| Auto-body assembly is one of important parts of the whole car. Its quality is a key factor that affects the quality of the whole car. The quality of auto-body reflects not only the design level of automobile factory, but also its manufacturing level and management level. The auto-body assembly requires hundreds of sheet metals. For accounting the effect of low stiffness of sheet metals, their tolerances based on analysis and synthesis have an influence on the quality of the assembly. The existing assembly tolerance analysis and synthesis are mainly applied to the rigid assembly, and not suited to the deformable sheet metal assembly. It is necessary to find a new method that applied to the deformable sheet metal assembly. There is great meaning that we use the new method to make clear the variances sources and to improve the quality of the sheet metal assembly.This study is started according to the above background. The purpose is to find a best variance analysis method for the deformable sheet metal assemblies. We can gain useful information to improve the quality of assembly by analyzing the variance sources.In this paper, a sheet metal assembly is as to the study object. MSC/PATRAN is used to modeling, calculating, and analyzing. The assembly variation is calculated using finite element method and pseudo random numbers which are produced by number theoretic method. This method can account for the effect of elastic and plastic deformation. It can be concluded that this method needs simpler computation and shorter time than Monte-Carlo Simulation for the same precision. In a word, this method is more efficiency than the method of Monte-Carlo Simulation.In this paper, we analyze the variations of sheet metal assembly according to the method of orthogonal design. It can be proved that the thicker sheet metals leading the variance of assembly in the deformable sheet metal assemblies.
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