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.

在常规形状公差设计中，给出了装配接头表面的允许范围。常规方法不限制表面的实际误差的分布形式，从而导致装配性能（即，几何精度和机械性能）的预测与实际状态的偏差较大。为了获得最佳的产品性能，应在设计阶段为每个功能分配适当的公差。提出了基于零件和装配误差模型的最佳形状公差设计方法。该方法根据加工或主动设计引起的平面度误差分布构造零件和装配的误差模型，评估性能；经过优化后，获得最佳的平面度误差幅度和分布形式，和组装力作为制造和组装的要求。最后，通过选择法兰平整度的公差设计来论证本文提出的方法，并根据分析结果获得平整度误差和装配力的最佳量值和分布形式。