Near-immersion active cooling for wire + arc additive manufacturing: from concept to application

• Autor(a) principal: Silva, Leandro João da
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFU
• Texto Completo: https://repositorio.ufu.br/handle/123456789/27393; http://dx.doi.org/10.14393/ufu.te.2019.2422
• topic: CNPQ::ENGENHARIAS::ENGENHARIA MECANICA::PROCESSOS DE FABRICACAO; Directed Energy Deposition; WAAM; Cold Metal Transfer; Thermal Management; Heat Accumulation; Active Cooling; Aluminum; Scalmalloy

Under the fundamental question on how to mitigate heat accumulation in Wire + Arc Additive Manufacturing (WAAM) of aluminum, without compromising the part performance and the production time, it was raised an hypothesis that if the preform is deposited near-immersed in water then heat accumulation would be uniformly mitigated, provided that the water evaporation neither destabilize the process nor increase porosity. Therefore, the core objective of this thesis was to answer the fundamental question by proofing the raised hypothesis. To reach this objective, the strategy was to work based on the Technology Readiness Levels – TRLs (ISO 16290), starting with the establishment of what was called Near-immersion Active Cooling (NIAC) concept (TRL 1-2), followed by the NIAC proof of concept (TRL 2-3), moving on to the development of a functional prototype for the NIAC application and for the elaboration of a parameter selection procedure for WAAM with the NIAC (TRL 3-4), and finally reaching the stage of assessment of the NIAC in a relevant environment through deposition of Scalmalloy® preforms (TRL 4-5). The experimental approach was based on single-pass multi-layer walls deposited with the CMT process. The results showed that the NIAC technique allowed significant real-time cooling of the preforms. The interpass temperature is kept low and unchanged independently of the preform height. There was no measurable increase in porosity due to use of water cooling. The parameter selection procedure proposed and validated allowed an adequacy based on surface quality. Suitable Scalmalloy® preforms were produced by WAAM and with better productivity with the NIAC. The flat hardness profiles revealed along the building height indicated that material overaging did not take place on WAAM of such alloy. Moreover, the hardness levels increased significantly on heat-treated samples, indicating that Sc was retained in a supersaturated solid solution during deposition. It was concluded that the NIAC technique is able to mitigate heat accumulation in WAAM of aluminum and, thus, to potentially cope with the related drawbacks.