Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processing heat treatments to improve the mechanical properties of the parts. An important aspect that still hinders this technology is certification and nondestructive testing of the parts, and this is discussed. Finally, a general perspective of future advancements is presented.

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Additive manufacturing technologies are becoming more popular, as they allow the fabrication of specific parts with complex geometries not achievable by conventional manufacturing. In metal additive manufacturing, one of the most widely used technologies is laser powder bed fusion. This work focuses on the influence of different processing parameters on the density of AISI 316L stainless parts obtained through this technology. The article presents a review of published works on the deposition of AISI 316L stainless steel using laser powder bed fusion to define an optimal range of parameters to produce parts with densities above 99%, complemented by density measurements for new sets of laser powder bed fusion processing parameters within the defined optimal range. The investigation provides a further insight on the effect of operating parameters such as vector size and gas atmosphere (Nitrogen and Argon) on the part density. The density measurements were performed using two techniques: micrograph analysis and Archimedes method. Results reveal that an increase in vector size has a negative influence on part density. With the Archimedes method, a maximum relative density of 99.87% was achieved using Nitrogen atmosphere, showing that it is possible to produce near fully dense parts by laser powder bed fusion without post-processing by laser re-melting.