Influence of ambient pressure on SS316L plate fabricated with single mode fiber laser

Stainless-steel type 316L (SS316L) plate was fabricated by selectively laser melting method (SLM) in vacuum. SS316L has excellent properties such as a high corrosion resistance and hardness, but fabricating complicated structures is challenging due to difficulties in processing the material. Although SLM can fabricate complicated shapes because it builds a 3D material layer-by-layer from a powder, some issues have yet to be resolved. One is that spatter is generated by metal powder scattering during laser irradiation. Another one is the denudation zone due to the balling effect. Spatter is considered to be dominated by the recoil pressure of fume caused by melting and evaporation of metal, and it is not possible to suppress the expansion of fume and reduce spattering by changing the atmospheric pressure. In addition, it is considered that the balling effect is dominated by the surface tension of the molten land under atmospheric pressure with a lot of convection. Therefore, in this study, SS316L plate was fabricated by changing the atmospheric pressure in the chamber, and the effect of atmospheric pressure on the spattering and balling effects was clarified. First, SS316L powder was set in a vacuum chamber, depressurized using a vacuum pump, and then irradiated with a single-mode fiber laser. Spatter was captured using a high-speed video camera during laser irradiation of SS316L powder. After that, polishing, edging, and cross-section observation were performed. As a result, it was found that when the atmospheric pressure was lowered, the spatter amount and bead the height decreased, and the denudation zone increased.