Optimization Of Car Body Assembly Structure Design Based On Modified Graph-based Decomposition Algorithm

In conceptual design phase of car body, after the body structural shape is determined, a blueprint of the assembly structure design of body-in-white is needed, it shows the position of the welding points and how all components being manufactured and assembled together. The distribution of welding points affects the structural performance and assembly cost tremendously, and the cost of manufacturing these components are also determined by the shape of each component, this paper called them:stiffness, assemblability and manufacturability. So it’s important to optimize this blueprint.Based on earlier researches, this paper proposed a new solution to this blueprint which is an optimization method combining a modified graph-based decomposition algorithm. A Fast Elitist Non-dominated Sorting Genetic Algorithm is an genetic algorithm, it means advantages in many aspects such as in non-differentiable field and global optimization, what’s more, a modified NSGA has an improvement on time complexity which do good to large scale numerical problems. Combined with the modified graph-base decomposition algorithm, a mapping was built between the structural graph of product and the topological graph of product that illustrates the connection relation of components, then with the expression of adjacent matrix, depth first algorithm and characteristic retaining strategy the irrational structural graph of product was judged and fixed. After that, the graph was encoded to be optimized through the iteration process and a best individual was chosen within the best population.In this research, a Pareto optimality principle was used to judge the individuals, so the best individual means that its objective function values in three aspects are not worse than any other individual as a whole, and the validity and reliability of the method proposed in this paper was proved by the results of numerical experiments. This method ensured the structural performance and decreased the cost of assembly and manufacture at the same time. the optimization of stiffness, assemblability and manufacturability was realized and the blueprint of assembly structure design in conceptual design phase of car body was given to satisfy the need of engineering design.