Hot melting process for carbon fiber frame of bicycle

Abstract

The invention discloses a bicycle carbon fiber frame hot melting process, and relates to the technical field of bicycle carbon fibers, the process comprises a plurality of sequential steps: pretreating carbon fiber cloth to make the carbon fiber cloth have low broken filament rate and high surface energy; the used hot melt adhesive is a composite system of a polyimide modified ethylene-vinyl acetate copolymer and a temperature-controlled release type polyester microcapsule fluxing agent; the carbon fiber cloth is laid in a segmented mode according to a set sequence, local preheating treatment is conducted after each layer of laying layer unit is laid, interface fusion is improved, and a structural body is formed; the structural body is placed in a hot melting mold to be cured and formed, and segmented pressurization is carried out in the curing period; an exhaust device is synchronously connected to extract interlayer air and redundant colloid; after forming is completed, constant-temperature tempering treatment is carried out to release structural stress; the process has good raw material adaptability, high adhesive property and short forming period, and the problems that an existing hot melting process is limited in forming quality and performance, long in forming period and low in curing efficiency are solved.

Description

Technical Field

[0001] The invention relates to the technical field of bicycle carbon fiber, in particular to a hot-melt process for a bicycle carbon fiber frame. Background Art

[0002] With the growing demand for lightweight, high-strength, and high-performance bicycles, carbon fiber composites have become the mainstream material for high-end bicycle frame manufacturing due to their excellent specific strength, corrosion resistance, and structural designability. Currently, the production of carbon fiber bicycle frames generally uses a hot melt adhesive-assisted curing process. The typical process includes carbon fiber cloth cutting, prepreg stacking, mold pressing, heating and melting, and thermal curing. In this process, the compatibility of the carbon fiber cloth and the hot melt adhesive resin system, the stability of the layer structure, and temperature control during the hot melt process all play a key role in the final performance of the frame.

[0003] In existing technologies, to ensure the overall strength and bonding quality of the molded frame, the carbon fiber cloth used is generally required to have extremely high homogeneity and consistency. However, in actual production, due to the influence of carbon fiber supply batches, storage environment and operating conditions, problems such as breakage, fuzzy fibers and uneven linear density are prone to occur. These defects not only affect resin permeability during the stacking and hot pressing processes, but may also cause internal defects such as delamination and voids, thereby reducing the structural performance of the frame.

[0004] In addition, the selection of hot melt adhesive resins is limited. Commonly used thermoplastic resin systems such as PA, PET, and EVA have low bonding efficiency in actual applications and are easily affected by humidity and pyrolysis temperature, resulting in insufficient interfacial bonding strength. In addition, the traditional hot melt process mainly uses continuous stacking and overall melting and pressurization, resulting in uneven heat field distribution, difficulty in controlling melt penetration, and a long curing cycle, which makes it difficult for the product consistency and molding efficiency to meet the needs of large-scale batch production.

[0005] To remedy the above-mentioned defects, some improvement plans have attempted to use prefabricated parts combined with local heating technology, dynamic temperature and pressure control systems, etc. However, since the overall process has not broken through the traditional process architecture, there are still problems such as narrow operating windows, large fluctuations in yield rates, and strong dependence on operator experience.

[0006] Therefore, how to optimize the stacking path, heating method and adhesive system based on the process itself has become a key technical direction that needs to be solved urgently.

[0007] The existing technology has the following technical problems: (1) Frequent problems of carbon fiber raw materials breaking and hairy fibers; (2) Limited selection of hot melt adhesive resin systems and unstable bonding performance; (3) Long molding cycle and low thermal curing efficiency; (4) The overall hot melt process is rigid and lacks means to finely control the lamination method and heating parameters, which restricts further improvement of product consistency and production efficiency.

[0008] In summary, it is found that the prior art has at least the following technical problems: The existing carbon fiber hot melt process has technical problems such as low tolerance to defects in carbon fiber raw materials, limited resin selection, limited bonding performance, long forming cycle, and low curing efficiency. Summary of the Invention

[0009] The purpose of the present invention is to provide a hot melt process for a bicycle carbon fiber frame to solve the technical problems of the existing carbon fiber hot melt process, such as low tolerance to defects in carbon fiber raw materials, limited resin selection, limited bonding performance, long forming cycle, and low curing efficiency.

[0010] The many technical effects that can be produced by the preferred technical solutions among the many technical solutions provided by the present invention are described in detail below.

[0011] To solve the above technical problems, the present invention provides the following technical solutions: The present invention provides a hot melt process for a bicycle carbon fiber frame, including the following steps: S1. Pretreat the carbon fiber cloth: The structure of the carbon fiber cloth is a multi-directional woven structure, and the hairiness rate on the surface is not higher than 0.5 filaments / cm 2 ; after the surface of the carbon fiber cloth is treated by plasma, its surface energy is not lower than 60 mN / m; S2. Composite adhesive: A hot melt adhesive is used as the composite adhesive between each layer of the carbon fiber cloth. The hot melt adhesive includes a polyimide-modified ethylene-vinyl acetate copolymer and a temperature-controlled release polyester microcapsule fluxing agent; S3. Lay to form a structure: Lay the pretreated carbon fiber cloth in segments according to a set lay-up sequence. Each segment lay-up includes multiple stacked lay-up units, and local preheating treatment is performed after each layer of the lay-up unit is laid; the preheating temperature is 90°C to 110°C, and the duration is 5 to 15 minutes, so that the carbon fiber cloth and the hot melt adhesive are initially combined to form a structure; S4. Hot melt curing and forming: Place the formed structure into a hot melt mold with multiple temperature control zones, and perform hot melt curing and forming on the structure; The curing and forming temperature of each temperature control zone is controlled at 90°C to 160°C; during the hot melt curing and forming process, the cavity of the hot melt mold is pressurized in stages until the curing is completed, and the pressure range of the pressurization is controlled at 0.2 to 0.6 MPa; S5. Exhaust and compact the interlayer structure: During the hot melt curing and forming process in step S4, an exhaust device is introduced to evacuate the cavity of the hot melt mold during hot melt curing and forming. The exhaust rate is 50 - 150 L / min and the exhaust time is 10 - 30 minutes, which is used to remove the interlayer air of the carbon fiber cloth of the structure body and the excessive hot melt adhesive, preventing voids from forming in the layup of the structure body. S6. Tempering: After the structure body is hot melt cured and formed, a constant temperature tempering treatment is carried out on the structure body. The tempering temperature is 100°C - 130°C and the tempering time is 1 - 3 hours to release the internal stress of the structure body and improve the stability of the bonding interface.

[0012] In one embodiment, in step S1, the multi - directional braided structure is one or a combination of 0° / 90° orthogonal braiding, ±45° diagonal braiding, or 0° / ±45° / 90° three - directional braiding.

[0013] In one embodiment, in step S1, the plasma treatment uses a mixed atmosphere of argon and oxygen, the treatment power is 100 - 300 W, and the treatment time is 30 - 90 seconds.

[0014] In one embodiment, the release temperature of the polyester micro - capsule flux is 80°C - 120°C.

[0015] In one embodiment, in step S3, the coating amount of the hot melt adhesive is 30 - 80 g / m 2 , and the coating method is hot melt spraying or gravure transfer.

[0016] In one embodiment, in step S4, the multiple temperature - controlled zones are respectively the head tube zone, the bottom bracket zone, and the rear fork zone, and the heating temperature is regulated by independent temperature curves respectively; each of the temperature - controlled zones of the hot melt mold is provided with an independent temperature sensor and a heating element, and is dynamically closed - loop regulated by a central controller arranged outside the hot melt mold; among them: the temperature control range of the head tube zone is 100°C - 130°C; the temperature control range of the bottom bracket zone is 130°C - 160°C; the temperature control range of the rear fork zone is 90°C - 120°C.

[0017] In one embodiment, the exhaust device includes a vacuum pump and an exhaust passage and a gas guide groove connecting the cavity of the hot melt mold; the central controller is electrically connected to the vacuum pump, and a timed - start exhaust program is set in the central controller to control the vacuum pump to evacuate the cavity of the hot melt mold before the hot melt mold is pressurized.

[0018] In one embodiment, in step S3, the laid segments include a main tube area, a five-way area, and a rear fork area; the carbon fiber cloth is laid in sequence according to the laying order of the main tube area, the five-way area, and the rear fork area, for establishing a main structural framework and improving the coherence of the stress transfer path.

[0019] In one embodiment, each of the laying units includes at least three layers of the carbon fiber cloth, and the laying angles of the three layers of the carbon fiber cloth are 0°, +45°, and -45° respectively, for bearing axial force and shear stress respectively.

[0020] In one embodiment, the stacking manner of the carbon fiber cloth between adjacent laying units is staggered stacking, and the stacking angle offset of the carbon fiber cloth is controlled within the range of 10° to 30°, for enhancing the interlayer shear strength and the interface bonding stability.

[0021] Compared with the existing hot melting process of carbon fiber bicycle frames, the hot melting process of the bicycle carbon fiber frame provided by the present invention has the following beneficial effects: 1. Improve the adaptability of carbon cloth By implementing low hairiness rate screening and surface plasma treatment on the carbon fiber cloth, the interface activity and processing stability of the carbon fiber cloth are improved, the discreteness between different batches of raw materials is effectively accommodated, and the influence of broken ends and floating filaments on the molding quality is reduced; 2. Optimize the bonding system and enhance the interlayer bonding performance The present invention adopts a composite hot melt adhesive composed of polyimide-modified ethylene-vinyl acetate copolymer and a temperature-controlled release type polyester microcapsule fluxing agent. Compared with the traditional single hot melt adhesive system, the composite hot melt adhesive adopted in this technical solution has a wider process window and staged penetration ability, and improves the bonding depth and interlayer strength; 3. Zone temperature control + segmented laying can improve the structural molding consistency By laying the carbon cloth in segments and performing local preheating after each laying unit of each layer is laid, each laying unit in each area of the segmented laying can obtain independent pre-melting treatment, so as to adapt to and match the heat capacity and lamination thickness of different areas, reduce the phenomenon of overheating or under-melting of the colloid in the formation of the structure body, and improve the interlayer uniformity of the laying; 4. Fine curing control to achieve high-efficiency short-cycle molding The hot melt mold is provided with multiple temperature control zones, and the temperature is respectively controlled within the range of 90°C to 160°C. Combined with the staged pressure control with a pressure range of 0.2 to 0.6 MPa, while ensuring the complete curing of the structure body, the curing cycle is greatly shortened, and the curing efficiency is increased by at least 20% to 35% compared with the conventional process; 5. Vacuum-assisted air extraction to compact the interlayer structure and prevent interlayer bubbles and dry glue defects By setting up an exhaust device, continuous extraction during the hot melt process can effectively remove residual gas and excess colloid between layers, prevent the formation of bubbles, interlayer voids and unbonded areas, and improve the overall molding quality; 6. Introduce the tempering stress release step to improve structural durability and dimensional stability The tempering temperature is set at 100℃~130℃ for 1~3 hours, which can release the internal stress of the cured carbon fiber structure, improve the interface stability and fatigue life of the product, and reduce the risk of deformation and delamination in long-term use; In summary, the carbon fiber frame hot melt process proposed in the present invention not only significantly improves the process adaptability and bonding reliability, but also significantly shortens the hot melt molding cycle, improves structural integrity and mass production consistency, and has clear technological advancement and industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] Figure 1 The present invention is a schematic flow chart of the hot-melt process for a bicycle carbon fiber frame. DETAILED DESCRIPTION

[0024] 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.

[0025] In a specific embodiment, a hot melt process for a bicycle carbon fiber frame is provided, which includes multiple steps performed in sequence: pre-treating the carbon fiber cloth to give it a low lint rate and high surface energy; the hot melt adhesive used is a composite system of polyimide-modified ethylene-vinyl acetate copolymer and a temperature-controlled release polyester microcapsule flux; the carbon fiber cloth is laid in sections according to a set order, and local preheating treatment is performed after each layer of laying unit is laid to enhance interface fusion and form a structure; the structure is placed in a hot melt mold for curing and molding, and pressurized in sections during curing; an exhaust device is simultaneously connected to remove interlayer air and excess colloid; after molding is completed, a constant temperature tempering treatment is performed to release structural stress; the process has good raw material adaptability, strong bonding performance and a short molding cycle, and is suitable for batch production of high-performance carbon fiber bicycle frames; it effectively solves the technical problems of the existing carbon fiber hot melt process, such as low tolerance to carbon fiber raw material defects, limited resin selection and limited bonding performance, long molding cycle and low curing efficiency.

[0026] The first implementation of the hot melt process for bicycle carbon fiber framesFigure 1 As shown, it includes steps S1 to S6, and the specific operations of each step are as follows: S1. Pretreat the carbon fiber cloth: The structure of the carbon fiber cloth is a multi-directional woven structure, and the hairiness rate on the disk surface is not higher than 0.5 hairs / cm 2 ; After the surface of the carbon fiber cloth is treated by plasma, its surface energy is not lower than 60 mN / m; S2. Composite adhesive: A hot-melt adhesive is used as the composite adhesive between each layer of carbon fiber cloth. The hot-melt adhesive includes a polyimide-modified ethylene-vinyl acetate copolymer and a temperature-controlled release type polyester microcapsule fluxing agent; S3. Lay to form a structure: The pretreated carbon fiber cloth is laid in segments according to the set lay-up sequence. Each segment laying includes multiple stacked lay-up units, and local preheating treatment is performed after each layer of lay-up unit is laid; The preheating temperature is 90°C to 110°C, and the duration is 5 to 15 minutes, so that the carbon fiber cloth and the hot-melt adhesive are initially combined to form a structure; S4. Hot-melt curing and forming: Place the formed structure into a hot-melt mold with multiple temperature control zones to perform hot-melt curing and forming on the structure; The curing and forming temperature of each temperature control zone is controlled at 90°C to 160°C; During the hot-melt curing and forming process, the cavity of the hot-melt mold is pressurized in stages until the curing is completed, and the pressure range of the pressurization is controlled at 0.2 to 0.6 MPa; S5. Exhaust and compact the interlayer structure: During the hot-melt curing and forming process in step S4, an exhaust device is introduced to evacuate the cavity of the hot-melt mold during hot-melt curing and forming. The exhaust rate is 50 to 150 L / min, and the exhaust time is 10 to 30 minutes, which is used to remove the interlayer air of the carbon fiber cloth of the structure and the excessive hot-melt adhesive to prevent voids from forming in the lay-up of the structure; S6. Tempering: After the structure is hot-melt cured and formed, perform an isothermal tempering treatment on the structure. The tempering temperature is 100°C to 130°C, and the tempering time is 1 to 3 hours to release the internal stress of the structure and improve the stability of the bonding interface.

[0027] Such as Figure 1As shown in the figure, when applying, the material preparation of steps S1 and S2 should be completed first, and then enter the carbon fiber cloth laying step of S3. Each layer laying unit contains multiple layers of carbon fiber cloth, and the carbon fiber cloths are bonded by a hot-melt adhesive. After laying the laying units of each segment in the laying order, preheating treatment is carried out, and then the stacking and preheating of the laying units are repeated, and finally a structure is formed; enter step S4, and then put the preliminarily formed structure into a hot-melt mold to complete hot-melt curing and forming, where the structure put into the mold needs to be heated, pressurized, and the process of vacuum pumping in step S5; after the structure is formed by hot-melt curing, enter the tempering step of step S6, and finally form a preliminary finished product of the carbon fiber frame structure.

[0028] Compared with the existing hot-melt process of carbon fiber frames, the hot-melt process of bicycle carbon fiber frames provided by the present invention has the following beneficial effects: improving the adaptability of carbon cloth: by implementing low hairiness rate screening and surface plasma treatment on carbon fiber cloth, the interfacial activity and processing stability of carbon fiber cloth are improved, effectively accommodating the discreteness between different batches of raw materials, and reducing the influence of broken ends and floating filaments on the forming quality; Optimizing the bonding system and enhancing the interlayer bonding performance: The present invention uses a composite hot-melt adhesive composed of polyimide-modified ethylene-vinyl acetate copolymer (polyimide-modified EVA) and a temperature-controlled release type polyester microcapsule fluxing agent. Compared with the traditional single hot-melt adhesive system, the composite hot-melt adhesive used in this technical solution has a wider process window and staged penetration ability, improving the bonding depth and interlayer strength; Zone temperature control + segmented laying can improve the structural forming consistency: By laying the carbon cloth in segments and performing local preheating after each layer laying unit is laid, each laying unit in each area of the segmented laying can obtain independent pre-melting treatment, so as to adapt to and match the heat capacity and lamination thickness of different areas, reduce the phenomenon of overheating or under-melting of the colloid during the formation of the structure, and improve the interlayer uniformity of the laying; Fine curing control to achieve high-efficiency short-cycle forming: The hot-melt mold is provided with multiple temperature control zones, which respectively control the temperature in the range of 90°C to 160°C, combined with staged pressure control with a pressure range of 0.2 to 0.6 MPa, which can ensure the complete curing of the structure while greatly shortening the curing cycle, and at least improve the curing efficiency by 20% to 35% compared with the conventional process; Vacuum-assisted air extraction compacts the interlayer structure to prevent interlayer bubbles and dry glue defects: By setting an exhaust device and continuously pumping air during the hot-melt process, the residual air and excess colloid between layers can be effectively removed, preventing the formation of bubbles, interlayer cavities and unbonded areas, and improving the overall forming quality; Introduce a tempering stress relief step to improve structural durability and dimensional stability: The tempering temperature is set at 100°C to 130°C for 1 to 3 hours, which can release the internal stress of the cured carbon fiber structure, enhance the interface stability and the fatigue life of the product, and reduce the risk of deformation and delamination during long-term use. The hot-melt process for carbon fiber frames proposed by the present invention not only significantly improves the process adaptability and bonding reliability, but also significantly shortens the hot-melt molding cycle, enhances the structural integrity and mass production consistency, and has clear technological progressiveness and industrial application value.

[0029] As one of the optional implementation methods: Regarding the multi-directional braided structure of the carbon fiber cloth used in the above step S1, specifically, the multi-directional braided structure is one or a combination of 0° / 90° orthogonal braiding, ±45° diagonal braiding, or 0° / ±45° / 90° three-directional braiding.

[0030] And the specific settings for the plasma treatment of the carbon fiber cloth. The plasma treatment uses a mixed atmosphere of argon and oxygen, with a treatment power of 100 - 300W and a treatment time of 30 - 90 seconds.

[0031] When in application, the carbon fiber cloth can be selected according to the load-bearing direction and the complexity of the shape of different structures of the frame: 0° / 90° orthogonal braiding is used for the main axial load-bearing area, such as the down tube area of the frame; ±45° diagonal braiding is used for the shear section, such as the connection area between the bottom bracket and the rear fork; the three-directional braided structure is used for the area with complex forces, such as the area below the bottom bracket and the connection section between the head tube and the top tube; thus, an optimized layup structure for stress coordination in each functional area can be achieved.

[0032] In the process of plasma treating the carbon fiber cloth, controlling the gas ratio as argon:oxygen = 2:1 makes it easier to form polar functional groups on the surface of the treated carbon fiber cloth, enhances the wetting and diffusibility of the hot-melt adhesive, and significantly reduces the "adhesive penetration obstacle" problem caused by hair filaments or dust; it improves the surface activity, material adaptability, and bonding consistency of the carbon cloth, and solves the technical defect of low raw material flaw tolerance.

[0033] In the composite adhesive constructed in step S2, the release temperature of the polyester microcapsule flux, which is one of its components, is 80°C to 120°C.

[0034] In the laying and bonding of the carbon fiber cloth in step S3, the coating amount of the hot-melt adhesive is 30 - 80 g / m 2 , and the coating method is hot-melt spraying or gravure transfer.

[0035] During application, the release temperature of the polyester microcapsule flux is controlled between 80°C and 120°C. Its release process has a gradient distribution characteristic, which helps the colloid between the laminated carbon fiber cloth structural layers to gradually soften and penetrate layer by layer, improving the internal wetting quality of the structure; The application method of the hot melt adhesive can adopt different coating processes according to the product structure: using the hot melt spraying method for tubular structures to improve coating uniformity; using the gravure roll transfer method for curved surfaces or small-angle areas to facilitate the control of the thickness of the colloid coating; which helps to enhance the interfacial affinity and penetration depth of the hot melt adhesive for carbon fiber cloths with different morphologies, reducing problems such as "false adhesion" and "local over-gluing", and improving the bonding stability.

[0036] The specific settings of the laying path and laying sequence in the above step S3 are that the laying segments include the main pipe area, the five-way area, and the rear fork area; the carbon fiber cloth is laid in sequence according to the laying sequence of the main pipe area, the five-way area, and the rear fork area, for establishing the main structure framework and improving the coherence of the stress transmission path.

[0037] Among them, each laying unit includes at least three layers of carbon fiber cloth, and the laying angles of the three layers of carbon fiber cloth are 0°, +45°, and -45° respectively, for bearing axial force and shear stress respectively.

[0038] The stacking method of the carbon fiber cloth between adjacent laying units is staggered stacking, and the stacking angle deviation of the carbon fiber cloth is controlled within the range of 10° to 30°, for enhancing the interlayer shear strength and the interface bonding stability.

[0039] During application, each laying unit gradually establishes the main stress-bearing framework according to the laying sequence of the main pipe area → the five-way area → the rear fork area, which is beneficial to controlling the distribution of the thermal field and the coherence of the stress streamline; the carbon fiber cloth in each laying unit is staggered and laid at angles of 0°, +45°, and -45° respectively, forming a three-dimensional shear network in each layer of laying unit; and the staggered stacking (laying) angle of the carbon fiber cloth of the adjacent laying units is controlled between 10° and 30°, and a ±15° gradient method can be adopted, so that the fiber orientation forms a "mechanical transfer channel" between layers, effectively alleviating the shear weak area caused by the overlap of fiber directions, and also strengthening the connection strength between adjacent laying units; making different fiber orientations formed between the carbon fiber cloths, and different fiber orientations can also be formed between the laying units, thereby enhancing the interlayer shear strength, reducing the occurrence of interface delamination failure in the structure, solving the problem of delamination caused by uneven local load bearing, and further enhancing the overall fatigue life of the structure and the overall quality of the structure.

[0040] Regarding the multiple temperature control zones set in the above-mentioned step S4, for the setting method of the specific heating temperatures they control, the multiple temperature control zones are respectively the head tube zone, the bottom bracket zone, and the rear fork zone, and the heating temperatures are regulated by independent temperature curves respectively; each temperature control zone of the hot melt mold is provided with an independent temperature sensor and a heating element, and dynamic closed-loop regulation is performed through a central controller arranged outside the hot melt mold; among them: the temperature control range of the head tube zone is 100°C to 130°C; the temperature control range of the bottom bracket zone is 130°C to 160°C; the temperature control range of the rear fork zone is 90°C to 120°C.

[0041] During application, the three major temperature control zones provided in the hot melt mold are subjected to closed-loop regulation through embedded thermocouples and an independent PID control system; the head tube zone mainly processes thin-walled and fast-heat-dissipating parts, and the temperature is controlled at 100°C to 130°C; the bottom bracket zone is large in volume and high in thickness, and the temperature is controlled at 130°C to 160°C to ensure sufficient flow of the colloid; the temperature of the rear fork zone is controlled at 90°C to 120°C to prevent overheating and deformation; independent temperature control of different regions can solve the problem of uneven thermal curing caused by differences in structural thickness, and achieve synchronous curing and synchronous bonding of each structural zone, thereby improving the overall strength of the structure.

[0042] Regarding the specific structure of the above-mentioned exhaust device, the specific connection method with the hot melt mold, and the start control method, the exhaust device includes a vacuum pump and an exhaust passage and a gas guide groove connecting the cavity of the hot melt mold; the central controller is electrically connected to the vacuum pump, and a timed start air extraction program is set in the central controller to control the vacuum pump to perform vacuum pumping on the cavity of the hot melt mold before the hot melt mold is pressurized.

[0043] During application, the exhaust system is controlled by the central controller, and the start of the vacuum pump is linked with the hot pressing process: it can be set to two modes of "pumping air first and then pressurizing" or "simultaneously pumping air and pressurizing", and the pressurizing and air extraction methods are automatically switched according to the complexity of the frame structure; a gas guide groove is preset in the inner cavity of the hot melt mold to drain the negative pressure area, and the residual gas pressure can be controlled below 0.1 bar after the vacuum pumping is completed; by discharging the gas in the inner cavity of the mold, problems such as residual air between layers and excessive colloid expansion can be eliminated, reducing defects such as bubbles, interlayers, and dry adhesive layers, and improving the internal structure density.

[0044] Among them, the hot melt mold can be pressurized after the vacuum pumping treatment of the cavity of the hot melt mold is completed or simultaneously with the vacuum pumping treatment.

[0045] In the staged pressurization of the hot melt mold in step S4, the pressure is increased by adding a wrapping pressure outside the hot melt mold, such as placing the hot melt mold in a pressurization chamber and pressurizing it by gas wrapping, or wrapping and pressurizing the hot melt mold through a structural member.

[0046] Specifically, the hot melt mold is placed in an external pressure chamber, and the wrapped and uniform pressure is applied through high-pressure gas (such as nitrogen or compressed air). Its staged pressure application includes: the initial pressure stage, with the pressure controlled at 0.1 - 0.2 MPa, the pressure holding stage with the pressure controlled at 0.4 - 0.6 MPa, and after the structure reaches the specified curing time, the slow-release pressure reduction stage is implemented. This pressure application method is different from the traditional in-mold mechanical top pressure method, with a more uniform pressure distribution, fast response, high wrapping property, and is suitable for complex curved surface structures. It can improve the uniformity of colloid flow, prevent fiber misalignment or colloid extrusion, and improve the forming efficiency and structural consistency of the carbon fiber structure.

[0047] The second embodiment of the hot melt process for the carbon fiber bicycle frame. The difference between this embodiment and the first embodiment is that another control method is adopted for the staged pressure application of the hot melt mold: the hot melt mold is divided into zones for pressure application through multiple gas injection devices arranged outside the hot melt mold.

[0048] Specifically, the hot melt mold is divided into three pressure application zones, corresponding to the head tube zone, the bottom bracket zone, and the rear fork zone. An independent gas injection device is detachably wrapped and connected to the outer wall of the mold shell of each zone. In the central controller, an independent pressure curve of the air pressure changing with time is set for each pressure application zone to control the pressure application process of the gas injection device to the pressure application zone, achieving: the bottom bracket zone is first pressurized to 0.6 MPa, and the air pressure value is first fixed in the area with a high carbon fiber thickness; the head tube zone is pressurized to 0.4 MPa 2 minutes later; the rear fork zone is slowly pressurized to 0.3 MPa 5 minutes later, and finally, the three major pressure application zones of the head tube zone, the bottom bracket zone, and the rear fork zone are depressurized synchronously.

[0049] This independent zone pressure application method is suitable for the carbon fiber frame structure with complex structures and asynchronous curing requirements, and is especially suitable for the forming of carbon fiber frames with irregular cross-sections.

[0050] When in application, this zone pressure application method can be combined with multi-zone temperature control to achieve the "dual regulation and matching" of the thermal field and the pressure field, which can improve the colloid saturation degree of large cross-section structures (such as the bottom bracket cylinder), avoid the risks of under-melting in the core and over-pressure on the outer layer; contribute to improving the adaptability of the hot melt process to complex structures, enhancing the forming fullness of areas with high thickness and the forming precision of fine areas, and improving the overall interface quality of the multi-layer composite carbon fiber frame structure.

[0051] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A hot-melt process for a bicycle carbon fiber frame, characterized in that it includes the following steps: S1. Pretreat the carbon fiber cloth: The structure of the carbon fiber cloth is a multi-directional woven structure, and the hairiness rate on the disk surface is not higher than 0.5 filaments / cm 2 ; After the surface of the carbon fiber cloth is treated by plasma, its surface energy is not lower than 60 mN / m; S2. Composite adhesive: A hot-melt adhesive is used as the composite adhesive between each layer of the carbon fiber cloth. The hot-melt adhesive includes a polyimide-modified ethylene-vinyl acetate copolymer and a temperature-controlled release polyester microcapsule fluxing agent; S3. Laying to form a structure: The pretreated carbon fiber cloth is laid in segments according to a set laying sequence. Each segment laying includes multiple stacked laying units, and local preheating treatment is performed after each layer of the laying unit is laid; The preheating temperature is 90°C to 110°C, and the duration is 5 to 15 minutes, so that the carbon fiber cloth and the hot-melt adhesive are initially combined to form a structure; S4. Hot-melt curing and forming: The formed structure is placed into a hot-melt mold with multiple temperature control zones, and the structure is hot-melt cured and formed; The curing and forming temperature of each temperature control zone is controlled at 90°C to 160°C; During the hot-melt curing and forming process, the cavity of the hot-melt mold is pressurized in stages until curing is completed, and the pressure range of the pressurization is controlled at 0.2 to 0.6 MPa; S5. Exhausting and compacting the interlayer structure: During the hot-melt curing and forming process in step S4, an exhaust device is introduced to evacuate the cavity of the hot-melt mold during hot-melt curing and forming. The exhausting rate is 50 to 150 L / min, and the exhausting time is 10 to 30 minutes, which is used to remove the interlayer air of the carbon fiber cloth of the structure and the excessive hot-melt adhesive to prevent voids from forming in the laying of the structure; S6. Tempering: After the structure is hot-melt cured and formed, the structure is subjected to a constant-temperature tempering treatment. The tempering temperature is 100°C to 130°C, and the tempering time is 1 to 3 hours to release the internal stress of the structure and improve the stability of the bonding interface.

2. The hot-melt process for a bicycle carbon fiber frame according to claim 1, characterized in that in step S1, the multi-directional braided structure is one or a combination of 0° / 90° orthogonal braiding, ±45° oblique braiding, or 0° / ±45° / 90° three-way braiding.

3. The hot-melt process for a bicycle carbon fiber frame according to claim 1, characterized in that in step S1, the plasma treatment uses a mixed atmosphere of argon and oxygen, the treatment power is 100 to 300 W, and the treatment time is 30 to 90 seconds.

4. The hot-melt process for a bicycle carbon fiber frame according to claim 1, characterized in that the release temperature of the polyester microcapsule fluxing agent is 80°C to 120°C.

5. The hot melt process of the bicycle carbon fiber frame according to any one of claims 1 or 4, characterized in that, In step S3, the coating amount of the hot melt adhesive is 30 to 80 g / m 2 , and the coating method is hot melt spraying or gravure transfer.

6. The hot-melt process for a bicycle carbon fiber frame according to claim 1, characterized in that in step S4, the multiple temperature control zones are respectively a head tube zone, a bottom bracket zone, and a rear fork zone, and the heating temperature is regulated by independent temperature curves respectively; each temperature control zone of the hot-melt mold is provided with an independent temperature sensor and a heating element, and is dynamically closed-loop regulated by a central controller arranged outside the hot-melt mold; wherein: the temperature control range of the head tube zone is 100°C to 130°C; The temperature control range of the five-way area is 130°C to 160°C; The temperature control range of the rear fork area is 90°C to 120°C.

7. The hot-melt process of the bicycle carbon fiber frame according to claim 6, characterized in that The exhaust device includes a vacuum pump and an exhaust passage and an air guide groove connecting the cavity of the hot-melt mold; The central controller is electrically connected to the vacuum pump, and a timed start air extraction program is set in the central controller to control the vacuum pump to perform vacuum pumping on the cavity of the hot-melt mold before the hot-melt mold is pressurized.

8. The hot-melt process of the bicycle carbon fiber frame according to claim 1, characterized in that In step S3, the laid segments include the main pipe area, the five-way area and the rear fork area; The carbon fiber cloth is laid in sequence according to the laying order of the main pipe area, the five-way area and the rear fork area, for establishing the main structure framework and improving the coherence of the stress transmission path.

9. The hot-melt process of the bicycle carbon fiber frame according to claim 8, characterized in that Each of the laying units includes at least three layers of the carbon fiber cloth, and the laying angles of the three layers of the carbon fiber cloth are 0°, +45° and -45° respectively, for bearing axial force and shear stress respectively.

10. The hot-melt process of the bicycle carbon fiber frame according to claim 9, characterized in that The stacking method of the carbon fiber cloth between adjacent laying units is staggered stacking, and the stacking angle deviation of the carbon fiber cloth is controlled within the range of 10° to 30°, for enhancing the interlayer shear strength and the interface bonding stability.

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