Tolerance design for products with correlated characteristics

This paper presents a design method for controlling dimensional tolerances of components with multiple functional characteristics. The discussions focus on the characteristics derived from common geometric dimensions. In order to approach the robust design, the tolerance design is achieved by minimizing the total expense, which is the sum of the manufacture cost and the quality loss. Since a product may fail because of any imperfect characteristic, the total quality loss includes all the contributions from individual losses. It is recommended that the losses in correlated characteristics be calculated in separate groups. The computation of the total loss involves the evaluation of the variances–covariance matrix of the related characteristics.