Leveraging multiple lasers in powder bed fusion

Laser powder bed fusion (L-PBF) additive manufacturing (AM) is a technology that produces 3D components by consecutively melting thin layers of powder. L-PBF makes use of a laser beam to melt the metal powder particles that promptly solidify as the laser spot moves on. The repeated melting-solidification cycles are responsible for the complex thermal history that leads to residual stresses and displacement of the manufactured components. One major challenge limiting the spread of L-PBF is the low productivity rate. Strategies to enhance the performance encompass the modification of process parameters, such as enlarging the laser beam diameter, layer thickness, and laser power. However, such solutions lead to a deterioration of the density and geometry accuracy of the component as well as the generation of internal defects. To overcome these limitations multi-laser powder bed fusion (ML-PBF) systems were introduced. Nonetheless, this technology establishes new challenges. In addition to the interactions between laser and material, interactions between the laser beams may be generated, and the latter can influence the material properties. This Ph.D. project aims to investigate the different interaction mechanisms in ML-PBF systems. Most of the efforts will go on ML-PBF process optimization through experimental work, thermal/thermomechanical simulations to estimate thermal distributions inside the component, and in situ process monitoring. Specifically, the following phases will be carried out: (1) mapping the inherent process variability in a ML-PBF system; (2) perform thermal/thermomechanical simulations of dual laser scanning; (3) the above results together with a deep understanding of the selected alloy will be exploited to optimize the ML-PBF process parameters in order to induce or avoid microstructural changes (allotropic transformations, secondary particle precipitation, solidification structures, cracking, …), and/or minimize residual stresses. The final outcome of the research will provide scan strategies that consider laser-laser interactions by either avoiding or leveraging them to enhance the mechanical properties of the component and manipulate the material microstructure.