Composite material product containing hollow channel and forming method and mold of composite material product

Abstract

The invention relates to the technical field of composite materials, in particular to a composite material product containing a hollow channel and a forming method and mold of the composite material product. The forming method comprises the following steps of: occupying the position of the reserved hollow channel through the occupying strip in a layering process, curing the layering containing the occupying strip through a compression molding or autoclave process, and pulling out the occupying strip from a formed product. By utilizing the characteristics of high creep rate, high strength and low friction coefficient of the placeholder strip material, the placeholder strip material deforms or displaces during pulling, so that the placeholder strip material is debonded with the interface of the composite material to form a hollow channel in the product. Compared with the prior art of forming through a pre-buried pipeline, the influence of thermal expansion coefficients of different materials is avoided, the rejection rate of composite material products is reduced, the procedure steps are reduced, and the production efficiency of the products is improved. The composite material product containing the hollow channel is not provided with an embedded pipeline. The forming mold can be used for forming a composite material product which is not provided with a pre-embedded pipeline and contains a hollow channel.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a composite material product containing a hollow channel and a molding method and a mold thereof. Background Art

[0002] In terms of composite product design: As the Mach number of today's aerospace vehicles continues to increase, the requirements for aircraft weight reduction are becoming more and more stringent. Based on the future functional and structural coordination requirements of aerospace equipment, on the premise of meeting the use requirements of composite products, space optimization, strength and stiffness calculations are performed, and multi-functions are integrated into the load-bearing structure, which helps to achieve the weight reduction requirements of aircraft and improve the power-to-weight ratio (functional density / mass) of aerospace equipment.

[0003] In terms of composite product manufacturing technology: by embedding functional components into the composite structure, the structure and function of the composite product are integrated, which can save the assembly steps of multiple independent components, improve the reliability of the composite product and greatly shorten the production cycle of the composite product.

[0004] Traditional hollow composite material products are formed by pre-embedded composite pipes or metal pipes in the layering process, and then the pre-embedded pipes and the newly laid prepreg are co-cured and formed into one. However, due to the different thermal expansion coefficients of different materials during the co-curing pressurization and heating process, the pre-embedded pipe surface and the prepreg cannot be effectively fitted, and the composite product will have defects such as delamination and bridging. In addition, the pre-embedded pipes also require positioning equipment to assist in positioning and fixing, laying adhesive layers and other pre-treatment work, and the process steps are complicated.

[0005] At present, some hollow channel forming methods in the prior art are difficult to meet the requirements of composite materials products with hollow channels without pre-buried pipelines in the aviation field. For example, the Chinese patent application with publication number CN116330702A, entitled Preparation method for integrally forming a composite hollow bracket, discloses a preparation method for integrally forming a composite hollow bracket, with a core mold rod as the backbone, and a rubber layer as the skin covering the outer periphery of the metal rod body of the core mold rod to form a forming core mold, and the overall shape of the forming core mold is consistent with the shape of the composite hollow bracket to be prepared; the bracket skin is laid on the surface of the forming core mold to form a preform; the preform is placed in the internal cavity of the mold, sent to the molding equipment for curing and molding, the mold is removed, and then the metal rods constituting the core mold rod are disassembled and extracted from the rubber layer, and finally the rubber layer in the channel is removed to obtain a hollow composite bracket. This belongs to the rubber mold expansion molding method. A core mold is made by coating a rubber layer on the outside of a straight metal rod of equal diameter. The overall shape of the molding core mold is consistent with the shape of the hollow bracket of the composite material to be prepared, and then the composite material is layered on the surface of the core mold. During the heating and curing process, the rubber is used to expand due to heat to apply pressure to the composite material layer. Due to the uneven pressure applied by the rubber expansion, the flatness and roughness of the specific surface of the product cannot be controlled. In addition, since the rubber core mold is too thin, it cannot provide enough pressure to the composite material layer during the heating process, which will cause defects such as looseness and gaps in the molded product. Moreover, the friction of rubber is relatively large, and extraction is relatively difficult, especially for larger products that are basically difficult to extract.

[0006] For another example, the Chinese patent application with publication number CN114603878A and titled "A Method for Forming a Composite Material Component with a Hollow Structure" discloses a method for forming a composite material component with a hollow structure, comprising the following process steps: S1, placing a carbon fiber layer (2) into a mold (3); S2, placing an air blowing bag (1) into the carbon fiber layer (2); S3, closing the mold (3), and using a press to heat and pressurize the upper and lower surfaces of the mold (3); S4, injecting heat transfer oil (4) into the air blowing bag (1); S5, taking the product out of the mold (3); S6, removing the air blowing bag (1) inside the product; S7, grinding, spraying paint, and polishing the product. The inner surface of the product formed by this air mold also cannot meet the flatness and roughness requirements and is difficult to control, and thin-walled structure products cannot be formed by this method. Summary of the invention

[0007] The first object of the present invention is to provide a method for molding a composite material product containing a hollow channel, which can realize the molding of the composite material product containing a hollow channel without pre-buried pipelines, thereby simplifying the process.

[0008] A second object of the present invention is to provide a composite material product containing hollow channels, which does not require pre-buried pipes and has a lighter product quality.

[0009] The third object of the present invention is to provide a molding die for a composite material product containing a hollow channel, which is used to realize the molding of a composite material product containing a hollow channel without pre-buried pipes.

[0010] In order to achieve the above object, in a first aspect, the present invention provides a method for forming a composite material product containing a hollow channel, comprising the following steps:

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

[0012] S2: curing the laminate with the placeholder strips by compression molding or autoclave process;

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

[0014] The material of the placeholder strip meets the following properties:

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

[0016] (b) Tensile strength ≥ 25 MPa;

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

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

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

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

[0021] Optionally, in the ply laying process of step S1, a layer-by-layer ply laying method is adopted, and the steps are as follows:

[0022] According to the designed ply angle of the composite product, multiple layers of prepreg are combined into one layer group, and each layer group is ironed flat to ensure that there are no gaps or bubbles between the layers of prepreg;

[0023] Compact each layer after laying to ensure there is no gap or air bubble between the layers.

[0024] Optionally, in the layer laying process in step S1, before laying out the placeholder strips and the layer group where the placeholder strips are located, the laid layer group and the female mold of the mold are placed in a vacuum bag as a whole to evacuate the vacuum, and pre-compacted according to the set temperature and time. After pre-compacting, the vacuum bag is removed after cooling to room temperature for subsequent layer laying.

[0025] Optionally, in step S1:

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

[0027] At least one end of the placeholder strip extends out of the composite material laminate.

[0028] Optionally, the extraction method includes applying a pulling force along the extraction direction, the extraction speed is 5-20 mm / min, and the temperature during extraction is controlled at 40-60°C.

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

[0030] Optionally in the second aspect, the hollow channel is used for fluid transmission, mechanical bearing, noise reduction, vibration reduction or functional element installation; and / or

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

[0032] In a third aspect, the present invention further provides a molding die for a composite material product containing hollow channels, comprising a male die, a female die, and placeholder strips having the same number as the hollow channels, wherein the material of the placeholder strips satisfies the following properties:

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

[0034] (b) Tensile strength ≥ 25 MPa;

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

[0036] (d) 1% ≤ creep rate ≤ 8% (20°C, 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 solution of the present invention has the following advantages:

[0040] The molding method of the composite material product containing a hollow channel provided by the present invention is to occupy the position of the reserved hollow channel with a placeholder strip in the plying process, then solidify the ply containing the placeholder strip by compression molding or autoclave process, and then extract the placeholder strip from the molded product. The high creep rate and high strength characteristics of the placeholder strip material are utilized to cause the placeholder strip itself to deform or displace when it is pulled out, thereby achieving debonding with the composite material interface, so as to form a hollow channel inside the composite material product. Compared with the prior art of pre-buried pipelines, the influence of different thermal expansion coefficients of different materials is avoided, and the scrap rate of composite material products is reduced. At the same time, the molding scheme of using placeholder strips to occupy the hollow channel reduces the process steps and improves the production efficiency of the product.

[0041] The composite material product with hollow channels provided by the present invention has no pre-buried pipelines, and the quality of the whole and the hollow pipeline is controllable, avoiding the influence of different thermal expansion coefficients of different materials, reducing the scrap rate of composite material products, and reducing weight. The hollow channel can be used for fluid transmission, mechanical bearing, noise reduction, shock absorption, fault tolerance, damage repair or functional component installation.

[0042] The present embodiment also provides a molding die for a composite material product containing hollow channels, comprising a male mold, a female mold, and placeholder strips having the same number as the hollow channels. The material of the placeholder strips has high creep rate and high strength properties, so that it deforms or displaces itself when pulled out, thereby achieving debonding from the composite material interface, and being able to mold composite material products containing hollow channels without pre-buried pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0045] Figure 2 yes Figure 1 Schematic diagram of the structure of a composite material product containing hollow channels after completion of layup and mold closing;

[0046] Figure 3 yes Figure 2 Schematic diagram of the cross-section of the structure of a composite product containing hollow channels after completion of layup and mold closing.

[0047] In the figure:

[0048] 1: Composite materials products;

[0049] 11: Hollow channel;

[0050] 12: Inner skin layer;

[0051] 13: Solid area ply;

[0052] 14: Outer skin layer;

[0053] 2: Mould;

[0054] 21: female mold;

[0055] 22: male mold;

[0056] 23: Placeholder bar. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] The molding method of the composite material product containing a hollow channel provided by the embodiment of the present invention is to occupy the position of the reserved hollow channel by a placeholder strip in the plying process, and then solidify the ply containing the placeholder strip by compression molding or autoclave process, and then extract the placeholder strip from the molded product. The high creep rate, high strength and low friction coefficient of the placeholder strip material are utilized to cause the placeholder strip to deform or displace itself during extraction, thereby achieving debonding with the composite material interface, so as to form a hollow channel inside the composite material product. The relatively low stiffness of the material is not only applicable to the case where the hollow channel has a certain curvature, but also makes it easier to extract the placeholder strip. During the extraction process, due to its considerable strength and low friction coefficient, the placeholder strip may directly displace and reduce the requirements for material strength. If the displacement cannot occur or stops moving after a certain displacement, the placeholder strip will creep deform under the condition of continuous extraction, ensuring that the placeholder strip can be debonded from the product and extracted. Appropriate strength and stiffness can meet the support requirements of the placeholder, and at the same time, the placeholder strip is easier to extract with creep deformation.

[0059] In order to meet the requirements of placeholder support and extraction, the material of the placeholder strip must meet the following properties: the melting point is greater than the curing temperature of the composite product, the placeholder strip cannot break during the extraction process, the stiffness must be suitable for the situation where the hollow channel has a certain curvature, it must have a certain creep rate and a low friction coefficient, and it is conducive to debonding from the hollow channel when the placeholder strip is deformed under force, so that the placeholder strip is easier to pull out during the extraction process and the hollow channel has a smaller surface roughness. At the same time, it must also meet the requirements of support and easy fixation of the relative position between the placeholder strip and the ply.

[0060] In one example, the material of the placeholder strip used meets the following properties:

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

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

[0063] (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.;

[0064] (d) 1% ≤ creep rate ≤ 8% (20°C, 20 MPa, 1000 h), 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 prior art of pre-buried pipelines, the influence of different thermal expansion coefficients of different materials is avoided, and the scrap rate of composite materials products is reduced. At the same time, the molding scheme of the pre-buried pipelines using placeholder strips to occupy the channel reduces the process steps and improves the production efficiency of the product.

[0067] It is worth noting that the cross-sectional shape of the hollow channel is designed according to needs, and can be, but is not limited to, designed to include a circle, an ellipse, a rectangle, or other polygons.

[0068] In one example, the hollow channel is used as an oil supply channel, and its cross-sectional shape is set to be a rectangle. In products with limited product thickness (thin-wall products), it has a better heat dissipation effect than a circular cross-sectional shape.

[0069] It is worth noting that in this embodiment, the layering process and mold required for molding can be realized by using existing technology to match the placeholder strip of the present invention. Therefore, in this embodiment, the layering process and mold required for molding are not limited here. The compression molding process and the autoclave process can use existing technology.

[0070] In one example, the material of the placeholder bar is polytetrafluoroethylene that can meet the material properties of the placeholder bar.

[0071] In one example, the extraction method includes applying a pulling force along the extraction direction, the extraction speed is 5-20 mm / min, and the temperature during extraction is controlled at 40-60° C. The applied pulling force can be provided by a pulling device or by manpower, which is not limited here. It is preferred to use a method that can stably and continuously provide the extraction force for extraction.

[0072] When pulling out, preferably, the pulling out sequence is to pull out every other placeholder strip.

[0073] In one example, the product layup process uses layer-by-layer layup, and the steps are as follows:

[0074] According to the ply angle designed for the composite product, multiple layers of prepreg are combined into one layer group, and each layer group is ironed flat to ensure that there are no gaps or bubbles between the layers of prepreg.

[0075] Roll and compact each layer after laying to ensure there are no gaps or bubbles between the layers.

[0076] In one example, in the product laying process, before laying out the placeholder strips and the layer group where the placeholder strips are located, the laid layer group and the female mold of the mold are placed in a vacuum bag as a whole to evacuate the vacuum, and pre-compacted according to the set temperature and time. After pre-compacting, the vacuum bag is removed after cooling to room temperature for subsequent laying.

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

[0078] In order to facilitate the extraction of the placeholder strip, in this embodiment, preferably, at least one end of the placeholder strip extends out of the composite material layer. Of course, in some examples, the length of the placeholder strip can also be set to be equal to the length of the hollow channel, and the placeholder strip can be inserted into the placeholder and fixed before extraction.

[0079] The molding process is further described below through a specific implementation method:

[0080] See also Figure 1 As shown, the composite material product 1 to be formed includes an integrated hollow channel 11, which is layered with carbon fiber / epoxy resin prepreg. The following steps are performed before forming:

[0081] Mold cleaning: remove excess materials on the surface of each part of the mold to make the surface smooth, free of oil stains, impurities, and rubber particles. If necessary, use metallographic sandpaper to polish it, wipe it clean with cotton cloth dipped in 120# gasoline and let it dry. Then use cotton cloth dipped in acetone to wipe the working surface of the mold. After the acetone dries, apply a release agent on the molding tooling surface.

[0082] Cutting: According to the layer angle designed for composite material product 1, the prepreg is laid together. Generally, 2 to 4 layers of prepreg form a layer group. The laid layers are ironed flat with an electric iron to ensure that there are no gaps or bubbles between the layers of prepreg. The laid layers are accurately cut with a cloth cutting machine according to the size of the blanking sample.

[0083] Inner skin of composite products: see Figure 2 and Figure 3 As shown, the inner skin layer 12 is laid on the female mold 21 of the mold 2. After each layer group is laid, it is rolled and compacted with a tool or vacuum compacted to ensure that there is no space or air bubble between each layer group.

[0084] Pre-compacting: After the inner skin layer 12 is laid, the inner skin layer 12 and the female mold 21 are integrally bagged to prepare for vacuum pre-compression. When vacuum bag packaging, the surface of the preform is covered with a non-porous film, a breathable felt, and a vacuum bag in sequence. The vacuum degree after packaging should not be less than 95Kpa. After vacuuming and compacting, pre-compact in an oven, set the oven at 70℃, and continue vacuuming and compacting for 1h. After pre-compacting, wait until it cools to room temperature, remove the vacuum bag, and proceed with subsequent layering.

[0085] Lay out the placeholder strips and lay the solid area layers (solid areas of composite materials on both sides of the same layer of the hollow channel): After laying each layer group of the solid area layer 13, use a tool to roll and compact it to ensure that there is no overhead or bubbles between the layers. The position of the placeholder strip 23 is located by the position mark on the female mold 21. Before laying out the placeholder strip 23, apply a layer of mold release agent on the surface of the placeholder strip 23 and let it dry.

[0086] The outer skin layer of the composite product is laid, after the placeholder strips 23 are laid and the core area layer 13 is laid, the outer skin layer 14 is laid, and after each layer group is laid, a tool is used to roll and compact it to ensure that there is no gap or bubble between the layers.

[0087] Mold closing: close the male mold 22 with the female mold 21 on which the ply is completed.

[0088] Curing: After mold closing, the mold 2 is hoisted onto the press, and the composite material ply group in the mold 2 is heated and pressurized for curing according to the curing procedure. After the press is pressurized, the mold closing gap is less than 0.1mm.

[0089] Pull out the placeholder strips: When the mold temperature drops to 40-60°C, use a clamp to clamp placeholder strips 23 and pull out placeholder strips 23. When pulling out, one person should apply force steadily and continuously until all placeholder strips 23 are pulled out. Pull out placeholder strips 23 at intervals. For example, pull out the first, third and fifth placeholder strips 23 from left to right, and then pull out the second and fourth placeholder strips 23.

[0090] Finishing: After mold opening, trim the surface flash and burrs of the composite material product, clean the residual rubber on the inner and outer surfaces, blow off the residual dust with high-pressure air, and wipe the inner and outer surfaces of the composite material product with cotton cloth dipped in acetone.

[0091] In this embodiment, a placeholder strip made of polytetrafluoroethylene has a melting point of 310°C, a tensile strength of 25MPa, an elastic modulus of 0.6GPa, a creep rate of 8%, and a friction coefficient of 0.2. The temperature is controlled between 40 and 60°C during extraction, and the extraction is performed at a uniform speed of 8mm / min. The obtained composite material product 1 without pre-buried pipelines is 0.5-0.7% lighter than the same product with pre-buried pipelines (resin-based composite materials). The surface roughness Ra of the hollow channel is 0.8-1.6 after detection, and the production cycle of a product is shortened by 10-15 hours. The quality of the overall product and the hollow pipeline is controllable, avoiding the influence of different thermal expansion coefficients of different materials and reducing the scrap rate of composite material products. At the same time, the use of placeholder strips to occupy the channel reduces the process steps and improves the production efficiency of the product.

[0092] In some other embodiments, for example, composite materials products are laminated using carbon fiber / bismaleimide resin prepreg or carbon fiber / polyimide resin prepreg, and the placeholder strips made of the above-mentioned polytetrafluoroethylene can also be used for placeholders.

[0093] During the research and development process, the applicant tried some different materials when selecting materials. The materials are as follows:

[0094]

[0095] The test results and cause analysis for each material are shown in the following table:

[0096]

[0097] In this embodiment, the composite material product containing the hollow channel can be a cabin, wing or other parts of an aircraft (unmanned aerial vehicle, spacecraft, etc.), which is not limited here.

[0098] Depending on the product's purpose, the hollow channel is used for fluid transmission (oil, gas, water, etc.), mechanical bearing, noise reduction, shock absorption or functional component installation (installation of sensors, fiber optic components, etc.).

[0099] See also Figure 2 and Figure 3 As shown, this embodiment also provides a forming mold 2 for a composite material product containing hollow channels, comprising a female mold 21, a male mold 22, and placeholder strips 23 having the same number as the hollow channels, wherein the material of the placeholder strips 23 meets the following properties:

[0100] (a) Melting point ≥ 200°C, for example, the curing temperature of the composite material product to be formed is 180°C, and the melting point of the placeholder 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 one example, the material of the placeholder bar 23 is polytetrafluoroethylene that can meet the performance requirements of the placeholder bar material.

[0106] The mold 2 can be used in the above-mentioned molding process and for molding composite material products containing hollow channels.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution. In the absence of a conflict of solutions, the various technical features mentioned in each embodiment can be combined in any manner to form other implementation methods that can be understood by those skilled in the art.

[0108] In addition, without departing from the scope of the present invention, the technical solutions described in the aforementioned embodiments may be modified, or some of the technical features may be replaced by equivalents, without causing the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for forming a composite material product containing a hollow channel, characterized in that: The following steps are involved: S1: In the composite material laying process, a placeholder strip is arranged at the reserved hollow channel position, and the cross-sectional shape of the placeholder strip is the same as the cross-sectional shape of the hollow channel; S2: curing the laminate with the placeholder strips by compression molding or autoclave process; S3: After the curing is completed, the placeholder strip is removed by pulling to form a hollow channel; The material of the placeholder strip meets the following properties: (a) The melting point is greater than the curing temperature of the composite material product to be formed; (b) Tensile strength ≥ 25 MPa; (c) 0.3 GPa ≤ elastic modulus ≤ 1 GPa; (d) 1% ≤ creep rate ≤ 8% (20°C, 20 MPa, 1000 h); (e)0.04≤friction coefficient≤0.

2.

2. The molding method according to claim 1, characterized in that: The material of the placeholder strip is polytetrafluoroethylene.

3. The molding method according to claim 1, characterized in that: In the ply laying process of step S1, a layer-by-layer ply laying method is adopted, and the steps are as follows: According to the designed ply angle of the composite product, multiple layers of prepreg are combined into one layer group, and each layer group is ironed flat to ensure that there are no gaps or bubbles between the layers of prepreg; Compact each layer after laying to ensure there is no gap or air bubble between the layers.

4. The molding method according to claim 3, characterized in that: In the layer laying process in step S1, before laying out the placeholder strips and the layer group where the placeholder strips are located, the laid layer group and the female mold of the mold are placed in a vacuum bag for evacuation, and pre-compacted according to the set temperature and time. After pre-compacting, the vacuum bag is removed after cooling to room temperature for subsequent layer laying.

5. The molding method according to claim 1, characterized in that: In step S1: The surface of the placeholder strip is coated with a release agent; and / or At least one end of the placeholder strip extends out of the composite material layer.

6. The molding method according to claim 1, characterized in that: The extraction method includes applying a pulling force along the extraction direction, the extraction speed is 5-20 mm / min, and the temperature during extraction is controlled at 40-60° C.

7. A composite material product containing hollow channels, characterized in that: Prepared by the method according to any one of claims 1 to 6.

8. The composite material product containing hollow channels according to claim 7, characterized in that: 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 0.2 μm≤Ra≤1.6 μm.

9. A forming die for a composite material product containing a hollow channel, characterized in that: It includes a male mold, a female mold, and placeholder strips with the same number as the hollow channels, wherein the material of the placeholder strips meets the following properties: (a) The melting point is greater than the curing temperature of the composite material product to be formed; (b) Tensile strength ≥ 25 MPa; (c) 0.3 GPa ≤ elastic modulus ≤ 1 GPa; (d) 1% ≤ creep rate ≤ 8% (20°C, 20 MPa, 1000 h); (e)0.04≤friction coefficient≤0.

2.

10. The forming die of the composite material product containing hollow channels according to claim 9, characterized in that: The material of the placeholder strip is polytetrafluoroethylene.

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