Product requirements, tolerance standards and design experience are three main aspects need to be considered during assembly tolerance design process. Currently the standards of tolerance has been included in the process of computer aided tolerance design. The representation for geometrical product specification and verification knowledge has been studied as well. However, the studies mentioned above is lack of a unified knowledge representation to visually express product requirements and design experience. A semantic hierarchical representation structure of assembly tolerance is proposed in this paper to establish the mapping between the geometric feature of the part and the tolerance type as well as tolerance value. A domain ontology model for assembly tolerance design is established with OWL ontology to describe domain information while SWRL rules to enrich the semantics of domain ontology. The application of the model in the proposed hierarchical representation structure enables the consideration tolerance standards, product requirements and design experience of in computer aided tolerancing process, by which the assembly tolerance design knowledge is able to be shared effectively. The application of proposed model is verified by an instance of assembly tolerance reasoning in this paper.

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