Optimal Tolerance Allocation Based on Fuzzy Comprehensive Evaluation and Genetic Algorithm

It is very important to know how to allocate tolerances economically for parts in a CAD/CAM system because this directly affects the machining costs of the parts. A new approach based on fuzzy comprehensive evaluation (FCE) and a genetic algorithm (GA) is presented to obtain a rational tolerance allocation for the parts. First, the current methods for tolerance allocation are reviewed in detail. Then, FCE is used to evaluate the machinability of a part; a new optimal model, which can fully exploit DFA (design for assembly) and DFM (design for manufacturing), is established by combining the functional sensitivity factors and machinability factors of parts. A genetic algorithm (GA) is developed and used to optimise the above model. Finally, an actual example is used to verify the feasibility of the above method; the computed result shows that the method can produce tolerance allocations economically and accurately.