Modeling method for thermal deformation of steel-aluminum mixed covering part for automobile

Abstract

The invention discloses a modeling method for thermal deformation of a steel-aluminum mixed covering part for an automobile, and the method comprises the following steps: S1, simulating the modeling simulation of the coating and baking process of the steel-aluminum mixed covering part according to a real working condition, and building a covering part model; s2, setting key parameters of a steel plate and an aluminum plate of the covering part model at different temperatures; s3, stamping simulation software LS-DYNA is used for stamping simulation modeling; s4, comparing the simulation model with the actually measured temperature change of the steel and aluminum, and simplifying the baking temperature into a linear relation; s5, analyzing the thermal deformation of the steel-aluminum mixed covering part; and S6, carrying out sensitivity analysis and optimization on each key parameter according to each key point in the step S5 to obtain actual model precision. The invention establishes a set of modeling reference and method for reliably representing the thermal deformation of the steel-aluminum mixed covering part for the automobile.

Description

Technical Field

[0001] The invention relates to forming technology, and more specifically to a modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile. Background Art

[0002] At present, with the further development of the automobile industry, energy conservation and safety have become the key directions of future development. Studies have shown that for every 10% decrease in automobile mass, its fuel economy will increase by 6-8% and emissions will decrease by 4%. Lightweighting is one of the most direct and effective means to achieve automobile energy conservation and emission reduction. Automobile aluminum plates have the advantages of low density, high specific strength, good pedestrian collision safety, and high recycling efficiency. In recent years, the use of aluminum instead of steel has achieved significant weight reduction effects, but the cost increase is also obvious. The steel-aluminum hybrid body structure can well combine the advantages of both to achieve lightweight and cost optimization.

[0003] When connecting steel and aluminum, it is necessary to consider the differences in thermal expansion coefficients and elastic moduli between steel and aluminum, as well as the large differences in heat dissipation rates. This is especially true for the use of aluminum in automobiles. The baking temperature of the steel-aluminum riveted parts in the painting process is high, and the strength and connection methods of the riveted parts are different during the baking and heating process. During the painting process, due to the different thermal expansion coefficients of steel and aluminum, the thermal expansion coefficient of aluminum is about twice that of steel under the same conditions. There is a risk of flexural deformation caused by the difference in thermal expansion of different parts under the condition of fixed constraints, which may cause quality defects and affect the delivery quality. In order to consider the impact of thermal deformation of riveted parts of painted steel-aluminum parts, it is necessary to establish an effective thermal deformation prediction model for steel-aluminum hybrid structures in combination with experiments, so as to provide an effective computational simulation modeling benchmark and method for further analysis of the thermal deformation of specific steel-aluminum hybrid parts.

[0004] Audi has also conducted extensive research on thermal deformation of steel-aluminum hybrid structures. Its engineer J.

[0005] Regensburger used Audi TT as a case study to study the effect of the creep aging behavior of aluminum alloy on the thermal deformation of the steel-aluminum body structure during baking. The focus was on the creep aging mechanism of aluminum alloy, and the overall modeling and simulation analysis of the thermal expansion properties of steel and aluminum materials was not performed.

[0006] Beihang University proposed a superplastic forming die design method based on finite element technology that considers thermal expansion (patent application number 201510778965.8, publication number CN105335568A). This technology uses different material thermal expansion properties in different simulation stages to solve the problem of part forming errors caused by the difference in thermal expansion properties between mold materials and part materials. This method focuses on thermal expansion forming compensation and mold repair of superplastic forming dies.

[0007] Zhuolang Textile Machinery Co., Ltd. has proposed an aluminum alloy movable cover plate with anti-thermal deformation function (patent publication number CN113802220A). This technology proposes to install a steel isothermal balance part with contact connection in the aluminum alloy cover plate frame to solve the problem of arc deformation of the structural bow bridge caused by the different thermal expansion characteristics of steel and aluminum.

[0008] Chongqing Changan Automobile proposed a front cover paint flip deformation prediction method, device and storage medium (patent application number is 202111438888.3, ​​publication number is CN1142154240A). This technology proposes loading constraints and calculations on the simulation cover model based on the electrophoretic process parameters of the steel front cover painting and the tooling support positioning parameters. The analysis software used is different from this article. The analysis method does not consider the thermal expansion characteristics and adhesion properties of steel and aluminum dissimilar materials.

[0009] The steel-aluminum modeling or design methods described in the above public documents have not been able to establish an effective method for characterizing the thermal deformation modeling of steel-aluminum hybrid cover parts. Summary of the invention

[0010] In view of the defects existing in the prior art, the purpose of the present invention is to provide a modeling method for thermal deformation of steel-aluminum hybrid covering parts for automobiles, and to establish a set of modeling benchmarks and methods for reliably characterizing the thermal deformation of steel-aluminum hybrid covering parts for automobiles.

[0011] To achieve the above object, the present invention adopts the following technical solution:

[0012] A modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile comprises the following steps:

[0013] S1. It is planned to simulate the painting and baking process of steel-aluminum hybrid cover parts under real working conditions and establish a cover part model;

[0014] S2. Setting key parameters of the steel plate and the aluminum plate of the cover model at different temperatures;

[0015] S3, use stamping simulation software LS-DYNA to perform stamping simulation modeling;

[0016] S4, comparing the simulated model with the measured temperature changes of steel and aluminum, and simplifying the baking temperature into a linear relationship;

[0017] S5. Analyze the thermal deformation of steel-aluminum hybrid cover parts;

[0018] S6. Perform sensitivity analysis and optimization on each key parameter according to the key points of step S5 to obtain the actual model accuracy.

[0019] Preferably, in step S2, the key parameters of the steel plate and the aluminum plate at different temperatures are elastic modulus, Poisson's ratio, yield strength, plastic hardening stiffness and thermal expansion coefficient;

[0020] The values ​​of key parameters at different temperatures are within the temperature range ΔT.

[0021] Preferably, in step S2, the temperature interval ΔT ranges from 30°C to 60°C.

[0022] Preferably, the specific steps of using stamping simulation software LS-DYNA to perform stamping simulation modeling in step S3 are as follows:

[0023] S31, selecting the cover model;

[0024] S32, meshing the cover model;

[0025] S33, boundary condition constraints of the cover model;

[0026] S34, using the implicit algorithm of thin shell elements for calculation;

[0027] S35. The riveting, spot welding, structural adhesive and shock-absorbing adhesive parts on the cover model are simulated by using the Tied contact connection method in the LS-DYNA simulation, and the remaining parts are simulated by the surface-to-surface automatic contact method.

[0028] Preferably, the cover model is a full-size model.

[0029] Preferably, in step S32, when processing the mesh of the cover model, the geometry is directly generated by the stamped mesh and then the mesh is divided; when dividing the mesh, the mesh is subdivided by 1mm to 2mm at key locations, and the mesh size is increased by 4mm to 8mm at other locations.

[0030] Preferably, in step S33, the cover component model is fixed to the external structural component by bolt hinges, and one vertical degree of freedom is constrained at the hinge position, and all translational degrees of freedom are constrained at one of the hinge positions.

[0031] Preferably, in step S5, after the electrophoresis process of the cover model is completed, the final stress-strain in the analysis result is transferred to the second step analysis and the properties of the adhesive are modified and converted into the properties and temperature curve of the cured adhesive.

[0032] The present invention provides a modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile, which has the following advantages:

[0033] Beneficial effects:

[0034] 1) The material model established by the present invention can reflect the different stamping forming characteristic properties of steel and aluminum materials by establishing a cover model, and can truly reflect the deformation state of the material through grid mapping and stress-strain mapping;

[0035] 2) Parameter acquisition and model establishment of thermal expansion, deformation morphology, connection characteristics, and adhesive thermal curing parameters of key steel and aluminum materials to ensure the accuracy and reliability of the simulation model;

[0036] 3) The selection of the cover model, meshing, boundary condition constraints, algorithm selection, optimization and setting of contact conditions in the model fully consider the actual working conditions and calculation accuracy and efficiency to form a set of effective thermal deformation modeling methods for characterizing steel-aluminum hybrid covers. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the flow chart of the modeling method of the present invention;

[0038] Figure 2 is a schematic flow chart of step S5 in the modeling method of the present invention;

[0039] Figure 3 Schematic diagram of a cover model in an embodiment of the modeling method of the present invention, (a) is the inner side surface, (b) is the outer side surface;

[0040] Figure 4 Schematic diagram of the true stress-strain curve of aluminum material under different temperature gradients in the embodiment of the modeling method of the present invention;

[0041] Figure 5 is a schematic diagram of a Tied contact area in an embodiment of the modeling method of the present invention;

[0042] Figure 6 Schematic diagram of baking temperature curve in the embodiment of the modeling method of the present invention. DETAILED DESCRIPTION

[0043] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0044] Combination Figure 1 As shown, the present invention provides a modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile, comprising the following steps:

[0045] S1. For typical automobile steel-aluminum hybrid covers, it is planned to simulate the painting and baking process of steel-aluminum hybrid covers under real working conditions and establish a cover model; through actual measurement and manual reference, ensure that the different elastic modulus, tensile properties and thermal expansion coefficients of steel and aluminum plates that change with temperature are truly and accurately imported into the simulation modeling model;

[0046] S2. Since the yield strength of steel is relatively high, in order to improve the calculation efficiency, it is necessary to set the elastic modulus, Poisson's ratio, yield strength, plastic hardening stiffness and thermal expansion coefficient of steel at different temperatures; the yield strength of aluminum plate is relatively low, so it is necessary to set the elastic modulus, Poisson's ratio, plastic stress-strain curve and thermal expansion coefficient of aluminum plate at different temperatures, and the values ​​of each parameter are taken in the temperature range △T within the range of 30℃~60℃;

[0047] S3. Use stamping simulation software LS-DYNA to perform stamping simulation modeling. The stamping deformation morphology, baking temperature process, riveting characteristics, and adhesive characteristics are the key input parameters for simulation modeling accuracy. The specific steps are as follows:

[0048] S31. Selection of cover model: full-size model is used. Considering that the residual stress and strain after stamping springback have a significant impact on the results, the stress and strain generated by simulating real stamping and springback need to be mapped to the analysis model before thermal simulation;

[0049] S32. Meshing of the cover model: When processing the mesh of the cover model, the geometry is directly generated through the stamping mesh, and then the mesh is divided; when dividing the mesh, the accuracy of the model and the calculation time must be considered, and the method is to subdivide the mesh by 1mm to 2mm at key locations and increase the mesh size by 4mm to 8mm at other locations;

[0050] S33, boundary condition constraints of the cover model: the cover model is fixed to the external structural member by bolt hinges, and one vertical degree of freedom is constrained at the hinge position, and all translational degrees of freedom are constrained at one of the hinge positions;

[0051] S34. The implicit algorithm of thin shell element is used for calculation. The deformation analysis of thermal-solid coupling is easy to converge, which can ensure the calculation accuracy and have an advantage in calculation time.

[0052] In the S35 and door models, the outer contour of the steel-aluminum hybrid cover is constructed by hemming, and the outer edge of the inner panel of the cover is embedded in the groove formed by the inward folding of the outer panel of the cover. Riveting, spot welding, structural adhesive, and shock-absorbing adhesive are distributed at the joints between the inner and outer panels of the cover and the reinforcement structure. The rivets, spot welding, structural adhesive, and shock-absorbing adhesive parts on the cover model are simulated by the Tied contact connection method in the LS-DYNA simulation, and the remaining parts are simulated by the automatic surface-to-surface contact method without any excessive constraints;

[0053] S4. According to the real baking thermal deformation characteristics, the simulation model and the measured temperature changes of steel and aluminum are compared. The influence of heat convection and heat conduction is very small and can be ignored. Only thermal expansion needs to be considered as the main influencing factor, and the baking temperature is simplified to a linear relationship to improve the calculation efficiency.

[0054] S5. In the actual baking process, the curing of the adhesive needs to be considered, so the thermal deformation analysis process of the cover includes two temperature loading processes: electrophoretic baking process and other baking processes. The curing of the adhesive is completed during the electrophoretic baking process. Consider that the curing process of the adhesive has a great influence on the final deformation of the door. The change curve of the structural performance of the adhesive during the baking process needs to be considered. At the same time, for the edge glue, structural glue, and shock-absorbing glue involved in the cover, the material properties before and after curing that meet the characteristics of the material itself need to be selected;

[0055] Considering the adhesive properties, the thermal deformation of the car door is decomposed into two processes: electrophoresis (curing) process and other baking process. After the electrophoresis process is completed, the final stress and strain in the analysis results are transferred to the second step analysis and the properties of the adhesive are modified and converted into the properties and temperature curve of the cured adhesive, such as Figure 2 As shown;

[0056] S6. Perform sensitivity analysis and optimization on each key parameter according to the key points of step S5 to obtain the actual model accuracy with high computational efficiency and easy convergence.

[0057] Example

[0058] The present embodiment provides a modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile, comprising the following steps:

[0059] S1. Select typical automotive steel DC56D+Z and aluminum 6016; for typical automotive steel-aluminum hybrid doors; plan to model and simulate the painting and baking process of steel-aluminum connecting parts under different working conditions, establish a door model, and characterize the hot forming state of the steel-aluminum hybrid cover under the simulation of the real painting and baking process 3C3B (3 coatings 3 baking).

[0060] Through experiments and manuals, elastic modulus, Poisson's ratio, thermal expansion coefficient and plastic stress-strain curves at different temperatures are obtained, and accurately imported into the simulation modeling model, such as Figure 3 shown.

[0061] S2. As shown in Tables 1 and 2 below, the elastic modulus and thermal expansion coefficient range from room temperature to coating baking, and the temperature difference in each temperature range is 50°C. The plastic stress-strain curves at different temperatures range from room temperature T = 20°C to coating baking, and the temperature range of each curve is △T = 60°C.

[0062] Table 1 Comparison of thermal expansion coefficients of steel and aluminum

[0063]

[0064] Table 2 Comparison of thermal expansion coefficient, elastic modulus and Poisson's ratio of steel and aluminum

[0065]

[0066] Metal materials have different mechanical properties under different temperature conditions. In order to accurately predict the thermal deformation of steel-aluminum hybrid structures, it is necessary to select a suitable material model for simulation. It is necessary to set the elastic modulus, Poisson's ratio, yield strength, plastic hardening stiffness and thermal expansion coefficient of steel at different temperatures; the yield strength of aluminum plate is relatively low, so it is necessary to set the elastic modulus, Poisson's ratio, plastic stress-strain curve and thermal expansion coefficient of aluminum plate at different temperatures, such as Figure 4 shown.

[0067] The measured parameters of deformation morphology, adhesive fastening method and preload, and baking temperature system are the key input parameters for simulation modeling accuracy.

[0068] S3, use stamping simulation software LS-DYNA to perform stamping simulation modeling;

[0069] S31. Selection of analysis model: A full-size model is used. Considering that the residual stress and strain after stamping springback have a significant impact on the results, the stress and strain generated by simulating real stamping and springback need to be mapped to the analysis model before thermal simulation. The dynain file of aluminum plate stamping springback analysis is imported into the hemisphere model through Hypermesh. The dynain file contains the mesh information and stress and strain information after stamping springback analysis.

[0070] S32. Mesh division: When processing the mesh of the cover model, the geometry is directly generated through the stamping mesh, and then the mesh is divided. The linear static simulation mesh size has a great influence on the results, and for the sake of computational efficiency, the mesh size of the model needs to be optimized. When dividing the mesh, the accuracy of the model and the calculation time must be taken into account. The method is to subdivide the mesh at key locations and increase the mesh size at other unimportant locations. In this example, the door model uses a 5mm mesh, and the bolt hole position is about 1mm; 1.5mm is used at locations with large stamping deformation and hemming because the stress and strain are large, and 5mm is used at other locations.

[0071] S33. Constraints of boundary conditions: The integral opening and closing cover is fixed to the fixed external structural member by bolt hinges. One vertical degree of freedom is constrained at the hinge position, and all translational degrees of freedom are constrained on one of the hinges.

[0072] S34. The calculation adopts the implicit algorithm of thin shell elements. The steel plate and aluminum plate are shell elements, the gasket is a shell element, and the adhesive bolt is a beam element. The implicit algorithm is easy to converge for the deformation analysis of thermal-solid coupling, which can ensure the calculation accuracy and have an advantage in calculation time.

[0073] In the S35 door model, the outer contour of the steel-aluminum hybrid cover is hemmed, and the outer edge of the inner panel of the cover is embedded in the groove formed by the inward folding of the outer panel of the cover. Riveting, spot welding, structural adhesive, and shock-absorbing adhesive are distributed at the connection between the inner and outer panels of the cover and the reinforcement structure. In the LS-DYNA simulation, the Tied contact connection method is used for simulation. The remaining parts are selected in the automatic contact method without any excessive constraints, such as Figure 5 shown.

[0074] According to the actual baking thermal deformation characteristics, the temperature change during the baking process takes place over a long period of time without drastic energy changes. Considering heat conduction and heat convection, it is necessary to input an accurate temperature curve, which takes a longer analysis time. After analysis, it is found that the effects of heat convection and heat conduction are very small and can be ignored. Only thermal expansion needs to be considered as the main influencing factor. The baking temperature can be simplified to the second linear loading mode. Because heat conduction and heat radiation do not need to be considered, the temperature loading curve only needs each peak temperature, which can greatly reduce the calculation time.

[0075] Correspondingly, in LS-DYNA, the loading curve of the temperature load is as follows: Figure 6 As shown, there are 4 fixed cell peaks (180℃, 170℃, 90℃ and 90℃) to reflect the actual coating process. Among them, due to the use of implicit calculation, the total time of temperature load (4.00s) does not mean that the actual processing process is only 4 seconds, but only reflects 4 temperature change stages of equal length, which are solved and converged in the implicit calculation.

[0076] S5. As shown in Table 2 below, during the hot forming process of the car door, the mechanical properties of different materials, especially various viscose materials, vary greatly at different temperatures. For viscose materials, there are mainly two stages. The first stage is the electrophoresis baking stage, which also includes the curing process of the viscose; the second stage is other baking processes, including the midcoat and topcoat processes.

[0077] Table 2 Temperature performance of different adhesives for car doors

[0078] Adhesive Type Before curing After curing (10℃~100℃) After curing (100℃~200℃) Vibration Damping Rubber <![CDATA[1×10 -5 MPa]]> 0.28MPa unchanged <![CDATA[1×10 -3 MPa]]> Structural adhesive <![CDATA[1×10 -5 MPa]]> 1500MPa~10MPa linear 10MPa constant Edge glue <![CDATA[1×10 -5 MPa]]> 1500MPa~10MPa linear 10MPa constant

[0079] In the actual baking process, the curing of the adhesive needs to be considered. Considering the adhesive properties, the thermal deformation of the car door is decomposed into two processes: electrophoresis (curing) process and other baking process. After the electrophoresis process, the final stress and strain in the analysis results are transferred to the second step of analysis and the properties of the adhesive are modified and converted into the properties and temperature curve of the cured adhesive.

[0080] The modeling parameters are subjected to sensitivity analysis and optimization according to the above points, and the actual model accuracy is relatively consistent with the actual situation. The thermal deformation CAE model of steel-aluminum hybrid cover parts established by the present invention has high reliability, efficiency and practicality. Subsequently, this can be used as a modeling benchmark to carry out thermal simulation modeling and analysis on specific automotive steel-aluminum hybrid cover parts.

[0081] This patent proposes a thermal deformation modeling method for steel-aluminum hybrid covers for automobiles. It combines experiments to fully acquire models of thermal expansion, deformation morphology, connection characteristics, and adhesive thermal curing parameters of key materials, and uses the mainstream thermal-mechanical coupling simulation platform LS-DYNA for stamping simulation modeling and optimization. It establishes a set of reliable and effective modeling benchmarks and methods for characterizing the thermal deformation of steel-aluminum hybrid covers for automobiles.

[0082] The modeling method for thermal deformation of steel-aluminum hybrid cover parts for automobiles proposed in the present invention is universal and practical. It can quickly analyze various sensitivity parameter indicators in design practice to provide a reliable and fast analysis model, and provide pre-production analysis and verification for the structure and process design of cover parts and the reliability of the connection of dissimilar materials.

[0083] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile, characterized in that: The following steps are involved: S1. It is planned to simulate the painting and baking process of steel-aluminum hybrid cover parts under real working conditions and establish a cover part model; S2. Setting key parameters of the steel plate and the aluminum plate of the cover model at different temperatures; S3, use stamping simulation software LS-DYNA to perform stamping simulation modeling; S4, comparing the simulated model with the measured temperature changes of steel and aluminum, and simplifying the baking temperature into a linear relationship; S5. Analyze the thermal deformation of steel-aluminum hybrid cover parts; S6. Perform sensitivity analysis and optimization on each key parameter according to the key points of step S5 to obtain the actual model accuracy.

2. The modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile according to claim 1, characterized in that: In step S2, the key parameters of the steel plate and the aluminum plate at different temperatures are elastic modulus, Poisson's ratio, yield strength, plastic hardening stiffness and thermal expansion coefficient. The values ​​of key parameters at different temperatures are within the temperature range ΔT.

3. The modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile according to claim 2, characterized in that: In step S2, the temperature interval ΔT ranges from 30°C to 60°C.

4. The modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile according to claim 1, characterized in that: The specific steps of using the stamping simulation software LS-DYNA to perform stamping simulation modeling in step S3 are as follows: S31, selecting the cover model; S32, meshing the cover model; S33, boundary condition constraints of the cover model; S34, using the implicit algorithm of thin shell elements for calculation; S35. The riveting, spot welding, structural adhesive and shock-absorbing adhesive parts on the cover model are simulated using the Tied contact connection method in the LS-DYNA simulation, and the remaining parts are simulated using the surface-to-surface automatic contact method.

5. The modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile according to claim 4, characterized in that: The cover model adopts a full-size model.

6. The modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile according to claim 4, characterized in that: In the step S32, when processing the mesh of the cover model, the geometry is directly generated by the stamping mesh and then the mesh is divided; when dividing the mesh, the mesh is subdivided by 1mm to 2mm at key locations, and the mesh size is increased by 4mm to 8mm at other locations.

7. The modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile according to claim 4, characterized in that: In the step S33, the cover component model is fixed to the external structural component by bolt hinges, and one vertical degree of freedom is constrained at the hinge position, and all translational degrees of freedom are constrained at one of the hinge positions.

8. The modeling method for thermal deformation of a steel-aluminum hybrid cover for an automobile according to claim 1, characterized in that: In the step S5, after the electrophoresis process of the cover model is completed, the final stress and strain in the analysis result is transferred to the second step of analysis and the properties of the adhesive are modified and converted into the properties and temperature curve of the cured adhesive.

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