A method for predicting springback of aluminum alloy profile roll bending considering anisotropy

Abstract

The present invention belongs to the technical field of metal plastic processing, and is specifically a method for predicting springback in roll bending of aluminum alloy profiles taking into account anisotropy. The method performs theoretical analysis based on the Mises and Hill48 yield criteria to obtain a formula for the curvature before and after springback. The roll bending data after springback compensation obtained through theoretical analysis is input into the model, and the profile equal curvature rolling analysis model is calculated. An edge line of the reconstructed profile digital model is extracted as a characteristic curve for curvature analysis. The present invention makes full use of the finite element calculation and analysis process, and uses ABAQUS to import the anisotropic parameters of the aluminum alloy into the model for numerical simulation. The theoretical analysis is verified by the simulation results, thereby achieving the purpose of reducing springback during the profile bending process.

Description

Technical Field

[0001] The present invention relates to the technical field of metal plastic processing, in particular to a method for predicting the springback of aluminum alloy profile roll bending considering anisotropy. Background Art

[0002] Roll forming is a new process and technology for sheet metal forming that saves materials, is energy-efficient, and highly efficient. It is suitable for the bending of profiles with large curvatures. The forming process is stable, efficient, and highly precise. It does not require special molds, can reduce costs, and has a high degree of flexibility. Finite element analysis is the main means of analyzing and verifying sheet metal forming processes today. With the help of finite element simulation of the profile roll bending process, the defects in the profile rolling process are analyzed, specific solutions are proposed, the rolling forming laws are derived, and the profile rolling process is simulated. Finally, the profile rolling process verification test is carried out. The use of finite element simulation methods can avoid blind trial rolling processes and minimize the number of rolling forming passes, thereby shortening the processing cycle of parts and improving the forming quality of rolled parts.

[0003] Previous methods for analyzing springback during roll bending of profiles were primarily based on the assumption of isotropy. A theoretical analysis model for roll springback was established, and the springback calculation model was used to derive the curvature required to compensate for springback. Finite element analysis software was then used to simulate the roll bending of the profiles, yielding specific springback values to verify the theoretical analysis. Further roll forming experiments were also conducted. However, the influence of the anisotropy of aluminum alloys on the forming process was not adequately considered, resulting in limited accuracy in the roll-formed profiles after springback compensation. Therefore, the anisotropy of aluminum alloys should be fully accounted for in roll bending. The Hill 48 yield criterion was introduced into the theoretical analysis model for roll springback, the corresponding anisotropic parameters were input into the finite element model, and the simulated springback values were compared with those under isotropy. This significantly reduced springback in roll-bent profiles, improved roll forming accuracy, and ultimately reduced costs and increased efficiency. Summary of the Invention

[0004] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid blurring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0005] In view of the problems existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to propose a method for predicting springback in roll bending of aluminum alloy profiles that takes into account anisotropy, addressing the large errors and low precision of existing roll bending processes. This method provides a theoretical analysis method with low error and high precision for springback compensation during roll bending. This method fully considers the influence of the anisotropy of aluminum alloys on springback in the theoretical analysis of roll bending. The theoretical formula is derived using the Mises and Hill48 yield criteria, taking into account both the tangential and thickness stresses of the profile. The distances from the elastic and plastic transition points to the neutral layer on both the inner and outer sides during bending are calculated based on the two yield criteria. The bending moments of the elastic and plastic parts during bending are then derived based on the stress distribution and geometric relationships of the profile cross section. This allows the calculation of the bending radius after springback compensation, as determined by theoretical analysis. A finite element analysis model for roll bending is then established based on the Mises and Hill48 yield criteria. The left and right roller displacements corresponding to the springback-compensated bending radius obtained through theoretical analysis are then input into the model for calculation. The resulting mesh model is then reconstructed to obtain a reconstructed digital model of the profile. Through the numerical simulation results based on these two different yield criteria, a theoretical analysis method considering anisotropy can be obtained, which has a more obvious effect on reducing the springback during the roll bending process of aluminum alloy.

[0007] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0008] A method for predicting springback of aluminum alloy profile roll bending considering anisotropy comprises the following steps:

[0009] Step 1: Analyze the kinematic relationship and geometric structure of the four-axis roll bending machine, analyze the principle of anisotropy affecting springback during the roll bending of aluminum alloy profiles, and prepare for a theoretical analysis of the bending process of the profiles;

[0010] Step 2: Through mechanical analysis of the roll bending process, the tangential stress and thickness stress of the profile during the roll bending process are calculated, and the two are respectively substituted into the Mises and Hill48 yield criterion formulas under the plane stress state. The distance from the elastic and plastic transition points on the inner and outer sides to the neutral layer during the bending process is calculated using the two yield criteria;

[0011] Step 3: Based on the stress distribution of the profile section and the geometric relationship of the profile section, the bending moment of the elastic part and the bending moment of the plastic part, as well as the total bending moment of the bending process, can be obtained respectively; from this, the bending radius after springback compensation obtained through theoretical analysis can be calculated;

[0012] Step 4: Based on the Mises and Hill48 yield criteria, respectively, a constant curvature roll bending analysis model for profiles is established. The left and right roller displacements corresponding to the bending radius after springback compensation obtained through theoretical analysis are input into the model. Meshing is performed, contact conditions are defined, and the constant curvature roll bending analysis model for profiles is calculated. The calculated constant curvature mesh model of the profile is reconstructed to obtain the reconstructed profile digital model.

[0013] Step 5: Extract an edge line of the digital model of the profile to be processed as a characteristic curve, perform curvature radius analysis, and obtain the curvature radius after compensating for springback based on the profile constant curvature rolling bending simulation under two yield criteria;

[0014] Step 6: Compare the curvature radius of the profile after unloading and springback simulated under the guidance of the two yield criterion theoretical analyses with the target forming radius to obtain the accuracy of the two theoretical springback compensation methods.

[0015] As a preferred solution of the method for predicting the springback of aluminum alloy profile roll bending considering anisotropy described in the present invention, the four-axis roll bending machine in step 1 includes an upper roll, a lower roll, a left roll, and a right roll.

[0016] Compared with the prior art, the beneficial effects of the present invention are: it adopts a roll bending springback prediction method for aluminum alloy profiles that fully considers anisotropy, which can effectively reduce the springback that is common in the roll bending process of the profile and improve the processing accuracy of the profile. The traditional theoretical analysis method based on isotropy is too idealistic, and some influencing factors are not taken into account, which is different from the actual situation. In the theoretical analysis of roll bending forming, the stresses in the tangential and thickness directions of the profile are taken into account, and the Mises and Hill48 yield criteria are used to derive formulas respectively, and the bending radius that compensates for springback under the two different yield criteria can be obtained respectively. At the same time, a roll bending finite element analysis model is established based on the Mises and Hill48 yield criteria, and the rebound compensation curvature radius results obtained through theoretical analysis are verified. The springback can be analyzed under conditions that are closer to reality, so that the formed profile is closer to the ideal shape, saving costs and improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort. Among them:

[0018] Figure 1 This is a schematic diagram of the digital model of the U-profile of the present invention;

[0019] Figure 2 A geometric diagram of the cross section of the profile of the present invention;

[0020] Figure 3 It is a schematic diagram of the four-roller bending digital module of the present invention. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] Next, the present invention is described in detail with reference to schematic diagrams. For ease of illustration, cross-sectional views of device structures may be partially enlarged and not to scale when describing the embodiments of the present invention. Furthermore, the schematic diagrams are merely illustrative and should not limit the scope of protection of the present invention. Furthermore, in actual production, three-dimensional dimensions, including length, width, and depth, should be included.

[0024] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] The present invention provides the following technical solutions: a method for predicting springback during roll bending of aluminum alloy profiles taking into account anisotropy, which can effectively reduce the springback commonly found in the profile during roll bending and improve the processing accuracy of the profile;

[0026] The specific steps include:

[0027] Step 1: Analyze the kinematic relationship and geometric structure of the four-axis roll bending machine, which includes upper, lower, left, and right rolls; analyze the principle of anisotropy affecting springback during the roll bending of aluminum alloy profiles, and prepare for a theoretical analysis of the profile bending process;

[0028] Step 2: Calculate the tangential stress and thickness stress of the profile during roll bending through mechanical analysis. Substitute these two stresses into the Mises and Hill48 yield criterion formulas under plane stress, and use the two yield criteria to calculate the distance from the elastic and plastic transition points to the neutral layer on both the inner and outer sides during bending.

[0029] Step 3: Based on the stress distribution and geometric relationship of the profile cross section, the bending moment of the elastic part and the bending moment of the plastic part, as well as the total bending moment of the bending process, can be obtained respectively. From this, the bending radius after springback compensation obtained through theoretical analysis can be calculated;

[0030] Step 4: Based on the Mises and Hill48 yield criteria, respectively, a profile constant curvature roll bending analysis model is established. The left and right roller displacements corresponding to the bending radius after springback compensation obtained through theoretical analysis are input into the model, and mesh division and contact conditions are defined. The profile constant curvature roll bending analysis model is calculated; the calculated profile constant curvature mesh model is reconstructed to obtain the reconstructed profile digital model;

[0031] Step 5: Extract an edge line of the digital model of the profile to be processed as a characteristic curve, perform curvature radius analysis, and obtain the curvature radius after compensating for springback obtained by the profile constant curvature rolling bending simulation based on two yield criteria;

[0032] Step 6: Compare the curvature radius of the profile after unloading and springback simulated under the guidance of the two yield criterion theoretical analyses with the target forming radius to determine the accuracy of the two theoretical springback compensation methods.

[0033] Example 1

[0034] A method for predicting springback of aluminum alloy profile roll bending considering anisotropy is proposed, which takes the numerical model of U-profile as the research object and includes the following steps:

[0035] Step 1: Figure 1 Taking the U-profile as an example, we will conduct a theoretical analysis of the bending process of the profile based on the Mises and Hill48 yield criteria respectively.

[0036] Step 2: Calculate the tangential stress and through-thickness stress of the profile during roll bending through mechanical analysis. Substitute these two into the Mises and Hill48 yield criterion formulas under plane stress, and calculate the distance from the elastic and plastic transition points to the neutral layer on both sides of the bending process using the two yield criteria. The formulas for tangential stress and through-thickness stress are as follows:

[0037]

[0038]

[0039] Where E is the elastic modulus, R is the radius of curvature of the neutral layer before rebound, d is the distance from the yield surface to the neutral layer during bending, and r is the curvature of the neutral layer before rebound. a and r b are the inner and outer surface radii of the profile when it is bent, r y1 and r y2are the inner and outer yield surface radii when the profile is bent;

[0040] Substituting the tangential and thickness stress formulas into the Mises and Hill48 yield criteria under plane stress, we can calculate the distance from the elastic and plastic transition points on both sides of the bending process to the neutral layer under the two yield criteria. The Mises and Hill48 yield criteria under plane stress are as follows:

[0041]

[0042]

[0043] Among them, F, G, H, and N can be calculated based on the r values obtained from tensile tests or simulations along the 0, 45, and 90° directions:

[0044]

[0045]

[0046]

[0047]

[0048] r 11 =r 13 =r 23 =1

[0049]

[0050]

[0051]

[0052] Step 3: Based on the stress distribution of the U-profile section and the geometric relationship of the profile section, the bending moment of the elastic part and the bending moment of the plastic part, as well as the total bending moment during the bending process, can be obtained respectively. From this, the bending radius after springback compensation obtained through theoretical analysis can be calculated. The bending moment formulas of the elastic part and the plastic part during the profile roll bending process are:

[0053]

[0054]

[0055] Where h1 and h2 are the distances from the inner and outer surfaces of the profile to the neutral layer during bending, respectively; d1 and d2 are the distances from the elastic and plastic transition points on the inner and outer sides to the neutral layer during bending under the two yield criteria, respectively.

[0056] Substituting the obtained bending moment formula into the formula for calculating the springback compensation radius, the bending radius after springback compensation obtained through theoretical analysis can be obtained. The springback compensation formula is as follows:

[0057]

[0058] Where ΔK is the curvature difference of the neutral layer of the profile before and after rebound, R T is the radius of curvature of the neutral layer before rebound, R T * is the radius of curvature of the neutral layer after rebound, I is the moment of inertia of the profile section in the coordinate system;

[0059] The bending radius after springback compensation can be expressed as:

[0060]

[0061] Step 4: Based on Mises and Hill48 yield criteria, Figure 1 Taking the U-profile as an example, a U-profile roll bending analysis model is established. The left and right roller displacements corresponding to the bending radius after springback compensation obtained through theoretical analysis are input into the model, and mesh division and contact conditions are defined. The profile constant curvature rolling analysis model is calculated; the calculated profile constant curvature mesh model is reconstructed to obtain the reconstructed profile digital model;

[0062] Step 5: Extract an edge line of the digital model of the profile to be processed as a characteristic curve, perform curvature radius analysis, and obtain the curvature radius after compensating for springback obtained by the profile constant curvature rolling bending simulation based on two yield criteria;

[0063] Step 6: Compare the curvature radius of the profile after unloading and springback simulated under the guidance of the two yield criterion theoretical analyses with the target forming radius to obtain the accuracy of the two theoretical springback compensation methods.

[0064]

[0065] Although the present invention has been described above with reference to embodiments, various modifications may be made thereto and equivalent components may be substituted without departing from the scope of the present invention. In particular, as long as there are no structural conflicts, the various features of the embodiments disclosed herein may be combined with each other in any manner, and the omission of an exhaustive description of such combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for predicting springback of aluminum alloy profile roll bending considering anisotropy, characterized by: The steps include: Step 1: Analyze the kinematic relationship and geometric structure of the four-axis roll bending machine, analyze the principle of anisotropy affecting springback during the roll bending of aluminum alloy profiles, and prepare for a theoretical analysis of the bending process of the profiles; Step 2: Through mechanical analysis of the roll bending process, the tangential stress and thickness stress of the profile during the roll bending process are calculated, and the two are respectively substituted into the Mises and Hill48 yield criterion formulas under the plane stress state. The distance from the elastic and plastic transition points on the inner and outer sides to the neutral layer during the bending process is calculated using the two yield criteria; Step 3: Based on the stress distribution of the profile section and the geometric relationship of the profile section, the bending moment of the elastic part and the bending moment of the plastic part, as well as the total bending moment of the bending process, can be obtained respectively; From this, the bending radius after springback compensation obtained through theoretical analysis can be calculated; Step 4: Based on the Mises and Hill48 yield criteria, respectively, a constant curvature roll bending analysis model for profiles is established. The left and right roller displacements corresponding to the bending radius after springback compensation obtained through theoretical analysis are input into the model. Meshing is performed, contact conditions are defined, and the constant curvature roll bending analysis model for profiles is calculated. The calculated constant curvature mesh model of the profile is reconstructed to obtain the reconstructed profile digital model. Step 5: Extract an edge line of the digital model of the profile to be processed as a characteristic curve, perform curvature radius analysis, and obtain the curvature radius after compensating for springback based on the profile constant curvature rolling bending simulation under two yield criteria; Step 6: Compare the curvature radius of the profile after unloading and springback simulated under the guidance of the two yield criterion theoretical analyses with the target forming radius to obtain the accuracy of the two theoretical springback compensation methods.

2. The method for predicting springback of aluminum alloy profile roll bending considering anisotropy according to claim 1, characterized in that: The four-axis roller bending machine in step 1 includes an upper roller, a lower roller, a left roller, and a right roller.

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