Abstract
In this study, a novel wire based plasma transferred arc (PTA)-laser hybrid additive manufacture process was proposed for deposition of large-scale titanium parts with high deposition rate and near-net shape. The optimum processing conditions, including the heat source configuration, wire feeding position, and arc-to-laser separation distance, were investigated. The benefits of using the hybrid process over the single PTA and laser deposition processes on their own were studied. The results show that compared to the single PTA process, the hybrid process has extended energy distribution and melt pool size, giving more interaction time of the wire with the heat sources and therefore a higher deposition rate. Compared to the laser process, the hybrid process has a much higher wire melting efficiency and tolerance to wire positioning accuracy. Owing to more distributed energy across the two heat sources, the likelihood of keyhole formation in the hybrid process is lower than that in the single PTA process. The best configuration for the hybrid process is the PTA leading, combined with front feeding of the wire. In this configuration, the PTA is used to melt the feedstock and the laser is used to control the melt pool size, which allows independent control of deposition rate and bead shape. A set of multi-layer walls was built to demonstrate the feasibility of this process for the manufacture of engineering parts. The results show that the achieved flat beads are very desirable for low surface waviness and lead to near-net-shape deposition. The main limitation of the hybrid process is remelting into the underlying layer. To overcome this, a multi-energy source process with more evenly distributed energy has been proposed.
Highlights
Directed energy deposition (DED) additive manufacture (AM) has developed rapidly due to advantages such as short lead-times compared to forgings, low material waste compared to machining, and high design flexibility, as described by Singh et al (2020)
In wire + arc additive manufac ture (WAAM), using the plasma transferred arc (PTA) process, reasonable deposition rates can be achieved (e.g. 1 kg/h for titanium) due to the high energy transfer efficiency of the electric arc compared to lasers, making large-scale parts achievable in reasonable times (Williams et al, 2016)
For arc-laser hybrid AM, there have been only a few research papers published in the past few years, and most of them are based on gas metal arc (GMA) process
Summary
Directed energy deposition (DED) additive manufacture (AM) has developed rapidly due to advantages such as short lead-times compared to forgings, low material waste compared to machining, and high design flexibility, as described by Singh et al (2020). For arc-laser hybrid AM, there have been only a few research papers published in the past few years, and most of them are based on gas metal arc (GMA) process This is because the GMA process has higher tolerance in path planning and omnidirectionality than gas tungsten arc (GTA) and PTA, owing to the coaxial configuration of the consumable electrode (i.e. wire) and torch. Miao et al (2020) compared the microstructure and mechanical properties of aluminium parts deposited by both the GTA-laser hybrid deposition process and GTA based deposition process They found that the addition of the laser led to more uniform element distribution and finer grains caused by the strengthened fluid flow and high cooling rate in the laser-affected zone. This is a multi-energy source (MES) approach utilising three heat sources (one PTA and two separate lasers)
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