Light Materials Application For The Cab BIW Of A Commercial Vehicle

Nowadays, the development trends of auto technology are energy-saving, environmental protection, safety, comfort, intelligence and so on. As energy and environmental problems are becoming increasingly prominent, the lightweight design of car has great signification. International Aluminum Institute pointed out that the fuel consumption of vehicle could be reduced by 6%～8% with the weight loss of 10%. The body mass accounts for 20% to 40% of the total mass of vehicle. The lightweight of body plays an important role in the vehicle's lightweight and the study of lightweight body is a hotspot of modern body design. Currently, there are two main ways for lightweight design of body. One way is using lightweight materials, such as high strength steel, aluminum alloy. But this method is not widely used as the limitations of costs and manufacturing process. The other way is optimizing the body structure which is relatively widely used and gets some results. With the further development of research and the improvement of manufacturing process, the combination of lightweight materials application and structural optimization can achieve the lightweight design that the overall performance of car body is not reduced and the weights of the components are lightened.In the paper, the cab BIW of a commercial vehicle was used as the research object. By the rational application of lightweight materials, the dynamic performance of the commercial vehicle cab was improved, and the weight BIW was lightened. Based on the design concept of a reasonable material for the right parts, considering the body mass, stiffness, strength and low level natural mode of vibration, the optimized lightweight materials and the optimized thickness for the components of the cab BIW were obtained.The main tasks of this paper included:1. Briefly introduced the status of lightweight materials application in BIW structure, and stated the meaning and contents of this paper.2. Analyzed the sensitivity of each component in the BIW of Commercial Vehicle, and selected high sensitive components as lightweight material application objects.3. Built surrogate models for the lightweight material optimization, compared the precision of polynomial response surface model, Kriging model and radial basis function model. Finally the most accurate model-radial basis function model was chosen for the material matching optimization to improve the efficiency.4. Optimized and matched the lightweight material in the commercial vehicle cab by NSGA-Ⅱand got Pareto optimal solutions. Finally, selected and verified one optimal solution as the optimal solution.In the part of analyzing the sensitive components, the DOE method was used, the overall body mass and the first torsion frequency were taken as experimental indexes,40 components as experimental factors were selected except very small parts. Based on 40 factors and 3 levels orthogonal array, the responses by computer simulation were calculated, the data in range method was processed, and 9 parts of commercial cab BIW, such as the floor, roof, rear wall, door frame and front wall, were selected as the application parts of lightweight materials. In this way, the efficient application of lightweight materials was ensured.In the part of creating surrogate model for the lightweight materials matching optimization, three surrogate models were introduced:polynomial response surface model, Kriging model and radial basis function model. Then, the models with the first torsion frequency, torsion rigidity and maximum stresses of lightweight materials parts were created respectively. The precision of these approximation methods were analyzed and compared. Finally, the radial basis function model with highest precision was chosen to be used for the materials matching optimization.In the part of the materials matching optimization for the cab BIW, the mathematical model for the lightweight materials matching optimization was created, considering the total mass of cab and the first torsion frequency as two optimization objectives, the torsion rigidity and strength as constraints. In the optimization, the types of materials and the thickness of components were simultaneously made as the optimization variables. According to the feature of the optimization, multi-objective genetic algorithm NSGA-Ⅱwas chosen to solve the optimization problem. Pareto optimal solution set was achieved successfully. Finally, a solution was chosen as the optimal solution from Pareto optimal solution based on cost and the performance of the cab BIW. The performance of the optimal solution was analyzed and compared with the original cab BIW of the commercial vehicle. For the optimal solution, the first torsion frequency was increased by 2.8Hz, and the mass of the total cab BIW was reduced by 43.8Kg, meanwhile the rigidity and strength met requirements.In the paper, a method for the lightweight materials application is presented, considering the structural performance of cab BIW. The example shows that the method is feasible and effective. The results show that based on the design concept that proper material type is selected for each component to build the lightweight structure, the lightweight design can be achieved that the structural performances are improved and the mass is reduced significantly. What's more, the study method is useful reference to the light materials application in the auto body in the future.