Protecting critical facets in layered manufacturing

In layered manufacturing, a three-dimensional polyhedral object is built by slicing its (virtual) CAD model, and manufacturing the slices successively . During this process, support structures are used to prop up overhangs. An important issue is choosing the build direction, as it affects, among othe r things, the location of support structures on the part, which in turn imp acts process speed and part finish. Algorithms are given here that (i) comp ute a description of all build directions for which a prescribed facet is n ot in contact with supports, and (ii) compute a description of all build di rections for which the total area of all facets that are not in contact wit h supports is maximum. A simplified version of the first algorithm has been implemented, and test results on models obtained from industry are given. (C) 2000 Elsevier Science B.V. All rights reserved.