A laser-shock-assisted creep aging forming method for thin-walled components with complex curvature

Abstract

This invention discloses a laser-shock-assisted creep aging forming method for thin-walled components with complex curvature. The method includes: simulating and obtaining difficult-to-form regions; performing laser shock on the difficult-to-form regions of a large-size aluminum alloy thin-walled component sheet; wrapping and fixing a breathable felt around the impacted component; placing the component in a sealed space formed between a vacuum bag and the mold surface; evacuating the sealed space; and then sending the mold into an autoclave for creep aging. After completion, the component springs back, yielding the target surface. This method uses a laser to impact localized areas of a large-size aluminum alloy thin-walled component, introducing dislocations while achieving pre-forming. This provides a good surface foundation for subsequent high-precision creep aging forming of the component, and is suitable for forming parts with complex curvature.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal material processing and manufacturing, specifically to a laser shock assisted creep aging forming method for thin-walled components with complex curvature. Background Technology

[0002] Aluminum alloys, due to their low density, ease of processing, and corrosion resistance, have become crucial structural materials for aerospace equipment, widely used in the manufacture of thin-walled components for aircraft and rockets. In recent years, to achieve form-and-property synergistic manufacturing of these components and meet the high-quality development requirements of the aerospace industry, creep aging forming technology has been widely applied in aerospace manufacturing. Creep aging forming introduces stress into the traditional aging strengthening process, simultaneously strengthening the component at high temperatures and converting the elastic deformation caused by stress into plastic deformation to achieve forming. It overcomes the shortcomings of traditional forming processes where material aging strengthening and component forming are separated in time and space, achieving simultaneous strengthening and forming. It is an ideal manufacturing process for large thin-walled aluminum alloy components. Currently, this technology has become one of the key manufacturing technologies for large aircraft panels and rocket propellant tanks.

[0003] In actual production, the creep aging forming process of aluminum alloy components is generally divided into three stages:

[0004] (1) Loading stage: Place the sheet material to be formed on the mold, adjust the relative position, apply pressure to the sheet material to ensure that the sheet material fits the mold surface after bending.

[0005] (2) Creep aging stage (heat preservation and pressure holding stage): The bonded sheet and the mold are sent into the autoclave together, the temperature is raised to the set temperature, the load is applied and held for a certain time. During the heat preservation and pressure holding process, the sheet undergoes creep deformation and aging strengthening at the same time, and the forming and property are realized simultaneously.

[0006] (3) Unloading stage: After the heat preservation and pressure holding time reaches the preset time, the autoclave begins to unload and cool down. Due to the internal stress, the sheet material will spring back, and the springback surface is the final surface.

[0007] In the context of aerospace equipment pursuing high load and long range, the aluminum alloy components used in space launch vehicles are becoming increasingly larger and thinner, while also exhibiting more complex curvature. The larger the component and the thinner it is, the more pronounced the springback after creep aging, resulting in under-curved surfaces that fail to meet the target surface accuracy requirements. Existing creep aging forming processes generally employ two approaches when manufacturing such large, complex, thin-walled components:

[0008] The first approach involves performing local roll bending before creep aging forming of the component. Local roll bending is performed on the portion of the component with insufficient creep (maximum curvature), causing plastic deformation in that area. This reduces the creep required to achieve the target profile. Simultaneously, the dislocations introduced by the plastic deformation effectively increase the creep in the subsequent creep process, working together to improve springback and under-bending issues.

[0009] Roll bending is generally used for single-curved components. For components with complex curvatures (such as hyperbolic saddle shapes), the forming accuracy of roll bending is relatively low, and it is mostly completed based on previous roll bending experience. Therefore, components that have undergone roll bending often have defects such as discontinuous surface shapes and local bulges in the rolled bending area during creep aging. The forming curvature of the component center is the largest, the creep deformation required is the largest, and this part is subjected to the greatest stress during creep aging. After roll bending, the center of the component is prone to defects such as local microcracks during the subsequent creep aging process.

[0010] The second approach involves subjecting the already creep-aged component to a second creep aging process. Since a significant number of dislocations are consumed during the first creep aging, the creep deformation caused by dislocation movement is greatly reduced during the second creep aging, resulting in little improvement in forming accuracy. While increasing the temperature of the second creep aging can improve creep deformation and springback to some extent, the two creep aging processes lead to excessively long high-temperature aging times, potentially causing the component to enter an over-aged state and resulting in a significant decrease in performance (strength and plasticity). Furthermore, the time, labor, material, and economic costs associated with two creep aging processes are significantly increased, and the process is cumbersome and labor-intensive.

[0011] In summary, the key to the form-property co-manufacturing of large, complex curved thin-walled aluminum alloy components lies in how to increase the creep deformation of the components while ensuring that the strength of the component material does not decrease. However, the existing creep aging process can no longer meet the form-property co-manufacturing requirements of large, complex curved thin-walled components. Therefore, it is urgent to propose a new creep aging forming method for large, complex curved thin-walled aluminum alloy components. Summary of the Invention

[0012] The purpose of this invention is to provide a laser-shock-assisted creep aging forming method for complex curvature thin-walled components, addressing the problem in the prior art that existing creep aging forming schemes for large, complex curvature thin-walled components cannot achieve good forming performance while ensuring the material properties of the component. This invention uses a laser to impact areas of the sheet metal to be formed where the creep deformation is insufficient, causing localized impact deformation. This allows for localized pre-forming while simultaneously introducing dislocations, providing a good surface foundation for subsequent high-precision creep aging forming of the component.

[0013] The present invention is achieved through the following technical solution.

[0014] A laser-shock-assisted creep aging forming method for thin-walled components with complex curvature includes the following steps:

[0015] S1: Obtain data on the change of creep over time in large-size aluminum alloy thin-walled components under different stresses and temperatures, select creep data at appropriate temperatures to establish a constitutive model, and combine finite element software to establish a simulation model of the creep aging process at the component scale to determine the difficult-to-form areas;

[0016] S2: Based on the difficult-to-form areas obtained in step S1, mark the corresponding areas on the large-size aluminum alloy thin-walled component sheet, and then lay a constraint layer and an energy absorption layer on the corresponding areas of the component.

[0017] S3: Based on the surface curvature change of the difficult-to-form area of ​​the component sheet obtained in step S1, set the parameters of the laser impact device, perform laser impact on the difficult-to-form area of ​​the component, and complete the pre-forming;

[0018] S4: Wrap and fix the breathable felt onto the component obtained in step S3, and then place the component in the sealed space formed between the vacuum bag and the mold surface;

[0019] S5: Vacuum the sealed space, then send the mold into the autoclave for creep aging. After completion, the component slowly springs back to obtain the final target shape.

[0020] Preferably, the component thickness is 3-5mm.

[0021] Preferably, in S1, the data on the change of creep over time of large-size aluminum alloy thin-walled component materials under different stresses and temperatures are obtained by conducting basic creep aging experiments using samples made from large-size aluminum alloy thin-walled component materials.

[0022] Preferably, in S1, the method for establishing a simulation model of the creep aging process of the component scale using finite element software is as follows: add the mold surface and autoclave working parameters of the actual forming and manufacturing process as boundary conditions. The working parameters include pressure, temperature and time, and obtain the simulation results of the formed surface.

[0023] Preferably, in S2, the constraint layer is flowing water and the energy absorption layer is black paint.

[0024] Preferably, in S3, the operating parameters include current magnitude, duty cycle, pulse frequency, laser wavelength, scanning rate, spot diameter, spot overlap rate, laser power, impact path, laser energy, and number of impacts.

[0025] Preferably, in S4, the operation of placing the component in the sealed space formed between the vacuum bag and the mold surface is as follows: a ring of high-temperature adhesive is pasted around the mold, and a vacuum bag is placed on the component. The vacuum bag is tightly bonded to the edge of the mold through the high-temperature adhesive, and the component is placed in the sealed space formed between the vacuum bag and the mold surface.

[0026] Preferably, in S5, the creep aging process is as follows: first, the autoclave is pressurized, and after reaching the set pressure, the temperature is increased. After reaching the set temperature, the pressure and temperature are maintained until the entire creep aging process is completed.

[0027] The beneficial effects of this invention are:

[0028] (1) Laser shock deformation utilizes the energy conversion body (composed of a transparent constraint layer and an opaque absorption layer) on the surface of the component to cause partial vaporization and ionization of the absorption layer and form a shock wave. The pressure of the shock wave causes the component sheet to undergo plastic deformation. It belongs to the category of cold working and will not generate heat to cause changes in the internal structure of the material.

[0029] (2) Laser shock calorimetry is a special forming method that uses high pressure, high speed, and high strain rate to achieve fully plastic bending. Its deformation pressure can reach the GPa level, and plastic deformation is completed within tens of nanoseconds, with a strain rate of 10. 6 ~10 7 S -1 It is hundreds of times or even more than conventional processing and forming methods, and can achieve full plastic bending. The surface does not spring back after impact, which in principle provides a feasible basis for precise preforming.

[0030] (3) This invention does not directly laser-shock form the component to the target surface, but rather performs local impact to complete the pre-forming. Laser shock deformation can achieve precise forming and multi-point step-by-step forming. By adjusting parameters such as impact path, number of times, spot overlap rate and impact method, the deformed surface can be precisely controlled, and problems such as uneven or discontinuous transition of the surface after rolling-creep and local protrusion will not occur.

[0031] (4) The high-density dislocations and grain refinement introduced by laser shock deformation have good high-temperature stability. In the subsequent creep aging forming process, the higher density dislocations can provide greater creep, and the refined grains can improve the plasticity of the component material and avoid the occurrence of microcracks.

[0032] (5) The surface grains of the component after laser shock are more refined, which can form a dense fine grain structure, exhibiting better elongation and strength, high surface quality, and can also improve the tensile strength of the surface layer; in addition, it can also generate considerable residual compressive stress on the surface of the component, and the surface corrosion resistance and fatigue resistance are significantly improved.

[0033] (6) The surface of the component is subjected to greater stress than the middle part of the component sheet during creep aging forming, and is the part most prone to cracking. Under the action of laser shock, the appearance of surface microcracks can be significantly suppressed during the subsequent creep process. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of laser impact on the component sheet of the present invention.

[0035] Figure 2 The diagram shows the components after laser shock deformation of the present invention being placed in the mold (a), during pressure application and film application (b), and after the creep aging process ends and the components spring back (c).

[0036] Figure 3 This is a schematic diagram of the surface microstructure of the laser-shocked area after the creep aging forming of the component sheet of the present invention.

[0037] Figure 4 This is a schematic diagram comparing components obtained using the roll bending-creep process with those obtained using the laser shock-creep process.

[0038] In the diagram: 1-Laser impact equipment; 2-Laser beam; 3-Black paint layer; 4-Water pipe outlet; 5-Component sheet material; 6-Component after local laser impact; 7-Mold. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The described embodiments are for illustrative purposes only and should not be construed as limiting the present invention.

[0040] A laser-shock-assisted creep aging forming method for thin-walled components with complex curvature includes the following steps:

[0041] S1: A creep aging basic experiment was conducted on a specimen made of a large-sized aluminum alloy thin-walled component to obtain data on the change of creep of the component material with time under different stresses and temperatures. The creep data at a suitable temperature was selected and fitted using mathematical software to establish a constitutive model based on the creep experimental data. A simulation model of the creep aging process at the component scale was established using finite element software. The mold surface and autoclave working process parameters (pressure 1-2MPa, temperature 160-180℃ and time 1-10h) of the actual forming and manufacturing process were added as boundary conditions to obtain the simulation results of the formed surface and determine the difficult-to-form areas.

[0042] The components are not limited to flat plates, the curvature of the components is not limited to single curvature, and the thickness of the components is 3-5mm.

[0043] This includes mathematical software such as MATLAB, Mathematica, and Maple, and finite element software such as ANSYS, Marc, and Comsol.

[0044] S2: Based on the difficult-to-form areas obtained in step S1, mark the corresponding areas on the large-size aluminum alloy thin-walled component sheet, and then lay a constraint layer (flowing water) and an energy absorption layer (black paint) on the corresponding areas of the component.

[0045] S3: Based on the surface curvature change of the difficult-to-shape area of ​​the component sheet obtained in step S1, set the parameters of the laser impact device, including current magnitude, duty cycle, pulse frequency, laser wavelength, scanning rate, spot diameter, spot overlap rate, laser power, impact path, laser energy and number of impacts, and then perform laser impact on the area of ​​the component to be preformed to achieve precise preforming.

[0046] For cases involving difficult-to-form surfaces with varying curvature, advance path design and parameter settings that vary with the path allow for the application of different impact forces based on thickness and structural variations.

[0047] S4: Completely wrap the component obtained in step S3 with breathable felt and fix the breathable felt to the component with high-temperature tape. Then place it on the mold, adjust the position of the component on the mold, stick a ring of high-temperature adhesive around the mold, and place a vacuum bag on the component. The vacuum bag is tightly bonded to the mold with the high-temperature adhesive, so that the component is in a sealed space between the vacuum bag and the mold surface. Put the vacuum nozzle into the vacuum bag and seal its surroundings with high-temperature adhesive.

[0048] S5: Send the mold prepared in step S4 into the autoclave equipment, and evacuate the vacuum bag through the vacuum nozzle connected by the vacuum tube, forcing the component to fit into the mold surface under vacuum pressure. Then, after setting the autoclave process parameters, start the autoclave to pressurize the inside of the tank. After reaching the set pressure, start heating. After heating to the set temperature, maintain pressure and heat until the entire creep aging process is completed.

[0049] S6: After the entire creep aging process is completed, the autoclave begins to unload and cool down. Then the door is opened, the mold is pulled out, and the vacuum bag, breathable felt and vacuum nozzle are removed. The component slowly springs back, and the surface of the component after springing back is the final target surface with complex curvature.

[0050] Example:

[0051] The component is made of 3mm thick 2xxx series aluminum alloy cold-rolled sheet, with specific dimensions of 1300mm*1000mm. The mold's external dimensions are 2000mm*2000mm*800mm, the base material is Q235, the profile material is 45# steel, the surface roughness is Ra1.6, the maximum working pressure is 2.0MPa, and the maximum working temperature is 250℃. The effective internal space diameter of the autoclave is φ2500mm*5000mm. The creep aging forming temperature is 180℃, the creep aging time is 8h, the heating rate is 3℃ / min, the temperature fluctuation does not exceed 5℃, and the loading rate is 0.3bar / min. The relevant parameters for laser shock are: current 2000-6000A, duty cycle 50%, pulse frequency 1500Hz, laser wavelength 1080nm, scanning rate 3m / s, spot diameter 3mm, spot overlap rate 50%, and laser power 6KW. Simulation shows the required impact deformation range for the component is 200*300mm. The strengthening path, based on the output model from 3D software, can be planned and set by the CNC machine tool. The number of repetitions is determined according to the actual forming effect. The laser energy is 3-15J. The constraint layer is a 3mm thick flowing water layer, and the absorption layer is a 2mm thick black paint layer. Figure 1 This is a schematic diagram of laser impact preforming of component sheet material, including laser impact equipment 1, laser beam 2, black paint layer 3, water pipe outlet 4, and component sheet material 5. Figure 2 These are schematic diagrams showing the component after laser-shock deformation of the present invention placed in the mold (a), during pressure application and film bonding (b), and after springback following creep aging (c). The laser-shocked region exhibits grain refinement, as shown in the diagram. Figure 3 The shape accuracy of the formed component is significantly improved. A comparison of the component obtained using the roll bending-creep process and the component obtained using the laser shock-creep process is shown below. Figure 4 .

[0052] Those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this application and their equivalents, the protection scope of this application should also include these modifications and variations.

Claims

1. A laser-shock-assisted creep aging forming method for thin-walled components with complex curvature, characterized in that: Includes the following steps: S1: Obtain data on the change of creep over time in large-size aluminum alloy thin-walled components under different stresses and temperatures, select creep data at appropriate temperatures to establish a constitutive model, and combine finite element software to establish a simulation model of the creep aging process at the component scale to determine the difficult-to-form areas; S2: Based on the difficult-to-form areas obtained in step S1, mark the corresponding areas on the large-size aluminum alloy thin-walled component sheet, and then lay a constraint layer and an energy absorption layer on the corresponding areas of the component. S3: Based on the surface curvature change of the difficult-to-form area of ​​the component sheet obtained in step S1, set the parameters of the laser impact device, perform laser impact on the difficult-to-form area of ​​the component, and complete the pre-forming; S4: Wrap and fix the breathable felt onto the component obtained in step S3, and then place the component in the sealed space formed between the vacuum bag and the mold surface; S5: Vacuum the sealed space, then send the mold into the autoclave for creep aging. After completion, the component slowly springs back to obtain the final target shape.

2. The laser shock assisted creep aging forming method for a thin-walled component with complex curvature according to claim 1, characterized in that: The component thickness is 3-5mm.

3. The laser shock assisted creep aging forming method for a thin-walled component with complex curvature according to claim 1, characterized in that: In S1, the data on the change of creep over time of large-size aluminum alloy thin-walled component materials under different stresses and temperatures were obtained by conducting basic creep aging experiments using specimens made of large-size aluminum alloy thin-walled component materials.

4. The laser shock assisted creep aging forming method for a thin-walled component with complex curvature according to claim 1, characterized in that: In S1, the method for establishing a simulation model of the creep aging process of the component scale using finite element software is as follows: add the mold surface and autoclave working parameters of the actual forming and manufacturing process as boundary conditions. The working parameters include pressure, temperature and time, and obtain the simulation results of the formed surface.

5. The laser shock assisted creep aging forming method for a thin-walled component with complex curvature according to claim 1, characterized in that: In S2, the constraint layer is flowing water, and the energy absorption layer is black paint.

6. The laser shock assisted creep aging forming method for a thin-walled component with complex curvature according to claim 1, characterized in that: In S3, the operating parameters include current magnitude, duty cycle, pulse frequency, laser wavelength, scanning rate, spot diameter, spot overlap rate, laser power, impact path, laser energy, and number of impacts.

7. The laser shock assisted creep aging forming method for a thin-walled component with complex curvature according to claim 1, characterized in that: In S4, the operation of placing the component in the sealed space formed between the vacuum bag and the mold surface is as follows: a ring of high-temperature adhesive is pasted around the mold, and a vacuum bag is placed on the component. The vacuum bag is tightly bonded to the edge of the mold through the high-temperature adhesive, and the component is placed in the sealed space formed between the vacuum bag and the mold surface.

8. The laser shock assisted creep aging forming method for a thin-walled component with complex curvature according to claim 1, characterized in that: In S5, the creep aging process is as follows: First, the autoclave is pressurized. After reaching the set pressure, the temperature is increased. After reaching the set temperature, the pressure and temperature are maintained until the entire creep aging process is completed.

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