Creep age forming method for deformation coordination of reinforced zone and thin skin zone and application

Abstract

The present application belongs to the technical field of sheet metal forming, and particularly relates to a creep age forming method for strengthening the coordination of deformation in the reinforced area and the thin skin area and application. The method comprises the following steps: calculating the required pressure for part fitting by using the finite element method; calculating the maximum axial stress when the part is fitted with the die surface; obtaining a gasket according to the maximum axial stress; placing the gasket on the surface of the thin skin area and fixing it; placing the part with the fixed gasket on the die, and sealing by using the vacuum method; placing it in a heating furnace or a hot press tank, and fitting the outer surface of the part with the inner surface of the die according to the calculated pressure and the pre-set process parameters; after the creep age is completed, unloading the temperature and pressure on the formed part. The purpose is to solve the problem that the inconsistency of springback after forming caused by the structural differences of the workpiece itself during creep age forming, thereby affecting the accurate forming of the part.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sheet metal forming, and particularly relates to a creep age forming method for coordinating deformation of a reinforced area and a thin skin area and application thereof. BACKGROUND

[0002] A new generation of advanced aircraft requires good aerodynamic performance while minimizing weight and improving service life. As the most important type of parts on the aircraft, the integral wall plate is not only an important part of the aircraft aerodynamic shape, but also the main load-bearing component of the wing, fuselage and the like. In the current aircraft structure design, the requirements for the aerodynamic performance, integrity and service life of the aircraft structure are also increasingly high. In order to improve the maneuverability and aerodynamic performance of the aircraft, the integral wall plate of the advanced aircraft not only has a complex double curvature shape, but also has a complex internal structure, such as local thickening, mouth frame and local thinning area, so as to meet the shape requirements while reducing the number of parts, reducing weight and improving service life. Therefore, the shape precision and comprehensive performance of such parts are directly related to the aerodynamic performance, structural strength, fatigue life and structural weight of the entire aircraft structure.

[0003] Compared with the traditional integral wall plate component forming technology, the creep age forming technology is a technology developed for forming complex shape parts, especially integral wall plate parts, that is, a forming method that synchronizes forming and aging by using the creep characteristics of the metal. Compared with the traditional forming process, this forming method improves the material strength, reduces the residual stress, enhances the stress corrosion resistance, and prolongs the service life of the part, and is suitable for forming integral wall plate components with large curvature complex shape and structure of integral rib and variable thickness. This technology is considered one of the most important metal forming processes for the next generation of large aircraft. With the increasing demand for large high-performance aircraft in military and civil aviation, this forming process will play a unique advantage in manufacturing large complex integral wall plates. It has a wide application prospect in the development of China's large aircraft project.

[0004] Due to the limitation of the aging period of the material itself, the existing elastic deformation in the workpiece cannot be completely converted into plastic deformation by the creep age forming technology, and there is a certain amount of springback after forming, so springback control is a key problem affecting the quality of creep age forming. In modern aircraft design and manufacturing, in order to improve the overall aerodynamic performance of the aircraft, many parts have complex shapes, such as skin surfaces with different curvatures and thicknesses, and also have complex internal structures, such as local thickening, mouth frame and local thinning area. When the size of the wall plate part is large and the curvature radius is small, the springback amount after forming is inconsistent due to structural differences in these key areas, thereby affecting the accurate forming of the part. SUMMARY

[0005] (I) Technical problems to be solved

[0006] The present application mainly aims at the above problems, and proposes a creep age forming method for coordinating deformation of reinforced areas and thin skin areas and application, which aims to solve the problem that the consistency of springback after forming is affected by the structural difference of the workpiece itself when the workpiece is subjected to creep age forming, thereby affecting the accurate forming of the part.

[0007] (II) Technical solutions

[0008] To achieve the above-mentioned purpose, the present application provides a creep age forming method for coordinating deformation of reinforced areas and thin skin areas, comprising the following steps:

[0009] The finite element method is used to calculate the pressure required for the complete adhesion of the outer surface of the part to the die profile;

[0010] When the part is adhered to the die profile, the maximum axial stress of the thin skin area along the bending deformation direction is calculated;

[0011] A same-material gasket with deformation stiffness compensation is obtained according to the maximum axial stress;

[0012] The gasket with specific deformation stiffness compensation is placed on the surface of the thin skin area and fixed;

[0013] The part with the fixed gasket is placed on the die with a certain outer profile, and is packaged in a vacuum manner;

[0014] The packaged whole is placed in a heating furnace or a hot press tank, and the outer profile of the part is adhered to the inner profile of the die according to the calculated pressure and the pre-set process parameters;

[0015] After the creep age is completed, the temperature and pressure on the formed part are unloaded.

[0016] Further, the step of obtaining a same-material gasket with deformation stiffness compensation according to the maximum axial stress comprises:

[0017] The thickness t of the gasket can be calculated by the following formula:

[0018]

[0019] Wherein L is the length of the gasket, E is the elastic modulus of the material, t0 is the original thickness of the skin, σ max is the maximum axial stress of the thin skin area along the bending deformation direction.

[0020] Further, the step of adhering the outer profile of the part to the inner profile of the die according to the pre-set process parameters comprises:

[0021] In a vacuum state, the heating furnace or hot press tank is heated, and when the part reaches the set temperature, it is kept warm;

[0022] When the set holding time is reached, the pressurization system is turned on to apply pressure to the surface of the part until the outer surface of the part is fitted with the inner surface of the mold.

[0023] Further, in the holding stage, the stress is slowly applied to the target pressure of the first stage by controlling the pressure increasing rate, and after reaching the target pressure, the pressure is kept for a certain time, and then the pressure is increased to the target pressure of the second stage.

[0024] Further, the pressure increasing rate is 0.01 MPa / min to 0.05 MPa / min.

[0025] Further, the target pressure of the first stage is 15% to 30% of the target pressure of the second stage.

[0026] Further, before creep age forming, the original plate of the part is also subjected to solid solution at a temperature of 460℃ to 490℃ for 50min, and then immediately water quenched, and then subjected to 2% to 3% pre-stretching.

[0027] Further, the gasket and the surface of the thin skin area of the part are fixed by using adhesive tape.

[0028] To achieve the above-mentioned purpose, the application provides a part formed by the forming method on the aircraft body structure.

[0029] (Three) beneficial effects

[0030] The above technical scheme of the application has the following advantages: by using the finite element method to design the gasket, the deformation stiffness compensation is realized through the gasket, the buckling instability defect of the thin skin area in the forming process is reduced, and the stiffness consistency of the reinforced area and the thin skin area is realized by using the gasket, and the deformation unevenness caused by the change of the internal structure is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical scheme in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0032] Figure 1 The process diagram of the creep age forming method for the reinforced area and the thin skin area deformation coordination of the application.

[0033] Figure 2 A structure diagram of creep age forming of a part of the present application.

[0034] Figure 3 A structure diagram of a complex part before forming of the present application.

[0035] Figure 4 A structure diagram of a complex part with a gasket on a mold of the present application.

[0036] Figure 5 A diagram of temperature-time synergistic loading of the present application.

[0037] In the figure: 1, part; 2, gasket; 3, mold; 101, thin skin area. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0039] Figure 1 A flowchart of a creep age forming method for deformation coordination of a reinforced area and a thin skin area of the present application.

[0040] As shown in Figure 1 , the creep age forming method for deformation coordination of a reinforced area and a thin skin area of the present application comprises:

[0041] S100: calculating the pressure required for the outer surface of the part 1 to completely fit the mold 3 profile by using the finite element method;

[0042] S200: when the part 1 and the mold 3 profile are fitted, calculating the maximum axial stress of the thin skin area 101 along the bending deformation direction;

[0043] S300: obtaining a gasket 2 of the same material with deformation stiffness compensation according to the maximum axial stress;

[0044] S400: placing the gasket 2 with deformation stiffness compensation on the surface of the thin skin area 101 and fixing it;

[0045] S500: placing the part 1 with the fixed gasket 2 on the mold 3 with a certain outer shape profile, and using vacuum to encapsulate;

[0046] S600: Put the encapsulated whole into a heating furnace or autoclave, and make the outer shape of the part 1 conform to the inner shape of the mold 3 according to the pre-set process parameters;

[0047] S700: After the creep aging is completed, unload the temperature and pressure on the formed part 1.

[0048] Creep aging forming refers to the integration of the forming environment and the heat treatment environment in time and space by using the creep and aging strengthening characteristics of the metal, so that the metal slowly deforms and ages under the action of a certain temperature (aging temperature) and stress (forming load). As shown in the figure, the creep aging forming process can be divided into three stages of loading, creep aging forming and unloading. Figure 2

[0049] Please refer to Figure 3 、 Figure 4 Before the creep aging forming process is performed, the pressure applied to the part 1 is simulated, and the pressure required when the part 1 and the mold 3 are tightly conformed is obtained by the finite element method, and the maximum axial stress of the thin skin area 101 (i.e. the thinning area) along the bending deformation direction when conforming, and then a same material gasket 2 with deformation stiffness compensation is designed according to the calculation, and the deformation stiffness compensation is performed through the gasket 2, so as to reduce the buckling defect of the thin skin area 101 in the subsequent creep forming process, and the gasket 2 is used to realize the consistency of the stiffness of the reinforced area and the thin skin area 101, and the deformation unevenness caused by the internal structure change is reduced.

[0050] After the gasket 2 is designed by the finite element method, the gasket 2 is fixed on the surface of the thin skin area 101, the part 1, the mold 3 and the gasket 2 are integrally encapsulated by air-permeable felt and vacuum bag, and vacuumizing is performed, and then the whole is pushed into a heating furnace or an autoclave, and the temperature and pressure are raised according to the pre-set process parameters, and the part 1 is kept at a suitable aging temperature and pressure for a period of time. In this process, the part 1 occurs creep, stress relaxation forming and aging precipitation strengthening, and the elastic deformation is converted into permanent plastic deformation, and the microstructure and macro performance of the material will also change with the precipitation of the strengthening phase. After the creep aging is completed, the temperature and pressure on the formed part 1 are unloaded, and the furnace door is opened to take out the part 1 and the tooling.

[0051] In step S300, the step of obtaining the same material gasket 2 with deformation stiffness compensation according to the maximum axial stress comprises:

[0052] The same material gasket 2 is placed on the surface of the thin skin area 101 for deformation stiffness compensation, wherein the thickness t of the gasket 2 can be determined by the following formula, wherein L is the length of the gasket 2, E is the elastic modulus of the material, t0 is the original thickness of the skin, and σ​max Maximum axial stress of the thin skin region 101 along the bending deformation direction.

[0053]

[0054] In step S600, the step of making the outer shape surface of the part 1 conform to the inner shape surface of the mold 3 according to the pre-set process parameters includes:

[0055] S601: Under vacuum, the heating furnace or hot press tank is heated, and when the part 1 reaches the set temperature, it is kept at temperature;

[0056] S602: After reaching the set holding time, the pressurization system is turned on to apply pressure to the surface of the part 1 until the outer shape surface of the part 1 conforms to the inner shape surface of the mold 3.

[0057] The embodiment is directed to a creep age forming method for deformation coordination control of the reinforcing region and the thin skin region of a complex shape integral wall panel, which uses vacuum pressure loading, the pressure is uniformly distributed, and there is no stress concentration point after forming. And by using the process of heating first and then loading, the overall forming limit of the part 1 can be effectively improved.

[0058] As a preferred solution in the above embodiment, the stress is slowly applied to the target pressure of the first stage during the holding stage, and after reaching the target pressure, the pressure is maintained for a certain time, and then the pressure is continuously increased to the target pressure of the second stage.

[0059] For details, please refer to Figure 5 After reaching the holding time, the pressurization system is turned on to apply pressure P to the surface of the part 1. In order to ensure uniform deformation of the reinforcing region and the thin skin region deformation area, the pressure needs to be slowly applied to P in stages, the first stage is 15%-30% of P, the pressure increase rate is controlled at 0.01MPa / min-0.05MPa / min, and after maintaining for 2-5h, the pressure is continuously increased to P, so that the outer shape surface of the wall panel part 1 completely conforms to the inner shape surface of the mold 3. The load is applied in stages during the holding stage, the stress is slowly applied at a controlled pressure increase rate in the first stage, which is beneficial to the overall uniform deformation of the gasket 2 and the part 1, further strengthens the stiffness of the thin skin region 101, and makes the deformation of the reinforcing region and the thin skin region coordinated and unified, which is beneficial to improve the creep age forming precision, ensure uniform deformation of the reinforcing region and the thin skin region, and on the other hand, it can effectively control the occurrence of thin skin deformation instability and other phenomena during the forming process.

[0060] Before step S100, the original plate of the part 1 is also pre-processed, and the pre-processing includes solid solution at a temperature of 460℃-490℃ for 50min, and then immediately water quenching, followed by 2%-3% pre-stretching.

[0061] As Figure 2As shown, in the unloading stage, due to the restriction of the aging heat treatment system, the creep deformation in the forming stage cannot convert all the elastic deformation in the loading stage into plastic deformation, and the part will rebound to a certain extent. As an example of obtaining the mold 3 surface in this embodiment, the mold 3 surface is a surface compensated for rebound by optimization calculation according to the patent "Wallboard Creep Aging Forming Method Based on Finite Element Mold Surface Rebound Compensation ZL201210466297.1". Therefore, before processing, the matching mold inner surface is made to make the final obtained part 1 shape meet the design requirements.

[0062] Preferably, the pad plate 2 and the surface of the thin skin area 101 of the part 1 are fixed by using a tape, which is a high-temperature resistant tape.

[0063] In another aspect of the present application, a part 1 formed by the above forming method is provided, which has a complex shape (such as a skin surface with different curvatures and thicknesses) and also has a complex internal structure (such as local thickening, a bezel, and a local thinning area), and the part 1 does not have the problem of inconsistent rebound after forming due to structural differences on the part 1, and can be used to form the aerodynamic shape of an airplane, or to form the main load-bearing components of a wing, a fuselage, etc.

[0064] To further reveal the nature of the present application, the following embodiments are described in detail. It should be understood that, except for the limitations specifically indicated in the appended claims, the present application is not limited by the specific conditions or details described in these embodiments.

[0065] Example 1:

[0066] Aluminum alloy 7B04 wallboard structural part, the part 1 is a whole wallboard, the shape is a complex double curvature shape such as Figures 2-4 As shown, the part 1 is formed by the following method.

[0067] Step 1: The original plate is a 7B04 solution quenching pre-stretching thick plate (460℃-490℃ solution for 50min, immediately water quenching, and then 2%-3% pre-stretching).

[0068] Step 2: The pressure 1.5MPa required for the complete adhesion of the outer surface of the part 1 to the mold 3 surface is calculated by using the finite element method.

[0069] Step 3: When the part 1 is adhered to the mold 3 surface, the maximum axial stress σ max = 278MPa of the thin skin area 101 along the bending deformation direction is calculated.

[0070] Step 4: Place the same material pad 2 on the surface of the thin skin area 101 to compensate for the deformation stiffness, wherein the thickness t of the pad 2 can be calculated by the above formula 1), and the thickness t of the pad is 12 mm in the following manner, wherein L is the length of the pad of 200 mm, E is the elastic modulus of the material of 69 GPa, and the original skin thickness is 2 mm.

[0071] Step 5: Place the stiffness compensation pad 2 on the surface of the thin skin area 101 and fix it with a high-temperature resistant adhesive tape.

[0072] Step 6: Use air-permeable felt and a vacuum bag to encapsulate the wallboard part 1, the mold 3 and the pad 2 as a whole, and perform vacuumizing.

[0073] Step 7: Keep the vacuumizing state, and put the wallboard part 1 into the autoclave together with the mold 3.

[0074] Step 8: Heat the autoclave, and when the wallboard part 1 reaches a temperature of 150℃, perform heat preservation, and in the aging process at this stage, the wallboard part 1 always keeps the vacuumizing state.

[0075] Step 9: After reaching the heat preservation time, open the pressurizing system to apply a pressure of 0.5 MPa to the surface of the part 1, and the pressure increasing rate is controlled at 0.02 MPa / min, and after increasing the pressure to 0.5 MPa, keep for 5 h and then continue to increase the pressure to 1.5 MPa.

[0076] Step 10: When reaching the heat preservation time of 20 h, the heat preservation is ended and the cooling is started. When the temperature of the mold 3 is reduced to below 50℃, the pressure is unloaded, the furnace door is opened, and the part 1 and the tooling are taken out.

[0077] In summary, the purpose of the present application is to solve the problem of coordinated deformation control of the wallboard, improve the forming limit and forming precision, effectively improve the buckling instability resistance of the thin skin area, ensure the forming / manufacturing integration of the complex wallboard component, effectively improve the part shape precision and further improve the service life of the wallboard.

[0078] Any process or method described in the flowchart or otherwise described herein can be understood as representing a module, segment, or portion of code that includes one or more executable instructions for implementing specific logical functions or steps, and the scope of preferred embodiments of the present application includes alternatives in which functions are performed in different orders, in substantially simultaneous fashion, or in reverse order, depending on the functionality involved, as will be understood by those skilled in the art of the embodiments of the present application.

[0079] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A creep aging forming method for coordinating deformation in the reinforced area and the thin skin area, characterized in that, Includes the following steps: The pressure required for the outer surface of the part to fit completely into the mold surface was calculated using the finite element method. When the part fits against the mold surface, calculate the maximum axial stress in the thin skin area along the bending deformation direction; Based on the maximum axial stress, obtain a pad of the same material with deformation stiffness compensation; The pad with deformation stiffness compensation is placed on the surface of the thin skin area and fixed. The part with the fixed pad is placed on the mold with a certain shape and surface, and then sealed by vacuum. The packaged assembly is placed in a heating furnace or autoclave, and the outer surface of the part is made to fit the inner surface of the mold according to the calculated pressure and the preset process parameters. After creep aging is completed, the temperature and pressure on the formed part are unloaded; The steps for obtaining a pad of the same material with deformation stiffness compensation based on the maximum axial stress include: The thickness t of the pad can be calculated using the following formula: Where L is the length of the pad, E is the elastic modulus of the material, t0 is the original thickness of the skin, and σ max This represents the maximum axial stress along the bending deformation direction in the thin skin region. The step of fitting the outer surface of the part to the inner surface of the mold according to the preset process parameters includes: In a vacuum state, the heating furnace or autoclave is heated, and the parts are kept at the set temperature. After the set heat preservation time is reached, the pressurization system is turned on to apply pressure to the surface of the part until the outer surface of the part fits into the inner surface of the mold. During the heat preservation stage, stress is slowly applied to the target pressure of the first stage by controlling the pressurization rate. After reaching the target pressure, the pressure is maintained for a certain period of time, and the pressure is continued to be increased to the target pressure of the second stage. The target pressure of the first stage is 15%-30% of the target pressure of the second stage.

2. The creep aging forming method for deformation coordination of the reinforced area and the thin skin area as described in claim 1, characterized in that, The pressure boosting rate is 0.01 MPa / min to 0.05 MPa / min.

3. The creep aging forming method for deformation coordination of the reinforced area and the thin skin area as described in claim 1, characterized in that, Before creep aging molding, the original sheet material of the part is solution-treated at 460℃~490℃ for 50 minutes, then immediately water-quenched, and then pre-stretched by 2%-3%.

4. The creep aging forming method for deformation coordination of the reinforced area and the thin skin area as described in claim 1, characterized in that, The pad is fixed to the surface of the thin skin area of ​​the part by tape.

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