EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Stainless steel 316L has traditionally been the material of choice for maritime industries due its combine strength and corrosion performance. The ability to produce reliable and reproducible components from 316L using additive manufacturing is nowadays crucial to serve the need for customization and on-demand manufacturing. Especially selective laser melting has attracted significant research interest for this purpose, with particular focus on process optimization dedicated to the increase of part density, wear properties and maintaining its corrosion properties. However, even small change in the processing parameters, equipment and feedstock powder characteristics can influence the microstructure and subsequently the mechanical properties of the fabricated parts.
In this work, full factorial and Taguchi design of experiment approaches have been employed to systematically examine the widely adopted, energy density factor as a means of evaluating the quality of the final component. Initially a three-level full factorial analysis investigating the effects of (a) laser power, (b) scanning speed, (c) hatch spacing, and (d) layer thickness on the resulting density and hardness has been employed. Density measurements determined by Archimedes’ principle and microhardness experiments indicated that, laser power consistently improved part density and hardness, while decreasing scanning speed had the opposite effect. Melt pools revealed through chemical etching validated regulated hatch spacings and layer thicknesses. In general, the results indicated a clear shift in the porosity formation mechanism from low to high energy density values due to lack of fusion effects or vaporization of alloying elements. Nevertheless, application of design of experiment regression models to predict the required process parameters should only be employed in known systems with significant approximations. This was especially evident in subsequent investigations focusing on the Taguchi approach indicating that parameters such as scanning strategy and powder size distribution can lead to significant deviations in the expected results.