Numerical investigation of balling defects in laser-based powder bed fusion of metals with Inconel 718

Abstract

Balling is one of the main single melt track defects limiting stable production of dense parts with laser-based powder bed fusion of metals (PBF-LB/M) additive manufacturing. A fundamental understanding of balling therefore is critical for process control and optimization. Violent interface dynamics present a severe challenge for mesh-based numerical schemes, and can be dealt with by particle methods. In this study, we focus on investigating single melt tracks by smoothed particle hydrodynamics (SPH). The considered regime is characterized by long liquid melt pools and remelting of the previous layer. The balling mechanism is driven by Marangoni and capillary forces. The resulting convective melt flux leads to the accumulation of melt in the tail region and leaves an exposed area of marginal layer build-up. In addition to the competing mechanisms of solidification and spreading, a competition between spreading and melt contraction shortly after the melt pinch-off is observed. We find a similar balling behavior yet different ball size at different laser power settings. We stress that SPH with accurate interface modeling has the capability to quantify balling processes and to improve the understanding of balling mechanisms.