Geometric elements for tolerance definition in feature-based product models

Product modelling is an essential part of all computerised design and manufacturing activities. A precise mathematical model of the geometry of products is important, but must be supplemented with technological information such as the material, mechanical properties, functional specifications and tolerances. Modern CAD systems can model and manipulate components with complex geometry. However, technological information is represented as text symbols on the computer screen or drawing, and subsequent application programs are frequently unable to use this information effectively. This paper discusses this problem, and establishes the geometric elements required for the representation or dimensions and tolerances in a feature-based product modelling environment.