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Projeto de investigação
Developments of wire and arc additive manufacturing
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Orthogonal cutting of Wire and Arc Additive Manufactured parts
Publication . Fonseca, Pedro P.; Vidal, Catarina; Ferreira, Francisco B.; Duarte, Valdemar R.; Rodrigues, Tiago A.; Santos, Telmo Gomes; Machado, Carla M.; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; Springer Science Business Media
This work aimed to evaluate whether the established scientific knowledge for machining homogeneous and isotropic materials remains valid for machining additively manufactured parts. The machinability of thin-walled structures produced through two different variants of wire and arc additive manufacturing (WAAM) was studied, namely conventional MIG deposition and the innovative hot forging variant (HF-WAAM). Cutting operations were carried out varying the undeformed chip thickness (UCT) and the cutting speed, using a tool rake angle of 25°. A systematic comparison was made between the existing theoretical principles and the obtained practical results of the orthogonal cutting process, where the relation between the material properties (hardness, grain size, yield strength) and important machining outcomes (cutting forces, specific cutting energy, friction, shear stress, chip formation and surface roughness) is addressed. Additionally, high-speed camera records were used to evaluate the generated shear angle and chip formation process during the experimental tests. The machinability indicators shown that, through the appropriate selection of the cutting parameters, machining forces and energy consumption can be reduced up to 12%, when machining the mechanical improved additive manufactured material. Therefore, it has been confirmed the feasibility of machining such materials following the traditional machining principles, without compromising the surface quality requirements.
In-situ hot forging directed energy deposition-arc of CuAl8 alloy
Publication . Duarte, Valdemar R.; Rodrigues, Tiago A.; Schell, N.; Miranda, R. M.; Oliveira, J. P.; Santos, Telmo G.; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; Elsevier
CuAl8 alloy finds applications in industrial components, where a good anti-corrosion and anti-wearing properties are required. The alloy has a medium strength and a good toughness with an elongation to fracture at room temperature of about 40%. Additionally, it has a good electrical conductivity, though lower than that of pure Al or pure Cu. Despite these characteristics, additive manufacturing of the CuAl8 alloy was not yet reported. In this work, the direct energy deposition-arc (DED-arc) with and without in-situ hot forging was used to determine the microstructure evolution and mechanical properties. No internal defects were seen on the parts produced. Hot forging combined with DED-arc was seen to reduce and homogenize the grain size, improve mechanical strength and isotropy of mechanical properties. Moreover, the use of this novel DED-arc variant was seen to reduce the magnitude of residual stresses throughout the fabricated part. We highlight that this alloy can be processed by DED-arc, and the hot forging operation concomitant with the material deposition has beneficial effects on the microstructure refinement and homogenization.
Developments in Directed Energy Deposition Additive Manufacturing: In-situ Hot Forging and Indirect Cooling
Publication . Duarte, Valdemar Rebelo; Santos, Telmo; Miranda, Rosa
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.
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Fundação para a Ciência e a Tecnologia
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Número da atribuição
SFRH/BD/139454/2018