Medium-sized unmanned aerial vehicle structure function integrated grid tank capable of being automatically integrally formed and forming method thereof

Abstract

The application provides a medium-sized unmanned aerial vehicle structure function integrated grid oil tank which can be automatically integrally formed and a forming method, and relates to the field of unmanned aerial vehicle structure design. The oil tank comprises an integrated oil tank body, a grid separation layer and an oil inlet and outlet interface. The oil tank body is integrally molded by upper and lower skin, the grid separation layer is co-cured with the skin by insert injection molding of short-cut carbon fiber reinforced thermoplastic resin to form a honeycomb grid, and the oil inlet and outlet interface is an aluminum alloy flange which is fixed on the bottom of the oil tank by welding of aluminum alloy and thermoplastic composite material. The application is based on the design and process technology of long and short fiber hybrid integrated oil tank. The main load-bearing shell can be automatically integrally formed. The oil tank skin uses long continuous fiber composite material to ensure the bearing capacity. The oil tank grid uses short-cut fiber composite material to realize sequential oil supply, anti-overload, anti-shaking and other functions, greatly reduces the number of oil tank parts, and has the potential for full automation manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of UAV structural technology, specifically relating to a medium-sized UAV structural and functional integrated grid fuel tank that can be automatically and integrally molded, and its molding method. Background Technology

[0002] Currently, most UAV fuel systems employ a modular design with metal or plastic fuel tanks, consisting of multiple plates assembled using bolts or welding to form a sealed cavity. Modular metal fuel tanks are made by stamping aluminum alloy plates and then welding them, supplemented by rubber seals and flange connections; this technology is mature and cost-effective. However, the welds are prone to fatigue cracking, and the tanks are heavy. Injection-molded plastic fuel tanks are made by blow molding polyethylene, offering good integrity and corrosion resistance; however, they have poor impact resistance, requiring additional anti-collision brackets and cannot integrate a load-bearing structure. Composite material assembled fuel tanks are made by molding prepreg into modular pieces and then bonding them together, achieving weight reduction, but the sealing reliability of the bonded surfaces is low, and the number of parts remains large. Therefore, existing fuel tanks suffer from the following problems: the need for multi-part assembly leads to multiple sealing interfaces (increasing the risk of leakage by more than 50%), assembly time (4-6 hours for a single fuel tank assembly), and difficulty in achieving synergistic optimization of overload resistance and fuel supply functions. In other words, the above designs require additional structural reinforcement to withstand aerodynamic loads and fuel inertial forces during flight, resulting in a large number of parts and complex assembly processes. In addition, in recent years, the application of carbon fiber reinforced composite materials in aerospace structures has gradually become more widespread, but their integration in fuel systems is still limited to simply replacing metal materials, and the designability advantages of composite materials have not been fully utilized. Summary of the Invention

[0003] To effectively solve the above problems, this invention proposes an automated integral molding method for a medium-sized UAV structural and functional integrated grille fuel tank, which has the advantages of fewer parts, shorter assembly time, high sealing performance, lightweight and impact resistance.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A modular, integrated bar grid fuel tank for medium-sized unmanned aerial vehicles (UAVs) that can be automatically and integrally molded, comprising:

[0006] The upper and lower skins, which are integrally molded, are welded together circumferentially to form a sealed fuel tank body.

[0007] Inserts are injection molded into the honeycomb-shaped grid partition layer between the upper and lower skins. The grid partition layer is integrally bonded to the skin by co-curing short-cut carbon fiber reinforced thermoplastic resin.

[0008] An aluminum alloy oil inlet / outlet port is fixed to the bottom of the oil tank and communicates with the interior of the grid partition layer. The port is welded to the lower skin for sealing connection through aluminum alloy-thermoplastic composite material.

[0009] The upper and lower skins are continuous fiber main load-bearing layers, and the grid partition layer is a chopped fiber functional layer. The two are formed sequentially in the same mold and support each other, thereby reducing the number of parts to three integrated components.

[0010] Furthermore, the upper and lower skins are made of thermoplastic carbon fiber laminates with alternating 0° / ±45° / 90° layups, and the grid separator layer is injection molded into a honeycomb grid in the same layup plane, so that the continuous fiber layer and the chopped fiber layer form a mechanical-chemical double interlock at the grid nodes, thereby eliminating the need for a secondary adhesive bonding process.

[0011] Furthermore, the honeycomb cell size of the grid separator layer is 100 mm in both the heading and lateral directions. In the high overload area near the wing root, it is locally densified to 30 mm × 30 mm. The densified area and the standard area are continuously formed by switching the injection molding parameters online, so as to achieve synchronous optimization of weight distribution and overload resistance.

[0012] Furthermore, the thickness of the grid partition layer of the lower skin gradually changes linearly from 2.5 mm at the top to 4 mm at the bottom, and the gradual contour is molded with the mold surface in one step, thereby directly forming the fuel flow ramp.

[0013] Furthermore, the aluminum alloy oil inlet / outlet interface is equipped with a flange that is co-cured with the lower skin.

[0014] Furthermore, the chopped carbon fiber volume content of the grid separator layer is 40%, and the fiber length is 8 mm. The continuous fiber layer uses T700 grade carbon fiber. The two are co-cured within the same window of the melt index of the thermoplastic matrix to ensure that the interfacial shear strength is higher than the intrinsic strength of the matrix.

[0015] Furthermore, the outer surface of the upper skin is provided with an integrated ear piece that docks with the main load-bearing frame of the UAV. This ear piece is formed synchronously with the skin during the molding stage.

[0016] Furthermore, the inner surface of the lower skin forms a funnel-shaped oil collection pit in the fuel pump port area through injection molding. This oil collection pit is aligned with the bottom honeycomb holes of the grille, so that the remaining fuel is sequentially guided to the pump port without an additional oil collector.

[0017] Furthermore, the upper skin, lower skin, and grid partition layer are all recyclable thermoplastic composite materials. The three are finally welded together to form a single material system, thereby meeting the requirements of overall hot melt welding repair and end-of-life recycling.

[0018] This invention also provides a fully automated molding method for a medium-sized UAV structural and functional integrated grille fuel tank that can be automatically formed as a whole, comprising the following steps:

[0019] Step 1: After the continuous carbon fiber / thermoplastic resin laminate is cut, it is fed into the heating mold by the robotic arm and radiantly heated to the pre-forming temperature.

[0020] Step 2: Close the mold and apply molding pressure to the laminate to obtain an upper or lower skin with ear pieces and a grid partition layer with varying thickness;

[0021] Step 3: While maintaining the skin temperature in the same mold, inject short-cut carbon fiber reinforced thermoplastic melt to fuse the melt with the inner surface of the skin and solidify it into a honeycomb-shaped separator layer in the grid cavity.

[0022] Step 4: After opening the mold, flip the mold over and repeat steps 1-3 to prepare another corresponding skin-grid assembly;

[0023] Step 5: Precisely position the two assemblies obtained in Step 3 and Step 4 at the welding station, and fuse the circumferential overlapping surfaces through heat conduction welding to form a sealed oil tank body.

[0024] Step 6: During the welding synchronization stage, the pre-embedded area of ​​the aluminum alloy oil inlet and outlet interface is heated a second time to complete the metallurgical-polymer dual connection of aluminum alloy-thermoplastic composite material, thereby obtaining a complete oil tank containing only three integrated components in one go.

[0025] Beneficial effects:

[0026] This invention boasts an overload resistance of 6g, representing a 36% weight reduction compared to aluminum alloy fuel tanks of the same size. The fuel passage and intake / exhaust passages are integrally molded during injection molding. The number of parts is reduced by 90% (from a typical 30 to 3 integrated components), shortening assembly time to within 30 minutes. Sealing performance is improved (leakage rate <0.01g / h), meeting MIL-T-83133A military standard. Full automation is possible, resulting in high product consistency. Manufacturing efficiency is significantly improved, and cost advantages are evident. The upper and lower skins are molded using a specific angle (0° / ±45° / 90°) alternating layering of carbon fiber / thermoplastic resin, fully utilizing the mechanical properties of carbon fiber to give the fuel tank excellent structural strength and fatigue resistance. The grid material can be replaced with carbon fiber chopped reinforced nylon, adapting to different environments such as dryness and low temperatures, enhancing the fuel tank's adaptability to various operating conditions. Fewer prefabricated parts are required, eliminating the need for prepreg and simplifying the process. The use of a thermoplastic composite material system allows for secondary welding. Attached Figure Description

[0027] Figure 1 This is a structural schematic diagram of a medium-sized UAV structural and functional integrated grid fuel tank that can be automatically and integrally formed according to the present invention; wherein, the left figure is the fuel tank body and the right figure is the grid segmentation layer;

[0028] Figure 2The images show an isometric axonometric view, top view, front view, and side view of an automated integrally formed medium-sized UAV structural and functional integrated grille fuel tank according to the present invention.

[0029] Figure 3 This is a flowchart of the fully automated molding method of the present invention.

[0030] Figure 4 This is a schematic diagram showing the thickness variation of the separator layer of the fuel tank grille; the left image is a side view of the main body of the grille, the middle image is a cross-sectional view of section AA in the left image, and the right image is an enlarged view of section B in the middle image. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0032] like Figures 1-2 As shown, the automatically integrally molded medium-sized UAV structural and functional integrated grid fuel tank of the present invention includes an integrated fuel tank body, a grid partition layer, and fuel inlet / outlet interfaces. The fuel tank body is integrally molded from upper and lower skins. Both the upper and lower skins have a grid partition layer inside, and then the upper and lower skins with grid partition layers are welded together to achieve integration.

[0033] The grid partition layer is a honeycomb mesh formed by co-curing short-cut carbon fiber reinforced thermoplastic resin with the skin through insert injection molding (co-curing means that the skin and grid partition layer are co-fused and polymerized at the interface at high temperature, forming an integral structure after cooling). The oil inlet and outlet interfaces are aluminum alloy flanges, which are fixed to the bottom of the oil tank by welding aluminum alloy and thermoplastic composite material. The upper and lower skins and the grid partition layer are integrated. Figure 1 , Figure 2 The left image shows the fuel tank itself. Figure 1 , Figure 2 The right image shows the grid segmentation layer.

[0034] This invention is based on an integrated fuel tank design and manufacturing technology using a mixture of long and short fibers. Both the skin and the grid (including the upper and lower skins and the grid partition layer) can be fully automated and integrally molded. The fuel tank skin utilizes long, continuous fiber composite materials to ensure load-bearing capacity, while the grid partition layer utilizes short-cut fiber composite materials to achieve sequential fuel supply, overload resistance, and anti-sway functions. This significantly reduces the number of fuel tank parts and has the potential for fully automated manufacturing.

[0035] Preferably, both the upper and lower skins are made of 5 layers of carbon fiber and thermoplastic resin, and the thickness of the vertical partitions in the grid separation layer is gradually varied, such as... Figure 4 As shown, the thickness gradually increases from the center outwards to the connecting area. The left image is a side view of the main body of the fuel tank, the middle image is a cross-sectional view AA of the left image, and the right image is an enlarged view of section B in the middle image.

[0036] Preferably, the carbon fiber is T700 grade carbon fiber, used for the main load-bearing layer of the skin, and the typical fiber length of the chopped carbon fiber is 8mm, with a volume content of 40%, used for the grid partition layer.

[0037] The working process of the integrated grille fuel tank for medium-sized unmanned aerial vehicles (UAVs) that can be automatically and integrally molded according to the present invention is as follows: the upper and lower skins utilize long continuous fiber composite materials to ensure load-bearing capacity, while the grille partition layer utilizes short-cut fiber composite materials. When fuel is injected from the fuel inlet, the grille partition layer suppresses liquid sloshing and reduces lateral impact force by 80%. Under overload conditions, the long continuous fiber composite skin bears the aerodynamic load, while the short-cut fiber composite grille partition layer absorbs energy through plastic deformation. During the fuel supply phase, the grille partition layer guides the fuel to flow to the fuel outlet along a preset path, achieving functions such as sequential fuel supply, overload resistance, and anti-sloshing, significantly reducing the number of fuel tank parts and possessing the potential for fully automated manufacturing.

[0038] Example 1

[0039] This embodiment of an automated integrally molded medium-sized UAV structural and functional integrated grid fuel tank includes an integrated fuel tank body, a grid partition layer, and fuel inlet / outlet interfaces. The fuel tank body is integrally molded from upper and lower skins. The skins are made of 5 layers of carbon fiber / thermoplastic resin (PEEK, PEKK, PPS, etc.) laid up (0° / ±45° / 90° alternating layers). The carbon fiber is T700 grade carbon fiber with a tensile modulus of 230 GPa, used as the main load-bearing layer of the skin. The grid partition layer has a gradient thickness design, from 2.5 mm at the top to 4 mm at the bottom. The grid partition layer is made of short-cut carbon fiber reinforced thermoplastic resin (PEEK, PEKK, PPS, etc.) co-cured with the skin through insert injection molding to form a honeycomb mesh. The grid has individual cell dimensions of 100mm forward × 100mm lateral × adaptive depth; the typical fiber length of the chopped carbon fiber is 8mm, with a volume content of 40%; the material of the grid partition layer can also be replaced with chopped carbon fiber reinforced nylon (PA66), which is suitable for dry, low-temperature environments; the grid partition layer can use a denser grid (30mm × 30mm) in high overload areas of the fuel tank, such as near the wing root, while maintaining a standard spacing in other areas to further optimize weight distribution; the fuel inlet and outlet ports are aluminum alloy flanges, which are fixed to the bottom of the fuel tank by welding aluminum alloy and thermoplastic composite material.

[0040] Example 2

[0041] This embodiment of an automated, integrally molded, medium-sized UAV structural and functional integrated grille fuel tank includes an integrated fuel tank body, a grille partition layer, and fuel inlet / outlet interfaces. The fuel tank body is integrally molded from upper and lower skins. The fuel tank grille partition layer adopts a gradient design. The grille partition layer is made of short-cut carbon fiber reinforced thermoplastic resin (PEEK, PEKK, PPS, etc.) and co-cured with the skin through insert injection molding to form a honeycomb mesh. The fuel inlet / outlet interfaces are aluminum alloy flanges, which are fixed to the bottom of the fuel tank by welding aluminum alloy and thermoplastic composite material.

[0042] The envelope dimensions of the fuel tank body are 1100mm (heading) × 1200mm (span) × 520mm (vertical). The fuel tank consists of two skin layers and two grid layers. The skin is made of long continuous fiber molding (quasi-isotropic layup), and the internal grid partition layer is made of short fiber injection molding, which is integrated with the skin through injection molding. The main load-bearing shell can be fully automated.

[0043] The fuel tank consists of the following components: the main load-bearing upper shell (upper skin + grid partition layer), the main load-bearing lower shell (lower skin + grid partition layer), and the overload-resistant fuel collection tank. The skin is made of long continuous fiber molding (quasi-isotropic layup), and the internal grid partition layer is made of short-cut fiber injection molding, which is integrated with the skin through injection molding; the main load-bearing shells can all be molded automatically.

[0044] like Figure 3 As shown, the fully automated molding method for a medium-sized UAV structural and functional integrated grille fuel tank, which can be automatically formed as a whole, according to the present invention, includes the following steps:

[0045] Step 1: The robot's end effector (robotic arm) picks up the carbon fiber skin raw material and sends it into the molding station;

[0046] Step 2: Prepare the carbon fiber skin raw material (i.e....) Figure 3 The raw materials are fed to the heating mold, and the materials are heated to the pre-forming temperature through thermal radiation or thermal conduction technology, making the materials deformable.

[0047] Step 3: The robotic gripper picks up the heated carbon fiber material and precisely places it into the molding cavity to ensure the material's positional accuracy within the mold, preparing it for subsequent molding.

[0048] Step 4: The carbon fiber is subjected to pressure inside the mold and gradually conforms to the mold surface, so that the skin begins to take shape and the material shape changes with the inner cavity of the mold.

[0049] Step 5: Inject short-fiber reinforced thermoplastic resin into the mold and co-cure it with the preliminarily formed skin to achieve integrated molding of the skin-grid partition layer structure, allowing the two materials to fuse in the mold.

[0050] Step 6: After the molding is completed, the upper and lower skins are assembled by welding.

[0051] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A medium-sized unmanned aerial vehicle (UAV) integrated grille fuel tank that can be automatically and integrally molded, characterized in that, include: The upper and lower skins, which are integrally molded, are welded together circumferentially to form a sealed fuel tank body. An insert is injection molded into a honeycomb-shaped grid partition layer between the upper and lower skins. This grid partition layer is integrally bonded to the upper and lower skins by co-curing short-cut carbon fiber reinforced thermoplastic resin. An aluminum alloy oil inlet / outlet port is fixed to the bottom of the oil tank and communicates with the interior of the grid partition layer. The port is welded to the lower skin for sealing connection through aluminum alloy-thermoplastic composite material. The upper and lower skins are continuous fiber main load-bearing layers, and the grid partition layer is a chopped fiber functional layer. The two are formed sequentially in the same mold and support each other, thereby reducing the number of parts to three integrated components. The upper and lower skins are made of thermoplastic carbon fiber laminates with alternating 0° / ±45° / 90° layups. The grid separation layer is injection molded into a honeycomb grid in the same layup plane, so that the continuous fiber main load-bearing layer and the chopped fiber functional layer form a mechanical-chemical double interlock at the grid nodes, thereby eliminating the secondary adhesive bonding process. The honeycomb cell size of the grid partition layer is 100 mm in both the heading and lateral directions. In the high overload area near the wing root, it is locally densified to 30 mm × 30 mm. The densified area and the standard area are continuously formed by switching the injection molding parameters online, so as to achieve synchronous optimization of weight distribution and overload resistance. The thickness of the grille partition layer of the lower skin gradually changes linearly from 2.5 mm at the top to 4 mm at the bottom. The gradual contour and the mold surface are molded in one step, thereby directly forming the fuel flow ramp. The chopped carbon fiber volume content of the grid partition layer is 40%, and the fiber length is 8 mm. The continuous fiber main load-bearing layer uses T700 grade carbon fiber. The two are co-cured within the same window of the thermoplastic matrix melt index to ensure that the interfacial shear strength is higher than the intrinsic strength of the matrix. The outer surface of the upper skin is provided with an integrated ear piece that docks with the main load-bearing frame of the UAV. The ear piece is formed synchronously with the upper skin during the molding stage. The inner surface of the lower skin forms a funnel-shaped oil collection pit in the fuel pump port area through injection molding. This oil collection pit is aligned with the bottom honeycomb holes of the grille, so that the remaining fuel is sequentially guided to the pump port without an additional oil collector.

2. The integrated grille fuel tank for medium-sized unmanned aerial vehicles (UAVs) with automated integral molding as described in claim 1, characterized in that, The aluminum alloy oil inlet / outlet interface is equipped with a flange that is co-cured with the lower skin.

3. The integrated grille fuel tank for medium-sized unmanned aerial vehicles (UAVs) that can be automatically and integrally molded as described in claim 1, characterized in that, The upper skin, lower skin, and grid partition layer are all recyclable thermoplastic composite materials. The three are finally welded together to form a single material system, thereby meeting the requirements of overall hot melt welding repair and end-of-life recycling.

4. A fully automated molding method for manufacturing a medium-sized UAV structural and functional integrated grille fuel tank as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: After the continuous carbon fiber / thermoplastic resin laminate is cut, it is fed into the heating mold by the robotic arm and radiantly heated to the pre-forming temperature. Step 2: Close the mold and apply molding pressure to the laminate to obtain an upper or lower skin with ear pieces; Step 3: Under the condition of maintaining the temperature of the upper skin or the lower skin in the same mold, inject short-cut carbon fiber reinforced thermoplastic fiber, so that the fiber fuses with the inner surface of the upper skin or the lower skin and is cured in the grid cavity to form a honeycomb-shaped partition layer, thereby obtaining the skin-grid assembly of the upper skin or the lower skin. Step 4: After opening the mold, flip the mold over and repeat steps 1-3 to prepare another corresponding skin-grid assembly; Step 5: Precisely position the skin-grid assembly of the upper and lower skins at the welding station, and fuse the circumferential overlapping surfaces through heat conduction welding to form a sealed fuel tank body. Step 6: During the welding synchronization stage, the pre-embedded area of ​​the aluminum alloy oil inlet and outlet interface is heated a second time to complete the metallurgical-polymer dual connection of aluminum alloy-thermoplastic composite material, thereby obtaining a complete oil tank containing only three integrated components in one go.

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