A manufacturing method of a UAV fuselage based on air inflation integrated forming technology

Abstract

This invention belongs to the field of unmanned aerial vehicle (UAV) manufacturing technology, specifically providing a method for manufacturing a UAV fuselage based on air-expansion integrated molding technology. The method involves laying prepreg in both the upper and lower molds, and then laying prepreg outside the core mold. The upper mold, lower mold, and core mold are then assembled into a whole, with the core mold connected between the upper and lower molds. The integrated mold is then placed in an oven for hot pressing. After hot pressing, the integrated mold is removed, disassembled, and the manufacturing process is complete. This invention solves the problems of cumbersome processes, high costs, poor structural strength at joints, and increased weight of the UAV fuselage caused by using split molding technology. This invention reduces weak points in the bonding of multiple components in traditional processes, improves structural continuity and mechanical properties, and reduces cost and weight of the UAV fuselage.

Description

Technical Field

[0001] This invention belongs to the field of unmanned aerial vehicle manufacturing technology, specifically relating to a method for manufacturing the fuselage of an unmanned aerial vehicle based on air-expansion integrated molding technology. Background Technology

[0002] Currently, the mainstream manufacturing process for the fuselage of small and medium-sized drones, especially multi-rotor and fixed-wing drones, is usually modular molding. The common process is as follows: the upper fuselage shell and the lower fuselage shell are manufactured separately (usually through injection molding, composite material molding or vacuum forming, autoclave molding, etc.), and then assembled and connected by means of adhesive bonding, screw fastening or welding, and finally the internal structure and electronic equipment are installed.

[0003] This traditional manufacturing method has many drawbacks: The process is complicated and costly: it requires the manufacture of two or more sets of molds and additional assembly steps, which consumes a lot of manpower, time and materials.

[0004] Structural strength and reliability issues: Connections (such as station joints and screw holes) are weak points in the structure. Under long-term vibration, impact, or thermal cycling, stress concentration or cracking can easily occur, affecting the overall rigidity of the fuselage.

[0005] Increased weight: To compensate for the loss of strength at the joint, it is often necessary to increase the amount of material used or add reinforcing ribs, resulting in additional weight gain.

[0006] Poor consistency: Errors may be introduced during the assembly process, affecting the consistency, appearance quality, and aerodynamic performance of the product.

[0007] Design limitations: Split designs make it difficult to achieve optimal continuous fiber composite layup designs, limiting the potential for integrated lightweight and high-strength designs.

[0008] Chinese patent document CN112298523A discloses the fuselage of an electric, high-payload multi-rotor unmanned aerial vehicle (UAV). The fuselage structure includes two main beams running from the nose to the tail, with multiple weight-reduction holes and reinforcing ribs along their length. These weight-reduction holes facilitate structural weight reduction and avionics wiring. The main beams are interconnected with the frame, base plate, connecting corner pieces, connecting components, and connectors to form the overall fuselage structure. The main beams are riveted to the frame, base plate, connecting corner pieces, and connecting components with multiple rivets. The main beams are also connected to the connecting components with multiple screws. This document still utilizes screw connections for assembly.

[0009] Therefore, a new manufacturing technology that can achieve one-piece molding of drone fuselages, simplify processes, improve performance, and reduce costs needs to be developed. Summary of the Invention

[0010] The present invention provides a method for manufacturing a drone fuselage based on air-expansion integrated molding technology. The purpose is to overcome the problems of cumbersome processes, high costs, poor structural strength at joints, and increased weight of the drone fuselage caused by the use of split molding technology in the prior art.

[0011] Therefore, the present invention provides a method for manufacturing a drone fuselage based on air-expansion integral molding technology, comprising the following steps: S1. Prepare the drone fuselage mold; the drone fuselage mold includes an upper mold, a lower mold, and a core mold; S2. Prepreg is laid inside both the upper and lower molds, and prepreg is laid outside the core mold. The upper mold, lower mold and core mold are then combined into a whole, wherein the core mold is connected between the upper mold and the lower mold. S3. Place the entire mold into an oven for hot pressing; S4. Remove the hot-pressed mold, disassemble the mold, and complete the manufacturing process.

[0012] Preferably, in step S2, before laying the prepreg, a release agent is uniformly coated on the inner surface of the upper mold, the inner surface of the lower mold, and the outer surface of the core mold.

[0013] Preferably, the core mold is wrapped in a vacuum bag.

[0014] Preferably, the prepreg includes carbon fiber twill prepreg and carbon fiber unidirectional tape prepreg.

[0015] Preferably, the core mold is made of foam material.

[0016] Preferably, the foam material is polystyrene.

[0017] Preferably, the density of the carbon fiber twill prepreg is 300 g / m³. 2 ~350g / m 2 The thickness is 0.2mm-0.3mm, and the ply thickness is 0.6mm-1mm.

[0018] Preferably, the density of the carbon fiber unidirectional tape prepreg is 150 g / m³. 2 -180g / m 2 The thickness is 0.14mm-0.16mm, and the ply thickness is 0.8mm-1mm.

[0019] Preferably, two layers of prepreg are laid on the inner surface of the upper mold, the inner surface of the lower mold, and the outer surface of the core mold.

[0020] Preferably, the layup angles of the two layers of prepreg on the inner surfaces of the upper and lower molds are 0° and +45° respectively, starting from the film-coating surface of the mold to which they are applied.

[0021] The beneficial effects of this invention are: This invention discloses a method for manufacturing a drone fuselage based on air-expansion integral molding technology. Prepreg is laid inside both an upper and lower mold, and then another prepreg is laid outside a core mold. The upper, lower, and core molds are then assembled into a single unit, with the core mold connecting the upper and lower molds. The entire mold is placed in an oven for hot pressing. The uniform pressure generated by the expansion of the core mold after heating and pressurizing the mold achieves integral curing of the prepreg. This method eliminates the need for large, energy-intensive equipment such as autoclaves, significantly simplifying the layup and subsequent assembly processes for the drone. The integral molding technology reduces weak points in the bonding of multiple components in traditional processes, improves structural continuity and mechanical properties, reduces cost, and lowers the weight of the drone fuselage. Attached Figure Description

[0022] The present invention will now be described in further detail with reference to the accompanying drawings.

[0023] Figure 1 This is a flowchart of the manufacturing method for a drone fuselage based on air-expansion unibody molding technology; Figure 2 This is a structural diagram of the connection frame between the drone fuselage mold and the mold. Figure 3 This is the upper mold structure diagram; Figure 4 Here is the structural diagram of the lower mold; Figure 5 This is a diagram of the core mold structure; Attached reference numerals: 1. Upper mold; 2. Lower mold; 3. Core mold. Detailed Implementation

[0024] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0025] Example 1: like Figures 1-5 As shown, a method for manufacturing a drone fuselage based on air-expansion unibody molding technology includes the following steps: S1. Prepare the drone fuselage mold; the drone fuselage mold includes an upper mold 1, a lower mold 2 and a core mold 3; S2. Prepreg is laid inside both the upper mold 1 and the lower mold 2, and prepreg is laid outside the core mold 3. The upper mold 1, the lower mold 2 and the core mold 3 are then combined into a whole, wherein the core mold 3 is connected between the upper mold 1 and the lower mold 2. S3. Place the entire mold into an oven for hot pressing; S4. Remove the hot-pressed mold, disassemble the mold, and complete the manufacturing process.

[0026] Specifically, this invention utilizes the uniform pressure generated by the expansion of the core mold 3 after heating and pressurizing the mold to achieve overall curing of the prepreg. This method eliminates the need for large, energy-intensive equipment such as autoclaves, significantly simplifying the layup and subsequent assembly processes for the drone. Through integral molding technology, adhesive components and mechanical seams in the fuselage are eliminated. The fuselage, as a complete mechanical unit, boasts high load-bearing efficiency, significantly improved fatigue and impact resistance, and its seamless structure naturally provides excellent dustproof, waterproof, and moisture-proof properties, enhancing the drone's adaptability to harsh environments. It avoids the added weight of adhesives and fasteners; typically only one outer mold and one inflated inner core mold 3 are needed; all assembly processes such as alignment, bonding, curing, and trimming of the upper mold 1 and lower mold 2 are eliminated; production cycles are shortened, reliance on manual labor is reduced, labor and time costs are lowered, there is no adhesive consumption, material utilization is high, and the scrap rate is reduced due to process simplification; the production process is highly controllable, and the product's dimensional accuracy and performance consistency are far superior to manually assembled products. The upper mold 1, lower mold 2, and core mold 3 are not limited to... Figure 2-5 The shape and structure shown.

[0027] Example 2: Based on Example 1, in step S2, before laying the prepreg, a release agent is uniformly coated on the inner surface of the upper mold 1, the inner surface of the lower mold 2, and the outer surface of the core mold 3. Applying the release agent facilitates subsequent mold removal.

[0028] Preferably, the release agent is a semi-permanent release agent.

[0029] Specifically, compared to traditional release waxes, semi-permanent release agents form a dry, non-transferable film, providing excellent release without contaminating the product surface and facilitating subsequent operations. Application can be done by spraying or wiping with a clean cotton cloth, typically applying 2-3 coats, ensuring a 5-10 minute interval between each coat to allow the solvent to completely evaporate.

[0030] Example 3: Based on Example 2, the core mold 3 is wrapped with a vacuum bag.

[0031] Specifically, when the core mold 3 is inflated and pressurized, the vacuum bag prevents air leakage during inflation and pressurization, ensuring stable pressure. At the same time, it protects the core mold 3 and prevents the prepreg from contacting the core mold 3, making it easier to demold the core mold 3 later. The vacuum bag allows the internal air pressure of the core mold 3 to be evenly transmitted to the entire inner surface of the prepreg, preventing defects such as insufficient local pressure, poor adhesion, bulging, and wrinkling. Complex shapes can also be formed in place.

[0032] Preferably, the vacuum bag is a Teflon vacuum bag.

[0033] Specifically, Teflon vacuum bags have excellent release properties, possessing the lowest coefficient of friction among solid materials and extremely strong non-stick properties. After the prepreg has cured, the Teflon vacuum bag can be easily peeled off from the mold or part surface without the need for chemical release agents. This not only simplifies the process but also protects the part surface to achieve a very high gloss. The vacuum bag wrapping the core mold 3 must ensure that the air inlet is unobstructed and that the strength meets the requirements to avoid phenomena such as vacuum bag rupture and air leakage during the pressurization process.

[0034] Preferably, the core mold 3 is made of foam material.

[0035] Specifically, the core mold 3 is made of foam material, which is lightweight and easy to process and mold. It can be quickly prepared into a suitable shape according to the complex internal cavity structure of the product. During the heating and curing process, the foam itself can undergo thermal expansion. With the internal air inflation and pressurization, it can expand outward evenly, pushing the prepreg to fit tightly into the inner wall of the mold, ensuring the quality of the integrated molding of complex shapes. At the same time, the foam is soft and will not damage the fiber reinforcement and the mold. It is also easy to break, remove or clean after molding. It is particularly suitable for molding closed cavities and irregular structural parts, and has both process adaptability and demolding convenience.

[0036] Preferably, the foam material is polystyrene.

[0037] Specifically, using polystyrene has the following technical advantages: Low cost and easy processing: The material cost is extremely low. Compared with metal core molds 3 that require precision machining or expensive soluble core molds 3, it can significantly reduce the mold manufacturing cost. It can be directly CNC machined according to the inner surface, and the machining accuracy can reach -0.1mm-0mm, greatly shortening the manufacturing cycle.

[0038] Unique heat-shrink self-demolding property: Polystyrene foam can withstand curing temperatures above 115℃, and at this temperature, it will undergo controllable heat shrinkage. During the curing process, the foam core mold 3 automatically shrinks after being heated and pressed, separating from the inner surface of the product. This solves the problem of difficult demolding of irregularly shaped barrel parts and avoids delamination or damage caused by forced demolding.

[0039] Uniform pressure is achieved by using a vacuum bag: Specifically, the core mold 3 is covered by a vacuum bag, and the core mold 3 is covered by a vacuum bag. The vacuum bag and the vacuum bag form an internal and external pressure balance. In the vacuum bag molding process, the vacuum cooperation between the polystyrene foam core mold 3 and the vacuum bag can play a greater role. When the vacuum bag is covered by the polystyrene foam core mold 3, the pressure on the inside and outside of the product is the same when vacuuming, which avoids the layer wrinkles or bridging caused by pressure difference. It is especially suitable for irregular parts that require high internal and external surface areas.

[0040] Preferably, the polystyrene has a density of 100 kg / m³. 3 -120kg / m 3 .

[0041] Specifically, the density of the polystyrene foam core mold 3 is controlled between 100kg / m³ and 120kg / m³. This density range ensures that the core mold 3 has sufficient structural rigidity, stable expansion and uniform pressure during heating and inflation, while also having good thermal expansion and easy demolding properties. At the same time, it is lightweight, easy to lay up and assemble and clean up, and is suitable for the inflation molding process of complex cavity components.

[0042] Preferably, the foam core mold 3 is designed with a 0.5mm compression allowance during processing to ensure the fit between the prepreg and the mold surface during the molding process.

[0043] Example 4: Based on Example 3, the prepreg includes carbon fiber twill prepreg and carbon fiber unidirectional tape prepreg.

[0044] Specifically, the two employ a combination of layered lamination and regional reinforcement: the main layup uses the length direction of the component as the 0° reference, and carbon fiber unidirectional prepreg (0°, 90°) and carbon fiber twill prepreg (+45°, -45°) are laid sequentially from the molding surface; areas requiring reinforcement, such as beams and trusses, are locally reinforced with carbon fiber unidirectional prepreg. This layup method can balance the in-plane shear performance and warp and weft strength of the prepreg: the carbon fiber twill prepreg provides good shear resistance, deformation resistance, and molding fit, while the carbon fiber unidirectional prepreg ensures high stiffness and high strength in the main load-bearing direction, thus enabling the component to possess both excellent structural strength and molding processability under complex stress conditions.

[0045] Preferably, the density of the carbon fiber twill prepreg is 300 g / m³. 2 -350g / m 2 The thickness is 0.2mm-0.3mm, and the layup thickness is 0.6mm-1mm. This ensures both the mold adherence and structural integrity of the prepreg during molding, while also meeting the rigidity and strength requirements of the manufactured parts.

[0046] Preferably, the density of the carbon fiber unidirectional tape prepreg is 150 g / m³. 2 -180g / m 2 The thickness is 0.14mm-0.16mm, and the layup thickness is 0.8mm-1mm. This ensures both the mold adherence and structural integrity of the prepreg during molding, while also meeting the rigidity and strength requirements of the manufactured parts.

[0047] Preferably, two layers of prepreg are laid on the inner surface of the upper mold 1, the inner surface of the lower mold 2, and the outer surface of the core mold 3.

[0048] Specifically, the process involves laying two layers of prepreg for molding. The compact layer structure ensures the overall strength and rigidity of the part through stacking, while avoiding poor resin flow and reduced molding fit due to excessive layers. Combined with the inflation and expansion process of the foam core mold 3, the prepreg can be evenly attached to the inner wall of the mold, effectively avoiding defects such as wrinkling and hollowing, and improving the molding quality and appearance flatness of complex structural parts.

[0049] Preferably, the two layers of prepreg on the inner surfaces of the upper mold 1 and the lower mold 2 are laid at angles of 0° and +45°, with the length direction of the part as the 0° reference reference, starting from the film-coating surface of the mold to be applied. The 0° layer uses carbon fiber unidirectional tape prepreg, and the +45° layer uses carbon fiber twill prepreg.

[0050] Specifically, by synergistically bearing the load of fibers in different directions, the multi-directional mechanical properties of prepreg parts are effectively improved, avoiding the problems of uneven stress and easy deformation caused by single-direction layup; at the same time, it ensures that the layup has good adhesion and shear resistance during the inflation and expansion molding process, making the overall strength, stiffness and dimensional stability of the parts better.

[0051] Preferably, the layup angles of the two layers of prepreg on the core mold 3 are 90 degrees and -45 degrees respectively, starting from the surface attached to the core mold 3; wherein, the 90-degree direction is perpendicular to the length direction of the part, and the -45-degree direction is rotated 45 degrees counterclockwise relative to the length direction of the part.

[0052] Specifically, the overall mold layup angles are arranged in the order of 0 degrees, 45 degrees, -45 degrees, and 90 degrees. This layup design makes the in-plane stiffness of the product approximately isotropic, suitable for multi-directional loads, and provides good impact resistance and stability. For the beam and stringer areas of the UAV that require reinforcement, six layers of carbon fiber unidirectional tape prepreg are used, with the fiber direction along the length of the part.

[0053] Example 5: Based on Example 4, step S3 involves placing the overall mold in an oven for hot pressing, including the following steps: placing the overall mold in the oven, and under a pressing pressure of 0.45MPa-0.6MPa, first raising the temperature from room temperature to 80℃ and holding it for 30 minutes; then raising the temperature from 80℃ to 120℃ and holding it for 90 minutes; then starting to cool down, during which the core mold 3 maintains pressure without depressurization, and after the mold cools down to below 40℃, depressurizing, disassembling the mold, and taking out the manufactured product, which is then sent to a fitter for repair.

[0054] Specifically, during the heating process, the resin in the prepreg gradually melts and flows, uniformly impregnating the fiber-reinforced material; during the heating stage from room temperature to 80°C, the foam core mold 3 is inflated and pressurized, causing the core mold 3 to expand and push the prepreg to fit tightly against the inner wall of the mold, achieving integrated molding of complex shapes; during the heating and heat preservation stage from 80°C to 120°C, the pressure is continuously maintained, and after reaching the preset curing temperature, the resin undergoes a cross-linking reaction, causing the prepreg to gradually cure and be molded into a composite material part.

[0055] This hot-pressing method has the following technical advantages: Reduce the resin viscosity in the prepreg and improve the fiber wetting degree in the prepreg: During the 80℃ heat preservation stage, the resin viscosity will decrease significantly as the temperature rises. At this time, the resin has the best fluidity, which can further wet the fiber, eliminate the air and micro voids introduced during the layup, and effectively reduce the porosity of the final product. Slowing down the exothermic reaction and controlling the risk of "bursting polymerization": The curing of resin in prepreg is an exothermic reaction. For thick-walled parts, if the temperature rises too quickly, the internal heat cannot dissipate in time, causing the temperature to exceed a specific 120°C, resulting in "bursting polymerization." This overheating can cause the inside of the product to turn yellow, crack, or even burn. Holding at 80°C allows the resin to react slowly, smoothly passing through the gelation stage and avoiding the instantaneous accumulation of heat. Reduce thermal stress and lower the risk of deformation and cracking: The carbon fiber in the mold has a large difference in thermal expansion coefficient. If the temperature is rapidly increased from room temperature to 120°C, internal stress will be generated between the mold and the product due to the different expansion rates. The 80°C heat preservation section acts as a "heat equalization buffer," synchronizing the temperature of the product and the mold, and reducing the risk of springback deformation and warping after demolding. Extending the resin gel time in the prepreg ensures a smooth operating and pressurization window: Compared to traditional autoclave processes, this solution maintains a temperature of 80°C, effectively extending the time the resin remains in a low-viscosity state. This ensures that the resin has fully flowed and impregnated the fiber reinforcement material in the prepreg before the pressure is fully established. This eliminates the need for large, energy-intensive equipment such as autoclaves, allowing for high-quality molding with only vacuum bag assistance or a simplified hot-pressing process, significantly reducing equipment costs and energy consumption.

[0056] Preferably, the cooling rate during the cooling process does not exceed 2°C / min.

[0057] Specifically, a cooling rate not exceeding 2℃ / min can maximize the elimination of internal stress in the product and prevent deformation. Since the thermal expansion coefficients of the carbon fibers in the prepreg and the resin matrix are inconsistent, slow cooling ensures a uniform temperature field inside and outside the product, avoiding residual stress caused by the surface layer hardening and shrinking while the interior continues to expand at high temperatures. This is especially important for large-sized, thin-walled, or high-curvature components, effectively preventing springback, warping, or dimensional deviations after demolding.

[0058] In the description of this invention, it should be understood that if terms such as "upper," "inner," or "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, it does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are for illustrative purposes only and should not be construed as limiting the invention.

[0059] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for manufacturing a drone fuselage based on air-expansion unibody molding technology, characterized in that: Includes the following steps: S1. Prepare the drone fuselage mold; the drone fuselage mold includes an upper mold (1), a lower mold (2) and a core mold (3); S2. Prepreg is laid in both the upper mold (1) and the lower mold (2), and prepreg is laid outside the core mold (3). The upper mold (1), the lower mold (2) and the core mold (3) are combined into a whole, wherein the core mold (3) is connected between the upper mold (1) and the lower mold (2). S3. Place the entire mold into an oven for hot pressing; S4. Remove the hot-pressed mold, disassemble the mold, and complete the manufacturing process.

2. The manufacturing method of the UAV fuselage based on air-expansion integrated molding technology as described in claim 1, characterized in that: In step S2, before laying the prepreg, a release agent is uniformly coated on the inner surface of the upper mold (1), the inner surface of the lower mold (2), and the outer surface of the core mold (3).

3. The manufacturing method of the UAV fuselage based on air-expansion integrated molding technology as described in claim 1, characterized in that: The core mold (3) is wrapped in a vacuum bag.

4. The manufacturing method of the UAV fuselage based on air-expansion integrated molding technology as described in claim 1, characterized in that: The prepreg includes carbon fiber twill prepreg and carbon fiber unidirectional tape prepreg.

5. The manufacturing method of the UAV fuselage based on the air-expansion integrated molding technology as described in claim 1, characterized in that: The core mold (3) is made of foam material.

6. The manufacturing method of the UAV fuselage based on the air-expansion integrated molding technology as described in claim 5, characterized in that: The foam material is polystyrene.

7. The manufacturing method of the UAV fuselage based on the air-expansion integrated molding technology as described in claim 4, characterized in that: The density of the carbon fiber twill prepreg is 300 g / m³. 2 ~350g / m 2 The thickness is 0.2mm-0.3mm, and the ply thickness is 0.6mm-1mm.

8. The manufacturing method of the UAV fuselage based on the air-expansion integrated molding technology as described in claim 4, characterized in that: The density of the carbon fiber unidirectional tape prepreg is 150 g / m³. 2 -180g / m 2 The thickness is 0.14mm-0.16mm, and the ply thickness is 0.8mm-1mm.

9. The manufacturing method of the UAV fuselage based on the air-expansion integrated molding technology as described in claim 1, characterized in that: Two layers of prepreg are laid on the inner surface of the upper mold (1), the inner surface of the lower mold (2), and the outer surface of the core mold (3).

10. The manufacturing method of the UAV fuselage based on the air-expansion integrated molding technology as described in claim 9, characterized in that: The layup angles of the two layers of prepreg on the inner surface of the upper mold (1) and the inner surface of the lower mold (2) are 0° and +45° respectively, starting from the film-coating surface of the mold to be coated.

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