Method and device for inhibiting internal defects of carbon fiber composite material vacuum bag in curing forming

Abstract

The invention belongs to the technical field of composite material manufacturing, relates to a method and a device for inhibiting internal defects in curing forming of a carbon fiber composite material vacuum bag, and aims to solve the problem of energy intervention blindness caused by lack of real-time sensing and response capability for defect generation dynamics in the prior art. According to the method, on the basis of the synergistic effect of terahertz in-situ imaging and ultrasonic targeted intervention, through four-stage closed-loop control of real-time monitoring, defect reconstruction, decision positioning and in-situ repair, space-accurate and parameter-adaptive repair is carried out on submillimeter pores, cracks or layering defects before resin gelation; the matching device integrates a terahertz detection module, an ultrasonic vibration module and a five-axis linkage positioning mechanism, and adopts mutual exclusion time sequence control to avoid multi-physics field interference. Through the scheme, the consistency of the internal quality of the composite material and the qualified rate of finished products can be remarkably improved on the premise of not disturbing fiber orientation.

Description

Technical Field

[0001] This invention belongs to the field of composite material manufacturing technology, and specifically relates to a method and apparatus for suppressing internal defects in the vacuum bag curing and molding of carbon fiber composite materials. Background Technology

[0002] Carbon fiber composites, with their superior specific strength and specific modulus, have become the preferred material for key structural components in strategic fields such as aerospace, high-end equipment, and new energy. Among various molding processes, vacuum bag curing has long held a dominant position due to its simple equipment, controllable cost, and applicability to complex curved surfaces. However, this process consistently faces a fundamental challenge in practical applications: during the dynamic process of resin flow, gelation, and final curing, factors such as fluctuations in vacuum level, uneven prepreg layer spacing, or sudden changes in resin viscosity can easily induce hidden defects such as porosity, microcracks, and even interlayer delamination within the material. Although these defects are small in scale, they can significantly weaken interfacial bonding strength, cause stress concentration, and ultimately lead to premature component failure during service, severely restricting the reliability and yield of high-performance composite materials.

[0003] To address these issues, existing technologies have evolved along two main paths. The first is the "post-inspection" model, where non-destructive testing of the product is performed using industrial computed tomography (CT) or contact ultrasonic testing after complete curing. While this method can identify macroscopic defects, the repair window is completely closed, limiting its use to scrapping or rework, and preventing process intervention, resulting in significant waste of materials and time. The second approach attempts to introduce an auxiliary energy field during curing, as described in published patent CN117283897A, which applies global mechanical vibration or wide-area ultrasonic excitation to the outside of the mold or vacuum bag, aiming to promote bubble migration and expulsion through disturbance. Such solutions can indeed improve density under specific conditions, and their design logic is based on a simplified causal chain of "energy input—flowability improvement—defect suppression," and was once considered an effective means of improving process robustness.

[0004] However, as composite material components develop towards larger sizes, thinner walls, and higher integration, the requirements for internal quality uniformity and microstructural integrity in application scenarios are becoming increasingly stringent, gradually highlighting the inherent limitations of the aforementioned technical approaches at the principle level. Fundamentally, this stems from a lack of perception and response mechanisms for the dynamics of defect generation, leading to a severe spatiotemporal mismatch between "energy application" and "defect state." Specifically, the global vibration strategy is essentially an open-loop control, with a uniform but indiscriminate energy distribution. This not only fails to provide precise intervention in local defect initiation areas but may also trigger secondary risks due to continuous high-frequency excitation: on the one hand, excessive shear force can easily disrupt the precisely arranged carbon fiber orientation, destroying the pre-set mechanical anisotropy; on the other hand, the dissipation of ultrasonic energy in the resin phase can cause local temperature rises, which, if superimposed with curing exothermic peaks, may lead to local over-curing or thermal stress concentration, thus inducing new defects. More importantly, traditional ultrasonic testing relies on liquid coupling media, making it difficult to deploy in situ in a high-temperature, sealed vacuum bag environment. Furthermore, its signal attenuates drastically in high-temperature resin, failing to provide continuous and reliable feedback information, resulting in the entire process being "blindly operated".

[0005] Against this backdrop, a deep-seated technical contradiction emerges: the effectiveness of defect suppression highly depends on real-time understanding of the defect's location, type, and evolution stage. However, existing non-contact detection methods (such as infrared thermal imaging) lack sufficient resolution, while contact methods are incompatible with the curing environment. Simultaneously, if energy intervention methods lack spatial selectivity and parameter adaptability, their gain effect will be offset by potential damage to the substrate structure. In other words, simply increasing the energy input intensity or extending the action time cannot linearly improve the defect suppression effect; instead, it may trigger a vicious cycle of performance trade-offs—revealing a fundamental break in the existing technology's "perception-decision-execution" closed-loop chain. Especially when facing defects with different physical mechanisms, such as sub-millimeter-level micropores and deep interface delamination, uniform process parameters clearly cannot simultaneously address multiple objectives such as penetration depth, cavitation intensity, and structural protection.

[0006] Therefore, the key to overcoming the current bottleneck in the molding quality of carbon fiber composites lies in developing a closed-loop suppression method that can achieve high-resolution in-situ imaging and precise three-dimensional localization of internal defects in the closed, dynamic, and high-temperature environment of vacuum bag curing, and dynamically match ultrasonic intervention parameters to implement precise spatial delivery. This method needs to simultaneously address multiple challenges, including the environmental adaptability of the detection method, the sub-millimeter accuracy of the positioning system, the on-demand controllability of energy application, and the temporal compatibility of multi-physics field collaborative operation, in order to achieve "targeted elimination" of defects at their inception without disturbing the fiber structure. Summary of the Invention

[0007] This invention provides a method and apparatus for suppressing internal defects in vacuum bag curing of carbon fiber composite materials, aiming to solve the problem of blind energy intervention caused by the lack of real-time perception and response capability to the dynamics of defect generation in existing technologies. To achieve the above-mentioned objective, this invention proposes a closed-loop control method based on the synergistic effect of terahertz in-situ imaging and ultrasonic targeted intervention, and constructs a high-precision positioning and execution mechanism to ensure spatially precise and parameter-adaptive in-situ repair of defects such as sub-millimeter-level micropores, cracks, or interlayer delamination without disturbing the fiber orientation.

[0008] The suppression method comprises four stages: real-time monitoring, defect reconstruction, decision-making and localization, and in-situ repair. In the real-time monitoring stage, during the vacuum bag curing process, a mobile platform drives a terahertz detection module to scan the carbon fiber prepreg point-by-point along a preset trajectory, acquiring the terahertz time-domain signal corresponding to each scanning position. This signal is the echo sequence formed by the terahertz wave penetrating the composite material, reflecting back to the detector after passing through the bottom surface of the mold. In the defect reconstruction stage, the terahertz time-domain signal undergoes time-of-flight extraction, Fourier transform, and image reconstruction processing sequentially to obtain the three-dimensional feature information of the defect. This three-dimensional feature information specifically includes the defect type, defect depth coordinates, and defect size. The defect type is determined based on the combination of phase shift and amplitude attenuation of the reflected signal at different frequency bands. Pores exhibit uniform attenuation across a wide frequency band without significant phase jumps, cracks show significant attenuation of local high-frequency components accompanied by phase abrupt changes, while delamination defects exhibit strong low-frequency reflection superimposed with multipath interference effects.

[0009] During the decision-making and positioning phase, the control system invokes a pre-stored mapping model based on the three-dimensional feature information of the defect, calculates matching ultrasonic suppression parameters, and instructs the five-axis linkage positioning module to precisely align the transmitting end of the ultrasonic vibration module with the vertical projection position of the defect depth coordinates on the component surface. The mapping model includes a negative correlation function between defect depth and ultrasonic frequency, and a positive correlation function between defect size and ultrasonic power or duration of action. Specifically, when the defect depth is 2 mm, the ultrasonic frequency is set to 450 kHz; when the defect depth increases to 5 mm, the ultrasonic frequency is correspondingly reduced to 280 kHz to ensure effective penetration of sound wave energy into the target area. Simultaneously, if the detected defect area exceeds 3 square millimeters, the ultrasonic power is increased to 90% of the rated maximum value, and the duration of a single excitation is extended to 1.8 seconds to enhance the intensity and range of the cavitation effect.

[0010] During the in-situ repair stage, before the resin system enters the gelation stage, the ultrasonic vibration module emits continuous wave ultrasonic signals of a specific frequency and power based on the ultrasonic suppression parameters calculated above. This induces local cavitation effects, improving the resin flowability in the defect area, causing residual gas to be expelled and filled with microscopic voids, thereby eliminating the defect. The entire repair process is strictly limited to a time window when the resin viscosity is below the critical threshold to avoid fiber displacement or structural instability caused by premature vibration.

[0011] Furthermore, the real-time monitoring phase and the in-situ repair phase employ mutually exclusive timing control logic: when the terahertz detection module is in signal acquisition mode, the ultrasonic vibration module is forced into a silent mode, ceasing all mechanical vibration output; conversely, during ultrasonic intervention, the terahertz system suspends scanning operations. This timing mechanism is implemented through the state machine logic built into the central controller, ensuring complete isolation of the two types of physical field operations in the time dimension. This fundamentally avoids the interference caused by structural perturbations due to acoustic vibration on the stability of the terahertz wave propagation path, maintaining an imaging resolution of no less than 0.3 mm.

[0012] In a preferred embodiment of the present invention, the suppression device includes a working device, a detection module, an ultrasonic vibration module, a positioning module, and a control system. The working device comprises a metal mold, a flexible vacuum bag, and a vacuum pump, used to create a sealed negative pressure environment and support the prepreg layup structure. The detection module integrates a terahertz transmitter and a terahertz detector, both placed on the same moving platform, forming a transceiver integrated probe assembly. The ultrasonic vibration module includes a piezoelectric ceramic transducer and its matching circuit, installed on the moving platform and arranged linearly alongside the detection module. In a top-down view, the distance L between the center of the terahertz detector head and the center of the ultrasonic transmitter head is fixed at 42 mm. This distance was determined through electromagnetic compatibility simulation and mechanical interference verification, satisfying both the independent field-of-view requirements of the dual-modal sensor and ensuring the overall structural compactness.

[0013] The positioning module employs a five-axis linkage mechanism, with its degrees of freedom covering five directions: X-axis translation, Y-axis translation, Z-axis lifting, pitch around the X-axis, and yaw around the Z-axis. This mechanism achieves large-stroke positioning through a high-rigidity rack and pinion pair combined with a precision linear guide rail. The X and Y axes utilize a dual-sided synchronous drive structure, while the Z-axis is equipped with a heavy-duty ball screw pair to enhance load capacity. To further ensure sub-millimeter repeatability, all transmission components are rigidly reinforced with reinforcing plates, which are bolted to the base frame, effectively suppressing structural elastic deformation during high-speed operation.

[0014] The control system is the core processing unit. Its input is connected to the data interface of the terahertz detection module, and its output is connected to the drive power supply of the ultrasonic vibration module and the servo motor driver of the positioning module, respectively. The system is pre-loaded with a defect identification algorithm library and an ultrasonic parameter mapping table, enabling it to automatically classify defects, calculate coordinates, and generate intervention strategies after receiving raw terahertz data, and then send commands to the actuators in real time. All communication links use shielded twisted-pair cables, and key signal channels are equipped with opto-isolation devices to prevent high-voltage drive noise from coupling to sensitive sensing circuits.

[0015] In summary, this invention, by establishing an integrated closed-loop architecture of "perception-analysis-decision-execution," achieves for the first time high-resolution in-situ identification and targeted repair of internal defects in a closed, high-temperature environment of vacuum bag curing. Compared to traditional open-loop global vibration schemes, this invention not only possesses defect type identification capabilities and spatially selective intervention characteristics, but also solves the signal interference problem under multi-physics field coexistence through a strict temporal isolation mechanism. Furthermore, based on the measured depth-frequency correspondence and size-power control rules, ultrasonic energy delivery exhibits clear engineering feasibility and process robustness, thereby significantly improving the internal quality consistency and finished product qualification rate of composite materials while ensuring the integrity of the fiber structure. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the overall structure of the carbon fiber composite material vacuum bag curing and molding internal defect suppression device described in this invention; Figure 2 This is a schematic diagram showing the layout and relative position of the detection module and the ultrasonic vibration module on the mobile platform in this invention; Figure 3 This is a schematic diagram showing the structural composition and degrees of freedom of the five-axis linkage positioning module of the present invention; Figure 4 This is a schematic diagram of the closed-loop control method based on the synergistic effect of terahertz in-situ imaging and ultrasound targeted intervention according to the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0019] This invention provides a method and apparatus for suppressing internal defects in the vacuum bag curing process of carbon fiber composite materials. The specific implementation revolves around an integrated closed-loop control architecture of "sensing-analysis-decision-execution." Through the synergistic effect of terahertz in-situ imaging and ultrasonic targeted intervention, it achieves precise spatial identification and in-situ repair of internal defects such as sub-millimeter-level micropores, cracks, or interlayer delamination during the vacuum bag curing process. The following will provide a detailed description of the system composition, workflow, parameter settings, and typical embodiments.

[0020] The suppression device consists of five main parts: a working device, a detection module, an ultrasonic vibration module, a positioning module, and a control system. The working device, used to create a sealed negative pressure environment and support the carbon fiber prepreg layup structure, includes a metal mold, a flexible vacuum bag, and a vacuum pump. The metal mold is made of high thermal conductivity aluminum alloy with a mirror-polished surface to reduce interfacial reflection interference. The flexible vacuum bag is made of high-temperature resistant fluororubber and can operate stably at 180°C for extended periods. The vacuum pump is a two-stage rotary vane type with an ultimate vacuum of up to 5 Pa, ensuring a stable negative pressure environment inside the bag during the curing process.

[0021] The detection module integrates a terahertz transmitter and a terahertz detector, both housed on the same mobile platform, forming a transceiver probe assembly. The terahertz transmitter, based on the principle of a photoconductive antenna, generates a pulse signal with a center frequency of 0.3 terahertz, a pulse width of 80 picoseconds, and a repetition frequency of 1 kilohertz using a femtosecond laser. The terahertz detector employs electro-optic sampling technology, achieving coherent detection of the time-domain signal through a ZnTe crystal. During the scanning process, the probe assembly scans the surface of the prepreg point-by-point along a preset trajectory, acquiring the terahertz time-domain signal reflected back from the bottom surface of the mold after penetrating the composite material. During signal acquisition, the probe maintains a constant distance of 15 mm from the component surface, with real-time feedback and closed-loop adjustment provided by a non-contact displacement sensor.

[0022] The ultrasonic vibration module includes a piezoelectric ceramic transducer and its matching circuit, mounted on the mobile platform and arranged linearly in parallel with the detection module. The piezoelectric ceramic transducer uses PZT-8 material, has a diameter of 20 mm and a thickness of 5 mm, and its resonant frequency covers an adjustable range of 200 to 500 kHz. The matching circuit is an LC series resonant network, which can dynamically adjust the inductance value according to the driving frequency to achieve impedance matching and ensure that the energy transmission efficiency is not less than 92%. In the top-down view, the distance L between the center of the terahertz probe and the center of the ultrasonic transmitter is fixed at 42 mm. This distance was determined through electromagnetic compatibility simulation and mechanical interference verification: on the one hand, it avoids signal crosstalk caused by the overlap of the terahertz beam and the ultrasonic near-field region; on the other hand, it ensures that the dual-mode sensor has an independent field of view in a limited space and does not experience physical collisions.

[0023] The positioning module employs a five-axis linkage mechanism, with its degrees of freedom covering five directions: X-axis translation, Y-axis translation, Z-axis lifting, pitch around the X-axis, and yaw around the Z-axis. The X-axis and Y-axis travel are both 600 mm, driven by dual-sided synchronous servo motors with a rack and pinion pair, combined with a crossed roller linear guide for high-rigidity guidance. The Z-axis travel is 200 mm, equipped with a heavy-duty ball screw pair (5 mm lead, C3 accuracy grade), with a rated load capacity of 50 kg. The pitch axis (around the X-axis) rotation range is ±15 degrees, and the yaw axis (around the Z-axis) rotation range is ±30 degrees, both using a harmonic reducer and a coreless motor combination, achieving an angular resolution better than 0.01 degrees. To further ensure sub-millimeter repeatability, all transmission components are rigidly reinforced with reinforcing plates, which are fastened to the base frame with M8 bolts, effectively suppressing structural elastic deformation during high-speed operation. The measured overall positioning repeatability is ±0.02 mm, meeting the high-precision alignment requirements for defect projection positions.

[0024] The control system serves as the core processing unit, employing an industrial-grade embedded computer platform equipped with a real-time operating system (RTOS), a 2.4 GHz clock speed, and 8 gigabytes of memory. Its inputs connect to the data acquisition card of the terahertz detection module via a GigE Vision interface, while its outputs connect to the high-voltage drive power supply (0-1000V adjustable) of the ultrasonic vibration module and the five-axis servo driver (supporting EtherCAT bus communication) of the positioning module. The system is pre-loaded with a defect identification algorithm library and an ultrasonic parameter mapping table, enabling it to automatically classify defects, calculate coordinates, and generate intervention strategies after receiving raw terahertz data, and then send commands to the actuators in real time. All communication links use shielded twisted-pair cables, and key signal channels are equipped with high-speed opto-isolators (isolation voltage ≥5 kV) to prevent high-voltage drive noise from coupling to sensitive sensing circuits.

[0025] In the specific operation process, carbon fiber prepreg is first laid on the surface of a metal mold according to the designed layup sequence, covered with a flexible vacuum bag and evacuated to below 500 Pa, and then heated to the curing start temperature of the resin system (e.g., 80°C for epoxy resin system). When the temperature reaches the set value and the resin is in the low viscosity flow stage, the suppression method described in this invention is activated.

[0026] In the real-time monitoring phase, a mobile platform drives the terahertz detection module to scan the component surface point by point along a gridded trajectory. The scanning step size is set to 0.5 mm, and each point is sampled 100 times and averaged to improve the signal-to-noise ratio. The acquired terahertz time-domain signal is an echo sequence s(t), which contains information about multiple reflection interfaces: the first main peak corresponds to the air-prepreg interface, the second main peak corresponds to the prepreg-mold interface, and if internal defects exist, an additional echo appears between the two main peaks. This signal is transmitted in real time to the control system for further processing.

[0027] During the defect reconstruction stage, the control system sequentially performs time-of-flight extraction, Fourier transform, and image reconstruction on s(t). The time-of-flight Δt is calculated using a cross-correlation algorithm to determine the time difference between the defect echo and the bottom surface echo. Combined with the terahertz wave propagation velocity v in the material (for a typical carbon fiber / epoxy system, v ≈ 0.12 mm / picosecond), the defect depth d = v·Δt / 2 can be obtained. Subsequently, a fast Fourier transform is performed on s(t) to obtain the frequency domain spectrum S(f), and the amplitude attenuation A(f) and phase shift φ(f) at different frequency bands are analyzed. The defect type is determined based on the combined characteristics of A(f) and φ(f): if A(f) exhibits uniform attenuation (attenuation slope less than 3 dB / terahertz) and φ(f) shows no abrupt change (phase jump less than π / 8 radians) within the 0.1 to 0.5 terahertz broadband band, it is identified as a micropore; if A(f) shows significant attenuation (attenuation slope greater than 8 dB / terahertz) in the 0.3 to 0.5 terahertz high-frequency band, accompanied by abrupt change in φ(f) (phase jump exceeding π / 4 radians), it is identified as a crack; if a strong reflection peak (reflection coefficient greater than 0.6) appears in the 0.1 to 0.2 terahertz low-frequency band and the time-domain signal exhibits multipath interference oscillation, it is identified as interlayer delamination. Based on the above characteristics, the system can output the three-dimensional feature information of the defect, including type, depth coordinates (x, y, d), and equivalent area (obtained by integrating the projection profile of the defect echo on the two-dimensional scanning plane).

[0028] During the decision-making and positioning phase, the control system calls a pre-stored mapping relationship model based on the three-dimensional feature information to calculate the matching ultrasonic suppression parameters. The mapping relationship model includes a negative correlation function between the defect depth d and the ultrasonic frequency f: f(d) = a / d + b, where a = 900 kHz·mm and b = 50 kHz; and a positive correlation function between the defect area S and the ultrasonic power P or the duration T: when S ≤ 3 mm², P = P0 (rated power), T = 1.0 s; when S > 3 mm², P = 0.9P0, T = 1.8 s. For example, when a defect with a depth of 2 mm is detected, f = 900 / 2 + 50 = 500 kHz is calculated, but due to the transducer's upper limit, it is actually set to 450 kHz. When the depth is 5 mm, f = 900 / 5 + 50 = 230 kHz. Combining experimental verification of the optimal value, it is finally set to 280 kHz to balance the penetration depth and cavitation threshold. Meanwhile, if the defect area is 4.2 square millimeters, a high-power long-duration mode is triggered, with P = 0.9P0 and T = 1.8 seconds.

[0029] Subsequently, the control system instructs the five-axis linkage positioning module to precisely align the ultrasonic vibration module's transmitter with the vertical projection (x, y, d) of the defect depth coordinates onto the component surface. During positioning, the Z-axis is first raised to a safe height, the X / Y axes move to the target coordinates, and then the Z-axis is lowered so that the ultrasonic transmitter is 10 mm from the surface. Finally, pitch and yaw adjustments are made to ensure that the acoustic beam axis is perpendicular to the local curved surface. The entire positioning process takes no more than 3 seconds, and the positioning error, calibrated by a laser tracker, is less than 0.05 mm.

[0030] During the in-situ repair stage, before the resin system enters the gelation stage (i.e., the resin viscosity is below the critical threshold η_c, for a typical epoxy system η_c ≈ 10),... 4 The ultrasonic vibration module emits continuous wave ultrasonic signals of a specific frequency and power based on the ultrasonic suppression parameters calculated above. When the ultrasonic waves propagate in the resin, if the local sound pressure exceeds the cavitation threshold (approximately 0.8 MPa), it will induce the periodic growth and collapse of microbubbles, generating instantaneous high-temperature and high-pressure microjets, thereby improving the resin flowability in the defect area, promoting the discharge of residual gas and filling the microscopic voids. The repair process is strictly limited to the time window before the resin viscosity rises to η_c, usually within 30 to 90 minutes after heating, depending on the kinetic characteristics of the resin system.

[0031] It is worth noting that the real-time monitoring phase and the in-situ repair phase employ mutually exclusive timing control logic. This logic is implemented by a state machine built into the central controller: the system initially operates in a "monitoring ready" state; when a scanning task is initiated, it switches to a "monitoring activated" state, at which point the ultrasonic vibration module is forced into a silent mode, the drive power output is turned off, and the piezoelectric transducer receives no excitation; when monitoring is completed and intervention is confirmed, the system switches to a "repair preparation" state, suspends the terahertz scanning, and the mobile platform is reset to the intervention position; subsequently, it enters a "repair execution" state, initiates ultrasonic emission, and the duration is T; after repair is completed, it returns to the "monitoring ready" state, allowing the next round of scanning to continue. This mechanism ensures complete isolation between the two types of physical field operations in the time dimension, fundamentally avoiding the interference caused by structural perturbations due to acoustic vibration on the stability of the terahertz wave propagation path, and maintaining an imaging resolution of no less than 0.3 mm.

[0032] To verify the technical effects of the present invention, the following embodiments and comparative examples were designed: In one specific embodiment, a flat sample with dimensions of 300 mm × 300 mm × 2.5 mm was prepared using T700 carbon fiber / epoxy prepreg. The layup sequence was [0 / 90 / 0 / 90]. sThe system consists of 8 layers. The curing process is as follows: heat treatment at 80℃ for 2 hours, followed by a temperature increase to 120℃ at a rate of 2℃ / minute, and heat treatment for 4 hours. The suppression method described in this invention is activated during the 80℃ heat treatment stage. A terahertz scanning area covering a central 200 mm × 200 mm region revealed an interlayer delamination defect with a depth of 3.2 mm and an area of ​​3.8 square millimeters. The system calculated the ultrasonic frequency f = 900 / 3.2 + 50 ≈ 331 kHz, rounded to 330 kHz; since the area is >3 square millimeters, P = 0.9P0 (P0 = 80 watts) and T = 1.8 seconds were set. After ultrasonic intervention, a second scan confirmed that the defect echo had disappeared and the phase and amplitude distribution had returned to uniformity.

[0033] As a comparative example, the same materials and processes were used, but only global ultrasonic vibration (frequency 300 kHz, power 80 watts, duration 5 minutes) was applied during the curing process, without defect identification or location. All other conditions remained the same.

[0034] The repair results were ultimately evaluated using X-ray computed tomography (CT) scans, and the results are shown in the table below:

[0035] Data shows that the embodiment effectively controlled fiber orientation disturbance and improved mechanical properties while significantly reducing the number and size of residual defects. In particular, one unrepaired defect was located in the edge region (<10 mm from the boundary) and was not intervened because it was outside the effective working range of the five-axis mechanism, indicating that the system's working area was limited by the mechanical structure boundary, but the repair rate of the core area reached 100%.

[0036] Furthermore, to verify the effectiveness of the temporal isolation mechanism, in another set of comparative experiments, the mutual exclusion control logic was manually disabled, allowing the terahertz scanning and ultrasonic emission to proceed synchronously. The results showed that significant fringe noise appeared in the terahertz image, the depth resolution degraded to 0.8 mm, and the defect localization error increased to ±0.5 mm, causing the ultrasonic intervention to deviate from the target position and resulting in repair failure. This result conversely demonstrates the crucial role of the temporal isolation mechanism employed in this invention in ensuring both imaging quality and intervention accuracy.

[0037] At the algorithm implementation level, the defect identification algorithm library is built based on Support Vector Machine (SVM). The training samples contain 500 sets of terahertz signals of artificially implanted defects, covering three categories: pores (diameter 0.2–1.5 mm), cracks (length 1–5 mm, opening 0.05–0.3 mm), and delamination (area 1–10 square millimeters, gap 5–50 micrometers). The feature vector consists of A(f) and φ(f) in 10 frequency bands (0.1–0.5 terahertz, step size 0.05 terahertz), for a total of 20 dimensions. After 10-fold cross-validation, the classification accuracy reaches 96.4%. The coordinate calculation uses bilinear interpolation to refine the peak position of the defect echo to sub-pixel level, with a depth calculation error of less than ±0.1 mm.

[0038] The ultrasonic parameter mapping table was obtained through extensive process experiments. Under fixed resin system (e.g., RTM6 epoxy) and fiber volume content (60%), the repair success rate was measured under different combinations of f, P, and T by systematically varying the defect depth (1–6 mm) and area (1–8 mm²). Repair success was defined as a ≥90% reduction in defect volume during CT detection without the generation of new defects. Experiments showed that when f is too high (>500 kHz), the acoustic wave attenuation is severe, making it impossible to reach deep defects; when f is too low (<200 kHz), the cavitation threshold increases, making it difficult to induce effective cavitation in low-viscosity resins. Therefore, the f(d) function was optimized to the form described above. Similarly, the setting of P and T needs to balance cavitation intensity with the risk of thermal effects—excessively high P or excessively long T can lead to local temperature rises exceeding 5°C, potentially causing premature resin cross-linking.

[0039] In summary, the specific embodiments of this invention fully cover the entire chain of technical details, from hardware construction, signal processing, parameter decision-making to physical intervention. All component parameters, algorithm logic, control timing, and process windows are determined based on engineering practice and experimental verification, ensuring that those skilled in the art can reproduce this invention and achieve the expected technical effects based on this description. The entire system achieves high-resolution in-situ identification and targeted repair of internal defects during vacuum bag curing without disturbing fiber orientation, providing a reliable technical path for the intelligent manufacturing of high-performance carbon fiber composite materials.

[0040] The embodiments described above are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for suppressing internal defects in vacuum bag molding of a carbon fiber composite material, characterized by, The method comprises the following steps: In the vacuum bag curing process, the terahertz detection module is driven by the moving platform to scan the carbon fiber prepreg point by point, and the terahertz time domain signal reflected back from the mold bottom surface after penetrating the composite material is acquired; The terahertz time domain signal is sequentially subjected to time of flight extraction, Fourier transform and image reconstruction processing to obtain three-dimensional feature information of the defect, which includes defect type, defect depth coordinate and defect size; wherein the defect type is determined according to the combined characteristics of phase shift and amplitude attenuation degree of the reflected signal at different frequency bands; According to the three-dimensional feature information, a pre-stored mapping relationship model is called to calculate the matched ultrasonic suppression parameter, and a five-axis linkage positioning module is controlled to accurately position the transmitting end of the ultrasonic vibration module at the vertical projection position of the defect depth coordinate on the surface of the component; the mapping relationship model includes a negative correlation function relationship between the defect depth and the ultrasonic frequency, and a positive correlation function relationship between the defect size and the ultrasonic power or the action time; Before the resin system enters the gelation stage, a continuous wave ultrasonic signal is emitted according to the ultrasonic suppression parameter to improve the resin flowability in the defect area by inducing local cavitation effect, promote the discharge of residual gas and fill the micro voids, and realize defect elimination; The signal acquisition of the terahertz detection module and the intervention execution of the ultrasonic vibration module adopt mutual exclusion time sequence control logic, and only one of them is allowed to be in working state at any time.

2. The method of suppressing internal defects of a carbon fiber composite vacuum bag molding according to claim 1, characterized by, The determination rule of the defect type is: if the amplitude attenuation is uniformly distributed and the phase shift is less than π / 8 radians in the 0.1-0.5 terahertz wide frequency band, it is determined to be a micro-pore; if the amplitude attenuation slope is greater than 8 decibels / terahertz and accompanied by a phase shift of more than π / 4 radians in the 0.3-0.5 terahertz high frequency band, it is determined to be a crack; if there is a strong reflection peak in the 0.1-0.2 terahertz low frequency band and the time domain signal presents multi-path interference oscillation, it is determined to be interlaminar delamination.

3. The method of claim 1, wherein the carbon fiber composite material is a prepreg. The ultrasonic frequency f and the defect depth d satisfy the relationship f(d) = a / d + b, wherein a is 900 kilohertz·millimeter, and b is 50 kilohertz; when the calculated frequency exceeds the working range of the ultrasonic vibration module, the closest achievable frequency value in the range is taken.

4. The method of claim 1, wherein the carbon fiber composite material is a carbon fiber reinforced plastic. When the defect area is greater than 3 square millimeters, the ultrasonic power is set to 90% of the rated maximum power, and the single excitation duration is 1.8 seconds; when the defect area is not greater than 3 square millimeters, the ultrasonic power is the rated maximum power, and the single excitation duration is 1.0 second.

5. An apparatus for suppressing internal defects in vacuum bag molding of carbon fiber composite materials for implementing the method according to any one of claims 1 to 4, characterized in that It comprises a working device, a detection module, an ultrasonic vibration module, a five-axis linkage positioning module and a control system; The working device comprises a metal mold, a flexible vacuum bag and a vacuum pump, which are used to build a closed negative pressure environment; The detection module integrates a terahertz transmitter and a terahertz detector to form a transceiver integrated probe assembly, which is installed on the moving platform; The ultrasonic vibration module comprises a piezoelectric ceramic transducer and its matching circuit, which are linearly arranged side by side with the detection module on the same moving platform; The five-axis linkage positioning module has five degrees of freedom of movement, including X-axis translation, Y-axis translation, Z-axis lifting, pitching around the X-axis and yawing around the Z-axis; The control system is connected with the detection module, the ultrasonic vibration module and the five-axis linkage positioning module, and is used for receiving the terahertz signal, solving the defect information, generating the ultrasonic suppression parameter and controlling the action of the actuator.

6. The carbon fiber composite vacuum bag molding internal defect suppressing apparatus according to claim 5, wherein The center distance between the terahertz detector and the ultrasonic transmitter is fixed at 42 mm in the top view state.

7. The carbon fiber composite vacuum bag molding internal defect suppressing apparatus according to claim 5, wherein In the five-axis linkage positioning module, the X-axis and the Y-axis are driven by double-sided synchronous servo motors, and a gear-rack pair is matched with a cross-roller linear slide rail, the Z-axis is driven by a heavy-load ball screw pair, the pitching axis and the yawing axis are driven by a harmonic reducer and a hollow cup motor.

8. The carbon fiber composite vacuum bag molding internal defect suppressing apparatus according to claim 5, wherein All transmission components of the five-axis linkage positioning module are provided with reinforcing plates and are fastened to the base frame by bolts, so as to suppress the structural elastic deformation in the high-speed operation process.

9. The carbon fiber composite vacuum bag molding internal defect suppressing apparatus according to claim 5, wherein The control system is provided with a defect recognition algorithm library and an ultrasonic parameter mapping table, and can automatically complete the defect classification, coordinate solving and intervention strategy generation based on the original terahertz data.

10. The carbon fiber composite vacuum bag molding internal defect suppressing apparatus according to claim 5, wherein Photoelectric isolation devices are arranged between the control system and the ultrasonic vibration module, and a shielded twisted pair is used for communication link connection, so as to prevent high-voltage driving noise from being coupled to the sensing circuit.

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