A method for manufacturing a composite pipe based on a negative pressure shaping inflatable bag core mold

Abstract

The application relates to the technical field of composite material forming, and discloses a composite material pipe manufacturing method based on a negative pressure shaping inflatable bag core mold, which comprises the following steps: placing an inflatable bag in a forming mold; filling dense granular materials into the inflatable bag; applying negative pressure to the inflatable bag by vacuumizing the inflatable bag, so as to form a temporary core mold which is consistent with the shape of the inner cavity of a pipe to be manufactured; maintaining the negative pressure in the inflatable bag, taking out the temporary core mold, and layer by layer laying and pasting prepreg on the surface of the temporary core mold under the condition of maintaining the negative pressure; putting the temporary core mold together with the prepreg layers into the forming mold and closing the mold; removing the negative pressure in the inflatable bag, inflating and pressurizing the inflatable bag, and performing curing forming according to a prepreg curing process; cooling and demolding after curing is completed, discharging the granular materials in the inflatable bag and recycling, taking out the inflatable bag from the pipe, and obtaining a composite material pipe, so that the composite material pipe is manufactured at low cost, prepreg laying and pasting are facilitated, and high-quality composite material pipes with space bending and variable diameter structures can be manufactured.

Description

Technical Field

[0001] This invention relates to the field of composite material molding technology, and in particular to a method for manufacturing composite material tubular components based on a negative pressure molding inflatable bag core mold. Background Technology

[0002] Aerospace and low-altitude economy aircraft are highly sensitive to structural weight; continuous carbon fiber composite tubing serves both lightweighting and structural load-bearing functions, as well as providing functional pathways. Currently, the manufacturing of spatially bent, variable-diameter composite tubing mainly faces the following challenges: Inflatable bag manufacturing process method 1: The prepreg is laid on both sides of the molding mold and then the mold is closed. In this method, the prepreg is only joined at the parting surface. The fibers are not continuous at the joining position, the overlap strength is low, and it is difficult to meet the structural load-bearing requirements.

[0003] Method 2 for inflatable bags: Prepreg is directly laid on the surface of the inflatable bag. Although this method can achieve staggered layer overlaps, the shape of the inflatable bag changes significantly after inflation in bends or pipes with varying diameters. Due to the inability of fibers to be stretched and the restriction of interlayer sliding, defects such as gaps, bridging, and delamination are easily generated at locations with large curvatures. Wrinkles are also prone to appear on the inner and outer walls of the pipe, resulting in a low yield.

[0004] Soluble core mold process: requires machining of the entire soluble material, resulting in a long manufacturing cycle and high cost; the core mold surface needs to be coated with a smooth coating, and dimensional scaling design is required to match the thermal expansion differences of metal tooling, making the process complex, and the core mold material cannot be reused.

[0005] Fusible metal core mold process: requires CNC machining of the core mold, and both material and processing costs are relatively high. It is suitable for small-batch, multi-variety manufacturing, and the metal core mold material needs to be purchased externally.

[0006] In summary, existing methods struggle to balance cost, quality, and efficiency. Summary of the Invention

[0007] The purpose of this invention is to provide a method for manufacturing composite material pipe fittings based on a negative pressure shaping inflatable bag core mold, aiming to solve or improve at least one of the above-mentioned technical problems, and to manufacture high-quality composite material pipe fittings that are cost-effective, easy to lay prepreg, and adaptable to spatial bending and variable diameter structures.

[0008] To achieve the above objectives, the present invention provides the following solution: The present invention provides a method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold, comprising the following steps: S1. Place the inflatable bag into the cavity of a molding die with a thickness compensation pad or wax sheet; S2. Fill the air bag with dense granular material; S3. Apply negative pressure to the air bag by evacuating it, so that the air bag fits the molding mold cavity under the action of external atmospheric pressure. The granular material in the air bag maintains its shape through static friction between the particles after being compressed, forming a temporary core mold that is consistent with the shape of the inner cavity of the pipe to be manufactured. S4. Maintain negative pressure inside the inflatable bag, open the mold and remove the temporary core mold, and lay prepreg layer by layer on the surface of the temporary core mold that maintains negative pressure, with the overlapping positions of each layer staggered. S5. After the paving is completed, the temporary core mold together with the prepreg layer is placed into the molding mold and the mold is closed. S6. Remove the negative pressure inside the air bag and pressurize it by filling it with air, and then cure and shape it according to the prepreg curing process. S7. After curing, cool and demold, discharge the particulate material in the air bag and recycle it, and pull the air bag out of the pipe to obtain the composite material pipe.

[0009] Optionally, the thickness of the thickness compensation pad or wax sheet is 1.1 times the product design wall thickness, and its edge is flush with the parting surface of the molding die.

[0010] Optionally, the inflatable bag is a reusable thermoplastic bag structure, and the inflation port is provided with a replaceable interface (5), which is used to connect to a vacuum source and a pressurized air source.

[0011] Optionally, the granular material is a mineral particle with a particle size of 0.5mm to 4.0mm, a temperature resistance of not less than 210°C, a smooth particle surface without sharp corners, and when the friction coefficient of the granular material is insufficient, rosin is used to perform surface impregnation treatment on the granular material.

[0012] Optionally, in step S3, the vacuum level of the vacuum pump is not less than 0.095 MPa, and the negative pressure maintenance time is not less than the setting time required for the air bag to completely fit the molding mold cavity, and not less than 10 minutes.

[0013] Optionally, in step S4, vacuum compaction is performed every 3 to 5 layers of prepreg, and each vacuum compaction takes no less than 15 minutes.

[0014] Optionally, in step S6, the curing temperature range is 70°C to 200°C, and the inflation pressure is 0.3MPa to 1.0MPa.

[0015] Optionally, in step S7, after curing, the mold is opened after cooling to below 60°C.

[0016] Optionally, the composite material fitting is a space-bent composite material fitting with variable diameter and / or axial bending.

[0017] Optionally, the composite material pipe fitting is a composite material duct, air conditioning vent pipe, space elbow, or connecting elbow used in aerospace or low-altitude economic vehicles.

[0018] The present invention discloses the following technical effects: The temporary core mold of this invention has a shape retention capability similar to that of a rigid core mold under negative pressure. Prepreg can be laid layer by layer outside the mold, and the overlap positions of each layer can be staggered to avoid fiber discontinuity at the parting surface, thereby improving the overlap strength and interlayer quality.

[0019] The prepreg of this invention is not directly laid in an inflated state, which avoids gaps, bridging, delamination and wrinkles in large curvature areas caused by the deformation of the inflatable bag, thus improving the yield.

[0020] The inflatable bag of this invention is first used as a rigid core mold for laying under negative pressure, and then used as a flexible pressurizing medium for curing under positive pressure, thus combining the quality advantages of low cost of inflatable bag process and easy laying of rigid core mold.

[0021] This invention reduces material costs, shortens the manufacturing cycle, and is suitable for repeated use.

[0022] This invention is particularly applicable to spatially bent composite material pipes with variable diameter and axial bending, such as ducts, air conditioning vents, space elbows, and connecting bends for aircraft in the aerospace or low-altitude economy fields. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the composite material pipe structure of the present invention; Figure 2 This is a schematic diagram of the temporary core mold structure of the present invention; Figure 3 This is a schematic diagram of the molding die structure of the present invention.

[0024] In the diagram: 1. Inflatable bag; 2. Molding mold; 3. Granular material; 4. Composite material fittings; 5. Replaceable interface. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Reference Figures 1 to 3 This invention provides a method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold, comprising the following steps: S1. Clean the grease and dirt on the inner surface of the molding mold 2, apply the release agent, lay the thickness compensation pad or wax sheet on the inner surface of the molding mold 2, place the air bag 1 in the cavity of the molding mold 2 with the thickness compensation pad or wax sheet, place the air inlet on the outside of the molding mold 2, close the mold and lock it. S2. Fill the air bag 1 with dense granular material 3. During filling, the granular material 3 can be compacted by vibration. The duration and frequency of vibration are determined according to the size of the air bag, the type of filler, the curvature of the tube, etc. S3. Apply negative pressure to the air bag 1 by drawing a vacuum, so that the air bag 1 fits into the cavity of the molding mold 2 under the action of external atmospheric pressure. The granular material inside the air bag 1 maintains its shape through static friction between the granules after being compressed, forming a temporary core mold that is consistent with the shape of the inner cavity of the pipe to be manufactured. S4. Maintain negative pressure inside the air bag 1, open the mold and remove the temporary core mold, and lay prepreg layer by layer on the surface of the temporary core mold that maintains negative pressure, with the overlapping positions of each layer staggered. S5. After the paving is completed, place the temporary core mold together with the prepreg layer into the molding mold 2 and close the mold. After closing the mold, check the mold gap to meet the design requirements. S6. Remove the negative pressure inside the air bag 1, and inflate and pressurize the air bag 1, then cure and shape it according to the prepreg curing process. S7. After curing, cool and demold, discharge the particulate material 3 inside the air bag 1 and recycle it, and pull the air bag 1 out of the pipe to obtain the composite material pipe 4.

[0028] In one embodiment of the present invention, the thickness of the thickness compensation shim or wax sheet is 1.1 times the designed wall thickness of the product, and the edge is flush with the parting surface of the molding die 2. The shim or wax sheet is used at room temperature and can compensate for the thickness changes during the curing shrinkage and compaction process of the prepreg, ensuring the final product wall thickness and avoiding steps, flash or dimensional deviations at the parting surface.

[0029] In one embodiment of the present invention, the air bag 1 is a reusable thermoplastic bag structure, and the air inlet is provided with a replaceable interface 5. The replaceable interface 5 is used to connect to a vacuum source and a pressurized air source to realize both negative pressure shaping and positive pressure curing functions, thereby reducing the cost of use and improving the efficiency of operation.

[0030] In one embodiment of the present invention, the granular material 3 is a mineral particle with a particle size of 0.5mm to 4.0mm and a temperature resistance of not less than 210°C. The particle surface is smooth and without sharp corners, which can ensure dense filling, smooth vacuuming, and stable shape, and avoid puncturing the air bag. When the friction coefficient of the granular material 3 is insufficient, rosin is used to impregnate the surface of the granular material 3. Rosin impregnation can increase the friction coefficient between particles and prevent the particles from sliding relative to each other after negative pressure molding.

[0031] In one embodiment of the present invention, in S3, the vacuum degree of the vacuum is not less than 0.095MPa, and the negative pressure is maintained for a time not less than the setting time required for the air bag 1 to completely fit into the cavity of the molding mold 2, and not less than 10 minutes, which can ensure that the air bag fits tightly into the mold cavity, so that the particulate material forms a stable and transferable temporary core mold.

[0032] In one embodiment of the present invention, in S4, vacuum compaction is performed every 3 to 5 layers of prepreg, and each vacuum compaction takes no less than 15 minutes. This can effectively remove interlayer air, reduce porosity and delamination, and improve the interlayer shear strength and density of the composite material.

[0033] In one embodiment of the present invention, in S6, the curing temperature range is 70°C to 200°C, and the inflation pressure is 0.3MPa to 1.0MPa, which can be matched with commonly used prepreg curing processes. The pressure is applied evenly through the inflation bag to ensure the quality of the inner and outer walls of the pipe fitting.

[0034] In one embodiment of the present invention, in step S7, after curing, cooling to below 60°C before mold opening can reduce the risk of thermal stress and deformation during demolding, ensuring the dimensional stability of the pipe fitting. The inflation port is then opened to discharge and recycle the particulate material 3 from the inflation bag 1. The inflation bag 1 is then extracted from the pipe fitting to obtain the composite material pipe fitting 4. The inner and outer surfaces of the pipe fitting are then inspected for quality, and the edges are trimmed.

[0035] In one embodiment of the present invention, the composite material pipe 4 is a spatially bent composite material pipe with variable diameter and / or axial bending, which can adapt to complex spatial orientation and cross-sectional changes, and solve the problems of traditional rigid core molds being difficult to demold and inflatable bags being prone to defects when directly laid.

[0036] In one embodiment of the present invention, the composite material pipe 4 is a composite material duct, air conditioning vent pipe, space elbow or connecting elbow used in aerospace or low-altitude economic vehicles. It can take advantage of the lightweight and structural-functional integration of composite materials to meet the requirements of aircraft for weight reduction and reliability.

[0037] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0038] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold, characterized in that, Includes the following steps: S1. Place the inflatable bag (1) into the cavity of the molding die (2) with a thickness compensation pad or wax sheet; S2. Fill the air bag (1) with dense granular material (3); S3. Apply negative pressure to the air bag (1) by vacuuming, so that the air bag (1) fits the cavity of the molding mold (2) under the action of external atmospheric pressure. The granular material in the air bag (1) maintains its shape through static friction between particles after being compressed, forming a temporary core mold that is consistent with the shape of the inner cavity of the pipe to be manufactured. S4. Maintain negative pressure inside the inflatable bag (1), open the mold and take out the temporary core mold, and lay prepreg layer by layer on the surface of the temporary core mold that maintains negative pressure, with the overlapping positions of each layer staggered. S5. After the paving is completed, the temporary core mold together with the prepreg layer is placed into the molding mold (2) and the mold is closed. S6. Remove the negative pressure inside the air bag (1), and pressurize the air bag (1) with air, and cure it according to the prepreg curing process; S7. After curing, cool and demold, discharge the particulate material (3) in the air bag (1) and recycle it, and extract the air bag (1) from the pipe to obtain the composite material pipe (4).

2. The method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, The thickness of the thickness compensation pad or wax sheet is 1.1 times the product design wall thickness, and its edge is flush with the parting surface of the molding die (2).

3. The method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, The inflatable bag (1) is a reusable thermoplastic bag structure with a replaceable interface (5) at the inflation port. The replaceable interface (5) is used to connect to a vacuum source and a pressurized gas source.

4. The method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, The granular material (3) is a mineral particle with a particle size of 0.5 mm to 4.0 mm and a temperature resistance of not less than 210°C. The particle surface is smooth and without sharp corners. When the friction coefficient of the granular material (3) is insufficient, rosin is used to perform surface impregnation treatment on the granular material (3).

5. The method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, In S3, the vacuum degree of the vacuum is not less than 0.095MPa, and the negative pressure is maintained for a time not less than the shaping time required for the air bag (1) to completely fit the cavity of the molding mold (2), and not less than 10 minutes.

6. The method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, In step S4, vacuum compaction is performed every 3 to 5 layers of prepreg, with each vacuum compaction lasting no less than 15 minutes.

7. The method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, In S6, the curing temperature range is 70°C to 200°C, and the inflation pressure is 0.3MPa to 1.0MPa.

8. A method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, In step S7, after curing, the mold is opened after cooling to below 60°C.

9. A method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, The composite material pipe fitting (4) is a spatially bent composite material pipe fitting with variable diameter and / or axial bending.

10. A method for manufacturing composite material tubular components based on a negative pressure shaping inflatable bag core mold according to claim 1, characterized in that, The composite material pipe fitting (4) is a composite material duct, air conditioning vent pipe, space elbow or connecting elbow used in aerospace or low-altitude economic field aircraft.

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