Composite Planar Tolerance Allocation with Dimensional and Geometric Specifications

A new optimal approach for planar tolerance allocation is proposed in which dimensional and orientation geometric specifications are included. To deal with the increased complexity of planar tolerance analysis, a special relevance graph (SRG) is used to represent the relationships between manufactured elements and their size and tolerance information. In addition, the SRG is also applied for the geometric dimensions and tolerances. Using a suitable algorithm, planar tolerance chains that include geometric specifications can be generated automatically during process planning. Through a graph based analysis, stacks of tolerance zones are obtained. The resultant tolerance zone contains all of the composite links of the tolerance zones. The links are assigned according to the process capacities, which can be considered as constraints. A linear optimal model is established to solve the tolerance allocation problem. A practical example is used to demonstrate the feasibility and effectiveness of the proposed method.