A composite material frame variable cross-section profile and a method for manufacturing the same

Abstract

The present application relates to a composite material frame variable cross-section profile and a preparation method thereof, the main beam profile structure is designed and manufactured in sections, the equal cross-section section is combined with a pultrusion forming process and a vacuum pouring process to be manufactured by a two-step method, the bending strength of the profile is improved, the shear strength of the profile is ensured, the metal inner layer and the composite material outer layer hybrid structure are adopted for the variable cross-section section, the stress is dispersed, the connection strength between the sections is improved, the two-step method manufacturing of the equal cross-section section only needs to adopt one pultrusion die, the die cost and the processing period are low, the pultrusion forming efficiency is high, and the profile manufacturing period is also reduced, the metal structure of the variable cross-section section is directly used as the die of the composite material layer, and the die cost and the manufacturing period are further reduced. The present application improves the carrying capacity while reducing the weight of the frame assembly, reduces the manufacturing period, meets the requirements of high performance and low cost, is beneficial to the popularization and application of the composite material frame, and provides certain technical support for high-end equipment manufacturing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lightweight manufacturing of special vehicles, and particularly relates to a composite material vehicle frame variable cross-section profile and a preparation method thereof. BACKGROUND

[0002] As the main load-bearing component of a special vehicle, the vehicle frame has a large self-weight and bears the weight of the vehicle body, power assembly, cab, personnel and goods. When driving on a complex road surface, the vehicle frame is subjected to the combined action of different bending moments, torques and shearing forces, and the working condition is relatively complex. Using a composite material to replace the original steel frame can greatly reduce the self-weight of the frame and improve the load-bearing capacity of the frame. The longitudinal beam of some models of vehicle frames must be designed into a variable cross-section profile due to assembly requirements of assemblies such as wheel hubs, and the cross-sectional profile is generally C-shaped, I-shaped or square-shaped. At present, the design and production of composite material vehicle frames using vacuum infusion, OOA and hot press tank processes can achieve good performance, but high-precision molds must be prepared, which greatly increases the production cycle and cost, and is not conducive to batch promotion and application. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a composite material vehicle frame variable cross-section profile and a preparation method thereof, which improves the structure of the main beam profile, designs and produces it in sections, and uses a two-step method to produce the equal cross-section section by combining the pultrusion process and the vacuum infusion process, thereby improving the bending strength of the profile while ensuring the shear strength of the profile. The variable cross-section section adopts a metal and composite material hybrid structure, which disperses stress and improves the connection strength between sections. The two-step production of the equal cross-section section only requires one pultrusion mold, which has low mold cost and processing cycle, high pultrusion efficiency, and reduced profile production cycle. The metal structure of the variable cross-section section is directly used as a mold for the composite material layer, further reducing the mold cost and production cycle. Therefore, the present application reduces the weight of the vehicle frame assembly while improving the load-bearing capacity, reduces the production cycle, meets the requirements of high performance and low cost, and is conducive to the promotion and application of composite material vehicle frames, providing certain technical support for high-end equipment manufacturing.

[0004] The technical solution adopted by the present application to solve the above technical problems is as follows:

[0005] A composite material frame profile with variable cross-section includes a front profile, a middle profile, and a rear profile. The front and rear profiles have equal cross-sections, while the middle profile has a variable cross-section. The height of the front profile differs from that of the rear profile. The front end of the middle profile has the same height as the front profile, and the rear end has the same height as the rear profile. The inner front end of the middle profile extends forward to form a front connecting section, and the inner rear end extends backward to form a rear connecting section. The rear end of the front profile has a front groove that fits into the front connecting section, allowing the front connecting section to be placed within the front groove. The inner and outer surfaces of the middle section profile are flush with those of the front section profile. The front end of the rear section profile has a rear groove that matches the rear connecting section, so that when the rear connecting section is placed in the rear groove, the inner and outer surfaces of the middle section profile and the rear section profile are flush. The front connecting section and the front groove are fixed by adhesive bonding and mechanical connection, and the rear connecting section and the rear groove are fixed by adhesive bonding and mechanical connection. The front and rear section profiles are made of composite materials, and the inner layer of the middle section profile is made of metal and the outer layer is made of composite materials.

[0006] In the above scheme, the front section profile, middle section profile and rear section profile all include a web, a top panel and a bottom panel. The webs of the three sections are flush. The top panel and bottom panel of the front section profile are parallel. The top panel and bottom panel of the rear section profile are parallel. The top panel and bottom panel of the middle section profile are not parallel.

[0007] In the above scheme, the length of the front-end connecting segment and the rear-end connecting segment is not less than 50mm.

[0008] In the above scheme, the front profile and the rear profile are manufactured in two steps: an outer layer and an inner layer. The outer layer is formed first, and then the inner layer is formed. The outer layer is formed by pultrusion, and the inner layer is formed by vacuum injection. When the inner layer is formed, no reinforcing material is laid in the groove areas of the front and rear sections.

[0009] In the above scheme, the outer layers of the front and rear profiles are manufactured using a pultrusion molding process. The reinforcing material in the pultrusion molding process is one or more of the following: carbon fiber filament, aramid fiber filament, glass fiber filament, quartz fiber filament, basalt fiber filament, and polyimide fiber filament. The resin is one of the following: epoxy resin, vinyl ester resin, polyurethane resin, polyester resin, and phenolic resin. After the outer layer is cured and demolded, the inner surface is polished and finished. The inner layer is manufactured using a vacuum injection molding process. After the reinforcing material is sequentially laid on the inner surface of the outer layer, vacuum injection is performed. The reinforcing material in the vacuum injection process is one or more of the following: carbon fiber fabric, aramid fabric, glass fiber fabric, quartz fiber fabric, basalt fiber fabric, and polyimide fiber fabric. The resin is one of the following: epoxy resin, vinyl ester resin, polyurethane resin, polyester resin, and phenolic resin.

[0010] In the above scheme, the metal inner layer of the middle section profile includes a front connecting section, a rear connecting section, and an intermediate section between the two. The entire metal inner layer is machined. The composite material outer layer of the middle section profile is formed by vacuum injection molding after reinforcing materials are sequentially laid on the outer surface of the intermediate section of the metal inner layer. The vacuum injection reinforcing materials are one or more of carbon fiber fabric, aramid fabric, glass fiber fabric, quartz fiber fabric, basalt fiber fabric, and polyimide fiber fabric. The resin is one of epoxy resin, vinyl ester resin, polyurethane resin, polyester resin, and phenolic resin. No reinforcing materials are laid on the front connecting section and the rear connecting section.

[0011] In the above scheme, the thickness of the inner metal layer of the middle section profile is the same as the thickness of the inner layers of the front and rear sections profiles, and the thickness of the outer composite material layer of the middle section profile is the same as the thickness of the outer layers of the front and rear sections profiles.

[0012] In the above scheme, the front-end connection segment and the rear-end connection segment are selected from areas where stress is not prominent.

[0013] Accordingly, the present invention also proposes a method for preparing the above-mentioned composite material frame variable cross-section profile:

[0014] Both the front and rear profiles are manufactured in two steps. The first step uses a pultrusion molding process to produce the outer layer: the reinforcing material is fully impregnated with resin and then guided into a mold through a guiding device. The mold is a cavity mold with a hollow structure, the shape of which is adapted to the front or rear profile. After initial heating and curing in the mold, it is shaped to the designed length by a traction device. After the outer layer is cured and demolded, the inner surface is polished and finished. The second step uses a vacuum infusion process to produce the inner layer: after finishing, the reinforcing material is laid on the inner surface of the outer layer in sequence. No reinforcing material is laid in the groove areas of the front and rear sections. After laying, the guide net and breathable felt are laid on the innermost layer, and the inner layer is sealed with vacuum bags and sealing strips. The inner layer is then formed using a vacuum infusion process.

[0015] The middle section profile is manufactured in two steps. The first step is to machine the inner metal layer. After the inner metal layer is machined, its outer surface is polished and cleaned. The second step is to use a vacuum injection process to manufacture the outer composite material layer: reinforcing materials are laid sequentially on the outer surface of the middle section of the inner metal layer. No reinforcing materials are laid on the front and rear connecting sections. After the reinforcement materials are laid, the outermost layer is covered with a flow guide net and a breathable felt. It is then sealed with a vacuum bag and sealing strips, and the outer layer is formed using a vacuum injection process.

[0016] After the front section profile, rear section profile, and middle section profile are all manufactured, they are assembled. The front end connecting section and rear end connecting section of the middle section profile are placed in the front groove of the front section profile and the rear groove of the rear section profile, respectively. The overlapping areas are bonded with structural adhesive.

[0017] After the structural adhesive has cured, at least two through holes are made along the length of the bonding area of ​​the panel and the web, and fastened together using connectors.

[0018] In the above method, the panel width is widened during the production of the front section profile, rear section profile, and middle section profile, and then cut to the designed width after production is completed.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention designs and manufactures segmented main beam profile structures. The constant cross-section segments are manufactured using a two-step process combining pultrusion and vacuum infusion, improving both bending and shear strength. Specifically, the outer layer uses pultrusion, with fiber reinforcement in the 0-degree direction and low resin content, effectively enhancing both bending and shear strength. The inner layer uses vacuum infusion, employing fabric as reinforcement. The fabric is laid at different angles, increasing fiber reinforcement in the 90° and ±45° directions, ensuring shear strength. This two-step process requires only one pultrusion die, resulting in low die cost and a short processing cycle, thus reducing the overall profile manufacturing time. Furthermore, pultrusion is highly efficient. Large-tow fibers can be used in the constant cross-section segments, reducing raw material costs by over 30% compared to small-tow fibers of the same grade. The pultrusion process also results in lower die costs compared to vacuum infusion, OOA, autoclave, and compression molding, while increasing molding efficiency by over 10%. A comprehensive assessment suggests that overall costs can be reduced by more than 30%.

[0021] The variable cross-section segment employs a hybrid structure of metal and composite materials, which disperses stress and improves the connection strength between segments. Specifically, the variable cross-section segment, due to its abrupt change in shape, is prone to stress concentration. Moreover, as a structure connecting the preceding and following segments, it experiences complex stress. If a pure composite material structure were used for connection, the composite material's shear resistance would be weak, making it prone to shear failure. However, the hybrid structure of metal and composite materials effectively disperses stress, improves the overall structure's shear resistance, and enhances connection strength. The inner metal layer of the variable cross-section segment is directly used as the mold for the outer composite material layer, further reducing mold costs and manufacturing cycle.

[0022] In summary, this invention improves load-bearing capacity while reducing the weight of the chassis assembly, and reduces manufacturing costs and time. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0024] Figure 1 This is an overall structural diagram of the composite material frame variable cross-section profile in an embodiment of the present invention;

[0025] Figure 2yes Figure 1 A magnified view of a local structural section of the variable cross-section region of the composite material frame profile shown;

[0026] Figure 3 yes Figure 1 A magnified view of the front section of the composite material frame variable cross-section profile shown;

[0027] Figure 4 yes Figure 1 A magnified view of the rear section of the composite material frame variable cross-section profile shown.

[0028] Figure 5 yes Figure 1 A magnified view of the middle section of the composite material frame variable cross-section profile shown.

[0029] Figure 6 yes Figure 1 The diagram shows the bonding of overlapping areas of the composite material frame variable cross-section profiles.

[0030] In the diagram: 10. Front profile; 11. Front groove;

[0031] 20. Middle section profile; 21. Front connecting section; 22. Rear connecting section; 23. Middle section;

[0032] 30. Rear profile; 31. Rear groove;

[0033] 41. Web; 42. Upper panel; 43. Lower panel. Detailed Implementation

[0034] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] like Figures 1-6As shown in the figure, a composite material frame variable cross-section profile provided in an embodiment of the present invention is divided into three sections: a front section profile 10, a middle section profile 20, and a rear section profile 30. The front section profile 10 and the rear section profile 30 have equal cross-sections, while the middle section profile 20 has a variable cross-section. The height of the front section profile 10 is different from that of the rear section profile 30. The front end height of the middle section profile 20 is the same as that of the front section profile 10, and the rear end height is the same as that of the rear section profile 30. The inner front end of the middle section profile 20 extends forward to form a front end connector. The connecting section 21 extends rearward from the inner rear end to form the rear connecting section 22. The rear end of the front profile 10 has a front groove 11 that matches the front connecting section 21, so that when the front connecting section 21 is placed in the front groove 11, the inner and outer surfaces of the middle profile 20 are flush with the front profile 10. The front end of the rear profile 30 has a rear groove 31 that matches the rear connecting section 22, so that when the rear connecting section 22 is placed in the rear groove 31, the inner and outer surfaces of the middle profile 20 are flush with the rear profile 30. The front connecting section 21 and the front groove 11 are fixed by adhesive bonding and mechanical connection, and the rear connecting section 22 and the rear groove 31 are fixed by adhesive bonding and mechanical connection. The front profile 10 and the rear profile 30 are made of composite materials, while the inner layer of the middle profile 20 is made of metal and the outer layer is made of composite materials.

[0036] Further optimization is achieved by including a web 41, an upper panel 42, and a lower panel 43 in the front section profile 10, the middle section profile 20, and the rear section profile 30. The webs of the three sections are flush. The upper and lower panels of the front section profile 10 are parallel, the upper and lower panels of the rear section profile 30 are parallel, and the upper and lower panels of the middle section profile 20 are not parallel.

[0037] Further optimization involves selecting areas where stress is not prominent for the front-end connecting section 21 and the rear-end connecting section 22. The lengths of the front-end connecting section 21 and the rear-end connecting section 22 are no less than 50mm.

[0038] Further optimization involves manufacturing the front profile 10 and the rear profile 30 in two steps: an outer layer and an inner layer. The outer layer is formed first, followed by the inner layer. The outer layer is formed using a pultrusion process, while the inner layer is formed using a vacuum injection process. During the inner layer forming process, no reinforcing material is applied to the areas of the front groove 11 and the rear groove 31.

[0039] Further optimization involves using a pultrusion molding process for the outer layers of the front profile 10 and the rear profile 30. The reinforcing material formed by pultrusion is one or more of the following: carbon fiber filaments, aramid fiber filaments, glass fiber filaments, quartz fiber filaments, basalt fiber filaments, and polyimide fiber filaments. In this embodiment, large-tow carbon fiber filaments are used, which have high strength and low material cost. The resin is one of the following: epoxy resin, vinyl ester resin, polyurethane resin, polyester resin, and phenolic resin. In this example, epoxy resin is used, which has good strength, toughness, and processability. After the outer layer is cured and demolded, the inner surface is polished and finished. The inner layer is formed using a vacuum injection molding process. Reinforcing materials are sequentially laid on the inner surface of the outer layer before vacuum injection. The laying angle is designed according to the stress conditions, and the number of layers is determined by the fabric thickness. The reinforcing materials used in vacuum injection are one or more of carbon fiber fabric, aramid fabric, glass fiber fabric, quartz fiber fabric, basalt fiber fabric, and polyimide fiber fabric. In this embodiment, large-tow carbon fiber fabric is used, which has high strength and low material cost. The resin is one of epoxy resin, vinyl ester resin, polyurethane resin, polyester resin, and phenolic resin. In this example, epoxy resin is used, which has good strength, toughness, and processability.

[0040] Further optimization is achieved by including the metal inner layer of the middle section profile 20, which includes a front connecting section 21, a rear connecting section 22, and an intermediate section 23 between them. The entire metal inner layer is machined and formed. The thickness of the metal inner layer is the same as that of the inner layers of the front section profile 10 and the rear section profile 30. The metal can be one of steel, aluminum alloy, or titanium alloy. The composite material outer layer of the middle section profile 20 is formed by vacuum injection molding after reinforcing materials are sequentially laid on the outer surface of the middle section 23 of the metal inner layer. The thickness of the composite material outer layer is the same as the outer layer thickness of the front section profile 10 and the rear section profile 30. The vacuum-injected reinforcing material is one or more of carbon fiber fabric, aramid fabric, glass fiber fabric, quartz fiber fabric, basalt fiber fabric, and polyimide fiber fabric. In this embodiment, large-tow carbon fiber fabric is used, which has high strength and low material cost. The resin is one of epoxy resin, vinyl ester resin, polyurethane resin, polyester resin, and phenolic resin. In this example, epoxy resin is used, which has good strength, toughness and processability. No reinforcing material is laid on the front connecting section 21 and the rear connecting section 22.

[0041] After further optimization, the front, middle and rear profiles 30 are formed and can be assembled. The assembled frame has the same thickness in all areas and is consistent with the initial shape. The specific assembly method is as follows: first, structural adhesive is used to bond the overlapping areas. After the adhesive cures, holes are made in the bonding areas of the profile panels and webs, and fasteners (such as bolts) are used for connection.

[0042] In the embodiment provided by this invention, all surfaces of the frame have the same thickness of 20mm. The front and rear sections are C-shaped profiles with uniform cross-sections, while the middle section is a C-shaped profile with variable cross-sections. The front C-shaped profile is 150mm high and 2000mm long, while the rear C-shaped profile is 250mm high and 4000mm long. The front end of the middle section is 150mm high, and the rear end is 250mm high and 800mm long.

[0043] The upper and lower panels of the front and rear sections are parallel and perpendicular to the web, with a panel width of 80mm. The upper and lower panels of the middle section are not parallel, but are both perpendicular to the web, with a panel width of 80mm. The upper panels of the front, middle, and rear sections are continuous, and the lower panels form a three-section structure that slopes downward from front to back.

[0044] The composite frame is designed in three sections. The connection areas between the front, middle, and rear sections are selected in areas where stress does not change abruptly. Therefore, the middle section extends 100mm from the front and rear sections. The front section is reduced to 1900mm in length, 150mm in height, and 20mm in thickness, with a thickness of 14mm in the 100mm section near the middle section. The rear section is reduced to 3900mm in length, 250mm in height, and 20mm in thickness, with a thickness of 14mm in the 100mm section near the middle section.

[0045] The middle section is a variable cross-section C-shaped profile with a thickness of 20mm. It extends 100mm to the front and rear sections respectively, for a total length of 1000mm. To connect with the front and rear sections and improve the connection strength, it extends another 100mm to both ends, forming an overlap area with the front and rear sections. The thickness of the overlap area in the middle section is 6mm. After superimposing with the 14mm overlap area of ​​the front and rear sections, the total thickness is 20mm. The total length of the middle section is 1200mm.

[0046] The specific method for preparing the above-mentioned composite material frame variable cross-section profile is as follows:

[0047] The front section is manufactured in two steps: the outer layer and the inner layer. The outer layer is 1900mm long and 14mm thick, produced using a pultrusion molding process. During the outer layer fabrication, the panel width is widened to 110mm, and the panel is widened by 30mm to provide a bagging area and process edge for the second step of vacuum injection molding. The fibers used are large-tow carbon fiber tows, and the resin used is epoxy resin. After the carbon fiber tows are fully impregnated with resin, they are guided into a mold. The mold is a cavity mold with a C-shaped hollow structure. After initial heating and curing within the mold, it is shaped to 1900mm using a traction device. After the outer layer cures and is demolded, the inner surface is polished and finished. After finishing, large-tow carbon fiber biaxial fabric is sequentially laid on the inner surface at angles of 0° / 45° / 90° / -45°. The number of layers depends on the fabric thickness. The inner layer needs to be made with a width increased to 90mm, leaving a pre-cut edge for later use along with the outer layer. This ensures precise profile width. In this embodiment, the fabric layer thickness is 0.4mm, with 15 layers. No fabric is needed in the 100mm section near the middle. After laying the fabric, the innermost layer consists of a flow guide mesh and breathable felt, sealed with vacuum bags and sealing strips. The inner layer is formed using a vacuum injection process, with a thickness of 6mm and a length of 1800mm. After the front section is formed, the outer panel width is 110mm, and the inner panel width is 90mm. The profile is then cut to a uniform panel width of 80mm to complete the front section fabrication.

[0048] The manufacturing method for the rear section is the same as that for the front section, consisting of two steps. The outer layer of the rear section is 3900mm long and 14mm thick, manufactured using a pultrusion molding process. During the outer layer fabrication, the panel width is widened to 110mm. The fibers used are large-tow carbon fiber bundles, and the resin used is epoxy resin. After the outer layer cures and is demolded, the inner surface is sanded and finished. After finishing, large-tow carbon fiber biaxial fabric is sequentially laid on the inner surface at angles of 0° / 45° / 90° / -45°. The fabric layer thickness is 0.4mm, and there are 15 layers. The width of the inner layer needs to be increased to 90mm during fabrication, with no fabric laid in the 100mm length area near the middle section. The inner layer is formed using a vacuum infusion process, with a thickness of 6mm and a forming length of 3800mm. After the rear section is formed, the outer panel width is 110mm, and the inner panel width is 90mm. The profile is then cut to a uniform panel width of 80mm to complete the rear section fabrication.

[0049] The middle section employs a hybrid metal-composite structure design. The inner layer is metal, and the outer layer is composite material. The inner metal structure is 1200mm long and 6mm thick, machined from Q460 steel. During machining, the width of the C-profile panel is widened to 110mm. After the inner layer is machined, the outer surface is sanded with fine sandpaper and cleaned with acetone. After cleaning, large-tow carbon fiber biaxial fabric is sequentially laid on the outer surface at angles of 0° / 45° / 90° / -45°. The number of layers depends on the fabric thickness; in this embodiment, the fabric layer thickness is 0.4mm, and the number of layers is 35. No fabric is needed in the 100mm length area near both ends. After laying the fabric, the outermost layer is covered with a flow guide net and breathable felt, sealed with vacuum bags and sealing strips. The outer 14mm layer is formed using a vacuum injection process, with a forming length of 1000mm. After the middle section is formed, the panel width is 110mm. The profile is then cut to a panel width of 80mm to complete the production of the middle section.

[0050] After the front, middle and rear sections are processed, they are assembled. The 100mm overlap area between the front and middle sections is bonded with epoxy structural adhesive, and the 100mm overlap area between the middle and rear sections is bonded with structural adhesive.

[0051] After the structural adhesive has cured, at least two through holes are made along the length of the bonding area between the panel and the web, and M16 bolts are used for fastening.

[0052] In this invention, the front and rear sections are formed using a pultrusion molding process for the outer layer. The pultruded profile has fiber reinforcement in the 0-degree direction and a low resin content, effectively improving the profile's flexural strength while ensuring shear strength. The inner layer uses a vacuum infusion process, employing fabric as reinforcement. The fabric is laid at different angles to increase fiber reinforcement in the 90° and ±45° directions, ensuring the profile's shear strength. This two-step process requires only one pultrusion mold, resulting in low mold cost and a short processing cycle, thus reducing the profile manufacturing cycle. Furthermore, pultrusion molding is highly efficient. Because the front and rear sections use large-tow carbon fiber, the raw material cost can be reduced by more than 30% compared to small-tow carbon fiber of the same grade. Using the pultrusion process further reduces mold cost compared to vacuum infusion, OOA, autoclave, and compression molding processes, while increasing molding efficiency by more than 10%. Overall, the total cost can be reduced by more than 30%.

[0053] The middle section has a variable cross-section, and the abrupt change in shape makes stress concentration easy. Furthermore, as the structure connecting the front and rear sections, the stress distribution is complex. If a pure composite material structure is used for connection, the composite material's shear resistance is weak, making it prone to shear failure. However, using a hybrid structure of metal and composite materials can effectively disperse stress, improve the overall shear resistance of the structure, and enhance the connection strength. In this hybrid structure, the metal layer can be directly used as a mold for the composite material layer, further reducing mold costs and time.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A composite material vehicle frame variable cross-section profile, characterized in that, The profile includes a front section, a middle section and a rear section, the front section and the rear section are constant cross-section, the middle section is variable cross-section, the height of the front section is different from that of the rear section, the front end of the middle section is the same height as the front section, and the rear end of the middle section is the same height as the rear section; the front end of the inner layer of the middle section extends forward to form a front end connecting section, and the rear end of the inner layer extends backward to form a rear end connecting section, the rear end of the front section is provided with a front section groove matched with the front end connecting section, so that when the front end connecting section is placed in the front section groove, the inner and outer surfaces of the middle section and the front section are flush, and the front end of the rear section is provided with a rear section groove matched with the rear end connecting section, so that when the rear end connecting section is placed in the rear section groove, the inner and outer surfaces of the middle section and the rear section are flush; the front end connecting section and the front section groove are fixed by adhesion and mechanical connection, and the rear end connecting section and the rear section groove are fixed by adhesion and mechanical connection; the front section and the rear section are made of composite material, and the inner layer of the middle section is made of metal material and the outer layer is made of composite material.

2. The composite material frame variable cross-section profile according to claim 1, characterized in that, The front section, the middle section and the rear section all include a web, an upper panel and a lower panel, the webs of the three sections are flush, the upper panel and the lower panel of the front section are parallel, the upper panel and the lower panel of the rear section are parallel, and the upper panel and the lower panel of the middle section are not parallel.

3. The composite material frame variable cross-section profile according to claim 1, characterized in that, The length of the front end connecting section and the rear end connecting section is not less than 50mm.

4. The composite material frame variable cross-section profile according to claim 1, characterized in that, The front section and the rear section are respectively made of two layers of outer layer and inner layer, the outer layer is formed first, and then the inner layer is formed; the outer layer is formed by pultrusion process, and the inner layer is formed by vacuum infusion process, and the areas of the front section groove and the rear section groove are not covered with reinforcing material when the inner layer is formed.

5. The composite material frame variable cross-section profile according to claim 4, characterized in that, The outer layer of the front section and the rear section is formed by pultrusion process, the reinforcing material of the pultrusion is one or more of carbon fiber wire, aramid fiber wire, glass fiber wire, quartz fiber wire, basalt fiber wire and polyimide fiber wire, and the resin is one of epoxy resin, vinyl resin, polyurethane resin, polyester resin and phenolic resin; after the outer layer is cured and demolded, the inner surface is polished and trimmed, the inner layer is formed by vacuum infusion process, the reinforcing material is one or more of carbon fiber fabric, aramid fabric, glass fiber fabric, quartz fiber fabric, basalt fiber fabric and polyimide fiber fabric, and the resin is one of epoxy resin, vinyl resin, polyurethane resin, polyester resin and phenolic resin.

6. The composite material frame variable cross-section profile according to claim 4, characterized in that, The metal inner layer of the middle section profile includes a front end connecting section, a rear end connecting section and an intermediate section between the two, and the metal inner layer is integrally formed by machining; the composite outer layer of the middle section profile is formed by vacuum infusion after the reinforcing material is sequentially laid on the outer surface of the intermediate section of the metal inner layer; the reinforcing material for vacuum infusion is one or more of carbon fiber fabric, aramid fabric, glass fiber fabric, quartz fiber fabric, basalt fiber fabric and polyimide fabric; the resin is one of epoxy resin, vinyl resin, polyurethane resin, polyester resin and phenolic resin; the front end connecting section and the rear end connecting section are not laid with reinforcing material.

7. The composite material frame variable cross-section profile according to claim 6, characterized in that, The thickness of the metal inner layer of the middle section profile is the same as the thickness of the inner layer of the front section profile and the rear section profile, and the thickness of the composite outer layer of the middle section profile is the same as the thickness of the outer layer of the front section profile and the rear section profile.

8. The composite material frame variable cross-section profile of claim 1, wherein, The front end connecting section and the rear end connecting section are selected from a region where stress is not prominent.

9. The preparation method of the composite material frame variable cross-section profile according to any one of claims 1-8, characterized in that, The front section profile and the rear section profile are both made in two steps: in the first step, the outer layer is made by using a pultrusion process: after the reinforcing material is fully impregnated with resin, it is introduced into a mold through a guide device, the mold is a cavity mold with a hollow structure, the shape of the hollow structure is matched with the front section profile or the rear section profile, after preliminary heating and curing in the mold, it is formed to the designed length by a traction device; after the outer layer is cured and demolded, the inner surface is polished and finished; in the second step, the inner layer is made by using a vacuum infusion process: after finishing, the reinforcing material is sequentially laid on the inner surface of the outer layer, the front section groove and the rear section groove are not laid with reinforcing material, after laying, the innermost layer is laid with a flow guide net and a breathable felt, sealed with a vacuum bag and a sealing rubber strip, and the inner layer is formed by using a vacuum infusion process; The middle section profile is made in two steps: in the first step, the metal inner layer is machined; after the machining of the metal inner layer is completed, the outer surface is polished and cleaned; in the second step, the composite outer layer is made by using a vacuum infusion process: the reinforcing material is sequentially laid on the outer surface of the intermediate section of the metal inner layer, the front end connecting section and the rear end connecting section are not laid with reinforcing material, after laying, the outermost layer is laid with a flow guide net and a breathable felt, sealed with a vacuum bag and a sealing rubber strip, and the outer layer is formed by using a vacuum infusion process; After the front section profile, the rear section profile and the middle section profile are all made, the front end connecting section and the rear end connecting section of the middle section profile are respectively placed in the front section groove of the front section profile and the rear section groove of the rear section profile, and the overlapping area is bonded with structural adhesive; After the structural adhesive is cured, at least two through holes are opened in the bonding area of the panel and the web along the length direction, and a connecting piece is used for fastening connection.

10. The method of claim 9, wherein the method further comprises the step of: When the front section profile, the rear section profile and the middle section profile are made, the width of the panel is widened, and after being made, it is cut to the designed width.

Images