In-process dimensional and geometrical characterization of laser-powder bed fusion lattice structures through high-resolution optical tomography

Additive Manufacturing (AM) technologies, i.e. Laser-Powder Bed Fusion (l-PBF), have made possible the fabrication of complex and lightweight components not feasible with conventional manufacturing processes. Lattice structures are one of the most representative examples and they have many advantages (high mechanical properties, thermal insulation and good energy absorption ability, etc.) which are limited by internal defects, poor surface quality and dimensional accuracy. In this context, X-ray-based Computed Tomography (XCT) is, currently, the only way for quality assessment of these structures, thanks to its capability to see also internal features, while optical scanning techniques can reconstruct only external surfaces. In this work, an innovative and cost-effective optical layerwise monitoring technique, for dimensional and geometrical characterization of lattice structures realized by l-PBF, was proposed. It exploited the high-resolution optical tomography (HR-OT) and it had a double purpose: it was used as a layerwise in-process monitoring method, able to detect timely and effectively the onset of geometric distortions and, in addition, it provided, at the end of the manufacturing process, a 3D reconstruction of the fabricated structure, comprising external and internal features, suitable for post-process quality assessment. This article is among the first to show a monitoring methodology suitable for lattice structures realized by l-PBF technologies.