Variation Analysis of Accumulative Stresses in Multistep Assembly Processes Using Output Transformation Matrices

Geometric variation produces gaps or interferences between the mating features of parts when assembling them. To accomplish the operation, forces need to be applied to deform the parts; while as a price, stresses arise around the structure and accumulate as the assembly process proceeds, which could impair the structural reliability. A tool modeling and analyzing the accumulation of assembly stresses can help us predict and control it. Associated with geometric variation, the levels of assembly stresses are variables as well, thus variation analysis of them is required rather than a single case analysis; however, research on assembly variation analysis has focused mainly on the geometric variation itself. In a previous study, we developed a compliant assembly variation analysis method which is based on a Finite Element (FE) model condensation technique of substructuring (Lin J, et al. “Compliant assembly variation analysis of aeronautical panels using unified substructures with consideration of identical parts.” Computer-Aided Design, 2014.). In this paper, by introducing Output Transformation Matrices (OTMs) into the unified substructure system, we add the analysis of assembly stresses onto that of assembly deviations: no extra modeling work is needed, but the assembly stresses within a part are recovered from its assembly deviations by OTMs. Though these OTMs need to be generated in advance, this one-off effort will be relatively small when the assembly process to be analyzed involves multiple steps. A case study on an aeronautical panel assembly is presented to illustrate the proposed method and investigate the characteristics of assembly stresses.