High-speed images of a common laser-based metal 3D printing process, coupled with newly updated computer models, have revealed the mechanisms behind material redistribution, a phenomenon that leads to defects in printed metal parts, Lawrence Livermore National Laboratory (LLNL) researchers reported. In a study published by Scientific Reports (link is external), LLNL scientists combined ultrafast imaging of melt-pool dynamics with high-resolution simulations, finding that particles of liquid metal ejected from the laser’s path during the powder-bed fusion additive manufacturing (PBFAM) process — commonly called “spatter” — is caused by the entrainment of metal particles by an ambient gas flow, not from the laser’s recoil pressure, as previously believed. “People have been assuming that recoil pressure leads to spatter because that’s what the laser welding community has seen,” said Sonny Ly, an LLNL physicist and the paper’s lead author. “We imaged right at the melt pool and you could see particles ejected right from the pool due to recoil, but a majority of particles are swept away and entrained by the gas flow. The entrained particles can go back into the laser beam and are melted, leading to a more dominant form of spatter.”“