Abstract:  An optimal tolerance design method of compliant sheet metal parts was proposed based on an assembly variation model of compliant sheet metal parts. The average variance model of all measurement points obtained from the determinate models of measurement points was adopted as the objective function of the tolerance design, and the process capacity index and the variance ratio of parts were the constraint functions. The rear floor assembly was used to validate the tolerance design method. The results showed that tolerance designs of parts were synchronously done in the lap welding structure, and independently done in the butt welding structure while in the corner welding structure the tolerance design of the butt part was firstly done and then that of the lap part was done. When there existed a very large rigidness difference between lap parts, the less rigidness part could adopt a bigger tolerance value.

Key words: tolerance function, tolerance design, process capacity index, compliant sheet metal, assembly variation