Feature-based design approach in the sheet metal industries

The present paper describes the use of design by features in building a system to automate the die layout for sheetmetal stamped parts. Starting from a CAD conventional drawing for stamped part, an algorithm is designed to extract the features of the part and to output a list of features. The list is interpreted by a graphics system as a sequence of calls to subroutines with arguments that define the characteristic dimensions of the features. The graphics system follows the sequence in the list and reconstructs the part one feature at a time for the user to check or modify the part if so desired. The feature list is a complete specification of the part equivalent to a conventional drawing but has several advantages. First, the detailed geometric description in a drawing contains a large amount of details about geometric primitive entities such as lines, arcs, and various views. This description is replaced by structured and aggregated entities-the features, which result in a much more concise description. Second, proper and adequate features correspond to the human conceptualization of the particular part and reflect the technical “jargon” used to exchange information. Thus features are a common language used by the group of people involved in the manufacture of the parts and are used to communicate precisely and efficiently. Third, and the most important aspect of description by features, is that the list of features is a syntactic description of the part rather than a geometric one. Design changes, for example can be made by editing the features list. Process sequencing can be achieved by changing the position of a specific feature in the features list. In short, the part description consists of strings of alphanumeric symbols which stand for objects (features), with their attributes (features dimensions). The symbols can be processed by text editors and can be reasoned about by expert systems. This conceptual framework will make it possible to design knowledge-based interfaces between CAD and CAM systems that interact and reason about a design and thus exhibit a degree of intelligence