Introduction
Structural optimization design refers to the process of optimizing the shape, size, and materials of engineering structures based on specific goals and constraints through the use of computer technology and numerical simulation methods. The goal is to maximize the lightweight and improve the relevant performance indicators of the structure while meeting design requirements. Structural optimization has derived different optimization techniques such as topology optimization, dimensional optimization, shape optimization, and shape optimization based on the needs of different design stages.
After optimizing the target, the optimization direction was determined to be an integrated die-casting subframe. The integrated die-casting subframe has high strength, quality, and durability in terms of structure and process It has the advantages of light weight, few welding seams, low manufacturing cost and high stability.
Optimization target extraction
The design of the subframe includes performance indicators such as strength, stiffness, NVH, modal, and crashworthiness. The benchmarking parts (welded subframes) are subjected to finite element analysis, and the analysis results of each performance indicator are used as optimization indicators.
Strength analysis of tailor welded sub-frame
The input of the strength condition of the subframe is constructed in a multi-body dynamics analysis software, and a multi-rigid body model is built for kinematic analysis. The subframe is extracted The load information of each attachment point of the frame is shown in the figure. The obtained load is input into the finite element model of the sub-frame and released using inertia release The analysis of the line strength. Considering the practical needs of structural optimization in the later stage, four envelope condition groups, including condition 1, condition 5, condition 6, and condition 9, were extracted as the strength indicators. The stress nephogram of the four envelope conditions is shown in the figure. To facilitate comparison, the stress extremes of the four strength conditions were summarized in a table.
| working condition | Maximum stress (MPa) |
| 1 | 141.3 |
| 2 | 303.4 |
| 3 | 269.0 |
| 4 | 318.4 |
Stiffness and modal of tailor welded sub-frame
Stiffness condition calculation: Apply three loads to the attachment points of the lower arm, motor, steering gear, and lateral stabilizer bar, and constrain the body suspension mounting points. The attachment points and constraint information are shown in the figure. Calculate and record the stiffness values as shown in the table. Constrain the 6 degrees of freedom at the body connection points, calculate the constrained modes as shown in the figure, and record the results of the first three modes as shown in the table. The three-dimensional stiffness calculation results for each attachment point are shown in the table.
Select the lower arm and motor mounting points for dynamic stiffness calculation and performance target extraction based on the actual connection method at each mounting point. The calculation results As shown in the figure, summarize the calculation results in a table.
Subframe structure
The structural optimization of the subframe is divided into two stages. The first stage is topology optimization, which re-plans the load transfer path of the structure to improve the performance of the subframe. The second stage is parameter optimization, which optimizes the thickness layout of the material to achieve lightweighting of the subframe. Topology optimization is a technique for optimizing design by changing the shape and layout of the structure. Topology optimization methods mainly include homogenization method, variable density method, progressive structural optimization method, level set method, etc. The basic principle of variable density method is to divide the design domain into many small units, each of which can have different pseudo-material densities. Then through iterative calculations, under the condition of satisfying constraints, materials are transferred from unnecessary areas to necessary areas to achieve optimization objectives such as stiffness, quality, and modal.
Optimization results
After multiple rounds of process and parameter adjustments, the ideal optimization results of the sub-frame are shown in the figure. From the optimization results, it can be seen that the new sub-frame is optimized with a single The structural layout is based on the principle of pulling the ribs, which is in line with the design idea of integrated die casting. The optimization results are clear and the load transfer path is reasonable. The optimization results are interpreted and reshaped as shown in the figure.
Optimization of subframe parameters
A reasonable sub-frame structure was obtained through topology optimization. In order to obtain a sub-frame structure with reasonable thickness distribution and lightweight design, the new structure was optimized Optimization of dimensional parameters. To obtain the extreme results of dimensional changes, the outer contour and all reinforcing ribs of the subframe are completely discretized, and the optimization upper and lower limits are set according to process requirements. A total of design variables are obtained through discretization, and the optimization objectives and constraints are set in line with topology optimization. The optimal design is obtained by minimizing the objective function The final optimization result is shown in the figure. The optimization result is updated to the model to complete the final design of the new structure.
New structure verification
Conduct a comprehensive analysis of the integrated die-casting sub-frame using the same modeling standards and calculation conditions, and compare the analysis results with those of the tailor-welded sub-frame to ensure the rationality of the new structural design.
Conclusion
(1) Improved performance of the subframe. In the optimization design of the subframe, a parametric optimization method was introduced. By optimizing the thickness of the subframe reinforcement ribs and outer profile, the stiffness, dynamic stiffness, and modal of the subframe were successfully improved. The increase in dynamic stiffness of the subframe can effectively reduce the distortion and deformation of the body, improving driving stability and ride comfort. From the optimization in this article, it can be seen that while achieving lightweight, there is also the possibility of performance improvement. Therefore, a more reasonable structural design is an important way to improve the cost-effectiveness of the subframe.
(2) Lightweighting of the sub-frame structure. Through topology optimization, the lightweight design of the sub-frame was successfully achieved. Compared with traditional designs, the newly designed sub-frame reduced its weight by 16.3% while meeting the performance requirements of stiffness, strength, dynamic stiffness, and modal. The three major lightweighting methods of structure, process, and material were comprehensively applied, forming a complete set of lightweighting technology routes for reference by the industry.
(3) Lightweighting and cost reduction of the sub-frame process. Replacing the welded sub-frame with an integrated die-casting sub-frame greatly reduces the processing steps, and the welded structure improves the structural strength. Through further optimization of the connection method, the new sub-frame achieves further cost reduction. The structural optimization design of the sub-frame is one of the important topics in the field of modern automotive engineering. Through the comprehensive application of topology optimization, material optimization, and structural parameter optimization methods, it can effectively improve the structural performance of the sub-frame and meet the requirements of automotive manufacturing for lightweight, safety, and economy. In the future, with the development of science and technology and the advancement of computer technology, sub-frame optimization design will play a more important role in automotive engineering, contributing to the realization of intelligent, green and sustainable development of automobile manufacturing.