Anisotropy, homogeneity and ageing in an SLS polymer

Purpose - The purpose of this paper is to rigorously determine the tensile properties of a selective laser sintering (SLS) material. Emphasis was placed on the anisotropy and inhomogeneity of the material, the repeatability of the SLS process, and the effect of age (actually moisture absorption) on the material properties. Design/methodology/approach - Two builds of 144 dogbone tensile specimens each were tested, with 18 specimens stored for 43 days in a non-desiccated environment before testing. Specimens were distributed throughout the build volume and aligned with the apparatus' principal axes. Tensile properties were treated statistically, using the t-test to determine the differences between various samples. Findings - The material was transversely isotropic in Young's modulus and strain to failure, and generally orthotropic in ultimate tensile strength. The material was inhomogeneous throughout the build volume and affected by age, with a 57 per cent reduction in University of Technology after 43 days (the changes in properties were suggested to be due to moisture absorption). Properties varied by up to 25 per cent from build-to-build with no change in nominal process parameters. Research limitations/implications - It was not possible to confirm the "ageing" effect was caused by moisture absorption, and further work is suggested in this area. The causes of inhomogeneity and the effect of re-coater action should also be studied further. Originality/value - This is the most complete study of an SLS material's mechanical properties to date. The statistical analyses used further allow increased confidence in the conclusions drawn. This is also the only study to use cross-fill scanning to produce specimens, and, therefore, isolate the effect of the re-coater action.