Concurrent design of a geometric parameter and tolerance for assembly and cost

Abstract

Geometric parameter and tolerance design are two important phases in product design and they will affect the assembly functionality and manufacturing cost of a product. The aim is to present a new method of parameter and tolerance design for concurrent engineering. In the nominal domain, a graphical representation of the linkage of geometric constraints is termed the nominal loop circuit, which helps to formulate the stack path of parameters into parameter equations. In the variational domain, the nominal loop circuit is extended as the variational loop circuit, which helps to established assembly stack-up functions. In the tolerance domain, tolerance types are designed and tolerance inequations formulated. Based on the empirical parameter and tolerance versus manufacturing cost data, manufacturing cost functions are established. Based on the assembly and cost functions, parameter equations and tolerances inequations, the mathematical model of parameter and tolerance design is established and a genetic algorithm is used to find multi-objective optimum solutions of parameters and tolerances. The method not only can design concurrently parameter and tolerance for assembly and cost, but also synthetically consider dimensional and geometric tolerances. Applications of the proposed method have been illustrated.