Experimental Analysis of Residual Stresses in the Selective Laser Melting Process

Selective Laser Melting (SLM) is becoming very diffused in layer manufacturing processes because of the possibility to build complex 3D parts. The process is mainly suited for the production of tools and inserts with internal undercuts and channels for conformal cooling in fast injection molding cycles. Manufacturing of parts is obtained by consolidating successive layers of metal powder material. This is done by means of the thermal energy supplied by a focused laser beam. In order to reach high density, metallic powder particles are fully molten by the laser beam. However, the laser melting process is difficult to control. The most important drawback is the generation of highly variable residual thermal stresses during the process. This paper aims to study the effect of positioning powders in the platform and part thickness on residual stresses of SLM-fabricated components. This is done in purpose to estimate reproducibility of SLM process results in terms of mechanical properties. Specimens fabricated through SLM have been submitted to tensile tests. Furthermore, residual stresses have been measured by means of the strain gage hole drilling method on the same set of specimens. The investigated material, the AISI 18 Maraging steel, possesses high hardness, is one of the most used materials in the moulds industry.