Protrusion-features handling in design and manufacturing planning

In a feature-based design system, a designer should be able to design with both protrusion and depression features. Since depression features loosely correspond to machining processes, they are easy to handle during process planning and NC cutter-path generation. However, the same cannot be said for protrusion features. Not only do the removal volumes surrounding the feature need to be extracted into depression features, but the original workpiece needs to increase in size so that there is enough material for the protruding features. A backward-growing methodology for handling protrusion features for process planning is discussed. Its implementation in an integrated design/ manufacturing system called QTC II is described.