Tolerances are specified by a designer to allow reasonable freedom by a manufacturer for imperfections and inherent variability without compromising performance. It takes knowledge and experience to create a good tolerance scheme. It is a tedious process driven by the type of parts, their features and controls needed for each one of them. In this paper, we investigate the extent to which GD&T schema development can be automated. Automated tolerance schema generation, requires identifying critical tolerance loops. The tolerance loop is a loop of dimensions between faces of features governing assembly conditions. For this purpose, the first major step is to identify mating features called assembly features. Also, in order to create the tolerance chains we need Local Constraints (assembly feature relationships), Global constraints (part feature relationships) and directions of control. In addition, we have to identify feature patterns since they have associated tolerances according to Dimensioning and Tolerancing Standard ASME Y14.5M. Directions in which these loops lie are also needed; we call them Direction of Control (DoC). Then we can create the GD&T schema, allocate tolerance values, and prepare it for tolerance evaluation. In this paper, we present an approach to automatically identify the dimensional loops based on assembly requirements. Assignment of tolerance values will be covered in future works as it is based on design function.

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