A geometric reasoning methodology for manufacturing feature extraction from a 3-D CAD model
Abstract
Geometric reasoning is to reason the geometry of a designed object. Manufacturing feature extraction, a kind of geometric reasoning, is to interpret the lower level geometry data of a boundary representation (B-Rep) into higher level feature description which is required by the downstream CAPP systems. The objective of this research is to study the issues of geometric reasoning in automating the interface between a 3-D B-Rep CAD model and CAPP systems. The concept and notation of a feature volume is defined as a swept volume which reflects the machining operations. A backward growing procedure is developed, which can (1) extract embedded manufacturing features from the 3-D CAD model, (2) determine manufacturing-related information for each recognized feature such as feature type, machining precedence, tool approach direction, and (3) generate the intermediate workpiece shapes for fixturing, NC programming, inspection planning, etc. A geometric formalization of the backward growing procedure has been presented and proven. The concept of backward growing is to reverse the sequence of the machining operations which transform the part specifications from an initial stock to the finished part. In specific, is is a procedure which constructs a machined volume from a set of machined faces and decomposes the constructed volume into a set of elementary machined shapes. The elementary machined shapes which can be handled include pockets, blind slots, slots, blind steps, steps, holes, fillets and their variations, wedges and their variations, etc. Complex machined volumes such as compound cavity features, protrusion features, and intersecting features can be decomposed into elementary machined shapes. Thus the problems of feature intersection are bypassed but are still solved effectively and efficiently. A prototype backward growing feature recognizer, B-Grow, has been implemented in C under the UNIX operating system. A polygonal solid modeler, TWIN, is used as the geometric engine. The results are displayed on a Silicon Graphics Personal IRIS workstation.
Degree
Ph.D.
Advisors
Chang, Purdue University.
Subject Area
Industrial engineering|Computer science
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