Forming process method for reducing porosity of parting area of composite U-shaped part

Abstract

The invention belongs to the technical field of composite material product forming, and particularly relates to a forming process method for reducing the porosity of a mold splitting area of a composite material U-shaped piece. Comprising the steps that firstly, a forming tool is prepared, and cleanliness and no dust are guaranteed; 2, laying a first layer of prepreg of the outer skin; (3) pasting a vacuum bag and pre-compacting, (4) laying a residual layer prepreg of the outer skin, and (5) laying a core material, and after completion, pasting the vacuum bag and pre-compacting once to ensure that the core material is compacted and attached; step 6, laying a first layer of prepreg of the inner skin, and after the laying is completed, pre-compacting the pasted vacuum bag once to ensure that the core material of the first layer of prepreg of the inner skin is compacted and attached; 7, laying a residual layer of prepreg of the inner skin; and 8, curing and discharging, starting the mold when the temperature is reduced to 60 DEG C or below, cleaning the workpiece after the mold is started, and carrying out nondestructive porosity detection.

Description

Technical Field

[0001] This invention belongs to the field of composite material product molding technology, and particularly relates to a molding process method for reducing the porosity of the parting area of ​​composite material U-shaped parts. Background Technology

[0002] Since their introduction in the 1960s, advanced composite materials have brought significant weight reduction and overall performance improvements in aerospace structures due to their lightweight, high strength, high stiffness, heat resistance, sound absorption and insulation, impact resistance, and fatigue resistance. Because these lightweight structural materials possess optimal specific strength, specific stiffness, maximum fatigue resistance, and smooth surface, their use in aircraft manufacturing has been steadily increasing in recent years. The amount of composite materials used has become one of the important indicators of an aircraft's sophistication. In the Boeing 787 and Airbus A350, the application rate exceeds 50%, and they are also widely used in China's aerospace industry. The molding process of composite material autoclave products refers to the process of curing the product into a finished product under heating and pressurization conditions in an autoclave; it is the result of the combined effects of temperature, pressure, and time. The application of composite materials in aircraft components has expanded to complex and load-bearing structures, such as some beams and ribs. However, some high-curvature parts, after curing, exhibit porosity that fails to meet design specifications. This defect significantly impacts the structural strength and stiffness of the parts, severely affecting aircraft safety performance. Therefore, reducing the porosity of composite materials to meet design acceptance requirements is crucial. Traditional molding methods are time-consuming and energy-intensive, and no longer meet the porosity requirements for high-curvature U-shaped parts, impacting product quality and production efficiency. As customers demand increasingly higher product quality, the company has proposed requirements for quality improvement, cost reduction and efficiency enhancement, and the creation of high-quality models. Therefore, further innovation in composite material molding technology is becoming increasingly important. Summary of the Invention

[0003] The purpose of this invention is to effectively solve the problem of excessive porosity in the parting area of ​​U-shaped parts made of large curvature composite materials, reduce the porosity of the parts after one-time molding and meet the design acceptance requirements, ensure the strength and rigidity of the parts, eliminate faults, eliminate scrap repairs, reduce waste, reduce labor intensity, reduce energy consumption, improve quality and efficiency, create high-quality products, and continuously improve customer satisfaction.

[0004] The technical solution of the present invention: A molding process for reducing the porosity of a composite U-shaped part in the parting zone, wherein the composite U-shaped part is composed of an outer skin 1, a core material 2, and an inner skin 3; the method includes: Step 1: Prepare the molding fixture, ensuring it is clean and dust-free; the molding fixture includes: a first molding mold splitting body 10, a second molding mold splitting body 11, and a molding mold base 12; the first molding mold splitting body 10 and the second molding mold splitting body 11 are fixed on the molding mold base 12, forming a U-shaped structure; Step 2: Lay the first layer of prepreg for the outer skin; Step 3: Pre-compact the vacuum bag after pasting. After pasting the vacuum bag, place the vacuum nozzle 8 and the inspection vacuum nozzle 9 on the vacuum bag. The vacuum nozzle 8 must be positioned below the parting point 13 between the molding mold and the product. The inspection vacuum nozzle 9 must be positioned above the parting point 13 between the molding mold and the product. After the vacuum bag is pasted, it needs to be vacuumed to 0.07-0.09MPa for pre-compactment. After vacuuming, keep it for 15-20 minutes to ensure that the first layer of prepreg is in close contact with and compacted with the tooling molding surface. Step 4: Lay the remaining layers of prepreg for the outer skin. After every 2-3 layers of prepreg, seal the vacuum bag and pre-compact it once until the outer skin is laid. After the last layer of prepreg for the outer skin is laid, a vacuum bag must be sealed and pre-compacted to ensure that the prepreg for the outer skin is compacted and adhered. Step 5: Lay out core material 2. After completion, press the vacuum bag once to ensure that the core material is compacted and adhered. Step 6: Lay the first layer of prepreg for the inner skin 3. After completion, make a vacuum bag and pre-compact it once to ensure that the core material of the first layer of prepreg for the inner skin is compacted and adhered. Step 7: Lay the remaining layers of prepreg for the inner skin. Every 2-3 layers of prepreg are laid, vacuum bags are pasted and pre-compacted once, until the inner skin is laid. Vacuum bags are pasted and pre-compacted again, and the airtightness of the vacuum bags is tested. Vacuuming is continuously performed before curing to ensure the pre-compacted state. Step 8: Curing and removal from the oven. Wait for the temperature to drop below 60℃ before opening the mold. After opening the mold, clean the part and perform non-destructive porosity testing.

[0005] Furthermore, after step 7 and before step 8, the method also includes: applying positive pressure for testing. Before formal curing, the vacuum nozzle on the product to be molded is connected to the vacuum system of the autoclave. After the autoclave is closed, positive pressure is applied to 1 atmosphere. The vacuum pipeline is connected to the atmosphere, and positive pressure is continued to be applied until the positive pressure specified in the product molding process parameters is reached. This is maintained for 5 minutes, and the airtightness of the vacuum bag is tested to ensure it meets the process specifications. If there are no problems, the product is cured and molded according to the process curing parameters. If there are any problems, the pressure is released and the vacuum bag is re-made until the positive pressure test is normal.

[0006] Furthermore, the first step specifically involves wiping the entire layup surface of the first molding die part 10 and the second molding die part 11, as well as the area where the molding die base 12 is bonded to the sealing strip 7, with a lint-free cloth soaked in acetone or methyl ethyl ketone to remove oil, residues, or dust until no new dust or grease is generated on the wiping cloth, ensuring that the area where the molding fixture lays the prepreg and other auxiliary materials of the vacuum bag is clean and dust-free.

[0007] Furthermore, in step 2, one protective film is removed from the prepreg fabric after it has been cut, so that the surface is in contact with the working surfaces of the first molding die parting body 10 and the second molding die parting body 11.

[0008] Furthermore, the layup range is 20-30mm larger than the theoretical shape of the product, and the layup process ensures that the layup fits tightly to the mold.

[0009] Furthermore, in step 3, the vacuum bag fabrication process specifically involves: laying a release film 4 on the first layer, covering the entire product area and extending at least 20-30mm beyond the perimeter of the layer; then laying a breathable felt 5 in the area of ​​greatest curvature (e.g., ...). Figure 1 (Mold parting interface area), the isolation membrane and breathable felt can be disconnected, with an overlap of 20-30mm, to avoid insufficient elongation of the isolation membrane and breathable felt, bridging in areas with excessive curvature, and laying vacuum bags 6 and sealing strips 7.

[0010] Furthermore, in step 3, the number of vacuum nozzles used for extraction should be greater than the number of vacuum nozzles used for testing, with at least one vacuum nozzle used for testing.

[0011] Furthermore, the testing vacuum nozzle must be positioned according to the suction vacuum nozzle to ensure that the distance between each suction vacuum point and the testing vacuum point does not exceed 1.3m. If the product surface area is large, it is generally recommended to exceed 1.5m. 2 A vacuum nozzle will be added accordingly.

[0012] The advantages of this invention are: 1. This method effectively solves the problem of excessive porosity in the parting area of ​​U-shaped parts made of high-curvature composite materials, reduces the porosity of products under non-destructive testing, improves the first-time delivery pass rate of parts, and increases customer satisfaction.

[0013] 2. This method can meet the design requirements in one molding process. For sandwich composite materials with thick upper and lower skins and large curvature, the general process is to mold the upper and lower skins separately and then co-cur them with the core material. However, after using the new model, this traditional method can no longer meet the new requirements of the design acceptance index. This patented method does not require three separate moldings, but only one co-curing molding process to meet the design acceptance requirements regarding porosity.

[0014] 3. This method achieves the goal of improving quality and efficiency through technological empowerment. Compared with traditional methods, this patent reduces the curing and molding process by two steps, which not only shortens the delivery cycle and reduces the labor intensity of workers, but also reduces the use of high-energy-consuming equipment such as autoclaves by two times, greatly reducing energy consumption in the manufacturing process and achieving high-quality, high-efficiency, and low-cost manufacturing.

[0015] 4. Take preventative measures to reduce the probability of failure. Before the parts are molded and cured, perform a positive pressure loading vacuum bag airtightness test in the autoclave. If a problem with the airtightness of the vacuum bag is found, the bag can be remade before formal curing to minimize the possibility of non-destructive porosity exceeding the tolerance due to air leakage in the vacuum bag during the formal curing process.

[0016] 5. This method improves product safety. Parts manufactured using this patented method can be delivered qualified after non-destructive testing, reducing product scrap and repairs caused by out-of-tolerance porosity, reducing product quality losses, improving product safety performance, and increasing customer satisfaction.

[0017] 6. The new method is the same as the method for laying prepreg fabric and vacuum bag pasting for composite material products. It is simple to operate and can be performed by general operators.

[0018] 7. This method has been promoted and used in some models and is a stable manufacturing process for U-shaped parts made of composite materials with large curvature. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the part forming process; Figure 1 Description: 1. Outer skin of part; 2. Core material of part; 3. Inner skin of part; 4. Separating membrane; 5. Breathable felt; 6. Vacuum bag; 7. Sealing strip; 8. Vacuum nozzle for extraction; 9. Vacuum nozzle for inspection; 10. Parting body of molding mold; 11. Parting body of molding mold; 12. Base of molding mold; 13. Parting interface of molding mold and joint point between molding mold and product. Detailed Implementation

[0020] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] This invention provides a molding process for reducing the porosity of the parting region of a composite material U-shaped part, wherein the composite material U-shaped part is composed of an outer skin 1, a core material 2, and an inner skin 3; the method includes: Step 1: Prepare the molding fixture. Use a lint-free cloth soaked in acetone or methyl ethyl ketone to wipe the entire layup surface of the molding mold parting body 10 and 11, as well as the area where the molding mold base 12 is bonded to the sealing strip 7, to remove oil, residues or dust until no new dust or grease is generated on the wiping cloth. Ensure that the area of ​​the molding fixture where the prepreg and other auxiliary materials of the vacuum bag are laid is clean and dust-free.

[0022] Step 2: Lay out the first layer of prepreg on the outer skin 1. Remove one side of the protective film from the prepreg fabric and make that side fit against the working surface of the molding die body 10 and 11. Generally, the layup range is 20-30mm larger than the theoretical shape of the product. During the layup process, ensure that the layup fits the mold tightly.

[0023] Step 3: Pre-compact the vacuum bag. On the first layer, lay the release film 4, covering the entire product area and extending at least 20-30mm beyond the perimeter of the release film. Then lay the breathable felt 5, in areas of maximum curvature (such as...). Figure 1 (Mold parting interface area), the release liner and breathable felt can be disconnected, overlapping 20-30mm to avoid insufficient elongation of the release liner and breathable felt, bridging in areas with excessive curvature, laying vacuum bags 6, sealing strips 7, and placing vacuum nozzles 8 and 9. The vacuum nozzles must be positioned below 13 at the mold parting interface and the product joint point (e.g., ...). Figure 1 (On the molding mold base 12), the vacuum nozzle must be positioned above the parting point 13 of the molding mold and the product (e.g., on the molding mold base 12). Figure 1 (On the molding die part 10), the number of vacuum nozzles should be greater than the number of detection vacuum nozzles, with at least one detection vacuum nozzle. The detection vacuum nozzles must be positioned according to the vacuum nozzles to ensure that the distance between each vacuum point and the detection vacuum point does not exceed 1.3m. If the product surface area is large, it is generally recommended to exceed 1.5m. 2 Add a vacuum nozzle accordingly. After the vacuum bag is pasted, it needs to be vacuumed to 0.07-0.09MPa for pre-compaction. After vacuuming, keep it for 15-20 minutes to ensure that the first layer of prepreg is in close contact with and compacted against the tooling forming surface.

[0024] Step 4: Lay the remaining layers of prepreg for the outer skin. Depending on the situation, after every 2-3 layers of prepreg, press a vacuum bag to compact it once, using the same method as in Step 3, until the outer skin is laid. After laying the last layer of prepreg for the outer skin, a vacuum bag must be pressed to compact it, using the same method as in Step 3, to ensure that the prepreg for the outer skin is compacted and adhered.

[0025] Step 5: Lay out core material 2. After completion, press the vacuum bag once, using the same method as in step 3, to ensure that the core material is pressed firmly and adhered.

[0026] Step 6: Lay the first layer of prepreg for the inner skin 3. After completion, press the vacuum bag once, using the same method as in Step 3, to ensure that the core material of the first layer of prepreg for the inner skin is compacted and adhered.

[0027] Step 7: Lay the remaining layers of prepreg for the inner skin. Depending on the situation, after every 2-3 layers of prepreg, press and compact the vacuum bag once, using the same method as in Step 3, until the inner skin is laid out. Press and compact the vacuum bag again, using the same method as in Step 3. At this step, the airtightness of the vacuum bag needs to be tested to ensure it meets the process requirements. If there are no problems, vacuuming can be continued before curing to ensure compaction.

[0028] Step 8: Apply positive pressure and run the test. Before formal curing, connect the vacuum nozzle on the product to be formed to the vacuum system of the autoclave. After the autoclave is closed, start applying positive pressure to 1 atmosphere. Connect the vacuum pipeline to the atmosphere and continue applying positive pressure to the positive pressure specified in the product forming process parameters. Maintain this pressure for 5 minutes and check if the airtightness of the vacuum bag meets the process specifications. If there are no problems, proceed with curing according to the process curing parameters. If there are any problems, depressurize and re-make the vacuum bag until the positive pressure test runs normally.

[0029] Step 9: Remove from the oven and wait for the temperature to drop below 60℃ before opening the mold. After opening the mold, clean the part and perform non-destructive porosity testing.

[0030] This research applies a novel molding technology for U-shaped composite parts with large curvature to address the issue of excessive non-destructive porosity in the parting zone of these parts. For U-shaped composite parts with thick upper and lower skins and large curvature, traditional molding processes typically involve molding the upper and lower skins separately before co-curing them with the core material. However, this traditional method, even after being used in new models, cannot meet the new porosity design acceptance criteria. This invention requires only a single co-curing process involving the upper skin, lower skin, and core material to meet the design porosity acceptance requirements. The invention establishes a new principle for vacuum nozzle placement and incorporates pressure loading and atmospheric ventilation testing before formal curing; the rest of the process is identical to traditional molding techniques. This invention is applicable to the molding technology of U-shaped parts made of composite materials with large curvature. The key points are twofold: First, based on the mold parting structure characteristics and the new vacuum nozzle placement principle, the placement and quantity of the vacuum nozzles are planned and tested to ensure correct airflow channels and proper layer compaction. Second, pressure loading and atmospheric ventilation are performed according to requirements before formal molding and curing to ensure the airtightness of the vacuum bag. Specifically, the vacuum nozzles are placed in the planned positions and quantities, and vacuum compaction is strictly carried out during the prepreg laying process to ensure close compaction between layers and reduce residual air. Before formal curing, the vacuum nozzles on the product to be molded are connected to the autoclave vacuum system. After the autoclave starts loading positive pressure to 1 atmosphere, the vacuum pipeline is vented to the atmosphere, and positive pressure is continued until the molding and curing parameters are met. This pressure is maintained for 5 minutes, and the airtightness of the vacuum bag is checked to ensure it meets the process specifications. If no problems are found, curing is carried out according to the curing parameters. If problems are found, the pressure is released, and the vacuum bag is re-made until the positive pressure test is normal.

Claims

1. A molding process for reducing the porosity of the parting region of a composite U-shaped part, characterized in that, The composite material U-shaped part is composed of an outer skin (1), a core material (2), and an inner skin (3); the method includes: Step 1: Prepare the molding fixture, ensuring it is clean and dust-free; the molding fixture includes: a first molding mold splitter body (10), a second molding mold splitter body (11), and a molding mold base (12); the first molding mold splitter body (10) and the second molding mold splitter body (11) are fixed on the molding mold base (12) to form a U-shaped structure; Step 2: Laying out the outer skin (1) First layer of prepreg; Step 3: Pre-compact the vacuum bag after pasting. After pasting the vacuum bag, place the vacuum nozzle (8) and the inspection vacuum nozzle (9) on the vacuum bag. The vacuum nozzle (8) must be positioned below the parting interface of the molding mold and the joint point (13) of the product. The inspection vacuum nozzle (9) must be positioned above the parting interface of the molding mold and the joint point (13) of the product. After the vacuum bag is pasted, it is necessary to vacuum to 0.07-0.09MPa for pre-compactment. After vacuuming, keep it for 15-20 minutes to ensure that the first layer of prepreg is in close contact with the tooling molding surface and compacted. Step 4: Lay the remaining layers of prepreg for the outer skin. After every 2-3 layers of prepreg, seal the vacuum bag and pre-compact it once until the outer skin is laid. After the last layer of prepreg for the outer skin is laid, a vacuum bag must be sealed and pre-compacted to ensure that the prepreg for the outer skin is compacted and adhered. Step 5: Lay out the core material (2). After completion, press the vacuum bag once to ensure that the core material is pressed firmly and adhered. Step 6: Lay out the first layer of prepreg for the inner skin (3). After completion, make a vacuum bag and pre-compact it once to ensure that the core material of the first layer of prepreg for the inner skin is compacted and adhered. Step 7: Lay the remaining layers of prepreg for the inner skin. Every 2-3 layers of prepreg are laid, vacuum bags are pasted and pre-compacted once, until the inner skin is laid. Vacuum bags are pasted and pre-compacted again, and the airtightness of the vacuum bags is tested. Vacuuming is continuously performed before curing to ensure the pre-compacted state. Step 8: Curing and removal from the oven. Wait for the temperature to drop below 60℃ before opening the mold. After opening the mold, clean the part and perform non-destructive porosity testing.

2. The molding process method for reducing the porosity of the parting region of a composite U-shaped part according to claim 1, characterized in that, After step 7 and before step 8, the method further includes: applying positive pressure for testing. Before formal curing, the vacuum nozzle on the product to be molded is connected to the vacuum system of the autoclave. After the autoclave is closed, positive pressure is applied to 1 atmosphere. The vacuum pipeline is connected to the atmosphere. At the same time, positive pressure is applied until it reaches the positive pressure specified in the product molding process parameters. This is maintained for 5 minutes. The airtightness of the vacuum bag is tested to ensure it meets the process specifications. If there are no problems, curing is carried out according to the process curing parameters. If there are any problems, the pressure is released and the vacuum bag is re-made until the positive pressure test is normal.

3. The molding process method for reducing the porosity of the parting region of a composite material U-shaped part according to claim 1, characterized in that, The first step is to wipe the entire layup surface of the first molding die part (10) and the second molding die part (11), as well as the area where the molding die base (12) is bonded with the sealing strip (7), with a lint-free cloth soaked in acetone or methyl ethyl ketone to remove oil, residues or dust, until no new dust or grease is generated on the wiping cloth, ensuring that the area where the molding tooling lays the prepreg and other auxiliary materials of the vacuum bag is clean and dust-free.

4. The molding process method for reducing the porosity of the parting region of a composite U-shaped part according to claim 1, characterized in that, In step 2, the protective film on one side of the prepreg fabric is removed so that the side is in contact with the working surfaces of the first molding die parting body (10) and the second molding die parting body (11).

5. A molding process method for reducing the porosity of the parting region of a composite U-shaped part according to claim 4, characterized in that, The layup area is 20-30mm larger than the theoretical shape of the product, and the layup process ensures that the layup fits the mold tightly.

6. The molding process method for reducing the porosity of the parting region of a composite material U-shaped part according to claim 1, characterized in that, In step 3, the vacuum bag is made as follows: on the first layer, lay the release film (4) to cover the entire product area and be at least 20-30mm larger than the perimeter of the layer, lay the breathable felt (5), in the area with the greatest curvature, disconnect the release film and the breathable felt, overlap by 20-30mm to avoid insufficient extensibility of the release film and the breathable felt, bridge in the area with excessive curvature, and lay the vacuum bag (6) and the sealing strip (7).

7. The molding process method for reducing the porosity of the parting region of a composite U-shaped part according to claim 1, characterized in that, In step 3, the number of vacuum nozzles used for extraction should be greater than the number of vacuum nozzles used for testing, with at least one vacuum nozzle used for testing.

8. A molding process method for reducing the porosity of the parting region of a composite U-shaped part according to claim 7, characterized in that, The vacuum testing nozzle must be positioned according to the vacuum extraction nozzle to ensure that the distance between each vacuum extraction point and the vacuum testing point does not exceed 1.3m. If the product surface area is large, it is generally recommended to exceed 1.5m. 2 A vacuum nozzle will be added accordingly.

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