Beyond layer-by-layer additive manufacturing - Voxel-wise directed energy deposition

Conventional additive manufacturing is a layer-by-layer process, reliant on the sequential deposition of 2-1/2 D layers oriented along a build axis. During directed energy deposition a feedstock is directed into a continuous melt pool formed by a laser or electron beam. The ability to produce overhangs is limited due to the gravitational, surface tensions, and fluid-flow force acting on unsupported melt pools. Here, we present a novel, directed-energy-deposition technique where vertical and overhanging structures are formed by laser power modulation and the motion of a laser beam in three dimensional space along the build-up direction, rather than strictly in a single layer. We demonstrate that highly-overhanging Ti-6Al-4V structure, i.e. in which the overhang angle exceeds 45 degrees with respect to the x-y plane, can be deposited using the developed technique. High-speed imaging is used to gain insight into the physics of the process. The use of a pulsed or power-modulated beam is found to be critical to the formation of overhangs.