Computational quality measures for evaluation of part orientation in freeform fabrication

Parts formed using freeform fabrication processes can vary significantly in quality depending on the orientation of the workpiece during manufacture. This paper presents four measures of quality for three performance measures in which this occurs, along with computational methods for computing their expected effects on faceted representations of a workpiece. The optimization of these quality measures is an important step in the automation of manufacturing straight from CAD models. The quality metrics developed quantify build time, material strength, and surface approximation error as functions of part orientation. A series of experiments performed on polycarbonate tensile specimens produced with selective laser sintering (SLS) shows how significant orientation can be. Although SLS and selective area laser deposition (SALD) are used in the examples, the measures are applicable to other technologies as well. A preliminary investigation into the optimization of orientation with these measures is discussed, showing how properties of the measures developed can be used to generate trial orientations for the global optimization problem where several measures are combined.