A laser shock assisted creep aging forming method for high-precision preforming

Abstract

The present invention discloses a method for assisted creep aging forming by laser impact to achieve high-precision preforming, comprising the following steps: simulating to obtain the distribution data of the area to be preformed and its underbend amount, obtaining the preforming profile, and then making a preforming mold; placing a large-sized aluminum alloy reinforced thin-walled component sheet on the preforming mold for laser impact; wrapping and fixing the impacted component with breathable felt, and then placing the component in a closed space formed between a vacuum bag and the forming mold profile; evacuating the closed space, and then sending the forming mold into an autoclave for a creep aging process, after which the component rebounds to obtain the target profile. The present invention uses laser to impact a local area of a component, thereby introducing dislocations and achieving precise preforming, providing a good profile foundation for subsequent creep aging high-precision forming of the component, and is suitable for forming large-sized aluminum alloy thin-walled parts with high-precision complex curvatures and reinforced structures.

Description

Technical Field

[0001] The present invention relates to the technical field of forming and manufacturing nonferrous metal components, and in particular to a method for auxiliary creep aging forming by laser shock to achieve high-precision preforming, which is particularly suitable for forming parts with high-precision complex curvature and reinforced structures. Background Art

[0002] In order to adapt to the needs of rapid and high-quality development in the modern aerospace field, "high load and long range" have become the characteristics of the new generation of aviation products. Under the background of new demands, aerospace products are developing towards large-scale and integrated development. To this end, the aerospace manufacturing industry has carried out lightweight design of aviation products and widely used aluminum alloys as materials for manufacturing aircraft parts. In order to improve the strength and reliability of parts and achieve a good aerodynamic layout, a large number of large-scale reinforced thin-walled components with complex curvatures are used in aerospace equipment structures, and precise forming is required. In view of the structural characteristics of the above-mentioned components, technicians have developed a creep aging forming process for the forming and manufacturing of such reinforced thin-walled components. The creep aging forming process utilizes the characteristics of creep deformation of materials under high temperature and high pressure environments to achieve aging strengthening while forming the components, so as to achieve the purpose of precise manufacturing of coordinated form and properties. It has now developed into one of the key technologies for the manufacturing of large thin-walled aerospace components.

[0003] The complex shapes, large sizes, thin walls, and reinforcements of modern aircraft components present new challenges and difficulties for creep aging forming. To address the challenges of low creep and high springback during creep aging forming for these large, complex-curvature, reinforced, thin-walled components, which ultimately result in underbend in the finished component profile, the component sheet is typically preformed by roll bending in a localized area (difficult-to-form areas). This preformed component is then subjected to creep aging forming to achieve a better profile.

[0004] Roll bending causes local plastic deformation of the component sheet, improving the underbending condition caused by insufficient creep during subsequent creep aging forming. At the same time, it introduces a large number of dislocations, increasing the creep of the rolled area during the subsequent creep aging forming process, in order to achieve precise forming of the profile. Due to the limitations of the working principle of the roll bending equipment, the use of the roll bending process for preforming has the following problems:

[0005] (1) Roll bending is generally only performed on flat plate components, and only single-curved surfaces can be formed by roll bending. In addition, the formed components will have a springback phenomenon, which affects the accuracy of roll bending.

[0006] (2) In order to meet the forming requirements of hyperbolic surfaces, the hyperbolic surface is generally achieved by stuffing different numbers of similar metal plates into the part to be rolled when the component is rolled. However, since rolling is often done based on experience, the forming effect is poor and unsatisfactory. At the same time, the stuffing of metal plates will cause local mutations and discontinuous deformation in the component, and local damage will be introduced, which can lead to cracks. Ultimately, the component will still have the same problems after subsequent creep aging forming, which seriously affects the forming accuracy and performance of the component. In addition, the rolling process is even more unable to cope with more complex surfaces.

[0007] (3) When there are many reinforcing ribs in the component sheet, if you want to roll-bend it for pre-forming, it is generally necessary to fill the area surrounded by the reinforcing ribs with silicone to make it a "flat" component. Due to the difference in the material properties of silicone and aluminum alloy components, it is easy to cause silicone extrusion, which will cause large stress in the ribs, resulting in root cracks or free end distortion. Secondly, due to the different structures of the reinforced and unreinforced parts of the aluminum alloy components, it is easy to have uncoordinated deformation in different directions, resulting in "orange peel" wrinkling in the unreinforced parts, which in turn causes deformation in the rib parts, seriously affecting the forming accuracy of the subsequent surface after creep aging forming.

[0008] (4) When locally rolling the component sheet, it is impossible to adjust the extrusion pressure in different regions or directions according to the changes in the structural characteristics of the component to be rolled (whether the wall thickness is uniform, whether there is reinforcement, and the curvature change trend, etc.) so that the surface after rolling becomes a continuous, gradual and smooth high-quality surface, thereby affecting the surface quality of the component after creep aging forming.

[0009] (5) Rolling causes local plastic deformation of the component sheet, which in turn causes the grains to elongate into flat grains along the direction of the rolling deformation, resulting in a preferred grain orientation and the formation of a texture. The greater the deformation, the stronger the texture, causing the rolled area of the component to exhibit significant anisotropy, seriously affecting the accuracy and mechanical properties of the pre-formed surface and reducing the actual bearing capacity of the area. In addition, local microcracks and defects that may be caused by rolling will further enhance anisotropy.

[0010] In summary, the existing roll-bending preforming process can no longer meet the manufacturing requirements for high-quality creep aging forming of large, thin-walled, and reinforced aluminum alloy components. Therefore, it is urgent to propose a new method that can accurately control the preforming process and achieve high-precision preforming for large aluminum alloy thin-walled components with complex curvature to assist in precise creep aging forming. Summary of the Invention

[0011] This invention provides a method for assisted creep aging forming using laser impact technology to achieve high-precision preforming. This method addresses the problem in the prior art of assisted preforming processes for creep aging forming of large, complex-curvature, reinforced, thin-walled components, which lacks precise control over the preforming process and accurate preforming. By using laser impact to localize the component, this method introduces dislocations and achieves precise preforming, providing a good surface foundation for subsequent high-precision creep aging forming of the component.

[0012] The present invention is achieved through the following technical solutions.

[0013] A method for assisted creep aging forming by laser shock to achieve high-precision preforming, comprising the following steps:

[0014] S1: Obtain creep data of large-scale aluminum alloy reinforced thin-walled components under different stresses and temperatures over time. Select creep data at a certain temperature to establish a constitutive model. Combined with finite element software, establish a component-scale creep aging process simulation model to obtain the distribution data of the area requiring pre-forming and its underbending amount.

[0015] S2: Obtain a pre-formed surface based on the distribution data of the area to be pre-formed and the under-bend amount thereof obtained in step S1;

[0016] S3: According to the preformed surface obtained in step S2, a hard rubber material is selected and processed to obtain a preformed mold having the preformed surface;

[0017] S4: Mark the corresponding area on the large-size aluminum alloy reinforced thin-walled component sheet according to the area to be preformed obtained in step S1, place the component sheet on the preforming mold obtained in step S3, so that the area to be preformed of the component corresponds to the surface of the preforming mold, and then lay a constraint layer and an energy absorption layer on the area to be preformed of the component;

[0018] S5: Setting parameters of the laser impact device according to the reinforcement condition of the component sheet and the curvature change of the pre-formed surface, performing laser impact on the component area to be pre-formed, and completing the pre-forming;

[0019] S6: Wrapping and fixing the breathable felt on the component obtained in step S5, and then placing the component in a closed space formed between the vacuum bag and the molding surface of the forming mold;

[0020] S7: Evacuate the enclosed space, then send the forming mold into the autoclave equipment for creep aging process. After completion, the component slowly rebounds to obtain the final target surface.

[0021] Preferably, the component thickness is 3-5 mm.

[0022] Preferably, in S1, the creep variation data of the large-size aluminum alloy reinforced thin-walled component material at different stresses and temperatures over time are obtained by conducting a creep aging basic experiment on a specimen made of the large-size aluminum alloy reinforced thin-walled component material.

[0023] Preferably, in S1, the method for establishing a component-scale creep aging process simulation model through finite element software is: adding the mold surface and autoclave working parameters of the actual forming manufacturing process as boundary conditions, the working parameters include pressure, temperature, and time, and obtaining the surface simulation results after forming.

[0024] Preferably, in S2, the method for obtaining the pre-formed surface is: importing the underbend distribution data of the area to be pre-formed into three-dimensional software for processing to obtain a curved surface formed by the underbend, i.e., the pre-formed surface.

[0025] Preferably, in S3, the method for making the pre-forming mold is: expanding the regional boundary size of the pre-forming surface outward by 10CM, processing a hard rubber block with a thickness exceeding 2CM of the depth of the pre-forming surface according to the expanded size, importing the digital model of the pre-forming surface into a CNC machine tool, processing the hard rubber block, and obtaining the mold.

[0026] Preferably, in S4, the constraining layer is flowing water, and the energy absorbing layer is black paint.

[0027] Preferably, in S5, the operating parameters include current size, duty cycle, pulse frequency, laser wavelength, scanning rate, spot diameter, spot overlap rate, laser power, impact path, laser energy and impact times.

[0028] Preferably, in S6, the operation of placing the component in the enclosed space formed between the vacuum bag and the forming mold surface is as follows: a circle of high-temperature glue is pasted around the forming mold, and the vacuum bag is laid on the component, and the periphery of the vacuum bag is tightly bonded to the edge of the forming mold through the high-temperature glue, and the component is in the enclosed space formed between the vacuum bag and the forming mold surface.

[0029] Preferably, in S7, the creep aging process is specifically as follows: first pressurizing the autoclave, and starting to heat up after reaching a set pressure, and then maintaining the pressure and temperature after reaching a set temperature until the entire creep aging process is completed.

[0030] The beneficial effects of the present invention are:

[0031] (1) Laser shock forming uses laser to shock the absorbing layer, inducing shock waves to act on the component to cause plastic deformation, while introducing residual compressive stress to achieve surface strengthening effect. It belongs to the category of cold processing and will not cause thermal effects on the material.

[0032] (2) Laser shock has ultra-high energy density. Using high pulse energy can generate shock wave pressure up to GPa level within tens of nanoseconds, causing local plastic deformation of components, and the strain rate can reach 10 6 ~10 7 S -1 , which is a hundred times or even higher than the conventional processing forming method, can achieve full plastic bending, and there is no rebound on the surface after impact, which provides a feasibility basis for precise pre-forming in principle.

[0033] (3) The laser shock process used in the present invention is not used to directly form the component to the target surface, but to use laser shock to pre-form the difficult-to-form local areas in order to compensate for the deformation in the subsequent creep aging forming process and provide a better surface foundation.

[0034] (4) By designing the path in advance according to the rib layout and the curvature of the preformed surface and setting the parameters that change with the path, different impact forces can be applied according to the thickness and structural changes, so that the deformation in different directions and positions can be coordinated, and the impact deformation process can be precisely controlled.

[0035] (5) A constitutive model is constructed based on the creep data of the component material. Then, the area to be preformed and the distribution of the underbending amount in the area are obtained through simulation. The underbending surface, i.e., the preformed surface, is obtained by combining three-dimensional software. The entire process is based on strict material creep test data, which ensures the rigor, reliability, and authenticity of the results and provides data and theoretical support for precise preforming.

[0036] (6) The mold used in laser shock is made of hard rubber material, which avoids the reverse plastic deformation that occurs when the thin-walled component collides with the commonly used metal forming mold during laser shock, and provides a basis for precise pre-forming in terms of forming conditions.

[0037] (7) Compared with roll bending, laser shock can provide a higher density of dislocations, providing more dislocation slip for subsequent creep aging, thereby increasing the creep amount and reducing the rebound phenomenon after creep.

[0038] (8) The area preformed by laser shock is the area that is difficult to form by creep, and is also the area that is subjected to the greatest force during creep, and is prone to defects such as microcracks. However, the surface quality of the component after laser shock is better, and the surface structure becomes finer, making the surface have better ductility and fatigue resistance. Therefore, the surface preformed by laser shock can effectively inhibit the generation and development of cracks during the subsequent creep aging process, avoiding the risk of scrapping the component due to cracks after forming.

[0039] (9) In order to solve the problem that the single rolling deformation direction easily produces texture and makes the pre-formed area anisotropic, laser shock can significantly refine the grains in the area to be pre-formed by planning a reasonable impact path and number of impacts, thereby inhibiting the preferential orientation of the grains during the forming process and effectively reducing the anisotropy. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram of laser shock preforming of component sheet materials in the present invention.

[0041] Figure 2 This is a schematic diagram of the planning of the laser shock path for the reinforced component according to the present invention.

[0042] Figure 3 Schematic diagram of the effect of the laser shock path on the microstructure of the impact area of the component sheet in the present invention.

[0043] Figure 4 This is a schematic diagram of the effect of the number of laser shocks on the microstructure of the impact area of the present invention.

[0044] Figure 5 This is a component after the laser shock preforming-creep aging process of the present invention.

[0045] Figure 6 It is a component after roll-bending preforming and creep aging process.

[0046] In the figure: 1-laser impact equipment; 2-component sheet; 3-water pipe; 4-preforming mold; 5-black paint layer; 6-preforming mold surface. DETAILED DESCRIPTION

[0047] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. 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. The described embodiments are only for illustrative purposes and should not limit the present invention.

[0048] A method for assisted creep aging forming by laser shock to achieve high-precision preforming, comprising the following steps:

[0049] S1: Basic creep aging experiments were conducted on specimens made of large-scale aluminum alloy reinforced thin-walled components. Data on the creep variation of the component material under different stresses and temperatures were obtained. Creep data at appropriate temperatures were selected and fitted using mathematical software to establish a constitutive model based on the creep experimental data. Finite element software was used to establish a component-scale creep aging process simulation model. The mold surface and autoclave process parameters (pressure 1-2 MPa, temperature 160-180°C, and time 1-10 hours) from the actual forming process were added as boundary conditions to obtain simulation results of the formed surface. By comparing the results with the target surface required by the product, the areas that require pre-forming (pre-forming areas) and the amount of underbend that needs to be compensated for in order to accurately form the target surface using creep aging alone were determined.

[0050] The components are not limited to flat plates, the reinforcement forms of the components can be varied, and the curvature of the components is not limited to a single curve. The thickness of the components is 3-5 mm.

[0051] Among them, mathematical software such as MATLAB, Mathematica, Maple, etc. Finite element software such as ANSYS, Marc, Comsol, etc.

[0052] S2: Extract the underbend distribution data of the area to be preformed and its underbend amount obtained in step S1, import it into 3D software for processing, and obtain a curved surface (preformed surface) formed by the underbend amount. 3D software such as ProE, SolidWorks, and UG is used.

[0053] S3: Based on the preformed surface obtained in step S2, the area boundary size is further expanded outward by 10CM, and a hard rubber block with a thickness exceeding the depth of the preformed surface by more than 2CM is processed according to the expanded size. The digital model of the preformed surface obtained in step S2 is imported into a CNC machine tool, and the hard rubber block is processed to obtain a preformed mold with an inner concave surface as the preformed surface.

[0054] S4: According to the area to be preformed obtained in step S1, mark the corresponding area on the large-size aluminum alloy reinforced thin-walled component sheet, place the component sheet on the preforming mold obtained in step S3, so that the area to be preformed of the component corresponds to the surface of the preforming mold, and then lay a constraint layer (flowing water) and an energy absorption layer (black paint) on the area to be preformed of the component.

[0055] S5: According to the reinforcement conditions of the component and the change in the curvature of the pre-formed surface, the parameters of the laser impact device are set, including current size, duty cycle, pulse frequency, laser wavelength, scanning rate, spot diameter, spot overlap rate, laser power, impact path, laser energy and number of impacts. Then, the laser impact is performed on the area to be pre-formed of the component to achieve precise pre-forming.

[0056] By pre-designing the path and setting parameters that change with the path based on the component reinforcement and the curvature of the preformed surface, different impact forces can be applied according to thickness and structural changes. Unlike roll bending, laser shock can achieve deformation matching that of unreinforced areas by increasing the number of impacts, increasing the impact energy, and varying the spot diameter, specifically targeting reinforced areas. This ensures the feasibility of precise preforming.

[0057] S6: Completely wrap the component obtained in step S5 with breathable felt and secure the breathable felt to the component with high-temperature adhesive tape. Then, place the component on the forming mold, adjust the position of the component on the forming mold, affix a circle of high-temperature adhesive around the perimeter of the forming mold, and place a vacuum bag on the component. The perimeter of the vacuum bag is tightly bonded to the perimeter of the forming mold with the high-temperature adhesive, so that the component is in the enclosed space formed between the vacuum bag and the forming mold surface. Place the vacuum nozzle into the vacuum bag and seal it with high-temperature adhesive.

[0058] S7: The forming mold prepared in step S6 is placed into the autoclave. The vacuum bag is evacuated through a vacuum tube connected to a vacuum nozzle, forcing the component to conform to the forming mold surface under vacuum pressure. The autoclave process parameters are then set and the autoclave is started to pressurize the tank body. Once the set pressure is reached, the temperature is raised. After reaching the set temperature, the pressure and temperature are maintained until the entire creep aging process is completed. The pre-forming mold refers to the mold required for laser impact testing, and the forming mold refers to the mold required for the final target surface.

[0059] S8: After the entire creep aging process is completed, the autoclave begins to unload and cool down, then the door is opened, the forming mold is pulled out, the vacuum bag, breathable felt and vacuum nozzle are removed, and the component slowly rebounds. The component surface after rebound is the final target surface.

[0060] Example:

[0061] The component is constructed of 8mm thick 2xxx aluminum alloy reinforced plates (cross-reinforced plates) that are cold-rolled and then thinned by milling. The specific dimensions are 1500mm*800mm, with ribs 5mm high and 5mm wide, and the remaining thickness is 3mm. The mold's outer dimensions are 2000mm*1500mm*500mm. The base is made of Q235 steel, the profile is made of 45# steel, and the surface roughness is Ra 1.6. The maximum operating pressure is 2.0MPa, and the maximum operating temperature is 250°C. The effective space inside the autoclave has a diameter of φ2500mm*5000mm. The creep aging forming temperature is 180°C, the creep aging duration is 8h, the autoclave is pressurized to 1.8MPa, the heating rate is 3-5°C / min, the temperature fluctuation does not exceed 5°C, and the loading rate is 0.3bar / min. The relevant parameters of laser shock are: current size 1000-5000A, duty cycle 50%, pulse frequency 1000-1500HZ, laser wavelength 1080nm, scanning rate 3-5m / s, spot diameter 3-5mm, spot overlap rate 50%, laser power 3-6KW. Through simulation, it is obtained that the impact deformation range of the component is about 200*300mm. Figure 1 This is a schematic diagram of laser shock preforming of component sheet materials, including laser shock equipment 1, component sheet material 2, water pipe 3, preforming mold 4, black paint layer 5, and preforming mold surface 6. The shock path is shown in Figure 2 , is based on the currently commonly used "cross" reinforcement form, and then plans the impact path to achieve the forming accuracy requirements of the reinforced component. The laser energy is 3-15J. The constraint layer is a 3mm thick flowing water, and the absorption layer is a 2mm thick black paint layer. The laser impact path set according to the reinforcement situation has different effects on the impact area of the component sheet. The reinforced area has a dense structure, while the non-reinforced area is loose. Figure 3 The grains in the laser shock area are refined, and the more shock times, the greater the degree of refinement. Figure 4 After the laser shock process is used for precise preforming, the surface accuracy of the component after creep aging is significantly improved. The comparison between the component obtained by the laser shock-creep process and the component obtained by the rolling-creep process (with rib distortion and thin-wall wrinkling in the central area) is shown in Figure 2. Figure 5 、 6 .

[0062] Those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of this application and their equivalents, the scope of protection of this application shall also include these modifications and variations.

Claims

1. A method for achieving high-precision preforming by laser shock assisted creep aging forming, comprising the following steps: S1: Obtain creep data of large-scale aluminum alloy reinforced thin-walled components under different stresses and temperatures over time. Select creep data at a certain temperature to establish a constitutive model. Combined with finite element software, establish a component-scale creep aging process simulation model to obtain the distribution data of the area requiring pre-forming and its underbending amount. S2: Obtain a pre-formed surface based on the distribution data of the area to be pre-formed and the under-bend amount thereof obtained in step S1; S3: According to the preformed surface obtained in step S2, a hard rubber material is selected and processed to obtain a preformed mold having the preformed surface; S4: Mark the corresponding area on the large-size aluminum alloy reinforced thin-walled component sheet according to the area to be preformed obtained in step S1, place the component sheet on the preforming mold obtained in step S3, so that the area to be preformed of the component corresponds to the surface of the preforming mold, and then lay a constraint layer and an energy absorption layer on the area to be preformed of the component; S5: Setting parameters of the laser impact device according to the reinforcement condition of the component sheet and the curvature change of the pre-formed surface, performing laser impact on the component area to be pre-formed, and completing the pre-forming; S6: Wrapping and fixing the breathable felt on the component obtained in step S5, and then placing the component in a closed space formed between the vacuum bag and the molding surface of the forming mold; S7: Evacuate the enclosed space, then send the forming mold into the autoclave equipment for creep aging process. After completion, the component slowly rebounds to obtain the final target surface.

2. The method of claim 1 for achieving high-precision preforming by laser shock assisted creep aging forming, characterized in that: The component thickness is 3-5mm.

3. The method of laser shock assisted creep aging forming for achieving high-precision preforming according to claim 1, characterized in that: In S1, the creep variation data of large-size aluminum alloy reinforced thin-walled component materials under different stresses and temperatures are obtained by conducting creep aging basic experiments on specimens made of large-size aluminum alloy reinforced thin-walled component materials.

4. The method of claim 1 for achieving high-precision preforming by laser shock assisted creep aging forming, characterized in that: In S1, the method of establishing a component-scale creep aging process simulation model using finite element software is as follows: adding the mold surface and autoclave working parameters of the actual forming manufacturing process as boundary conditions. The working parameters include pressure, temperature, and time to obtain the simulation results of the surface after forming.

5. The method of laser shock assisted creep aging forming for achieving high-precision preforming according to claim 1, characterized in that: In S2, the method for obtaining the pre-formed surface is: importing the underbend distribution data of the area to be pre-formed into three-dimensional software for processing to obtain a curved surface formed by the underbend, namely the pre-formed surface.

6. The method of laser shock assisted creep aging forming for achieving high-precision preforming according to claim 1, characterized in that: In S3, the method for making the pre-formed mold is as follows: the regional boundary size of the pre-formed surface is expanded outward by 10CM, a hard rubber block with a thickness exceeding 2CM of the depth of the pre-formed surface is processed according to the expanded size, the digital model of the pre-formed surface is imported into the CNC machine tool, and the hard rubber block is processed to obtain the mold.

7. The method of claim 1 for achieving high-precision preforming by laser shock assisted creep aging forming, characterized in that: In S4, the constraining layer is flowing water and the energy absorbing layer is black paint.

8. The method of laser shock assisted creep aging forming for achieving high-precision preforming according to claim 1, characterized in that: In S5, the operating parameters include current size, duty cycle, pulse frequency, laser wavelength, scanning rate, spot diameter, spot overlap rate, laser power, impact path, laser energy and impact times.

9. The method of claim 1 for achieving high-precision preforming by laser shock assisted creep aging forming, characterized in that: In S6, the operation of placing the component in the enclosed space formed between the vacuum bag and the forming mold surface is as follows: a circle of high-temperature glue is pasted around the forming mold, and the vacuum bag is laid on the component. The periphery of the vacuum bag is tightly bonded to the edge of the forming mold through the high-temperature glue, and the component is in the enclosed space formed between the vacuum bag and the forming mold surface.

10. The method of laser shock assisted creep aging forming for achieving high-precision preforming according to claim 1, characterized in that: In S7, the creep aging process is specifically as follows: first, pressurizing the autoclave, and starting to heat up after reaching a set pressure. After heating to a set temperature, the pressure and temperature are maintained until the entire creep aging process is completed.

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