Integrated Approach for Assembly Tolerance Analysis

In mechanical design, tolerance assignment is a critical but complex task since the designer will not only have to consider the associated cost to achieve a certain tolerance level, but also the cost due to failure in assembling task. These associated tolerance costs as well as the failure rate are fuzzy in nature. This paper presents an integrated approach to incorporate manufacturing costs of certain tolerance specifications into design stages for automatic tolerance assignment and design. Tolerance design is interdisciplinary in nature and is characterized by a highly uncertain environment. In recent years, fuzzy logic has appeared as a credible alternative for tolerance design. A fuzzy based tolerance representation scheme is presented to model three dimensional (3D) tolerances. With this representation, relative assembly tolerance constraints can be expressed. A fuzzy tolerance generation and assignment process for assembly is discussed. Fuzzy tolerance equations are generated for 3D assembly considerations. Manufacturing process information, along with uncertain cost information modelled in fuzzy terms, is added to the system to arrive at a cost-optimal tolerance assignment.