Developments in Directed Energy Deposition Additive Manufacturing: In-situ Hot Forging and Indirect Cooling

Additive Manufacturing (AM) by Directed Energy Deposition-arc (DED-arc) is competing with other AM technologies due to its high deposition rate, ability to produce large parts with medium/high geometric complexity and low capital and running costs. However, residual stresses, coarse microstructures, and defects on parts, such as cracks and pores, may compromise in-service industrial applications and need to be overcome. This work aimed to develop and validate two innovative process variants: one based on in-situ hot forging; and the other on temperature control, that is, indirect cooling of deposited material and hot forging. The hot forging variant consisted of locally forging the deposited layer at high temperatures using low forces. The goal is to create an uniform plastic deformation zone along the layer, to promote grain refinement, reduce material anisotropy and collapse defects. The variant based on temperature control consisted of cooling the hammer components and the shielding gas used to protect the molten pool, to increase the solidification rate and thus, prevent grain coalescence. For this, dedicated DED-arc equipment was designed and manufactured with specific features for research. The effect of hot forging was analysed in detail on 316LSi stainless steel, and the feasibility of its application was verified in other relevant industrial materials. It was concluded that hot forging can induce dynamic recrystallization, increase nucleation sites and prevent epitaxial grain growth. Thus, it contributes to an overall refined and homogeneous microstructure with improved mechanical properties. The developed cooling system lowered the average temperature of the nozzle and hammer during consecutive depositions. Cooling of the shielding gas had no major effect on the cooling rates and microstructure of the materials, however, it was observed that the hot forging changes the heat flow conditions of the part, promoting higher cooling rates.A tecnologia de deposição direta de energia por arco (DED-arc) tem competido com outras tecnologias de fabrico aditivo devido à sua elevada taxa de deposição, capacidade de produzir componentes de grandes dimensões com média/alta complexidade geométrica e baixos custos de implementação e funcionamento. Contudo, as elevadas tensões residuais, as microestruturas grosseiras, ou os defeitos do tipo poros, podem comprometer algumas aplicações industriais e necessitam de ser superados. Este trabalho visou desenvolver e validar duas variantes inovadoras de processo DED- arc: uma baseada no forjamento a quente; e outra no controlo de temperatura. A variante baseada no forjamento, consistiu em forjar o material depositado imediatamente após a deposição, utilizando baixas forças. O objetivo foi a produção de uma zona de deformação plástica uniforme ao longo de cada camada, para promover alterações microestruturais, nomeadamente o refinamento dos grãos e a redução da anisotropia. A variante baseada no trabalho termodinâmico consistiu em arrefecer os componentes do martelo e o gás utilizado para proteger o banho de fusão, com o objetivo de aumentar a taxa de arrefecimento e assim evitar a coalescência dos grãos. Neste sentido, foi concebido e fabricado um equipamento de DED-arc, com características específicas para investigação. O efeito do forjamento a quente foi estudado detalhadamente no aço inoxidável 316LSi, e foi verificada a viabilidade da sua aplicação noutros materiais relevantes industrialmente. Concluiu-se que o forjamento induz recristalização dinâmica, aumenta os pontos de nucleação e impede o crescimento de grãos epitaxiais, contribuindo para uma microestrutura globalmente mais fina, homogénea e com melhores propriedades mecânicas. O sistema de arrefecimento desenvolvido baixou a temperatura do bocal e do martelo durante as deposições consecutivas. O arrefecimento do gás de proteção não teve efeito nas taxas de arrefecimento nem na microestrutura do material, contudo, observou-se que o forjamento altera as condições de fluxo de calor, promovendo taxas de arrefecimento maiores

Additive manufacturing of a high resistance steel by MIG/MAG

Additive manufacturing (AM) is considered to be part of the 4th Industrial Revolution in digital era with advances in product design, materials, process engineering and simulation and data transfer software. Recent developments focus in the production of metallic components with more complex shapes, big sizes at reduced costs. Special highlight has been given to welding technologies where the electric arc is the heat source and the consumable wire, the material to deposit. High deposition rate, relatively low costs and accessibility are the main reasons for the interest in wire and arc additive manufacturing (WAAM). This study focused on using WAAM to produce simple shapes in high strength low alloy steel and characterize: the process, the geometrical features and the mechanical and structural properties of deposited material. The influence of the process parameters on the deposition characteristics was also studied. It was concluded that arc welding is a feasible technology to produce components by WAAM in the material under study without internal defects. Both mechanical and structural characterization confirmed the integrity of produced parts. A constant material deposition was achieved, with a deposition width of about 5 mm and a waviness around 110 m, which is very much below reported results for other metallic materials. Tensile strength was above the one specified for the wire and is consistent with hardness measured, ranging from 800 MPa to 1 GPa depending on the heat input. Deposition rates from 122.9 to 427.5 cm3/h were obtained

Arc-based directed energy deposited Inconel 718: role of heat treatments on high-temperature tensile behavior

This study evaluated the effect of dedicated heat treatments (1050°C, 1100°C, 1142°C, and 1185°C/2 h + double-aging) on the uniaxial tensile properties at elevated temperature (650°C) of Inconel® 718 fabricated via arc plasma directed energy deposition. They enabled to meet, for the first time, the AMS 5662 requirements at elevated temperature. Tensile tests exhibited ductile strain–stress curves. The 1100°C/2 h + double-aging showed the best performance (YS0.2%, UTS, and elongation of 967 MPa, 1126 MPa, and 18.7%, respectively). Additionally, vertical specimens evidenced dynamic strain aging, although no brittle-like features were observed