Improvement and tailoring of parts fabricated with Wire and Arc Additive Manufacturing

• Autor(a) principal: Rodrigues, Tiago Miguel André
• Data de Publicação: 2022
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/150178
• topic: Functionally Graded Material (FGM); Heat-Treatments; Inoculants; Materials Characterization; Parts’ Properties Improvement; Wire and Arc Additive Manufacturing (WAAM); Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Mecânica

Wire and arc additive manufacturing (WAAM) is an Additive Manufacturing (AM) process that finds applications in different industrial sectors. It shows to be competitive compared to other AM technologies, mainly due to its low implementation costs, high deposition rates, and the ability to produce medium to large complex parts. Improvement of parts’ properties has been the primary goal of the scientific community and was also the main objective of this work, where significant scientific and technological developments were implemented. Different approaches were tested: i) by performing heat treatments; ii) by adding grain refiners to the molten metal; iii) by fabricating Functionally Graded Materials (FGM); iv) by developing a new process variant called Ultra cold Wire and Arc Additive Manufacturing (UC-WAAM). To fulfill these objectives, laboratory means were developed. Including the development of a multi-wire gas tungsten arc welding (GTAW) torch for creating components with a functional gradient, two prototypes to introduce ceramic particles in the molten pool, and a customized gas metal arc welding (GMAW) torch. The feasibility of using ceramic particles to refine the grain structure of WAAM parts was experimentally demonstrated on a High Strength Low Alloy (HSLA) steel and Inconel 625. Parts characterization was performed with multi-phenomena techniques: optical and scanning electron microscopy assisted by energy dispersive spectroscopy and electron backscatter diffraction, synchrotron X-ray diffraction, and mechanical testing. Despite the potential applications of FGM, one of the main limitations is related to significant stresses, chemical incompatibilities, and the possible formation of undesirable intermetallics. In this work, manufacturing of different FGM was successfully produced without defects by applying different building strategies. The results showed that a direct-type interface resulted in superior mechanical properties without intermetallics and smaller residual stresses than a smooth transition build-type. The development of UC-WAAM lowered the average temperatures experienced by the material and increased the cooling rates during parts fabrication compared to traditional GMAW. An overhang structure was fabricated, highlighting the potential for UC-WAAM to be used for this type of structures.