In-depth comparison of polyamide 12 parts manufactured by Multi Jet Fusion and Selective Laser Sintering

Recently, the possibility of producing medium-to-large batches has increased the interest in polymer powder bed fusion technologies such as selective laser sintering (SLS) and multi jet fusion (MJF). Only scant data about the characterization of parts produced by MJF can be found in the literature, and fatigue behavior studies are absent. This study analyzes the material properties of Polyamide 12 (PA12) powders and printed specimens using both SLS and MJF technologies. The morphology, crystalline phases, density, porosity, dimensional accuracy, and roughness are measured and compared; tensile and fatigue tests are performed to assess the effect of the technologies on the mechanical behavior of the produced structures. In addition, lattice structure specimens obtained by different geometric modeling approaches are tested to understand the influence of modeling methods on the fatigue life. The PA12 powders printed by both SLS and MJF mainly show by X-Ray Diffraction γ-phase and a small shoulder of α-phase. The crystallinity decreases after printing the powders both in SLS and MJF technology. The printed parts fabricated using the two technologies present a total porosity of 7.95% for SLS and 6.75% for MJF. The roughness values are similar, Ra ≈ 11 µm along the building direction. During tensile tests, SLS samples appear to be stiffer, with a lower plastic deformation than MJF samples, that are tougher than SLS ones. Fatigue tests demonstrate higher dispersion for MJF specimens and an enhancement of fatigue life for both SLS and MJF printed lattice structures modeled with a novel geometric modeling approach that allows the creation of smoother surfaces at nodal points. Scanning electron microscopy on fracture surfaces shows a brittle failure for the SLS tensile specimens, a more ductile failure for the MJF tensile specimens, a crazing failure mechanism for the SLS fatigue tested samples, and a crack initiation and slow growth and propagation for the MJF fatigue tested samples.