Surface Characterization of Polycarbonate Parts from Selective Laser Sintering

Selective Laser Sintering Irem Y. Tumer David C. Thompson Graduate Research Asst. Graduate Research Asst. Richard H. Crawford Kristin L. Wood Assistant Professor Associate Professor Mechanical Engineering Department The University of Texas at Austin Abstract Surfaces of polycarbonate Selective Laser Sintering parts are investigated to determine the characteristics a ecting part quality. Surfaces are obtained from experiments by varying four factors, namely, layer thickness, laser power, part orientation, and build angle. First, spatial modes on SLS surfaces are decomposed using a qualitative spectral analysis in an attempt to nd their origins. Thermal modes on the top surfaces of polycarbonate SLS parts result in the other modes being obscured; melting and part curl are concluded to be the dominant modes on these surfaces. Furthermore, surface modes resulting from building the part at an angle to the powder bed are identi ed and modeled. Then, mathematical measures are computed for the surfaces to determine surface precision quantitatively. An analysis-of-variance study is performed to reveal the trends in surface precision with respect to control factors. Surface precision is shown to change signi cantly with laser power and part orientation, and trade-o s with part strength are presented. Introduction The quality of parts fabricated with Selective Laser Sintering (SLS) [7] is a crucial consideration. Functional prototyping, which is a major advantage of the SLS process, depends heavily upon the ability to build accurate parts on a repeatable basis. In an attempt to model part quality, this paper aims at investigating the di erent spatial modes on surfaces from SLS and the di erent factors that in uence part quality. Background and Motivation The quality of parts from SLS has been investigated in the literature in terms of measures such as part overall dimensions [2], part strength [6], and sintering depth and density [1]. These studies give a broad picture of what parameters a ect part quality in order to present the operators with a set of preferred parameters when building SLS parts. However, none of these studies attempt to provide an insight on why surface deviations occur on SLS parts. As in every manufacturing process, the nished part is the end product that the SLS researchers are interested in improving. The nature of the signal from surfaces of manufactured parts contains very useful information that can provide great insight into the types of modes present in the system [13]. As a result, an investigation of signals from polycarbonate SLS part surfaces will provide more insight on the nature of error generating mechanisms in SLS. Here, we take errors to be surface deviations that produce spatial modes, such as the modes presented in Figure 1.