Determining Optimal Building Direction for Rapid Prototyping Based on Unit Sphere Searching

Although Rapid prototyping, as a material-additive process, is able to create complex geometries that traditional material-removal processes cannot achieve, it still suffers from its limitation due to the layer manufacturing nature. In order to minimize staircase effects, selection of building orientation is an important step in implementing rapid prototyping processes. This paper presents a method to select the optimal direction that leads to minimized volumetric error in building a part from layer manufacturing processes. A unit sphere is discretized first to give potential directions in a 3-D space, and then each facet comprising an STL geometric model is mapped onto the discretized unit sphere as a great circle individually. Both an exhaustive search and a chain searching strategy are presented to identify the globally optimal direction for building a 3-D geometry. At the end of the paper, examples are presented to show the effectiveness of the method.