Evaluation of the influence of nozzle cooling during the Hot Forging Wire and Arc Additive Manufacturing process

• Autor(a) principal: Amendoeira, Daniel Alexandre Estima
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/164242
• topic: WAAM; hot forging; cooling; HSLA steel; microstructure; grain refinement; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Mecânica

Additive manufacturing processes have emerged to complement the conventional processes, allowing the production of components with high geometrical complexity and reducing raw material waste. Among additive manufacturing processes for metals, the Wire and Arc Additive Manufacturing (WAAM) technology has aroused particular interest due to its capacity to produce large-scale components in useful time. However, there are common limitations in additive manufacturing processes that need to be overcome in order to industrialize the process, particularly the formation of porosities, coarse microstructures and anisotropy. This work focused on the design and study of a new variant of WAAM technology that combines the advantages of mechanical deformation with forced cooling. This variant consisted of hot forging between the deposition of each layer using a cooled hammer with the aim of increasing the cooling rate of the material, reducing the peak temperature, promoting grain refinement and reducing the anisotropy. Samples of a high-strength low-alloy (HSLA) steel were produced, with and without the use of the hammer, on which uniaxial tensile tests, microhardness, electrical conductivity and optical microscopy were performed. Moreover, thermography was used to analyze the thermal cycles that occurred in the material. It was found that hot forging contributes to refining the microstructure and reducing the anisotropy of the material. Combining the cooling system with hot forging led to a 77% reduction in hammer temperature and a 12% reduction in peak temperature and has helped to increase the material's cooling rate. After the tensile tests, the samples registered an increase in their mechanical strength and all exhibited ductile fracture. Furthermore, the use of the hammer caused a considerable reduction in the quantity and size of pores. Keywords: