Sequential Design of Optimum Sized and Geometric Tolerances

Tolerancing has great impact on the cost and quality of a product. Dimensional and geometric tolerancing are designed to ensure that products meet both designed functionality and minimum cost. The task of dimensioning and tolerancing in process planning stage is to determine the working dimensions and tolerances of the machined parts by given blueprint (B/P) specifications. A lot of research work has been carried out in dimensioning and tolerancing. In earlier studies, optimal solutions to tolerance charts have been developed to meet B/P specifications. Most researches concentrated on dimensioning and tolerancing with optimal objectives to maximize the total working tolerances based on the constraints of tolerance accumulation and machining accuracy. Linear or nonlinear programming models have been applied to obtain the optimal tolerances (Ngoi, 1992; Ngoi & Ong, 1993; Ji, 1993a; Ji, 1993b; Wei & Lee, 1995; Lee & Wei, 1998; Ngoi & Cheong, 1998a; Lee et al., 1999; Chang et al., 2000; Huang et al., 2002; Chen et al., 2003; Gao & Huang, 2003; Huang et al., 2005). Optimal methods have also been presented to allocate B/P tolerances in product design using tolerance chart in process planning (Ngoi & Cheong, 1998; Ngoi & Ong, 1999; Swift et al., 1999) but the generation of dimensional and tolerance chains being one of the most important problems. In onedimensional (1D) cases, the apparent path tracing and tree approach were commonly used to tolerance chart for manual treatment (Ngoi & Ong, 1993; Ji, 1993a; Ji, 1993b; Wang & Ozsoy, 1993; Ngoi & Cheong, 1998b). Automatic generation of dimensional chains in assembly based on the data structure has been presented (Treacy et al., 1991; Wang & Ozsoy, 1993). Using an Expert System, assembly tolerances analysis and allocation have been implemented by appropriate algorithm in CAD system (Ramani et al., 1998). An intelligent dimensioning method for mechanical parts based on feature extraction was also introduced (Chen et al., 2001). This method could generate the dimensions of