Abstract: The evolutionary tolerance design strategy and its characteristics are studied based on the automation technology in the product structure design. And a function tolerance design theory in the process of the product growth design is put forward, to guarantee a successful transformation from the functional requirement to geometry constraints between parts, and to dimension constraints finally. A mathematical model with a correlated sensitivity function between the cost and the tolerance is built up, in which the design cost, the manufacturing cost, the usage cost, and the depreciation cost of the product are regarded as the control constraint of the tolerance allocation, and with the consideration of these costs, a multifactor-cost function to express the quality loss of the product is applied into the model. In the mathematical model, the minimum cost is used as the objective function, a reasonable process capability index, the assembly function, and the assembly quality, are taken as the constraints, while the depreciation cost in the ob- jective function is expressed as the discount rate - terminology in the economics. Thus, the allocation of the dimension tolerance considering the function and the cost in the whole lifetime of the product is realized. Finally, a design example is used to demonstrate the successful application of the proposed function tolerance theory in the incremental growth design of the product.

Key words: Function tolerance theory, Functional structure design, Incremental growth design