Structural Optimization Research For Body In White Of JL030 Car

In modern world, automobile has become a part of people's life. It has been a very important vehicle for us. The level of a country's automobile manufacturing reflects the level of its scientific and technological development largely. With the rapid development of computer technology, CAE analysis technology has been rapid development. In the Western developed countries, CAE technology is widely used in the automobile design, and achieves great success. But the use of CAE technology at home is relatively backward, particularly the dynamic nature of the new product analysis, still in its infancy.Most modern automobiles are integral body. The structure of car body directly influences the overall performance. Therefore, auto body structure analysis is particularly important. The body's bending rigidity, the torsion rigidity and modal frequency is the body of the most important performance. They affect the comfort and safety directly. Auto body is composed of many thin-walled structure components. It is a multi-freedom elastic system. It will deform in external excitation and cause the system vibration. When external vibration frequency and systems inherent frequency close to, or multiple relations, will resonance occur. Resonance not only make occupant felt uncomfortable, and bring the noise and components of fatigue damage, also undermine the body surface protective layer and body sealing, thus weakening the corrosion resistance. Vibration characteristics and body stiffness are closely related. High stiffness body is not only beneficial to suspension supports, make cars the normal work of the system, but also helps to improve vibration characteristics. Therefore, in car design, must understand body stiffness and modal characteristics.This article is based on a company's development of a automobile. It makes a finite element model for body in white and analysis. According to the results of analysis, the size optimization is made for the thickness of auto body parts.The main task of this paper included:1. Build white body of finite element model.2. Analyze the static bending stiffness and torsion stiffness of auto body.3. Modal analysis of auto body.4. Size optimization of auto body.The finite element analysis method is introduced briefly in the auto body FE modeling. The FEM(finite element method) was proposed in the 1940's. After nearly seven years of development and perfection, its theory has quite mature. Finite element method of basic idea is piece-wise approximation. The main steps of finite element analysis are: discrete structure and choose unit displacement patterns, unit analysis and the overall analysis. The modeling of auto body is introduced in detail. The detailed instructions on geometric model of simplified and cleaning, grid cell type selection, unit size selection, material properties, mesh quality control and simulation of solder unit are made. The FE model of auto body is made in Hypermesh. The model includes 176914 nodes, 161072 quadrilateral elements, 6744 triangular elements (the total 4.02%) and 3159 rigid elements.The basic methods of static stiffness analysis are introduced firstly in the white body stiffness analysis section. It points out that the static stiffness analysis generally choose two extreme conditions in the automobile driving process, namely torsion bending condition and working conditions. In the analytical process, the constraints and load simulation are described in detail. During the bending stiffness analysis, three degrees freedom of front and rear suspension (X, Y, Z direction freedom) is set. The uniform load is applied on the installation position of seats. Each and crew take 150kg. During the torsion rigidity analysis, the rear suspension's freedom degrees are set all. Around front wheel cover suspension point position exert equal in opposite directions in vertical direction of concentration, produce 2970 Nm torque. The analysis results show that the auto body stiffness is lower than the similar models. So, the structure parameters should be adjusted to improve body static stiffness properties.The basic theory of modal analysis and the evaluation principles of the results are introduced in the modal analysis section. Solving the white body various order modal parameters, the various models of frequency and vibration model are obtained. With analysis and evaluation method of results are analyzed. The body in white first order torsion frequency is 18.65 Hz, which is during the engine's vibration frequency. Therefore, the resonance occurs easily between body in white and engine. While the first bending frequency for 35.34 Hz, and first-order integral torsion frequency obvious stagger, won't happen strikeout coupling. So the structure parameters should be adjusted in order to improve the body first order integral torsion frequency and body dynamic performance.In the size optimization section takes into consideration the static stiffness and dynamic stiffness at the same time. The white body total quality increases slightly circumstances, the white body static stiffness and dynamic stiffness are improved greatly. This paper uses structure size optimization. Every major parts with white body thickness as optimization design variables (79 optimization design variables), and the white body first-order integral torsion frequency, bending rigidity of vertical displacement of A dam, the torsion rigidity of vertical displacement of B and C of vertical displacement dam as constraint, with white body of total quality as optimized object, an optimization model is established. After eleven time iterative optimization, white body first-order torsion frequency by original 18.65 Hz increases to now 22.7 Hz. The white body structure performance is improved. Based on this, the total mass white body has slightly increased.From this paper, we established the finite element model of the auto body; analyzed the finite element model by finite element method, mastered its stiffness and low order modal information, and primarily predicted its stiffness and dynamic characteristic; then optimized auto body's dimension by changing the main parts'thickness for the low stiffness, improved the cab's static and dynamic characteristic.