Tolerance optimization method based on flatness error distribution

In conventional shape tolerance design, allowable ranges are given for the assembly joint surfaces. The conventional method does not restrict the distribution form of the actual errors of surfaces, resulting in a large deviation in the prediction of assembly performance (i.e., geometric accuracy and mechanical property) from those of actual state. In order to obtain the best performance of product, appropriate tolerance should be allocated for each feature during design stage. The design method of optimum shape tolerance based on the error model of part and assembly is proposed. This method constructs error models of part and assembly considering the error distribution of flatness caused by machining or active design, evaluates performances; and after optimization, obtains the best magnitude and distribution form of flatness error, and assembly force as the requirements for manufacturing and assembling. Finally, the tolerance design of the flatness of a flange is selected to demonstrate the method proposed in this article, the optimum magnitude and distribution form of flatness error and assembly force are obtained based on the analysis results.