Hollow composite material skin forming system and method

Abstract

The invention provides a hollow composite material skin forming system and method.A skin forming mold is supported at the top of a workbench, and a hollow composite material prefabricated body to be formed is laid at the top of the skin forming mold; demolding cloth is laid on the upper surface of the hollow composite material prefabricated body, a flow guide net is laid on the upper surface of the demolding cloth, and a vacuum bag is laid on the upper surface of the flow guide net; a sealing rubber strip is arranged between the vacuum bag and the skin forming mold; a glue inlet pipe is arranged in the vacuum bag and located at one end of the hollow composite material prefabricated body, the glue inlet pipe is connected with a glue storage barrel through a first communicating pipe, an exhaust pipe is arranged at the other end in the vacuum bag, and the exhaust pipe is connected with a resin collector through a second communicating pipe; the resin collector is connected with the vacuum pump through a third communicating pipe. The system and the method can be used for forming the aircraft trimmer of the 3D felt skin structure, the forming quality is guaranteed while the performance structure of the trimmer is met, and the forming efficiency is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft rudder and rudder trim tab repair, and particularly relates to a hollow composite skin forming system and method. Background Art

[0002] The elevator trim tab and rudder trim tab of a certain type of aircraft are composite structural parts, and the elevator trim tab and rudder trim tab are 3D felt structures. During aircraft overhaul, it is found that the scrap rate of the elevator trim tab and rudder trim tab is about 50%. The main reason for scrapping is that the radial clearance of the articulated bearing of the suspension bracket exceeds the tolerance (it is found after disassembly that this fault is caused by the wear of the mounting bolts). At this time, it is necessary to remanufacture the trim tab.

[0003] At present, only Shaanxi Aircraft Corporation in China can maturely produce 3D felt skin parts based on the hand lay-up molding process, but its production capacity is severely limited. In addition, due to the limitations of the hand lay-up process, the quality stability of the product is poor and the cost is high, which leads to a long single-piece manufacturing cycle of the trim tab. Coupled with the large demand for trim tabs and the limited capacity of the original manufacturing unit, it is difficult to purchase the products required for aircraft overhaul, far from meeting the aircraft repair needs of our factory. Summary of the Invention

[0004] The purpose of the present invention is to provide a hollow composite skin forming system and method, which can be used for the forming of the aircraft trim tab with a 3D felt skin structure. While meeting the performance structure of the trim tab, it ensures the forming quality, effectively improves the forming efficiency, and improves the aircraft repair efficiency.

[0005] To achieve the above technical features, the purpose of the present invention is realized as follows: A hollow composite skin forming system includes a workbench, on the top of which a skin forming mold is supported. On the top of the skin forming mold, a hollow composite preform to be formed is laid; a release cloth is laid on the upper surface of the hollow composite preform, a flow guide net is laid on the upper surface of the release cloth, and a vacuum bag is laid on the upper surface of the flow guide net; a sealing rubber strip is arranged between the vacuum bag and the skin forming mold to seal the entire hollow composite preform; an inlet pipe is arranged inside the vacuum bag and at one end of the hollow composite preform. The inlet pipe is connected to a glue storage barrel through a first connecting pipe. An air extraction pipe is arranged inside the vacuum bag and at the other end of the hollow composite preform. The air extraction pipe is connected to a resin collector through a second connecting pipe; the resin collector is connected to a vacuum pump through a third connecting pipe.

[0006] The outer shape structure of the upper surface of the skin forming mold is determined according to the outer shape structure of the 3D felt skin part to be formed.

[0007] The hollow composite preform is a three-dimensional braided hollow composite material made of glass fibers and can be impregnated and cured with an epoxy resin adhesive to form a 3D felt skin.

[0008] Before forming, a release agent is pre-coated between the upper surface of the skin forming mold and the hollow composite preform to form a release agent layer.

[0009] The interior of the glue storage barrel is used to store the epoxy resin adhesive.

[0010] The resin collector adopts a closed barrel structure and is equipped with a vacuum gauge.

[0011] A breather felt is provided between the exhaust pipe and the skin forming mold.

[0012] A pressure valve for vacuum pressure is provided on the resin collector.

[0013] A method for forming a hollow composite skin, which is realized by using the hollow composite skin forming system, includes the following steps: S1, Tooling preparation: Manufacture a corresponding skin forming mold according to the outer shape structure of the 3D felt skin part to be formed, and prepare the positioning blocks and clamping plates required during the forming process; S2, Fabric cutting: Cut the three-dimensional braided hollow composite material with corresponding dimensions according to the 3D felt skin part to be manufactured to form a hollow composite preform; S3, Fabric positioning: Clean the skin forming mold, apply the release agent, position the hollow composite preform on the skin forming mold, and then lay the release cloth and the flow guide net; S4, Bag making: Cut and manufacture a corresponding vacuum bag according to the dimensions of the hollow composite preform and the skin forming mold, and ensure that the vacuum bag can cover the entire hollow composite preform. Arrange the corresponding glue inlet pipe and exhaust pipe on the skin forming mold, connect the glue inlet pipe to the glue storage barrel, and connect the exhaust pipe to the resin collector and the vacuum pump; then bond the vacuum bag to the upper surface of the skin forming mold with a sealing strip; S5, Resin preparation: Prepare the corresponding epoxy resin adhesive according to the forming performance requirements of the three-dimensional braided hollow composite material, and store the epoxy resin adhesive in the interior of the glue storage barrel for standby; S6, Vacuum infusion: Start the vacuum pump to evacuate the inside of the vacuum bag, and then guide the epoxy resin adhesive in the glue storage barrel into the hollow composite material preform through the glue inlet pipe, and flow through the hollow composite material preform to infiltrate it. At this time, the hollow composite material preform will expand upright by capillary action to form a 3D felt structure; After the entire hollow composite material preform is impregnated, the pressure is maintained for a period of time; S7, vacuum release: Before the epoxy resin adhesive inside the hollow composite material preform is completely cured, the vacuum pump is stopped and the vacuum bag is depressurized, thereby allowing the hollow composite material preform to be completely unfolded to form a 3D felt structure; S8, curing: After the dipping and molding is completed, the 3D felt structure is taken out and then cured under certain temperature conditions; S9, demoulding: After curing is completed, demoulding is performed to take out the formed 3D felt skin parts; S10, detection: Use the card plate, feeler gauge and vernier caliper tools to perform surface inspection on the skin thickness and outer surface of 3D felt skin parts; Use visual inspection to check the quality of 3D felt skin parts after curing. No indentations or scratches that may damage the fibers are allowed on the surface. Check whether there are wrinkles on the surface and whether there are lodgings and depressions in the hollow areas in the thickness direction. Observe whether the resin is evenly distributed after curing. Try to avoid glue nodules and excessive resin residue in the hollow layer.

[0014] During the curing process, a method combining experiments and numerical simulations is used to determine in advance the key parameters of the 3D felt structure curing process: curing temperature, heating rate, cooling rate, vacuum degree, curing time, resin viscosity and resin content; according to the characteristics of the molding process and material requirements, the environmental requirements and equipment requirements are clarified; based on the technical requirements and process, the inspection process is formulated.

[0015] The present invention has the following beneficial effects: Compared with the hand lay-up process, the vacuum-assisted forming process used in this study to manufacture 3D felt skins has the following advantages: 1. The present invention uses molds and vacuum-assisted molding technology to significantly improve the surface quality and resin uniformity of 3D felt skins compared to hand lay-up molding.

[0016] 2. The present invention makes the overall hollow layer height of the 3D felt skin have better dimensional stability through reasonable process parameter setting.

[0017] 3. The vacuum-assisted forming used in the present invention has higher production efficiency. By adjusting the vacuum degree and the viscosity of the resin, the resin can uniformly impregnate 1 m within 3 minutes. 2 3D woven material.

[0018] 4. The successful development of the 3D felt composite skin in the present invention can be applied to the enlarged repair of the rudder and elevator trim tabs of a series of aircraft models, solving the problem that the overhaul cycle of the aircraft is affected by the uncontrollable purchase cycle of the two types of trim tabs in the company.

[0019] 5. The vacuum-assisted forming technology of the present invention can not only be used for the forming of 3D felt composites, but also for the forming of fiber composite structures and fiber sandwich structures. At the same time, through improvement, this technology can also be applied to the repair of aircraft composites, improving the repair quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the drawings and embodiments.

[0021] Figure 1 It is a forming system diagram of the present invention.

[0022] Figure 2 It is a forming process diagram of the present invention.

[0023] Figure 3 It is a physical diagram of the vacuum-assisted formed 3D felt skin of the present invention.

[0024] Figure 4 (a) (b) are the specimen manufacturing and physical diagrams during the forming process of the forming system of the present invention.

[0025] Figure 5 It is a physical diagram of the aircraft trim tab prepared by the present invention before demolding.

[0026] Figure 6 It is a physical diagram of the aircraft trim tab prepared by the present invention after cutting.

[0027] In the figure: glue storage bucket 1, first connecting pipe 2, workbench 3, sealing rubber strip 4, release agent layer 5, skin forming mold 6, glue inlet pipe 7, vacuum bag 8, flow guide net 9, release cloth 10, hollow composite preform 11, air extraction pipe 12, breathable felt 13, second connecting pipe 14, vacuum gauge 15, resin collector 16, third connecting pipe 17, vacuum pump 18. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The embodiments of the present invention will be further described below in conjunction with the drawings.

[0029] Example 1: See Figure 1-6, A hollow composite skin forming system, including a workbench 3, on the top of the workbench 3 there is supported a skin forming die 6, on the top of the skin forming die 6 there is laid a hollow composite preform 11 to be formed; on the upper surface of the hollow composite preform 11 there is laid a release cloth 10, on the upper surface of the release cloth 10 there is laid a flow guiding net 9, on the upper surface of the flow guiding net 9 there is laid a vacuum bag 8; between the vacuum bag 8 and the skin forming die 6 there is provided a sealing strip 4 to seal the entire hollow composite preform 11; inside the vacuum bag 8 and at one end of the hollow composite preform 11 there is provided a resin inlet pipe 7, the resin inlet pipe 7 is connected to a glue storage barrel 1 through a first connecting pipe 2, inside the vacuum bag 8 and at the other end of the hollow composite preform 11 there is provided an air extraction pipe 12, the air extraction pipe 12 is connected to a resin collector 16 through a second connecting pipe 14; the resin collector 16 is connected to a vacuum pump 18 through a third connecting pipe 17. By adopting the above-mentioned vacuum assisted forming process, the main advantages compared with the hand lay-up process are that the adhesive infiltration is more uniform, the control accuracy of the adhesive impregnation amount is higher, and it can be well used for the forming of the elevator tab of the 3D felt skin structure. While meeting the performance structure of the tab, it ensures the forming quality, and effectively improves the forming efficiency and the aircraft repair efficiency. In the specific forming process, through the vacuum infusion molding process, specifically, the gas in the three-dimensional braided hollow composite material is excluded under vacuum, and the resin is used to flow and penetrate to realize the impregnation of the fibers and their fabrics, and it is cured under certain temperature conditions to form a 3D felt skin part with a certain resin / fiber ratio.

[0030] Further, the outer shape structure of the upper surface of the skin forming die 6 is determined according to the outer shape structure of the 3D felt skin part to be formed. Through the above-mentioned skin forming die 6, the corresponding skin forming die 6 can be prefabricated according to the structure of the part to be formed.

[0031] Among them, the elevator tab and the rudder tab wing skins of the aircraft are both curved surfaces, and it is required that the hollow thickness of the skin should be consistent. Using the vacuum infusion molding process for manufacturing can improve the production efficiency while ensuring the product quality. The corresponding skin forming die 6 is made according to the outer shape structure of the elevator tab and the rudder tab of the aircraft.

[0032] Further, the hollow composite preform 11 is a three-dimensional braided hollow composite material, woven from glass fibers, and can be impregnated and cured by an epoxy resin adhesive to form a 3D felt skin. Among them, the glass fibers should have flame retardancy, and are impregnated and cured by an epoxy resin adhesive to form a 3D felt skin, and the resin also has flame retardancy.

[0033] Further, before forming, a release agent is pre-coated between the upper surface of the skin forming die 6 and the hollow composite material preform 11, thereby forming a release agent layer 5. Coating the release agent facilitates demolding after subsequent forming, thereby improving the demolding efficiency.

[0034] Further, the interior of the glue storage barrel 1 is used to store epoxy resin adhesive. The above-mentioned glue storage barrel 1 facilitates the storage of the epoxy resin adhesive required during the forming process.

[0035] Further, the resin collector 16 adopts a closed barrel structure and is equipped with a vacuum gauge 15. The vacuum gauge 15 facilitates the display of the vacuum degree during the impregnation process, thereby ensuring the impregnation effect of the bracket.

[0036] Further, a breather felt 13 is provided between the air extraction pipe 12 and the skin forming die 6. The above-mentioned breather felt 13 ensures the air permeability of the air extraction pipe 12 and prevents the air extraction pipe 12 from being blocked.

[0037] Further, a pressure valve for vacuum pressure is provided on the resin collector 16. The above-mentioned pressure valve facilitates the pressure control during the curing process.

[0038] Example 2: A method for forming a hollow composite material skin, the forming method is realized by using the hollow composite material skin forming system, and includes the following steps: S1, Tooling preparation: According to the outer shape structure of the 3D felt skin part to be formed, a corresponding skin forming die 6 is made, and the positioning blocks and clamping plates required during the forming process are prepared; S2, Fabric cutting: According to the 3D felt skin part to be produced, three-dimensional braided hollow composite materials of corresponding sizes are cut, thereby forming a hollow composite material preform 11; S3, Fabric positioning: The skin forming die 6 is cleaned, a release agent is coated, the hollow composite material preform 11 is positioned on the skin forming die 6, and then the release cloth 10 and the flow guiding net 9 are laid; S4, Bag making: According to the sizes of the hollow composite material preform 11 and the skin forming die 6, a corresponding vacuum bag 8 is cut and made, and it is ensured that the vacuum bag 8 can cover the entire hollow composite material preform 11. Corresponding glue inlet pipes 7 and air extraction pipes 12 are arranged on the skin forming die 6. The glue inlet pipe 7 is connected to the glue storage barrel 1, and the air extraction pipe 12 is connected to the resin collector 16 and the vacuum pump 18; then the vacuum bag 8 is bonded to the upper surface of the skin forming die 6 through the sealing strip 4; S5, Resin preparation: According to the molding performance requirements of the three-dimensional braided hollow composite material, the corresponding epoxy resin adhesive is prepared and stored in the glue storage barrel 1 for standby use; S6, vacuum infusion: The vacuum pump 18 is started to evacuate the interior of the vacuum bag 8, thereby guiding the epoxy resin adhesive in the glue storage barrel 1 to enter the hollow composite material preform 11 through the glue inlet pipe 7 and flow through the hollow composite material preform 11 to infiltrate the hollow composite material preform 11. At this time, the hollow composite material preform 11 will expand upright by capillary action to form a 3D felt structure. After the entire hollow composite material preform 11 is completely impregnated, the pressure is maintained for a period of time; S7, vacuum release: Before the epoxy resin adhesive inside the hollow composite material preform 11 is completely cured, the vacuum pump 18 is stopped and the vacuum bag 8 is depressurized, thereby completely unfolding the hollow composite material preform 11 to form a 3D felt structure. S8, curing: After the dipping and molding is completed, the 3D felt structure is taken out and then cured under certain temperature conditions; S9, demoulding: After curing is completed, demoulding is performed to take out the formed 3D felt skin parts; S10, detection: Use the card plate, feeler gauge and vernier caliper tools to perform surface inspection on the skin thickness and outer surface of 3D felt skin parts; Use visual inspection to check the quality of 3D felt skin parts after curing. No indentations or scratches that may damage the fibers are allowed on the surface. Check whether there are wrinkles on the surface and whether there are lodgings and depressions in the hollow areas in the thickness direction. Observe whether the resin is evenly distributed after curing. Try to avoid glue nodules and excessive resin residue in the hollow layer.

[0039] During the curing process, a method combining experiments and numerical simulations is used to determine in advance the key parameters of the 3D felt structure curing process: curing temperature, heating rate, cooling rate, vacuum degree, curing time, resin viscosity and resin content; according to the characteristics of the molding process and material requirements, the environmental requirements and equipment requirements are clarified; based on the technical requirements and process, the inspection process is formulated.

[0040] Example 3: The present invention compiled a process specification and clarified the process plan according to the development requirements. The surface quality, dimensional stability and mechanical properties of the newly manufactured parts were tested. The test results of the main items are as follows: (1) Surface quality such as Figure 3As shown, the surface has no wrinkles and the hollow part has no collapse; the resin is uniform without resin accumulation and lack of resin phenomenon. The resin content is also within the range of 55% ± 1% by weighing before and after curing.

[0041] (2) The thickness dimension stability is obtained by multiple groups of random measurements. The average thickness is 3.108 mm and the variance is 1.336×10 -3 , showing good process stability.

[0042] (3) A universal testing machine is used to conduct mechanical tests on three groups of specimens. The specimens and test standards all refer to ASTM standards. The values are shown in Table 1, all meeting the usage requirements equivalent to the original parts.

[0043] Table 1 Mechanical properties of vacuum-assisted molding 3D felt skin .

Claims

1. A hollow composite skin forming system, characterized in that, It includes a workbench (3), on the top of the workbench (3) is supported a skin forming die (6), and on the top of the skin forming die (6) is laid a hollow composite material preform (11) to be formed; on the upper surface of the hollow composite material preform (11) is laid a release cloth (10), on the upper surface of the release cloth (10) is laid a flow guiding net (9), and on the upper surface of the flow guiding net (9) is laid a vacuum bag (8); a sealing strip (4) is arranged between the vacuum bag (8) and the skin forming die (6) to seal the whole hollow composite material preform (11); an inlet pipe (7) is arranged inside the vacuum bag (8) and at one end of the hollow composite material preform (11), the inlet pipe (7) is connected to a glue storage barrel (1) through a first connecting pipe (2), an air extraction pipe (12) is arranged inside the vacuum bag (8) and at the other end of the hollow composite material preform (11), the air extraction pipe (12) is connected to a resin collector (16) through a second connecting pipe (14); the resin collector (16) is connected to a vacuum pump (18) through a third connecting pipe (17).

2. The hollow composite skin forming system according to claim 1, wherein: The outer shape structure of the upper surface of the skin forming die (6) is determined according to the outer shape structure of the 3D felt skin part to be formed.

3. The forming system for a hollow composite skin according to claim 1, wherein: The hollow composite material preform (11) is a three-dimensional braided hollow composite material, which is woven by glass fibers and can be impregnated and cured with an epoxy resin adhesive to form a 3D felt skin.

4. The forming system for a hollow composite skin according to claim 1, wherein: Before forming, a release agent is pre-coated between the upper surface of the skin forming die (6) and the hollow composite material preform (11) to form a release agent layer (5).

5. The forming system for a hollow composite skin according to claim 1, wherein: The inside of the glue storage barrel (1) is used to store the epoxy resin adhesive.

6. The forming system for a hollow composite skin according to claim 1, wherein: The resin collector (16) adopts a closed barrel structure form and is equipped with a vacuum gauge (15).

7. The forming system for a hollow composite skin according to claim 1, wherein: An air permeable felt (13) is arranged between the air extraction pipe (12) and the skin forming die (6).

8. The forming system for a hollow composite skin according to claim 1, wherein: A pressure valve for vacuum pressure is arranged on the resin collector (16).

9. A forming method for a hollow composite skin, characterized in that, The forming method is realized by using the hollow composite material skin forming system according to any one of claims 1-8, and includes the following steps: S1, Tooling preparation: According to the outer shape structure of the 3D felt skin part to be formed, a corresponding skin forming die (6) is made, and the positioning blocks and clamping plates required during the forming process are prepared; S2, Fabric cutting: According to the 3D felt skin part to be made, the three-dimensional braided hollow composite material of corresponding size is cut to form a hollow composite material preform (11); S3, Fabric positioning: The skin forming die (6) is cleaned, the release agent is coated, the hollow composite material preform (11) is positioned on the skin forming die (6), and then the release cloth (10) and the flow guiding net (9) are laid; S4, Bag making: According to the size of the hollow composite material preform (11) and the skin forming mold (6), a corresponding vacuum bag (8) is cut and manufactured, and it is ensured that the vacuum bag (8) can cover the entire hollow composite material preform (11), and a corresponding glue inlet pipe (7) and an air extraction pipe (12) are arranged on the skin forming mold (6), the glue inlet pipe (7) is connected to the glue storage barrel (1), and the air extraction pipe (12) is connected to the resin collector (16) and the vacuum pump (18); and the vacuum bag (8) is then bonded to the upper surface of the skin forming mold (6) through a sealing strip (4); S5, prepare resin: According to the molding performance requirements of the three-dimensional braided hollow composite material, a corresponding epoxy resin adhesive is prepared, and the epoxy resin adhesive is stored inside the adhesive storage barrel (1) for standby use; S6, vacuum infusion: Starting the vacuum pump (18) to evacuate the interior of the vacuum bag (8) through the vacuum pump (18), thereby guiding the epoxy resin adhesive in the glue storage barrel (1) to enter the hollow composite material preform (11) through the glue inlet pipe (7), and flowing through the hollow composite material preform (11) to infiltrate the hollow composite material preform (11). At this time, the hollow composite material preform (11) will expand upright by capillary action to form a 3D felt structure; After the entire hollow composite material preform (11) is completely impregnated, the pressure is maintained for a period of time; S7, vacuum release: Before the epoxy resin adhesive inside the hollow composite material preform (11) is completely cured, the vacuum pump (18) is stopped and the vacuum bag (8) is depressurized, thereby allowing the hollow composite material preform (11) to be completely unfolded to form a 3D felt structure; S8, curing: After the dipping and molding is completed, the 3D felt structure is taken out and then cured under certain temperature conditions; S9, demoulding: After curing is completed, demoulding is performed to take out the formed 3D felt skin parts; S10, detection: Use the card plate, feeler gauge and vernier caliper tools to perform surface inspection on the skin thickness and outer surface of 3D felt skin parts; Use visual inspection to check the quality of 3D felt skin parts after curing. No indentations or scratches that may damage the fibers are allowed on the surface. Check whether there are wrinkles on the surface and whether there are lodgings and depressions in the hollow areas in the thickness direction. Observe whether the resin is evenly distributed after curing. Try to avoid glue nodules and excessive resin residue in the hollow layer.

10. The method for forming a hollow composite skin according to claim 9, wherein During the curing process, a method combining experiments and numerical simulations is used to determine in advance the key parameters of the 3D felt structure curing process: curing temperature, heating rate, cooling rate, vacuum degree, curing time, resin viscosity and resin content; according to the characteristics of the molding process and material requirements, the environmental requirements and equipment requirements are clarified; based on the technical requirements and process, the inspection process is formulated.

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