Simulation Method for Milling-Creep Aging Forming Process Considering Residual Stress Field

Abstract

This invention relates to a full-process simulation method for milling-creep aging forming that considers residual stress fields, belonging to the field of sheet metal forming technology. It solves the problems of low simulation efficiency and inaccurate results in existing simulation methods. This invention considers the influence of initial and milling residual stress fields in creep aging forming simulation. The initial residual stress test values ​​and milling forces are imported into the staged milling simulation process to obtain simulated predicted values ​​of residual stress on the surface and throughout the entire thickness of the component after milling. Furthermore, the staged simulation predicted values ​​of residual stress are reconstructed to obtain overall residual stress reconstructed values. By considering the overall residual stress reconstructed values ​​in the creep aging forming simulation, the simulation efficiency and accuracy of the method are improved.

Description

Technical Field

[0001] This invention belongs to the field of sheet metal forming technology and relates to a simulation method for the entire process of milling-creep aging forming that considers residual stress field. Background Technology

[0002] The forming and manufacturing of aluminum alloy panels requires a combination of various manufacturing processes. A typical manufacturing route involves first preparing a slab from rolled block raw materials through milling, and then simultaneously forming and shaping it through creep aging forming (CAF) to obtain a final product with the desired shape and performance. The generation and influence of residual stress between the milling and CAF processes during the forming and manufacturing of aluminum alloy panels are crucial to the final component, especially for aerospace products with high precision and performance requirements. However, due to the complexity of residual stress itself, it is difficult to directly observe and obtain it in real time through experimental methods. Destructive experimental methods such as drilling and delamination are costly and difficult to use, while non-destructive methods can only test residual stress on the material surface or in the shallow layer, and are technically complex and require expensive equipment. Using finite element simulation to predict residual stress and study its effects is an effective alternative to experimental methods and has been applied in various processes. However, for the milling process, residual stress mainly exists on the material surface (micrometer level). Therefore, it is necessary to divide the overall model surface into extremely fine micrometer-level meshes, resulting in a huge number of meshes in the overall simulation model, extremely low simulation efficiency, and extremely long simulation time, which cannot meet the application requirements. Therefore, existing CAF finite element simulations rarely consider the residual stress generated by the preceding milling process, and only simulate the single CAF process. They cannot fully consider the deformation and residual stress of the sheet metal caused by the milling process, thus significantly affecting the accuracy of CAF forming prediction, and consequently making it difficult to accurately guide the actual milling and CAF machining process. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to provide a simulation method for the entire process of milling-creep aging forming that considers the residual stress field, in order to solve the problems of low simulation efficiency and inaccurate results of existing simulation methods.

[0004] This invention provides a simulation method for the entire milling-creep aging forming process considering residual stress fields, the specific steps of which include:

[0005] The initial residual stress of the aluminum alloy block was tested to obtain the initial residual stress test value of the aluminum alloy block;

[0006] Aluminum alloy blocks were milled, and the milling force during the milling process was tested.

[0007] A milling model for aluminum alloy blocks was established, and a graded milling simulation was performed on the aluminum alloy blocks. The initial residual stress test values ​​and milling forces obtained were then imported into the graded milling simulation process to obtain the graded simulation prediction values ​​of residual stress on the surface and throughout the entire thickness of the component after milling.

[0008] The simulated values ​​of residual stress at different stages are reconstructed to obtain the overall reconstructed value of residual stress.

[0009] A model of the component after milling is established, the overall residual stress reconstruction value is imported into the model of the component after milling, and the deformation simulation of the component after milling is carried out to obtain the initial state model of creep aging forming with balanced residual stress and deformation after milling.

[0010] The creep aging forming process is simulated on the initial state model of creep aging forming to obtain the shape and performance prediction results of the formed part after the creep aging forming process.

[0011] Optionally, the initial residual stress test values ​​of the aluminum alloy block are obtained in two ways: the initial residual stress test values ​​distributed along the thickness direction of the aluminum alloy block in the rolling direction and the initial residual stress test values ​​perpendicular to the rolling direction.

[0012] Optionally, the initial residual stress test values ​​of the obtained aluminum alloy block are processed, and the specific processing steps are as follows:

[0013] The initial residual stress values ​​obtained from the fitting process for the aluminum alloy block along the rolling direction and perpendicular to the rolling direction are as follows:

[0014]

[0015] Where, σ x (z) represents the fitted value of the initial residual stress in the rolling direction of the aluminum alloy block along the thickness direction, σ y (z) represents the fitted value of the initial residual stress perpendicular to the rolling direction distributed along the thickness direction of the aluminum alloy block, z is the position value of the aluminum alloy block in the thickness direction, i is the degree of the term, n is the degree of the highest term of the polynomial, and a i and b i is the coefficient of the term in the polynomial.

[0016] Optionally, the aluminum alloy block is milled, and the milling forces in the x, y and z axes of the block are tested during the milling process.

[0017] Optionally, when establishing a simulation model for milling aluminum alloy blocks,

[0018] A full-size initial aluminum alloy block milling simulation master model was established, and the full-size initial aluminum alloy block milling process was simulated using the birth and death element method; the volume residual stress σ in the rolling direction and perpendicular to the rolling direction in the simulation master model of the milled component after milling and before fixture release was obtained. bx (z), σby (z) Simulated distribution values;

[0019] A simulation sub-model for local milling of aluminum alloy block surface was established, and a two-dimensional representative model with refined surface mesh was used to simulate the local single-pass milling process of aluminum alloy block surface; the micron-level residual stress σ on the surface of the milled component in the rolling direction was obtained in the simulation sub-model of the milled component before the fixture was released after a single pass of milling. sx (z) Simulated distribution values;

[0020] Extract σ bx (z), σ by (z) and σ sx (z) The simulated distribution value is used as the simulation prediction value, and the surface micron-level residual stress σ perpendicular to the rolling direction is set. sy (z)=σ sx (z).

[0021] Optionally, the simulated values ​​of bulk residual stress and surface micron-level residual stress are added and integrated to obtain the overall residual stress σ in the rolling direction and perpendicular to the rolling direction of the reconstructed milled component. mx (z)=σ bx (z)+σ sx (z),σ my (z)=σ by (z)+σ sy (z).

[0022] Optionally, a shell element component model is established after milling, and the overall residual stress reconstruction value is imported into the shell element model to realize the transmission of the simulated overall residual stress from the volume element to the shell element.

[0023] Optionally, when establishing the full-size initial aluminum alloy block milling simulation master model and when establishing the local aluminum alloy block surface milling simulation sub-model, the initial aluminum alloy block master model and the local aluminum alloy block surface sub-model are meshed; different mesh element types are used for the two.

[0024] Optionally, the initial residual stress test values ​​in the rolling direction and perpendicular to the rolling direction of the aluminum alloy block can be imported into the initial main model of the aluminum alloy block milling simulation.

[0025] Optionally, the simulated distribution values ​​of the volume residual stress in the in-plane rolling direction perpendicular to the thickness direction and the unit integration point perpendicular to the rolling direction, as well as the simulated distribution values ​​of the surface micron-level residual stress in the rolling direction, are extracted layer by layer along the thickness direction of the aluminum alloy component. The average value of the multiple simulated distribution values ​​of volume residual stress and surface micron-level residual stress extracted from each layer is then used as the simulated predicted value of the volume residual stress and surface micron-level residual stress of the corresponding layer.

[0026] Compared with the prior art, the present invention can achieve at least the following beneficial effects:

[0027] (1) This invention comprehensively considers the effects of initial material residual stress, milling surface residual stress and milling deformation on creep aging forming springback and performance evolution, thereby improving the forming prediction accuracy of aluminum alloy wall panels.

[0028] (2) This invention combines a master model and a sub-model for graded milling simulation. The master model uses the birth and death element method to obtain the volume residual stress due to material removal and redistribution, while the sub-model uses two-dimensional single-pass milling simulation to obtain the residual stress on the milled surface. This simulation method solves the problem that the birth and death element method cannot predict the micron-level residual stress of surface milling, and at the same time, it greatly improves the simulation efficiency compared with the three-dimensional full-size milling simulation method.

[0029] (3) This invention uses different element types for simulation of different processes. The milling simulation model uses solid elements, while the CAF model uses shell elements, which solves the problem of data transfer between different element types. The residual stress on the milled surface is introduced into the CAF model through the integration points of the shell elements, avoiding the problem that using solid elements for CAF simulation under the same conditions requires dividing the surface into extremely fine meshes, resulting in extremely low simulation efficiency. Attached Figure Description

[0030] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Figure 1 This is an overall flowchart of the present invention;

[0032] Figure 2 (a) is a schematic diagram of the initial residual stress in the X direction in Embodiment 1 of the present invention;

[0033] Figure 2 (b) is a schematic diagram of the initial residual stress in the Y direction in Embodiment 1 of the present invention;

[0034] Figures 3(a) and (b) are schematic diagrams of staged milling simulation of aluminum alloy flat parts according to Embodiment 1 of the present invention;

[0035] Figure 4 This is a simulation flowchart of creep aging forming of an aluminum alloy milled flat plate according to Embodiment 1 of the present invention;

[0036] Figure 5 (a) and (b) are schematic diagrams of staged milling simulation of aluminum alloy ribbed parts in Embodiment 2 of the present invention;

[0037] Figure 6 This is a simulation flowchart of creep aging forming of an aluminum alloy milled ribbed part according to Embodiment 2 of the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0039] A specific embodiment of the present invention, such as Figure 1-6 A simulation method for the entire milling-creep aging forming process considering residual stress field is disclosed, and the specific steps include:

[0040] Step 1: Test the initial residual stress of the aluminum alloy block and obtain the initial residual stress test value of the aluminum alloy block.

[0041] Step 2: Correct the initial residual stress test value of the aluminum alloy block obtained in Step 1;

[0042] Step 3: Mill the aluminum alloy block and test the milling force during the milling process;

[0043] Step 4: Establish an aluminum alloy block milling model, perform graded milling simulation on the aluminum alloy block, and import the corrected initial residual stress test value obtained in Step 2 and the milling force obtained in Step 3 into the graded milling simulation process to obtain the graded simulation prediction value of the residual stress of the component after milling.

[0044] Step 5: Reconstruct the residual stress classification simulation prediction values ​​from Step 4 to obtain the overall residual stress reconstruction values.

[0045] Step 6: Establish the milled component model, import the overall residual stress reconstruction value from Step 5 into the milled component model, perform deformation simulation of the milled component, and obtain the CAF initial state model with balanced residual stress and deformation after milling.

[0046] Step 7: Perform CAF process simulation on the initial state model of CAF from Step 6 to obtain the predicted shape and performance of the formed part after CAF process.

[0047] Optionally, step one specifically involves: using a residual stress tester to test the initial residual stress of the aluminum alloy block and obtaining the initial residual stress test value of the aluminum alloy block; wherein, the initial residual stress test value of the aluminum alloy block is divided into the initial residual stress test value distributed along the thickness direction of the aluminum alloy block (i.e., z-axis) in the rolling direction (i.e., x-axis) and the initial residual stress test value perpendicular to the rolling direction (i.e., y-axis).

[0048] Optionally, step two specifically involves:

[0049] (1) Fit the initial residual stress test values ​​of the aluminum alloy block in the rolling direction and perpendicular to the rolling direction in step one:

[0050]

[0051] Where, σ x(z) represents the fitted value of the initial residual stress in the rolling direction of the aluminum alloy block along the thickness direction, σ y (z) represents the fitted value of the initial residual stress perpendicular to the rolling direction distributed along the thickness direction of the aluminum alloy block, z is the position value of the aluminum alloy block in the thickness direction, i is the degree of the term, n is the degree of the highest term of the polynomial, and a i and b i is the coefficient of the term in the polynomial.

[0052] (2) Calculate the resultant force value of the initial residual stress in the rolling direction and perpendicular to the rolling direction of the aluminum alloy block based on the fitted values ​​of the initial residual stress in the rolling direction and perpendicular to the rolling direction:

[0053]

[0054] Among them, F x F is the resultant force value in the rolling direction. y σ is the resultant force perpendicular to the rolling direction, h is the thickness of the block material, z is the position of the aluminum alloy block material in the thickness direction, and σ is the resultant force perpendicular to the rolling direction. x (z) represents the fitted value of the initial residual stress in the rolling direction of the aluminum alloy block, σ y (z) is the fitted value of the initial residual stress of the aluminum alloy block perpendicular to the rolling direction;

[0055] If the resultant force value is not zero, the constant term of the fitted value is corrected:

[0056] Make F x =F y =0.

[0057] Where c and d are both constant terms.

[0058] Correcting the initial residual stress test values ​​of aluminum alloy blocks can improve the accuracy of the test values.

[0059] Optionally, step three specifically involves: milling the aluminum alloy block and using a force gauge to test the milling forces along the x, y, and z axes of the block during the milling process.

[0060] Optionally, step four specifically includes:

[0061] (1) Establish a full-size initial aluminum alloy block milling simulation master model, and use the birth and death element method to simulate the full-size initial aluminum alloy block milling process; obtain the volume residual stress σ in the rolling direction and perpendicular rolling direction in the simulation master model of the milled component after milling and before fixture release. bx (z), σ by (z) Simulated distribution value.

[0062] Furthermore, when establishing the main simulation model for milling a full-size initial aluminum alloy block, the initial aluminum alloy block is divided into mesh elements. The mesh element type for the full-size initial aluminum alloy block is C3D8R element. The length, width, and thickness of each mesh element of the full-size initial block are divided according to the rules corresponding to the milling process parameters. In conjunction with the milling parameters, the milling length in a single analysis step is the total length composed of multiple mesh elements (i.e., the total length along the x-axis), the milling width in a single analysis step is the total width composed of multiple mesh elements (i.e., the total length along the y-axis), and the milling depth in a single analysis step is the total thickness composed of multiple mesh elements (i.e., the total length along the z-axis).

[0063] Furthermore, the SIGINI subroutine in ABAQUS is used to import the fitted values ​​of the initial residual stress in the rolling direction and perpendicular to the rolling direction of the aluminum alloy block, which were corrected in step two, into the main model of the initial aluminum alloy block milling simulation. This incorporates the influence of the initial residual stress into the milling simulation to obtain more accurate stress and deformation data of the component after milling.

[0064] Furthermore, using the static equivalent method, the three-axis milling forces of x, y, and z obtained in step three are evenly distributed on the eight nodes of the mesh element to be milled and removed, according to the order of mesh element removal during the milling process using the aforementioned birth and death element method.

[0065] Furthermore, the MODEL CHANGE function in ABAQUS is used to make the mesh cells to be milled disappear sequentially in the order they are milled from the aluminum alloy block in the next analysis step after the x, y, and z axes milling forces are applied.

[0066] Furthermore, after the milling simulation ends and before the fixture is released, the simulated distribution values ​​of the volumetric residual stress of the aluminum alloy component are extracted layer by layer along the thickness direction in the in-plane rolling direction perpendicular to the thickness direction and at the element integration points perpendicular to the rolling direction. During layer-by-layer extraction, the thickness of each layer is the thickness of one mesh element.

[0067] Furthermore, the average of the multiple simulated distribution values ​​of volumetric residual stress extracted from each layer is taken as the volumetric residual stress σ of the corresponding layer. bx (z), σ by (z) Simulation prediction value.

[0068] (2) Establish a simulation sub-model for local milling of aluminum alloy block surface, and use a two-dimensional representative model with refined surface mesh to simulate the single-pass milling process of aluminum alloy block; obtain the micron-level residual stress σ on the surface of the milled component in the rolling direction in the simulation sub-model of the milled component after single-pass milling and before the fixture is released. sx (z) Simulated distribution value.

[0069] Furthermore, when establishing the simulation sub-model for local milling on the surface of the aluminum alloy block, a two-dimensional sub-model of the local surface of the aluminum alloy block is established in ABAQUS. The mesh element type of the two-dimensional sub-model of the local surface of the aluminum alloy block is CPE4RT element. For the material within the range of the thickness of the layer affected by the milling residual stress (e.g., 0.5-1mm), the mesh is refined. The x and y dimensions of the refined mesh elements are 0.01-0.1mm.

[0070] Furthermore, a tool model corresponding to the milling experiment was established, and a single-pass milling simulation of the aluminum alloy block was performed based on the corresponding experimental parameters.

[0071] Furthermore, after the single-pass milling simulation is completed, the simulated distribution values ​​of surface micron-level residual stress at the unit integration points along the thickness direction of the aluminum alloy component are extracted layer by layer. During layer-by-layer extraction, the thickness of each layer is the thickness of a refined unit.

[0072] Furthermore, the average of the multiple simulated surface micron-level residual stress distribution values ​​extracted from each layer is taken as the surface micron-level residual stress σ of the corresponding layer. sx (z) Simulation prediction values, and setting the surface micron-level residual stress σ perpendicular to the rolling direction. sy (z)=σ sx (z).

[0073] Optionally, step five specifically involves: summing and integrating the simulated predicted values ​​of the bulk residual stress and the surface micron-level residual stress of each layer to obtain the overall residual stress σ in the rolling direction and perpendicular to the rolling direction of the corresponding layer of the reconstructed milled component. mx (z)=σ bx (z)+σ sx (z),σ my (z)=σ by (z)+σ sy (z).

[0074] Optionally, step six specifically involves: when creating the model of the milled component, meshing the milled component; the mesh element type of the milled component is S4R shell element; using the SIGINI subroutine in ABAQUS, the overall residual stress σ of the corresponding layer in step five is calculated. mx (z) and σ my (z) The reconstructed values ​​are imported into the shell element model to realize the transfer of the overall residual stress from the volume element to the shell element. Preferably, when defining the number of thickness direction integration points of the shell element model of the aluminum alloy milled component, it is necessary to ensure that the distribution trend of the overall residual stress can be accurately introduced into the shell element model of the aluminum alloy milled component. A CAF initial state model with deformation prediction of the milled component and equilibrium residual stress after milling is obtained.

[0075] Optionally, step seven specifically involves: based on the above-mentioned CAF initial state model with milled component deformation and milled residual stress equilibrium, using the CREEP subroutine in ABAQUS to perform creep aging forming simulation, predicting the deformation and performance evolution of the creep aging formed part; and obtaining springback and performance evolution data of the creep aging formed part.

[0076] Using the data on springback and performance evolution of creep-aged formed parts obtained in this application to guide the actual milling and CAF process, the formed parts after CAF can obtain the expected shape and performance.

[0077] Example 1

[0078] The workpiece selected is a 2219-T37 aluminum alloy block with a length of 150mm, a width of 45mm, and a thickness of 18mm. The specific steps are as follows:

[0079] Step 1: Use a PRISM residual stress tester to test the initial residual stress of the aluminum alloy block and obtain the initial residual stress test value. During the test, the test depth interval is 1mm, and the initial residual stress test values ​​are obtained along the thickness direction of the aluminum alloy block in the rolling direction and perpendicular to the rolling direction. Since the aluminum alloy block in this embodiment is cut from the pre-stretched plate, its initial residual stress is symmetrical along the thickness center plane. Therefore, only the initial residual stress of half the thickness of the aluminum alloy block (i.e., 9mm) is tested, and the initial residual stress of the other half is treated symmetrically.

[0080] Step 2: Correct the initial residual stress test value of the aluminum alloy block obtained in Step 1:

[0081] (1) Fit the initial residual stress test values ​​of the aluminum alloy block in the rolling direction and perpendicular to the rolling direction in step one:

[0082] σ x (z) = -3.47323 + 0.74207z 2 -0.00379z 4 -0.000887419z 6 +0.0000121495z 8 ,

[0083] σ y (z) = 20.31626 - 2.89105z 2 +0.27545z 4 -0.00836z 6 +0.000066493z 8 ;

[0084] Where z is the position value in the thickness direction of the aluminum alloy block, σx (z) represents the fitted value of the initial residual stress in the rolling direction of the aluminum alloy block, σ y (z) is the fitted value of the initial residual stress in the vertical rolling direction of the aluminum alloy block, where the thickness direction position value is the coordinate value of the cross section at the middle position of the thickness direction of the aluminum alloy block as the 0 coordinate, and the coordinate value of the two surfaces of the aluminum alloy block that are parallel to the cross section along this 0 coordinate.

[0085] like Figure 2 As shown, the dots represent the initial residual stress test values ​​obtained from the experiment, the squares represent the initial residual stress fitted values, and the triangles represent the initial residual stress correction values.

[0086] (2) Calculate the resultant force value of the initial residual stress in the rolling direction and perpendicular to the rolling direction of the aluminum alloy block based on the fitted values ​​of the initial residual stress in the rolling direction and perpendicular to the rolling direction:

[0087]

[0088] Among them, F x F is the resultant force value in the rolling direction. y σ is the resultant force value perpendicular to the rolling direction, h is the block thickness of 18mm, z is the position value of the aluminum alloy block in the thickness direction, and σ is the resultant force value perpendicular to the rolling direction. x (z) represents the fitted value of the initial residual stress in the rolling direction of the aluminum alloy block, σ y (z) is the fitted value of the initial residual stress in the direction perpendicular to the rolling of the aluminum alloy block;

[0089] If the resultant force value is not zero, the constant term of the fitted value is corrected:

[0090] σ x (z) = -4.91541 + 0.74207z 2 -0.00379z 4 -0.000887419z 6 +0.0000121495z 8 ,

[0091] σ y (z) = 32.97521 - 2.89105z 2 +0.27545z 4 -0.00836z 6 +0.000066493z 8 ,

[0092] Make F x =F y =0.

[0093] Step 3: Mill the aluminum alloy block and use a KISTELER force gauge to test the milling forces along the x, y, and z axes of the aluminum alloy block during the milling process.

[0094] Step four, specifically:

[0095] (1) Establish a full-size initial aluminum alloy block milling simulation master model, and use the birth and death element method to simulate the full-size initial aluminum alloy block milling process; extract the volume residual stress σ in the rolling direction and perpendicular to the rolling direction in the component after milling and before the fixture is released. bx (z), σ by (z) Simulated distribution value.

[0096] First, when establishing the main simulation model for milling a full-size initial aluminum alloy block, the initial aluminum alloy block is meshed. The mesh element type for the full-size initial aluminum alloy block is C3D8R element. Each mesh element of the full-size initial aluminum alloy block has a length of 7.5mm, a width of 4.5mm, and a thickness of 0.5mm, which corresponds to the milling parameters of feed rate of 5400mm / min, single-blade milling width of 9mm, and single-blade milling depth of 1.5mm. This ensures that in a single analysis step of the simulation, milling removes 2 mesh elements in the length direction, 2 mesh elements in the width direction, and 3 mesh elements in the thickness direction simultaneously.

[0097] Then, the SIGINI subroutine in ABAQUS is used to import the initial residual stress correction values ​​of the aluminum alloy block rolling direction and perpendicular rolling direction from step two into the initial aluminum alloy block milling simulation master model.

[0098] Secondly, based on the static equivalent method, the three-axis milling forces of x, y and z obtained in step three are distributed evenly on the eight nodes of the milling mesh cells to be removed in the order of removal of the milling mesh cells.

[0099] Furthermore, the MODEL CHANGE function in ABAQUS is used to make the milling mesh elements disappear sequentially in the order in which the aluminum alloy block is milled away in the next analysis step after the application of milling forces along the x, y, and z axes.

[0100] Finally, the simulated volumetric residual stress distribution values ​​of the aluminum alloy component in the in-plane rolling direction perpendicular to the thickness direction and at the unit integration points perpendicular to the rolling direction are extracted layer by layer along the thickness direction. The average of the multiple simulated volumetric residual stress distribution values ​​extracted from each layer is taken as the volumetric residual stress σ of the corresponding layer. bx (z), σ by (z) Simulation data. Among them, when extracting layer by layer, the thickness of each layer is the thickness of one grid cell.

[0101] (2) Establish a simulation sub-model for local milling of aluminum alloy block surface. Use a two-dimensional representative model with refined surface mesh to simulate the local single-pass milling process of aluminum alloy block surface. Obtain the micron-level residual stress σ on the surface of the milled component in the rolling direction in the simulation sub-model before the fixture is released after single-pass milling. sx (z) Simulation distribution.

[0102] First, a two-dimensional sub-model of the local surface of the aluminum alloy block is created in ABAQUS. The mesh element type of the two-dimensional sub-model of the local surface of the aluminum alloy block is CPE4RT element. The mesh element is refined within a 2mm thickness range of the model surface, and the mesh element size in both the x and y directions is 0.05mm.

[0103] Then, a single-cutting-edge tool model corresponding to the milling experiment was established, with a rake angle of 30°, a clearance angle of 5°, and a tool tip radius of 0.2mm. Based on the corresponding experimental parameters, a feed rate of 5400mm / min and a milling depth of 1.5mm were used to conduct a single-pass milling simulation.

[0104] Finally, the simulated distribution values ​​of surface micron-level residual stress at the unit integration points along the rolling direction of the aluminum alloy component are extracted layer by layer along the thickness direction; the average of the multiple simulated distribution values ​​of surface micron-level residual stress extracted for each layer is taken as the surface micron-level residual stress σ of the corresponding layer. sx (z) Simulation data, and setting σ sy (z)=σ sx (z). Among them, when extracting layer by layer, the thickness of each layer is the thickness of a refined mesh unit. As shown in Figure 3, the thickness range with volume residual stress obtained by the main model simulation is 3 mm thick after milling of the flat plate, and the thickness range with surface residual stress obtained by the sub-model simulation is 0.5 mm away from the milled surface.

[0105] Step five, specifically: The simulation data of volumetric residual stress and surface micron-level residual stress of each layer are added together and integrated to obtain the overall residual stress σ in the rolling direction and perpendicular to the rolling direction of the corresponding layer of the reconstructed milled component. mx (z)=σ bx (z)+σ sx (z),σ my (z)=σ by (z)+σ sy (z).

[0106] Step six, as follows Figure 4 As shown, specifically: when creating the model of the milled component, the milled component is meshed; the element type of the milled component is S4R shell element; using the SIGINI subroutine in ABAQUS, the overall residual stress σ of the corresponding layer in step five is calculated.mx (z) and σ my (z) The reconstructed values ​​are imported into the shell element model to realize the transfer of overall residual stress from the volume elements to the shell elements in the simulation. The thickness of the S4R shell element is defined as 3mm, and the number of thickness integration points of the aluminum alloy shell element plate model is defined as 61, with a distance of approximately 0.049mm between each integration point, so that the distribution trend of residual stress on the simulation surface can be accurately introduced into the shell element. The initial state model of CAF with the deformation of the component after milling and the equilibrium residual stress after milling is obtained.

[0107] Step seven, as Figure 4 As shown, based on the above CAF initial state model with the deformation of the component after milling and the residual stress after milling equilibrium, the CREEP subroutine in ABAQUS secondary development is used to perform creep aging forming simulation, and the deformation and performance evolution of the creep aging formed part are predicted; the springback and performance evolution data of the creep aging formed part are obtained.

[0108] Example 2

[0109] The initial aluminum alloy block and steps one to three are the same as in Example 1. The aluminum alloy block is then processed into a milled part with ribs.

[0110] Step four, specifically:

[0111] (1) Establish the main simulation model for full-size initial aluminum alloy block milling: The full-size initial aluminum alloy block milling process is simulated using the birth and death element method; the residual stress σ in the rolling direction and perpendicular to the rolling direction of the bottom plate and ribs in the ribbed part after milling and before the fixture is released is taken. 1bx (z), σ 2bx (z), σ 1by (z) and σ 2by (z) Simulated distribution value.

[0112] First, the element type of the full-size initial aluminum alloy block is C3D8R solid element. Each mesh element of the full-size initial aluminum alloy block has a length of 15mm, a width of 10.875mm, and a thickness of 1.5mm. This corresponds to the milling experiment parameters of feed rate 5400mm / min, single-blade milling width of 10.875mm, and single-blade milling depth of 1.5mm. This allows the milling simulation to remove one element in the length direction, one element in the width direction, and one element in the thickness direction in a single analysis step. The thickness of the ribbed base plate and the ribs after milling is 1.5mm, and the rib height is 3mm.

[0113] Secondly, based on the static equivalent method, the three-axis milling forces of x, y and z obtained in step three are distributed evenly on the eight nodes of the milling mesh cells to be removed in the order of removal of the milling mesh cells.

[0114] Finally, the MODEL CHANGE function in ABAQUS is used to make the milling mesh elements disappear sequentially in the order in which the aluminum alloy block is milled away in the next analysis step after the three-axis milling forces of x, y, and z are applied.

[0115] Finally, after the simulated milling is completed and before the fixture is released, the simulated distribution values ​​of the volumetric residual stress at the unit integration points in the plane perpendicular to the thickness direction and perpendicular to the rolling direction of the aluminum alloy ribbed base plate are extracted layer by layer along the thickness direction; and the simulated distribution values ​​of the volumetric residual stress at the unit integration points in the plane perpendicular to the thickness direction and perpendicular to the rolling direction of the aluminum alloy ribbed strip are extracted layer by layer along the thickness direction; the average of the multiple simulated distribution values ​​of volumetric residual stress extracted in each layer is taken as the volumetric residual stress σ of the corresponding layer's base plate. 1bx (z), σ 1by (z) and residual stress σ of the stiffener 2bx (z), σ 2by (z) Simulation data. Among them, when extracting layer by layer, the thickness of each layer is the thickness of one grid cell.

[0116] (2) Establish a simulation sub-model for local milling of aluminum alloy block surface: Use a two-dimensional representative model with refined surface mesh to simulate the local single-pass milling process of the bottom plate and ribs on the surface of aluminum alloy block, and obtain the micron-level residual stress σ on the surface of the bottom plate and ribs in the rolling direction in the simulation sub-model after single-pass milling and before the fixture is released. 1sx (z) and σ 2sx (z) Simulation distribution.

[0117] First, two-dimensional sub-models of the local surface of the aluminum alloy base plate and rib milling blocks were established in ABAQUS. Corresponding to the milling experiment, the milling method in the base plate milling model was end milling, and the milling method in the rib milling model was circular milling. The element type was CPE4RT element. The material within a 1.5mm thickness range of the aluminum alloy base plate and rib surface was refined into mesh elements, and the mesh element size in the x and y directions was 0.05mm.

[0118] Then, tool models corresponding to the milling experiments were established, with a rake angle of 30°, a clearance angle of 5°, and a tool tip radius of 0.2mm. The tool model for the base plate milling was a single-cutting-edge end mill, while the tool model for the rib milling was a four-cutting-edge peripheral mill. Based on the corresponding simulation parameters, with a feed rate of 2400mm / min, a milling width of 9mm, and a milling depth of 1mm, single-pass milling simulations were performed on the base plate and ribs respectively.

[0119] Finally, the simulated surface micron-level residual stress distribution values ​​at the unit integration points along the thickness direction of the aluminum alloy ribbed base plate and the rib strip along the thickness direction were extracted layer by layer. The average of the multiple simulated surface micron-level residual stress distribution values ​​extracted from each layer of the base plate and rib strip was then taken as the surface micron-level residual stress σ of the corresponding layer of the base plate. 1sx (z) Simulation data, surface micron-level residual stress σ of the layer corresponding to the rib. 2sx (z) Simulation data, and setting σ jsy (z)=σ jsx (z), where j = 1 to 2. In the layer-by-layer extraction, the thickness of each layer is the thickness of a refined mesh cell. For example... Figure 5 As shown, the thickness range of the base plate and ribs with residual stress obtained from the main model simulation is 1.5mm after milling of the base plate and ribs, while the thickness range of the base plate and ribs with residual stress obtained from the sub-model simulation is 0.5mm away from the milled surface.

[0120] Step five, specifically: The biaxial residual stress and surface residual stress of each layer of the base plate and ribs are added together to obtain the overall residual stress in the rolling direction and perpendicular to the rolling direction of the corresponding layers of the reconstructed milled ribbed base plate and ribs: σ jmx (z)=σ jbx (z)+σ jsx (z),σ jmy (z)=σ jby (z)+σ jsy (z), j = 1 to 2.

[0121] Step six, as follows Figure 6 As shown, specifically:

[0122] First, using the SIGINI subroutine in ABAQUS, the overall residual stress σ of the milled ribbed base plate and ribs in step five is calculated. jmx (z) and σ jmy (z) The reconstructed values ​​were imported into the CAF model. The element type was S4R shell element, and the shell element thickness was 1.5 mm. The number of thickness integration points for the aluminum alloy component's base plate and stiffeners was defined as 31 each, with a distance of approximately 0.048 mm between each integration point. This ensured that the distribution trend of the overall residual stress in the simulation could be accurately incorporated into the shell element. An initial state model of the CAF model with post-milling component deformation and post-milling equilibrium residual stress was obtained.

[0123] Step seven, as Figure 6As shown, based on the above CAF initial state model with component deformation after milling and residual stress after milling equilibrium, the creep aging process simulation is performed using the CREEP subroutine in ABAQUS secondary development to predict the deformation and performance evolution of creep-aged formed parts; and data on springback and performance evolution of creep-aged formed parts are obtained.

[0124] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A simulation method for the entire milling-creep aging forming process considering residual stress field, characterized in that, The specific steps include: The initial residual stress of the aluminum alloy block was tested to obtain the initial residual stress test value of the aluminum alloy block; Aluminum alloy blocks were milled, and the properties of the blocks during the milling process were tested. x , y and z Three-axis milling force; A milling model for aluminum alloy blocks was established, and a graded milling simulation was performed on the aluminum alloy blocks. The initial residual stress test values ​​and milling forces obtained were then imported into the graded milling simulation process to obtain the graded simulation prediction values ​​of residual stress on the surface and throughout the entire thickness of the component after milling. When establishing the milling model for aluminum alloy blocks... A full-size initial aluminum alloy block milling simulation master model was established, and the full-size initial aluminum alloy block milling process was simulated using the birth and death element method; the volume residual stress in the rolling direction and perpendicular to the rolling direction in the simulation master model of the milled component after milling and before fixture release was obtained. , Simulated distribution values; A simulation sub-model for local milling of aluminum alloy block surface was established, and a two-dimensional representative model with refined surface mesh was used to simulate the local single-pass milling process of aluminum alloy block surface; after single-pass milling, the micron-level residual stress on the surface of the milled component before fixture release in the milling simulation sub-model was obtained in the rolling direction. Simulated distribution values; extract , and The simulated distribution values ​​are used as simulation prediction values, and the surface micron-level residual stress perpendicular to the rolling direction is set. The simulated values ​​of residual stress at different stages are reconstructed to obtain the overall reconstructed residual stress values. A model of the component after milling is established, the overall residual stress reconstruction value is imported into the model of the component after milling, and the deformation simulation of the component after milling is carried out to obtain the initial state model of creep aging forming with balanced residual stress and deformation after milling. The creep aging forming process is simulated on the initial state model of creep aging forming to obtain the shape and performance prediction results of the formed part after the creep aging forming process.

2. The simulation method for the entire milling-creep aging forming process considering residual stress field as described in claim 1, characterized in that, The initial residual stress test values ​​of aluminum alloy blocks are obtained in two ways: the initial residual stress test values ​​distributed along the thickness direction of the aluminum alloy block in the rolling direction and the initial residual stress test values ​​perpendicular to the rolling direction.

3. The simulation method for the entire milling-creep aging forming process considering residual stress field according to claim 2, characterized in that, The initial residual stress test values ​​of the obtained aluminum alloy blocks are processed. The specific processing steps are as follows: The initial residual stress values ​​obtained from the fitting process for the aluminum alloy block along the rolling direction and perpendicular to the rolling direction are as follows: ， ； in, This represents the fitted value of the initial residual stress in the rolling direction of the aluminum alloy block, distributed along the thickness direction. This represents the fitted value of the initial residual stress perpendicular to the rolling direction, distributed along the thickness direction of the aluminum alloy block. z This represents the position value along the thickness direction of the aluminum alloy block. i For the number of terms, n Let the highest term of the polynomial be the degree. a i and b i is the coefficient of the term in the polynomial.

4. The simulation method for the entire milling-creep aging forming process considering residual stress field as described in claim 3, characterized in that, By summing and integrating the simulated values ​​of bulk residual stress and surface micron-level residual stress, the overall residual stress in the rolling direction and perpendicular to the rolling direction of the reconstructed milled component is obtained. , .

5. The simulation method for the entire milling-creep aging forming process considering residual stress field according to claim 4, characterized in that, A shell element component model is established after milling, and the overall residual stress reconstruction value is imported into the shell element model to realize the simulation of the transfer of overall residual stress from the volume element to the shell element.

6. The simulation method for the entire milling-creep aging forming process considering residual stress field according to claim 5, characterized in that, When establishing the full-size initial aluminum alloy block milling simulation master model and the aluminum alloy block surface local milling simulation sub-model, the initial aluminum alloy block master model and the aluminum alloy block surface local sub-model are meshed; different mesh element types are used for the two.

7. The simulation method for the entire milling-creep aging forming process considering residual stress field according to claim 1, characterized in that, The initial residual stress test values ​​of the aluminum alloy block in the rolling direction and perpendicular to the rolling direction are imported into the initial simulation master model of aluminum alloy block milling.

8. The simulation method for the entire milling-creep aging forming process considering residual stress field according to claim 1, characterized in that, The simulated distribution values ​​of volume residual stress and surface micron-level residual stress at the unit integration points perpendicular to the thickness direction of the aluminum alloy component are extracted layer by layer along the thickness direction. The simulated distribution values ​​of multiple volume residual stress and surface micron-level residual stress extracted from each layer are averaged and used as the simulated predicted values ​​of volume residual stress and surface micron-level residual stress for the corresponding layer.

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