High deposition rate approach of selective laser melting through defocused single bead experiments and thermal finite element analysis for Ti-6Al-4V

Abstract

Selective laser melting (SLM) is a commonly used powder bed fusion metal additive manufacturing (AM) process. Although SLM is preferred due to its near-net-shape part commitment, the deposition rate of this process is slower compared with alternative metal processes. A higher deposition rate of SLM can be obtained by increasing the laser scanning velocity and laser power; however, this results in decreased part quality due to the SLM process’s physical limits. This study presents the conditions for a higher deposition rate for various process parameters with defocused beams to eliminate the void defects due to keyholing formed in the melt pool. Single bead experiments were conducted, and the thresholds of the process parameters resulting in voids were identified. A melt pool depth-to-width ratio of 0.85 was found to be a critical value for preventing voids in the process. The melt pool aspect ratio was related with the process parameters by using the normalized enthalpy and the volumetric energy density. The threshold values of the normalized enthalpy due to voids were independent from the beam diameters. Moreover, unstable single bead track thresholds were plotted as a function of the beam diameters. In addition to the experiments, a finite element analysis model was built with calibrated absorptivity and heat source parameters to predict the melt pool geometries for a wide range of process parameters (power = 100–370 W, velocity = 200–2000 mm/s, and beam diameter = 100–260 μm).