Surface Roughness Improvement of PBF-LB Manufactured 316L with Dry Electropolishing

Abstract

Laser powder bed fusion (PBF-LB) technique can currently offer the lowest surface roughness among all available techniques for metal additive manufacturing. Still the measured values for Ra can easily be over 10 μm depending on the used layer thickness and printing parameters. The current work focuses on improving the surface roughness by utilizing dry electropolishing machine. While suitable for many materials, the material selected for this study is one of the most used in PBF-LB manufacturing, stainless steel 316L. In addition, multistep pre-grinding with the grade of the final finish varied was used to investigate what is the most efficient way to distribute manual preparation work and automated polishing to reach the desired surface roughness. Furthermore, severe shot peening was used before the polishing to study the effect on residual stresses and fatigue life of the material. Laser optical microscopy was used to investigate the surface properties and it was found that dry electropolishing with pre-grinding could be succesfully used to obtain average roughness levels as low as 0.13 μm. The highest reductions in surface roughness were reached with the rougher initial surfaces where it could be reduced by 80% at best. Residual stresses measured after the severe shot peening were preserved after the polishing but did not result in increased fatigue strength.