Mechanism analysis of deviation sourcing and propagation for mechanical assembly

For mechanical precision predicting, mechanism of deviation sourcing and propagation for rigid part assembly is discussed. Considering dimension and geometric precision, and part situation precision, the deviation source that affects assembly precision or accuracy is clustered into three types: deviation of geometric location and orientation, variation of geometric form and deviation of part location and orientation. Unified statistical model with deviation evaluation for these three kinds of deviation source are built, and plus-minus influence factor of deviation source referring to functional requirement is calculated. In addition, mechanism of deviation propagation between two mating surfaces or key characteristics is discussed. Three deviation propagating types are proposed and intermittent and continuous propagation model according to mating status are particularly built. Based on the directed graph representation for deviation, the directed graph for deviation propagation between two mating surfaces or key characteristics are built, and directed graph modeling for whole assembly is discussed. Finally, an example with deviation sourcing and propagation is introduced to verify the effectiveness of each model.