  In a powder bed fusion additive manufacturing (AM) process, the balling
effect has a significant impact on the surface quality of the printing parts.
Surface wetting helps the bonding between powder and substrate and the
inter-particle fusion, whereas the balling effect forms large spheroidal beads
around the laser beam and causes voids, discontinuities, and poor surface
roughness during the printing process. To better understand the transient
dynamics, a theoretical model with a simplified 2D configuration is developed
to investigate the underlying fluid flow and heat transfer, phase transition,
and interfacial instability along with the laser heating. We demonstrate that
the degree of wetting and fast solidification counter-balance the balling
effect, and the Rayleigh-Plateau flow instability plays an important role for
cases with relatively low substrate wettability and high scanning rate.

Fluid Dynamics;Soft Condensed Matter