated tooling; after the T-rib blank is pre-compacted, the blank can be easily removed by moving the movable L-shaped parting mold, avoiding fiber damage and shape distortion of the blank caused by the forced disassembly of traditional fixed tooling, and ensuring the integrity of the blank forming;

[0063] The fixed L-shaped parting mold is fixedly connected to the tooling surface to form a stable reference. The movable L-shaped parting mold is adjusted in position with reference to this reference. It can accurately control the relative position of the two L-shaped parting molds, ensuring that the verticality of the web, the parallelism of the flanges, and the cross-sectional dimensions (such as flange thickness and web height) of the T-shaped rib blank after mold closing meet the design requirements. This avoids the mold closing misalignment caused by the lack of a fixed reference in traditional split tooling, thereby reducing the adaptation deviation of subsequent skin assembly.

[0064] In the pre-compaction process, the fixed L-shaped parting mold provides rigid support for the billet, while the movable L-shaped parting mold can adaptively fit the surface of the billet according to the pre-compression pressure, so that the pressure can be evenly transmitted to the web, flange and R-angle area of ​​the T-rib, avoiding local pressure loss due to insufficient tooling rigidity or loose fit, reducing defects such as air bubbles and interlayer delamination inside the billet, and improving the density and structural strength of the T-rib billet.

[0065] Specifically, in step S2, the rubber is domestically produced PAD rubber, and the reinforcing material is carbon fiber; and the T-shaped pressure pad base plate area of ​​the T-shaped soft mold is not covered with reinforcing material, this area is two layers of pure domestically produced PAD rubber, the R-corner area of ​​the T-shaped pressure pad is covered with a 5-10mm thick domestically produced PAD rubber strip, the domestically produced PAD rubber strip is sandwiched between the two layers of pure domestically produced PAD rubber, the width of the pure domestically produced PAD rubber in the T-shaped pressure pad base plate area is 20mm, and it forms a slope shape under the curing pressure in step S2.

[0066] In this embodiment, carbon fiber reinforcement material is used to give the soft mold overall structural rigidity, ensuring that the soft mold is not prone to surface distortion during autoclave curing and subsequent pressure transmission, and ensuring the overall dimensional accuracy of the T-rib reinforced skin; at the same time, domestic PAD rubber is used as the main material, and its flexibility allows the soft mold to closely fit the complex contour of the T-rib (including the web, flange and transition area), avoiding the pressure transmission dead angle problem caused by the inability of traditional rigid tooling to adapt to irregular structures.

[0067] By inserting a 5-10mm thick domestic PAD rubber strip into the R-corner area, the gap in the R-corner contour can be specifically filled, ensuring that the fit between the soft mold and the T-shaped rib R-corner is ≥98%. This ensures that the pressure of the autoclave can be evenly transmitted to the R-corner area, effectively avoiding defects such as fiber accumulation, bubble residue, or interlayer delamination caused by uneven pressure transmission in traditional processes, and improving the structural strength and molding quality of the R-corner area.

[0068] Specifically, in step S2, when laying the reinforcing material, the reinforcing material is broken at the top of the T-shaped soft mold, and the break is filled with thin strips of domestic PAD rubber.

[0069] In this embodiment, if the reinforcing material is not filled after being broken, the gap will form a pressure transmission blind zone, causing the pressure in the autoclave to be unable to be effectively transmitted to the top area of ​​the T-rib, which can easily lead to defects such as insufficient compactness and residual air bubbles in the blank in this area. However, the filling with domestic PAD rubber strips can accurately fill the gap, forming a continuous pressure transmission surface at the top of the soft mold, ensuring that the pressure is evenly transmitted to the top of the T-rib along the top of the soft mold. At the same time, the sealing properties of domestic PAD rubber are used to prevent pressure leakage from the gap, ensuring pressure transmission efficiency and stability.

[0070] Specifically, in step S3, the blanking diagram of the flexible tooling reinforcement material is exported using Fibersim simulation software;

[0071] The laminate skin blank is laid on the forming fixture by projection positioning, and the T-rib blank is laid on the T-rib pre-compacting fixture by engraving on the surface of the fixture.

[0072] In this embodiment, the projection positioning method can directly project the design model outline of the laminate skin onto the surface of the molding tooling, forming a visual laying reference. Operators do not need to manually draw lines on the tooling surface (avoiding the cumulative error, blurred lines, or line deformation caused by the curvature of the tooling in traditional manual drawing). It can quickly align the carbon fiber prepreg with the projected outline for laying, ensuring that the deviation between the layup position and layup boundary of the skin blank and the design model is ≤ ±0.1mm.

[0073] Especially for large-sized or complex-curvature laminate skins, projection positioning can achieve full-area reference coverage, avoid local positioning blind spots, improve laying efficiency, and ensure the overall surface accuracy of the skin blank, laying the foundation for subsequent precise assembly with T-shaped ribs.

[0074] Specifically, in step S3, the two L-shaped molds are closed using a "screw + pin hole" positioning method to achieve precise mold closing.

[0075] Specifically, in step S4, the T-shaped rib blank is positioned using a net-size laser projection positioning method. The positioning outline of the T-shaped rib is projected onto the surface of the laminate skin blank using laser projection. The T-shaped rib blank is then attached to the positioning outline, and a hot air gun is used to assist in heating so that the T-shaped rib blank is bonded to the surface of the laminate skin blank.

[0076] In this embodiment, the net-size laser projection positioning can accurately project the design model outline of the T-rib onto the surface of the laminate skin blank at a 1:1 scale. The line width of the projected outline is ≤0.2mm and the positioning accuracy is ±0.1mm. This completely avoids the defects of traditional manual scribing (which is prone to cumulative errors of ±0.5mm or more) and reference block positioning (which has poor adaptability and is difficult to match complex outlines). It ensures that after the T-rib blank is laid in accordance with the projected outline, its relative position with the skin (such as T-rib spacing, web verticality, and flange alignment) fully meets the design requirements, laying a precise positional foundation for the subsequent "wet-wet" co-curing interface integration.

[0077] The visual positioning benchmark formed by laser projection eliminates the need for operators to perform secondary calculations or compare drawings, and can directly guide the T-rib blank to quickly align, significantly shortening the positioning and adjustment time (efficiency is improved by more than 30% compared to traditional positioning methods); at the same time, it avoids repeated disassembly and reassembly due to human judgment errors, reduces the risk of scratches or fiber damage to the blank surface, and ensures the integrity of the blank forming.

[0078] Specifically, in step S6, breathable felt is not used during encapsulation, and pressure pads are set in the encapsulation area corresponding to the T-shaped rib blank, while vacuum bags are directly attached to the encapsulation area corresponding to the laminate skin blank.

[0079] In this embodiment, the use of breathable felt in traditional packaging is eliminated, which can completely eliminate defects such as surface contamination and internal fiber inclusion caused by the shedding of breathable felt fibers during the autoclave curing process. At the same time, it avoids surface damage to parts caused by the adhesion of breathable felt to prepreg resin, and ensures that the surface roughness (such as Ra1.6-Ra3.2 in the adhesive area) and internal cleanliness of the T-rib reinforced skin structure meet the high precision requirements of the aerospace field, reducing subsequent surface treatment processes.

[0080] Due to the irregular contour of the T-shaped rib blank containing web, flange, and R-angle transition zone, pressure is easily lost in the complex contour area under traditional sealing methods, resulting in insufficient local density. By setting pressure pads in this area, the flexible deformation characteristics of the pressure pads can be used to accurately compensate for the pressure transmission blind spots of the irregular contour, so that the pressure of the autoclave is evenly applied to the web, flange, and interface with the skin of the T-shaped rib. This effectively reduces defects such as residual bubbles and interlayer delamination in this area, and significantly improves the overall density and load-bearing strength of the T-shaped rib structure.

[0081] Specifically, in step S3, if the thickness of the laminate skin blank is greater than the preset thickness or the number of reinforcing layers is greater than the preset number of layers, a low-temperature high-pressure hot compaction process is adopted for the laminate skin blank. During hot compaction and encapsulation, a thin glass fiber cover plate is set at the curvature change inflection point area of ​​the laminate skin blank to prevent uneven stress accumulation of carbon fiber prepreg from causing wrinkles.

[0082] In this embodiment, when the thickness of the laminate skin blank is large or the number of reinforcing interlayers is large, traditional atmospheric pressure or low-pressure hot compaction is difficult to eliminate the interlayer gaps inside the blank, and defects such as residual bubbles and interlayer delamination are easy to remain. However, the low-temperature high-pressure hot compaction process can force the air inside the blank to be expelled by high pressure, under the premise of avoiding premature curing of the prepreg resin (the low-temperature environment ensures that the resin maintains reasonable fluidity and does not affect the interface fusion of subsequent co-curing) and significantly improve the interlayer density of thick blanks / multi-interlayer laminates, reduce internal porosity, and lay the foundation for the structural strength of subsequent co-curing molding.

[0083] At the curvature inflection point of the laminate skin blank, due to the abrupt change in the direction of force, traditional hot-pressed real-time prepreg is prone to fiber accumulation and wrinkling due to uneven local stress (especially in thick blanks / multi-layer scenarios, this problem is more prominent). By setting a thin glass fiber cover plate in this area, the rigid support characteristics of the glass fiber cover plate can be used to form a uniform constraint on the prepreg in the inflection point area, disperse the local concentrated stress during the hot pressing process, guide the fibers to be arranged in a preset direction, effectively prevent fiber accumulation and wrinkling, and ensure the surface accuracy and fiber continuity in the inflection point area.

[0084] Specifically, after step S5 and before step S6, there is also a step of applying the covering layer:

[0085] Twisted wires are used to fill the contact surface between the bottom plate of the T-shaped rib blank and the laminate skin blank, turning the right-angle stepped structure of the contact surface into a gentle slope structure. Then, the outermost covering layer is laid, and a peelable fabric is laid in the bonding area between the laminate skin blank and the central wing beam rib.

[0086] In step S2, the domestically produced PAD rubber is a flexible, high-temperature resistant silicone rubber with a minimum temperature resistance of ≥190℃ and an elongation of ≥300%.

[0087] The number of reinforcing material layers is set to 2 or 5 layers of carbon fiber, depending on the inner and outer positions of the T-shaped soft mold, the thickness of the laminate skin, and the conformal requirements.

[0088] In this embodiment, the contact surface between the T-rib blank base plate and the laminate skin blank is filled with twisted wire to form a right-angle stepped structure and a gentle slope. This can effectively disperse the local stress concentration caused by the stepped structure during co-curing (the stress concentration coefficient is reduced by more than 40%), and avoid defects such as cracking and delamination at the interface due to excessive stress. At the same time, the outermost coating layer can form an overall constraint on the bonding area between the T-rib and the skin, preventing the prepreg fiber from shifting during co-curing, further ensuring the integrated bonding strength of the interface between the two and improving the overall fatigue resistance of the part.

[0089] A peelable fabric is laid in the bonding area between the laminate skin blank and the central wing beam rib. The release properties and surface texture of the peelable fabric can be used to directly form a roughness (Ra1.6-Ra3.2) that meets the design requirements after co-curing. No secondary processing such as subsequent grinding and polishing is required. This avoids damage to the bonding surface caused by manual processing, shortens the production cycle, and ensures the surface cleanliness of the bonding area, laying a high-quality interface foundation for subsequent bonding and assembly with the central wing beam rib.

[0090] In step S2, the domestic PAD rubber is specified as a flexible high-temperature resistant silicone rubber with a minimum temperature resistance of ≥190℃ and an elongation of ≥300%. On the one hand, it can withstand the high-temperature environment during the autoclave co-curing process (the curing temperature of composite materials is usually 120-180℃), ensuring the structural stability of the soft mold during the curing cycle and avoiding deformation, aging or failure of the soft mold caused by high temperature. On the other hand, the high elongation characteristic allows the soft mold to adapt to the complex contour of the T-rib (such as the R-angle and web sidewall), ensuring that the pressure is evenly transmitted to each area of ​​the T-rib. At the same time, the domestic material can reduce the material procurement cost by 30%-50% compared with the imported flexible material, taking into account both performance and economy.

[0091] Based on the inner and outer positions of the T-shaped soft mold (the inner side needs to conform to the shape, and the outer side needs to maintain the shape), the thickness of the laminate skin (thick skin requires stronger rigidity support), and the conformity requirements, the number of reinforcing material (carbon fiber) layers is differentiated into 2 or 5 layers. This allows for precise matching of the soft mold performance. Two layers of carbon fiber ensure the flexible conformity of the inner side of the soft mold, ensuring a close fit to the irregular contour of the T-shaped rib. Five layers of carbon fiber enhance the rigidity of the outer side of the soft mold, avoiding surface distortion of the soft mold caused by a thicker skin. Thus, both "flexible pressure transmission" and "rigid shape preservation" are considered in the same soft mold structure, ensuring that the T-shaped rib reinforced skin with different structural parameters can achieve the design dimensional accuracy (dimensional deviation ≤ ±0.2mm), broadening the scope of process applicability.

[0092] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-cost soft mold manufacturing method applicable to T-rib reinforced skin structures, characterized in that: Includes the following steps: Step S1: Based on the part model of the T-rib reinforced skin structure, the reinforced rib wall panel structure is divided into two parts: laminate skin and T-rib. A forming tooling for forming the laminate skin, a T-rib pre-compacting tooling for pre-compacting the T-rib, and a soft mold forming tooling for soft mold forming are designed respectively. Step S2: According to the exported drawing of the flexible tooling reinforcement material, rubber and reinforcement material are laid on the flexible mold forming tooling. After the laying is completed, the flexible mold forming tooling is sealed with a release film, breathable felt and vacuum bag. The sealed flexible mold forming tooling is sent into a thermostatic jar and cured under the curing conditions of the reinforcement material. After curing, a release cloth is laid on the forming surface of the flexible mold to obtain a T-shaped flexible mold. Step S3: Carbon fiber prepreg is laid on the molding fixture to form a laminate skin blank. During the laying process, a release film, breathable felt and vacuum bag are used to pre-compact the laminate skin blank. Simultaneously, carbon fiber prepreg is laid on the T-shaped rib pre-compacting fixture. The T-shaped rib is formed by two L-shaped molds. After the molds are closed, a base plate is laid on the bottom of the two L-shaped structures to form the T-shaped rib blank. Then, the T-shaped rib blank is pre-compacted using a release film, breathable felt and vacuum bag. Step S4: Remove the pre-compacted T-rib blank from the T-rib pre-compacting fixture and transfer it to the forming fixture where the pre-compacted laminate skin blank is located to position the T-rib blank. Step S5: The T-shaped soft mold obtained in step S2 is positioned and fitted with the positioned T-shaped rib blank. Step S6: The laminate skin blank, T-rib blank and T-shaped soft mold on the molding tooling are encapsulated by an isolation film and a vacuum bag. According to the curing requirements allowed by the material specifications of carbon fiber prepreg, the "wet" laminate skin and "wet" T-rib are co-cured and molded in an autoclave to obtain a T-rib reinforced skin structure. In step S2, the rubber is domestically produced PAD rubber, and the reinforcing material is carbon fiber; the T-shaped pressure pad base plate area of ​​the T-shaped soft mold is not covered with reinforcing material, and this area consists of two layers of pure domestically produced PAD rubber. The R-corner area of ​​the T-shaped pressure pad is covered with a 5-10mm thick domestically produced PAD rubber strip, which is sandwiched between the two layers of pure domestically produced PAD rubber. The width of the pure domestically produced PAD rubber in the T-shaped pressure pad base plate area is 20mm, and it forms a sloping shape under the curing pressure in step S2.

2. The low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: In step S1, the T-shaped rib pre-compacting fixture includes two L-shaped parting molds, one of which is fixedly connected to the fixture surface as a whole, and the other L-shaped parting mold is a movable parting mold that can move relative to the fixed L-shaped parting mold.

3. The low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: In step S2, when laying the reinforcing material, the reinforcing material is broken at the top of the T-shaped soft mold, and the break is filled with thin strips of domestic PAD rubber.

4. The low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: In step S3, the blanking diagram of the flexible tooling reinforcement material is exported using Fibersim simulation software; The laminate skin blank is laid on the forming fixture by projection positioning, and the T-rib blank is laid on the T-rib pre-compacting fixture by engraving on the surface of the fixture.

5. The low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: In step S3, the two L-shaped molds are closed using a "screw + pin hole" positioning method to achieve precise mold closing.

6. The low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: In step S4, the T-rib blank is positioned using a net-size laser projection positioning method. The positioning outline of the T-rib is projected onto the surface of the laminate skin blank using laser projection. The T-rib blank is then attached to the positioning outline, and a hot air gun is used to assist in heating so that the T-rib blank is bonded to the surface of the laminate skin blank.

7. The low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: In step S6, breathable felt is not used during encapsulation, and pressure pads are set in the encapsulation area corresponding to the T-shaped rib blank, while vacuum bags are directly attached to the encapsulation area corresponding to the laminate skin blank.

8. A low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: In step S3, if the thickness of the laminate skin blank is greater than the preset thickness or the number of reinforcing layers is greater than the preset number of layers, a low-temperature high-pressure hot compaction process is adopted for the laminate skin blank. During hot compaction and encapsulation, a thin glass fiber cover plate is set in the curvature change inflection point area of ​​the laminate skin blank to prevent uneven stress accumulation of carbon fiber prepreg and the generation of wrinkles.

9. A low-cost soft mold manufacturing method applicable to T-shaped rib reinforced skin structures according to claim 1, characterized in that: After step S5 and before step S6, the process also includes the application of the covering layer: Twisted wires are used to fill the contact surface between the bottom plate of the T-shaped rib blank and the laminate skin blank, turning the right-angle stepped structure of the contact surface into a gentle slope structure. Then, the outermost covering layer is laid, and a peelable fabric is laid in the bonding area between the laminate skin blank and the central wing beam rib. In step S2, the domestically produced PAD rubber is a flexible, high-temperature resistant silicone rubber with a minimum temperature resistance of ≥190℃ and an elongation of ≥300%. The number of reinforcing material layers is set to 2 or 5 layers of carbon fiber, depending on the inner and outer positions of the T-shaped soft mold, the thickness of the laminate skin, and the conformal requirements.

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