Wrapping algorithms for multi-axis additive rapid prototyping

The 'bottom-up' layered manufacturing approach to rapid prototyping of free-form artifacts has gained prominence in recent years. However, the method is generally implemented on specialised, purpose-built machinery and requires special support structures wherever overhangs are present. Vertical machining centres provide a platform allowing 4 or 5 axis positioning of an artifact and deposition heads may be straightforwardly added to them. In this paper we investigate methods for additive rapid prototyping taking advantage of this ability to deposit material from a range of directions. We develop algorithms to define a build path to be followed by a deposition system which is able to rotate the artifact during deposition. In outline these algorithms follow the artifact's surface, while 'wrapping' it with a bead or ribbon of material. Criteria for optimum build quality cannot be simultaneously satisfied for many surfaces. The problem is most severe when the corner between two non-coplanar facets is being rounded. We therefore define measures of the build error and develop straightforward optimisation schemes to minimise the error. Speedy optimisation is facilitated by specialised data-structures permitting rapid location of a facet and its neighbours. The method is demonstrated on simple artifacts, where we show that the build quality is effectively enhanced by the optimisation.