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Tolerance Analysis of Compliant Sheet Metal Assemblies

 

Abstract: Statistical tolerance analysis has an essential role to associate product design with manufacture, aiding to increase quality, while lowering production costs. Conventional tolerance analysis methods are limited by the assumption of part rigidity. These methods could not be carried out on compliant assemblies and may lead to over- or under¬ estimation of assembly specifications. Since compliant parts deform under assembly loads, there are additional variations in components incorporated in manufacturing tolerances. Therefore, compliant tolerance analysis methods have been developed to improve rigid body tolerance analysis using finite element methods. A significant application of compliant tolerance analysis can be associated to sheet metal assemblies such as aerospace fuselage, the automotive panel parts, or the interior panels of a passenger railway compartment. During assembling a sheet metal structure, there will be some deformations in the process which are arisen as a result of dealing with uncertain manufacturing dimensions. In this regard, these deformations can be considered as the assembly variables of interest. The objective of the procedure is to predict the sensitivity of deformations to manufacturing tolerances. It can be accomplished by accounting for the statistical multivariate distribution of these variables in terms of manufacturing tolerances. It should be noted that the variations of deformations among the various nodes are correlated rather than independent. This correlation, in fact, is occurred in consequence of interdependency between mating nodes throughout the assembly. Finally, the acceptance fraction can also be calculated by integrating the multivariate distribution of the assembly variables of interest. Thus, tolerance analysis procedure can predict the cost effectiveness of an assembly when parts are designed and before being manufactured.

Keywords: Compliant tolerance analysis, Sheet metal assemblies, Assembly specification, Finite element methods, Multivariate distribution, Acceptance fraction. ­

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