Investigation of porosity and mechanical properties of nylon SLS structures

Abstract

Selective Laser Sintering (SLS) is a popular method of 3-dimensional printing, which is commonly used to create prototype parts. However, due to the sintering process, the parts are very porous and have poor mechanical properties when compared to injection molded, cast, or machined equivalents. Thus, there is an opportunity to develop post treatment processes to reinforce these structures. In order to predict the possible improvement in mechanical properties, the shape, size, and permeability of the pores needed to be characterized. This study captures the baseline tensile mechanical properties, and investigates the levels of porosity via fluid penetration and optical tests. Parts were immersed in both high and low viscosity substances to fill the pores, so as to investigate the extent of penetration, and thus, observing porosity levels. In order to achieve greater penetration levels a vacuum was applied to evacuate the entrapped air, causing the fluid to be adsorbed readily. Initial results showed that nylon SLS specimens are inhomogeneous in terms of porosity levels i.e. the density in different areas of the specimen can vary. Capillary action was found to be insufficient to penetrate the internal structure of a SLS specimen, though the vacuum technique can achieve far superior levels, to multiple mm of penetration.