Simulated toleranced CAD geometrical model and automatic generation of 3D dimension chains

In current research of computer aided tolerancing (CAT), how to build models with tolerance and how to generate 3D dimension chains automatically have been tough problems and still unsolved. This paper builds a simulated toleranced CAD geometrical model (STCAD model) based on the feature-based original idealized CAD geometrical model (OICAD model), which can simulate real parts with manufacturing dimension errors from different aspects. Further more, an automatic generation method of 3D dimension chains based on some newly proposed definitions is put forward. In this method, firstly the conception of part instantiation (PI) is realized, secondly performance feature is defined, thirdly through building STCAD models, drive dimensions can be obtained which are vectorized to build drive dimension skeleton model (DDSM), and finally 3D dimension chains can be obtained by DDSM and the method of space projection. This method can generate 1D, 2D, and 3D dimension chains of parts or assemblies. It is verified in our own-developed automatic generation system of 3D dimension chains.