Low-cost rapid verifying and mold repairing method for composite material forming tool

Abstract

The invention discloses a low-cost rapid verification and mold repair method for a composite material forming tool, which realizes low-cost rapid verification and iterative mold repair of the tool by taking a reuse substrate and composite material paving layer compensation as a core through cooperative connection of three stages of process design, manufacturing implementation and test verification, and specifically comprises the following steps: step (A), a process design stage; (B) a manufacturing implementation stage; (C) a test verification stage; the method has the advantages that the reuse substrate and composite material laying layer compensation serve as the core, an original forming tool, a similar structure tool or a flat plate tool of a product is adopted as the reuse substrate, a traditional metal tool substrate does not need to be newly manufactured, the cost of composite materials such as tool prepreg is lower than that of metal materials, and compared with a traditional all-metal newly-manufactured tool verification method, the verification method has the advantages that the verification efficiency is high, and the verification cost is low. The comprehensive cost of tool verification and mold repair can be reduced, and the technical problem that in the prior art, the cost is high due to the fact that a base needs to be repeatedly manufactured for tool verification is effectively solved.

Description

Technical Field

[0001] This invention relates to a low-cost method for rapid verification and mold repair of composite material molding tooling. Background Technology

[0002] Composite materials, with their superior properties such as high strength, lightweight, and corrosion resistance, have been widely used in core fields such as aerospace, rail transportation, and high-end equipment manufacturing. Composite material molding fixtures, as a key guarantee for the precise molding of parts, directly determine the final dimensional accuracy and mechanical property consistency of composite material parts through their surface accuracy and structural stability, making them one of the core links in the industrial application of composite materials.

[0003] In the early stages of R&D and mass production of composite parts, tooling needs to undergo multiple rounds of verification and modification to adapt to the part molding process requirements and correct design deviations. Currently, the mainstream tooling verification and modification methods in the industry still rely on the manufacture of new all-metal tooling. That is, for each round of verification, a complete metal tooling base is redesigned and manufactured, and then the surface is modified by machining. In the traditional method, the deviation compensation between the tooling surface and the base relies heavily on manual experience judgment, lacking quantitative deviation analysis and precise layup design support. This easily leads to problems such as insufficient compensation (tooling surface deviation) or overcompensation (waste of composite materials). At the same time, the material selection lacks clear mechanical performance matching standards, and the layup scheme does not consider the gradual transition requirements of surface differences. As a result, the tooling is prone to failure during autoclave curing (high temperature and high pressure environment) and subsequent part molding processes due to insufficient mechanical properties and stress concentration, leading to plastic deformation, cracking, or debonding of the composite shell from the base. In view of this, this invention proposes a low-cost rapid verification and modification method for composite molding tooling to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost method for rapid verification and mold repair of composite material molding tooling, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A low-cost method for rapid verification and modification of composite molding tooling is proposed. This method achieves rapid, low-cost verification and iterative tooling modification through the coordinated integration of three stages: process design, manufacturing implementation, and experimental verification. It focuses on reusable substrates and composite layup compensation. Specifically, it includes:

[0007] Step (A), Process Design Stage:

[0008] Based on the theoretical surface requirements of the tooling to be verified, the original molding tooling, similar structural tooling, or flat tooling of the product are used as the reuse base. The compensation area and thickness of the composite shell are determined through deviation analysis. High fiber density and high resin content tooling prepreg and compatible structural adhesives are selected for matching materials. Gradient layup scheme and supporting processes such as material cutting, laser projection, and autoclave curing are designed to provide technical basis for manufacturing implementation.

[0009] Step (B), Manufacturing Implementation Phase:

[0010] The reusable substrate is cleaned and roughened without the need for release agent. The composite prepreg and adhesive are cut and laid according to the process design. After vacuum compaction and thermocouple encapsulation in sections, it is cured and formed in an autoclave. Then, it is machined to the theoretical shape and the debonding of the composite shell and the substrate is detected simultaneously. The qualified composite tooling is obtained after surface, airtightness and appearance inspection.

[0011] Step (C), Experimental Verification Phase:

[0012] Qualified composite tooling is used to form parts, and the rationality of tooling design and forming process is verified by reverse verification through the surface data of the formed parts;

[0013] If adjustments are needed, the existing composite shell can be modified by milling or by adding prepreg to the existing composite shell and curing it. This creates a modified surface, allowing for rapid iteration of the tooling surface without needing to redo the tooling base.

[0014] As an improvement to the above technical solution, the specific method of "deviation analysis and reuse of the basis" in step (A) is as follows:

[0015] Computer-aided design tools are used to complete the theoretical surface design of the tooling. The software deviation analysis function is used to compare the surface difference between the theoretical surface and the reused substrate, generate a surface difference cloud map, and accurately mark the area and thickness of the composite shell that need to be compensated. The compensation thickness is determined according to the maximum deviation between the substrate and the theoretical surface, ranging from 0.5 to 5 mm.

[0016] For reusable substrates, the original molding tooling of the product should be selected with priority. Before selection, the substrate surface should be checked for defects such as cracks and corrosion through penetrant testing (PT). It can only be used if the defects do not affect the bonding reliability between the composite shell and the substrate.

[0017] As an improvement to the above technical solution, the specific parameters for "material selection and gradient layup scheme" in step (A) are as follows:

[0018] Material selection: The tooling prepreg is a T300 grade carbon fiber fabric prepreg with a fiber areal density of 650 g / m², resin content of 35%, single layer thickness of 0.6 mm, tensile strength after curing ≥1500 MPa, flexural modulus ≥120 GPa, and structural adhesive is a high-strength adhesive for composite materials that cures at 180℃ with a nominal area weight of 244 g / m² and a nominal thickness of 0.2 mm, and has good compatibility with the prepreg resin system;

[0019] Gradual layup scheme: Divide the surface into 3-5 layup thickness zones according to the surface difference cloud map, and use a gradual transition between adjacent zones (thickness difference ≤ 1mm). The layup direction is set according to [90 / 0 / 45 / -45 / 90]s (overall layup) or [45 / -45 / 0 / 45 / -45]s (dropped layer). The total number of overall layups is 10 layers, and the number of dropped layers is 2-5 layers.

[0020] As an improvement to the above technical solution, the specific content of the "supporting process procedure" in step (A) is as follows:

[0021] Using the composite materials module of CAD software, a material cutting program (including material number, size and laying position) and a laser projection program (positioning accuracy ±0.1mm) were exported based on the gradient layup scheme.

[0022] The autoclave curing program is set according to the prepreg resin system: heating rate 2-3℃ / min, holding at 180℃ for 2-3h, cooling rate 1-2℃ / min, curing pressure 0.5-0.8MPa, matching the curing characteristics of the prepreg resin.

[0023] As an improvement to the above technical solution, the specific operation of "reusing substrate treatment and laying composite material" in step (B) is as follows:

[0024] Substrate preparation: Clean the substrate surface with acetone (to remove oil, dust and other excess substances), and roughen the area to be laid by sandblasting or sanding to achieve a surface roughness of Ra=1.6-3.2μm. No release agent is required.

[0025] Composite material laying: Based on the laser projection program positioning, the first layer of structural adhesive film is laid in one piece (the size of the adhesive film exceeds the prepreg layer area by 10mm). Subsequent layers are laid according to the laying plan, with the maximum overlap between the sheets ≤6mm and the maximum gap ≤1.5mm. Vacuum compaction is performed every 2-3 layers (vacuum degree -80~-95KPa, pressure holding time ≥15min).

[0026] As an improvement to the above technical solution, the specific requirements for "partitioned packaging and autoclave curing" in step (B) are as follows:

[0027] Thermocouple arrangement: In the remaining area of ​​the composite prepreg, the thermocouples are arranged according to the principle of "leading thermocouples in corner / thin layer areas and lagging thermocouples in center / thick layer areas". The spacing between adjacent thermocouples is ≤300mm, which is used to monitor the temperature uniformity of different areas during the curing process.

[0028] Encapsulation process: Sequentially cover the release film (completely covering the prepreg area, with edges extending 50mm beyond), the breathable felt (2-3mm thick, no overlap), and the vacuum bag. Leave a 100mm sealing area between the edge of the vacuum bag and the substrate surface, and press it firmly with sealing strips. No pressure equalization plate is required.

[0029] Pre-curing inspection: After the vacuum bag is evacuated to -80KPa, the vacuum system is turned off. The vacuum gauge reading should not drop by more than 17kPa within 5 minutes. If it exceeds the tolerance, the vacuum bag should be checked for leaks such as damage or misalignment of the sealing strip. After repair, the test should be repeated.

[0030] As an improvement to the above technical solution, the specific method of "machining and debonding detection" in step (B) is as follows:

[0031] Machining: A gantry-type five-axis linkage machining center is used, equipped with diamond end mills (face mill diameter 50-80mm, end mill diameter 10-16mm). Roughing (milling speed 800m / min, feed rate 500mm / min, depth of cut 1mm, with 2mm allowance), semi-finishing (milling speed 1000m / min, feed rate 300mm / min, depth of cut 0.5mm, with 0.5mm allowance), and finishing (milling speed 1200m / min, feed rate 200mm / min, depth of cut 0.2mm) are performed. The surface accuracy of the tooling is controlled within ±0.15mm after machining. The forming lines and feature holes are machined simultaneously.

[0032] Debonding test: During the processing, a special rubber hammer with a hardness of 50±5 Shore A is used to tap along the connection edge between the composite shell and the substrate at intervals of 50-100mm. If a hollow sound is heard, the debonding area is marked. After removing the adhesive layer on the surface of the debonding area, structural adhesive is applied, and 1-2 layers of tooling prepreg are covered. The autoclave curing procedure designed in step (A) is followed for re-curing. After curing, a re-inspection test is conducted.

[0033] As an improvement to the above technical solution, the "inspection standard for qualified composite tooling" in step (B) is as follows:

[0034] Surface inspection: A laser tracker with a measurement accuracy of ±0.01mm is used to continuously scan points on the tooling surface at a grid density of 50mm×50mm. The point cloud data is compared with the theoretical surface. If the surface deviation is ≤±0.15mm, it is considered qualified.

[0035] Grating inspection: At least 4 points are randomly selected for inspection on each length side, with a total of no less than 16 inspection points. The gradation width deviation is ≤ ±0.05mm, the depth deviation is ≤ ±0.1mm, and the positional accuracy is ≤ ±0.2mm.

[0036] Air tightness and appearance: During air tightness testing, the tooling surface is sealed and pressurized to 0.2MPa. After holding the pressure for 30 minutes, the pressure drop is ≤0.01MPa. For appearance testing, under a light source with a brightness of ≥500 lux, visually inspect the tooling surface from 300mm away. There should be no cracks with a length >1mm, bubbles with a diameter >2mm, or missing glue with an area >10mm², and no gel coat dripping. The surface roughness should be ≤Ra0.8μm. Ultrasonic non-destructive testing can be added as needed to check for internal defects in the composite shell.

[0037] As an improvement to the above technical solution, the specific operational requirements for "dual-path iterative adjustment" in step (C) are as follows:

[0038] Milling modification path: If the tooling surface deviation is ≤1mm, the existing composite shell is directly milled using a CNC machine tool. The milling parameters are consistent with the finishing parameters in step (B). After milling, the surface is re-inspected to ensure that the deviation is ≤±0.15mm.

[0039] Repair layer curing path: If the tooling surface deviation is >1mm, first sand the gel coat surface of the existing composite shell to Ra=1.6μm with 80-grit alumina sandpaper, clean the surface with acetone to remove dust and residual adhesive, and repair the tooling prepreg in the deviation area according to the layup scheme designed in step (A). The number of repair layers is determined according to the deviation amount (1 layer of prepreg corresponds to every 0.6mm deviation). After repair, cure according to the autoclave curing procedure in step (A), and then go through the finishing and inspection in step (B) to obtain the new surface tooling.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] With reusable substrates and composite layup compensation as the core, this method uses existing product molding tooling, similar structural tooling, or flat tooling as reusable substrates. This eliminates the need to manufacture new traditional metal tooling substrates, and the cost of composite materials such as tooling prepreg is lower than that of metal materials. Compared with traditional all-metal tooling verification methods, this method can reduce the overall cost of tooling verification and mold repair, effectively solving the technical problem of high costs caused by repeated substrate manufacturing for tooling verification in existing technologies.

[0042] By coordinating the three stages of process design, manufacturing implementation, and testing and verification, a dual-path iterative solution is provided for the tooling surface adjustment needs during the testing and verification stage. This solution involves milling the existing composite shell for shaping and adding prepreg to the existing composite shell for curing. This eliminates the need to remake the tooling base, significantly reducing the time spent on repeated manufacturing and assembly of the tooling base in traditional methods. Attached Figure Description

[0043] Figure 1 The reusable substrate selected for this invention;

[0044] Figure 2 This is a schematic diagram showing the position of the molded part and theoretical surface of the present invention;

[0045] Figure 3 This is the modified surface of the present invention.

[0046] In the diagram: 1. Reusable substrate; 2. Laying area; 3. Molded part; 4. Theoretical surface; 5. Modified surface. Detailed Implementation

[0047] 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.

[0048] Example:

[0049] like Figure 1-3 As shown, this embodiment proposes a low-cost method for rapid verification and mold repair of composite material molding tooling. Through the coordinated integration of three stages—process design, manufacturing implementation, and experimental verification—it achieves low-cost, rapid verification and iterative mold repair of the tooling, with reused substrate 1 and composite layup compensation as the core. Specifically, it includes:

[0050] Step (A), Process Design Stage:

[0051] Based on the theoretical surface requirements of the tooling to be verified, the original molding tooling, similar structural tooling, or flat tooling of the product is used as the reuse base 1. The compensation area and thickness of the composite shell are determined through deviation analysis. The tooling prepreg with high fiber density and high resin content and the compatible structural adhesive are selected to match the material selection. The gradient layup scheme and the material cutting, laser projection, and autoclave curing procedures of the supporting processes are designed to provide technical basis for manufacturing implementation.

[0052] Step (B), Manufacturing Implementation Phase:

[0053] The reusable substrate 1 is cleaned and roughened without the need for release agent. The composite prepreg and adhesive are cut and laid according to the process design. After vacuum compaction and thermocouple encapsulation by zoning, it is cured and formed in an autoclave. Then, it is machined and trimmed to the theoretical surface 4. The debonding of the composite shell and the substrate is detected simultaneously. The qualified composite tooling is obtained after surface, airtightness and appearance inspection.

[0054] Step (C), Experimental Verification Phase:

[0055] The parts are formed using qualified composite tooling, and the rationality of the tooling design and forming process is verified by reverse verification of the surface data of the formed part 3.

[0056] If adjustments are needed, the existing composite shell can be modified by milling or by adding prepreg to the existing composite shell and curing it, forming the modified surface 5. This allows for rapid iteration of the tooling surface without having to redo the tooling base.

[0057] In this embodiment, the core is to reuse the substrate 1 and the composite material layup compensation. By using the original molding tooling, similar structural tooling or flat tooling of the product as the reuse substrate 1, there is no need to make a new traditional metal tooling substrate. Moreover, the cost of composite materials such as tooling prepreg is lower than that of metal materials. Compared with the traditional all-metal tooling verification method, the overall cost of tooling verification and mold repair can be reduced, which effectively solves the technical problem that tooling verification requires repeated manufacturing of the substrate, resulting in high costs in the prior art.

[0058] By coordinating the three stages of process design, manufacturing implementation, and testing and verification, a dual-path iterative solution is provided for the tooling surface adjustment needs during the testing and verification stage. This solution involves milling the existing composite shell for shaping and adding prepreg to the existing composite shell for curing. This eliminates the need to remake the tooling base, significantly reducing the time spent on repeated manufacturing and assembly of the tooling base in traditional methods.

[0059] Specifically, the method for "deviation analysis and reuse of base 1" in step (A) is as follows:

[0060] Computer-aided design tools were used to complete the design of the theoretical surface 4 of the tooling. The software deviation analysis function was used to compare the surface differences between the theoretical surface 4 and the reused substrate 1, and a surface difference cloud map was generated to accurately mark the area and thickness of the composite shell that need to be compensated. The compensation thickness was determined based on the maximum deviation between the substrate and the theoretical surface 4, with a range of 0.5-5mm.

[0061] For reusable substrate 1, the original molding tooling of the product should be selected with metal material. Before selection, the substrate surface should be checked for defects such as cracks and corrosion through penetrant testing (PT). It can only be used if the defects do not affect the bonding reliability between the composite shell and the substrate.

[0062] In this embodiment, the theoretical surface 4 of the tooling is designed using computer-aided design tools. The software's deviation analysis function compares the surface differences between the theoretical surface 4 and the reused substrate 1, generating a surface difference cloud map. This allows for intuitive and precise location of the areas requiring compensation in the composite shell layer. Simultaneously, the compensation thickness is controlled within a reasonable range of 0.5-5mm based on the maximum deviation between the substrate and the theoretical surface 4. This design method effectively solves the technical problems of insufficient compensation (tooling surface deviation) or overcompensation (waste of composite materials) caused by "fuzzy areas and thickness set based on experience" in traditional compensation designs. It provides precise dimensional basis for subsequent composite shell layer installation, ensuring from the source that the final tooling surface accuracy meets design requirements (which can be subsequently adjusted to the theoretical surface 4 through machining).

[0063] Existing metal molding fixtures are prioritized as reusable substrates. This leverages the high rigidity and dimensional stability of metal to provide stable support for the application, curing, and subsequent use of the composite shell, preventing substrate deformation that could lead to misalignment in the composite shell molding process. Furthermore, by using penetrant testing (PT) to detect surface defects such as cracks and corrosion, only substrates where defects do not affect the bonding reliability between the composite shell and the substrate are permitted for use. This effectively avoids the risk of stress concentration caused by surface defects (such as cracks or surface unevenness caused by corrosion) damaging the bonding interface between the composite shell and the substrate, leading to delamination of the composite shell during subsequent use of the fixture. This significantly improves the structural reliability and service life of the composite tooling.

[0064] Specifically, the parameters for "material selection and gradient layup scheme" in step (A) are as follows:

[0065] Material selection: The tooling prepreg is a T300 grade carbon fiber fabric prepreg with a fiber areal density of 650 g / m², resin content of 35%, single layer thickness of 0.6 mm, tensile strength after curing ≥1500 MPa, flexural modulus ≥120 GPa, and structural adhesive is a high-strength adhesive for composite materials that cures at 180℃ with a nominal area weight of 244 g / m² and a nominal thickness of 0.2 mm, and has good compatibility with the prepreg resin system;

[0066] Gradual layup scheme: Divide the surface into 3-5 layup thickness zones according to the surface difference cloud map, and use a gradual transition between adjacent zones (thickness difference ≤ 1mm). The layup direction is set according to [90 / 0 / 45 / -45 / 90]s (overall layup) or [45 / -45 / 0 / 45 / -45]s (dropped layer). The total number of overall layups is 10 layers, and the number of dropped layers is 2-5 layers.

[0067] In this embodiment, the tooling prepreg is selected as T300 grade carbon fiber fabric prepreg (tensile strength ≥1500MPa and flexural modulus ≥120GPa after curing). Its high strength and high rigidity characteristics ensure that the tooling can withstand its own weight, composite material laying pressure, and curing thermal stress during autoclave curing (0.5-0.8MPa pressure, 180℃ temperature) and subsequent part molding processes, avoiding failure problems such as plastic deformation and cracking. At the same time, the structural adhesive is selected as a high-strength type that cures at 180℃. Its mechanical properties match those of the prepreg and can work together to support the overall load-bearing capacity of the tooling. This effectively solves the technical problem that the tooling cannot adapt to the harsh working conditions of composite material molding due to the vague selection of traditional materials and insufficient mechanical properties, and provides mechanical protection for the stable molding of parts.

[0068] By dividing the material into 3-5 thickness zones using a gradient layup scheme, with the thickness difference between adjacent zones ≤1mm, and combining this with the fixed parameter of 0.6mm thickness for a single layer of T300 grade prepreg, the 0.5-5mm profile compensation thickness determined in the previous deviation analysis can be precisely matched by adjusting the number of layups (e.g., 0.6mm compensation for 1 layer of prepreg, 1.2mm compensation for 2 layers). This avoids the problem of insufficient or excessive compensation caused by the coarse thickness control of traditional layup schemes. At the same time, the design of a total of 10 layups ensures the overall stiffness of the composite shell, and the control of the number of missing layers (2-5 layers) allows for local thickness adjustments to adapt to profile differences while avoiding excessive layer loss that leads to local weakness. This achieves a precise balance between "local compensation" and "overall stiffness," laying the foundation for subsequent tooling profile accuracy.

[0069] Specifically, the details of the "supporting process procedure" in step (A) are as follows:

[0070] Using the composite materials module of CAD software, a material cutting program (including material number, size and laying position) and a laser projection program (positioning accuracy ±0.1mm) were exported based on the gradient layup scheme.

[0071] The autoclave curing program is set according to the prepreg resin system: heating rate 2-3℃ / min, holding at 180℃ for 2-3h, cooling rate 1-2℃ / min, curing pressure 0.5-0.8MPa, matching the curing characteristics of the prepreg resin.

[0072] In this embodiment, the cutting program containing the sheet number, size and laying position is exported by the composite material module of CAD software. Combined with the laser projection program with a positioning accuracy of ±0.1mm, the problem of large sheet cutting error and fuzzy laying positioning in traditional composite laying is effectively solved, which leads to the deviation of the composite shell surface. It realizes precise control of sheet cutting and laying, and provides a precise process execution basis for the composite shell to be formed according to the preset gradient layup scheme, ensuring the consistency of the composite shell compensation area and thickness with the theoretical design.

[0073] A customized autoclave curing program for prepreg resin systems (heating rate 2-3℃ / min, 180℃ holding time 2-3h, cooling rate 1-2℃ / min, curing pressure 0.5-0.8MPa) achieves precise matching between resin curing characteristics and process parameters. This effectively avoids defects such as incomplete resin curing, internal stress concentration, or weak bonding between the composite shell and the substrate caused by poor adaptability of traditional curing parameters. It ensures that the composite shell obtains stable mechanical properties (such as tensile strength and flexural modulus meeting standards) and dimensional stability after curing. At the same time, it improves the bonding reliability between the composite shell and the reused substrate 1, providing process assurance for the overall structural strength of the tooling and the feasibility of subsequent iterative mold repair.

[0074] The aforementioned supporting process procedures, along with the gradual layup scheme and material selection in the process design stage, form a technical synergy, constructing a closed-loop process system of "design-execution-solidification". This effectively solves the technical problems of low tooling forming accuracy and poor consistency caused by poor connection between various links and discrete parameters in traditional processes. It significantly improves the controllability and stability of the composite tooling manufacturing process, laying a solid foundation for rapid iteration in the subsequent manufacturing implementation stage, including machining and finishing, inspection and qualification, and experimental verification. This ensures the realization of the core objective of this invention: "low cost + rapid verification and mold repair".

[0075] Specifically, the specific operations for "reusing substrate 1 for treatment and applying composite material" in step (B) are as follows:

[0076] Substrate preparation: Clean the substrate surface with acetone (to remove oil, dust and other excess substances), and roughen the laying area 2 by sandblasting or sanding to achieve a surface roughness of Ra=1.6-3.2μm. No release agent is required.

[0077] Composite material laying: Based on the laser projection program positioning, the first layer of structural adhesive film is laid in one piece (the size of the adhesive film exceeds the prepreg layer area by 10mm). Subsequent layers are laid according to the laying plan, with the maximum overlap between the sheets ≤6mm and the maximum gap ≤1.5mm. Vacuum compaction is performed every 2-3 layers (vacuum degree -80~-95KPa, pressure holding time ≥15min).

[0078] In this embodiment, acetone cleaning thoroughly removes oil, dust, and other excess substances from the substrate surface, preventing impurities from obstructing the bonding interface between the composite shell and the substrate. Sandblasting or sandpaper polishing precisely controls the surface roughness to Ra=1.6-3.2μm, significantly increasing the contact area and interfacial friction between the substrate and the adhesive and composite prepreg. At the same time, the step of applying release agent is eliminated, avoiding the damage to the bonding reliability caused by release agent. This effectively solves the technical problems of weak bonding and easy detachment between the composite shell and the substrate caused by incomplete cleaning and poor surface condition compatibility in traditional substrate treatment, providing an interface guarantee for the two to form a stable integrated structure.

[0079] Utilizing laser projection technology, precise positioning of the prepreg is achieved, ensuring that the placement matches the design and avoiding deviations caused by traditional manual positioning. The first layer of structural adhesive film extends 10mm beyond the prepreg layer area, allowing the adhesive to fully cover the edges and eliminating the risk of delamination due to insufficient adhesive at the edges. By controlling the maximum overlap between sheets to ≤6mm and the maximum gap to ≤1.5mm, stress concentration caused by excessive overlap or insufficient adhesive filling due to excessive gaps is avoided. Vacuum compaction is performed after every 2-3 layers at a vacuum degree of -80~-95KPa and a holding time of ≥15min, effectively removing air and excess resin between layers and preventing defects such as bubbles and pores inside the composite shell after curing. This significantly improves the interlayer density and structural integrity of the composite shell, providing a good structural foundation for subsequent curing and machining.

[0080] Specifically, the requirements for "partitioned packaging and autoclave curing" in step (B) are as follows:

[0081] Thermocouple arrangement: In the remaining area of ​​the composite prepreg, the thermocouples are arranged according to the principle of "leading thermocouples in corner / thin layer areas and lagging thermocouples in center / thick layer areas". The spacing between adjacent thermocouples is ≤300mm, which is used to monitor the temperature uniformity of different areas during the curing process.

[0082] Encapsulation process: Sequentially cover the release film (completely covering the prepreg area, with edges extending 50mm beyond), the breathable felt (2-3mm thick, no overlap), and the vacuum bag. Leave a 100mm sealing area between the edge of the vacuum bag and the substrate surface, and press it firmly with sealing strips. No pressure equalization plate is required.

[0083] Pre-curing inspection: After the vacuum bag is evacuated to -80KPa, the vacuum system is turned off. The vacuum gauge reading should not drop by more than 17kPa within 5 minutes. If it exceeds the tolerance, the vacuum bag should be checked for leaks such as damage or misalignment of the sealing strip. After repair, the test should be repeated.

[0084] In this embodiment, the partitioned packaging, pre-curing inspection, and thermocouple arrangement form a closed-loop process control. This ensures the uniformity of the curing reaction through precise temperature monitoring and the stability of the vacuum environment through reliable packaging and pre-inspection. At the same time, it simplifies the packaging process and reduces auxiliary costs. This effectively solves the technical problems of inaccurate temperature control, vacuum seal failure, and poor air permeability in traditional autoclave curing, which lead to many tooling defects and poor consistency. It provides core curing process support for composite tooling to achieve a surface accuracy of ±0.15mm, qualified airtightness, and appearance quality after subsequent processing.

[0085] Specifically, the method for "machining and debonding detection" in step (B) is as follows:

[0086] Machining: A gantry-type five-axis linkage machining center is used, equipped with diamond end mills (face mill diameter 50-80mm, end mill diameter 10-16mm). Roughing (milling speed 800m / min, feed rate 500mm / min, depth of cut 1mm, with 2mm allowance), semi-finishing (milling speed 1000m / min, feed rate 300mm / min, depth of cut 0.5mm, with 0.5mm allowance), and finishing (milling speed 1200m / min, feed rate 200mm / min, depth of cut 0.2mm) are performed. The surface accuracy of the tooling is controlled within ±0.15mm after machining. The forming lines and feature holes are machined simultaneously.

[0087] Debonding test: During the processing, a special rubber hammer with a hardness of 50±5 Shore A is used to tap along the connection edge between the composite shell and the substrate at intervals of 50-100mm. If a hollow sound is heard, the debonding area is marked. After removing the adhesive layer on the surface of the debonding area, structural adhesive is applied, and 1-2 layers of tooling prepreg are covered. The autoclave curing procedure designed in step (A) is followed for re-curing. After curing, a re-inspection test is conducted.

[0088] In this embodiment, machining and debonding detection are carried out simultaneously. High-precision stepped machining ensures the accuracy and feature integrity of the tooling surface, while real-time debonding detection and closed-loop repair promptly eliminate structural defects, forming an integrated process control system of "machining-detection-repair". This collaborative solution effectively solves the problem of "rework and re-manufacturing required after molding" caused by the disconnect between machining and detection in traditional processes, avoiding waste of materials and time. At the same time, it eliminates the need for additional dedicated detection procedures, taking into account machining accuracy, structural reliability and process efficiency, and further supporting the realization of the core goal of this invention: "low cost + rapid verification and mold repair".

[0089] Specifically, the "inspection standards for qualified composite tooling" in step (B) are as follows:

[0090] Surface inspection: A laser tracker with a measurement accuracy of ±0.01mm is used to continuously scan points on the tooling surface at a grid density of 50mm×50mm. The point cloud data is compared with the theoretical surface 4. If the surface deviation is ≤±0.15mm, it is considered qualified.

[0091] Grating inspection: At least 4 points are randomly selected for inspection on each length side, with a total of no less than 16 inspection points. The gradation width deviation is ≤ ±0.05mm, the depth deviation is ≤ ±0.1mm, and the positional accuracy is ≤ ±0.2mm.

[0092] Air tightness and appearance: During air tightness testing, the tooling surface is sealed and pressurized to 0.2MPa. After holding the pressure for 30 minutes, the pressure drop is ≤0.01MPa. For appearance testing, under a light source with a brightness of ≥500 lux, visually inspect the tooling surface from 300mm away. There should be no cracks with a length >1mm, bubbles with a diameter >2mm, or missing glue with an area >10mm², and no gel coat dripping. The surface roughness should be ≤Ra0.8μm. Ultrasonic non-destructive testing can be added as needed to check for internal defects in the composite shell.

[0093] In this embodiment, the testing standards form a comprehensive closed-loop testing system encompassing "dimensional accuracy, feature accuracy, sealing performance, appearance quality, and internal structure." The quantitative indicators and operational specifications for each testing item are clearly defined, ensuring the consistency and reliability of qualified tooling while avoiding the problems of "over-testing and wasting costs" or "under-testing and missing defects" caused by the ambiguity of traditional testing standards. Through strict qualification thresholds, it is ensured that qualified tooling can be directly adapted to the part forming requirements, reducing the frequency of rework in the subsequent testing and verification stages, and further supporting the realization of the core objective of this invention: "low cost + rapid verification and mold repair."

[0094] Specifically, the operational requirements for "dual-path iterative adjustment" in step (C) are as follows:

[0095] Milling modification path: If the tooling surface deviation is ≤1mm, the existing composite shell is directly milled using a CNC machine tool. The milling parameters are consistent with the finishing parameters in step (B). After milling, the surface is re-inspected to ensure that the deviation is ≤±0.15mm.

[0096] Repair layer curing path: If the tooling surface deviation is >1mm, first sand the gel coat surface of the existing composite shell to Ra=1.6μm with 80-grit alumina sandpaper, clean the surface with acetone to remove dust and residual adhesive, and repair the tooling prepreg in the deviation area according to the layup scheme designed in step (A). The number of repair layers is determined according to the deviation amount (1 layer of prepreg corresponds to every 0.6mm deviation). After repair, cure according to the autoclave curing procedure in step (A), and then go through the finishing and inspection in step (B) to obtain the new surface tooling.

[0097] In this embodiment, the two iterative paths precisely adapt to different adjustment needs based on the magnitude of surface deviation, forming a comprehensive iterative system of "rapid milling correction for small deviations and precise patching compensation for large deviations." This effectively solves the technical problem that traditional tooling adjustment schemes are singular and cannot flexibly adapt to different deviation scenarios. Both paths are based on "reusing existing tooling bases + using previously mature process parameters," eliminating the need to remake the base or redesign the process. On the one hand, this significantly reduces the time spent on base manufacturing, assembly, and process development in traditional adjustments; on the other hand, it avoids material waste caused by repeated base manufacturing, further reducing the overall cost of tooling verification and mold repair. This aligns perfectly with the core objective of this invention: "low cost + rapid verification and mold repair." Simultaneously, the structural continuity between the tooling base and the composite shell is ensured during the iteration process. Combined with the matching advantages of the thermal expansion coefficients of the composite shell and composite material parts, surface deviations during tooling curing after iteration can be reduced, providing continuous and reliable tooling support for the stable molding of subsequent parts.

[0098] In this embodiment, the method is applicable to the verification of composite material skin panel tooling with dimensions ≥1000mm×500mm and a minimum radius of curvature ≥500mm, compared to traditional all-metal new tooling verification methods:

[0099] Costs are reduced by more than 55% (no need to create a new metal substrate, and the cost of composite materials is lower than that of metal materials).

[0100] Costs are reduced by more than 55% (no need to create a new metal substrate; the cost of composite materials is lower than that of metal materials).

[0101] The matching degree between the tooling thermal expansion coefficient and the composite material parts is improved by more than 40% (the thermal expansion coefficient of the composite shell is close to that of the parts, reducing the deviation of the surface after curing).

[0102] 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 rapid verification of a composite forming tooling repair method, characterized in that: Through the coordinated connection of the three stages of process design, manufacturing implementation, and test verification, the low-cost rapid verification and iterative mold repair of the tooling is realized by reusing the base (1) and the composite layer compensation, specifically including: Step (A), process design stage: Based on the theoretical profile (4) requirements of the tooling to be verified, the original forming tooling of the product, similar structure tooling or flat plate tooling is used as the reusable base (1), the compensation area and thickness of the composite shell layer are determined through deviation analysis, the material selection matches the tooling prepreg with high fiber density and high resin content and compatible structural adhesive, the gradual layering scheme and the matching process of material cutting, laser projection and autoclave curing program are designed to provide technical basis for manufacturing implementation; Step (B), manufacturing implementation stage: The reusable base (1) is cleaned and roughened without the need for applying release agent, the composite prepreg and adhesive are cut and attached according to the process design, after vacuum compaction and partitioning of thermocouple packaging, autoclave curing is used for forming, and then mechanical processing is used to trim to the theoretical profile (4), and the debonding of the composite shell layer and the base is detected simultaneously, and the qualified composite tooling is obtained through profile, air tightness and appearance detection; Step (C), test verification stage: The qualified composite tooling is used for part forming, and the profile data of the formed part (3) is used to verify the rationality of the tooling design and forming process in reverse; If adjustment is needed, the double path of milling the existing composite shell layer or supplementing the prepreg on the existing composite shell layer is used for forming the modified profile (5), which realizes the rapid iteration of the tooling profile without the need to redo the tooling base.

2. The low-cost rapid verification of a composite forming tool repair method of claim 1, wherein: The specific way of "deviation analysis and reusable base (1)" in step (A) is: The computer-aided design tool is used to complete the design of the theoretical profile (4) of the tooling, the profile difference between the theoretical profile (4) and the reusable base (1) is compared through the software deviation analysis function, the profile difference cloud map is generated, and the area and thickness of the composite shell layer that needs to be compensated are accurately marked. The compensation thickness is determined according to the maximum deviation between the base and the theoretical profile (4), and the range is 0.5-5mm; The reusable base (1) preferentially selects the original forming tooling of the product made of metal material, and the surface of the base is checked for defects such as cracks and corrosion through penetration testing (PT) before selection, and only when the defects do not affect the bonding reliability of the composite shell layer and the base can the base be used.

3. The low cost composite forming tooling rapid verification rework method of claim 1, wherein: The specific parameters of "material selection and gradual layering scheme" in step (A) are: Material selection: T300 grade carbon fiber fabric prepreg with a fiber surface density of 650g / m², a resin content of 35%, a single layer thickness of 0.6mm, a tensile strength of ≥1500MPa after curing, a bending modulus of ≥120GPa, and a structural adhesive with a nominal area weight of 244g / m² and a nominal thickness of 0.2mm, which is compatible with the prepreg resin system. Gradient layup scheme: 3-5 layup thickness regions are divided according to the profile difference nephogram, and gradient transition is adopted between adjacent regions (thickness difference ≤1mm), the layup direction is set as [90 / 0 / 45 / -45 / 90]s (overall layup) or [45 / -45 / 0 / 45 / -45]s (missing layer), the total number of overall layup is 10 layers, and the number of missing layers is 2-5 layers.

4. The low cost composite forming tooling rapid verification rework method of claim 1, wherein: The specific content of "matching process procedure" in step (A) is: Using the composite material module of CAD software, the blank cutting program (including blank number, size and laying position) and laser projection program (positioning accuracy ±0.1mm) are exported based on the gradient layup scheme; The autoclave curing program is set according to the resin system of the prepreg: the heating rate is 2-3℃ / min, the holding temperature is 180℃ for 2-3h, the cooling rate is 1-2℃ / min, the curing pressure is 0.5-0.8MPa, and the curing characteristics of the prepreg are matched.

5. The low cost composite tooling rapid verification rework method of claim 1, wherein: The specific operation of "reusing substrate (1) treatment and laying composite material" in step (B) is: Substrate treatment: clean the substrate surface with acetone (remove oil stains, dust and other unnecessary substances), and use sandblasting or sandpaper polishing method to roughen the laying area (2), so that the surface roughness reaches Ra=1.6-3.2μm, and there is no need to apply release agent; Composite laying: according to the laser projection program, the first layer of structural adhesive film (the film size exceeds the prepreg layup area by 10mm), and then lay the prepreg according to the layup scheme, the maximum overlap between the blanks is ≤6mm, and the maximum gap is ≤1.5mm, and vacuum compaction is carried out once every 2-3 layers (vacuum degree-80~-95KPa, holding time ≥15min).

6. The low cost composite tooling rapid verification rework method of claim 1, wherein: The specific requirements of "partition packaging and autoclave curing" in step (B) are: Thermocouple arrangement: arrange the leading thermocouple in the corner / thin layer area and the lagging thermocouple in the center / thick layer area according to the principle, and the distance between adjacent thermocouples is ≤300mm, which is used to monitor the temperature uniformity of different areas in the curing process; Packaging operation: cover the release film (cover the prepreg area completely, the edge exceeds 50mm), air-permeable felt (thickness 2-3mm, no overlap) and vacuum bag in turn, the edge of the vacuum bag and the substrate surface is reserved 100mm sealing area, and the sealing is compacted with sealing tape, and there is no need to use pressure equalizing plate; Pre-curing detection: after the vacuum bag is evacuated to-80KPa, the vacuum system is closed, and the vacuum table reading should not decrease by more than 17kPa within 5 minutes, if the error is exceeded, check the leakage points such as vacuum bag damage and sealing tape misalignment, and retest after repair.

7. The low cost composite tooling rapid verification rework method of claim 1, wherein: The specific way of "machining and debonding detection" in step (B) is: Machining: Using gantry five-axis machining center, equipped with diamond milling cutter (face milling cutter diameter 50-80mm, end milling cutter diameter 10-16mm), in turn, rough machining (milling speed 800m / min, feed rate 500mm / min, back engagement 1mm, 2mm allowance), semi-finish machining (milling speed 1000m / min, feed rate 300mm / min, back engagement 0.5mm, 0.5mm allowance), finish machining (milling speed 1200m / min, feed rate 200mm / min, back engagement 0.2mm), after machining, the tooling surface precision control in ±0.15mm, synchronous processing forming line and feature hole; Debonding detection: During processing, using special rubber hammer with hardness 50±5 Shore A, along the edge of the connection between the composite shell and the substrate, knock point by point at 50-100mm intervals, if "hollow sound" is emitted, mark the debonding area, remove the surface glue layer of the debonding area, brush the structural adhesive, cover 1-2 layers of tooling prepreg, re-solidify according to the autoclave curing program designed in step (A), and retest after curing.

8. The low cost composite tooling rapid verification rework method of claim 1, wherein: The "qualified composite tooling detection standard" in step (B) is: Surface detection: using a laser tracker with a measurement accuracy of ±0.01mm, continuously scanning points on the tooling surface at a grid density of 50mm×50mm, comparing the point cloud data with the theoretical surface (4), the surface deviation ≤±0.15mm is judged to be qualified; Line detection: at least 4 points are detected for each length edge, and the total number of detection points is not less than 16, the line width deviation ≤±0.05mm, the depth deviation ≤±0.1mm, and the position accuracy ≤±0.2mm; Air tightness and appearance: when detecting air tightness, seal the tooling surface and pressurize to 0.2MPa, keep pressure for 30min, pressure drop ≤0.01MPa; Appearance detection under light source with brightness ≥500lux, visual inspection at 300mm from the tooling surface, surface without crack length >1mm, bubble diameter >2mm, glue area >10mm², and no glue flow phenomenon, surface roughness ≤Ra0.8μm; according to the requirements, ultrasonic nondestructive testing can be added to check the internal defects of the composite shell.

9. The low cost composite tooling rapid verification rework method of claim 1, wherein: The specific operation requirements of "double path iterative adjustment" in step (C) are: Milling repair path: if the tooling surface deviation ≤1mm, directly use the numerical control machine tool to mill the existing composite shell, the milling parameters are consistent with the finishing parameters in step (B), and the tooling surface is detected after milling to ensure that the deviation ≤±0.15mm; Supplement layer curing path: if the tooling surface deviation >1mm, first polish the glue surface of the existing composite shell to Ra=1.6μm with 80 mesh aluminum oxide sandpaper, clean the surface with acetone to remove dust and residual glue, supplement the tooling prepreg in the deviation area according to the layering scheme designed in step (A), the number of supplementary layers is determined according to the deviation (1 layer of prepreg corresponds to 0.6mm deviation), and the new surface tooling is obtained after supplementing, curing according to the autoclave curing program in step (A), and finishing and detecting in step (B).

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