On the varieties of build features during multi-layer laser directed energy deposition

Abstract

Laser directed energy deposition (DED) is an additive manufacturing (AM) process involving progressive deposition of individual layers to form a multi-layer build. A deep understanding of the spatiotemporal variations of the entire build, individual tracks and layers, and the molten pool is critical to the control of undesired deposition profiles and the production of targeted laser DED components. In this work, diverse build features during multi-layer laser DED of Ti-6Al-4 V are systematically explored on multiple scales via advanced 3D numerical modeling and corresponding experiments for various process conditions. The layer wise increments on the build top are demonstrated with distinct additive features of individual layers in transverse and longitudinal sections. The results show that the layer bottom boundaries vary from concave to flat and further convex at higher layers. Moreover, the influences of scanning strategies on the deviations of build profiles are investigated considering the reinforcement or the compensation of the uneven layer geometries along the scanning direction. The underlying mechanisms are revealed through dimensionless numbers and the transport phenomena of energy, mass, and momentum in the freeform molten pool during the multi-layer deposition process. The scientific findings provide useful insight for the deep understanding of the physical processes, and support further researches on microstructure evolution and resultant mechanical properties of the DED components.