Sensitivity of surface roughness to laser parameters used for polishing additively manufactured Co-Cr alloy

Abstract

Poor fatigue life, which is impacted by a rough and irregular surface, is a critical challenge that additive manufacturing needs to overcome to facilitate widespread engineering use. Laser polishing, in which a laser irradiates, melts, and smooths a surface through surface tension, is one solution. This work studies the laser polishing of laser powder bed fusion cobalt‑chromium samples through experimentation and microscopy of the surface before and after polishing. The laser processing parameters that contribute to the smoothing performance of four different surface texture parameters are analyzed. It is found that laser power plays an outsized role in smoothing the surface, followed by hatch spacing, scanning velocity, and beam diameter. The greater role of power compared to beam diameter and velocity is explained using analytical temperature models of a Gaussian heat flux on a semi-infinite surface. The influence of the starting surface is also discussed, and the variability in the final laser polished surfaces is partially attributed to the variability that occurs on the original printed surface due to the sporadic adherence of particles and particle agglomerates. This work provides an overview of important processing aspects for furthering the commercialization of the technology for the finishing of additively manufactured parts.