Effect of the build orientation on the mechanical performance of polymeric parts produced by multi jet fusion and selective laser sintering

As the selective laser sintering (SLS), multi jet fusion (MJF) is a powder bed fusion additive manufacturing (AM) process that emerged in the last few years. The possibility to nest parts into the build volume and the absence of support structures make both technologies attractive for the large series production of polymeric components. However, to exploit these process features, it is essential to understand the part orientation's effect on the final material performance. A comparison between polyamide 12 (PA12) parts printed by SLS and MJF was carried out in this work. A design of experiment (DoE) approach is adopted to characterise the tensile strength of specimen printed in different orientations and rotations with respect to the machine reference system. Tomography has been used to characterise the porosities present in the printed sample. The results show that it is not sufficient to define only the orientation of the principal axes of the part because the material proprieties may also vary according to the part rotation with respect to the build direction. MJF technology offers greater breaking strength, while SLS prevails over other calculated features. According to the specimen orientation and printing technology, the levels of porosities and the pores have different morphology and distribution in the specimen. A tight correlation was pointed out between the pores and their descriptors and the samples' mechanical behaviour.