Tolerance allocation of assemblies using fuzzy comprehensive evaluation and decision support process

Tolerances play an important role in product fabrication and have a significant impact on manufacturing costs. The factors affecting manufacturing cost (geometry, material, etc.) of a part are fuzzy or subjective in nature since they have no appropriate numerical measure. This paper proposes a framework that overcomes the drawbacks of traditional tolerance control methods and reduces subjectivity via fuzzy comprehensive evaluation and conjoint analysis. In the fuzzy comprehensive evaluation process, the relationship between the machining costs and part tolerance is expressed through a mathematical formula, with the objective of minimizing the total machining cost. The conjoint analysis method is introduced to provide a systematic method of deciding weights for each of the factors in the tolerance allocation procedure. The application of the framework is demonstrated with practical engineering problems of allocating tolerances of an accumulator’s O-ring seal and a clutch assembly.