A bicycle carbon fiber frame docking point strengthening connection process

Abstract

The present invention discloses a bicycle carbon fiber frame docking point strengthening connection process, which relates to the field of carbon fiber frame technology, including the steps of docking structure pretreatment, carbon fiber reinforcement layer laying, mold positioning, vacuum assisted curing, demoulding, testing and rework; a carbon fiber sleeve made of multi-axial carbon fiber braiding is coated on the docking area of ​​the frame, and a bidirectional or tridirectional carbon fiber prepreg is stacked to construct a carbon fiber reinforcement layer in the docking area, and then an externally arranged pressure-wrapping mold and an internally arranged removable inner mold are used to provide bidirectional molding pressure for the docking area, thereby improving the fit and interface density between the carbon cloths; after hot pressing and curing, the quality status is determined by non-destructive testing, and if defects are found, rework can be performed; the process effectively improves the structural strength and fatigue life of the carbon fiber frame docking point, is suitable for the high-strength connection preparation of bicycle carbon fiber frames, and solves the problem that the existing carbon fiber frame docking technology is difficult to effectively improve the mechanical properties of the docking point.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber frames, and in particular to a process for reinforcing the connection of butt joints of a bicycle carbon fiber frame. Background Art

[0002] With the growing popularity of cycling and the widespread adoption of high-performance cycling equipment, carbon fiber frames have gradually become the mainstream material of choice for mid- to high-end bicycles due to their lightweight, high rigidity, and excellent mechanical properties. Carbon fiber's excellent specific strength and modulus significantly reduce vehicle weight, improving riding efficiency and handling. Consequently, carbon fiber frames are widely used in mountain, road, and racing bicycles.

[0003] Currently, the manufacturing of carbon fiber frames mostly adopts composite material processes such as compression molding, roll forming or vacuum bag assisted curing. The frame structure is usually composed of multiple sections of carbon fiber prefabricated tubes, which are connected to form a complete frame through butt joints, such as the connection between the head tube and the upper tube and down tube, the connection between the upper tube and the seat tube, and the connection between the seat tube and the bottom bracket. These butt joints are usually connected and fixed by gluing, lamination, in-mold forming and other methods. However, since carbon fiber itself has a layered structure and the stress environment in the butt joint area is complex and the stress concentration is obvious, if the connection process is not properly controlled, it is very easy to cause failure problems such as delamination between carbon cloth layers, local tearing or even overall cracking due to repeated loads, vibrations or impacts during use.

[0004] Specifically, traditional connection processes often ignore the fiber continuity design in the docking area. In the case of fiber direction mismatch, local resin enrichment, high void rate or lack of effective mechanical locking, the fatigue life of the docking point is much lower than that of other parts of the overall structure.

[0005] In addition, the existing technology mostly relies on increasing the number of layers or increasing the resin content in the joint area. This not only fails to fundamentally improve the interlayer bonding strength, but is also prone to cause curing stress concentration, affecting the stability and long-term durability of the overall connection.

[0006] In summary, it is found that the existing technology has at least the following technical problems:

[0007] The existing carbon fiber frame docking point connection technology has technical problems such as unstable structural strength, lack of continuous reinforcement and directional reinforcement structure of the docking points, and the connection process fails to take into account structural strength, connection reliability and production controllability, making it difficult to effectively improve the overall mechanical properties of the docking points. Summary of the Invention

[0008] The purpose of the present invention is to provide a bicycle carbon fiber frame docking point strengthening connection process to solve the technical problems of existing carbon fiber frame docking point connection technology, such as unstable structural strength, lack of continuous reinforcement and directional reinforcement structure of the docking point, and failure of the connection process to take into account structural strength, connection reliability and production controllability, making it difficult to effectively improve the overall mechanical properties of the docking point.

[0009] The various technical effects that can be produced by the preferred technical solutions among the various technical solutions provided by the present invention are described in detail below.

[0010] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0011] The present invention provides a process for strengthening the connection of a carbon fiber bicycle frame butt joint, comprising steps S1 to S7 performed in sequence: S1, butt joint structure pretreatment: performing precision cutting and end face shaping on the ends of prefabricated carbon fiber tubes at the frame connection portion to form a butt joint surface with a positioning accuracy within ±0.05 mm, and performing surface roughening or micro-groove etching on the connection area;

[0012] S2. Carbon fiber reinforcement layer laying: A set of carbon fiber sleeves made of multi-axial carbon fiber braids are wrapped around the outside of the frame joint area, and bidirectional or tridirectional carbon fiber prepregs are laid at the seam. Based on the results of structural stress simulation, bidirectional or tridirectional carbon fiber prepregs are laid in high stress areas for directional reinforcement.

[0013] S3, Molding Positioning: The butted frame is placed in a compression mold, and a removable inner mold is placed inside the pipe fitting in the frame butt joint area to provide radial support to the butt joint area of ​​the frame. This allows the carbon fiber reinforcement layer coated in step S2 to adhere to the pipe surface during the subsequent molding process under the dual pressure of the compression mold providing pressure from the outside toward the frame and the inner mold providing support from the inside toward the frame.

[0014] S4, vacuum assisted curing: remove air through vacuum bag packaging, and hot press curing for 12 to 18 hours under constant temperature of 130 ° C and pressure of 0.6 to 0.8 MPa to complete the cross-linking and curing of carbon fiber and resin and the interface bonding;

[0015] S5, demoulding: after cooling, remove the compression mold and inner mold;

[0016] S6. Inspection: Perform non-destructive inspection on the joint area of ​​the frame. If the inspection reveals defects such as delamination, voids, peeling or poor bonding, the frame will enter the repair process. If the inspection does not find any defects such as delamination, voids, peeling or poor bonding, the frame will enter the qualified production line and flow to the next process.

[0017] S7, repair: local grinding of the defective area, patching with bidirectional or tridirectional carbon fiber prepreg, and re-circulating S3 and S4 steps for positioning and curing to complete the repair.

[0018] In one embodiment, in step 2, the braided structure of the carbon fiber sleeve is a three-dimensional multi-axial braided structure, wherein the ratio of axial, radial and hoop fibers is 4:3:3.

[0019] In one embodiment, in step 2, the bidirectional carbon fiber prepreg includes oblique layers with an angle of ±45°, longitudinal layers with an angle of 0°, or circumferential layers with an angle of 90°, and the laying order is alternating, and the number of laid layers is not less than 5 layers.

[0020] In one embodiment, in step 2, the tri-directional carbon fiber prepreg includes an oblique layer with an angle of ±45°, a longitudinal layer with an angle of 0°, and a circumferential layer with an angle of 90°, and the laying order is alternating, and the number of laid layers is not less than 5 layers.

[0021] In one embodiment, in step S3, the inner mold includes a thermal expansion inner mold or an airbag inner mold.

[0022] In one embodiment, in step S3, the thermal expansion inner mold is a heat-expandable silicone inner mold, and its radial expansion amount is 1.5-2.5% of the original diameter.

[0023] In one embodiment, in step S4, a slow heating section and a slow cooling section are set during the vacuum hot pressing curing process, each section lasting 1 to 2 hours, and the control curves of the slow heating section and the slow cooling section are linear, which is used to reduce the stress generated during hot pressing curing.

[0024] In one embodiment, in step S6, the non-destructive testing method is at least one of ultrasonic C-scan, infrared thermal imaging or acoustic emission testing.

[0025] In one embodiment, when a defect is detected in the docking area of ​​the frame, the repair step S7 includes: S7.1, locally grinding the defective area to remove the defective carbon fiber layer;

[0026] S7.2. Use bidirectional or tridirectional carbon fiber prepreg with a direction and material matching the original structure for re-laying;

[0027] S7.3. Re-perform hot pressing curing under the same temperature and pressure as the original curing under the conditions of mold positioning and vacuum bag packaging to complete the defect repair.

[0028] The existing carbon fiber frame docking point connection technology has the following technical problems: unstable structural strength, lack of continuous reinforcement and directional reinforcement structure of the docking point, and the connection process fails to take into account structural strength, connection reliability and production controllability, making it difficult to effectively improve the overall mechanical performance of the docking point. The present invention proposes a bicycle carbon fiber frame docking point strengthening connection process to improve the performance of the carbon fiber frame docking point. Compared with the existing technology, it has the following beneficial effects:

[0029] (1) Improve structural strength and connection stability: By wrapping the joint area of ​​the frame with a carbon fiber sleeve made of multi-axial carbon fiber weaving and laying bidirectional or tridirectional carbon fiber prepreg, a high-continuity, directionally reinforced carbon fiber reinforcement layer is constructed, thereby significantly improving the shear and fatigue strength of the frame joint point and avoiding structural tearing or fracture caused by stress concentration.

[0030] (2) Enhance the density of the interlayer interface: A compression mold and a removable inner mold are used to ensure that the carbon fiber reinforcement layer coated in step S2 is tightly attached to the surface of the tube body under the action of a bidirectional compression force from the outside to the inside and from the inside to the outside, further enhancing the interlayer bonding force and reducing the void rate and interlayer debonding risk during the curing process.

[0031] (3) Improve the curing quality and process controllability: Introduce vacuum bag auxiliary packaging and extract vacuum, and cooperate with hot pressing curing control under constant temperature and pressure conditions to ensure that the resin in the carbon fiber is fully infiltrated and evenly distributed, effectively improving the overall interface quality and molding consistency of the carbon fiber components and carbon fiber reinforcement layers in the joint area.

[0032] (4) Introducing a repair mechanism to improve the yield rate: Setting up a non-destructive testing and repair process. When there are defects in the frame docking area, it can be repaired by local grinding, patching and repeated molding and curing, which effectively reduces the scrap rate of carbon fiber frames caused by frame docking defects, and improves the production flexibility of the carbon fiber frame docking production line, enhances the industrial adaptability and economic benefits of the process, ensures the quality of the finished carbon fiber frame and reduces costs.

[0033] The carbon fiber frame docking point reinforcement connection process provided by the present invention is not only applicable to various types of carbon fiber frames such as road bikes and mountain bikes, but can also be adapted to various pipe diameters and connection structures. It has good versatility and scalability, and meets the high-performance docking requirements of carbon fiber in the mid-to-high-end bicycle manufacturing field. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are only some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 The present invention is a schematic flow chart of a process for strengthening the connection of butt joints of a carbon fiber bicycle frame. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0037] In a specific embodiment, a process for strengthening the connection of the docking points of a bicycle carbon fiber frame is provided, including the steps of pretreatment of the docking structure, laying of a carbon fiber reinforcement layer, molding positioning, vacuum-assisted curing, demolding, testing and rework; a carbon fiber sleeve made of multi-axial carbon fiber braiding is coated on the docking area of ​​the frame, and a bidirectional or tridirectional carbon fiber prepreg is superimposed to construct a carbon fiber reinforcement layer in the docking area, and then an externally arranged pressure mold and an internally arranged removable inner mold are used to provide bidirectional molding pressure for the docking area to improve the fit and interface density between the carbon cloths; after hot pressing and curing, the quality status is determined by non-destructive testing, and if there are defects, rework can be performed; this process effectively improves the structural strength and fatigue life of the carbon fiber frame docking points, and is suitable for the high-strength connection preparation of bicycle carbon fiber frames; it effectively solves the technical problems of the existing carbon fiber frame docking point connection technology, such as unstable structural strength, lack of continuous reinforcement and directional reinforcement structure of the docking points, and failure of the connection process to take into account structural strength, connection reliability and production controllability, making it difficult to effectively improve the overall mechanical properties of the docking points.

[0038] The first implementation of the carbon fiber bicycle frame docking point strengthening process Figure 1 As shown, the steps are performed in order from S1 to S7: S1, butt joint structure pretreatment: the ends of the prefabricated carbon fiber tubes at the frame connection parts are precisely cut and the end faces are shaped to form butt joint surfaces with a positioning accuracy within ±0.05mm, and the surface of the connection area is roughened or micro-grooved;

[0039] S2. Carbon fiber reinforcement layer laying: A set of carbon fiber sleeves made of multi-axial carbon fiber braids are wrapped around the outside of the frame joint area, and bidirectional or tridirectional carbon fiber prepregs are laid at the seam. Based on the results of structural stress simulation, bidirectional or tridirectional carbon fiber prepregs are laid in high stress areas for directional reinforcement.

[0040] S3, Molding Positioning: The butted frame is placed in a compression mold, and a removable inner mold is placed inside the pipe fitting in the frame butt joint area to provide radial support to the butt joint area of ​​the frame. This allows the carbon fiber reinforcement layer coated in step S2 to adhere to the pipe surface during the subsequent molding process under the dual pressure of the compression mold providing pressure from the outside toward the frame and the inner mold providing support from the inside toward the frame.

[0041] S4, vacuum assisted curing: remove air through vacuum bag packaging, and hot press curing for 12 to 18 hours under constant temperature of 130 ° C and pressure of 0.6 to 0.8 MPa to complete the cross-linking and curing of carbon fiber and resin and the interface bonding;

[0042] S5, demoulding: after cooling, remove the compression mold and inner mold;

[0043] S6. Inspection: Perform non-destructive inspection on the joint area of ​​the frame. If the inspection reveals defects such as delamination, voids, peeling or poor bonding, the frame will enter the repair process. If the inspection does not find any defects such as delamination, voids, peeling or poor bonding, the frame will enter the qualified production line and flow to the next process.

[0044] S7, repair: local grinding of the defective area, patching with bidirectional or tridirectional carbon fiber prepreg, and re-circulating S3 and S4 steps for positioning and curing to complete the repair.

[0045] When a defect is detected in the docking area of ​​the frame, the S7 repair step includes: S7.1, locally grinding the defective area to remove the defective carbon fiber layer;

[0046] S7.2. Use bidirectional or tridirectional carbon fiber prepreg with a direction and material matching the original structure for re-laying;

[0047] S7.3. Re-perform hot pressing curing under the same temperature and pressure as the original curing under the conditions of mold positioning and vacuum bag packaging to complete the defect repair.

[0048] Specifically, when covering the carbon fiber sleeve or the bidirectional or tridirectional carbon fiber prepreg in step S2, resin glue should be applied for bonding and preliminary fixation.

[0049] The existing carbon fiber frame docking point connection technology has the technical problem of difficulty in effectively improving the overall mechanical performance of the docking point. The present invention's bicycle carbon fiber frame docking point strengthening connection process can improve the performance of carbon fiber frame docking points and has the following advantages: Improved structural strength and connection stability: By covering the docking area of ​​the frame with a carbon fiber sleeve made of multi-axial carbon fiber braids and laying bidirectional or tridirectional carbon fiber prepreg, a highly continuous, directionally reinforced carbon fiber reinforcement layer is constructed, thereby significantly improving the shear and fatigue resistance of the frame docking point and avoiding structural tearing or fracture caused by stress concentration;

[0050] Enhance the density of the interlayer interface: A compression mold and a removable inner mold are used to ensure that the carbon fiber reinforcement layer coated in step S2 is tightly attached to the surface of the tube body under the action of bidirectional compression forces from the outside to the inside and from the inside to the outside, further enhancing the interlayer bonding strength and reducing the void rate and interlayer debonding risk during the curing process;

[0051] Improved curing quality and process controllability: Introducing vacuum bag-assisted packaging and vacuum extraction, combined with hot-press curing control under constant temperature and pressure conditions, ensures full resin infiltration and uniform distribution in the carbon fiber, effectively improving the overall interface quality and molding consistency between the carbon fiber component and the carbon fiber reinforcement layer in the joint area;

[0052] Introducing a repair mechanism to improve yield: Setting up a non-destructive testing and repair process. When defects are found in the frame joint area, repairs can be performed through local grinding, patching, and repeated molding and curing. This effectively reduces the scrap rate of carbon fiber frames caused by frame joint defects, improves the production flexibility of the carbon fiber frame joint production line, enhances the industrial adaptability and economic benefits of the process, ensures the quality of the finished carbon fiber frame, and reduces costs.

[0053] The carbon fiber frame docking point reinforcement connection process provided by the present invention is not only applicable to various types of carbon fiber frames such as road bikes and mountain bikes, but can also be adapted to various pipe diameters and connection structures. It has good versatility and scalability, and meets the high-performance docking requirements of carbon fiber in the mid-to-high-end bicycle manufacturing field.

[0054] As one optional implementation method:

[0055] Regarding the specific structure of the carbon fiber sleeve made of the above-mentioned multi-axial carbon fiber weaving, in step 2, the weaving structure of the carbon fiber sleeve is a three-dimensional multi-axial weaving, and the ratio of the axial, radial and circumferential fibers is 4:3:3.

[0056] During application, in the carbon fiber sleeve woven from three-dimensional multi-axial carbon fiber, the ratio of axial, radial and circumferential fibers is 4:3:3, wherein the axial fibers are used to enhance the longitudinal tensile properties of the connection area, the radial fibers are used to improve the compression and wrapping capacity of the docking point, and the circumferential fibers are used to inhibit interlayer delamination.

[0057] The three-way weaving method is used to build spatial structural continuity, effectively improving the stress dispersion ability and reducing stress concentration problems. It is particularly suitable for reinforcing areas with sudden structural corner changes such as the head tube and the bottom bracket, and is especially suitable for withstanding the cyclic stress during bicycle riding while maintaining the structural strength of the docking point area or achieving high-strength connection of pipes on both sides of the frame docking point with an extremely low structural strength attenuation rate.

[0058] Among them, the braiding structure of the carbon fiber sleeve can also be changed to a 3D five-axis braiding structure to adapt to the high-performance and high-strength connection of carbon fiber frame tubes with special cross-sections.

[0059] Regarding the specific structure of the bidirectional carbon fiber prepreg in the above-mentioned carbon fiber prepreg, in step 2, the bidirectional carbon fiber prepreg includes oblique layers with an angle of ±45°, longitudinal layers with an angle of 0°, or circumferential layers with an angle of 90°, and the laying order is alternating, and the number of laid layers is not less than 5 layers.

[0060] During application, bidirectional carbon fiber prepreg is laid in alternating arrangements of ±45° oblique layers and 0° longitudinal layers or 90° circumferential layers. The ±45° oblique layers are used to enhance shear strength and fatigue crack resistance, and the 0° / 90° layers are used to enhance axial or circumferential load bearing capacity. The number of layers laid is not less than 5 to meet the reliability and stability requirements of structural strength. During the laying process, a stacking positioning tool is used to ensure that the laid fiber direction is accurate and consistent.

[0061] This layup sequence avoids the problem of uneven performance of carbon fiber in all directions in the docking area, and can significantly improve the overall structural uniformity and fatigue life of the docking area. The number of layers can be adjusted to 7 to 9 according to different frame designs to further enhance the structural strength requirements of high-load strength areas.

[0062] Regarding the specific structure of the tri-directional carbon fiber prepreg in the above-mentioned carbon fiber prepreg, in step 2, the tri-directional carbon fiber prepreg includes an oblique layer with an angle of ±45°, a longitudinal layer with an angle of 0°, and a circumferential layer with an angle of 90°, and the laying order is alternating, and the number of laid layers is not less than 5 layers.

[0063] During application, the tri-directional carbon fiber prepreg includes prepreg layers in the directions of ±45°, 0° and 90°, and the layers in the three directions are alternately stacked to form a three-directional equal-strength structure. This structure can effectively resist complex cyclic stresses from different directions during riding, and is particularly suitable for mountain bike frames and frames with variable impact conditions. At least 1 to 2 layers are repeatedly laid in each direction, and the total number of layers is not less than 5. Through simulation analysis, it is found that the utilization efficiency of fiber force can be effectively improved by laying prepreg in three directions and laying the prepreg alternately in the docking area in a distributed manner.

[0064] Among them, the tri-directional carbon fiber prepreg can also expand the prepreg laying starting angle to ±30° or ±60°, which can achieve load path optimization for specific vehicle frame configurations.

[0065] Regarding the specific device used for the above-mentioned inner mold, in step S3, the inner mold includes a thermal expansion inner mold or an airbag inner mold.

[0066] During application, the inner mold described in step S3 can be a thermal expansion inner mold or an airbag inner mold, wherein the thermal expansion inner mold is made of silicone or polyurethane material, and can achieve radial expansion by heating, providing a stable support force for outward expansion; while the airbag inner mold type inner mold forms a stable support force for outward expansion by inflation and pressurization.

[0067] Both types of inner molds can provide controllable and uniform outward expansion support force, and together with the wrapping mold that provides external pressure from the outside to the inside, form a clamping pressure field, thereby achieving high-density compression molding of the wrapped carbon fiber reinforcement layer; through this molded positioning structure, the carbon cloth fit and resin distribution uniformity in the molded area of ​​the frame docking point are improved, effectively preventing voids and bubbles.

[0068] In addition, different specifications of inner molds can be selected according to the tube diameter, so as to improve the versatility of the bicycle carbon fiber frame docking point strengthening connection process in the production of carbon fiber frames of various configurations.

[0069] Regarding the above-mentioned control method for the heating and cooling process of vacuum hot pressing curing, in step S4, a slow heating section and a slow cooling section are set in the process of vacuum hot pressing curing, each section lasting 1 to 2 hours, and the control curves of the slow heating section and the slow cooling section are linear, which is used to reduce the stress generated during hot pressing curing.

[0070] During application, the vacuum hot pressing curing process is equipped with a slow heating section and a slow cooling section, each section lasting 1 to 2 hours, and the temperature control curve rises or falls linearly, which is used to slow down the thermal gradient change and avoid internal stress concentration or interface cracking caused by local excessive heating.

[0071] Among them, the slow heating section allows the resin to be fully preheated, flow slowly, and fully impregnate the fibers; the slow cooling section helps to gradually release the internal residual stress in the frame docking area, preventing thermal cracks or delamination in the docking area after molding; this vacuum hot pressing curing method improves the dimensional stability and bonding strength of the frame docking structure.

[0072] The duration of the slow heating section and the slow cooling section during the vacuum hot pressing curing process is independent of the constant temperature and constant pressure hot pressing curing time; in addition, a segmented temperature control strategy can be set during the hot pressing process of vacuum hot pressing curing to achieve fine control of the entire curing process.

[0073] Regarding the above-mentioned non-destructive testing method, in step S6, the non-destructive testing method selects at least one of ultrasonic C-scan, infrared thermal imaging or acoustic emission testing.

[0074] During application, the non-destructive testing method of step S6 may be selected from at least one of ultrasonic C-scanning, infrared thermal imaging or acoustic emission testing according to the structural thickness and pipe diameter of the frame docking area.

[0075] Ultrasonic C-scanning is suitable for detecting internal defects such as delamination and bubbles; infrared thermal imaging can identify areas of abnormal heat conduction to determine voids or debonding; and acoustic emission technology is used for early identification of microcrack propagation signals during frame alternating load tests. This multi-faceted detection strategy can achieve full coverage and high-reliability detection of frame connection areas, effectively ensuring product quality.

[0076] Among them, according to actual production needs, automated inspection can be achieved through an automated defect recognition system that integrates ultrasonic C-scan, infrared thermal imaging or acoustic emission testing to improve the inspection efficiency of finished vehicle frames.

[0077] The second embodiment of the process for strengthening the connection of the docking points of a bicycle carbon fiber frame is different from the first embodiment in that, in step S3, the thermal expansion inner mold is a heat-expandable silicone inner mold, and its radial expansion amount is 1.5-2.5% of the original diameter.

[0078] During application, the thermal expansion inner mold in the second embodiment is a heat-expandable silicone inner mold, and its radial expansion is 1.5 to 2.5% of the original diameter. The expansion amplitude is precisely controlled by adjusting the heating power supply by the temperature control system; the inner mold is synchronously expanded by the heat driven by the inner mold under the regulation of the temperature control system, and acts synchronously with the pressure mold on the frame docking area to achieve uniform compaction between the carbon fiber sleeve of the carbon fiber reinforcement layer and the two-way or three-way carbon fiber prepreg, as well as a close fit with the prefabricated carbon fiber tube at the connection part of the frame; it can effectively avoid the problem of insufficient fit of traditional rigid core molds to the curvature parts of special configuration frames, and significantly improve the molding consistency and interface bonding strength of the special-shaped docking area of ​​the frame.

[0079] The technical features of the above embodiments may be combined arbitrarily. To simplify the description, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A bicycle carbon fiber frame docking point strengthening connection process, characterized in that: The method comprises the following steps, which are performed in order from S1 to S7: S1. Butt joint structure pretreatment: Precision cutting and end face shaping of the prefabricated carbon fiber tubes at the frame connection parts to form a butt joint surface with a positioning accuracy within ±0.05mm, and roughening the surface of the connection area; S2. Carbon fiber reinforcement layer laying: A set of carbon fiber sleeves made of multi-axial carbon fiber braids are wrapped around the outside of the frame joint area, and bidirectional or tridirectional carbon fiber prepregs are laid at the seam. Based on the results of structural stress simulation, bidirectional or tridirectional carbon fiber prepregs are laid in high stress areas for directional reinforcement. In step 2, the braided structure of the carbon fiber sleeve is a three-dimensional multi-axial braid, and the ratio of axial, radial and hoop fibers is 4:3:3; In step 2, the bidirectional carbon fiber prepreg includes oblique layers with an angle of ±45° and longitudinal layers with an angle of 0° or circumferential layers with an angle of 90°, and the laying order is alternating, and the number of layers laid is not less than 5; In step 2, the tri-directional carbon fiber prepreg includes oblique layers with an angle of ±45°, a longitudinal layer with an angle of 0°, and a circumferential layer with an angle of 90°, and the laying order is alternating, and the number of layers laid is not less than 5; S3, Molding Positioning: The butted frame is placed in a compression mold, and a removable inner mold is placed inside the pipe fitting in the frame butt joint area to provide radial support to the butt joint area of ​​the frame. This allows the carbon fiber reinforcement layer coated in step S2 to adhere to the pipe surface during the subsequent molding process under the dual pressure of the compression mold providing pressure from the outside toward the frame and the inner mold providing support from the inside toward the frame. S4, vacuum assisted curing: remove air through vacuum bag packaging, and hot press curing for 12 to 18 hours under constant temperature of 130 ° C and pressure of 0.6 to 0.8 MPa to complete the cross-linking and curing of carbon fiber and resin and the interface bonding; In step S4, a slow heating section and a slow cooling section are set during the vacuum hot pressing curing process, each section lasting 1 to 2 hours, and the control curves of the slow heating section and the slow cooling section are linear, so as to reduce the stress generated during the hot pressing curing; S5, demoulding: after cooling, remove the compression mold and inner mold; S6. Inspection: Perform non-destructive inspection on the joint area of ​​the frame. If the inspection reveals defects such as delamination, voids, peeling or poor bonding, the frame will enter the repair process. If the inspection does not find any defects such as delamination, voids, peeling or poor bonding, the frame will enter the qualified production line and flow to the next process. S7, repair: local grinding of the defective area, patching with bidirectional or tridirectional carbon fiber prepreg, and re-circulating S3 and S4 steps for positioning and curing to complete the repair.

2. The bicycle carbon fiber frame docking point strengthening connection process according to claim 1, characterized in that: In step S3, the inner mold includes a thermal expansion inner mold or an airbag inner mold.

3. The bicycle carbon fiber frame docking point strengthening connection process according to claim 2, characterized in that: In step S3, the thermal expansion inner mold is a silicone inner mold that can be expanded by heating, and its radial expansion amount is 1.5-2.5% of the original diameter.

4. The bicycle carbon fiber frame docking point strengthening connection process according to claim 1, characterized in that: In step S6, the non-destructive testing method is at least one of ultrasonic C-scan, infrared thermal imaging or acoustic emission testing.

5. The bicycle carbon fiber frame docking point strengthening connection process according to claim 1, characterized in that: When defects are detected in the frame's docking area, the S7 repair steps include: S7.

1. Locally grind the defective area to remove the defective carbon fiber layer; S7.

2. Use bidirectional or tridirectional carbon fiber prepreg with a direction and material matching the original structure for re-laying; S7.

3. Re-perform hot pressing curing under the same temperature and pressure as the original curing under the conditions of mold positioning and vacuum bag packaging to complete the defect repair.

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