RTM (Resin Transfer Molding) forming mold and forming method for composite material cylindrical part

Abstract

The invention belongs to the technical field of composite material product manufacturing, and discloses a composite material cylindrical part RTM forming die which comprises a core die, an upper die, a lower die, a sealing ring and a connector. The invention further discloses a forming method using the composite material cylindrical part RTM forming mold. According to the invention, the heavy and difficult problems of mold closing, air tightness and the like of the composite material cylindrical part mold are solved, and the reasonable cylindrical part RTM molding process is designed to solve the problems of dry spots and air holes after the product is cured. The RTM forming mold and the RTM forming process provided by the invention are a near-net forming technical scheme which is low in cost, good in product internal quality and surface quality, high in dimensional precision and relatively high in automation degree.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material product manufacturing, and relates to an RTM molding die and a molding method for a composite material cylindrical part. Background Art

[0002] Common molding processes for composite cylindrical parts include winding, autoclave molding, vacuum induction molding, pultrusion molding, etc. The wet-wound cylindrical parts require a large process margin, and the material utilization rate is not high; the surface quality after molding is poor, the dimensional accuracy is low, and post-processing or surface treatment is often required; additional pressurization cannot be performed during the curing process, and the resin is in an unrestricted flow state, and the fiber content and internal quality cannot be guaranteed. The dry winding process uses prepreg tape for winding, which requires a large process margin and a high cost of prepreg tape. After winding, a large amount of auxiliary materials are required to establish a vacuum bag system for curing. The process is complex and the manufacturing cost is high. The autoclave molding process can provide stable and uniform temperature and pressure conditions for the product, which is conducive to ensuring and improving the internal quality of the product, but its raw material cost and equipment cost are high, the process is complex, and the manufacturing cost is high; and because there is no external mold restriction, the surface quality and dimensional accuracy after molding are not high. The surface quality of cylindrical parts formed by vacuum induction molding process is poor, and the dimensional accuracy is low, and post-processing or surface treatment is often required; by establishing a vacuum bag system to pressurize through the atmosphere, the curing pressure is small, and it is difficult to ensure the internal quality of the product, and it is only used for products with low molding quality requirements. The pultrusion molding process has a high degree of automation and production efficiency, but it is only used for the molding of products with equal cross-sections. The circumferential and radial mechanical properties of the molded products are low, and the scope of application is relatively limited.

[0003] The manufacturing of composite cylindrical parts through RTM molding process has a high degree of automation, production efficiency and material utilization rate; the raw materials are mostly fiber cloth, fiber felt, resin, etc., with low material cost and flexible material design and matching; during the curing process, the inner and outer molds are pressurized, the pressure is sufficient and stable, the dimensional accuracy is high, and the surface quality and internal quality are good. The difficulties of RTM molding process of composite cylindrical parts are mainly: ① In order to realize the pressure control of the inner and outer molds, the cylindrical parts should use a combination mold with multiple modules accurately combined, but the original state of the reinforcing material fiber felt / cloth or preform is fluffy, and it is often difficult to close the mold after being placed in the cavity; ② RTM needs to be vacuumed or pressurized for resin injection, and a closed space with good airtightness needs to be established. The combination mold of multiple modules has many closing surfaces, and it is difficult to ensure airtightness; ③ The flow behavior of resin and gas during the resin injection of cylindrical parts is complex, which is easy to cause incomplete resin impregnation and air encapsulation, and finally form dry spots and pores on the product. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art of mold closing and air tightness of composite cylindrical parts, and to provide a composite cylindrical part RTM molding mold and molding method, which has low cost, high degree of automation, good internal quality and surface quality of the product and high dimensional accuracy.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A composite material cylindrical part RTM molding die, comprising a core die, an upper die, a lower die, a sealing ring, and a joint.

[0007] The lower mold comprises a mold frame, a lower mold surface arranged in the mold frame, the lower mold surface is connected to a lower mold cavity, two ends of the lower mold cavity are provided with core mold limiting steps, the outer periphery of the lower mold cavity is provided with a sealing groove, the edge of the lower mold surface is provided with a positioning step, the lower mold surface is connected to an injection hole, and the injection hole is connected to a pipeline through a joint;

[0008] The upper mold comprises a mold frame, an upper mold surface arranged in the mold frame, the upper mold surface is connected to an upper mold cavity, core mold limiting steps are arranged at both ends of the upper mold cavity, a positioning step is arranged at the edge of the upper mold surface, and an exhaust hole is connected to the upper mold surface, the exhaust hole passes through the core mold limiting step, and the exhaust hole is connected to the pipeline through a joint;

[0009] The core mold is a hollow cylindrical part with closed ends, and the core mold is arranged between the upper mold and the lower mold; the core mold surface is set with an inclination, and the large end diameter is set to: the maximum limit size of the inner diameter of the cylindrical part - (10%-20%) inner diameter tolerance value, and the small end diameter is set to: the minimum limit size of the inner diameter of the cylindrical part + (10%-20%) inner diameter tolerance value;

[0010] The sealing ring is an integrally formed sealing ring, which is arranged in the sealing groove, and forms a sealing structure with the sealing groove of the lower mold and the mating surface of the upper mold. Two sealing grooves are set within the injection pressure range of 0-0.4MPa, and three sealing grooves are set above the injection pressure of 0.4MPa.

[0011] As a preferred embodiment, the exhaust hole and the injection hole respectively include a smooth hole section and a sealing thread section, the sealing thread section is connected and sealed with the joint, the smooth hole section serves as a flow channel, and the diameter of the smooth hole section is smaller than the inner diameter of the pipe connected to the joint.

[0012] As a preferred embodiment, the cross-section of the lower model cavity and the upper model cavity is a semi-ellipse, the major axis of the semi-ellipse is set to: the maximum limit size of the outer diameter of the cylindrical part - (10%~20%) outer diameter tolerance value, and the minor axis gradually changes with the outer circle size of the core mold; the molding surface of the lower model cavity and the upper model cavity is set with a slope along the length direction, and the slope value is 30%-40% of the outer diameter tolerance value.

[0013] The present invention also discloses a molding method using a composite material cylindrical part RTM molding die, comprising the following steps:

[0014] S1, laying fiber felt and fiber cloth on the core mold layer by layer, or inserting the cylindrical part preform made of fiber felt and fiber cloth into the core mold from the small end to the large end of the core mold, vacuum bag packaging with the edges of both ends of the core mold as boundaries, and vacuumizing to pre-compact the reinforcement material;

[0015] S2. Remove the vacuum bag, place the core mold into the lower mold cavity, put the sealing ring in the sealing groove of the lower mold, slowly place the upper mold on the lower mold and the core mold, and the positioning steps of the upper mold and the lower mold form a small gap in the width direction to achieve width positioning. The two ends of the core mold limit the upper mold; install flat washers, spring washers and screws in sequence, and use a torque wrench to tighten the screws to the same torque in multiple times according to the cross-symmetry principle and sequence; use a 0.02mm thick feeler gauge to check the mold clearance, and the clearance ≤0.02mm is qualified.

[0016] S3. Install joints at the injection hole and exhaust hole, connect the vacuum system, and perform vacuum degree detection;

[0017] S4, using vacuum-assisted resin injection to evacuate the air inside the mold to a vacuum state before performing resin injection, placing the mold in a manner where the lower mold is at the bottom and the upper mold is at the top, and performing anti-gravity injection;

[0018] S5. Place the entire mold in a curing furnace or oven for curing. After the curing is completed and the mold is cooled to room temperature, demoulding and post-processing are performed.

[0019] As a preferred embodiment, in step S4, the prepared resin is placed in a vacuum tank and vacuumed to degas the resin before injection, and the degassing is completed if there is no obvious bubble overflow within 2 minutes.

[0020] As a preferred embodiment, in step S1, the fiber cloths or fiber felts are spliced ​​with each other, the splicing gap is ≤1mm, the seams of each layer are staggered by ≥30mm, and the ends of the plies are fixed by needle stitching using reinforcing material fibers; the vacuum bag is evacuated to -0.100MPa to -0.090MPa, and the vacuum degree of -0.100MPa to -0.090MPa is maintained for 30-40min.

[0021] As a preferred method, in step S2, check the two ends of the core mold to ensure that the gap between the two ends of the core mold and the lower mold cavity is 1-2 mm, check whether there are protrusions in the reinforcing material at the mold closing position of the upper mold and the lower mold, and if there are protrusions, use a scraper to evenly scrape them flat; stick polytetrafluoroethylene cloth on the end face of the core mold.

[0022] As a preferred method, in step S4, the injection pipe and the exhaust glue overflow pipe are connected to the corresponding joints, the joint switch is turned on, and resin injection is performed from the injection port of the lower mold with a gradually increasing gradient injection pressure, and the injection pressure range is 0.2-0.6MPa; when the upper mold exhaust port above the injection hole begins to continuously overflow bubble-free resin, the exhaust port corresponding to the joint switch is closed, and when another exhaust hole of the upper mold continuously overflows resin, the injection pressure is reduced to 0MPa, the switch of the injection port joint is closed, and the switches of all exhaust port joints are turned on.

[0023] The present invention reduces the number of mold joint surfaces through the mold structure of a core mold + upper and lower molds, sets the sealing surface as a plane and sets multiple seals to reduce the difficulty of sealing material arrangement and improve the airtight reliability of the structure; pre-compacts the reinforcing material through a vacuum bag system to reduce the thickness of the reinforcing material, and increases the tolerance of the mold cavity to the reinforcing material through improved design of products and molds within the tolerance range, thereby ensuring smooth completion of the mold joint; and ensures normal resin infiltration and exhaust by setting reasonable injection port and exhaust port positions, hole structures and formulating a reasonable injection process, thereby avoiding the formation of dry spots and pores in products.

[0024] The present invention has the following advantages:

[0025] The surface quality and dimensional accuracy of cylindrical parts are better than those of other processes; the internal quality of cylindrical parts is comparable to that of autoclave molding process, and higher than that of winding molding, vacuum infusion molding, and pultrusion molding processes; the utilization rate of reinforcing materials can reach more than 80%, and the utilization rate of resin can reach more than 90%; the batch production cost is about 40% of that of autoclave molding process, 90% of that of winding molding process, and 85% of that of vacuum infusion molding process; the degree of process automation is comparable to that of winding molding process, and higher than that of autoclave molding and vacuum infusion molding processes; the product designability and process adaptability are comparable to those of autoclave molding process, better than that of winding molding process, and significantly better than that of pultrusion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of the molding die of the present invention;

[0027] Figure 2 Schematic diagram of the core mold structure;

[0028] Figure 3 Schematic diagram of the lower die structure;

[0029] Figure 4 Schematic diagram of the upper die structure;

[0030] Figure 5 Schematic diagram of resin flow direction (arrow) and flow front (curve) during resin injection;

[0031] Figure 6 Schematic diagram of the injection hole structure;

[0032] Figure 7 Schematic diagram of the exhaust hole structure.

[0033] Among them: 1-core mold, 2-lower mold, 3-upper mold, 4-sealing ring, 5-joint, 6-screw, 7-mold frame, 8-reinforcement rib, 9-positioning step, 10-lower mold surface, 11-lower mold cavity, 12-core mold limiting step, 13-sealing groove, 14-threaded through hole, 15-injection hole, 16-exhaust hole, 17-upper mold surface, 18-upper mold cavity, 19-screw through hole. 20-countersunk screw mounting hole. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] Example:

[0037] A carbon fiber reinforced epoxy resin-based composite material cylindrical product with a length of 420±0.8mm, an outer diameter of Φ420±0.8mm, and an inner diameter of Φ400±0.8mm was prepared.

[0038] The composite cylindrical product is improved in design, with a 5mm margin reserved at both ends, the length set to 430±0.8mm, a slope set along the length direction, an outer diameter of the large end Φ420.5mm, an outer diameter of the small end Φ419.5mm, an inner diameter of the large end Φ400.5mm, and an inner diameter of the small end Φ399.5mm.

[0039] A composite material cylindrical part RTM forming mold comprises a core mold, an upper mold, a lower mold, a sealing ring, a joint and a connecting piece.

[0040] The core mold is a hollow cylindrical part with closed ends. The core mold length is 450±0.8mm, the core mold surface is set with an inclination, the large end diameter is set to Φ400.5±0.05mm, and the small end diameter is set to Φ399.5±0.05mm, so as to facilitate the demoulding of the core mold and the assembly of the reinforcement material preform. A countersunk screw mounting hole is set at the edge of each end surface of the core mold for installing an M16mm hexagon socket countersunk screw. After the countersunk screw is installed, the head is lower than the end surface of the core mold. When the core mold is transported, the countersunk screw can be unscrewed to serve as a handle or hanging point. When encapsulating or injecting, the countersunk screw can be tightened to achieve the blocking of the hole.

[0041] The lower mold adopts a frame structure, including a lower mold surface, a mold frame, and a reinforcing rib plate. The lower mold surface is provided with a cavity, a core mold limit step, a sealing groove, a threaded through hole, a positioning step, an injection hole, etc. The cavity is used to form the outer semicircle of the composite cylindrical product. In order to increase the cavity space to eliminate the enrichment of the fluffy reinforcing material at the mold closing position during the mold closing process, the cavity cross section is set to a semi-ellipse, the major axis of the semi-ellipse is set to 420.5±0.05mm, and the minor axis changes gradually with the outer circle size of the core mold. The cavity length is set to 453±0.8mm, which is convenient for the placement and demolding of the core mold. The mold surface of the cavity is set with an inclination along the length direction, the large end radius is set to Φ210.25±0.025mm, and the small end radius is set to Φ199.75±0.025mm. Core mold limiting steps are set at both ends of the cavity. When the mold is assembled, the core mold is placed on the core mold limiting steps. The cavity formed by the core mold and the lower mold is the reinforcing material and resin filling area, and the step height is 10±0.1mm. Two sealing grooves are set on the periphery of the cavity. The size of the sealing groove matches the specification of the O-ring with a wire diameter of Φ5mm. The molding surface and the mating surface area within the sealing groove meet the airtightness requirements. 12 M10mm threaded through holes are set on the outer edge of the sealing groove, and the threaded holes are used to connect the upper and lower molds. A boss is set on the edge of the lower mold surface as a positioning step for the upper mold, with a height of 8mm, which is used for precise positioning of the upper mold in the width direction. The symmetry of the lower mold positioning step relative to the lower mold cavity is ≤0.05mm. An injection hole is set at the center of the lower mold end face. The injection hole consists of a light hole section and a sealing thread section. The diameter of the light hole section is Φ4mm, and the sealing thread specification is NPT 3 / 8. The sealing thread section is used for connection and sealing with the joint. The light hole section is used as a flow channel for the resin to enter the mold cavity during injection. The diameter of the light hole section is smaller than the inner diameter of the pipe connected to the joint to ensure that the resin entering the mold cavity has sufficient pressure or driving force. The mold frame is mainly used to support the lower mold surface and increase the rigidity of the lower mold. The mold frame is composed of multiple steel plates. Multiple large-sized holes are opened on the frame steel plate, which can reduce the weight on the one hand and reduce the influence of the frame steel plate on the hot air convection and product heating during the curing process on the other hand. Multiple reinforcing ribs are set around the frame to increase the rigidity of the screw connection position at the edge of the lower mold surface, reduce the deformation of the lower mold surface during screw installation and pressurized injection, and prevent structural damage and sealing problems caused by deformation.

[0042] The upper mold adopts a frame structure, including an upper mold surface, a mold frame, and a reinforcing rib plate. The upper mold surface is provided with a cavity, a core mold limit step, a screw through hole, a threaded through hole, a positioning step, an exhaust hole, etc. The cavity is used to form the outer semicircle of a composite cylindrical product. In order to increase the cavity space to eliminate the enrichment of the fluffy reinforcing material at the mold closing position during the mold closing process, the cavity cross section is set to a semi-ellipse, the major axis of the semi-ellipse is set to 420.5±0.05mm, and the minor axis changes gradually with the outer circle size of the core mold. The cavity length is set to 453±0.8mm, which is convenient for the placement and demolding of the core mold. The mold surface of the cavity is set with an inclination along the length direction, the large end radius is set to Φ210.25±0.025, and the small end radius is set to Φ199.75±0.025mm. The core mold limiting steps are set at both ends of the cavity. When the mold is assembled, the core mold limiting steps are placed on the core mold. The cavity formed by the core mold and the upper mold is the reinforcing material and resin filling area, and the step height is 10±0.1mm. 12 screw holes with a diameter of Φ11mm and 4 M6 mm threaded through holes are set on the outer edge of the upper mold surface, which are used for the connection of the upper and lower molds and the demoulding of the upper mold respectively. A sunken area is set on the edge of the upper mold surface as a positioning step for matching with the lower mold. The step height is 8.5mm. The positioning steps of the upper and lower molds are matched with a small gap in the width direction for the precise positioning of the upper mold in the width direction. The symmetry of the upper mold positioning step relative to the upper mold cavity is ≤0.05mm. An exhaust hole is set at the edge of the end face of the upper mold surface. The exhaust hole passes through the core mold limiting step. The exhaust hole consists of a light hole section and a sealing thread section. The diameter of the light hole section is Φ4mm, and the sealing thread specification is NPT 3 / 8. The sealing thread section is used for connection and sealing with the joint. The light hole section is used as a discharge channel for resin and air. The diameter of the light hole section is Φ4mm. The mold frame is mainly used to support the upper mold surface and increase the rigidity of the upper mold. The mold frame is composed of multiple steel plates, and multiple large-sized holes are opened on the frame steel plates. On the one hand, it plays a role in weight reduction, and on the other hand, it can reduce the impact of the frame steel plates on hot air convection and product heating during the curing process. Multiple reinforcing ribs are set around the frame to increase the rigidity of the screw connection position at the edge of the upper mold surface, reduce the deformation of the upper mold surface during screw installation and pressurized injection, and prevent structural damage and sealing problems caused by deformation.

[0043] The sealing ring is used to seal the mold surface. The sealing ring adopts an integrally formed silicone rubber O-ring with a suitable length and a wire diameter of 5mm.

[0044] The joint is used to connect the mold to the pipeline. The end connected to the mold adopts NPT 3 / 8 sealing pipe thread, and the other end is connected to the pipeline.

[0045] The length direction position of the core mold in the lower mold cavity is limited by the cavity, and a gap of 1-2mm is maintained between the two end faces of the core mold and the cavity; the width direction position is self-positioned by the core mold limit step. When installing the upper mold, the length direction is limited by the core mold, and the width direction is accurately positioned by the positioning steps of the upper and lower molds. The upper and lower molds are fixed and pre-tightened with screws, flat washers and spring washers. The upper and lower mold joint surfaces are sealed by two sealing rings to form a closed cavity inside the cavity. Setting the sealing structure composed of multiple sealing rings on the upper and lower mold joint planes can significantly reduce the difficulty of sealing ring arrangement, improve the reliability of the airtight structure, and facilitate the inspection of airtightness problems.

[0046] A composite material cylindrical part RTM molding process implementation method and steps are as follows:

[0047] (1) Mold treatment: Use alcohol or acetone to clean the mold, and then apply the release agent after drying.

[0048] (2) Material preparation: The carbon fiber cloth is cut into appropriate sizes according to a preset fiber angle. The fiber cloth can be made into a preform by knitting or the like. Epoxy resin is prepared.

[0049] (3) Assembly of reinforcement materials: lay the carbon fiber cloth on the core mold layer by layer according to the preset layup. The layup should be compact and can be pre-bonded with a small amount of epoxy resin spray. The fiber cloths or fiber felts are spliced ​​with a gap of ≤1mm. The seams of each layer should be staggered by 30mm or more. The ends of the layup should be fixed with carbon fiber stitches. Compared with the finished product, a 5-10mm margin is reserved on one side of the reinforcement material after laying. The edges of both ends of the core mold are used as the boundary for vacuum bag packaging. The vacuum is evacuated to -0.090MPa or below, and the vacuum degree of -0.090MPa or below is maintained for more than 30 minutes to pre-compact the reinforcement material.

[0050] (4) Assembly of the core mold: After the pre-compacting of the reinforcement material is completed, remove the vacuum bag, place the core mold in the lower mold cavity, check both ends of the core mold to ensure that there is a 1-2mm gap between both ends and the lower mold cavity, and check whether there are obvious protrusions in the reinforcement material at the upper and lower mold positions. If there are protrusions, use a scraper to evenly scrape them flat. Screw the screws used as handles or hanging points completely into the core mold, and stick polytetrafluoroethylene cloth on the end surface of the core mold to prevent the resin from entering the threaded hole during injection.

[0051] (5) Mold closing: Check and confirm the surface quality and excess materials of the upper and lower molds, and put an O-ring with an appropriate length and a wire diameter of 5mm in the sealing groove of the lower mold. After the sealing ring is placed, there is no obvious distortion or protrusion in the natural state. Slowly place the upper mold on the lower mold and the core mold. The upper mold positioning step and the lower mold positioning step form a small gap in the width direction to achieve width positioning. The two ends of the core mold limit the upper mold. Install the flat washer, spring washer and M10 mm screw in sequence, and use a torque wrench to tighten the screws to 40N·m in multiple times according to the cross-symmetry principle and sequence. Use a 0.02mm thick feeler gauge to check the mold gap. The gap is qualified if it is ≤0.02mm.

[0052] (6) Vacuum inspection: Install joints at the injection hole and exhaust hole, connect the vacuum system, and conduct vacuum inspection. Evacuate to -0.100MPa to -0.090MPa or below, stop evacuating, and the vacuum degree is qualified if the change of vacuum degree does not exceed 0.010MPa within 5 minutes after the vacuum degree stabilizes.

[0053] (7) Resin degassing: Place the prepared resin in a vacuum tank and evacuate the tank for resin degassing. If there is no obvious bubble overflow within 2 minutes, the degassing is complete. The resin viscosity should be within the range of 0.1-0.8 Pa·s under the injection temperature.

[0054] (8) Resin injection: Use vacuum-assisted resin injection for resin injection. Place the mold with the lower mold at the bottom and the upper mold at the top and perform anti-gravity injection. Connect the injection pipe and the exhaust glue overflow pipe to the joint, turn on the switches of each joint, and inject the resin at an initial pressure of 0.2MPa and increase by 0.05MPa per minute. After 4 minutes, the injection pressure stabilizes at 0.4MPa. When the upper mold exhaust port above the injection hole begins to continuously overflow with bubble-free resin, close the exhaust port joint switch. When another exhaust hole of the upper mold continuously overflows with resin, reduce the injection pressure to 0MPa, close the injection port joint switch, and open all exhaust port joint switches. When there are no bubbles discharged from the exhaust port for 5 consecutive minutes, turn off the vacuum system, remove all pipes, and the injection is completed.

[0055] (9) Curing: Place the entire mold in a curing furnace or oven for curing.

[0056] (10) Demolding: Demolding is performed after curing is completed and the mold has cooled to room temperature. Remove all connecting screws and washers, screw 2-4 M6 mm screws into the threaded holes of the upper mold to push the upper mold out and separate it from the lower mold. Tear off the polytetrafluoroethylene cloth on the end face of the core mold, unscrew the M16 mm countersunk screw as a handle, and remove the core mold vertically from the lower mold cavity. Push the core mold out of the product, with the force direction pointing from the small end of the core mold to the large end.

[0057] (11) Post-processing: clean the resin on the mold surface of the product, polish the mold line to make it smooth, cut off or process the excess area on the end surface of the product to obtain a composite cylindrical product.

[0058] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A composite material cylindrical part RTM molding die, characterized in that: Including core mold, upper mold, lower mold, sealing ring, joint, The lower mold comprises a mold frame, a lower mold surface arranged in the mold frame, the lower mold surface is connected to a lower mold cavity, two ends of the lower mold cavity are provided with core mold limiting steps, the outer periphery of the lower mold cavity is provided with a sealing groove, the edge of the lower mold surface is provided with a positioning step, the lower mold surface is connected to an injection hole, and the injection hole is connected to a pipeline through a joint; The upper mold comprises a mold frame, an upper mold surface arranged in the mold frame, the upper mold surface is connected to an upper mold cavity, core mold limiting steps are arranged at both ends of the upper mold cavity, a positioning step is arranged at the edge of the upper mold surface, and an exhaust hole is connected to the upper mold surface, the exhaust hole passes through the core mold limiting step, and the exhaust hole is connected to the pipeline through a joint; The core mold is a hollow cylindrical part with closed ends, and the core mold is arranged between the upper mold and the lower mold; the core mold surface is set with an inclination, and the large end diameter is set to: the maximum limit size of the inner diameter of the cylindrical part - (10%-20%) inner diameter tolerance value, and the small end diameter is set to: the minimum limit size of the inner diameter of the cylindrical part + (10%-20%) inner diameter tolerance value; The sealing ring is an integrally formed sealing ring, which is arranged in the sealing groove, and forms a sealing structure with the sealing groove of the lower mold and the mating surface of the upper mold. Two sealing grooves are set within the injection pressure range of 0-0.4MPa, and three sealing grooves are set above the injection pressure of 0.4MPa.

2. The RTM forming mold for composite cylindrical parts according to claim 1, characterized in that: The exhaust hole and the injection hole respectively include a smooth hole section and a sealing thread section, the sealing thread section is connected and sealed with the joint, the smooth hole section serves as a flow channel, and the diameter of the smooth hole section is smaller than the inner diameter of the pipe connected to the joint.

3. The RTM forming mold for composite cylindrical parts according to claim 1, characterized in that: The cross-sections of the lower model cavity and the upper model cavity are semi-elliptical, the major axis of the semi-ellipse is set to: the maximum limit size of the outer diameter of the cylindrical part - (10% to 20%) the outer diameter tolerance value, and the minor axis gradually changes with the outer circle size of the core mold; the molding surfaces of the lower model cavity and the upper model cavity are set with an inclination along the length direction, and the inclination value is 30%-40% of the outer diameter tolerance value.

4. A molding method using the RTM molding mold for composite tubular parts according to any one of claims 1 to 3, characterized in that: The steps include: S1, laying fiber felt and fiber cloth on the core mold layer by layer, or inserting the cylindrical part preform made of fiber felt and fiber cloth into the core mold from the small end to the large end of the core mold, vacuum bag packaging with the edges of both ends of the core mold as boundaries, and vacuumizing to pre-compact the reinforcement material; S2. Remove the vacuum bag, place the core mold into the lower mold cavity, put the sealing ring in the sealing groove of the lower mold, slowly place the upper mold on the lower mold and the core mold, and the positioning steps of the upper mold and the lower mold form a small gap in the width direction to achieve width positioning. The two ends of the core mold limit the upper mold; install flat washers, spring washers and screws in sequence, and use a torque wrench to tighten the screws to the same torque in multiple times according to the cross-symmetry principle and sequence; use a 0.02mm thick feeler gauge to check the mold clearance, and the clearance ≤0.02mm is qualified. S3. Install joints at the injection hole and exhaust hole, connect the vacuum system, and perform vacuum degree detection; S4, using vacuum-assisted resin injection to evacuate the air inside the mold to a vacuum state before performing resin injection, placing the mold in a manner where the lower mold is at the bottom and the upper mold is at the top, and performing anti-gravity injection; S5. Place the entire mold in a curing furnace or oven for curing. After the curing is completed and the mold is cooled to room temperature, demoulding and post-processing are performed.

5. A molding method according to claim 4, characterized in that: In the step S4, before injection, the prepared resin is placed in a vacuum tank and vacuumed to degas the resin. The degassing is completed if there is no obvious bubble overflow within 2 minutes.

6. A molding method according to claim 4, characterized in that: In the step S1, the fiber cloths or fiber felts are spliced ​​with a splicing gap of ≤1 mm, the seams of each layer are staggered by a distance of ≥30 mm, and the ends of the plies are fixed by needle stitching using reinforcing material fibers; the vacuum bag is evacuated to -0.100 MPa to -0.090 MPa, and the vacuum degree of -0.100 MPa to -0.090 MPa is maintained for 30-40 minutes.

7. A molding method according to claim 4, characterized in that: In step S2, check the two ends of the core mold to ensure that the gap between the two ends of the core mold and the lower mold cavity is 1-2 mm, check whether there are bulges in the reinforcing material at the mold closing position of the upper mold and the lower mold, and use a scraper to evenly scrape it if there are bulges; stick polytetrafluoroethylene cloth on the end surface of the core mold.

8. A molding method according to claim 4, characterized in that: In the step S4, the injection pipe and the exhaust and overflow glue pipe are connected to the corresponding joints, the joint switch is turned on, and resin is injected from the injection port of the lower mold with a gradually increasing gradient injection pressure, and the injection pressure range is 0.2-0.6MPa; when the upper mold exhaust port above the injection hole begins to continuously overflow bubble-free resin, the joint switch corresponding to the exhaust port is closed, and when another exhaust hole of the upper mold continuously overflows resin, the injection pressure is reduced to 0MPa, the switch of the injection port joint is closed, and the switches of all exhaust port joints are turned on.

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