STEP-based feature extraction from STEP geometry for Agile Manufacturing

Abstract

Feature recognition, from low level geometric entities of product design representations within a CAD model to facilitate process planning and manufacturing activities, has been of significant importance in computer integrated manufacturing (CIM). However, the emerging paradigm of Agile Manufacturing has imposed additional requirements of “neutral format” so that form-feature information can be readily shared among multiple partners of a virtual enterprise. Recently, the STandard for the Exchange of Product model data (STEP) has emerged as the means for neutral form exchange of product related data. The “STEP efforts” have broken down the domain of manufacturing related activities in the form of application protocols (APs) target for specific functions which include drafting, configuration control and feature-based process planning to mention a few. Efforts are still on to increase the acceptance and use of this international standard (IS). This paper focuses on our efforts to support the STEP standard with the development of a standards-oriented form-feature extraction system. The developed feature extraction system takes as a input a STEP file defining the geometry and topology of a part and generates as output a STEP file with form-feature information in AP224 format for form feature-based process planning. The system can also be interfaced with a recent IGES to AP202 translator [M.P. Bhandarkar, B. Downie, M. Hardwick, R. Nagi, Migration from IGES to STEP: one-to-one translation of IGES drawing to STEP drafting data, accepted by Computers in Industry, July, 1999; M.P. Bhandarkar, Satisfying information needs in Agile Manufacturing through translation and feature extraction into STEP product data models, MS Thesis, State University of New York at Buffalo, 1997.] to allow conversion of legacy data. The feature recognition algorithm is boundary-representation (B-Rep) based and follows a sequential approach through an existing classification of features. Properties of each feature class are exploited to enable their extraction. The algorithm is currently developed for prismatic solids produced by milling operations and that contain elementary shapes such as plane and cylindrical surfaces (possibly using non-uniform rational B-splines (NURBS)). Special attention has been paid to implementation issues. We demonstrate the efficacy of the system using representative parts.