Characterization of the strength of support structures used in powder bed fusion additive manufacturing of Ti-6Al-4V

Abstract

Support structures are required in powder bed fusion (PBF) additive manufacturing of metallic components with overhanging structures in order to reinforce and anchor the part, preventing warping during fabrication. In this study, we tested the tensile structural strength of support structures with four different 2-dimensional lattice geometries by fabricating samples composed of solid material on the bottom, followed by support material in the middle, followed by solid material on the top. The support structure regions were fabricated with a lower linear heat input than the solid material, providing deliberate geometrical stress concentrations to enable the removal of support material after processing. These samples were subjected to tension in the vertical direction to measure the strengths of the support structure-solid material interfaces. Two strengths were computed: an effective structural strength defined as the total force that the structure withstood normalized by the full cross-sectional area, and a ligament structural strength, defined as the effective structural strength normalized by the density of the solid material, thereby ignoring the volume of the surrounding powder and voids that do not contribute to the strength of the lattice. The effective structural strength was 14–32% of the strength of fully dense Ti-6Al-4V made by PBF and the ligament structural strength was 34–49% of the strength of fully dense material. These interface strengths are lower than that of fully-dense material due to the stress concentrations at the support structure-solid material interfaces, not any intrinsic difference in the intrinsic strength of support structure versus solid material. These results can be used to tailor the support structure geometry to balance sufficient anchoring strength during fabrication and ease of part removal and subsequent machining during post-processing.