Variable dimensional chain of strokerelated mechanical assemblies

In traditional assembly dimensional chain theory, actual geometrical features are obtained by translating or rotating from the nominal geometrical features. Thus, the deviation stack-up function is irrelevant with the machining stroke. In order to solve this problem, a model describing the variation in the dimensional chain of stroke-related mechanical assemblies is proposed. The geometrical features of assembly parts are discretized as a set of coordinate points, and the traditional geometrical dimensional chain is equivalently replaced by several linear dimensional chains. For every linear dimensional chain, the assembly datum of two parts is deformed due to gravity or thermal effect and so on, resulting in the nonclosure of dimensional chain. In this article, the closure of the dimensional chain is guaranteed by replacing the assembly datum by the plane determined by three highest points. Finally, an experiment was carried out to verify the necessity of constructing the variable dimensional chain and its accuracy. Combining this new model with Monte Carlo simulation method, the influence of gravity on tolerance analysis was analyzed, and the results show that the variation in the dimensional chain induced by working conditions cannot be ignored in the tolerance design stage.