Laser Polishing of Laser Additive Manufactured Hastelloy-X: Parametric Dependence and Process Optimization

Abstract

The components built using laser additive manufacturing (LAM) suffer from various issues, like—stair-stepping effect, balling effect and presence of partially melted powders, which results in higher surface roughness. Thus, the surface finish of LAM built components is not suitable for various engineering applications in the as-built condition. Therefore, post-processing is necessary to improve the aesthetics and surface quality of LAM built components. Laser polishing is one of the advanced post-processing techniques that can be used for improving the surface quality of LAM built components. Laser polishing can be used to improve the surface quality of various engineering components for aerospace, automobile, biomedical, construction, cryogenics and nuclear industries due to its inherent advantages, like—smaller processing time, ability to access intricate shapes and smaller areas, etc. Hastelloy-X is the one of the nickel superalloys processed by LAM for building complex shaped components for nuclear and aerospace sector. As LAM is used for building components with complex geometry, it is difficult to deploy conventional polishing techniques for polishing of LAM built components. Thus, laser polishing can be considered as an ideal choice for improving the surface finish of such components. In the present work, an experimental investigation is carried out to optimize the process parameters during continuous wave fibre laser-based laser polishing of LAM built Hastelloy-X surface. The parametric dependence is investigated through design of experiments as per Taguchi L9 array with laser power, process speed, percentage of laser line overlapping and stand-off distance. Analysis of variance (ANOVA) is performed to identify significant laser parameters and it is observed that the laser power and line overlapping are the most significant factors. An improvement in average surface finish by ~30% (from a value of Ra = 8.46 µm to 5.7 µm) is achieved at the optimum process parameters. The study open avenues for the potential deployment of laser polishing for post-processing of LAM built components.