A knowledge-based approach to design for manufacturability

Abstract

In the light of growing global competition, organizations are increasingly under pressure to produce products of high quality and reliability at reasonable cost. The integration of design and manufacturing activities into one common engineering effort has been recognized as a key strategy for survival and growth. Design for Manufacturability (DFM) aims at integrating product design and process design to achieve cost and quality objectives. The implementation of the DFM approach requires the collaboration of both the design and manufacturing functions within an organization. However, due to the divergent orientations of these functions, implementation of the DFM approach has been found to be neither straightforward nor easy. Of the several methodologies available, process-driven design is recognized as one of the more effective DFM approaches. The primary objective of this research is to address the major criteria for manufacturability in the DFM approach using expert systems methodology. An expert system has been developed in two modules--one for process selection and manufacturing cost estimation and the other for evaluation of design features for manufacturability on a CAD system. The expertise for primary process selection is developed for casting and forging processes. The specialized processes considered are die casting, investment casting, sand casting, precision forging, conventional die forging, and open die forging. The processes considered for secondary process selection are end milling and drilling. The cost estimation expertise is developed for the die casting process, milling and drilling operations, and manual assembly operations. A design for a hanger used in the furniture industry is used to demonstrate the process selection and cost estimation capability of the expert system. Three different solid models created in CATIA are used to demonstrate evaluation of design features for manufacturability with respect to milling and drilling operations on a CNC milling machine. The set of manufacturability criteria considered are: (1) perpendicularity of holes to drill entry and exit surfaces, (2) conformance of hole diameters to available standard tool sizes, (3) compatibility of hole depths with respect to hole diameters, (4) adjacency of holes lying on the same surface, (5) rounded inside corners instead of sharp corners in square holes, and (6) chamfered corners instead of rounded external corners. The results obtained from the application of the expert system suggest that the use of a knowledge-based approach to generate accurate cost estimates and analyze design features for manufacturability during the design phase is certainly feasible. Such systems would enhance the quality of design decisions in organizations, resulting in improved competitiveness in the market.