Residual stress on AISI 300 sintered materials: effect of thickness

Selective Laser Melting (SLM) is one of the most interesting technologies in the rapid prototyping processes because it allows to build complex 3D metal parts. Moreover, full density can be reached and mechanical properties are similar to those obtained with conventional manufacturing processes. However, the most important drawback is related to the thermal transient encountered during solidification which generates highly variable residual thermal stresses in SLM parts. Parameters such as laser power, scanning strategy and velocity should be optimized also in order to allow full melting of the powders used in the process and minimize residual stresses that are strictly dependent on the manufacturing process and cannot be completely avoided. Geometry of parts should be optimized in order to keep residual stresses and distortions low. The aim of this paper is to investigate on residual stress distribution in SLM rectangular plates built by means of a new scanning strategy, implemented by dividing the fused zone in very small square sectors. The strain gauge hole drilling method is used to measure residual stress profiles in a set of test samples manufactured from the AISI Maraging 300 steel and characterized by different thickness. An analysis is performed in order to investigate the effect of thickness, position on the building platform and of distance from the surface of the specimens coming from the same process parameters on maximum and minimum principal residual stresses. The experimental results show that the melting/ solidification mechanism generates highly variable thermal residual stresses in the SLM parts used in this study.