A composite product containing a hollow channel and a method of forming the same, a mold

Abstract

The present application relates to the technical field of composite materials, and particularly relates to a composite material product containing a hollow channel, a forming method thereof and a mold. The forming method is to reserve the position of the hollow channel through an occupying strip in a layering process, then to solidify the layer containing the occupying strip through mold forming or autoclave process, and then to pull out the occupying strip from the formed product. The occupying strip material has the characteristics of high creep rate, high strength and low friction coefficient, so that it deforms or displaces itself when pulled out, and then the interface debonding with the composite material is realized to form a hollow channel in the product. Compared with the existing technology of forming through pre-embedded pipeline, the influence of the thermal expansion coefficients of different materials is avoided, the composite product rejection rate is reduced, the process steps are reduced, and the production efficiency of the product is improved. The composite material product containing a hollow channel has no pre-embedded pipeline. The forming mold can form the composite material product containing a hollow channel without pre-embedded pipeline.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, and in particular to a composite material product containing hollow channels and a forming method and mold thereof. BACKGROUND

[0002] In terms of composite product design: while the Mach number of today's aerospace vehicles is constantly increasing, the requirement for weight reduction of the vehicle body is becoming increasingly stringent. Based on the functional and structural synergy requirements of future aerospace equipment, under the premise of meeting the use requirements of composite products, space optimization, strength and stiffness calculation are performed on the composite products, and multi-function is integrated into the load-bearing structure, which helps to achieve the weight reduction requirement of the aircraft and improve the power-to-mass ratio (functional density / mass) of the aerospace equipment.

[0003] In terms of composite product manufacturing process: by embedding functional components into the interior of the composite structure, the composite product structure-function integration can be achieved, the assembly steps of multiple independent components can be omitted, and the reliability of the composite product can be improved while the production cycle of the composite product is greatly shortened.

[0004] Traditional composite material products containing hollow channels are formed by pre-embedding composite pipes or metal pipes in the layering process, and then pre-embedding pipes and newly laid pre-preg are integrally formed by co-curing. Due to the difference in thermal expansion coefficient of different materials in the process of co-curing and pressurized heating, the pre-embedded pipe profile and the pre-preg cannot be effectively fitted, and then the composite product will have defects such as delamination and bridging. In addition, the pre-embedded pipes also need positioning equipment to assist positioning and fixing, laying of adhesive layers and other pretreatment work, and the process steps are complex.

[0005] At present, some hollow channel forming methods in the prior art are difficult to meet the requirements of composite material products containing hollow channels without pre-embedded pipelines in the field of aviation. For example, a Chinese patent application with the publication number CN116330702A and the title of "Preparation method of composite material hollow bracket integrated forming" discloses a preparation method of composite material hollow bracket integrated forming. A core mold is formed by taking a core mold rod as the backbone and a rubber layer as the skin covering the outer periphery of the metal rod of the core mold rod. The overall shape of the core mold is consistent with the shape of the composite material hollow bracket to be prepared. A bracket skin is laid on the surface of the core mold to form a preform. The preform is placed in the internal cavity of the mold, sent into the forming equipment for curing and forming, and then the mold is removed. Then the metal rod constituting the core mold rod is disassembled and separated from the rubber layer. Finally, the rubber layer in the channel is removed to obtain the hollow composite material bracket. This belongs to the rubber mold expansion forming method. The core mold is made by covering a rubber layer on a straight rod metal rod with the same diameter. The overall shape of the core mold is consistent with the shape of the composite material hollow bracket to be prepared. Then the composite material layer is laid on the surface of the core mold. In the process of temperature rising and curing, the rubber is expanded by heating to apply pressure to the composite material layer. Due to the unevenness of the pressure applied by the rubber expansion, the flatness and roughness of the inner surface of the product cannot be controlled. In addition, the rubber core mold is too thin to provide sufficient pressure to the composite material layer during the heating process, which may cause defects such as looseness and voids in the formed product. Moreover, the rubber has relatively high friction, and it is relatively difficult to pull out, especially for larger products.

[0006] For another example, a Chinese patent application with the publication number CN114603878A and the title of "Forming method of composite material part with hollow structure" discloses a forming method of a composite material part with hollow structure. The method includes the following process steps: S1, placing a carbon fiber layer (2) into a mold (3); S2, placing a blowing bag (1) into the carbon fiber layer (2); S3, closing the mold (3) and using a press to warm and pressurize the upper and lower surfaces of the mold (3); S4, injecting heat-conducting oil (4) into the blowing bag (1); S5, taking the product out of the mold (3); S6, removing the blowing bag (1) inside the product; and S7, polishing, painting and polishing the product. The inner surface of the product formed by this air mold is also difficult to control in terms of flatness and roughness, and the method cannot be used to form thin-walled structure products. SUMMARY

[0007] The first object of the present application is to provide a forming method of a composite material product containing a hollow channel, which simplifies the process without pre-embedding pipelines to form the composite material product containing a hollow channel.

[0008] The second object of the present application is to provide a composite material product containing a hollow channel, which is lighter in quality without pre-embedding pipelines.

[0009] A third object of the present application is to provide a molding die for a hollow channel-containing composite product, for realizing molding of a hollow channel-containing composite product without pre-embedded pipes.

[0010] To achieve the above object, in a first aspect, the present application provides a molding method for a hollow channel-containing composite product, comprising the following steps:

[0011] S1: In the composite material layering process, a placeholder strip is arranged at the position of the reserved hollow channel, the cross-sectional shape of the placeholder strip being the same as the cross-sectional shape of the hollow channel;

[0012] S2: The layer containing the placeholder strip is cured by die molding or autoclave process;

[0013] S3: After curing is completed, the placeholder strip is removed by pulling out to form a hollow channel;

[0014] Wherein, the material of the placeholder strip satisfies the following properties:

[0015] (a) The melting point is greater than the curing temperature of the composite product to be molded;

[0016] (b) The tensile strength is ≥25MPa;

[0017] (c) 0.3GPa≤elastic modulus≤1GPa;

[0018] (d) 1%≤creep rate≤8%(20℃, 20MPa, 1000h);

[0019] (e) 0.04≤friction coefficient≤0.2.

[0020] Optionally, the material of the placeholder strip is polytetrafluoroethylene.

[0021] Optionally, in the layering process of step S1, a layer group type layering is adopted, and the steps are as follows:

[0022] According to the layering angle of the composite product design, multiple layers of prepreg are combined into a layer group, and each layer group is ironed flat by an electric iron to ensure that there is no air gap or bubble between the layers of prepreg;

[0023] After each layer group is laid, it is compacted to ensure that there is no air gap or bubble between the layer groups.

[0024] Optionally, in the layering process of step S1, before laying the placeholder strip and the layer group where the placeholder strip is located, the laid layer group and the female die of the mold are integrally placed in a vacuum bag, pre-compacted at a set temperature and time, and after pre-compaction, the vacuum bag is removed after cooling to room temperature, and subsequent layering is performed.

[0025] Optionally, in step S1:

[0026] the surface of the placeholder strip is coated with a release agent; and / or

[0027] the placeholder strip has at least one end extending outside the composite material layer.

[0028] Optionally, the pulling mode comprises applying a pulling force along the pulling direction, the pulling speed is 5-20 mm / min, and the temperature during pulling is controlled at 40-60℃.

[0029] In a second aspect, the present application further provides a composite material product containing hollow channels, which is prepared by the molding method of any implementation form of the first aspect.

[0030] Optionally in the second aspect, the hollow channels are used for fluid transmission, mechanical bearing, noise reduction, shock absorption or functional element installation; and / or

[0031] the surface roughness of the inner wall of the hollow channel is 0.2 μm≤Ra≤1.6 μm.

[0032] In a third aspect, the present application further provides a molding mold for a composite material product containing hollow channels, which comprises a male mold, a female mold and a number of placeholder strips equal to the number of hollow channels, wherein the material of the placeholder strip satisfies the following properties:

[0033] (a) the melting point is greater than the curing temperature of the composite material product to be molded;

[0034] (b) the tensile strength is ≥25 MPa;

[0035] (c) 0.3 GPa≤elastic modulus≤1 GPa;

[0036] (d) 1%≤creep rate≤8%(20℃, 20 MPa, 1000 h);

[0037] (e) 0.04≤friction coefficient≤0.2.

[0038] Optionally in the third aspect, the material of the placeholder strip is polytetrafluoroethylene.

[0039] The above technical solutions of the present application have the following advantages:

[0040] The application provides a forming method of a composite product containing a hollow channel, which is characterized by the following steps: in a layering process, a position of a reserved hollow channel is occupied by an occupying strip; then, the layering containing the occupying strip is cured by a mold pressing forming or a hot pressing tank process; and finally, the occupying strip is pulled out from the formed product. The occupying strip material has high creep rate and high strength characteristics, so that the occupying strip material is deformed or displaced when being pulled out, and then the interface between the occupying strip and the composite material is debonded, so that the hollow channel is formed in the composite product. Compared with the prior art, the method avoids the influence of different thermal expansion coefficients of different materials, and reduces the scrap rate of the composite product. Meanwhile, the occupying strip is used to occupy the hollow channel, so that the process steps are reduced and the production efficiency of the product is improved.

[0041] The composite product containing the hollow channel provided by the application has no pre-embedded pipeline, the quality of the whole and the hollow pipeline is controllable, the influence of different thermal expansion coefficients of different materials is avoided, the scrap rate of the composite product is reduced, and the weight is reduced. The hollow channel can be used for fluid transmission, mechanical bearing, noise reduction, shock absorption, fault tolerance, damage repair or functional element installation.

[0042] The embodiment also provides a forming mold of a composite product containing a hollow channel, which comprises a male mold, a female mold and occupying strips same in number as the hollow channels. The occupying strip material has high creep rate and high strength characteristics, so that the occupying strip material is deformed or displaced when being pulled out, and then the interface between the occupying strip and the composite material is debonded, so that the composite product containing the hollow channel without the pre-embedded pipeline can be formed. BRIEF DESCRIPTION OF DRAWINGS

[0043] The drawings of the application are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not be consistent with the actual product.

[0044] Figure 1 is a structural schematic diagram of a composite product containing a hollow channel in the embodiment of the application;

[0045] Figure 2 is Figure 1 a structural schematic diagram of a composite product containing a hollow channel after layering and mold closing;

[0046] Figure 3 is Figure 2 a cross-sectional schematic diagram of the structure of the composite product containing the hollow channel after layering and mold closing.

[0047] In the drawings:

[0048] 1: composite product;

[0049] 11: hollow channel;

[0050] 12: inner skin layer;

[0051] 13: solid ply;

[0052] 14: outer skin ply;

[0053] 2: mold;

[0054] 21: female mold;

[0055] 22: male mold;

[0056] 23: placeholder strip. DETAILED DESCRIPTION

[0057] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0058] The forming method of the composite product containing a hollow channel provided by the embodiments of the present application is that the position of the reserved hollow channel is occupied by a placeholder strip in a laying process, then the laying containing the placeholder strip is cured by mold pressing or autoclave process, and finally the placeholder strip is pulled out from the formed product. The placeholder strip is deformed or displaced by itself during pulling out due to its characteristics of high creep rate, high strength and low friction coefficient, and then the interface between the placeholder strip and the composite material is debonded, so as to form a hollow channel in the composite product. The relatively low stiffness of the material can not only be suitable for the case that the hollow channel has a certain curvature, but also make it easier to pull out the placeholder strip. During the pulling process, the placeholder strip can be directly displaced due to its considerable strength and low friction coefficient, and the requirement for the strength of the material is reduced. If the displacement does not occur or stops after a certain displacement, the placeholder strip is deformed by creep in the case of continuous pulling, so as to ensure that the placeholder strip can be debonded from the product and pulled out. The appropriate strength and stiffness can not only meet the support requirements of the placeholder, but also make the placeholder strip easier to be pulled out by creep deformation.

[0059] In order to meet the requirements of the placeholder support and pulling of the placeholder strip, the material of the placeholder strip meets the following performances: the melting point is higher than the curing temperature of the composite product, the placeholder strip cannot be broken during the pulling process, the stiffness can be suitable for the case that the hollow channel has a certain curvature, has a certain creep rate and a low friction coefficient, is beneficial to debonding from the hollow channel when the placeholder strip is deformed under stress, so as to make the placeholder strip easier to be pulled out and the hollow channel has a smaller surface roughness during the pulling process, and also meets the requirements of easy fixing of the relative position between the support and the laying and easy fixing of the relative position between the placeholder strip and the laying.

[0060] In an example, the material of the placeholder strip used satisfies the following properties:

[0061] (a) Melting point ≥ 200℃, for example, the solidification temperature of the composite product to be formed is 180℃, and the melting point of the placeholder strip material is 200℃, 250℃, 300℃, etc.

[0062] (b) Tensile strength ≥ 25MPa, for example, 25MPa, 28MPa, 32MPa, 40MPa, etc.

[0063] (c) 0.3GPa ≤ Elastic modulus ≤ 1GPa, for example, 0.5GPa, 0.6GPa, 0.65GPa, 0.8GPa, 0.9GPa, etc.

[0064] (d) 1% ≤ Creep rate ≤ 8% (20℃, 20MPa, 1000h), for example, 2%, 3%, 5%, 6%, etc.

[0065] (e) 0.04 ≤ Friction coefficient ≤ 0.2, for example, 0.06, 0.08, 0.1, 0.15, etc.

[0066] Compared with the pre-embedded pipeline in the prior art, the influence of the different thermal expansion coefficients of different materials is avoided, and the scrap rate of the composite product is reduced. At the same time, the placeholder strip is used to occupy the channel, which reduces the process steps compared with the pre-embedded pipeline forming scheme and improves the production efficiency of the product.

[0067] It is worth noting that the cross-sectional shape of the hollow channel is designed as needed, which can be but is not limited to being designed as including a circular shape, an elliptical shape, a rectangular shape, and other polygonal shapes, etc.

[0068] In an example, the hollow channel serves as an oil supply channel, and the cross-sectional shape thereof is set as a rectangular shape. In a product with limited thickness (a thin-walled product), the rectangular cross-sectional shape has a better heat dissipation effect compared with a circular cross-sectional shape.

[0069] It is worth noting that in the present embodiment, the lay-up process and mold required for forming can be realized by matching the placeholder strip of the present application with the existing technology, and therefore, the lay-up process and mold required for forming are not limited in the present embodiment. The compression molding process and autoclave process can use the existing technology.

[0070] In an example, the material of the placeholder strip uses polytetrafluoroethylene that can satisfy the properties of the placeholder strip material.

[0071] In an example, the pulling method includes applying a pulling force in the pulling direction, the pulling speed is 5-20 mm / min, and the temperature during pulling is controlled at 40-60°C. The pulling force can be provided by a pulling device or by manpower, which is not limited herein. Preferably, the pulling is performed in a manner that can stably and continuously provide the pulling force.

[0072] During pulling, preferably, the pulling sequence is performed in the order of every other placeholder strip.

[0073] In an example, the product is laid in a layer group manner in the laying procedure, and the steps are as follows:

[0074] According to the laying angle of the composite product design, the multiple layers of prepreg are combined into one layer group, and each layer group is ironed by an electric iron to ensure that there is no empty space or bubble between the layers of prepreg.

[0075] After each layer group is laid, it is rolled and compacted to ensure that there is no empty space or bubble between the layer groups.

[0076] In an example, before the placeholder strip and the layer group where the placeholder strip is located are laid, the laid layer group and the female mold of the mold are integrally placed in a vacuum bag for vacuumizing, pre-compacted at a set temperature and time, and after pre-compaction, the vacuum bag is removed after cooling to room temperature, and subsequent laying is performed.

[0077] Of course, in order to facilitate better implementation of the pulling of the placeholder strip, in the present embodiment, the surface of the placeholder strip is coated with a release agent. The type of release agent is not limited, as long as it meets the process requirements.

[0078] In order to facilitate the pulling operation of the placeholder strip, in the present embodiment, preferably, the placeholder strip has at least one end extending outside the composite material laying. Of course, in some examples, the length of the placeholder strip can be set to be equivalent to the length of the hollow channel, and the pulling is performed by inserting into the inside of the placeholder and fixing.

[0079] The forming process is further described below through a specific embodiment:

[0080] Referring to Figure 1 , the composite product 1 to be formed includes an integrated hollow channel 11, which is laid by carbon fiber / epoxy prepreg. Before forming, the following steps are performed:

[0081] Mold cleaning: remove the excess material on the surface of each part of the mold, make the surface smooth, no oil stains, no impurities, no glue particle protrusions, if necessary, polish with metallographic sandpaper, and then wipe clean with cotton dipped in 120# gasoline, dry, then wipe the mold working surface with cotton dipped in acetone, and after the acetone is dry, coat the release agent on the surface of the forming tool.

[0082] Cutting: according to the designed ply angle of the composite product 1, the prepreg is laminated, generally 2-4 layers of prepreg are a layer group, and the laminated layer group is ironed flat with an electric iron to ensure that there is no air gap or bubble between the layers of prepreg. The laminated layer group is accurately cut according to the size of the cutting template by a cutting machine.

[0083] Ply the inner skin of the composite product: as shown in Figure 2 and Figure 3 , ply the inner skin ply 12 on the female die 21 of the mold 2, and use a tool to roll and compact after each layer group is pasted to ensure that there is no air gap or bubble between the layer groups.

[0084] Pre-compaction: after the inner skin ply 12 is completed, the inner skin ply 12 and the female die 21 are collectively bagged for vacuum pre-pressing. When the vacuum bag is sealed, a non-porous film, air-permeable felt, and a vacuum bag are sequentially wrapped around the preform. After sealing, the vacuum degree should be no less than 95 Kpa. After vacuum compression, pre-compaction is performed in an oven set at 70°C for 1 hour while continuously vacuuming. After pre-compaction, wait for it to cool to room temperature, remove the vacuum bag, and proceed with the subsequent plies.

[0085] Lay the spacer strip and ply the solid area ply (the composite solid area on both sides of the hollow channel): after each layer group of the solid area ply 13 is pasted, use a tool to roll and compact to ensure that there is no air gap or bubble between the layers. The position of the spacer strip 23 is positioned by the position mark on the female die 21. Before laying the spacer strip 23, apply a layer of release agent to the surface of the spacer strip 23 and let it dry.

[0086] Ply the outer skin ply of the composite product: after laying the spacer strip 23 and the solid area ply 13, ply the outer skin ply 14. After each layer group is pasted, use a tool to roll and compact to ensure that there is no air gap or bubble between the layers.

[0087] Mold closing: close the male die 22 with the female die 21 with the completed plies.

[0088] Curing: after the mold 2 is closed, it is hoisted onto the press, and the composite ply group in the mold 2 is heated and pressurized according to the curing program. After the press is pressurized, the mold gap is less than 0.1 mm.

[0089] Pull out the spacer strip: when the mold temperature drops to 40-60°C, use a clamp to clamp the spacer strip 23 and pull it out. When pulling out, a single person should steadily and continuously exert force until the spacer strip 23 is completely pulled out. The spacer strip 23 is pulled out in intervals, for example, the first, third, and fifth spacer strips 23 are pulled out from left to right, and then the second and fourth spacer strips 23 are pulled out.

[0090] Trimming: After the mold is opened, the flash and burr on the surface of the composite product are trimmed, the residual glue on the inner and outer surfaces is cleaned, the residual dust is blown away with high-pressure gas, and the inner and outer surfaces of the composite product are wiped clean with cotton dipped in acetone.

[0091] In this embodiment, the placeholder strip made of polytetrafluoroethylene has a melting point of 310°C, a tensile strength of 25 MPa, an elastic modulus of 0.6 GPa, a creep rate of 8%, and a friction coefficient of 0.2. The temperature is controlled between 40-60°C during pulling, and the pulling speed is 8 mm / min. The weight of the composite product 1 without embedded pipeline is reduced by 0.5-0.7% compared to the same product with embedded pipeline (resin-based composite material). The surface roughness Ra of the hollow channel is 0.8-1.6, and the production cycle of one product is shortened by 10-15 hours. The quality of the product as a whole and the hollow pipeline is controllable, avoiding the influence of different materials with different thermal expansion coefficients, and reducing the scrap rate of composite products. At the same time, using the placeholder strip to occupy the channel reduces the process steps compared to the molding scheme of embedded pipeline, and improves the production efficiency of the product.

[0092] In other embodiments, for example, the composite product uses carbon fiber / bismaleimide resin prepreg or carbon fiber / polyimide resin prepreg for lamination, and the above-mentioned polytetrafluoroethylene placeholder strip can also be used for placeholder.

[0093] During the development process, the applicant tried different materials when selecting materials, as shown in the following table:

[0094]

[0095] The test results and reason analysis of each material are as follows:

[0096]

[0097] In this embodiment, the composite product with a hollow channel can be a warehouse body, a wing, or other components of an aircraft (such as a drone or a spacecraft), without limitation.

[0098] According to different product uses, the hollow channel is used for fluid transmission (oil, gas, water transmission), mechanical bearing, noise reduction, shock absorption, or functional element installation (installation of sensors, optical fiber elements, etc.).

[0099] Referring to FIGS. 1 and 2, Figure 2 and Figure 3 The embodiment also provides a molding mold 2 of a composite product with a hollow channel, which comprises a female mold 21, a male mold 22, and a number of placeholder strips 23 equal to the number of hollow channels, wherein the material of the placeholder strip 23 satisfies the following properties:

[0100] (a) melting point ≥ 200 °C, for example, the solidification temperature of the composite product to be formed is 180 °C, the melting point of the space-occupying strip material is 200 °C, 250 °C, 300 °C, etc.;

[0101] (b) tensile strength ≥ 25 MPa, for example, 25 MPa, 28 MPa, 32 MPa, 40 MPa, etc.;

[0102] (c) 0.3 GPa ≤ elastic modulus ≤ 1 GPa, for example, 0.5 GPa, 0.6 GPa, 0.65 GPa, 0.8 GPa, 0.9 GPa, etc.;

[0103] (d) 1% ≤ creep rate ≤ 8% (20 °C, 20 MPa, 1000 h), for example, 2%, 3%, 5%, 6%, etc.;

[0104] (e) 0.04 ≤ friction coefficient ≤ 0.2, for example, 0.06, 0.08, 0.1, 0.15, etc.

[0105] In an example, the material of the space-occupying strip 23 adopts polytetrafluoroethylene which can meet the performance of the space-occupying strip material.

[0106] The mold 2 can be used for the above-mentioned forming process and for forming a composite product containing a hollow channel.

[0107] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: not every example contains only one independent technical solution, in the absence of scheme conflict, the technical features mentioned in each example can be combined in any way to form other embodiments that can be understood by those skilled in the art.

[0108] In addition, without departing from the scope of the present application, the technical solutions described in the foregoing examples are modified, or some of the technical features are replaced, without changing the essence of the corresponding technical solutions out of the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of forming a composite product containing hollow channels, characterized by, The method comprises the following steps: S1: In the composite layering process, a placeholder strip is arranged at the position of the reserved hollow channel, the cross-sectional shape of the placeholder strip is the same as that of the hollow channel; S2: The layering containing the placeholder strip is cured by mold forming or autoclave process; S3: After curing is completed, the placeholder strip is removed by pulling to form a hollow channel; The material of the placeholder strip is polytetrafluoroethylene and meets the following properties: (a) The melting point is greater than the curing temperature of the to-be-formed composite product; (b) The tensile strength is ≥25 MPa; (c) 0.3 GPa≤elastic modulus≤1 GPa; (d) The creep rate is 8% (20℃, 20 MPa, 1000h); (e) 0.04≤friction coefficient≤0.2; In the layering process of step S1, a layer group type layering is adopted, and the steps are as follows: According to the layering angle of the composite product design, a plurality of layers of prepreg are combined into a layer group, and each layer group is ironed by an electric iron to ensure that there is no air gap or bubble between the layers of prepreg; After each layer group is laid, it is compacted to ensure that there is no air gap or bubble between the layer groups; In the layering process of step S1, before the placeholder strip is laid and the layer group where the placeholder strip is located, the laid layer group and the female mold of the mold are put into a vacuum bag for vacuumizing, and pre-compaction is performed according to the set temperature and time. After pre-compaction, the vacuum bag is removed after cooling to room temperature, and subsequent layering is performed.

2. The forming method according to claim 1, wherein: In step S1: The surface of the placeholder strip is coated with a release agent; and / or The placeholder strip has at least one end extending outside the composite layering.

3. The molding method according to claim 1, characterized by: The pulling method includes applying tension in the pulling direction, and the pulling speed is 5-20 mm / min, and the temperature during pulling is controlled at 40-60℃.

4. A composite product comprising a hollow channel, characterized by: Prepared by any one of claims 1-3.

5. The composite product containing a hollow channel according to claim 4, wherein: The hollow channel is used for fluid transmission, mechanical bearing, noise reduction, shock absorption or functional element installation; and / or The surface roughness of the inner wall of the hollow channel is 0.2μm≤Ra≤1.6μm.

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