In-situ uniform heating, curing and forming device and method for helicopter skin composite material

Abstract

The invention belongs to the technical field of composite material curing forming, and particularly relates to an in-situ uniform heating curing forming device and method for a helicopter skin composite material. The device comprises a forming mold, a temperature control system and a vacuum system, the forming mold comprises a bottom supporting block and a graphene heating layer arranged on the upper surface of the bottom supporting block. The graphene heating layer sequentially comprises upper tooling cloth, a graphene film, a heat insulation material and lower tooling cloth from top to bottom; a plurality of groups of electrodes and thermocouples are distributed in the graphene film; the heat insulation material is used for preventing heat from being conducted downwards; the lower tool cloth is in contact with the upper surface of the bottom supporting block; the temperature control system receives a measurement signal from the thermocouple and controls the heating power of the electrode according to the measurement signal; based on real-time temperature information sensed by a thermocouple, heating power of electrodes at different positions is controlled, so that a graphene edge area with relatively fast heat dissipation and a central area with relatively slow heat dissipation have the same heating rate, and the temperature uniformity of a graphene film is ensured, so that the prepreg is uniformly heated; the vacuum system is arranged outside the forming mold and used for forming and maintaining a vacuum environment in the curing forming process.

Description

Technical Field

[0001] This invention belongs to the field of composite material curing and molding technology, specifically relating to an in-situ uniform heating curing and molding device and method for helicopter skin composite materials. Background Technology

[0002] Helicopter skin is the outer structure covering the fuselage, rotor, and other parts. It needs to meet requirements such as aerodynamic shape, protection of internal structure, and bearing aerodynamic loads. With the continuous iteration and development of helicopter models, the manufacturing materials of helicopter skin have been gradually changed from metal materials such as aluminum alloy and titanium alloy to composite materials such as carbon fiber and glass fiber. This meets the requirements of helicopter structure for lightweighting, achieving weight reduction and improving maneuverability and load capacity.

[0003] Helicopter skin made from composite materials is typically manufactured using a prepreg process (where reinforcing fibers are pre-impregnated into an uncured resin matrix), followed by a specific layup design and high-temperature curing. High-temperature curing of the prepreg refers to the process of forming a stable interfacial bond between the reinforcing material and the matrix material through physical or chemical action. Currently, autoclave molding is the most commonly used method for curing helicopter skin composite materials.

[0004] An autoclave is a large pressure vessel with an integrated heating system. A typical autoclave molding system consists of a tank body, cooling system, vacuum system, pressure system, heating system, sealing system, and control system. The working principle of autoclave molding is to use the pressure generated by high-temperature compressed gas inside the tank to heat and pressurize the composite material blank to complete the curing process. Autoclave molding technology can produce composite material parts of various shapes, and due to this advantage, autoclaves are widely used in the production of aerospace components. However, because autoclaves have very high requirements for dimensions, temperature, and pressure, their manufacturing costs are quite high. In addition, auxiliary equipment, such as air or ammonia pipelines, cooling pipelines, heating furnaces, and monitoring equipment, also increase costs. The total cost of a large industrial autoclave and auxiliary equipment is approximately 1 million yuan. The high manufacturing costs caused by the autoclave molding process have attracted considerable attention.

[0005] During the curing process of prepreg, the uniformity of the ambient temperature field directly affects the final molding quality of the product. Uneven heating of the prepreg during curing will cause various defects in the molded composite material, such as local delamination and excessive porosity. As the composite material parts used in modern large helicopters become increasingly complex in contour and larger in size, traditional autoclave processes cannot achieve uniform heating of the prepreg in the edge areas of the parts, and can no longer meet the actual application requirements of new product manufacturing. Therefore, there is an urgent need to develop a new non-autoclave molding process that can achieve uniform heating of the prepreg, and is energy-saving, environmentally friendly, safe, reliable, and easy to operate.

[0006] With the continuous iteration and upgrading of prepreg curing methods, the concept of in-situ curing has received widespread attention. This involves directly curing the prepreg after layup on the prepreg molding die. This requires addressing two key issues: the uniformity of temperature and the uniformity of external pressure during the curing process.

[0007] Graphene is a novel material composed of only a single carbon atom layer (0.335 nm) thick, making it the thinnest two-dimensional material in the world. It also possesses stable mechanical properties, superior electrical and thermal conductivity, and an extremely large specific surface area. The electron mobility of a single-layer graphene is 200,000 cm⁻¹. 2 V -1 s -1 It has a Young's modulus and tensile strength as high as 1 TPa and 130 GPa, respectively, and a specific surface area as high as 2600 m². 2 g -1 Pure, defect-free monolayer graphene has a thermal conductivity as high as 5300 W / m·K, making it the carbon material with the highest thermal conductivity to date, but its density is only 2.2 g / cm³. -3 It has significant application prospects in materials science, micro-nano fabrication, aerospace and other fields, and is considered a revolutionary material for the future.

[0008] Vacuum bagging is a molding method that uses vacuum pressure to press prepreg tightly against the surface of a molding die and creates a vacuum by removing air. A vacuum environment means that the prepreg can be uniformly compressed under negative pressure.

[0009] During the prepreg curing process, the molding device is a precision working unit that integrates molding molds, vacuum systems, and heating systems. High-quality molding of composite materials requires the efficient collaborative work of molding molds, vacuum systems, and heating systems. The molding molds give the product shape and dimensional accuracy; the vacuum system provides and controls the pressure required for curing; and the heating system provides and precisely controls the temperature required for curing.

[0010] In summary, this invention uses graphene film as the basic electrothermal element, divides the surface of the graphene film into regions and places thermocouples and electrodes thereon, and senses temperature information at different locations in real time to adjust the electrode power in different regions, so that the prepreg is heated uniformly. In addition, this invention uses vacuum bag technology to provide uniform external pressure, and based on the concept of in-situ curing and pressurization, proposes an in-situ uniform heating curing molding device and method for helicopter skin composite materials. Summary of the Invention

[0011] The purpose of this invention is: The purpose of this invention is to solve the problems of long curing cycle, high energy consumption and poor heating uniformity of large parts in traditional autoclave molding process, and to propose an in-situ uniform heating curing molding device and method for helicopter skin composite materials.

[0012] The technical solution of this invention is: To achieve the above objectives, according to a first aspect of the present invention, an in-situ uniform heating and curing molding device for helicopter skin composite materials is provided, comprising a molding die, a temperature control system, and a vacuum system; The molding die includes a bottom support block and a graphene heating layer disposed on the upper surface of the bottom support block; The graphene heating layer comprises, from top to bottom, an upper tooling cloth, a graphene film, a heat insulation material, and a lower tooling cloth; the graphene film contains multiple sets of electrodes and thermocouples; the heat insulation material is used to prevent heat from being conducted downwards; the lower tooling cloth is in contact with the upper surface of its corresponding bottom support block. The temperature control system receives measurement signals from thermocouples and controls the heating power of the electrodes accordingly. Based on the real-time temperature information sensed by the thermocouples, the heating power of electrodes at different positions is controlled so that the graphene edge region with faster heat dissipation and the center region with slower heat dissipation have the same heating rate, ensuring the temperature uniformity of the graphene film and thus making the prepreg uniformly heated. The vacuum system is located outside the molding die and is used to create and maintain a vacuum environment during the curing process.

[0013] In one possible embodiment, the temperature control system includes: a power supply and a temperature control computer; the power supply is electrically connected to the electrodes, thermocouples, and temperature control computer respectively, and is used to provide voltage to the electrodes, thermocouples, and temperature control computer; the temperature control computer is electrically connected to the electrodes and thermocouples, and is used to monitor the temperature of each area in real time, and calculate and set the electrode power, heating rate, and holding time according to the heating target temperature.

[0014] In one possible embodiment, the vacuum system includes: a vacuum bag, a breathable felt, a membrane, a vacuum port, and an air pump; the vacuum bag is used to seal and provide uniform vacuum pressure; the breathable felt is used to guide airflow to the vacuum port and block resin penetration; the membrane is used to cover the prepreg to avoid contamination; the vacuum port is used to connect the vacuum bag to an external air pump and serve as a gas exhaust channel; the air pump is used to extract air from the bag to create and maintain a vacuum environment.

[0015] In one possible embodiment, the upper tooling fabric and the lower tooling fabric are made of either epoxy resin-based composite material or bismaleimide resin-based composite material.

[0016] In one possible embodiment, the graphene film is divided into multiple partitions according to the shape of the inner surface of the bottom support block, and the electrodes and thermocouples built into each partition are independently controlled.

[0017] In one possible embodiment, the insulation material is either foam or aerogel.

[0018] In one possible embodiment, the upper tooling fabric, graphene film, heat insulation material, and lower tooling fabric in the graphene heating layer are integrally formed by co-curing, and the electrodes and thermocouples are directly embedded inside the graphene film during the curing process.

[0019] In one possible embodiment, the graphene heating layer is glued to the bottom support block to ensure that slippage does not occur during the layup process.

[0020] In one possible embodiment, the bottom support block is made of steel.

[0021] In one possible embodiment, the bottom support block adopts an internal hollow structure to reduce manufacturing costs, provided that the strength of the molding die is met.

[0022] The upper tooling fabric, graphene film, heat insulation material, lower tooling fabric, and bottom support block that make up the molding die are all CNC machined according to the actual product shape, so that the shape of the molding die is consistent with the product shape.

[0023] According to a second aspect of the present invention, an in-situ uniform heating and curing method for helicopter skin composite materials is provided, employing the aforementioned in-situ uniform heating and curing molding apparatus for helicopter skin composite materials, comprising the following steps: Step 1: Place the prepreg to be cured on the surface of the molding die, and set the electrode heating power in the graphene film to achieve the target prepreg resin flow temperature T1, and then energize and heat it. The purpose of heating up at this time is to preheat the molding die, so that the resin fluidity is enhanced when the prepreg comes into contact with the molding die, making it easier to lay up.

[0024] Step 2: After the layup is completed, a vacuuming operation is performed using a vacuum system; The purpose of vacuuming is to provide the uniform external pressure required for the curing of prepreg; Step 3: After vacuuming, the graphene film is heated a second time to achieve the prepreg curing temperature T2. The electrode heating power inside the graphene film is set to achieve the target temperature T2. The film is then heated by electricity. The temperature is then maintained according to the prepreg curing curve to achieve in-situ uniform curing.

[0025] Prepreg curing is an exothermic process. By using real-time temperature information from thermocouples, local overheating caused by curing heat can be effectively avoided. That is, during the heat preservation stage, when the thermocouple temperature in a certain area exceeds the target temperature, the electrode power in that area is appropriately reduced to avoid overheating the prepreg and causing internal damage.

[0026] In one possible embodiment, in step 1, to meet the requirements of the prepreg molding process, the heating rate during the preheating process is typically selected to be between 1°C / min and 2°C / min.

[0027] In one possible embodiment, in steps 1 and 3, electrodes are arranged at the edges of different regions of the graphene film, and the temperature control computer adjusts the heating power of the electrodes in different regions according to the real-time temperature information of the thermocouples, until the maximum temperature difference displayed by all thermocouples is less than 5°C.

[0028] As a further explanation of the present invention, in step 3, in order to meet the requirements of the prepreg molding process, the heating rate during the second heating can typically be selected in the range of 0.5℃ / min to 2℃ / min.

[0029] The advantages of this invention are: (1) The present invention is a process method for in-situ uniform heating of graphene film and in-situ uniform pressure molding of helicopter skin composite material in vacuum bag, which is a brand-new composite material molding scheme.

[0030] (2) The present invention uses graphene film as a heating component and designs it for zoned heating. By arranging multiple thermocouples and electrodes, the power of electrodes at different positions is adjusted based on the temperature feedback of thermocouple sensing information, so that the temperature of the edge area and the center area of ​​the graphene film are the same, ensuring that the prepreg is heated evenly during the curing process. At the same time, it can avoid the local overheating phenomenon caused by the heat release of the prepreg curing, and realize high-quality molding of helicopter skin.

[0031] (3) During the prepreg layering, the present invention can preheat the molding die by using graphene film to improve resin fluidity and thus improve the prepreg coverage, thereby further ensuring the high-quality molding of helicopter skin.

[0032] (4) The present invention forms a vacuum system based on vacuum bag technology, which can provide uniform vacuum pressure for any complex molding mold. It is extremely compatible with the graphene-based uniform heating system. It does not require entering the high-energy-consuming equipment autoclave or curing oven, which greatly reduces the equipment cost and energy consumption cost in the prepreg manufacturing process. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the in-situ uniform heating and curing molding device for helicopter skin composite material of the present invention. Figure 2 This is a schematic diagram (concave mold) of the graphene in-situ uniform heating molding mold of the present invention. Figure 3 This is a schematic diagram of the thermocouple array, electrodes, and temperature control system inside the graphene film of the present invention; In the diagram: 1. Molding mold; 11. Bottom support block; 12. Integrated structure of the upper surface of the molding mold; 121. Lower tooling fabric; 122. Thermal insulation material; 123. Graphene film; 1231. Thermocouple; 1232. Electrode; 124. Upper tooling fabric; 2. Prepreg; 3. Adhesive film; 4. Breathable felt; 5. Vacuum bag; 6. Vacuum port; 7. Air pump; 8. Power supply; 9. Temperature control computer. Detailed Implementation

[0034] To make the objectives, technical solutions, and priorities of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] like Figure 1 As shown, a graphene in-situ heated and pressurized helicopter skin composite material molding device includes a molding die, a temperature control device, and a vacuum system.

[0036] The molding die 1 includes a bottom support block 11, an integral upper surface structure 12, a lower tooling cloth 121, a heat insulation material 122, a graphene film 123, a thermocouple 1231, an electrode 1232, and an upper tooling cloth 124. The entire molding die 1 structure, from top to bottom, consists of the upper tooling cloth 124, the graphene film 123, the heat insulation material 122, and the bottom support block 11. The thermocouple 1231 and the electrode 1232 are located inside the graphene film 123.

[0037] As a further explanation of the present invention, the upper tooling fabric 124 and the lower tooling fabric 121 can be made of either epoxy resin-based prepreg or bismaleimide resin-based composite material.

[0038] As a further explanation of the present invention, the thermal insulation material 122 can be any one of foam or aerogel.

[0039] As a further explanation of the present invention, the electrode 1232 material can be silver.

[0040] As a further explanation of the present invention, the upper tooling fabric 124, the graphene film 123, the heat insulation material 122, and the lower tooling fabric 121 are integrally formed by co-curing, and the electrode 1232 and the thermocouple 1231 are directly embedded inside the graphene film 123 during the curing process.

[0041] As a further explanation of the present invention, the upper tooling fabric 124, graphene film 123, heat insulation material 122, and lower tooling fabric 121, which are co-cured and integrally molded, are bonded together with the bottom support block 11 by a secondary adhesive bonding method to ensure that the prepreg 2 will not slip during the layup.

[0042] As a further illustration of the present invention, the bottom support block 11 is made of steel.

[0043] As a further explanation of the present invention, under the condition of satisfying the strength and rigidity of the molding die, the bottom support block 11 adopts an internal hollow structure to reduce manufacturing costs.

[0044] As a further explanation of the present invention, the outer shapes of the upper tooling cloth 124, graphene film 123, heat insulation material 122, lower tooling cloth 121 and bottom support block 11 constituting the molding die are all CNC machined according to the actual product shape, so that the outer shape of the molding die 1 is consistent with the product shape.

[0045] As a further explanation of the present invention, an array of thermocouples 1231 is placed on the surface of the graphene film 123 for temperature measurement to ensure that the temperature field on the entire surface of the graphene film 123 is uniform.

[0046] The temperature control system consists of a temperature control computer 9 and a power supply 8. The heating method adopts a zoned heating method. The control computer 9 is used to set parameters such as the heating rate and target temperature, and the power supply 8 is used to provide the rated voltage.

[0047] As a further explanation of the present invention, the temperature control system controls the heating power of electrodes 1232 at different positions through the temperature control computer 9 program, so that the edge region and the middle region of the graphene 123, which dissipates heat faster, have the same heating rate, ensuring the temperature uniformity of the graphene film 123, thereby ensuring that the prepreg 2 is heated evenly.

[0048] The vacuum system comprises a film 3, a breathable felt 4, a vacuum bag 5, a vacuum port 6, and an air pump 7. The vacuum bag 5 is used for sealing and providing uniform vacuum pressure during the curing process; the breathable felt 4 is used to guide airflow to the vacuum port 6 and prevent resin penetration from the prepreg 2; the film 3 is used to cover the prepreg 2 to avoid contamination; the vacuum port 6 is used to connect the vacuum bag 5 to the external air pump 7, serving as a gas exhaust channel; the air pump 7 is used to extract air from inside the vacuum bag 5, forming and maintaining a vacuum environment.

[0049] A method for in-situ uniform heating and curing of helicopter skin composite materials includes the following steps: (1) Clean the surface of the helicopter skin composite material molding mold 1 and spray a release agent to facilitate the demolding of the cured product; (2) Place the prepreg 2 to be cured on the surface of the molding die 1, and then heat the graphene film 123 by electric current to reach the high resin flow temperature T1. (3) Based on the prepreg 2 layup information, the prepreg 2 is laid layer by layer onto the surface of the mold 1 manually; (4) After the layering is completed, the surface of the molding mold 1 is covered with a vacuum bag 5 and a vacuuming operation is performed.

[0050] (5) After the vacuuming is completed, the graphene material 123 is heated a second time to reach the curing temperature T2 of the prepreg 2. Then, the prepreg 2 is kept warm according to the curing curve to achieve in-situ curing.

[0051] (6) After curing, turn off the power supply 8 and let it cool to room temperature naturally. Then remove the vacuum bag 5, the breathable felt 4, and the adhesive film 3 in sequence to obtain the molded helicopter skin material.

[0052] It is worth noting that in the helicopter skin in-situ curing method proposed in this paper, the graphene film 123 is energized by the power source 8 to generate heat, providing the temperature conditions required for the curing of the prepreg 2. Since the graphene film 123 adopts a zoned heating temperature control method, the prepreg 2 can be heated uniformly. The method of this invention can achieve efficient in-situ uniform curing and molding of the prepreg 2.

[0053] To further explain, when using the autoclave process for curing and molding, it takes about 10 hours to complete the curing process, which not only affects production efficiency but also leads to a large consumption of electricity.

[0054] The graphene in-situ uniform heating and pressure curing method proposed in this paper can complete the entire preheating-layout-curing process in about 4 hours. It only requires a voltage of 220V or less to power it, which greatly saves energy consumption. Preheating during the layup process will also improve the layup properties of the prepreg 2, and the helicopter skin has excellent curing and molding effects.

[0055] Specifically, in step (2), the initial heating rate V1 and the target temperature T1 are first set by the temperature control computer 9, and then the power supply 8 is turned on to power the graphene film 123 to generate heat. Since the heat insulation material 122 is below the graphene film to prevent the heat from being conducted downward, the heat generated by the graphene film 123 will be conducted upward to achieve the purpose of preheating the molding mold 1.

[0056] To further clarify, the adjustable heating rate range is 0.5℃ / min to 2℃ / min.

[0057] To further explain, by preheating the molding mold 1, the resin fluidity can be improved, allowing the prepreg 2 to easily conform to the shape of the molding mold 1.

[0058] To further explain, the temperature at which prepreg resin has good flowability is typically between 60°C and 70°C.

[0059] Specifically, in step (3), the prepreg 2 is laid onto the surface of the molding mold 1 manually according to the actual product layup information. At the same time, the laying effect of the prepreg 2 is detected and corrected by visual inspection.

[0060] Specifically, in step (4), after the prepreg 2 is laid up, the prepreg 2 is wrapped with a film 3, covered with a breathable felt 4, and then the entire surface of the molding die 1 is covered with a vacuum bag 5. After the bag is made, the air pump 7 performs vacuuming treatment on the inside of the vacuum bag 5 through the vacuum port 6. The condition for completing the vacuuming is that the vacuum degree inside the vacuum bag 5 reaches 0.08 MPa until the vacuum degree stabilizes. After 15 minutes, the air pump 7 is turned off or shut off. The vacuum gauge reading should not drop by more than 0.017 MPa within 5 minutes.

[0061] To further explain, the purpose of vacuuming is to provide the external pressure required for the curing of the prepreg 2 through the vacuum bag 5.

[0062] To further explain, the vacuum bag process can provide a vacuum environment for molding dies 1 of any shape. When it is difficult to vacuum a certain part of a complex-shaped molding die 1, an additional vacuum port 6 can be added in the vicinity to achieve the purpose of providing uniform vacuum pressure.

[0063] Specifically, in step (5), the secondary heating rate V2 and the target temperature T2 are first set by the temperature control computer 9, and then the power supply 8 is turned on to further heat up the graphene film 123. After reaching the target temperature T2, the heat preservation time is set according to the curing curve of the prepreg 2.

[0064] To further explain, the graphene film 123 is designed with partitions, and thermocouples 1231 are placed in different regions to realize real-time temperature information sensing to the temperature control computer 9.

[0065] To further explain, electrodes 1232 are arranged at the edges of different regions of the graphene film 123. The temperature control computer 9 adjusts the heating power of the electrodes 1232 in different regions according to the real-time temperature information of the thermocouples 1231, so that the maximum temperature difference displayed by all thermocouples 1231 is less than 5°C.

[0066] To further explain, since the edge effect results in lower heat dissipation at the edge of graphene 123, the heating power of the central region electrode 1232 can be set to 50%-80% of the power of the edge region electrode 1231 when setting the power. The specific value needs to be adjusted according to the actual temperature information.

[0067] To further clarify, power adjustment should be completed before reaching the curing temperature T2 to ensure that the prepreg 2 is heated evenly throughout the insulation stage.

[0068] To further explain, the curing of prepreg is an exothermic process. By using the temperature information sensed in real time by thermocouple 1231, local overheating caused by exothermic processes can be effectively avoided. That is, during the heat preservation stage, when the temperature of thermocouple 1231 exceeds the target temperature, the power of electrode 1232 in that area is appropriately reduced to avoid overheating of the prepreg 2 and causing internal damage.

[0069] To further explain, in order to meet the molding process requirements of prepreg 2, the heating rate during the second heating can typically be selected within the range of 0.5℃ / min to 2℃ / min.

[0070] Specifically, in step (6), after curing is completed, the power supply 8 is turned off. After the temperature display of thermocouple 1232 cools down to room temperature, the vacuum bag 5, breathable felt 4 and adhesive film 3 are removed, and the cured helicopter skin is taken out.

[0071] In summary, this invention provides a novel in-situ uniform heating and curing method for prepreg composite materials used in helicopter skin molding. By embedding graphene within the molding die as a heating element, heat is generated through electrical current. Differential power distribution between the electrodes in the edge and center regions ensures uniform heating throughout the prepreg curing process. By covering the molding die with a vacuum bag and creating a vacuum, the necessary external pressure for prepreg curing is provided, ultimately creating an in-situ molding device that provides uniform temperature and pressure. This replaces the energy-intensive and time-consuming autoclave curing process, significantly reducing production costs in the prepreg curing process. Furthermore, during the prepreg layup process before molding, the graphene film can also provide heat to preheat the molding die, improving resin flowability and thus enhancing the prepreg's layup properties, which is beneficial for high-quality molding of helicopter skin composite materials.

[0072] The technical solution will be further illustrated below with reference to the embodiments.

[0073] Example 1 This embodiment describes a curing method for flat composite material parts, using a medium-temperature resin system prepreg as the raw material, and includes the following steps: (1) Clean the surface of the molding mold with a cleaning agent and spray a release agent. Place the prepreg to be cured on the surface of the molding mold, then turn on the power of the temperature control system, set the heating rate of the graphene film to 1.5℃ / min and the target temperature to 60℃ through the temperature control computer. After reaching the target temperature, lay the prepreg according to the layup information of [0° / 45° / 90° / 90° / 45° / 0° / 0° / 45° / 90° / 90° / 45° / 0°] and visually inspect the laying effect.

[0074] (2) After the layup is completed, wrap the prepreg with a film, and then cover the surface of the prepreg with a breathable felt. Cover the surface of the molding die with a vacuum bag, turn on the air pump to evacuate through the vacuum port until the vacuum degree in the vacuum bag reaches 0.08 MPa and remains stable. After 15 minutes, turn off or shut off the vacuum source and observe whether the vacuum gauge reading drops by more than 0.017 MPa within 5 minutes. If it does not, it means that the vacuum degree meets the usage conditions.

[0075] (3) After the vacuuming is completed, the heating power of the electrode in the edge area of ​​the graphene film is first set to 70% of the power in the center area, and then adjusted appropriately according to the thermocouple temperature information during the heating process until the maximum temperature difference shown by all thermocouples is less than 5℃. The temperature of the graphene film is raised to 125℃ at a heating rate of 1.5℃ / min, and then kept at 125℃ for 1.5h. After the heat preservation is completed, the power is turned off, and after natural cooling, the vacuum bag, breathable felt and adhesive film are removed in sequence, and the cured medium-temperature resin composite material plate is taken out.

[0076] Example 2 This embodiment describes a curing method for U-shaped composite material parts, using a high-temperature resin prepreg as the raw material, and includes the following steps: (1) Clean the surface of the molding mold with a cleaning agent and spray a release agent. Place the prepreg to be cured on the surface of the molding mold, then turn on the power of the temperature control system, set the heating rate of the graphene film to 2℃ / min and the target temperature to 60℃ through the temperature control computer. After reaching the target temperature, lay the prepreg according to the layup information of [0° / 45° / 90° / 90° / 45° / 45° / 90° / 90° / 45° / 0°] and visually inspect the laying effect.

[0077] (2) After the layup is completed, wrap the prepreg with a film, and then cover the surface of the prepreg with a breathable felt. Cover the surface of the molding die with a vacuum bag, turn on the air pump to evacuate through the vacuum port until the vacuum degree in the vacuum bag reaches 0.08 MPa and remains stable. After 15 minutes, turn off or shut off the vacuum source and observe whether the vacuum gauge reading drops by more than 0.017 MPa within 5 minutes. If it does not, it means that the vacuum degree meets the usage conditions.

[0078] (3) After the vacuuming is completed, due to the curved geometry of the U-shaped structure, the edge forms a discontinuous curved surface, and the effective heat dissipation area is greater than that of the flat plate structure. First, the heating power of the electrode in the edge area of ​​the graphene film is set to 60% of the power in the center area. According to the thermocouple temperature information during the heating process, it is adjusted appropriately until the maximum temperature difference shown by all thermocouples is less than 5℃. Then, the temperature of the graphene film is raised to 180℃ at a heating rate of 2℃ / min. After that, it is kept at 180℃ for 2 hours. After the heat preservation is completed, the power is turned off. After natural cooling, the vacuum bag, breathable felt and adhesive film are removed in sequence, and the cured high-temperature resin composite material U-shaped plate is taken out.

Claims

1. A device for in-situ uniform heating and curing of helicopter skin composite materials, characterized in that, Including molding dies, temperature control systems, and vacuum systems; The molding die includes a bottom support block and a graphene heating layer disposed on the upper surface of the bottom support block; The graphene heating layer comprises, from top to bottom, an upper tooling cloth, a graphene film, a heat insulation material, and a lower tooling cloth; the graphene film contains multiple sets of electrodes and thermocouples; the heat insulation material is used to prevent heat from being conducted downwards; the lower tooling cloth is in contact with the upper surface of its corresponding bottom support block. The temperature control system receives measurement signals from thermocouples and controls the heating power of the electrodes accordingly. Based on the real-time temperature information sensed by the thermocouples, the heating power of electrodes at different positions is controlled so that the graphene edge region with faster heat dissipation and the center region with slower heat dissipation have the same heating rate, ensuring the temperature uniformity of the graphene film and thus making the prepreg uniformly heated. The vacuum system is located outside the molding die and is used to create and maintain a vacuum environment during the curing process.

2. The in-situ uniform heating and curing molding device for helicopter skin composite materials according to claim 1, characterized in that, The temperature control system includes a power supply and a temperature control computer. The power supply is electrically connected to the electrodes, thermocouples, and temperature control computer to provide voltage to the electrodes, thermocouples, and temperature control computer. The temperature control computer is electrically connected to the electrodes and thermocouples to monitor the temperature of each area in real time and calculate and set the electrode power, heating rate, and holding time based on the target heating temperature.

3. The in-situ uniform heating and curing molding device for helicopter skin composite materials according to claim 1, characterized in that, The vacuum system includes: a vacuum bag, a breathable felt, a membrane, a vacuum port, and an air pump; the vacuum bag is used to seal and provide uniform vacuum pressure; the breathable felt is used to guide airflow to the vacuum port and block resin penetration; the membrane is used to cover the prepreg to avoid contamination; the vacuum port is used to connect the vacuum bag to an external air pump and serve as a gas exhaust channel; the air pump is used to extract air from the bag to form and maintain a vacuum environment.

4. The in-situ uniform heating and curing molding device for helicopter skin composite materials according to claim 1, characterized in that, The upper and lower tooling fabrics are made of either epoxy resin-based composite material or bismaleimide resin-based composite material.

5. The in-situ uniform heating and curing molding device for helicopter skin composite materials according to claim 1, characterized in that, The insulation material can be either foam or aerogel.

6. The in-situ uniform heating and curing molding device for helicopter skin composite materials according to claim 1, characterized in that, The upper tooling fabric, graphene film, heat insulation material, and lower tooling fabric in the graphene heating layer are integrally formed by co-curing, and the electrodes and thermocouples are directly embedded inside the graphene film during the curing process.

7. The in-situ uniform heating and curing molding device for helicopter skin composite materials according to claim 1, characterized in that, The graphene heating layer is glued to the bottom support block to ensure that it will not slip during the laying process.

8. A method for in-situ uniform heating and curing of helicopter skin composite materials, using the in-situ uniform heating and curing molding apparatus for helicopter skin composite materials as described in any one of claims 1-7, comprising the following steps: Step 1: Place the prepreg to be cured on the surface of the molding die, and set the electrode heating power in the graphene film to achieve the target prepreg resin flow temperature T1, and then energize and heat it. Step 2: After the layup is completed, a vacuuming operation is performed using a vacuum system; Step 3: After vacuuming, the graphene film is heated a second time to achieve the prepreg curing temperature T2. The electrode heating power inside the graphene film is set to achieve the target temperature T2. The film is then heated by electricity. The temperature is then maintained according to the prepreg curing curve to achieve in-situ uniform curing.

9. The in-situ uniform heating and curing method for helicopter skin composite materials according to claim 8, characterized in that, In step 1, to meet the requirements of the prepreg molding process, the heating rate during the preheating process is usually selected in the range of 1℃ / min-2℃ / min.

10. The in-situ uniform heating and curing method for helicopter skin composite materials according to claim 8, characterized in that, In steps 1 and 3, electrodes are arranged at the edges of different regions of the graphene film. The temperature control computer adjusts the heating power of the electrodes in different regions according to the real-time temperature information of the thermocouples, until the maximum temperature difference displayed by all thermocouples is less than 5°C.

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