Build orientation effects on mechanical properties and porosity of polyamide-11 fabricated via multi jet fusion

The HP Multi Jet Fusion (MJF) technology is a relatively recent addition to powder bed fusion additive manufacturing techniques. It differs from selective laser sintering (SLS) technology through the use of fusing and detailing agents to control part geometry, and the use of a planar infra-red radiation (IR) source, which sweeps over the powder bed, to initiate the sintering process. The results in this study suggest that the MJF-fabricated polyamide-11 (PA11) parts showed very low porosity of less than 1%, but different amounts depending on the build orientation. Our study also indicates that there is significant build orientation-dependent anisotropy in the mechanical properties, which are correlated to the porosity in the parts. We also found that the specimens oriented at a 45 degrees angle relative to the build platform consistently performed the best in terms of tensile mechanical properties by simultaneously avoiding the negative influences of poor intra-layer powder packing in the horizontal plane (observed in the horizontally-oriented specimens) and the orientation of the inter-layer interface against the load direction (observed in the vertically-oriented specimens). The strategies usually adopted in SLS printing by aligning the build orientation of parts to the direction of the tensile loads for improved Young's modulus and/or tensile strength seem not to be applicable for MJF-fabricated PA11 parts.