Composite material oil tank and manufacturing method thereof

Abstract

The invention provides a composite material oil tank and a manufacturing method thereof, relates to the technical field of composite material oil tanks, and greatly simplifies the mold manufacturing and assembling process through the integrated design of a modular numerical control mold and a three-dimensional digital model. The die purchasing and processing cost is greatly reduced through partition die assembly and reuse of the supporting prosthesis, repeated investment of a special core die is avoided through accurate matching of the silicone rubber soft die and the air bag, and the laying quality of corners and narrow parts is improved. Through cooperation of two times of curing and a stepped lap joint structure, defects of fiber wrinkles, cavities, bridging and the like are effectively eliminated, and fiber continuity and resin bonding strength of a complex curved surface area are ensured. The finally formed composite material oil tank shell not only has excellent mechanical properties of high strength, high rigidity and light weight, but also has excellent sealing performance and durability, and an efficient and reliable solution is provided for large-scale application of a composite material oil tank with a complex structure.

Description

Technical Field

[0001] This application relates to the field of composite material fuel tank technology, and more specifically, to a composite material fuel tank and its manufacturing method. Background Technology

[0002] Currently, fuel tanks used on drones are mainly divided into two categories: metal fuel tanks and plastic flexible fuel tanks. Metal fuel tanks have high strength and rigidity, but they are usually assembled from multiple parts, resulting in a large overall weight and complex manufacturing process, making integrated production difficult. While plastic flexible fuel tanks have advantages in weight reduction, they require additional support structures for fixation, cannot withstand flight loads, and are prone to punctures and leaks when colliding with sharp parts of the aircraft. In addition, plastic materials are prone to aging and have a short service life, making them unsuitable for long-term use as load-bearing components in drones.

[0003] Composite material integral fuel tanks, with their high specific strength, high specific stiffness, and integrated manufacturing characteristics, can significantly reduce the number of parts and fasteners, lower the structural weight, and bear flight loads to a certain extent, effectively improving sealing and durability. However, when the fuel tank has a complex shape and requires integrated functions, its manufacturing difficulty increases significantly. Vacuum bags at concave and convex surfaces and sharp corners are prone to bridging, leading to defects such as fiber wrinkles and voids. At the same time, it is necessary to optimize the internal structural layout of the fuel tank while ensuring reliable sealing performance and sufficient strength and stiffness after multiple flights.

[0004] Existing publicly available technologies have varying degrees of shortcomings in addressing these issues. Patent CN104044277 B discloses a vacuum-assisted resin transfer molding integral molding process based on water-soluble or fusible mandrels, which enables the integrated manufacturing of composite fuel tanks. However, this process is complex, requiring the fabrication and dissolution of fusible mandrels each time, followed by surface finishing after molding. It is costly and only suitable for fuel tank components with a wall thickness greater than 1 mm and relatively simple structures.

[0005] Patent CN108749029A proposes a method for integral molding using a foam core mold: first, a foam core mold conforming to the required shape is obtained through CNC cutting; then, prepreg is laid on it, cured, and the foam is broken and removed. However, this method is more suitable for the research and development stage or small-batch production. The dimensional tolerances of the molded fuel tank shell are large, the foam breaking process is cumbersome, and the epoxy resin coating on the inner wall is prone to brittle cracks with increasing flight frequency, ultimately leading to oil leakage.

[0006] The document with patent number CN 109555860 A proposes a secondary adhesive bonding sealing and repair method for fuel tanks of all-composite wing components. It can repair minor defects in the short term, but it is difficult to completely eliminate larger defects. Moreover, with the increase of flight flights, the problem of imperfect sealing will still be aggravated, and long-term reliability cannot be guaranteed.

[0007] In summary, existing composite material fuel tank technologies or molding processes are complex and costly, or lack sufficient molding precision and long-term sealing reliability, making it difficult to meet the demands of mass production, low cost, and high quality for complex and integrated UAV fuel tanks. Summary of the Invention

[0008] The purpose of this application is to provide a composite material fuel tank and a method for manufacturing the same, addressing the shortcomings of the aforementioned technologies.

[0009] To achieve the above objectives, the technical solution adopted in this application is as follows: In one aspect of this application, a composite material fuel tank is provided, including a fuel tank shell. The fuel tank shell includes a main shell with an opening at one end, a top cover covering the top of the main shell, and an end cover covering the periphery of the opening end of the main shell. The main shell includes a base and two side shells respectively connected to the top two sides of the base. The base has a first oil storage tank, and each side shell has a second oil storage tank communicating with the first oil storage tank.

[0010] Furthermore, the surface of the tank shell is uneven, the thickness of the side shell is less than the thickness of the base, and the thickness of the side shell gradually increases from the open end to the closed end of the main shell.

[0011] Another aspect of this application provides a method for manufacturing a composite material fuel tank, for manufacturing any of the above-mentioned composite material fuel tanks, the method comprising: Mold preparation: Based on the structural dimensions of the fuel tank shell of the composite fuel tank, a digital model is established. The inner shape of the digital model is consistent with the outer shape of the fuel tank shell. Based on the digital model, the mold is manufactured. The mold includes independently manufactured bottom mold, upper left mold, upper right mold, upper middle mold, and end face mold. The upper left mold and upper right mold are used to assemble on the upper left and upper right of the bottom mold to manufacture the main shell of the fuel tank shell. The upper middle mold is used to assemble on the upper middle of the bottom mold to manufacture the upper cover of the fuel tank shell. The end face mold is used to assemble on the periphery of the end face corresponding to the opening end of the main shell of the bottom mold to manufacture the end cover of the fuel tank shell. Silicone rubber soft mold preparation: Prepreg is laid on the working surfaces of the bottom mold, the upper left mold, and the upper right mold respectively. After the bottom mold, the upper left mold, and the upper right mold are closed and cured, a support prosthesis is formed. The inner shape of the support prosthesis is consistent with the inner shape of the main shell. The A and B components of silicone rubber are mixed and poured into the cavity corresponding to the second oil reservoir of the support prosthesis and the main shell. The vulcanized silicone rubber is removed and the inner silicone rubber is cut off to obtain a silicone rubber soft mold with three sides enclosed. Airbag fabrication: Based on the structural dimensions of the fuel tank shell, airbags are fabricated. The inflated shape of the airbag is consistent with the inner shape of the main shell. Main shell preparation: Prepreg is laid on the working surfaces of the bottom mold, the upper left mold and the upper right mold respectively. After laying, the silicone rubber soft mold is placed at the position corresponding to the side shell of the main shell on the bottom mold. After the bottom mold, the upper left mold and the upper right mold are closed, vacuum curing is performed to form the main shell. Fuel tank shell preparation: Prepreg is laid on the working surfaces of the upper and middle molds and the end molds respectively. After the air bladder is inserted into the main shell, the upper and middle molds and the end molds are closed with the bottom mold, the upper left mold and the upper right mold that have already been closed. The air bladder is then inflated and cured to form the fuel tank shell.

[0012] Furthermore, in the preparation of the main shell, two layers of 0° or 90° carbon fiber prepreg and three layers of 45° or -45° carbon fiber prepreg are laid sequentially from bottom to top on the working surface of the bottom mold. The bottommost carbon fiber prepreg layer extends beyond the working surface of the bottom mold by at least 5 mm on each side, and the upper carbon fiber prepreg layer of the two adjacent layers extends beyond the lower carbon fiber prepreg layer by at least 5 mm on each side.

[0013] Furthermore, in the preparation of the main shell, after the prepreg is laid on the working surface of the bottom mold, pressure strips and auxiliary molding materials covering the pressure strips are arranged in the concave area of ​​the working surface to press the prepreg into the concave area. After the mold is closed and cured, a main shell with an uneven surface is formed.

[0014] Furthermore, in the preparation of the main shell, after laying prepreg on the working surfaces of the bottom mold, the upper left mold, and the upper right mold, a non-porous isolation membrane is fixedly laid on the prepreg layers of the different molds.

[0015] Furthermore, in the preparation of the main shell, after the main shell is formed, the silicone rubber soft mold is removed.

[0016] Furthermore, in the preparation of the fuel tank shell, before inflating the airbag, a baffle is used to seal the opening of the end face mold, and a through hole is opened on the baffle. An air nozzle is inserted through the through hole, one end of the air nozzle is connected to the airbag, and the other end of the air nozzle is connected to the air source.

[0017] Furthermore, in the preparation of the fuel tank shell, the inflation of the airbag includes: inflating the airbag in three stages at inflation pressures of 0.05 MPa, 0.1 MPa, and 0.5 MPa in sequence, so as to expel the air between the airbag and the inner wall of the fuel tank shell and make the outer wall of the airbag fit against the inner wall of the fuel tank shell.

[0018] Furthermore, the airbag is made of a PU membrane that can withstand a pressure of 0.6 MPa.

[0019] The beneficial effects of this application include: This application provides a composite fuel tank and its manufacturing method. Through the integrated design of modular CNC molds and three-dimensional digital models, the mold manufacturing and assembly process is significantly simplified. Partitioned mold assembly and reuse of support prostheses greatly reduce mold procurement and processing costs. Precise matching of the silicone rubber soft mold and the airbag avoids the repeated investment in dedicated core molds and improves the layup quality in corners and narrow areas. Two-stage curing combined with a stepped overlapping structure effectively eliminates defects such as fiber wrinkles, voids, and bridging, ensuring fiber continuity and resin bonding strength in complex curved areas. The final composite fuel tank shell not only possesses excellent mechanical properties such as high strength, high rigidity, and light weight (with a maximum deformation displacement of less than 7mm under 20kPa internal pressure), but also exhibits excellent sealing and durability, and a beautiful surface requiring no secondary finishing. Its high strength and high rigidity design meets flight load requirements, and its dimensional accuracy meets fuselage assembly standards, ensuring a tight fit with the aircraft wings and fuselage. The optimization of the process route and the reuse of resources not only achieved the stability of mass production, but also shortened the manufacturing cycle and reduced the manufacturing cost, providing an efficient and reliable solution for the large-scale application of complex composite material fuel tanks. Attached Figure Description

[0020] Figure 1 A schematic diagram of the structure of a composite material fuel tank shell provided in this application; Figure 2 This application provides a schematic diagram of the main shell structure of a composite material fuel tank. Figure 3 A flowchart illustrating a method for manufacturing a composite material fuel tank provided in this application; Figure 4 This is a schematic diagram of the structure of a mold prepared by the method provided in this application; Figure 5 This is a schematic diagram of the structure of a silicone rubber soft mold prepared by the method provided in this application; Figure 6 This is a schematic diagram of the structure of an airbag prepared by the method provided in this application.

[0021] Icons: 1-Fuel tank housing; 2-Main housing; 3-Top cover; 4-End cover; 5-Base; 6-Side shell; 7-Bottom mold; 8-Upper left mold; 9-Upper right mold; 10-Upper middle mold; 11-End mold; 12-Silicone rubber soft mold; 13-Airbag; 14-Air nozzle; 15-Baffle. Detailed Implementation

[0022] One aspect of this application provides a composite material fuel tank, including a tank housing 1. For example... Figure 1 and Figure 2 As shown, the fuel tank housing 1 includes a main housing 2 with an opening at one end, a top cover 3 covering the top of the main housing 2, and an end cover 4 covering the periphery of the opening end of the main housing 2. The main housing 2 includes a base 5 and two side shells 6 respectively connected to the top two sides of the base 5. A first oil storage tank is formed inside the base 5, and each side shell 6 has a second oil storage tank communicating with the first oil storage tank. The two second oil storage tanks are connected to the first oil storage tank to form an integral oil storage space.

[0023] To accommodate the aircraft's shape requirements, the base 5 is thicker, while the side shells 6 are relatively thinner, resulting in a flat structure. This makes the main shell 2 have a lower center and higher sides. Correspondingly, the first oil storage tank has a greater vertical depth, while the second oil storage tank within the side shell 6 has a smaller vertical depth. Furthermore, the thickness of the side shell 6 gradually increases from the open end to the closed end, and also gradually increases from the end furthest from the base 5 to the end closest to the base 5. That is, the thickness of the front edge of the side shell 6 is less than the thickness of the rear edge, and the thickness of the side shell 6 furthest from the base 5 is less than the thickness of the end closest to the base 5. This makes the oil storage method of the entire oil storage space more reasonable, which helps to improve the load-bearing capacity of the fuel tank. In this embodiment, the fuel tank shell 1 has a wall thickness of 0.6 mm, a maximum length of 835 mm, and a maximum thickness of 180 mm. The thickness of the front edge of the side shell 6 gradually increases from 10 mm to 20 mm in the direction from the end away from the base 5 to the end closer to the base 5, and the thickness of the rear edge of the side shell 6 gradually increases from 30 mm to 50 mm in the direction from the end away from the base 5 to the end closer to the base 5. In addition, the surface of the fuel tank shell 1 is provided with protruding ribs, giving it an uneven surface and enhancing the overall rigidity of the fuel tank shell 1.

[0024] However, due to the complex structure of the tank shell 1, especially the many sharp edges on both sides, the narrow operating space, and the uneven surface, defects such as fiber wrinkles, voids, and bridging often occur when using traditional lay-up molding methods, which in turn affect the strength, sealing performance, and appearance quality of the tank.

[0025] To address these issues, another aspect of this application provides a method for manufacturing a composite material fuel tank, used to manufacture any of the aforementioned composite material fuel tanks, thereby overcoming conventional manufacturing defects and ensuring high-quality production of the fuel tank shell 1, such as... Figure 3 As shown, the method specifically includes the following steps: S1, Mold Preparation: Based on the structural dimensions of the fuel tank shell 1 of the composite material fuel tank, a digital model is established. The inner shape of the digital model is consistent with the outer shape of the fuel tank shell 1. The mold is manufactured based on the digital model, such as... Figure 4 As shown, the mold includes independently manufactured bottom mold 7, upper left mold 8, upper right mold 9, upper middle mold 10, and end mold 11. Upper left mold 8 and upper right mold 9 are respectively used to assemble on the upper left and upper right of bottom mold 7 to manufacture the main shell 2 of the fuel tank shell 1. Upper middle mold 10 is used to assemble on the upper middle of bottom mold 7 to manufacture the upper cover 3 of fuel tank shell 1. End mold 11 is used to assemble on the periphery of the end face of bottom mold 7 corresponding to the opening end of main shell 2 to manufacture the end cover 4 of fuel tank shell 1.

[0026] Specifically, firstly, based on the overall geometry and structural dimensions of the fuel tank shell 1, a numerical model of the mold is precisely constructed using 3D modeling software. The inner shape of the numerical model corresponds one-to-one with the outer shape of the fuel tank, ensuring both the fit of the subsequent lay-up surfaces and the operational space during demolding. Considering the complexity of the cross-sectional contour of the fuel tank shell 1 and the feasibility of CNC machining, the mold is divided into five parts: bottom mold 7, upper left mold 8, upper right mold 9, upper middle mold 10, and end mold 11. Each component is precision-machined by a CNC milling machine according to the model data. Among them, the upper left mold 8 and the upper right mold 9 are assembled to the upper left and upper right of the bottom mold 7 by bolts or locating pins, respectively, for mold closing to manufacture the main shell 2. After the main shell 2 is formed, there is no need to disassemble the mold. The upper middle mold 10 is assembled on the upper middle of the bottom mold 7 with bolts or positioning pins, and the end mold 11 is assembled on the bottom mold 7 at the periphery of the end face corresponding to the opening end of the oil tank with bolts or positioning pins. This is used to complete the overall mold closing to manufacture the upper cover 3 and the end cover 4, thereby forming the entire oil tank shell 1.

[0027] Overall, by adopting modular CNC mold design and partitioned mold assembly process, the key challenges in the integrated manufacturing of complex irregular-shaped fuel tanks have been fundamentally solved. Precise 3D modeling and high-precision CNC machining reduce the fitting errors between mold components; segmented assembly and double curing reduce bridging and wrinkling of the prepreg at uneven edges, significantly improving product molding rate and consistency. This ultimately produces lightweight, high-rigidity, dimensionally accurate, and aesthetically pleasing composite fuel tanks, meeting the stability and cost control requirements of mass production.

[0028] S2, Preparation of silicone rubber soft mold 12: Prepreg is laid on the working surfaces of bottom mold 7, upper left mold 8 and upper right mold 9 respectively, and bottom mold 7, upper left mold 8 and upper right mold 9 are closed and cured to form a support prosthesis. The inner shape of the support prosthesis is consistent with the inner shape of the main shell 2. The A component and B component of silicone rubber are mixed and poured into the cavity corresponding to the second oil storage tank of the support prosthesis and the main shell 2. The vulcanized silicone rubber is taken out and the inner silicone rubber is cut off to obtain the silicone rubber soft mold 12 with three sides enclosed.

[0029] Specifically, firstly, using the precise coordination of the bottom mold 7, the upper left mold 8, and the upper right mold 9, one or more layers of carbon fiber prepreg are laid on their respective working surfaces according to design requirements. After the layers are laid, the three molds are joined together using bolts and cured in an autoclave or oven to form a support prosthesis whose shape is completely consistent with the inner cavity of the main shell 2 of the fuel tank. To ensure that the support prosthesis can be easily removed during subsequent silicone rubber injection, a layer of high-efficiency release cloth is covered on the inner surface of the support prosthesis after trimming to prevent the silicone rubber from sticking to the support prosthesis.

[0030] To address the complex geometry of the second oil reservoir, the required filling volume was precisely calculated based on the expansion coefficient of the selected silicone rubber. The A and B components of the silicone rubber were mixed and then steadily injected into the cavity enclosed on three sides corresponding to the support prosthesis and the second oil reservoir. Component A contains a crosslinking agent, primarily providing the basic components and structural framework of the silicone rubber; component B contains a catalyst or curing agent to accelerate the vulcanization reaction of the silicone rubber. During vulcanization, the silicone rubber, constrained by the support prosthesis, expands to a shape and size matching the second oil reservoir, ensuring that the molded soft mold completely fills the corners and narrow areas of the second oil reservoir. Figure 5 As shown, after vulcanization is completed and the mold is removed, excess silicone rubber inside is removed to obtain a frame-type silicone rubber soft mold 12 that is enclosed on three sides and open on one side.

[0031] The silicone rubber soft mold 12 is placed into the corresponding front and rear edges, complex corners, edges, concave and convex parts, and areas with limited operating space during the subsequent manufacturing of the main shell 2. It provides uniform and controllable support pressure, effectively eliminating molding defects such as bridging, fiber wrinkles, and voids in traditional vacuum bags. Its frame structure not only ensures sufficient mechanical support but also facilitates quick removal after subsequent vacuum curing, avoiding any impact on the demolding of the main shell 2. Furthermore, when the soft mold is damaged or ages during use, it can be re-injected, vulcanized, and removed according to the preparation process of S2, ensuring that each batch of main shell 2 can achieve consistent molding quality and high reliability.

[0032] By utilizing the mold for multiple purposes, it can not only be used to manufacture the fuel tank shell 1, but also to pre-manufacture a support prosthesis that perfectly matches the inner shape of the main shell 2. After curing, the support prosthesis can be directly used as a template for the silicone rubber soft mold 12 without additional disassembly or processing. This eliminates the need for separate design and processing of a dedicated mold for the silicone rubber soft mold 12, significantly reducing mold design and manufacturing steps and fully leveraging the reusability of mold resources. The process, which traditionally requires two or more dedicated molds, is condensed into a single multi-purpose mold to complete the preparation of both the silicone rubber soft mold 12 and the fuel tank shell 1. This significantly reduces mold procurement, processing, and maintenance costs, while simplifying the production process. This integrated mold utilization method not only shortens the mold-making cycle but also reduces production errors and improves process stability, providing an economical and efficient solution for the mass production of high-quality composite fuel tanks.

[0033] S3, Airbag 13 preparation: Based on the structural dimensions of the fuel tank shell 1, airbag 13 is prepared. The inflated shape of airbag 13 is consistent with the inner shape of the main shell 2.

[0034] Specifically, based on the internal geometry and dimensions of the fuel tank shell 1, and considering the expansion characteristics of the airbag 13 during inflation, the initial dimensions of the airbag 13 in each direction are calculated, with an additional safety margin of 3%–10% to compensate for minor changes caused by material elastic recoil and thermal expansion and contraction. In this embodiment, the airbag 13 is made of polyurethane (PU) film. The PU film has a pressure resistance of 0.6 MPa, excellent ductility and fatigue resistance, and low production cost. The airbag 13 is manufactured using hot welding or high-frequency welding technology, precisely aligning and welding several PU film sheets under specific temperature and pressure conditions to ensure that the weld is smooth and its strength is higher than the tear strength of the film itself. After welding, the airbag 13 is inflated. It is initially inflated at a low pressure of 0.1 MPa, and then gradually increased to 0.6 MPa for a sealing test to check for leaks in the weld and the overall film. To ensure high-temperature resistance and long-term reliability, the air nozzle 14 is made of high-temperature resistant nylon material and is integrated with the airbag 13 by ultrasonic or hot pressing. An O-ring or oil-resistant sealant is added at the interface to enhance the sealing effect.

[0035] like Figure 6 As shown, the inflated airbag 13 perfectly fits the inner cavity of the fuel tank shell 1 in terms of shape and size. Whether along the straight wall section of the main shell 2 or in the corners, curved surfaces, and recessed areas, it can provide uniform and controllable internal support, effectively reducing the defect rate caused by the airbag 13 rupture or leakage. In addition, the airbag 13 only needs to be used once during the molding process, without the need for disassembly and multiple installations. After use, it can be removed and replaced along with the demolding process of the main shell 2.

[0036] S4, Preparation of main shell 2: Prepreg is laid on the working surfaces of bottom mold 7, upper left mold 8 and upper right mold 9 respectively. After laying, silicone rubber soft mold 12 is placed at the positions corresponding to the side shell 6 of bottom mold 7 and main shell 2. After closing bottom mold 7, upper left mold 8 and upper right mold 9, vacuum curing is performed to form main shell 2.

[0037] Specifically, during the fabrication of the main shell 2, two layers of 0° or 90° carbon fiber prepreg and three layers of 45° or -45° carbon fiber prepreg are first laid sequentially from bottom to top on the working surface of the bottom mold 7. For example, 0°, 90°, 45°, -45°, and 45° carbon fiber prepreg are laid sequentially from bottom to top, or 90°, 0°, -45°, 45°, and -45° carbon fiber prepreg are laid sequentially from bottom to top. The edge of each side of the bottom layer of prepreg extends at least 5 mm beyond the working surface of the mold, and the upper edge of each adjacent layer also extends outward by at least 5 mm to ensure a reliable stepped overlap with the subsequent layers of the upper left mold 8 and upper right mold 9. After the layup is completed, a non-porous release film is applied tightly to the surface and fixed with pressure-sensitive tape. Then, metal or composite pressure strips are arranged in the concave area, followed by the non-porous release film and breathable felt as auxiliary molding materials. This firmly presses the prepreg into the concave area, allowing it to accurately form an uneven surface contour during subsequent pressure curing, while ensuring that resin and gas are evenly discharged along the breathable felt.

[0038] Two layers of 0° or 90° carbon fiber prepreg and three layers of 45° or -45° carbon fiber prepreg are laid sequentially from top to bottom on the working surfaces of the upper left mold 8 and the upper right mold 9, with the edges of each prepreg layer flush with the edges of the mold working surfaces. After the layup is completed, a non-porous release liner is placed and fixed with pressure-sensitive tape to prepare for the subsequent stepped overlap with the bottom prepreg layer. Then, the silicone rubber flexible mold 12 is accurately placed at the position corresponding to the layup of the bottom mold 7 and the side shell 6 of the main shell 2, and the bottom prepreg layer is flipped along the side of the silicone rubber flexible mold 12 to the top surface of the silicone rubber flexible mold 12.

[0039] Next, the bottom mold 7, upper left mold 8, and upper right mold 9 are bolted together, pressing the prepreg layers of the upper left and upper right molds onto the top surface of the silicone rubber soft mold 12. This creates a stepped overlap with the prepreg layer of the bottom mold 7, ensuring that the prepreg on the end faces, edges, and corners of the side shell 6 is fully expanded without voids or wrinkles, resulting in full edges and evenly distributed stress, thus improving the overall sealing performance and mechanical strength of the structure. After molding, a breathable felt and a vacuum bag are placed sequentially on the inner surface of the mold cavity, and a vacuum environment is created around the mold using sealing tape. Finally, the entire assembly is placed in an autoclave or oven for heating and pressure curing, ultimately forming the main shell 2 with a precise geometric shape. After curing, there is no need to disassemble the mold; only the silicone rubber soft mold 12, pressure strip, non-porous release membrane, and breathable felt need to be removed from the main shell 2. Simultaneously, the adhesive surfaces of the main shell 2 are finely polished and deburred.

[0040] S5, Preparation of fuel tank shell 1: Prepreg is laid on the working surfaces of the upper and middle molds 10 and the end molds 11 respectively. After the airbag 13 is inserted into the main shell 2, the upper and middle molds and the end molds are closed with the bottom mold, the upper left mold and the upper right mold that have already been closed. The airbag 13 is inflated and then cured to form the fuel tank shell 1.

[0041] Specifically, in the fabrication of the fuel tank shell 1, the prepreg is first precisely laid up on the working surfaces of the upper and middle molds 10 and the end molds 11. During the layup process, according to the structural stress distribution characteristics from the inside out, two layers of 0° or 90° carbon fiber prepreg and three layers of 45° or -45° carbon fiber prepreg are placed sequentially to achieve stress bearing capacity of the fibers in the axial and shear directions. After the layup is completed, a stepped flange is reserved at the edge of each layer of prepreg to overlap with the main shell 2, so that the prepreg of the upper and middle molds 10 and the end molds 11 can seal and overlap with the surface of the cured inner cavity of the main shell 2 during subsequent mold closing. After the layup is completed and covered with a non-porous release film, it is fixed with pressure-sensitive tape, and the prepreg layup is flanged.

[0042] Next, the prepared airbag 13 is placed into the inner cavity of the main shell 2. Then, the upper middle mold 10 and the end face mold 11 are combined with the already molded bottom mold 7, upper left mold 8, and upper right mold 9 to form an integral molding mold. This allows the prepreg layers of the upper middle mold 10 and the end face mold 11 to be laminated onto the inner surface of the main shell 2, forming a reliable stepped overlap. The end face mold 11 is closed by a baffle 15 and has a pre-drilled through hole. An air nozzle 14 is inserted through the through hole, with one end of the air nozzle 14 passing through the through hole and connecting to the airbag 13, and the other end used in conjunction with an air source. After assembly, the integral mold is placed in an oven or hot press. The airbag 13 is first slowly inflated at a low pressure of 0.05 MPa and maintained for 5 minutes to fully expel free air between the airbag 13 and the inner wall. Then, the pressure is increased to 0.1 MPa and maintained for 5 minutes to ensure the airbag 13 adheres tightly to the inner wall of the fuel tank and eliminates any minor gaps. Next, a 5-minute sealing test is performed at a high pressure of 0.5 MPa to confirm there is no leakage. Afterward, curing is carried out under a set temperature and vacuum. During the curing process, by simultaneously applying heat and uniform internal air pressure, the prepreg layers of the upper and middle molds 10 and the end molds 11 are fully bonded to the main shell 2, forming an integrated fuel tank shell 1. After curing, the entire unit is demolded, and the airbag 13 and auxiliary molding materials are removed. The bonding surfaces and edges of the inner cavity of the fuel tank shell 1 are then polished and trimmed to remove burrs and improve the sealing accuracy.

[0043] In summary, by employing segmented layup and stepped overlap, controllable airbag 13 support and graded inflation and deflation, and two-stage curing for tight bonding, the prepreg layup on complex, uneven surfaces maintains continuous stress transfer and tight adhesion, avoiding molding defects such as fiber wrinkles, voids, and bridging found in traditional methods. The resulting fuel tank shell 1 not only possesses excellent mechanical properties such as high strength, high rigidity, and light weight (with a maximum deformation displacement of less than 7 mm under 20 kPa internal pressure), but also exhibits excellent sealing performance, durability, and surface finish, achieving high-precision mass production.

[0044] This application also provides an aircraft, such as a drone, comprising a composite fuel tank manufactured by any of the methods described above. Since the aircraft uses the aforementioned composite fuel tank, it also possesses the same beneficial effects as the composite fuel tank, which will not be elaborated further here.

[0045] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite material fuel tank, characterized in that, The system includes a fuel tank housing, which includes a main housing with an opening at one end, a top cover covering the top of the main housing, and an end cover covering the periphery of the opening end of the main housing. The main housing includes a base and two side shells respectively connected to the top of the base. The base has a first oil storage tank, and each side shell has a second oil storage tank communicating with the first oil storage tank.

2. The composite material fuel tank according to claim 1, characterized in that, The surface of the fuel tank shell is uneven, the thickness of the side shell is less than the thickness of the base, and the thickness of the side shell gradually increases from the open end to the closed end of the main shell.

3. A method for manufacturing a composite material fuel tank, characterized in that, A method for manufacturing the composite material fuel tank according to claim 1 or 2 includes: Mold preparation: Based on the structural dimensions of the fuel tank shell of the composite fuel tank, a digital model is established. The inner shape of the digital model is consistent with the outer shape of the fuel tank shell. Based on the digital model, the mold is manufactured. The mold includes independently manufactured bottom mold, upper left mold, upper right mold, upper middle mold, and end face mold. The upper left mold and upper right mold are used to assemble on the upper left and upper right of the bottom mold to manufacture the main shell of the fuel tank shell. The upper middle mold is used to assemble on the upper middle of the bottom mold to manufacture the upper cover of the fuel tank shell. The end face mold is used to assemble on the periphery of the end face corresponding to the opening end of the main shell of the bottom mold to manufacture the end cover of the fuel tank shell. Silicone rubber soft mold preparation: Prepreg is laid on the working surfaces of the bottom mold, the upper left mold, and the upper right mold respectively. After the bottom mold, the upper left mold, and the upper right mold are closed and cured, a support prosthesis is formed. The inner shape of the support prosthesis is consistent with the inner shape of the main shell. The A and B components of silicone rubber are mixed and poured into the cavity corresponding to the second oil reservoir of the support prosthesis and the main shell. The vulcanized silicone rubber is removed and the inner silicone rubber is cut off to obtain a silicone rubber soft mold with three sides enclosed. Airbag fabrication: Based on the structural dimensions of the fuel tank shell, airbags are fabricated. The inflated shape of the airbag is consistent with the inner shape of the main shell. Main shell preparation: Prepreg is laid on the working surfaces of the bottom mold, the upper left mold and the upper right mold respectively. After laying, the silicone rubber soft mold is placed at the position corresponding to the side shell of the main shell on the bottom mold. After the bottom mold, the upper left mold and the upper right mold are closed, vacuum curing is performed to form the main shell. Fuel tank shell preparation: Prepreg is laid on the working surfaces of the upper and middle molds and the end molds respectively. After the air bladder is inserted into the main shell, the upper and middle molds and the end molds are closed with the bottom mold, the upper left mold and the upper right mold that have already been closed. The air bladder is then inflated and cured to form the fuel tank shell.

4. The method according to claim 3, characterized in that, During the preparation of the main shell, two layers of 0° or 90° carbon fiber prepreg and three layers of 45° or -45° carbon fiber prepreg are laid sequentially from bottom to top on the working surface of the bottom mold. The bottommost carbon fiber prepreg layer extends beyond the working surface of the bottom mold by at least 5 mm on each side, and the upper carbon fiber prepreg layer of the two adjacent layers extends beyond the lower carbon fiber prepreg layer by at least 5 mm on each side.

5. The method according to claim 3 or 4, characterized in that, In the preparation of the main shell, after the prepreg is laid on the working surface of the bottom mold, pressure strips and auxiliary molding materials covering the pressure strips are arranged in the concave area of ​​the working surface to press the prepreg into the concave area. After the mold is closed and cured, a main shell with an uneven surface is formed.

6. The method according to claim 3 or 4, characterized in that, In the preparation of the main shell, after prepreg is laid on the working surfaces of the bottom mold, the upper left mold and the upper right mold, a non-porous isolation membrane is fixedly laid on the prepreg layers of the different molds.

7. The method according to claim 3 or 4, characterized in that, During the preparation of the main shell, after the main shell is formed, the silicone rubber soft mold is removed.

8. The method according to claim 3 or 4, characterized in that, In the preparation of the fuel tank shell, before the airbag is inflated, a baffle is used to seal the opening of the end face mold, and a through hole is made on the baffle. An air nozzle is inserted through the through hole, one end of the air nozzle is connected to the airbag, and the other end of the air nozzle is connected to the air source.

9. The method according to claim 3 or 4, characterized in that, In the preparation of the fuel tank shell, the inflation of the airbag includes: inflating the airbag in three stages with inflation pressures of 0.05MPa, 0.1MPa and 0.5MPa in sequence, so as to expel the air between the airbag and the inner wall of the fuel tank shell and make the outer wall of the airbag fit against the inner wall of the fuel tank shell.

10. The method according to claim 3 or 4, characterized in that, The airbag is made of PU film that can withstand pressure of 0.6MPa.

Images