Radial thermal expansion pressure forming process and mold for composite material

Abstract

The invention relates to the technical field of chemical engineering, in particular to a radial thermal expansion pressure forming process and mold for a composite material, and the process comprises the following steps: S1) arranging prepreg of the composite material on the surface of a core mold; s2, the core mold is placed in an outer mold, a thermal expansion layer is arranged on the inner surface of the outer mold, the mold is assembled, and negative pressure is formed in the mold; s3, heating and heat preservation are conducted on the mold, so that the thermal expansion layer is heated and expanded to achieve radial pressurization on the composite material, and S4, the thermal expansion layer in the mold is shrunk through cooling, and the formed composite material product is obtained.The composite material radial thermal expansion pressurization forming technology has the advantages of being low in cost, high in efficiency, high in success rate and uniform in radial pressurization.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a radial thermal expansion pressurization molding process and mold for composite materials. Background Technology

[0002] Fiber thermoforming refers to a process in which prepreg fibers are softened by heating and then shaped into specific shapes using external force. It is widely used in composite materials, textiles, packaging, and other fields. Based on differences in forming principles and equipment, it can be divided into thermoforming, thermostretching, thermoblowing, and thermorolling.

[0003] Hot pressing involves placing continuous fiber prepreg (such as carbon fiber or glass fiber) in a mold, heating it to a softening temperature, and applying pressure to make it conform to the shape of the mold. Due to its high molding precision, it is widely used and suitable for complex structural parts.

[0004] Traditional hot pressing molding processes typically involve axial loading. Continuous fiber-wound fiber preforms are only subjected to axial pressure during hot pressing, resulting in uneven stress transmission and the continuous fibers easily generating significant fiber tension. This can lead to uneven material stress, stress concentration, and warping deformation. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a radial thermal expansion pressurization molding process and mold for composite materials, which realizes radial uniform and stable pressurization of fiber preforms.

[0006] To achieve the above objectives, the present invention provides a mold for radial thermal expansion and pressurization molding of composite materials, wherein a thermal expansion layer is provided on the inner surface of the outer mold; the thermal expansion layer expands when heated at high temperature and contracts when heated at low temperature.

[0007] Optionally, the thermal expansion layer is made of silicone rubber and / or fluororubber.

[0008] Optionally, the thickness of the thermal expansion layer is 5~30mm.

[0009] Optionally, the high temperature is 120~200℃; the low temperature is 20~60℃.

[0010] Optionally, the thermal expansion layer is cast and vulcanized onto the inner surface of the outer mold.

[0011] This invention provides a method for radial thermal expansion compression molding of composite materials, comprising:

[0012] S1) The prepreg of the composite material is placed on the surface of the mandrel;

[0013] S2) Place the above-mentioned core mold inside the outer mold. The inner surface of the outer mold is provided with a thermal expansion layer. Assemble the mold to make the mold under negative pressure.

[0014] S3) The mold is heated and kept warm, so that the thermal expansion layer expands under heat to achieve radial pressure on the composite material;

[0015] S4) Cooling causes the thermal expansion layer inside the mold to shrink, resulting in a molded composite material product.

[0016] Optionally, the prepreg of the composite material is a prepreg made by impregnating fiber material with resin.

[0017] Optionally, the fiber material includes one or more of cotton fiber, linen fiber, wool fiber, nylon fiber, polyester fiber, aramid fiber, carbon fiber, and glass fiber;

[0018] The resin includes one or more of unsaturated polyester resin, epoxy resin, phenolic resin, bismaleimide resin, and silicone resin.

[0019] Optionally, the heating and heat preservation temperature is 100~180℃; the heating rate is 1~15℃ / min; and the heating and heat preservation pressure is 0.1~20Mpa.

[0020] Optionally, the cooling temperature is 30~120℃; the cooling rate is 1~15℃ / min.

[0021] Compared with existing technologies, the radial thermal expansion pressurization molding process for composite materials provided by this invention has the advantages of low cost, high efficiency, high success rate, and uniform radial pressurization. Specifically:

[0022] 1. It can achieve stable stress release of the winding body, and the molded parts are uniform and have stable dimensions;

[0023] 2. For anisotropic heterogeneous materials, the molding pressure of different regions can be differentiated by selecting thermal expansion materials and controlling thickness, so as to achieve zoned control of density and mechanical properties in integrated molding;

[0024] 3. It can realize the one-piece molding of variable diameter irregular shaped rotary parts, avoiding physical or chemical bonding and improving the overall consistency;

[0025] 4. No need for high-cost large-scale equipment such as autoclaves and hot press molding machines. It uses oven heating and curing, which is simple, efficient, requires less equipment investment, and has low preparation cost. Attached Figure Description

[0026] Figure 1 A schematic diagram of the process for radial thermal expansion and pressurization molding of composite materials provided by the present invention;

[0027] Figure 2This is a schematic diagram of the composite material radial thermal expansion pressure molding die used in this invention. 1-Outer mold; 2-Lower flange 1; 3-Lower flange 2; 4-Core mold; 5-Wrapping body; 6-Thermal expansion layer; 7-Equalizing plate; 8-Upper cover plate. Detailed Implementation

[0028] The present invention provides a mold for radial thermal expansion and pressure molding of composite materials, wherein a thermal expansion layer is provided on the inner surface of the outer mold; the thermal expansion layer expands when heated at high temperature and contracts when heated at low temperature.

[0029] Preferably, the high temperature is 120~200℃, at which temperature the thermal expansion material expands due to heat, comes into contact with the material of the mandrel and applies radial pressure, causing the material to deform.

[0030] In this invention, the radial pressure refers to the force applied along the diameter or radius of the object's cross-section and perpendicular to the object's central axis. For example, in a cylindrical object, the radial pressure is perpendicular to the axis.

[0031] The preferred low temperature is 20~60℃. At this temperature, the thermally expanded material shrinks back to its original size and separates from the deformed material. By opening the mold, the deformed material part can be obtained.

[0032] The applicable temperature of the thermal expansion material is 50~200℃, and it can be reused multiple times within the applicable temperature range.

[0033] Preferably, when the thermal expansion material is in its original state, a gap of 1-5mm is reserved between it and the core mold material to facilitate assembly and demolding.

[0034] The present invention does not impose any special limitation on the formation method of the thermal expansion material. Preferably, it is formed by casting and vulcanizing onto the inner surface of the outer mold.

[0035] In some implementation schemes, a cylindrical metal casting inner mold is machined according to the designed thickness and fixed to a rigid outer mold by detachable bolts. A thermal expansion layer material is poured into the gap and a top plate is added before the mold is closed for vulcanization molding.

[0036] The preferred temperature for vulcanization molding is 150~185℃, and the preferred time is 15~45min.

[0037] This invention controls the expansion of the thermal expansion material by controlling the thickness and modulus of the thermal expansion layer, as well as the curing temperature and heating rate after mold closing, in order to ensure stress loading.

[0038] The expansion stress is calculated as follows:

[0039] Expansion stress σ = EαΔT, where E is the elastic modulus of the material; α is the coefficient of linear expansion; and ΔT is the temperature change.

[0040] Select a matching thermal expansion material based on the temperature and pressure of the material curing process.

[0041] Preferably, the material of the thermal expansion layer is one or more of silicone rubber, fluororubber, etc.

[0042] The preferred selection of the expansion layer thickness is as follows: expansion amount L = αΔTL0, where α is the linear expansion coefficient; ΔT is the temperature change; and L0 is the initial thickness of the expansion layer.

[0043] The appropriate thickness of the expansion layer is designed based on the design compression amount and demolding clearance.

[0044] In the preferred embodiment of the present invention, when designing the thickness of the expansion layer and the mold matching, a demolding gap space should be reserved, preferably 1~5mm.

[0045] Preferably, the thickness of the thermal expansion layer is 5 to 30 mm, for example, it can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 mm, or any of the above values ​​can be used as the upper or lower limit.

[0046] By setting the above parameters, the mold provided by the present invention can apply appropriate radial pressure to the material during the heating and curing process when performing pressure molding of composite materials, and can separate from the material during the cooling and demolding process to obtain a complete molded part, and can maintain a high yield rate.

[0047] The present invention also provides a method for radial thermal expansion compression molding of composite materials, comprising:

[0048] S1) The prepreg of the composite material is placed on the surface of the mandrel;

[0049] S2) Place the above-mentioned core mold inside the outer mold. The inner surface of the outer mold is provided with a thermal expansion layer. Assemble the mold to make the mold under negative pressure.

[0050] S3) The mold is heated and kept warm, so that the thermal expansion layer expands under heat to achieve radial pressure on the composite material;

[0051] S4) Cooling causes the thermal expansion layer inside the mold to shrink, resulting in a molded composite material product.

[0052] First, a prepreg is prepared. In this invention, the prepreg of the composite material is preferably a prepreg made by impregnating fiber material with resin.

[0053] The fiber can be any common fiber material well known to those skilled in the art, and the present invention is not specifically limited to it, including but not limited to one or more blends or weaves of cotton fiber, linen fiber, wool fiber, nylon fiber, polyester fiber, aramid fiber, carbon fiber, glass fiber, etc. The fiber can be a smooth fiber without texture, or a fiber with texture, the texture including but not limited to plain weave, twill weave, satin weave, etc.

[0054] The resin may be a resin material known to those skilled in the art for impregnating fibers, including but not limited to one or more of unsaturated polyester resin, epoxy resin, phenolic resin, bismaleimide resin, and silicone resin.

[0055] In some specific embodiments, the resin material for impregnating the fibers also includes one or more of fillers, dispersants, crosslinking agents, etc.

[0056] In some specific implementations, the above-mentioned resin material is mixed with fillers, dispersants, crosslinking agents, etc. to obtain a composite adhesive solution, which is then used to impregnate fibers.

[0057] The present invention does not specifically limit the types of fillers, dispersants, and crosslinking agents that can be selected, and they can be applicable compounds well known to those skilled in the art. In some specific embodiments, the filler is an inorganic filler, including but not limited to dolomite; the dispersant includes but is not limited to sodium pyrophosphate; and the crosslinking agent includes but is not limited to hexamethylenetetramine. The content of the above-mentioned fillers, dispersants, and crosslinking agents is not specifically limited in this application, and those skilled in the art can add them according to the material properties. Optionally, the mass content of the filler in the composite adhesive can be 10% to 60%, for example, 10%, 20%, 30%, 40%, 50%, or 60%; the mass content of the dispersant in the composite adhesive can be 1% to 10%, for example, 1%, 3%, 5%, 7%, or 10%; and the content of the crosslinking agent in the composite adhesive can be 1% to 10%, for example, 1%, 3%, 5%, 7%, or 10%.

[0058] In some implementations, the fibers or fiber fabrics are impregnated with resin in a designed ratio, and the resin content and solids content of the prepreg are controlled using extrusion rollers and drying tunnels.

[0059] During the impregnation process, the temperature of the drying tunnel is preferably 120~140℃, and the impregnation speed is preferably 1~10m / min.

[0060] The prepreg is then placed on the surface of the core mold, specifically by laying it out.

[0061] Optionally, the prepreg can be cut to size according to the structural design requirements before operation.

[0062] In some embodiments, a winding machine is used to wind the prepreg onto the surface of the mandrel according to the designed structure and dimensional requirements. Preferably, the winding density of the prepreg is not less than 70% of the target density of the product.

[0063] Then, the core mold of the above-mentioned wound prepreg is placed inside the outer mold, the inner surface of which is provided with a thermal expansion layer. The mold is assembled so that the mold is under negative pressure.

[0064] The thermal expansion layer, its material, thickness, and other parameters, as well as the setting method, are the same as described above and will not be repeated here.

[0065] In some implementations, the wound preform is fixed to the mold base plate using a mandrel, for example, by bolting the mandrel to the mold base plate to ensure a seamless connection between the mandrel and the base plate, preventing resin from flowing through gaps and causing excessive glue overflow during the preform's heating and pressurization process. Optionally, during mold assembly, release films are applied to the upper and lower surfaces and radial surfaces of the preform to facilitate curing and demolding. The radial release film is preferably applied with multiple overlapping ends to allow circumferential slippage under radial pressure, reducing wrinkle formation.

[0066] The method to create a negative pressure inside the mold can be a conventional method such as vacuuming.

[0067] Then the mold is heated and kept warm, so that the thermal expansion layer expands due to heat. The thickness of the thermal expansion layer is controlled by temperature, thereby achieving radial pressure on the preform, eliminating the entanglement gap and realizing the curing and molding of the fiber preform.

[0068] The preferred heating and heat preservation temperature is 100~180℃, more preferably 140~170℃.

[0069] The heating rate is preferably 1~15℃ / min, more preferably 5~10℃ / min.

[0070] Preferably, the heat preservation time for each temperature segment is not less than 1 hour, and more preferably 1 to 2 hours.

[0071] The heating and heat preservation pressure is preferably 0.1~20 MPa, more preferably 3~6 MPa.

[0072] In this invention, the above-mentioned heating, heat preservation and curing can be carried out in an oven, which greatly reduces the cost of the equipment and simplifies the process.

[0073] Finally, the temperature is lowered so that the thermal expansion layer inside the mold shrinks back to its original size, and the molded composite material product can be obtained by opening the mold.

[0074] The preferred temperature for cooling is 30~120℃.

[0075] The cooling rate is 1~15℃ / min, more preferably 5~10℃ / min.

[0076] Preferably, after the mold cools to room temperature, it is left in a room temperature environment for 0.5 to 2 hours to allow the thermal expansion layer to fully shrink and recover.

[0077] To further illustrate the present invention, a detailed description is provided below with reference to embodiments. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims.

[0078] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0079] Example 1

[0080] 1. Precast body forming

[0081] The fibers are made of nylon, aramid, and cotton blends, and the resins are thermosetting resins such as phenolic resin, silicone resin, and epoxy resin.

[0082] Composite adhesive composition: 60 parts by weight of phenolic resin, 30 parts by weight of inorganic filler dolomite, 5 parts by weight of dispersant sodium pyrophosphate, and 5 parts by weight of crosslinking agent hexamethylenetetramine.

[0083] The prepreg is obtained by fully and uniformly pre-curing the composite adhesive, and then the preform is wound into shape. The continuous fiber prepreg is wound onto the surface of the mandrel according to the process parameters. During the winding process, the winding tension is monitored and controlled at 0.5~2N / dtex to ensure the density of the preform and the winding quality, and to ensure that the winding density of the preform is not less than 70% of the target density of the product.

[0084] 2. Casting of thermal expansion layer

[0085] The thermal expansion layer is poured into the inner side of a rigid outer mold. A cylindrical metal inner mold, manufactured according to the designed thickness, is fixed to the rigid outer mold with detachable bolts. The thermal expansion layer material is poured into the gap, and a top plate is added before closing the mold for vulcanization. The poured thermal expansion layer material is fluororubber, with a thickness of 30mm, a vulcanization temperature of 185℃, and a vulcanization time of 45 minutes. The cast thermal expansion layer can be reused multiple times within an applicable temperature range of 50-200℃.

[0086] 3. Oven curing and molding

[0087] The preform, formed by winding, is fixed to the mold base plate using a core mold. A bolted structure is used to lock the core mold to the mold base plate, ensuring a seamless connection between them and preventing resin overflow during the preform's heating and pressurization process. During mold assembly, release films are applied to the upper and lower surfaces and radial surfaces of the preform to facilitate curing and demolding. The radial release film should be applied with multiple overlapping ends to allow circumferential slippage under radial pressure, reducing wrinkles.

[0088] The preform, pressure equalization plate, and outer mold of the thermal expansion layer are assembled and locked together, and a mold top cover is added for fixation. A gap of 1~5mm is reserved between the thermal expansion layer and the radial surface of the preform to facilitate assembly and demolding.

[0089] The assembled mold and preform are placed in an oven for curing at a temperature of 150℃ and a heating rate of 10℃ / min. The holding time for each temperature range is not less than 1 hour.

[0090] 4. Cooling and demolding

[0091] The temperature of the cured mold is lowered to room temperature at a rate of 10℃ / min. After the mold is cooled to room temperature, it is left to stand in the room for 2 hours to allow the thermal expansion layer to fully shrink and recover.

[0092] After the thermal expansion layer shrinks and recovers, open the top cover of the mold to confirm that the thermal expansion layer and the part are fully separated to create a demolding gap, and disassemble the mold to complete the demolding of the part.

[0093] Example 2

[0094] 1. Precast body forming

[0095] The fibers are made of nylon, aramid, and cotton blends, and the resins are thermosetting resins such as phenolic resin, silicone resin, and epoxy resin.

[0096] Composite adhesive composition: 60 parts by weight of phenolic resin, 30 parts by weight of inorganic filler dolomite, 5 parts by weight of dispersant sodium pyrophosphate, and 5 parts by weight of crosslinking agent hexamethylenetetramine.

[0097] The prepreg is obtained by fully and uniformly pre-curing the composite adhesive, and then the preform is wound into shape. The continuous fiber prepreg is wound onto the surface of the mandrel according to the process parameters. During the winding process, the winding tension is monitored and controlled at 0.5~2N / dtex to ensure the density of the preform and the winding quality, and to ensure that the winding density of the preform is not less than 70% of the target density of the product.

[0098] 2. Casting of thermal expansion layer

[0099] The thermal expansion layer is poured into the inner side of a rigid outer mold. A cylindrical metal inner mold, manufactured according to the designed thickness, is fixed to the rigid outer mold with detachable bolts. The thermal expansion layer material is poured into the gap, and a top plate is added before closing the mold for vulcanization. The poured thermal expansion layer material is fluororubber, with a thickness of 20mm, a vulcanization temperature of 185℃, and a vulcanization time of 45 minutes. The cast thermal expansion layer can be reused multiple times within an applicable temperature range of 50-200℃.

[0100] 3. Oven curing and molding

[0101] The preform, formed by winding, is fixed to the mold base plate using a core mold. A bolted structure is used to lock the core mold to the mold base plate, ensuring a seamless connection between them and preventing resin overflow during the preform's heating and pressurization process. During mold assembly, release films are applied to the upper and lower surfaces and radial surfaces of the preform to facilitate curing and demolding. The radial release film should be applied with multiple overlapping ends to allow circumferential slippage under radial pressure, reducing wrinkles.

[0102] The preform, pressure equalization plate, and outer mold of the thermal expansion layer are assembled and locked together, and a mold top cover is added for fixation. A gap of 1~5mm is reserved between the thermal expansion layer and the radial surface of the preform to facilitate assembly and demolding.

[0103] The assembled mold and preform are placed in an oven for curing at a temperature of 145℃ and a heating rate of 10℃ / min. The holding time for each temperature range is not less than 1 hour.

[0104] 4. Cooling and demolding

[0105] The temperature of the cured mold is lowered to room temperature at a rate of 10℃ / min. After the mold is cooled to room temperature, it is left to stand in the room for 2 hours to allow the thermal expansion layer to fully shrink and recover.

[0106] After the thermal expansion layer shrinks and recovers, open the top cover of the mold to confirm that the thermal expansion layer and the part are fully separated to create a demolding gap, and disassemble the mold to complete the demolding of the part.

[0107] Example 3

[0108] 1. Precast body forming

[0109] The fibers are made of a blend of nylon, aramid, and cotton fibers, and the resin is phenolic resin.

[0110] Composite adhesive composition: 60 parts by weight of phenolic resin, 30 parts by weight of inorganic filler, 5 parts by weight of dispersant, and 5 parts by weight of crosslinking agent.

[0111] The prepreg is obtained by fully and uniformly pre-curing the composite adhesive, and then the preform is wound into shape. The continuous fiber prepreg is wound onto the surface of the mandrel according to the process parameters. During the winding process, the winding tension is monitored and controlled at 0.5~2N / dtex to ensure the density of the preform and the winding quality, and to ensure that the winding density of the preform is not less than 70% of the target density of the product.

[0112] 2. Casting of thermal expansion layer

[0113] The thermal expansion layer is poured into the inner side of a rigid outer mold. A cylindrical metal inner mold, manufactured according to the designed thickness, is fixed to the rigid outer mold with detachable bolts. The thermal expansion layer material is poured into the gap, and a top plate is added before closing the mold for vulcanization. The poured thermal expansion layer material is fluororubber, with a thickness of 15mm, a vulcanization temperature of 185℃, and a vulcanization time of 45 minutes. The cast thermal expansion layer can be reused multiple times within an applicable temperature range of 50-200℃.

[0114] 3. Oven curing and molding

[0115] The preform, formed by winding, is fixed to the mold base plate using a core mold. A bolted structure is used to lock the core mold to the mold base plate, ensuring a seamless connection between them and preventing resin overflow during the preform's heating and pressurization process. During mold assembly, release films are applied to the upper and lower surfaces and radial surfaces of the preform to facilitate curing and demolding. The radial release film should be applied with multiple overlapping ends to allow circumferential slippage under radial pressure, reducing wrinkles.

[0116] The preform, pressure equalization plate, and outer mold of the thermal expansion layer are assembled and locked together, and a mold top cover is added for fixation. A gap of 1~5mm is reserved between the thermal expansion layer and the radial surface of the preform to facilitate assembly and demolding.

[0117] The assembled mold and preform are placed in an oven for curing at a temperature of 145℃ and a heating rate of 5℃ / min. The holding time for each temperature range is not less than 1 hour.

[0118] 4. Cooling and demolding

[0119] The temperature of the cured mold is lowered to room temperature at a rate of 10℃ / min. After the mold is cooled to room temperature, it is left to stand in the room for 2 hours to allow the thermal expansion layer to fully shrink and recover.

[0120] After the thermal expansion layer shrinks and recovers, open the top cover of the mold to confirm that the thermal expansion layer and the part are fully separated to create a demolding gap, and disassemble the mold to complete the demolding of the part.

[0121] Comparative Example 1

[0122] 1. Precast body forming

[0123] The fibers are made of a blend of nylon, aramid, and cotton fibers, and the resin is phenolic resin.

[0124] Composite adhesive composition: 60 parts by weight of phenolic resin, 30 parts by weight of inorganic filler, 5 parts by weight of dispersant, and 5 parts by weight of crosslinking agent.

[0125] The prepreg is obtained by fully and uniformly pre-curing the composite adhesive, and then the preform is wound into shape. The continuous fiber prepreg is wound onto the surface of the mandrel according to the process parameters. During the winding process, the winding tension is monitored and controlled at 0.5~2N / dtex to ensure the density of the preform and the winding quality, and to ensure that the winding density of the preform is not less than 70% of the target density of the product.

[0126] 2. Oven curing and molding

[0127] The preform, formed by winding, is fixed to the mold base plate using a core mold. A bolted structure is used to lock the core mold to the mold base plate, ensuring a seamless connection between them and preventing resin overflow during the preform's heating and pressurization process. During mold assembly, release films are applied to the upper and lower surfaces and radial surfaces of the preform to facilitate curing and demolding. The radial release film should be applied with multiple overlapping ends to allow circumferential slippage under radial pressure, reducing wrinkles.

[0128] The assembled mold and preform are placed in a hot press molding machine for curing. The curing pressure is 1 MPa, the curing temperature is 145℃, the heating rate is 10℃ / min, and the holding time for each temperature segment is not less than 1 hour.

[0129] 3. Cooling and demolding

[0130] The temperature of the cured mold is lowered to room temperature at a rate of 10℃ / min. After the mold is cooled to room temperature, it is left to stand in the room for 2 hours to allow the thermal expansion layer to fully shrink and recover.

[0131] After the thermal expansion layer shrinks and recovers, open the top cover of the mold to confirm that the thermal expansion layer and the part are fully separated to create a demolding gap, and disassemble the mold to complete the demolding of the part.

[0132] Performance testing

[0133] The performance of the parts prepared in Examples 1-3 and Comparative Example 1 was tested, and the results are shown in Table 1.

[0134] Table 1

[0135]

[0136] The data in Table 1 show that, using the molding process provided by the present invention, the workpiece is subjected to more uniform pressure during the pressing process, and the mechanical properties of the final part are more uniform.

[0137] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A mold for radial thermal expansion and pressure molding of composite materials, characterized in that, The inner surface of the outer mold is provided with a thermal expansion layer; the thermal expansion layer expands when heated at high temperatures and contracts when heated at low temperatures.

2. The mold for radial thermal expansion and pressurization molding of composite materials according to claim 1, characterized in that, The thermal expansion layer is made of silicone rubber and / or fluororubber.

3. The mold for radial thermal expansion and pressurization molding of composite materials according to claim 1, characterized in that, The thickness of the thermal expansion layer is 5~30mm.

4. The mold for radial thermal expansion and pressure molding of composite materials according to claim 1, characterized in that, The high temperature is 120~200℃; the low temperature is 20~60℃.

5. The mold for radial thermal expansion and pressurization molding of composite materials according to claim 1, characterized in that, The thermal expansion layer is cast and vulcanized onto the inner surface of the outer mold.

6. A method for radial thermal expansion and pressurization molding of composite materials, characterized in that, include: S1) The prepreg of the composite material is placed on the surface of the mandrel; S2) Place the above-mentioned core mold inside the outer mold. The inner surface of the outer mold is provided with a thermal expansion layer. Assemble the mold to make the mold under negative pressure. S3) The mold is heated and kept warm, so that the thermal expansion layer expands under heat to achieve radial pressure on the composite material; S4) Cooling causes the thermal expansion layer inside the mold to shrink, resulting in a molded composite material product.

7. The method according to claim 6, characterized in that, The prepreg of the composite material is a prepreg made by impregnating fiber material with resin.

8. The method according to claim 7, characterized in that, The fiber material includes one or more of the following: cotton fiber, linen fiber, wool fiber, nylon fiber, polyester fiber, aramid fiber, carbon fiber, and glass fiber. The resin includes one or more of unsaturated polyester resin, epoxy resin, phenolic resin, bismaleimide resin, and silicone resin.

9. The method according to claim 6, characterized in that, The heating and heat preservation temperature is 100~180℃; the heating rate is 1~15℃ / min; and the heating and heat preservation pressure is 0.1~20Mpa.

10. The method according to claim 6, characterized in that, The cooling temperature is 30~120℃; the cooling rate is 1~15℃ / min.

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