中文摘要：

考虑产品质量特征随着时间退化的影响，用多变量质量损失函数在连续复利条件下，把产品特征的退化作为一个连续的现金流量函数建模，从而建立了相关特征产品的期望质量损失现值与其公差的函数关系；在此基础上把质量损失的现值和产品随时间退化的影响集成到总成本模型中，提出了相关特征产品公差设计新的优化模型．产品的优化公差通过使总成本（制造成本与期望质量损失现值之和）最小化而获得，一个板簧公差设计的实例验证了该模型的有效性．

英文摘要：

Considering product degradation on quality characteristics over time, the multivariate quality loss function is used to model quality loss due to product degradation as a continuous cash flow function under continuous compounding. As a result, the functional relationship between the present worth of expected loss of product with correlated characteristics and its related tolerances is derived. The present worth of quality loss and product degradation over time is integrated into the total cost model, and a new optimization model for the tolerance design of products with correlated characteris- tics is presented. The optimal tolerance design is achieved by minimizing the total cost, which is the sum of manufacturing cost and the present worth of expected quality loss. An example of the leaf spring involving optimal tolerance design is given to demonstrate the effectiveness of the proposed model.