Preparation method of thin-wall composite material tubular beam with large length-diameter ratio and prepared tubular beam

Abstract

The invention discloses a preparation method of a large-length-diameter-ratio thin-wall composite material tubular beam and the prepared tubular beam. The method comprises the following steps that S1, a foam core mold is prepared; s2, the foam core mold is sleeved with a tubular air bag, and vacuumizing is conducted; step S3, paving a prepreg sheet on the air bag; s4, integrally transferring the foam core mold and the air bag which are paved with the material sheets into a mold cavity of a metal mold; s5, high-pressure gas is inflated into the gas bag, and then the gas bag is sent into a drying oven to be heated, cured and formed; and S6, after curing is finished, mold opening is conducted, a product is obtained, air bag and foam core mold residues are extracted from the interior of the product, and therefore a tubular beam product is obtained. The problems that in a conventional metal male mold paving-vacuum bag forming-autoclave curing method, demolding is difficult, and due to mold deformation, the straightness of a product is out of tolerance, and the surface quality is poor are solved.

Description

Technical Field

[0001] The invention relates to the field of composite material tube beam preparation methods, in particular to a method for preparing a large aspect ratio thin-wall composite material tube beam and the prepared tube beam. Background Art

[0002] At present, the application scope of advanced composite materials in the field of aircraft manufacturing is constantly expanding, from various secondary load-bearing structures such as floors and fairings to main load-bearing structural parts. Beam structural parts are the main load-bearing structures of aircraft. They are large in size, heavy in weight, and complex in force. The use of carbon fiber composite materials to make beam structural parts can reduce the weight of the structure and improve the rigidity, which is of great significance.

[0003] The composite beam structure of large UAV has the structural characteristics of large aspect ratio and thin wall thickness. The conventional metal positive mold laying-vacuum bag forming-autoclave curing process has problems such as demoulding difficulty, poor mold rigidity affecting product straightness, and poor outer surface quality. It is difficult to meet the high-precision dimensional requirements during aircraft tube beam assembly, and the production cost is high. Summary of the invention

[0004] The present invention provides a method for preparing a thin-wall composite material tubular beam with a large aspect ratio and the prepared tubular beam, so as to overcome the deficiencies and defects mentioned in the above background technology.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A method for preparing a thin-walled composite material tube beam with a large aspect ratio, comprising the following steps: Step S1, preparing a foam core mold; Step S2, inserting a tubular air bag outside the foam core mold, wherein one axial end of the air bag is closed and the other axial end is open, and vacuuming is performed through the open end of the air bag so that the air bag is tightly wrapped and fits the circumferential outer wall of the foam core mold; Step S3, laying multiple layers of prepreg sheets on the circumferential outer wall of the airbag, each layer of prepreg is composed of multiple sheets spliced ​​together, the splicing seams between adjacent sheets along the fiber direction are butted, the splicing seams between adjacent sheets perpendicular to the fiber direction are overlapped, and the splicing seams of the upper and lower layers of prepreg are staggered along the thickness direction; Step S4, transferring the foam core mold and the air bag after the sheet paving in step S3 to the mold cavity of the metal mold as a whole, and closing the upper and lower molds of the metal mold until the mold clearance meets the process requirements; Step S5, filling the air bag with high pressure air through the open end of the air bag, using the air pressure to make the laid sheet and the mold cavity of the metal mold fully adhere to each other, and then sending the metal mold as a whole into an oven for heating and curing; Step S6, after the curing is completed, the mold is opened to obtain the product, and the air bag and the foam core mold residue are extracted from the inside of the product, thereby obtaining a pipe beam product.

[0006] In a further step S1, a foam core mold is formed by splicing and assembling multiple EPS foam blocks according to required sizes.

[0007] Furthermore, the size of each EPS foam block is reduced by 1-2 mm on one side compared to the inner surface size of the product obtained in step S6.

[0008] Furthermore, the tubular air bag in step S2 is made of nylon, latex, or polyester.

[0009] Furthermore, the prepreg described in step S3 is one or more of carbon fiber resin prepreg, glass fiber resin prepreg, and aramid fiber resin prepreg.

[0010] Furthermore, the heating and curing molding process in step S5 is as follows: First, the pressure is increased step by step by 0.1MPa to the target pressure of 0.8~1.5MPa, and the pressure is maintained for 3~5 minutes at each step; after reaching the target pressure of 0.8~1.5MPa, the curing curve is started: the temperature is increased to 60~100℃ at a heating rate of 0.5~2℃ / min, and the temperature is maintained for 0.5~1 hour, and then the temperature is continued to be increased to 120~150℃, and the temperature is maintained for 1~3 hours; finally, the pressure is released when the temperature is lowered to no more than 60℃, thereby completing the heating and curing molding.

[0011] Furthermore, in step S5, the target pressure is 1.2 MPa.

[0012] A large aspect ratio thin-wall composite material tubular beam is prepared by using the large aspect ratio thin-wall composite material tubular beam preparation method.

[0013] Compared with the prior art, the beneficial effects of the present invention are that, since the outer dimensions and surface quality of the EPS foam + air bag bulging molded product are guaranteed by the metal mold, and the metal mold does not need to be suspended during solidification, and no flexural deformation will occur, the product formed by this process method has good straightness, high dimensional accuracy, smooth surface, and dense internal structure, which overcomes the problems of demolding difficulties, product straightness out-of-tolerance caused by mold deformation, and poor surface quality in the conventional metal positive mold paving-vacuum bag forming-autoclave curing method of large aspect ratio thin-walled composite pipe beams, and no autoclave equipment is needed, which reduces production costs and has obvious advantages in the forming of large aspect ratio thin-walled composite pipe beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the cross-sectional structure of the composite material tube beam air bag internal bulging: Figure 2 This is a schematic diagram of the longitudinal section structure of the composite material tube beam air bag internal expansion forming: Numbers in the figure: 1-foam core mold; 2-air bag; 3-sheet; 4-metal upper mold; 5-metal lower mold; 6-metal mold locking bolt; 7-inflating joint; 8-air supply pipeline. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0016] This embodiment discloses a method for preparing a circular variable cross-section pipe beam of a thin-walled composite material with a large aspect ratio, such as Figure 1~Figure 2 As shown, the following steps are included: Step S1, assembling multiple EPS foam blocks into a foam core mold 1 according to the required size, and fixing the adjacent EPS foam blocks with paper tape at the joints. The size of each EPS foam block is 1-2 mm smaller than the inner surface size of the final product.

[0017] Step S2: insert a tubular air bag 2 with a width of 140 mm (circumference of 280 mm) outside the foam core mold 1. The material of the air bag 2 is nylon, latex, or polyester. The air bag 2 is open at one axial end and sealed at the other axial end. The length of the air bag 2 is greater than the total length of the foam core mold 1, and a margin of 100-150 mm is reserved at the sealed end of the air bag 2, and a margin of 200-250 mm is reserved at the open end of the air bag 2.

[0018] Then, the open end of the air bag 2 is sealed with a sealing tape and connected to a vacuum nozzle, and the inside of the air bag 2 is evacuated through the vacuum nozzle at the open end, so that the air bag 2 is tightly wrapped and fits the circumferential outer wall of the foam core mold 1.

[0019] Step S3, laying 9 layers of prepreg sheets 3 on the circumferential outer wall of the airbag 2, wherein the prepreg is one or more of carbon fiber resin prepreg, glass fiber resin prepreg, and aramid fiber resin prepreg.

[0020] During paving, each layer of prepreg is composed of multiple pieces of material. The adjacent pieces of material along the fiber direction are butted, with a butt gap of 0-2 mm; the adjacent pieces of material perpendicular to the fiber direction are overlapped, with an overlap width of 15-20 mm. The joints of the upper and lower layers of prepreg are staggered by at least 30 mm in the thickness direction.

[0021] Step S4, transfer the foam core mold 1 and the air bag 2 with the completed sheet paving as a whole to the lower mold cavity of the metal lower mold 5 in the metal mold, connect the inflation joint 7 to the open end of the air bag 2 and place it in the slot at the end of the metal lower mold 5, and then close the metal upper mold 4 of the metal mold on the metal lower mold 5 to form a complete metal mold. The complete mold cavity is composed of the lower mold cavity of the metal lower mold 5 and the upper mold cavity of the metal upper mold 4, and the bolts 6 connecting the metal upper and lower molds are used to pressurize so that the mold clearance between the metal upper and lower molds meets the process requirements (less than 0.1 mm in this embodiment).

[0022] Step S5, connect the external air supply pipeline 8 to the inflation connector 7 at the end of the metal mold 5, slowly fill the air bag 2 with high pressure gas, use the inflation pressure to make the laid sheet 3 and the mold cavity of the metal mold fully adhere, and then send the metal mold into an oven for heating and curing. The heating and curing process is as follows: First, the pressure is increased step by step by 0.1MPa to the target pressure of 0.8~1.5MPa, and the pressure is maintained for 3~5 minutes at each step; after reaching the target pressure of 0.8~1.5MPa, the curing curve is started: the temperature is increased to 60~100℃ at a heating rate of 0.5~2℃ / min, and the temperature is maintained for 0.5~1 hour, and then the temperature is continued to be increased to 120~150℃, and the temperature is maintained for 1~3 hours; finally, the pressure is released when the temperature is lowered to no more than 60℃, thereby completing the heating and curing molding.

[0023] In this embodiment, the target pressure of the step pressurization is 0.8-1.5MPa, which can meet the molding process requirements. However, after testing, considering the pressure bearing capacity of the air bag and the internal quality of the product, the target pressure of 1.2MPa is the optimal value.

[0024] S6. Since EPS foam shrinks during heating, the product is obtained by opening the mold after curing, and the air bags and foam core mold residues are extracted from the inside of the product, thereby obtaining a pipe beam product.

[0025] The thin-walled composite pipe beam product with a large aspect ratio finally obtained in this embodiment has a cross-sectional shape of a circle, an ellipse, a rounded rectangle, or other geometric shapes, and a cross-sectional size of a constant cross-section or a variable cross-section. When preparing the product, it is only necessary to select a foam core mold 1 with a suitable cross-section and a metal mold with a matching cross-section for the mold cavity to complete the preparation.

[0026] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and such combinations should also be regarded as the contents disclosed in the present disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0027] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by technical personnel in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A method for preparing a thin-walled composite pipe beam with a large aspect ratio, characterized in that: The following steps are involved: Step S1, preparing a foam core mold; Step S2, inserting a tubular air bag outside the foam core mold, wherein one axial end of the air bag is closed and the other axial end is open, and vacuuming is performed through the open end of the air bag so that the air bag is tightly wrapped and fits the circumferential outer wall of the foam core mold; Step S3, laying multiple layers of prepreg sheets on the circumferential outer wall of the airbag, each layer of prepreg is composed of multiple sheets spliced ​​together, the splicing seams between adjacent sheets along the fiber direction are butted, the splicing seams between adjacent sheets perpendicular to the fiber direction are overlapped, and the splicing seams of the upper and lower layers of prepreg are staggered along the thickness direction; Step S4, transferring the foam core mold and the air bag after the sheet paving in step S3 to the mold cavity of the metal mold as a whole, and closing the upper and lower molds of the metal mold until the mold clearance meets the process requirements; Step S5, filling the air bag with high pressure air through the open end of the air bag, using the air pressure to make the laid sheet and the mold cavity of the metal mold fully adhere to each other, and then sending the metal mold as a whole into an oven for heating and curing; Step S6, after the curing is completed, the mold is opened to obtain the product, and the air bag and the foam core mold residue are extracted from the inside of the product, thereby obtaining a pipe beam product.

2. The method for preparing a thin-walled composite material tube beam with a large aspect ratio according to claim 1, characterized in that: In step S1, a foam core mold is formed by splicing and assembling multiple EPS foam blocks according to required sizes.

3. The method for preparing a thin-walled composite material tube beam with a large aspect ratio according to claim 2, characterized in that: The size of each EPS foam block is 1-2 mm smaller than the inner surface size of the product obtained in step S6.

4. The method for preparing a thin-walled composite material tube beam with a large aspect ratio according to claim 1, characterized in that: The material of the tubular air bag in step S2 is nylon, latex, or polyester.

5. The method for preparing a thin-walled composite material tube beam with a large aspect ratio according to claim 1, characterized in that: The prepreg described in step S3 is one or more of carbon fiber resin prepreg, glass fiber resin prepreg, and aramid fiber resin prepreg.

6. The method for preparing a thin-walled composite material tube beam with a large aspect ratio according to claim 1, characterized in that: The heating and curing molding process in step S5 is as follows: First, the pressure is increased step by step by 0.1MPa to the target pressure of 0.8~1.5MPa, and the pressure is maintained for 3~5 minutes at each step; after reaching the target pressure of 0.8~1.5MPa, the curing curve is started: the temperature is increased to 60~100℃ at a heating rate of 0.5~2℃ / min, and the temperature is maintained for 0.5~1 hour, and then the temperature is continued to be increased to 120~150℃, and the temperature is maintained for 1~3 hours; finally, the pressure is released when the temperature is lowered to no more than 60℃, thereby completing the heating and curing molding.

7. The method for preparing a thin-walled composite material tube beam with a large aspect ratio according to claim 1, characterized in that: In step S5, the target pressure is 1.2 MPa.

8. A thin-walled composite tubular beam with a large aspect ratio, characterized in that: The thin-wall composite tubular beam having a large aspect ratio is prepared by the method for preparing the thin-wall composite tubular beam having a large aspect ratio as described in any one of claims 1 to 7.

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