A rigid-flexible composite forming method for high-strength aluminum alloy large diameter ratio pipe fittings

Abstract

The present invention provides a method for forming a high-strength aluminum alloy large diameter ratio pipe fitting with a rigid-flexible composite in multiple steps, which belongs to the field of metal forming and manufacturing technology. It comprises: determining the initial conical tube size according to the diameter reduction and expansion strain of the part and making the conical tube by coil welding of the plate blank, then placing the conical tube into a rigid-flexible composite mold for diameter reduction in two steps, and the flexible mold provides uniform support as it deforms, and obtaining a one-step diameter reduction part and a preformed part in sequence; then placing the preformed part in a preheated hot air expansion mold for heat preservation and solution treatment, pressurizing the closed tube cavity to form it into a mold, quenching and aging treatment after mold opening, and finally machining to remove the excess to obtain a high-strength aluminum alloy large diameter ratio pipe fitting. The present invention achieves the technical effect of uniformly supporting the stress field of the deformation zone in the multi-step rigid-flexible composite diameter reduction by the flexible mold to prevent wrinkling, combining solution treatment to improve the plasticity and elongation of the material, and quenching and aging treatment after expansion to precipitate the strengthening phase, thereby achieving the formed part without wrinkling, uniform wall thickness, and significantly improved strength and fatigue properties.

Description

Technical Field

[0001] The present invention relates to the technical field of metal forming and manufacturing, in particular to a rigid-flexible composite step-by-step forming method for a high-strength aluminum alloy large diameter reduction ratio pipe fitting. Background Art

[0002] High-strength aluminum alloy pipe fittings with large diameter reduction ratios typically feature large diameter differences and large curvature profiles. They are widely used in high-end equipment applications such as aerospace, automotive, energy and chemical industries, and shipbuilding and marine engineering. Examples include aircraft engine rear cones and aeroengine cones. At the same time, the requirements for high-diameter reduction ratio components are constantly increasing.

[0003] The methods currently available for forming high-strength aluminum alloy pipes with large diameter reduction ratios include split forming and welding, high pressure forming, hot air bulging and superplastic forming. Specifically:

[0004] Among them, the petal forming and welding method uses stamping to divide the curved surface of the large diameter ratio pipe fitting into blocks, and then welds the formed curved surface into a complete large diameter ratio pipe fitting; the components obtained by this method have internal stress release, large springback, low dimensional accuracy, and uneven deformation of the weld and heat-affected zone, high welding difficulty, and complex microstructure at the weld, which is difficult to meet the high-quality requirements of such components; internal high-pressure forming uses high-pressure liquid medium to drive the deformation of the component, but this method is easy to exceed the forming limit of the material and cause the component to crack when forming the complex feature areas of such components. At the same time, internal high-pressure forming has high requirements for equipment; hot air expansion forming can utilize the high elongation of the material at high temperature to form. If a single hot air expansion method is used to form large diameter ratio components, the local strain is too large, resulting in serious local thinning of the component wall thickness, which cannot meet the service requirements of the component; superplastic forming is difficult to prepare uniform fine-grained materials, and the long forming time greatly reduces the manufacturing efficiency.

[0005] In summary, existing forming methods cannot meet the requirements of high-strength aluminum alloy large-diameter-reduction-ratio pipe fittings. Therefore, to address the manufacturing difficulties of high-strength aluminum alloy large-diameter-reduction-ratio pipe fittings in forming accuracy and microstructure-performance coupling, an integrated forming method for high-precision shape and property control of aluminum alloy is urgently needed to solve the bottleneck problem of high-strength aluminum alloy large-diameter-reduction-ratio pipe fitting forming. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a rigid-flexible composite multi-pass forming method for high-strength aluminum alloy large diameter reduction ratio pipe fittings. The flexible mold in the multi-pass rigid-flexible composite diameter reduction uniformly supports the stress field in the deformation zone to prevent wrinkling. Combined with the solution treatment to improve the plasticity and elongation of the material, and the quenching and aging treatment after bulging to precipitate the strengthening phase, the technical effect of wrinkle-free formed parts, uniform wall thickness, and significantly improved strength and fatigue performance is achieved.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A method for forming a high-strength aluminum alloy large diameter reduction ratio pipe with rigid-flexible composite steps, comprising the following steps:

[0009] S1. Determine the initial conical tube size according to the shrinkage strain and bulging strain of the formed part, and obtain the conical tube by coil welding the slab;

[0010] S2, placing the tapered tube into a rigid-flexible composite mold, and reducing the diameter of the tube by closing the mold with a press, while the flexible mold deforms along with the tapered tube and provides uniform support, thereby obtaining a one-step diameter reduction part;

[0011] S3, placing the one-step diameter-reduced part into the rigid-flexible composite mold for secondary diameter reduction, closing the mold again for diameter reduction, and allowing the flexible mold to deform with the part and provide uniform support to obtain a preformed part;

[0012] S4, placing the preformed part into a hot expansion mold for solution treatment and heat preservation, and applying pressure to the closed tube cavity of the hot expansion mold to form the preformed part into a mold, thereby obtaining a formed part;

[0013] S5. After completing S4, the mold is opened to quickly remove the formed parts, and quenching treatment, aging treatment and heat preservation are carried out in sequence. Finally, the formed parts are machined and the excess is removed to obtain high-strength aluminum alloy large diameter ratio pipe fittings.

[0014] Preferably, in S1, the shrinkage strain and bulging strain of the formed part do not exceed 80% to 85% of the maximum strain of the formed material; the shrinkage strain is:

[0015] ;

[0016] The bulging strain is:

[0017] ;

[0018] ;

[0019] in, L 1. L 2 are the characteristic dimensions before and after diameter reduction, L 3. L 4 are the characteristic dimensions before and after bulging; is the bulging strain, is the maximum bulging strain of the forming material; is the shrinkage strain, is the maximum shrinkage strain of the formed material.

[0020] Preferably, in S2 and S3, the material of the flexible supporting mold is one or more of polyurethane, silicone rubber or TPE.

[0021] Preferably, in S2 and S3, the rigid-flexible composite mold includes a flexible support mold, a rigid support mold, a diameter reduction mold and a limiting mold; the flexible support mold is used to provide uniform support to suppress wrinkling on the part surface, the rigid support mold is used to provide support for the flexible mold and jointly position the cone tube with the limiting mold, and the diameter reduction mold is used to apply a diameter reduction force.

[0022] Preferably, in S2 and S3, the mold closing process is closed-loop controlled by a displacement control system, which includes a displacement sensor, a controller, a hydraulic cylinder and a feedback device for real-time monitoring and adjustment of the mold closing speed and displacement.

[0023] Preferably, in S4, the hot air expansion mold includes upper and lower expansion molds, insulation plates, heating rods, water-cooling structures and high-pressure inflation holes; after the upper and lower expansion molds are closed, a forming cavity matching the target part is formed, and the heating rod is controlled by a temperature control system to heat to the solid solution temperature. The temperature control system consists of a temperature sensor, a controller, a heating rod and a feedback adjustment mechanism, which is used to monitor and control the temperature of the expansion mold in real time; the water-cooling structure and the insulation plate are used to prevent heat from being transferred to the press.

[0024] Preferably, the sealed lumen is formed by welding sealing plates at both ends of the preformed part to seal the preformed part.

[0025] Preferably, in S4, before the preformed part is placed in the hot inflation mold, the method further includes: preheating the hot inflation mold to the solution temperature; and determining the solution temperature and holding time according to the material state of the preformed part.

[0026] Preferably, in S5, the quenching treatment is water quenching.

[0027] Preferably, in S5, the aging treatment temperature is 160-190° C., and the holding time is 6-24 hours.

[0028] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0029] (1) The present invention uses a flexible mold support member in the multi-pass diameter reduction process. Due to the low strength of the flexible mold, it elastically deforms when in contact with the tube blank during the diameter reduction process, so that the mold and the tapered tube are in close contact. The stress field generated by this contact mode is more evenly distributed, thereby effectively preventing wrinkling of the formed part.

[0030] (2) The initial conical tube coupled expansion strain and diameter reduction strain adopted in the present invention avoids the local wrinkling of the part caused by a single large strain diameter reduction and the serious wall thickness thinning caused by a single expansion; the present method adopts a rigid-flexible composite mold for multiple diameter reductions and then uses a hot air expansion process for final forming, which simultaneously reduces the diameter reduction and expansion strains and makes the wall thickness of the formed part more uniform.

[0031] (3) The forming method provided by the present invention promotes the complete dissolution of the strengthening phase in the aluminum matrix during the solution treatment of the preformed parts, forming a uniform microstructure, significantly reducing the hardness of the material and improving its plasticity, thereby optimizing the bulging deformation process and effectively eliminating internal stress, thereby improving dimensional stability and deformation resistance. Subsequently, a supersaturated solid solution is formed through rapid cooling through a quenching process, significantly improving the strength of the material. The final aging treatment further enhances the material strength and improves the fatigue performance of the material through the formation of precipitation phases. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 A flow chart of a rigid-flexible composite step-by-step forming method for a high-strength aluminum alloy large diameter reduction ratio pipe fitting according to the present invention is provided;

[0034] Figure 2 Dimensional drawing of a component obtained by the rigid-flexible composite step-by-step forming method for a high-strength aluminum alloy large diameter reduction ratio pipe provided by an embodiment of the present invention;

[0035] Figure 3 Schematic diagram of multi-pass diameter reduction of the rigid-flexible composite forming method for high-strength aluminum alloy large diameter reduction ratio pipe provided by an embodiment of the present invention; wherein, Figure 3 (a) is a schematic diagram of forming a one-step diameter reduction part. Figure 3 (b) is a schematic diagram of the forming of the preformed part;

[0036] Figure 4 A flow chart of heat treatment of a rigid-flexible composite step-by-step forming method for a high-strength aluminum alloy large diameter reduction ratio pipe provided by an embodiment of the present invention;

[0037] Figure 5 A diagram for determining the initial billet size of the rigid-flexible composite step-by-step forming method for high-strength aluminum alloy large-diameter-variable-ratio pipe fittings provided in an embodiment of the present invention;

[0038] Figure 6Schematic diagram of the device for the rigid-flexible composite step-by-step forming method of high-strength aluminum alloy large diameter ratio pipe fittings provided by an embodiment of the present invention; wherein, Figure 6 (a) is a structural diagram of a rigid-flexible composite mold. Figure 6 (b) is a schematic diagram of the structure of the hot air expansion mold.

[0039] Description of reference numerals:

[0040] 1. Upper table; 2. Reduction die; 3. Flexible support die; 4. Rigid support die; 5. Limit die; 6. Lower table; 7. Hot air expansion die; 8. Upper die; 9. Lower die; 10. Preformed part; 11. High-pressure inflation hole; 12. Insulation board; 13. Heating rod; 14. Water-cooling structure. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] The present invention aims to perform local diameter reduction through a rigid-flexible composite mold, utilize the flexible uniformly distributed loading characteristics to achieve uniform loading in the diameter reduction deformation zone to suppress wrinkling defects during the diameter reduction process, and then use a non-steady-state hot expansion process to perform solution temperature final forming to form large diameter-reduced pipe fittings. Finally, rapid quenching and aging are performed to improve the strength of the components, avoiding the disadvantage of poor reliability of the segmented welding structure.

[0043] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] Example 1

[0045] like Figure 1 As shown, this embodiment provides a method for forming a high-strength aluminum alloy large diameter ratio pipe with rigid-flexible composite in stages, comprising the following steps:

[0046] S1. Determine the initial conical tube size according to the shrinkage strain and bulging strain of the formed part, and obtain the conical tube by coil welding the slab;

[0047] S2, placing the tapered tube into a rigid-flexible composite mold, and reducing the diameter of the tube by closing the mold with a press, while the flexible mold deforms along with the tapered tube and provides uniform support, thereby obtaining a one-step diameter reduction part;

[0048] S3, placing the one-step diameter-reduced part into the rigid-flexible composite mold for secondary diameter reduction, closing the mold again for diameter reduction, and allowing the flexible mold to deform with the part and provide uniform support to obtain a preformed part;

[0049] S4, placing the preformed part into a hot expansion mold for solution treatment and heat preservation, and applying pressure to the closed tube cavity of the hot expansion mold to form the preformed part into a mold, thereby obtaining a formed part;

[0050] S5. After completing S4, the mold is opened to quickly remove the formed parts, and quenching treatment, aging treatment and heat preservation are carried out in sequence. Finally, the formed parts are machined and the excess is removed to obtain high-strength aluminum alloy large diameter ratio pipe fittings.

[0051] Reference Figure 2 In step S1, the upper diameter of the cone is d1, the lower diameter is D, and the axial height is H; Figure 5 As shown, the maximum diameter reduction of the initial material is determined according to formula (1), and the maximum bulging amount of the initial material is determined according to formula (2). The diameter reduction strain is:

[0052] ; (1)

[0053] The bulging strain is:

[0054] ; (2)

[0055] Furthermore, the shrinkage strain and bulging strain of the formed part do not exceed 80% to 85% of the maximum strain of the formed material; the formula is shown in formula (3)

[0056] ; (3)

[0057] in, L 1. L 2 are the characteristic dimensions before and after diameter reduction, L 3. L 4 are the characteristic dimensions before and after bulging; is the bulging strain, is the maximum bulging strain of the forming material; is the shrinkage strain, is the maximum shrinkage strain of the formed material.

[0058] Furthermore, the small end diameter of the initial forming material is determined to be d And cone height H , and the range of their values ​​is determined by the following formulas (4) to (8):

[0059] ; (4)

[0060] ; (5)

[0061] ; (6)

[0062] ; (7)

[0063] ; (8)

[0064] in, d is the initial billet small end diameter; H 1 is the height of the upper process end; H 2 is the distance between the maximum expansion position of the cone tube and the bottom surface of the cone tube; It is the angle between the generatrix of the initial billet cross section and the bottom edge.

[0065] Furthermore, in S2, the forming process of the once-reduced part is as follows: Figure 3 (a) and Figure 6 In (a), the lower mold of the rigid-flexible composite mold is first fixed on the lower table 6 of the press, and the upper table 1 of the press is connected to a slider, and then the conical tube is placed on the flexible support mold 3, wherein a rigid support mold 4 is provided below the flexible support mold 3, and limit molds 5 are provided at both ends of the rigid support mold 4; the press drives the reducing mold 2 to close the mold at a closing speed v1, and at the same time, the flexible support mold 3 deforms with the part and supports the part, reducing the upper end diameter of the conical tube from d1 to d2, thereby obtaining a one-step reduced diameter part; wherein the material of the flexible support mold 3 is one or more of polyurethane, silicone rubber or TPE.

[0066] In S3, the forming process of the preformed parts is: Figure 3 (b) and Figure 6 In (a), the lower mold of the rigid-flexible composite mold with secondary diameter reduction is first fixed on the lower table 6 of the press, and the upper table 1 of the press is connected to a slider. Then, the one-step diameter reduction part is placed on the flexible support mold 3 with secondary diameter reduction. The press drives the diameter reduction mold 2 to close the mold at a closing speed of v2, and the upper end diameter of the one-step diameter reduction part is reduced from d2 to d3 to obtain a preformed part 10.

[0067] Reference Figure 6 In (a), the rigid-flexible composite mold includes a flexible support mold 3, a rigid support mold 4, a diameter reduction mold 2 and a limiting mold 5; the flexible support mold 3 is used to provide uniform support to suppress wrinkling on the surface of the part, the rigid support mold 4 is used to provide support for the flexible mold and jointly position the tapered tube with the limiting mold 5, and the diameter reduction mold 2 is used to apply a diameter reduction force.

[0068] Furthermore, in S2 and S3, the mold closing process is controlled in a closed loop by a displacement control system. This displacement control system includes a displacement sensor, a controller, a hydraulic cylinder, and a feedback device, which monitors and adjusts the mold closing speed and displacement in real time. Specifically, the displacement sensor monitors the position changes of the press in real time and transmits the signal to the controller. The controller compares the feedback signal with preset parameters, calculates the deviation, and issues a command. The hydraulic cylinder then receives the command and drives the upper mold of the press. The feedback device transmits the actual displacement data back to the controller, forming a closed-loop control loop to ensure accuracy and stability.

[0069] Furthermore, in S4, the forming process of the preformed part 10 in the hot expansion mold is as follows: first, the hot expansion mold is heated to the solution temperature T1, and the solution temperature and holding time are determined according to the material state of the preformed part. Taking Al2219-T6 state as an example, the solution temperature T1 is 515-565°C, and the holding time t1 is 10-40min; then the preformed part 10 is placed in the hot expansion mold 7 for mold closing and holding t1, and then the pressurization rate is increased. Pressurize the sealed tube cavity to p, make the part gradually stick to the mold, and maintain the pressure for t2. Figure 6 In (b), the hot air expansion mold 7 includes an upper bulging mold 8, a lower mold 9, an insulation plate 12, a heating rod 13, a water-cooling structure 14, and a high-pressure inflation hole 11. The upper bulging mold 8 and the lower mold 9 are combined to form a forming cavity that matches the target part. The heating rod 13 is controlled by a temperature control system to heat to the solution temperature. The temperature control system consists of a temperature sensor, a controller, the heating rod 13, and a feedback adjustment mechanism for real-time monitoring and control of the bulging mold temperature. The water-cooling structure 14 and the insulation plate 12 are used to prevent heat from being transferred to the press. In addition, the closed tube cavity is formed by welding sealing plates at both ends of the preformed part 10 to form a sealed cavity.

[0070] It should be noted that the temperature control system consists of a temperature sensor, a controller, a heating rod 13, and a feedback control mechanism. The temperature sensor monitors the bulge die temperature in real time and transmits the signal to the controller. Based on the difference between the set temperature and the actual temperature, the controller calculates and outputs a control signal to adjust the power of the heating rod 13. If the temperature is below the set value, the heating rod 13 increases heat output; if it is above the set value, heating is reduced or stopped. The feedback control mechanism continuously monitors and adjusts the temperature to ensure that it remains within the solution temperature range, thereby achieving temperature control.

[0071] Furthermore, in S5, the part forming process is as follows: after completing step S4, the mold is opened and the part is quickly removed, followed by quenching treatment, and immediately after completion, aging treatment at temperature T2 and time t3. The quenching treatment is water quenching, and the aging treatment temperature T2 is 160-190°C, and the holding time t3 is 6-24 hours.

[0072] Reference Figure 4 As shown in the heat treatment flow chart, the method provided in this embodiment performs solution treatment simultaneously during the hot air bulging forming stage of the preformed parts. By heating the mold to the solution temperature and keeping it warm, the strengthening phase in the high-strength aluminum alloy is fully dissolved in the aluminum matrix to form a uniform α solid solution structure, which significantly improves the plasticity of the material; then, during the pressure-holding bulging process, high temperature and high plasticity are used to achieve mold-fitting forming to avoid local strain concentration; after forming, rapid quenching treatment is performed to retain the supersaturated solid solution to form a metastable structure, and then artificial aging treatment is performed to precipitate dispersed strengthening phases (such as θ' ​​phase and GP zone), and finally a composite strengthening mechanism of "solid solution strengthening + precipitation strengthening" is constructed inside the component to achieve a synergistic improvement in organizational homogenization and mechanical properties (such as strength and fatigue performance).

[0073] The above method is further described below using aluminum alloy 2219 and aluminum alloy 7075 as examples.

[0074] Example 2

[0075] In this embodiment, a forming method of aluminum alloy 2219 is provided, and the specific steps include:

[0076] Step 201: Determine the initial conical tube size based on the shrinkage strain and bulging strain of the part, and coil-weld the slab to obtain the conical tube. The conical tube has an upper diameter d1 = 100 mm, a lower diameter D = 200 mm, and an axial height H = 150 mm.

[0077] Step 202: The lower mold of the rigid-flexible composite mold is fixed to the lower table of a press, and a slider is connected to the upper table of the press. The conical tube is then placed on the flexible support mold, wherein a rigid support mold is provided below the flexible support mold, and limit molds are provided at both ends of the rigid support mold. The press drives the reducing mold to close the mold at a closing speed of 10 mm / s. At the same time, the flexible support mold deforms with the part and supports the part, reducing the upper end diameter of the conical tube from 100 mm to 90 mm, thereby obtaining a one-step reduced diameter part.

[0078] Step 203: The lower die of the secondary-reduction rigid-flexible composite die is fixed to the lower table of a press, and a slider is connected to the upper table of the press. The single-reduction part is then placed on the secondary-reduction flexible support die. The press drives the reduction die to close at a closing speed of 10 mm / s, reducing the upper end diameter of the single-reduction part from 90 mm to 85 mm, thereby obtaining a preformed part.

[0079] Step 204: The hot air expansion mold is heated to a solution temperature of 535°C, the tapered tube after diameter reduction is placed in the hot air expansion mold, and the mold is closed. The heat preservation time is 40 minutes, and then the pressure is applied at a rate of 0.5 MPa / min to 1 MPa, so that the component is gradually attached to the mold, and the pressure is maintained for 5 minutes.

[0080] Step 205: The mold is opened and the formed component is quickly taken out, and quenched, followed by an aging treatment at a temperature of 175° C. for 12 hours. Finally, the formed component is machined to remove excess material, thereby obtaining aluminum alloy 2219.

[0081] Example 3

[0082] In this embodiment, a forming method of aluminum alloy 7075 is provided, and the specific steps include:

[0083] Step 300: Determine the initial conical tube size based on the shrinkage strain and bulging strain of the part, and coil-weld the slab to obtain a conical tube with an upper diameter d1 = 100 mm, a lower diameter D = 200 mm, and an axial height H = 150 mm.

[0084] Step 301: The lower mold of the rigid-flexible composite mold is fixed to the lower table of a press, and a slider is connected to the upper table of the press. The conical tube is then placed on the flexible support mold, wherein a rigid support mold is provided below the flexible support mold, and limit molds are provided at both ends of the rigid support mold. The press drives the diameter reduction mold to close the mold at a closing speed of 10 mm / s. At the same time, the flexible support mold deforms with the part and supports the part, reducing the upper end diameter of the conical tube from 100 mm to 90 mm, thereby obtaining a one-step diameter reduction part.

[0085] Step 302: The lower die of the secondary-reduction rigid-flexible composite die is fixed to the lower table of a press, and a slider is connected to the upper table of the press. The single-reduction part is then placed on the secondary-reduction flexible support die. The press drives the reduction die to close at a closing speed of 10 mm / s, reducing the upper end diameter of the single-reduction part from 90 mm to 85 mm, thereby obtaining a preformed part.

[0086] Step 304: The hot air expansion mold is heated to the solution temperature of 475°C, the tapered tube after diameter reduction is placed in the hot air expansion mold and the mold is closed. The mold is kept at temperature for 40 minutes, and then the pressure is applied at a rate of 0.5 MPa / min to 1 MPa to gradually fit the component into the mold. The pressure is then maintained for 5 minutes.

[0087] Step 305: The mold is opened and the formed component is quickly taken out, and quenched, followed by an aging treatment at 130° C. for 20 hours. Finally, the formed component is machined to remove excess material, thereby obtaining aluminum alloy 7075.

[0088] Therefore, the above-mentioned rigid-flexible composite multi-pass forming method for high-strength aluminum alloy large diameter reduction ratio pipe fittings is adopted. The flexible mold in the multi-pass rigid-flexible composite diameter reduction uniformly supports the stress field in the deformation zone to prevent wrinkling. Combined with the solution treatment to improve the plasticity and elongation of the material, and the quenching and aging treatment after bulging to precipitate the strengthening phase, the technical effect of wrinkle-free formed parts, uniform wall thickness, and significantly improved strength and fatigue performance is achieved.

[0089] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A rigid-flexible composite forming method for high-strength aluminum alloy large diameter ratio pipe fittings, characterized in that: The following steps are involved: S1. Determine the initial conical tube size according to the shrinkage strain and bulging strain of the formed part, and obtain the conical tube by coil welding the slab; S2, placing the tapered tube into a rigid-flexible composite mold, and reducing the diameter by a press, while the flexible support mold deforms with the tapered tube and provides uniform support, thereby obtaining a one-step diameter reduction part; S3, placing the one-step diameter-reduced part into the rigid-flexible composite mold for secondary diameter reduction, closing the mold again for diameter reduction, and the flexible support mold deforms with the part and provides uniform support to obtain a preformed part; In S2 and S3, the rigid-flexible composite mold includes a flexible support mold, a rigid support mold, a diameter reduction mold, and a limiting mold; the flexible support mold is used to provide uniform support to suppress wrinkling on the part surface, the rigid support mold is used to support the flexible mold and jointly position the tapered tube with the limiting mold, and the diameter reduction mold is used to apply a diameter reduction force; S4, placing the preformed part into a hot expansion mold for solution treatment and heat preservation, and applying pressure to the closed tube cavity of the hot expansion mold to form the preformed part into a mold, thereby obtaining a formed part; The hot air bulging die includes an upper bulging die, a lower die, a heat preservation plate, a heating rod, a water-cooling structure, and a high-pressure inflation hole. When the upper bulging die and the lower bulging die are closed, a forming cavity matching the target part is formed. The heating rod is controlled by a temperature control system to heat to the solution temperature. The temperature control system consists of a temperature sensor, a controller, a heating rod, and a feedback adjustment mechanism for real-time monitoring and control of the bulging die temperature. The water-cooling structure and the heat preservation plate are used to prevent heat from being transferred to the press. In S4, before the preformed part is placed in the hot expansion mold, the method further includes: preheating the hot expansion mold to a solution temperature; and determining the solution temperature and holding time according to the material state of the preformed part; S5. After completing S4, the mold is opened to quickly remove the formed parts, and quenching treatment, aging treatment and heat preservation are carried out in sequence. Finally, the formed parts are machined and the excess is removed to obtain high-strength aluminum alloy large diameter ratio pipe fittings.

2. The method for forming a high-strength aluminum alloy large diameter reduction ratio pipe with rigid-flexible composite steps according to claim 1, characterized in that: In S1, the shrinkage strain and bulging strain of the formed part do not exceed 80% to 85% of the maximum strain of the formed material; the shrinkage strain is: ； The bulging strain is: ； ； in, are the characteristic dimensions before and after diameter reduction, are the characteristic dimensions before and after bulging respectively; is the bulging strain, is the maximum bulging strain of the forming material; is the shrinkage strain, is the maximum shrinkage strain of the formed material.

3. The method for forming a high-strength aluminum alloy large diameter reduction ratio pipe with rigid-flexible composite steps according to claim 1, characterized in that: In S2 and S3, the material of the flexible supporting mold is polyurethane, silicone rubber, or polyurethane and silicone rubber.

4. The method for forming a high-strength aluminum alloy large diameter reduction ratio pipe with rigid-flexible composite steps according to claim 1, characterized in that: In S2 and S3, the mold closing process is closed-loop controlled by a displacement control system, which includes a displacement sensor, a controller, a hydraulic cylinder and a feedback device for real-time monitoring and adjustment of the mold closing speed and displacement.

5. The method for forming a high-strength aluminum alloy large diameter reduction ratio pipe with rigid-flexible composite steps according to claim 1, characterized in that: The sealed lumen is formed by welding sealing plates at both ends of the preformed part to seal the part.

6. The method for forming a high-strength aluminum alloy large diameter reduction ratio pipe with rigid-flexible composite steps according to claim 1, characterized in that: In S5, the quenching treatment is water quenching.

7. The method for forming a high-strength aluminum alloy large diameter reduction ratio pipe with rigid-flexible composite steps according to claim 1, characterized in that: In S5, the aging treatment temperature is 160-190° C., and the holding time is 6-24 hours.

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