Optimum Tolerance Allocation in Assembly

Dimensioning and tolerancing are both important phases of product design. Although dimensions can usually be assigned based on design constraints and aestheticism without much difficulty, tolerancing is often a major problem to designers. Traditionally, tolerances are assigned intuitively followed by an analysis to check for any violation of the assembly requirements. Based on the analysis results, modifications are made manually by a "trial and error" method. This method relies on the experience of the designers and the results may not be optimal.This paper presents a new approach to optimum tolerancing of components in an assembly such that all interaction requirements are met. The requirements may be for unilateral tolerance for control of clearance and interference or they may be for bilateral tolerance control. A model showing the relationship between components is constructed directly from the design. Using the model, coupled with a unique algorithm, a set of linear equations is formulated based on the design constraints and assembly requirements. The linear equations are then solved to determine the optimum tolerances of the assembly.