Selective Laser Sintering of Polycarbonate at Varying Powers, Scan Speeds and Scan Spacings

A benchmark study (1) has shown selective laser sintering to be the equal of or to have accuracy advantages over other processes for creating parts of size over 10 mm. Experience is needed to achieve best accuracies, as with other processes. This paper is (for us) a first step in understanding the relation between sintering parameters, part size and acuracy. Work at the University of Texas at Austin (2-4) has established that the sintering of polycarbonate can be understood in terms of a rate model driven by viscous and surface tension effects. Material properties are such that a sharp boundary exists between sintered and unsintered material. When full density is not achieved in a part, density within a single layer varies from fully sintered to totally unsintered; measured part density is thus a mean of widely varying values. Published work (3-4) uses a onedimensional non-steady state heat flow model to calculate the temperature profile and densification beneath the surface and concentrates on the effects on this of material properties varying with temperature and during sintering. In this paper, these variations are ignored but a three dimensional non-steady heat flow is used to enable edge effects to be estimated. Density gradients at edges are assumed to be responsible for variations of accuracy with sintering parameters, part size, part shape and orientation.