3D tolerances analysis, from preliminary study

A mechanical assembly is made up of parts and links. Its definition by solids and linkages, and the definition of tolerances for the linkages (these can be 3D position tolerances, clearances...), enables us to calculate functional conditions on the assembly. 3D tolerance analysis is performed like a unidirectional chain of dimensions, with computed coefficients (sensitivities) that fully take into account the 3D effects. Results are presented as calculation tables, and are fully explained. A 3D graphical representation of the sensitivities and contributions enables us to understand immediately where greater precision is (or is not) required. The matching of a car door, positioned by an assembly tool on the "body in white" will be presented, in order to compute the clearances and the surfaces alignments. These calculations only require the definition of the linkages (or functional surfaces) between parts and can be done on the basis of preliminary studies (choice of the mechanical assembly architecture, of the tolerancing type, of references..., choice of the assembly process...) until the final tolerance distribution is optimized. The whole assembly process of an airplane is currently being studied by a major aeronautics company, before the parts are designed, using the wireframe architecture. MECAmaster software, standalone (Windows) or integrated in Cad systems (Cadds5, Euclid3, Catia) works this way and is used daily by major automobile and aeronautics companies.