Tolerance Chain Detection by Geometrical Constraint Based Coupling Analysis

Assembly tolerance chains are often the root cause for low geometrical robustness and high manufacturing costs. This paper presents a framework for function means modeling in configuration design that allows for modeling and analysis of geometrical couplings, and detection of potential tolerance chains. Requirement decomposition is described, and geometrical couplings on different hierarchical assembly levels are modeled, analyzed and explained. The treatment of sub-assemblies is especially described. The presented framework includes the use of locating schemes for positioning parts in assemblies. A general positioning system for modeling datum frames and locating schemes for parts and sub-assemblies are presented and used. An automotive example is used to show how an overall geometrical product constraint is decomposed into locating schemes on individual parts and how potential tolerance chains are detected. Finally, geometrical coupling quantification and the use of fixtures as a mean for breaking tolerance chains are discussed. The proposed framework enables potential tolerance chains to be detected already in the configuration design phase. By detecting potential tolerance chains in very early configuration design, design solutions with low robustness, needing tight tolerances to fulfill their functional requirements, may be avoided.