Mathematical representation of feature conversion for CAD/CAM system integration

Abstract

Automatic generation of machining information from a design system has been the research focus in feature-based CAD/CAPP/CAM applications for many years. Design data from a CAD model cannot be directly used in a CAPP system due to the difficulties arising from different feature viewpoints in each application and in various feature representations. To create a process-planning model automatically using machine features, feature mapping or conversion is the key issue to solve this problem. This paper addresses the problem of how to convert the design feature representation into machining feature representation in a mathematical model. Design features in the design domain are represented by a set of faces of each feature geometry and a set of attributes such as dimensions and material feature. Machining features in the manufacturing domain are represented by a number of faces and relationships between these faces that are meaningful for the process/machining operations. Using a mathematical description of the feature mapping process, machining features can be deduced and formed by the Set Operation, and the difficult problem of feature interaction can be described mathematically and converted in theory. On the basis of feature representations in the design and manufacturing domains, the mathematical model of feature mapping is represented by a mapping function g d−m which is a synthesis function of the process mapping functions g 1 and g 2. The first function, g 1, extracts the topological elements of a feature from a design model, and forms its own face model which including an interactive feature topological elements. The second function, g 2, groups these extracted elements into a machining feature according to the geometrical relationship between these elements and matches them with the pre-defined machining features. Examples are given in this paper to show the procedure of the feature mapping process. A feature-based CAD/CAPP/CAM integration system is described with the help of the formulation and representation of machining features.