Dimension and tolerance modeling and transformations in feature based design and manufacturing

This paper describes the development and application of a geometric dimension and tolerance (GD&T) model for use in both design and process planning. The model meets criteria for computability and compatibility with the Y14.5M standard. The model is first used to capture the designers GD&T scheme on a feature based design model, validate its completeness, and then transfer the GD&T to machining features extracted automatically by feature recognition. The model is based on relative degrees of freedom of geometric entities: feature axes, edges, faces and features-of-size. Dimension graphs are created based on the degrees of freedom for each control direction. Datum reference frames and standard tolerance classes are incorporated into the graph. The model allows dimension specification, dimension scheme modification, and dimension scheme validation. A methodology to automatically determine the GD&T of machining volumes obtained by feature recognition is also described.