A method for bending forming an aluminum alloy cylinder with a large diameter-thickness ratio

Abstract

This invention relates to the field of aircraft cylinder manufacturing technology, specifically to a bending forming method for aluminum alloy cylinders with a large diameter-to-thickness ratio. The method includes the following steps: vertically placing and fixing a straight cylinder with a uniform cross-section using a support clamp, ensuring that the contact area between the inner arc wall of the support clamp and the straight cylinder has a crisscrossing grid pattern; filling the straight cylinder with a low-melting-point alloy and cooling it; bending the cooled straight cylinder to a predetermined bending state to form a bent cylinder with a uniform cross-section; and sequentially performing annealing, hydroforming, and excess material cutting on the bent cylinder to obtain the bent aluminum alloy cylinder with a large diameter-to-thickness ratio. The purpose of this bending forming method for aluminum alloy cylinders with a large diameter-to-thickness ratio is to solve the problem of reduced manufacturing accuracy caused by wavy deformation in these cylinders.

Description

Technical Field

[0001] This invention relates to the field of aircraft cylinder manufacturing technology, and specifically to a bending forming method for aluminum alloy cylinders with a large diameter-to-thickness ratio. Background Technology

[0002] To enhance takeoff and landing safety and increase wingspan, medium and large aircraft, both domestically and internationally, often incorporate slat rail sleeves on the leading edge of their wings. These sleeves provide space for the I-shaped or π-shaped slat rails to pass through the integral fuel tank without interfering with it. Due to the limited internal space of the integral fuel tank, one typical structural form of the slat rail sleeve is a cavity structure with a variable diameter and a slightly curved central axis, such as... Figure 1 As shown. The radius R of the arc along the central axis of the slide rail sleeve is between 500mm and 2000mm, the sleeve wall thickness is between 2mm and 5mm, the total height H of the sleeve is between 300mm and 1000mm, the minor semi-axis n of the ellipsoidal bottom is between 20mm and 50mm, and the sleeve body diameter... Between 150mm and 200mm.

[0003] For slat rail sleeves in medium or large aircraft, their service environment involves only low loads from fuel oscillations within the fuel tank environment. Even considering the necessary safety factor, aluminum alloy can meet the requirements for the entire service life. While higher-performance titanium alloys can meet the requirements, they result in significant strength loss and increased weight. Therefore, aluminum alloy rail sleeves have broader application and promotion value.

[0004] For aluminum alloy cylinders with a diameter-to-thickness ratio greater than 50, wave deformation is likely to occur in the inner arc area of ​​the cylinder. The severity of wave deformation is closely related to the bending radius. That is, the smaller the bending radius, the greater the degree of bending of the cylinder and the more severe the wave deformation.

[0005] Therefore, the inventors have provided a bending forming method for aluminum alloy cylinders with a large diameter-to-thickness ratio. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] This invention provides a bending forming method for aluminum alloy cylinders with a large diameter-to-thickness ratio, which solves the technical problem that the manufacturing accuracy of aluminum alloy cylinders with a large diameter-to-thickness ratio is reduced due to the easy occurrence of wave deformation.

[0008] (2) Technical solution

[0009] This invention provides a method for bending and forming aluminum alloy cylinders with a large diameter-to-thickness ratio, comprising the following steps:

[0010] The straight cylinder with a uniform cross-section is placed vertically and fixedly clamped by a support clamp, and the contact area between the inner arc wall of the support clamp and the straight cylinder with a uniform cross-section is a grid shape with crisscrossing lines.

[0011] A low-melting-point alloy is filled into the straight cylinder with a uniform cross-section, and then cooled.

[0012] The cooled, straight cylindrical body with equal cross-section is bent to a preset bending state to form a bent cylindrical body with equal cross-section.

[0013] The uniform cross-section bent cylinder is subjected to annealing, hydraulic bulging and allowance cutting in sequence to obtain a large diameter-to-thickness aluminum alloy bent cylinder.

[0014] Furthermore, the support fixture includes a support base, a first arc-shaped wall, and a second arc-shaped wall. The support base is used to support the ellipsoidal bottom of the straight cross-section cylinder. The first arc-shaped wall and the second arc-shaped wall are symmetrically distributed, and the cylindrical cavity formed therein is used to support the cylindrical body of the straight cross-section cylinder.

[0015] Furthermore, the support base includes a base and a boss located on the base, the boss having a cavity adapted to the ellipsoidal bottom profile of the straight cylindrical body with uniform cross-section.

[0016] Furthermore, the first arc-shaped wall includes a first flange end and a first support end, and the second arc-shaped wall includes a second flange end and a second support end; the first flange end and the second flange end are fixed on the base, and the inner wall of the first support end and the inner wall of the second support end form a cylindrical cavity with a symmetrical radial distribution and a central angle of 2α.

[0017] Furthermore, the angle range of α is 90° to 180°.

[0018] Furthermore, both the first arc-shaped wall and the second arc-shaped wall are hollow shell structures with internal flow channels.

[0019] Furthermore, the base has a positioning notch located at the mirror center plane of the first arc-shaped wall and the second arc-shaped wall.

[0020] Furthermore, the grid shape is square or rhombus.

[0021] Furthermore, the melting point of the low-melting-point alloy is 250–350°C.

[0022] Furthermore, the low-melting-point alloy includes at least one of Sn alloy, Sn-Pb alloy, and Sn-Ag alloy.

[0023] (3) Beneficial effects

[0024] In summary, this invention utilizes a symmetrical support fixture with cooling function to maintain a grid-like contact with the straight cylinder wall, achieving the basic function of supporting the aluminum alloy straight cylinder for filling with liquid low-melting-point alloy. During the subsequent cooling process, due to the rapid heat dissipation at the contact points, a square or rhomboid grid-like stress distribution is formed on the surface of the straight cylinder. Setting this stress distribution in the area of ​​the cylinder with the greatest bending deformation can limit the sudden change of local stress in this area during bending, improve the uniform deformation capability of the cylinder wall in this area, significantly improve the wave deformation of the inner arc surface area of ​​the cylinder, and reduce the probability of defects such as tearing and local over-thinning in the outer arc surface area of ​​the cylinder, further improving the manufacturing accuracy of the curved cylinder. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of a typical slide rail sleeve structure;

[0027] Figure 2 This is a schematic flowchart of a bending forming method for a large diameter-to-thickness aluminum alloy cylinder provided in an embodiment of the present invention;

[0028] Figure 3 This is a top view of a support clamp provided in an embodiment of the present invention;

[0029] Figure 4 This is a structural front view of a support clamp provided in an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of the structure of a support base for a support clamp provided in an embodiment of the present invention;

[0031] Figure 6 This is a grid-like stress distribution diagram formed by a straight cylindrical wall with a uniform cross-section, provided by an embodiment of the present invention.

[0032] In the picture:

[0033] 1-Support base; 11-Base; 12-Boss; 13-Cavity; 14-Positioning notch; 2-First arc-shaped wall; 21-First flange end; 22-First support end; 3-Second arc-shaped wall; 31-Second flange end; 32-Second support end; 4-First liquid inlet; 5-First liquid outlet; 6-Second liquid inlet; 7-Second liquid outlet; 8-Marking line; 9-Grid; 100-Straight cylinder with uniform cross-section. Detailed Implementation

[0034] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. That is, the present invention is not limited to the described embodiments, and any modifications, substitutions and improvements to the parts, components and connection methods are covered without departing from the spirit of the present invention.

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, 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. Therefore, they should not be construed as limitations on this invention.

[0037] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "install" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] Figure 2 This is a schematic flowchart of a bending forming method for a large diameter-to-thickness aluminum alloy cylinder provided in an embodiment of the present invention, as shown below. Figure 2 As shown, the method may include the following steps:

[0039] S100. The straight cylinder with uniform cross-section is placed vertically and fixedly clamped by the support clamp, and the contact part between the inner wall of the arc wall of the support clamp and the straight cylinder with uniform cross-section is a grid shape with crisscrossing.

[0040] S200: Low-melting-point alloy is filled into a straight cylinder with a uniform cross-section and then cooled.

[0041] S300: The cooled, straight cylindrical body with a constant cross-section is bent to a preset bending state to form a bent cylindrical body with a constant cross-section.

[0042] S400 aluminum alloy bent cylinders with equal cross-sections are annealed, hydraulically expanded, and the allowance is cut in sequence to obtain aluminum alloy bent cylinders with a large diameter-to-thickness ratio.

[0043] In the above embodiment, after filling the straight cylinder with a low-melting-point alloy, during the cooling process, the parts of the straight cylinder that are in contact with or close to the inner wall of the curved surface dissipate heat faster, thus forming a square or rhomboid grid-like stress distribution in a specific area of ​​the straight cylinder wall. The marking lines on the straight cylinder are roughly aligned with the demolding surfaces of the bending molds, and the cylinder is placed in the bending mold for bending operations. Under the restraining effect of the square or rhomboid grid-like stress distribution on the surface of the straight cylinder and the easily deformable effect of the square or rhomboid grid, the outer curved surface area of ​​the cylinder is stretched and thinned more uniformly, and the inner curved surface area is compressed and thickened more uniformly. The effect is particularly significant in improving the wave deformation of the inner curved surface area of ​​the cylinder, further improving the manufacturing accuracy of the cylinder's shape.

[0044] Low-melting-point alloys have a melting point of 250–350°C. Low-melting-point alloys include at least one of Sn alloys, Sn-Pb alloys, and Sn-Ag alloys.

[0045] As an optional implementation method, such as Figure 3 and 4 As shown, the support clamp includes a support base 1, a first arc-shaped wall 2, and a second arc-shaped wall 3. The support base 1 supports the ellipsoidal bottom of the straight cylindrical body 100. The first arc-shaped wall 2 and the second arc-shaped wall 3 are symmetrically distributed, and the cylindrical cavity formed by them supports the cylindrical body of the straight cylindrical body 100 with a uniform cross-section. One of the two arc-shaped walls is a fixed reference sidewall, and the other is a relatively movable clamping arc wall. The distance between the two arc-shaped walls can be adjusted according to the diameter of the straight cylindrical body 100 with a uniform cross-section placed between the two arc-shaped walls, thereby ensuring that the straight cylindrical body 100 with a uniform cross-section is stably clamped.

[0046] As an optional implementation method, such as Figure 5 As shown, the support base 1 includes a base 11 and a boss 12 located on the base 11. The boss 12 has a cavity 13 that is adapted to the ellipsoidal bottom profile of the straight cylindrical body 100 with a constant cross section. Specifically, the connection methods between the first arc-shaped wall 2, the second arc-shaped wall 3 and the base 11 include, in addition to fastener connection methods, hinge-type rotation clamping, translational sliding clamping, etc.

[0047] As an optional implementation method, such as Figure 4 As shown, the first arc-shaped wall 2 includes a first flange end 21 and a first support end 22, and the second arc-shaped wall 3 includes a second flange end 31 and a second support end 32. The first flange end 21 and the second flange end 31 are fixed to the base 11. The inner walls of the first support end 22 and the second support end 32 form a symmetrically radially distributed cylindrical cavity with a central angle of 2α. The angle α ranges from 90° to 180°.

[0048] As an optional implementation method, such as Figure 4As shown, both the first arc-shaped wall 2 and the second arc-shaped wall 3 are hollow shell structures with internal flow channels. By designing flow channels within the pair of arc-shaped wall structures of the support fixture, and making the area where the inner wall of the arc-shaped wall contacts the straight cylinder a crisscrossing square or rhomboid grid shape, after filling the straight cylinder with a low-melting-point alloy, during the cooling process, the straight cylinder dissipates heat faster due to the area in contact with or close to the inner wall of the arc-shaped wall, thereby forming a square or rhomboid grid-like stress distribution in a specific area of ​​the straight cylinder wall.

[0049] As an optional implementation method, such as Figure 3 As shown, the base 11 has a positioning notch 14 at the position of the mirror center plane of the first arc-shaped wall 2 and the second arc-shaped wall 3. The positioning notch 14 on the side of the support seat can be used to easily mark positioning lines on the straight cylinder body, which is convenient for locating the interface of subsequent cylinder bending deformation. This ensures that the square or rhomboid grid-like stress distribution area on both sides of the cylinder body is located in the middle of the inner arc surface area and the outer arc surface area of ​​the cylinder body, which is also more conducive to uniform compression or tensile deformation in this area.

[0050] As an optional implementation method, such as Figure 6 As shown, the grid shape is square or rhomboid. The single-line width of the grid is 2mm–8mm, and the grid width is 15mm–40mm. Forming a square or rhomboid grid-like stress distribution on the surface of the aluminum alloy cylindrical body, under the restraining effect of the grid-like stress distribution and the easily deformable effect of the square or rhomboid grid, significantly improves the uniform deformation capacity of this area of ​​the cylindrical body. Setting this area in the inner and outer arc surfaces where the bending deformation of the cylinder is greatest can limit the sudden changes in local stress during bending, improving the uniform deformation capacity of the cylinder wall in this area. It is particularly effective in improving the wave deformation of the inner arc surface area of ​​the cylinder, and further improves the surface manufacturing accuracy of the bending forming of aluminum alloy cylinders with a diameter-to-thickness ratio greater than 50, thereby improving the service safety and reliability of the slide rail sleeve.

[0051] Example 1

[0052] This invention produces a high-diameter-to-thickness aluminum alloy bent cylinder. The arc radius R of the sleeve's central axis is 650 mm, the total height H of the sleeve is 820 mm, the cylinder wall thickness is 2.5 mm, and the circular cross-section diameter Ф of the cylinder is 190 mm. Therefore, the diameter-to-thickness ratio of the bent cylinder is 190 / 2.5 = 76. This diameter-to-thickness ratio is relatively large, while the arc radius R of the central axis is relatively small, making manufacturing difficult. The flange wall thickness is 5 mm, and the short semi-axis n of the ellipsoidal bottom is 30 mm. The flange with variable neck structure is manufactured using integral machining. The length of the uniform cross-section bent cylinder is approximately 560 mm, and it is manufactured using the following steps.

[0053] Step 1: Deep drawing and spinning to form a uniform cross-section straight cylinder. A 4.5mm thick O-state 6061 aluminum alloy sheet is selected and deep-drawn and spun to form a uniform cross-section straight cylinder with an ellipsoidal bottom. The cylinder wall thickness is 2.5mm ± 0.2mm, the outer diameter is Ф = 190mm, and the minor axis of the ellipsoidal bottom is n = 30mm. The O-state aluminum alloy sheet has very low strength and good ductility, making it more suitable for deep drawing and spinning deformation. During several deep drawing passes, to restore the deformation-strengthened aluminum alloy to the low-strength, high-ductility O-state, a stress-relieving annealing process is added as needed, depending on the strength changes of the base material. The stress-relieving annealing uses an incomplete annealing process, with a holding temperature of 350℃ ± 10℃ for 0.5h to 0.8h, followed by air cooling to room temperature.

[0054] Step Two: Fill the uniform cross-section straight cylinder 100 with a low-melting-point alloy and perform cooling treatment. Place the ellipsoidal bottom of the cylinder downwards into a support fixture. The support seat 1 of the fixture supports the ellipsoidal bottom of the uniform cross-section straight cylinder 100, and the first arc-shaped wall 2 and the second arc-shaped wall 3 of the fixture support the cylinder body. The first arc-shaped wall 2 and the second arc-shaped wall 3 can be in contact with the cylinder body or partially out of contact. Fill the uniform cross-section straight cylinder with a low Sn-Pb melting point alloy, and cool after filling. The melting point of the low-melting-point alloy is in the range of 230℃ to 250℃; the heating temperature of the low-melting-point alloy is 350℃. During the process of filling the cylinder with the liquid low-melting-point alloy, the cylinder undergoes an incomplete annealing process. During the natural cooling process of the low-melting-point alloy, the first arc-shaped wall 2 of the support fixture achieves cooling through the first liquid inlet 4 and the first liquid outlet 5, while the second arc-shaped wall 3 achieves cooling through the second liquid inlet 6 and the second liquid outlet 7. Because the portion of the uniform cross-section straight cylinder 100 that contacts or is close to the inner wall of the arc-shaped wall of the support fixture dissipates heat relatively faster during cooling, a square or rhomboid grid-like stress distribution is formed in a specific area of ​​the straight cylinder wall. Before removing the uniform cross-section straight cylinder 100, a marking line 8 can be easily marked on the cylinder body through the positioning notch 14 on the side of the base 11 of the support seat 1. The marking line 8 is used to locate the bending deformation interface in subsequent processes.

[0055] Step 3: Place the straight cylinder into the bending mold, and use the bending mold and hydraulic press to bend the straight cylinder with a constant cross-section to the designed bending state, forming a bent cylinder with a constant cross-section. Align the marking line 8 on the straight cylinder 100 with the demolding surface of the bending mold, place it into the bending mold, and slowly bend the straight cylinder 100 with a constant cross-section to the designed bending state using a hydraulic press, so that the arc radius R of the cylinder's central axis reaches the set value of 650mm, forming a bent cylinder with a constant cross-section.

[0056] Step 4: The uniform cross-section bent cylinder undergoes annealing, hydrostatic bulging, excess material cutting, and non-destructive testing in sequence. Hydrostatic bulging aims to eliminate rigid springback deformation during bending, further improving the roundness and other dimensional accuracy of the cylinder. A specialized cutting fixture is used to remove excess material from the open end of the bent cylinder, ensuring the length of the sealed-bottomed cylinder reaches the design length. Non-destructive testing includes 100% non-destructive testing using fluorescent penetrant testing; only qualified cylinders continue processing.

[0057] Step 5: Using laser welding, laser filler wire welding, or laser-arc hybrid welding, weld the flange and drain nozzle to the front and rear ends of the cylinder, respectively.

[0058] This invention is more suitable for bending aluminum alloy cylinders with a diameter-to-thickness ratio greater than 50. By forming a square or rhomboid grid-like stress distribution on the surface of the aluminum alloy cylinder, the uniform deformation capability of the thin wall of the aluminum alloy cylinder is further improved. It is more effective in improving the wave deformation in the inner arc area of ​​the cylinder bending. At the same time, it can also significantly improve defects such as tearing and local over-thinning in the outer arc area of ​​the cylinder bending, further improving the surface manufacturing accuracy of the bent cylinder and the forming qualification rate of the aluminum alloy bent cylinder.

[0059] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0060] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art without departing from the scope of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A method of bend forming a large aspect ratio aluminum alloy cylinder, characterized by, The method includes the following steps: The straight cylinder with a uniform cross-section is placed vertically and fixedly clamped by a support clamp, and the contact area between the inner arc wall of the support clamp and the straight cylinder with a uniform cross-section is a grid shape with crisscrossing lines. A low-melting-point alloy is filled into the straight cylinder with a uniform cross-section, and then cooled. The cooled, straight cylindrical body with equal cross-section is bent to a preset bending state to form a bent cylindrical body with equal cross-section. The uniform cross-section bent cylinder is sequentially annealed, hydraulically expanded, and the allowance is cut to obtain a large diameter-to-thickness aluminum alloy bent cylinder. The support fixture includes a support base (1), a first arc-shaped wall (2), and a second arc-shaped wall (3). The support base (1) is used to support the ellipsoidal bottom of the cross-section straight cylinder (100). The first arc-shaped wall (2) and the second arc-shaped wall (3) are symmetrically distributed and the cylindrical cavity formed therein is used to support the cylindrical body of the equal cross-section straight cylinder (100). Both the first arc-shaped wall (2) and the second arc-shaped wall (3) are hollow shell structures with internal flow channels.

2. The bending forming method for a large diameter-to-thickness aluminum alloy cylinder according to claim 1, characterized in that, The support base (1) includes a base (11) and a boss (12) located on the base (11), the boss (12) having a cavity (13) adapted to the ellipsoidal bottom profile of the straight cylindrical body (100) with equal cross section.

3. The bending forming method for a large diameter-to-thickness aluminum alloy cylinder according to claim 2, characterized in that, The first arc-shaped wall (2) includes a first flange end (21) and a first support end (22), and the second arc-shaped wall (3) includes a second flange end (31) and a second support end (32); the first flange end (21) and the second flange end (31) are fixed on the base (11), and the inner wall of the first support end (22) and the inner wall of the second support end (32) form a cylindrical cavity with a symmetrical radial distribution and a central angle of 2α.

4. The bending forming method for a large diameter-to-thickness aluminum alloy cylinder according to claim 3, characterized in that, The angle range of α is 90° to 180°.

5. The bending forming method for a large diameter-to-thickness aluminum alloy cylinder according to claim 2, characterized in that, The base (11) has a positioning notch (14) at the position of the mirror center plane of the first arc-shaped wall (2) and the second arc-shaped wall (3).

6. The bending forming method for a large diameter-to-thickness aluminum alloy cylinder according to claim 1, characterized in that, The grid shape is either square or rhomboid.

7. The bending forming method for a large diameter-to-thickness aluminum alloy cylinder according to claim 1, characterized in that, The melting point of the low-melting-point alloy is 250–350°C.

8. The bending forming method for a large diameter-to-thickness aluminum alloy cylinder according to claim 1 or 7, characterized in that, The low-melting-point alloy includes at least one of Sn alloy, Sn-Pb alloy and Sn-Ag alloy.

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