A method for in-situ composite repair of thermoplastic CFRP components

Abstract

This invention belongs to the technical field of aerospace composite material repair, specifically relating to a method for in-situ composite repair of thermoplastic CFRP components. The method first uses additive manufacturing technology to prepare a thermoplastic CFRP repair patch matching the damaged area; then, the interface between the patch and the substrate to be repaired undergoes laser surface texturing and chemical activation composite treatment to enhance the mechanical interlocking and chemical bonding capabilities of the interface; finally, a laser welding process is used to connect the patch and the substrate, and the repair quality is evaluated through non-destructive testing. This invention achieves rapid customization of repair patches and high-strength, high-efficiency connection, and is particularly suitable for in-situ rapid repair of complex curved surface CFRP components such as aircraft fuselages, solving the problems of long repair cycles, poor environmental resistance, and increased weight due to mechanical connections associated with traditional adhesive bonding.

Description

Technical Field

[0002] This invention belongs to the technical field of aerospace composite material repair, specifically relating to a method for in-situ composite repair of thermoplastic CFRP components. Background Technology

[0003] Carbon fiber reinforced thermoplastic composite (CFRTP) is a high-quality lightweight material with advantages such as high specific strength, high damage tolerance, recyclability, and thermoforming, and its application in secondary load-bearing structures such as modern aircraft fuselages and wings is becoming increasingly widespread. However, during service, these components are prone to damage such as scratches, perforations, or delamination due to impacts, affecting structural integrity and safety. Therefore, a reliable repair method is necessary.

[0004] Currently, the aerospace industry has relatively mature standards for the repair of thermosetting CFRP (such as patching or adhesive bonding), but these methods have significant limitations when applied to thermoplastic CFRP. Traditional adhesive bonding repair relies on adhesives such as epoxy resins, which have long curing cycles, poor compatibility with thermoplastic matrices, poor long-term resistance to damp heat fatigue at the interface, and the bonding quality is greatly affected by surface treatment, resulting in insufficient process stability. Mechanical connections (such as riveting) are reliable, but they introduce additional drilling stress concentration points and weight, disrupting fiber continuity and failing to meet the principles of lightweight aircraft. Autoclave repair, while ensuring quality, involves large equipment and is costly, making it difficult to use for in-situ field repairs.

[0005] Laser welding is a precision welding method characterized by concentrated heat source, high energy density, and high degree of automation, which has provided a new approach for joining thermoplastic composites in recent years. It achieves bonding by rapidly heating the resin locally, resulting in high efficiency, high automation, and no additional materials required. However, directly applying laser welding to the repair of carbon fiber reinforced thermoplastic composites requires solving the following technical challenges: first, how to accurately match the complex curved surface damage morphology of the repair patch; second, how to effectively strengthen the bonding interface to withstand aerospace loads; and third, the lack of a complete process system integrating rapid patch fabrication, efficient interface strengthening, and high-quality welding. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies and provide a method for in-situ composite repair of thermoplastic CFRP components. This method integrates digital design, customized additive manufacturing, interface microstructure strengthening and precision laser welding to achieve a closed-loop process from damage identification to high-quality repair.

[0007] The technical solution of this invention is as follows: A method for in-situ composite repair of thermoplastic CFRP components, comprising the following steps: (1) Perform a three-dimensional scan on the damaged area of ​​the thermoplastic CFRP component, and design a three-dimensional model of the repair patch based on the scan data. The three-dimensional scan can be performed using laser three-dimensional scanning or structured light three-dimensional scanning.

[0008] The precise geometric shape of the damaged area is obtained using 3D scanning equipment. Based on this data, a 3D model of a repair patch that precisely matches the damaged area is designed in software. The aforementioned software is all commercially available software known in the field. After importing the point cloud data obtained from the 3D scan, the surface reconstruction of the damaged area and the 3D model design of the repair patch can be completed. This is an operation that can be performed by those skilled in the art without creative effort. The designed repair patch has a planar or stepped shape that matches the damaged area.

[0009] The software used can be 3D modeling / reverse engineering software such as CADfix, CATIA, Siemens NX, SolidWorks, or Materialise Magics. CATIA, Siemens NX, and SolidWorks are general-purpose CAD software in the aerospace manufacturing field, Materialise Magics is commonly used in the field of additive manufacturing data preparation, and CADfix excels in the repair and simplification of 3D models. Those skilled in the art will understand upon seeing the above software names that using them to design the 3D model for repairing patches is a routine operation.

[0010] Flat butt joints are generally used. Flat butt joints allow the patch and the substrate surfaces to be joined to achieve surface-to-surface bonding in a plane perpendicular to the thickness direction, forming a uniform adhesive / fusion interface. The main reason for using flat butt joints instead of more complex joint types such as X-joints or finger joints is twofold. First, considering that CFRP / CFRP laser welding is still a relatively new field, the inherent properties of the materials make it susceptible to localized overheating during the welding process. Therefore, to ensure technological accessibility, this technique aims to avoid localized overheating or interface fusion defects caused by uneven heat accumulation during laser welding, which are common with complex joint types. Second, for patch repair scenarios, flat overlap provides a sufficiently large bonding area, ensuring efficient load transfer. In summary, flat butt joints are the most commonly used and economical joint type in laser welding repair of thermoplastic composite materials.

[0011] Furthermore, when the damage to the thermoplastic CFRP component is penetrating, a stepped patching design is adopted to optimize load transfer; the specific design is as follows: First, determine the number of steps based on the thickness H of the substrate plate of the thermoplastic CFRP component, and control the height h of each step to be between 0.5-1mm. Then, the total number of steps N = H / h.

[0012] The ratio of the width w of each step to the height of the step (i.e., the reciprocal of the cut slope) is designed to be 1:(10-25).

[0013] Research has shown that when the reciprocal of the patch slope is less than 1:10 (i.e., w / h < 10), the step width is too small and the slope is too steep, resulting in insufficient front surface provided by the step surface and limited load transfer area. Under tensile load, significant stress concentration is likely to occur at the interface between the patch and the base material, causing the interface to fail under low load. The strength recovery rate of the repaired structure usually drops to less than 60% of the strength of the raw material, which is difficult to meet the usage requirements of aerospace components.

[0014] When the reciprocal of the cut slope is greater than 1:25 (i.e., w / h>25), although increasing the step width is beneficial to increasing the bonding area, the step is too gentle, resulting in an excessively large area to be removed from the damaged area, damaging more healthy material areas and significantly increasing the weight. At the same time, the excessively large step width significantly increases the total length to be welded during laser welding, and the heat accumulation is more serious. This can easily cause local overheating of the interface and thermal degradation of the resin during welding, which in turn leads to uneven joint quality and reduced repair efficiency.

[0015] The 1:(10-25) range selected in this invention comprehensively balances the bonding area and the amount of structural damage removed, ensuring sufficient load transfer efficiency while avoiding excessive removal of healthy material, thus achieving the optimal design for repair strength and structural damage control.

[0016] When the damage to thermoplastic CFRP components is surface scratches or delamination, a beveled lap joint design is adopted, as detailed below: The lap angle (i.e., the angle between the sloping surface and the plane of the component) of the inclined lap joint is controlled between 3° and 15°, corresponding to an lap length of approximately (3.8H-19.1H), where H is the component thickness. When the lap angle is less than 3°, the lap length is too long, significantly increasing the laser welding path and making heat accumulation difficult to control. When the lap angle is greater than 15°, the shear stress concentration on the lap surface increases, making the lap surface prone to debonding failure under tensile loads. The preferred lap angle is 5°-10°. Within this range, the stress distribution on the lap surface is uniform, the welding quality is high, and the strength recovery rate of the repaired structure can reach over 85%.

[0017] In addition, the key parameters of the beveled overlap design should also be considered in conjunction with the following factors: 1. The fiber orientation of the overlap surface should be as consistent as possible with the surface orientation of the original component; 2. The thickness of the overlap end should ensure that the thinnest end of the patch has sufficient structural rigidity, usually not less than 0.2 mm, and the surface roughness Ra of the overlap surface should be ≤ 3.2 μm (after laser treatment); 3. The step overlap length of the overlap surface should ensure that the laser beam can fully heat it to a molten state, and the minimum width of the overlap surface is generally set at 5 mm.

[0018] (2) Select a continuous carbon fiber reinforced thermoplastic composite material that is the same as or compatible with the matrix material of the thermoplastic CFRP component to be repaired, and fabricate the customized repair patch of step (1) by layer-by-layer deposition through fused deposition modeling (FDM) or selective laser sintering (SLS) additive manufacturing process. The continuous carbon fiber reinforced thermoplastic composite material is either filament or powder.

[0019] Furthermore, the fused deposition modeling employs a multi-axis robotic FDM system, which enables normal printing on complex curved surfaces and optimizes the fiber placement direction.

[0020] Furthermore, the printing path is optimized based on the patch's 3D model and stress direction to ensure oriented fiber arrangement. During the printing process, robot path planning ensures that the continuous fiber laying direction aligns with the main load-bearing direction of the repair area, maximizing the mechanical properties of the repair patch.

[0021] For different types of thermoplastic matrices, the printing temperature should be set according to their melting characteristics: for PA12-based composites, the printing temperature should be controlled at 200-230℃; for PA6-based composites, the printing temperature should be controlled at 270-300℃; for PP (polypropylene)-based composites, the printing temperature should be controlled at 180-220℃; for PEI (polyetherimide)-based composites, the printing temperature should be controlled at 340-380℃; for PPS (polyphenylene sulfide)-based composites, the printing temperature should be controlled at 300-330℃. The printing layer thickness should be controlled at 0.15-0.5mm, and the run spacing (i.e., fill line spacing) should be optimized to 0.4-0.8mm, adjusted according to the substrate type.

[0022] For crystalline, non-crystalline and semi-crystalline thermoplastic composites, the temperature setting of the printing chamber should be differentiated as follows: (1) For semi-crystalline polymers (such as PEEK, PA6), the temperature of the printing chamber should be 70-100℃ to control the crystallinity and avoid warping and deformation of the components; (2) For non-crystalline polymers (such as PEI, PPSU), the temperature of the printing chamber should be 50-70℃, mainly to prevent internal stress concentration caused by excessive temperature gradient; (3) For highly crystalline polymers (such as PA66), the temperature of the printing chamber should be 80-110℃, and it is advisable to use slow cooling with the furnace to promote full crystallization and dimensional stability.

[0023] (3) Laser surface treatment was performed on the damaged area of ​​the substrate of the thermoplastic CFRP component and the surface to be connected of the repair patch, including cleaning and activation and microtexturing. The specific operation is as follows: First, pulsed laser is used to remove surface contaminants and activate the surface; Then, short-pulse lasers (such as nanosecond or femtosecond lasers) are used to construct micro-textures on the activated surface, creating an array of micro-pits or micro-grooves. This micro-texture can significantly increase surface roughness and mechanical interlocking area. Precise and controllable micro-textures can be constructed on the interface to be welded using nanosecond or femtosecond pulsed lasers.

[0024] To further promote interface integration, after constructing the microtexture, a pure thermoplastic film or powder with the same composition as the matrix resin can be pre-laid on the treated surface as an intermediate layer.

[0025] Furthermore, the micro-pit array is constructed as follows: laser parameters are set to wavelength 1064 nm, pulse width 100 ns-500 fs, and single pulse energy 0.1-1 mJ. An array of micro-pits is formed by scanning the surface to be treated. The pit diameter is controlled at 50-150 μm, the depth at 30-100 μm, and the ratio of the spacing (center-to-center distance) to the diameter (i.e., area occupancy) of adjacent pits is optimized to 40%-60%.

[0026] Furthermore, the microgroove array is constructed by using femtosecond laser cross-scanning to form a grid-like or parallel microgroove. The groove width is 30-80 μm, the depth is 20-50 μm, and the groove spacing is 100-200 μm. This grid structure not only increases the bonding area but also guides the flow of molten resin, forming a uniform interlocking layer.

[0027] (4) Align the repair patch processed in step (3) with the component substrate, and use a laser beam to scan the welding area to melt and bond the interface resin. The laser welding uses an infrared fiber laser or a semiconductor laser with a laser power of 100-500W and a scanning speed of 5-50mm / s. The welding process is carried out under inert gas protection.

[0028] The prepared patch is precisely assembled onto the damaged area of ​​the substrate, and slight pressure is applied to ensure interface contact. A fiber laser or similar device is used as a heat source to scan the welding area along the designed path. The laser energy is absorbed by the surface and converted into heat, causing the resin and intermediate layer material at the interface between the patch and the substrate to melt, flow, diffuse, and fill the microtexture. After cooling and solidification, a high-strength metallurgical-chemical bond is formed, primarily based on mechanical interlocking and secondarily by the diffusion and entanglement of molecular chains.

[0029] Furthermore, to address the heat accumulation issue during welding of large areas or complex contours, step (4) employs a segmented laser path, as detailed below: First, the preheating stage path: For the initial welding area of ​​the repair patch, a reciprocating scanning path is used for preheating. The laser beam rapidly oscillates back and forth in the initial section within an area of ​​approximately 100-400 mm (e.g., 10 mm × 10 mm to 20 mm × 20 mm) until the temperature in this area rises slightly above the resin melting point Tm but below the decomposition temperature Td. Specifically, for PEEK-based composites, the preheating temperature is controlled at 360-400℃ (PEEK's Tm ≈ 343℃, Td ≈ 550℃); for PA6-based composites, the preheating temperature is controlled at 230-270℃ (PA6's Tm ≈ 220℃, Td ≈ 350℃). Using this preheating temperature effectively eliminates the "heating hysteresis" effect without causing resin thermal decomposition, resulting in a more uniform interface temperature distribution during the subsequent fusion stage. 2 Then, the fusion stage path: After the initial area is preheated, it switches to an adaptive fusion path. The laser head moves according to a preset trajectory (such as circular, spiral, or grating).

[0030] For ring-shaped patches, spiral scanning from the inside out or from the outside in is used; For long strip patches, segmented variable-speed scanning is used.

[0031] By monitoring online or predicting based on finite element models, the scanning speed is automatically increased or the laser power is reduced in areas with severe heat accumulation (such as the end of a path or a corner), ensuring that the highest temperature of the entire welding interface is always controlled below the resin decomposition temperature, and the temperature fluctuation range is controlled within ±40℃.

[0032] For example, when welding PEEK-CF, the peak interface temperature should be controlled between 400-450℃.

[0033] (5) Post-process the welded joint and evaluate the repair quality using non-destructive testing methods. Non-destructive testing includes ultrasonic C-scan testing or infrared thermography.

[0034] After welding, any excess material at the weld toe is lightly ground to ensure a smooth transition. Finally, non-destructive testing techniques such as ultrasonic C-scanning or pulsed thermography are used to comprehensively inspect the repaired area to confirm the fusion quality of the weld interface and to ensure there are no defects such as porosity, cracks, or lack of fusion.

[0035] The beneficial effects of the present invention are as follows: The method described in the present invention first prepares a thermoplastic CFRP repair patch that matches the damaged area using additive manufacturing technology; then, the interface between the patch and the substrate to be repaired is subjected to laser surface texturing and chemical activation composite treatment to enhance the mechanical interlocking and chemical bonding ability of the interface; finally, the patch and the substrate are connected by laser welding process, and the repair quality is evaluated by non-destructive testing.

[0036] This invention enables rapid customization and high-strength, high-efficiency connection of repair patches, and is particularly suitable for in-situ rapid repair of complex curved CFRP components such as aircraft fuselages. It solves the problems of long repair cycles, poor environmental resistance, and increased weight of mechanical connections in traditional adhesive bonding.

[0037] This invention proposes a composite repair method for damaged thermoplastic CFRP using additive manufacturing and laser welding. This method seamlessly integrates digital design, additive manufacturing, and laser processing technologies to achieve customized, rapid, and automated patch connection. Simultaneously, laser processing combined with electrochemical treatment enhances the surface microtexture during pre-weld preparation, thereby strengthening the interfacial bonding strength. Ultimately, the interfacial bonding strength far exceeds that of traditional adhesive bonding, and the joint mechanical properties can reach over 80% of the original material, achieving effective customized welding repair. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the process of the composite repair method described in this invention.

[0039] Figure 2 A two-dimensional cross-sectional schematic diagram of the stepped excavation and repair design.

[0040] Figure 3 Schematic diagram of laser interface processing: constructing microtexture.

[0041] Figure 4 This is a schematic diagram illustrating the principle of mechanical interlocking formed by the microtexture at the interface filled with molten resin during laser welding. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0043] Example 1 This embodiment addresses the repair of perforations in PA6-CFRP components used in aircraft flat panels.

[0044] Specifically: Repair a φ10mm perforation on a 2mm thick PA6 (Nylon 6) based carbon fiber reinforced composite plate.

[0045] The method for in-situ composite repair of thermoplastic CFRP components comprises the following specific steps: (1) Use a laser 3D scanner to acquire 3D point cloud data of the perforation and its surrounding area. In CAD software (CATIA V5 in this embodiment), design a circular stepped patch with a diameter 0.5-1mm larger than the perforation. Specifically, the patch diameter is 10.5-11mm, with two steps, each layer 1mm thick. The ratio of the step width w to the step height h (the reciprocal of the cut slope) is 1:20, and the total number of cut layers N=2.

[0046] (2) The patch was printed using PA6-CF filament of the same grade as the base material via a dual-nozzle FDM 3D printer. One nozzle deposited continuous carbon fiber to provide strength, while the other nozzle deposited pure PA6 resin to fill the gaps and ensure interface weldability. The printing parameters used in this embodiment were: printing temperature 280℃, heated bed temperature 45℃, layer thickness 0.2mm, runner spacing 0.6mm, and printing speed 40mm / s. During the printing process, the printing chamber was kept at a constant temperature of 70℃ (PA6 is a non-high-temperature material, so the chamber temperature was set relatively low); the fiber was laid radially to ensure the patch's load-bearing capacity during perforation repair.

[0047] (3) Laser treatment is performed on the stepped surface inside the perforated substrate and the back of the patch.

[0048] First, a low-power infrared laser (10W power, 1064nm wavelength, 50ns pulse width, 200mm / s scanning speed) is used to scan and remove the release agent and activate the surface.

[0049] Subsequently, a nanosecond pulsed ultraviolet laser was used, with a wavelength of 355 nm, a pulse width of 15 ns, and a single pulse energy of 0.5 mJ, to create an array of micro-pits with a depth of approximately 50 μm and a spacing of approximately 100 μm on the surface. After treatment, a layer of PA6 powder was lightly applied to both surfaces. The purpose of the above surface activation and microtexturing treatment was: (1) to remove contaminants such as release agents and increase surface energy; (2) to construct a mechanically interlocking structure and enhance interfacial bonding; and (3) to improve the wetting and diffusion conditions of the molten resin.

[0050] (4) Embed the patch into the stepped hole in the substrate and gently press it in place with a clamp. Use a 500W fiber laser and a segmented laser welding path, as follows: Preheating stage: First, reciprocating scanning preheating is performed at the starting position of the patch circumference (approximately 10° arc length area), with a laser power of 80W and a scanning speed of 30mm / s, raising the interface temperature to 240-260℃ (Tm≈220℃ for PA6) to eliminate the heating hysteresis effect.

[0051] Fusion Stage: After preheating, switch to the adaptive fusion path, set the power to 150W, scanning speed to 15mm / s, and spot diameter to 1mm, and perform welding along the circumference of the patch. During welding, the interface temperature is monitored in real time by online infrared thermography. When the temperature in a local area exceeds 300℃ (the decomposition temperature of PA6 is approximately 350℃, with a 50℃ safety margin), the scanning speed is automatically increased to 25mm / s to ensure that the peak temperature of the entire welding interface is always controlled below the decomposition temperature, and the temperature fluctuation range is controlled within ±40℃.

[0052] Argon gas is used for protection throughout the welding process, with a gas flow rate of 5L / min.

[0053] (5) After cooling, lightly polish the outer surface to make it smooth. Ultrasonic C-scan inspection was used, and the image showed good interface fusion and no defects.

[0054] Tests showed that the tensile strength of the repaired area recovered to 85% of the original board strength.

[0055] Example 2 This embodiment focuses on the repair of impact damage to PEEK-CFRP curved aircraft skin.

[0056] Specifically, the task is to repair low-energy shock delamination damage on a piece of aircraft skin (PEEK-based CFRP) with single curvature.

[0057] (1) A handheld structured light scanner was used to scan the concave damage area and reconstruct the surface model. A variable thickness patch model matching the curvature of the surface was designed. The patch was 2 mm at its thickest point and 0.5 mm at its thinnest point. The transition area changed continuously according to the curvature.

[0058] (2) A robot-assisted FDM system was used for printing. The robot arm held the print head and deposited material along the normal direction of the curved surface, ensuring that the patch fibers were arranged along the principal stress direction and perfectly fitted to the curved surface. The printing parameters used in this embodiment were: printing temperature 400℃, constant temperature of the printing chamber 90℃, printing layer thickness 0.15mm, track spacing 0.5mm, and printing speed 30mm / s. The fiber placement direction was optimized by finite element analysis and was consistent with the direction of the maximum principal stress in the impact damage zone.

[0059] (3) A femtosecond laser was used to treat the damaged area of ​​the substrate (after the delaminated portion) and the back side of the patch. The femtosecond laser parameters were set as follows: wavelength 800 nm, pulse width 150 fs, single pulse energy 0.2 mJ, and scanning spacing 50 μm. While precisely controlling the heat-affected zone, the femtosecond laser processed finer cross-grid microgrooves with a groove width of 40 μm, a depth of approximately 30 μm, and a groove spacing of 150 μm. Subsequently, a layer of PEEK suspension (5 wt% solid content) was sprayed as an intermediate layer.

[0060] (4) The patch is accurately placed in the repair area using a robot-assisted positioning system. A coaxial vision-monitored laser welding head is used to scan and weld according to a preset curved surface path. A segmented laser welding path is adopted, as follows: Preheating stage: Preheating is carried out using a spiral scanning path from the inside out. The preheating area is about 20mm in diameter, with a laser power of 150W and a scanning speed of 20mm / s, raising the interface temperature to 380-400℃ (PEEK's Tm ≈ 343℃).

[0061] Fusion Stage: After preheating, the laser power is 300W, the scanning speed is 10mm / s, the spot diameter is 0.8mm, and the laser scans spirally from the inside out (pitch 0.5mm), with argon gas protection throughout (gas flow rate 8L / min). During welding, real-time feedback is provided by coaxial infrared thermography. When the interface temperature exceeds 460℃, the laser power automatically drops to 200W; when the temperature is below 380℃, the power automatically rises back to 300W, ensuring that the interface temperature is controlled between 380-460℃ (PEEK decomposition temperature is approximately 550℃, leaving a safety margin).

[0062] (5) After welding, the edges of the patch are lightly ground to make the surface smooth. Then, pulsed thermal imaging is used to conduct a comprehensive inspection of the repaired area to confirm that the weld interface is well fused, the delaminated areas have been completely repaired, and there are no defects such as incomplete fusion, porosity or cracks. A uniform and firm mechanical interlocking layer is formed between the patch and the substrate. Ultrasonic C-scan is used for re-inspection to further verify the interface fusion quality.

[0063] After on-site repairs, the aerodynamic shape of the skin was restored well. Shear tests showed that the interface strength met the maintenance requirements for secondary load-bearing structures in aerospace applications.

[0064] Tests showed that the tensile strength of the repaired area recovered to 89% of the original board strength.

[0065] Example 3 This embodiment addresses the surface scratch repair of the PEI-CFRP (polyetherimide-based carbon fiber reinforced composite) curved structure on the inner wall of an aero-engine nacelle.

[0066] Specifically, the task is to repair surface scratches on a 3mm thick PEI-CFRP laminate (scratch depth 0.5mm, length 50mm).

[0067] (1) The scratched area was scanned using a structured light 3D scanner to reconstruct the surface morphology. Based on the scan data, a 3D model of the beveled overlapping patch was designed in CATIA software. The overlapping slope angle was 8°, the overlapping bevel was along the scratch direction, the overlapping length was about 30mm, and the patch thickness gradually changed from 0.2mm (overlapping end) to 0.5mm (thickest part).

[0068] (2) The repair patch was prepared using selective laser sintering (SLS). PEI-CF powder (20% carbon fiber volume fraction) was selected, and the SLS processing parameters were: laser power 25W, scanning speed 3500mm / s, and layer thickness 0.12mm. Pure PEI powder was used as the interface layer material, and a PEI interlayer film with a thickness of about 0.05mm was also prepared by SLS to enhance interface fusion in the subsequent welding process.

[0069] (3) Laser surface treatment was performed on the surface of the scratched area of ​​the substrate and the back of the patch. First, surface contaminants were removed and activated using an infrared nanosecond laser (laser parameters: wavelength 1064nm, average power 15W, pulse width 30ns, scanning speed 100mm / s). Then, parallel microgrooves were constructed on the surface using a femtosecond laser (parameters: wavelength 1030nm, pulse width 500fs, single pulse energy 0.15mJ, scanning speed 200mm / s), with a groove width of 30μm, a depth of 20μm, and a groove spacing of 80μm. After treatment, the PEI interlayer film was placed on the overlapping surface.

[0070] (4) Place the PEI interlayer film and the repair patch sequentially on the surface of the damaged area and fix them with a clamp. Use a fiber laser (wavelength 1070nm, maximum power 200W) to perform laser welding along the lap length of the inclined plane. Segmented welding path: In the preheating stage, perform reciprocating scanning preheating in the lap start area (5mm long), with a power of 50W, a scanning speed of 20mm / s, and a target preheating temperature of 250-270℃ (PEI's Tm ≈ 217℃); in the fusion stage, use a laser power of 100W, a scanning speed of 10mm / s, and a spot diameter of 0.6mm. Argon gas protection is maintained throughout the process (gas flow rate 5L / min), and the interface temperature is controlled to not exceed 330℃ by online infrared temperature measurement, with temperature fluctuations controlled within ±40℃.

[0071] (5) After welding, the edges of the patch were lightly ground to make the surface smooth. Ultrasonic C-scan and pulsed thermal imaging were used to confirm that the weld interface was uniform and firm, without delamination, porosity or lack of fusion defects. The test showed that the bending strength of the repaired area was restored to 87% of the original sheet strength.

[0072] Comparative Example 1 The difference from Example 1 is that in step (1), the ratio of the step width w to the step height h (i.e., the reciprocal of the cut slope) is designed to be 1:30 (exceeding the upper limit of the preferred range of 1:10-25).

[0073] The other steps and parameters are the same as in Example 1, including: PA6-CF filament printing parameters (printing temperature 280℃, layer thickness 0.2mm, track spacing 0.6mm), laser welding parameters (preheating power 80W, welding power 150W, scanning speed 15mm / s), and the same surface treatment and inspection methods.

[0074] Results: Due to the excessively small cut-out angle (w / h=30) and excessively large step width, the area to be removed from the damaged region increased significantly, the total weld length increased by approximately 20%, and heat accumulation became more severe. The tensile strength recovery rate was only 68%, significantly lower than that of Example 1 (85%), and localized resin carbonization occurred at the distal end of the welded area. This comparative example shows that when the reciprocal of the cut-out angle exceeds 1:25, the repair effect deteriorates significantly.

[0075] Tests showed that the tensile strength of the repaired area recovered to 68% of the original board strength.

[0076] Comparative Example 2 The difference from Example 1 is that in step (2), the spacing between FDM print lines (fill line spacing) is set to 1.2 mm (significantly greater than the preferred value of 0.4-0.8 mm).

[0077] Other steps and parameters are the same as in Example 1, including: the inverse of the cut slope is 1:20, laser welding parameters, surface treatment methods, etc.

[0078] Results: Due to the excessive interlayer spacing, the internal filling density of the patch was insufficient, increasing the interlayer porosity by approximately 2%, which led to a decrease in the patch's own stiffness and localized thermal deformation during welding. The tensile strength recovery rate was only 72%, lower than that of Example 1 (85%), and the failure mode changed from cohesive failure in Example 1 to delamination failure at the patch-base interface. This comparative example shows that when the interlayer spacing exceeds 0.8 mm, the quality of the patch itself decreases, which is not conducive to obtaining high-strength repairs.

[0079] Tests showed that the tensile strength of the repaired area recovered to 72% of the original board strength.

Claims

1. A method for in-situ composite repair of thermoplastic CFRP components, characterized in that, Includes the following steps: (1) Perform three-dimensional scanning of the damaged area of ​​the thermoplastic CFRP component and design a three-dimensional model of the repair patch based on the scanning data; (2) Select a continuous carbon fiber reinforced thermoplastic composite material that is the same as or compatible with the matrix material of the thermoplastic CFRP component to be repaired, and build up the customized repair patch in step (1) layer by layer through melt deposition molding or selective laser sintering additive manufacturing process. (3) Laser surface treatment was performed on the damaged area of ​​the thermoplastic CFRP component and the surface of the repair patch to be joined, including cleaning, activation and microtexturing; the specific operation is as follows: First, pulsed laser is used to remove surface contaminants and activate the surface; Then, short-pulse lasers are used to construct micro-textures on the activated surface, creating an array of micro-pits or micro-grooves. (4) Align the repair patch after step (3) with the component substrate, and use a laser beam to scan the welding area to melt and bond the interface resin; the laser welding uses an infrared fiber laser or a semiconductor laser with a laser power of 100-500W and a scanning speed of 5-50mm / s, and the welding process is carried out under inert gas protection. (5) Post-treatment of the welded joint and evaluation of the repair quality using non-destructive testing methods.

2. The method for in-situ composite repair of thermoplastic CFRP components according to claim 1, characterized in that, In step (1), when the damage to the thermoplastic CFRP component is penetrating damage, a stepped patching design is adopted; the specific design is as follows: First, determine the number of steps based on the thickness H of the substrate plate of the thermoplastic CFRP component, and control the height h of each step to be between 0.5-1mm. Then, the total number of steps N = H / h. Then, the ratio of the width w of each step to the height of the step is designed to be 1:(10-25).

3. The method for in-situ composite repair of thermoplastic CFRP components according to claim 1, characterized in that, In step (1), when the damage to the thermoplastic CFRP component is surface scratches or delamination, a beveled lap joint design is adopted, as follows: The lap angle of the inclined surface overlap is controlled between 3° and 15°, and the corresponding lap length is controlled between 3.8H and 19.1H, where H is the thickness of the component.

4. The method for in-situ composite repair of thermoplastic CFRP components according to claim 1, characterized in that, In step (2), the fused deposition modeling process employs a multi-axis robot FDM system. For PA12-based composite materials, the printing temperature should be controlled at 200-230℃; For PA6-based composite materials, the printing temperature should be controlled between 270-300℃; For PP-based composite materials, the printing temperature should be controlled between 180-220℃; For PEI-based composite materials, the printing temperature should be controlled between 340-380℃; For PPS-based composite materials, the printing temperature should be controlled at 300-330℃; The printing layer thickness is controlled at 0.15-0.5mm, and the track spacing is controlled at 0.4-0.8mm.

5. The method for in-situ composite repair of thermoplastic CFRP components according to claim 1, characterized in that, During the melt deposition molding process in step (2), for semi-crystalline polymers, the printing chamber is kept at a constant temperature of 70-100℃. For non-crystalline polymers, the printing chamber temperature is kept constant at 50-70℃; For highly crystalline polymers, the printing chamber is kept at a constant temperature of 80-110℃.

6. The method for in-situ composite repair of thermoplastic CFRP components according to claim 1, characterized in that, The construction of the micro-pit array in step (3) is as follows: the laser parameters are set to wavelength 1064nm, pulse width 100ns-500fs, and single pulse energy 0.1-1mJ; An array of micro-pits is formed by scanning the surface to be treated. The pit diameter is controlled between 50-150 μm, the depth is controlled between 30-100 μm, and the ratio of the spacing between adjacent pits to their diameter is controlled between 40%-60%.

7. The method for in-situ composite repair of thermoplastic CFRP components according to claim 1, characterized in that, The construction of the microgroove array in step (3) is achieved by using femtosecond laser cross-scanning to form a grid-like or parallel microgroove. The trench width is 30-80μm, the depth is 20-50μm, and the trench spacing is 100-200μm.

8. The method for in-situ composite repair of thermoplastic CFRP components according to claim 1, characterized in that, The segmented laser path is used in step (4), as follows: First, the preheating stage path: For the initial welding area of ​​the repair patch, a reciprocating scanning path is used for preheating; The laser beam initially has an area of ​​100-400 mm². 2 The region is rapidly oscillating back and forth until the temperature of that region rises to between the resin melting point Tm and the decomposition temperature Td. Then, the fusion stage path: after the initial area is preheated, switch to the adaptive fusion path; the laser head moves according to the preset trajectory; For ring-shaped patches, spiral scanning from the inside out or from the outside in is used; For long strip patches, segmented variable-speed scanning is used.

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