A creep forming pre-deformation method for ultra-large thin-walled parts

Abstract

This invention relates to a creep-forming pre-deformation method for ultra-large thin-walled parts. The method includes: processing a grid onto a blank sheet to obtain a wall panel; completely covering the wall panel with a breathable felt; placing the wall panel on a mold; calculating the size of a vacuum bag and determining the bridging position based on the stress characteristics of the vacuum bag; sealing the vacuum bag, with the outer periphery of the vacuum bag extending outwards from the mold; evacuating the enclosed space until a first preset pressure value is reached, then placing the panel in an autoclave; maintaining the pressure until the wall panel deforms to the target size when the first preset pressure value rises to a second preset pressure value. The creep-forming pre-deformation method for ultra-large thin-walled parts provided in this application utilizes atmospheric pressure to apply pressure to the sheet material, determines the bridging position based on the stress characteristics of the vacuum bag, ensuring uniform stress area on the wall panel, and by changing the air pressure, adjusting the pressure value, the product gradually transforms from elastic deformation to plastic deformation, resulting in uniform deformation.

Description

Technical Field

[0001] This invention relates to the technical field of thin-walled aerospace parts processing, and in particular to a creep forming pre-deformation method for ultra-large-sized thin-walled parts. Background Technology

[0002] With the continuous improvement of launch vehicle carrying capacity, rocket structures are developing towards larger size, lighter weight, and modularity. Large structural component manufacturing technology is one of the key technologies for developing heavy-lift rockets. The challenges posed by large structural components in forming, welding, and assembly technologies, combined with advanced lightweight materials and advanced manufacturing technologies, are driving the realization of the goals of lightweight and efficient structures.

[0003] Large thin-walled rocket components mainly include tank walls, tank bottoms, lobes, and top covers. These components are large in size and thickness, and require high mechanical properties and dimensional accuracy after molding. Large tank walls are cylindrical in shape and generally feature thin-walled belts with T-shaped reinforcing longitudinal ribs, triangular or quadrilateral grids, resulting in an uneven structure.

[0004] Traditional mesh panel forming methods include roll forming and filling roll bending. However, the selection of filling materials and forming process parameters are unstable and require long-term experimental confirmation. During the roll bending process, abrupt changes are very likely to occur at the junction of the skin and reinforcing ribs, resulting in reverse deformation and mutual constraints. The control of arc gaps and mesh straightness is poor.

[0005] This led to the development of creep aging forming technology, which utilizes the evolution of the microstructure and internal stress of aluminum alloys under the action of a thermo / mechanical coupled energy field to simultaneously carry out creep deformation and aging strengthening of the material. This technology offers advantages such as uniform deformation, low residual stress, high forming accuracy, dimensional stability, uniform performance, and good repeatability. The creep aging process consists of three stages: loading and film application stage, stress relaxation stage, and unloading and springback stage. To ensure a small gap between the part and the mold, traditional processes require pre-bending deformation using a plate rolling machine for both single-curvature panels and double-curvature petal-shaped products. This pre-bending method not only relies on the plate rolling machine equipment but also makes it difficult to control the bending curvature, resulting in inaccurate plastic deformation and making it impossible to achieve ultra-large specifications and high-ribbed panels. Moreover, after bending, the panel directly transforms from elastic deformation to strong plastic deformation, leading to severe dislocation accumulation, stress concentration, and a tendency to develop cracks. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a creep forming pre-deformation method for ultra-large thin-walled parts. This method involves applying progressive pressure to the sheet material in a flat state, utilizing atmospheric pressure, and determining bridging positions based on the stress characteristics of the vacuum bag to ensure uniform stress distribution on the sheet material. By changing the air pressure and adjusting the pressure value, the product gradually transforms from elastic deformation to plastic deformation, resulting in uniform deformation.

[0007] The technical solution of the present invention is as follows:

[0008] A creep forming pre-deformation method for ultra-large thin-walled parts includes: processing a grid after finishing the surface of a whole blank to obtain a wall panel; completely covering the wall panel with a breathable felt and placing the wall panel on a mold; calculating the size of a vacuum bag and determining the bridging position based on the stress characteristics of the vacuum bag to ensure symmetry at the bridging points on both sides of the mold; sealing the vacuum bag, with the outer periphery of the vacuum bag extending outwards from the outside of the mold, forming a closed space between the vacuum bag and the mold; evacuating the closed space until a first preset pressure value is reached, then placing the part in an autoclave; maintaining the pressure until the wall panel is deformed to the target size.

[0009] Preferably, the process of processing the whole plate blank into a grid after surface finishing includes: using a flat surface of the whole plate blank as a rough machining reference, using a small cutting amount and high rotation speed machining method to finish the surface and form a grid machining reference; flipping the blank over and machining the grid based on the grid machining reference.

[0010] Preferably, before placing the wall panel on the mold, the mold is positioned in the middle of the track vehicle, symmetrically on both sides; the mold surface is cleaned until it is smooth.

[0011] Preferably, the step of completely covering the wall panel with breathable felt includes: wrapping the wall panel with breathable felt from bottom to top and fixing it with pressure-sensitive tape.

[0012] Preferably, the calculation of the vacuum bag size and the determination of the bridging positions based on the stress characteristics of the vacuum bag include: the number of bridging points being evenly distributed at both ends of the mold and at each corner.

[0013] Preferably, the calculation of the vacuum bag size and the determination of the bridging position based on the stress characteristics of the vacuum bag include: at least 4 bridging positions, including the four corners of the mold, the corner of the mold, the position near the 3 / 4 position of the arc surface, and each end of the mold.

[0014] Preferably, the outer periphery of the vacuum bag extends 10-15 cm outward from the outside of the mold.

[0015] Preferably, before sealing the vacuum bag, high-temperature adhesive is applied to the vacuum nozzle support.

[0016] Preferably, the vacuum bag is pressed by hand or with a scraper, and there should be no air bubbles between the vacuum bag and the high-temperature adhesive.

[0017] Preferably, the first preset pressure value is 1000 kPa; the second preset pressure value is 6000 kPa, and the pressure holding time is at least 4 hours.

[0018] Compared with existing technologies, the creep forming pre-deformation method for ultra-large thin-walled parts provided in this application first processes a mesh (if the mesh is processed after the wall panel is formed, mechanical stress will cause the wall panel to deform). The wall panel is then completely covered with a breathable felt and placed on a mold. A vacuum bag is sealed to form a closed space between the vacuum bag and the mold. The wall panel is placed in the closed space for vacuum creep aging forming. At the same time, the outer periphery of the vacuum bag extends outward to the outside of the mold, so that there is no gap between the vacuum bag and the mold, and the vacuum bag and the mold form a closed space. On the other hand, the bridging position is determined according to the stress characteristics of the vacuum bag to make the stress area of ​​the wall panel uniform. By changing the air pressure, the pressure value is adjusted, and the product gradually transforms into plastic deformation under elastic deformation, resulting in uniform deformation of the mesh wall panel. Therefore, the creep forming pre-deformation method for ultra-large thin-walled parts provided in this application applies progressive pressure to the plate in a flat state, using atmospheric pressure to apply pressure to the plate. On the other hand, the bridging position is determined according to the stress characteristics of the vacuum bag, so that the stress area of ​​the wall panel is uniform. By changing the air pressure, the pressure value is adjusted, and the product gradually transforms into plastic deformation under elastic deformation, resulting in uniform deformation. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart of the creep forming pre-deformation method for ultra-large thin-walled parts provided in the embodiments of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of this application.

[0022] In the description of this invention, it should be understood that the terms "upper" and "lower" indicate orientation or positional relationship only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0023] Please Figure 1 As shown, this application provides a creep forming pre-deformation method for ultra-large thin-walled parts. The method includes: processing a grid after finishing the surface of a whole plate blank to obtain a wall panel; completely covering the wall panel with a breathable felt and placing the wall panel on a mold; calculating the size of a vacuum bag and determining the bridging position according to the stress characteristics of the vacuum bag so that the bridging points on both sides of the mold remain symmetrical; sealing the vacuum bag, with the outer periphery of the vacuum bag extending outwards from the outside of the mold, forming a closed space between the vacuum bag and the mold; evacuating the closed space until a first preset pressure value is reached, and then entering a thermostatic precipitator; when the first preset pressure value rises to a second preset pressure value, maintaining the pressure until the wall panel is deformed to the target size.

[0024] Compared with existing technologies, the creep forming pre-deformation method for ultra-large thin-walled parts provided in this application first processes a mesh (if the mesh is processed after the wall panel is formed, mechanical stress will cause the wall panel to deform). The wall panel is then completely covered with a breathable felt and placed on a mold. A vacuum bag is sealed to form a closed space between the vacuum bag and the mold. The wall panel is placed in the closed space for vacuum creep aging forming. At the same time, the outer periphery of the vacuum bag extends outward to the outside of the mold, so that there is no gap between the vacuum bag and the mold, and the vacuum bag and the mold form a closed space. On the other hand, the bridging position is determined according to the stress characteristics of the vacuum bag to make the stress area of ​​the wall panel uniform. By changing the air pressure, the pressure value is adjusted, and the product gradually transforms into plastic deformation under elastic deformation, resulting in uniform deformation of the mesh wall panel. Therefore, the creep forming pre-deformation method for ultra-large thin-walled parts provided in this application applies progressive pressure to the plate in a flat state, using atmospheric pressure to apply pressure to the plate. On the other hand, the bridging position is determined according to the stress characteristics of the vacuum bag, so that the stress area of ​​the wall panel is uniform. By changing the air pressure, the pressure value is adjusted, and the product gradually transforms into plastic deformation under elastic deformation, resulting in uniform deformation.

[0025] The specific steps are as follows:

[0026] S01. After finishing the surface of the whole plate blank, a mesh is processed to obtain the wall panel;

[0027] S02. Completely cover the wall panel with breathable felt and place the wall panel on the mold;

[0028] S03. Calculate the size of the vacuum bag and determine the bridging position according to the stress characteristics of the vacuum bag so that the bridging points on both sides of the mold remain symmetrical.

[0029] S04, Sealed vacuum bag, the outer periphery of the vacuum bag extends outward toward the outside of the mold, and the vacuum bag and the mold form a closed space;

[0030] S05. Evacuate the enclosed space until the first preset pressure value is reached, then enter the autoclave. When the first preset pressure value rises to the second preset pressure value, maintain the pressure until the wall panel is deformed to the target size.

[0031] Specifically, the process of machining the grid after finishing the blank to obtain the wall panel includes: using one plane of the blank as a rough machining reference, machining with a small cut and high speed to finish the blank, forming a grid machining reference; flipping the blank over and machining the grid based on the grid machining reference. Large thin-walled rocket components mainly include tank wall panels, tank bottoms, lobes, and top covers, etc., with large structural specifications and thick dimensions, requiring high mechanical properties and dimensional accuracy after forming. Large-size tank wall panels are cylindrical, generally with thin-walled belts, T-shaped reinforcing longitudinal ribs, triangular or quadrilateral grids, and their structure is uneven. Because of their grid-like structure, if these thin-walled panels are processed after creep forming, it will cause mechanical residual stress concentration. During natural aging, the stress will slowly release, leading to deformation and warping of the thin-walled component. Therefore, grid machining is placed as the first step in the thin-walled component machining process. In this embodiment, the rough machining reference is set by first finishing the blank, and then a small cut and high speed machining method is used to reduce the contact time with the material, resulting in rapid heat dissipation and reducing thermal deformation of the thin-walled component.

[0032] Furthermore, before placing the wall panel on the mold, position the mold in the center of the track carriage, symmetrically from left to right; clean the mold surface until it is smooth. Prevent the wall panel from tilting or becoming unstable due to foreign objects, ensuring the wall panel fits snugly against the mold without gaps.

[0033] In the embodiments provided in this application, completely covering the wall panel with breathable felt includes: wrapping the wall panel with breathable felt from bottom to top and securing it with pressure-sensitive adhesive tape. The breathable felt is taut and there is no exposed material surface.

[0034] Preferably, the calculation of the vacuum bag size and the determination of the bridging positions based on the stress characteristics of the vacuum bag include: the number of bridging points being evenly distributed at both ends of the mold and at each corner. The core of this application lies in determining the bridging positions based on the vacuum bag size and characteristics, so that the wall panel fits as closely as possible to the mold or remains in close contact during the creep forming process, avoiding uneven deformation of the wall panel due to excessive local stress.

[0035] Specifically, the vacuum bag dimensions are calculated, and the bridging locations are determined based on the stress characteristics of the vacuum bag, including at least four bridging points: the four corners of the mold, the corners of the mold, the location near the 3 / 4 mark of the curved surface, and each end of the mold. Taking a blank size of 75mm as an example, the mesh is processed, the skin thickness is 10mm, the rib height is 65mm, and the rib width is 10mm. After calculating the vacuum bag dimensions, the bag is made from one side of the long side of the mold to the other, ensuring the required allowance while effectively controlling the bridging height. The bridging locations include at least the four corners of the mold, the corners of the mold, the location near the 3 / 4 mark of the curved surface, and each end of the mold. This ensures that bridging occurs at locations where stress concentration on the wall panel is likely to occur, aiming to make the wall panel fit the mold as closely as possible.

[0036] The outer periphery of the vacuum bag extends 10-15cm outward from the mold. Excessive outward extension of the vacuum bag would increase the overall dimensions of the sealed space and would not aid in actual creep forming; therefore, the outward extension of the vacuum bag is controlled to 10-15cm.

[0037] Preferably, before sealing the vacuum bag, apply high-temperature adhesive to the vacuum nozzle support.

[0038] Further, press the vacuum bag down with your hand or a scraper, ensuring there are no air bubbles between the vacuum bag and the high-temperature adhesive. Attach the high-temperature adhesive to the vacuum nozzle support and place it inside the vacuum bag to secure it (the number of vacuum nozzles depends on the vacuuming recorder). After the vacuum bag is laid out, press it down with your hand or a scraper to increase adhesion, ensuring there are no air bubbles between the vacuum bag and the high-temperature adhesive.

[0039] In the embodiments provided by this invention, the first preset pressure value is 1000 kPa; the second preset pressure value is 6000 kPa, and the pressure holding time is at least 4 hours. A vacuum device is used to evacuate the part to a pressure of 1000 kPa, followed by placement in an autoclave where the pressure is increased to 6000 kPa and held for 4 hours. After the pressure holding period, the vacuum is released, and the part undergoes significant plastic deformation with a bending radius of approximately R2600 mm. This bending deformation demonstrates that the part has undergone plastic deformation, and the bending radius does not exceed the post-forming dimensional requirements, providing a basis for subsequent creep aging film evaluation of the part.

[0040] To better understand the inventive intent of this application, preferred embodiments are now selected for illustration:

[0041] The wall panel is meshed in its flat state using a three-axis gantry milling machine. A 75mm thick flat plate is used.

[0042] 1. First, perform a full-plate finishing process on one side. To eliminate residual stress from machining, perform a full-plate finishing process on the other side and then add a mesh. The skin thickness is 10mm, the rib height is 65mm, and the rib width is 10mm.

[0043] 2. The mold is positioned in the middle of the railcar, symmetrically arranged, with a curvature radius of R2500mm;

[0044] 3. Clean the mold surface until it is smooth and free of any small particles or foreign matter; ensure there is no residual kerosene on the mold surface.

[0045] 4. Use breathable felt to wrap the wall panel from bottom to top, and use pressure-sensitive tape to stick and fix it. The breathable felt is taut and there is no exposed material surface.

[0046] 5. Then, place the flat part in the middle of the mold.

[0047] 6. Apply high-temperature adhesive to the four edges of the mold surface; at the corners of the mold, apply the high-temperature adhesive in an arc shape to avoid leakage where the adhesive overlaps.

[0048] 7. Calculate the dimensions of the vacuum bag and punch the bag from one side of the long side of the mold to the other side. This ensures the required allowance and effectively controls the "bridge height".

[0049] 8. Determine the bridging position based on the stress characteristics of the vacuum bag; to ensure that the bridging points on both sides of the mold are as symmetrical as possible, quantify the number and height of the bridging.

[0050] Number of bridges: Set the number of bridges on the side of the mold to 4, the number of bridges at both ends to 6, and the number of bridges at each corner to 1.

[0051] Bridge locations: at the four corners of the mold, at the corner of the mold, at the 3 / 4 position of the arc surface, and three evenly distributed at each end of the mold.

[0052] Bridge height: 100mm at the four corners and bends, 150mm at the 3 / 4 position of the arc surface, and 240mm at the end of the mold.

[0053] 9. When sealing the vacuum bag, the portion of the vacuum bag that leaks out onto the outside of the mold should be approximately 10-15cm, and the mold should be symmetrical at both ends.

[0054] 10. Before sealing the vacuum bag, apply high-temperature adhesive to the vacuum nozzle support and place it inside the vacuum bag to secure it (the number of vacuum nozzles should be selected based on the vacuuming record). After the vacuum bag is laid out, press it down with your hand or a scraper to increase the adhesion. There should be no air bubbles between the vacuum bag and the high-temperature adhesive.

[0055] 11. Use a vacuum pump to evacuate the parts to a pressure of 1000 kPa, then put them into an autoclave where the pressure is increased to 6000 kPa and held for 4 hours.

[0056] 12. After the pressure holding period is over, the vacuum is released, and the part undergoes significant plastic deformation with a bending radius of approximately R2600mm.

[0057] 13. Through this bending deformation, the part undergoes plastic deformation and the bending radius does not exceed the size requirements after molding, which provides a basis for subsequent creep aging film evaluation of the part.

[0058] The embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A creep forming pre-deformation method for ultra-large thin-walled parts, characterized in that, The method includes: The process of finishing the surface of a whole plate blank and then processing it into a grid to obtain a wall panel specifically includes: using one plane of the whole plate blank as a rough machining reference, and using a small cutting amount and high speed machining method to finish the surface and form a grid machining reference; Flip the surface and process the mesh according to the mesh processing reference; The wall panel is completely covered with breathable felt and then placed on the mold. Calculate the size of the vacuum bag and determine the bridging position according to the stress characteristics of the vacuum bag so that the bridging points on both sides of the mold remain symmetrical. Specifically, the number of bridging points is evenly distributed at both ends of the mold and at each corner. There are at least 4 bridging points, including the four corners of the mold, the corners of the mold, the position near the 3 / 4 position of the arc surface, and each end of the mold. A sealed vacuum bag, with the outer periphery of the vacuum bag extending outwards towards the outside of the mold, forming a closed space between the vacuum bag and the mold; The enclosed space is evacuated until a first preset pressure value is reached. Then, the pressure is maintained in an autoclave until the wall panel is deformed to the target size.

2. The creep forming pre-deformation method for ultra-large thin-walled parts according to claim 1, characterized in that, Before placing the wall panel on the mold, position the mold in the middle of the track car, symmetrically on both sides; Clean the mold surface until it is smooth.

3. The creep forming pre-deformation method for ultra-large thin-walled parts according to claim 1, characterized in that, The complete covering of the wall panel with breathable felt includes: The wall panels are wrapped from bottom to top with breathable felt and then fixed with pressure-sensitive tape.

4. The creep forming pre-deformation method for ultra-large thin-walled parts according to claim 1, characterized in that, The outer periphery of the vacuum bag extends 10-15 cm outward from the outside of the mold.

5. The creep forming pre-deformation method for ultra-large thin-walled parts according to claim 1, characterized in that, Before sealing the vacuum bag, apply high-temperature adhesive to the vacuum nozzle support.

6. The creep forming pre-deformation method for ultra-large thin-walled parts according to claim 5, characterized in that, Press the vacuum bag with your hand or a scraper, ensuring there are no air bubbles between the vacuum bag and the high-temperature adhesive.

7. The creep forming pre-deformation method for ultra-large thin-walled parts according to claim 1, characterized in that, The first preset pressure value is 1000 kPa; The second preset pressure value is 6000 kPa, and the pressure holding time is at least 4 hours.

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