A study of high frequency laser beam oscillation induced keyhole dynamics in laser powder bed fusion additive manufacturing process

Abstract The metal additive manufacturing (AM) industry is actively developing instruments and strategies to enable higher productivity, optimal build quality, and controllable as-built microstructure. One of the beam controlling techniques, laser oscillation has shown potential in all these aspects in laser welding; however, few attempts have been made to understand the underling physics of the oscillating keyholes/melt pools which are the prerequisites for the these strategies to become a useful tool for laser-based AM processes. To address this gap, we utilized a synchrotron-based X-ray operando technique to image the dynamic keyhole oscillation in Ti-6Al-4V using a miniature laser powder bed fusion setup. We found good agreement between the experimental observations and simulations performed with a validated Lattice Boltzmann multi-physics model. The study revealed the continuous and periodic fluctuations in the characteristic keyhole parameters that are unique to the oscillating laser beam processing and responsible for the chevron pattern formation at solidification. Despite the intrinsic longer-range fluctuation, the oscillating technique displayed potential for reducing keyhole instability, mitigating porosity formation, and altering surface topology. The results provide important insights about the dynamics of the oscillating keyholes which are valuable guidelines for the future development and application of this technique.