The manufacture of multiple parts on the same platform is a common procedure in the Laser Powder Bed Fusion (L-PBF) process. The main advantage is that the entire working volume of the machine is used and a greater number of parts are obtained, thus reducing inert gas volume, raw powder consumption, and manufacturing time. However, one of the main disadvantages of this method is the possible differences in quality and surface finish of the different parts manufactured on the same platform depending on their orientation and location, even if they are manufactured with the same process parameters and raw powder material. Throughout this study, these surface quality differences were studied, focusing on the variation of the surface roughness with the angle of incidence of the laser with respect to the platform. First, a characterization test was carried out to understand the behavior of the laser in the different areas of the platform. Then, the surface roughness, microstructure, and minimum thickness of vertical walls were analyzed in the different areas of the platform. These results were related to the angle of incidence of the laser. As it was observed, the laser is completely perpendicular only in the center of the platform, whilst at the border of the platform, due to the incidence angle, it melts an elliptical area, which affects the roughness and thickness of the manufactured part. The roughness increases from values of Sa = 5.489 μm in the central part of the platform to 27.473 μm at the outer borders while the thickness of the manufactured thin walls increases around 40 μm.

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One of the key aspects of the laser powder bed fusion (L-PBF) process is the quality of the raw powder since it affects the final properties of the manufactured parts. In this study, 13 batches of Inconel® 718 powder were analysed, all of them being specially designed for L-PBF technology and meeting similar requirements but coming from different suppliers. Therefore, these batches have certain differences in their characteristics, including the particle size distribution (PSD). This study presents the relationship between the PSD of each batch and the surface roughness obtained in the manufactured parts. For the roughness study, Sa and Sz parameters are presented; in addition, the size and frequency of the particles adhered to the surface were quantified, and an autocorrelation analysis was carried out. Furthermore, after this analysis, the parts were sandblasted in order to repeat the same analysis after removing the adhered particles from the surface. This work points to the fact that the particles adhered to the surface are the smallest particles in the powder batch, and their size affects the roughness of the final part. This means that the surface roughness is strongly related to the fraction of smaller particles within the PSD of the batch, while there is no relationship between the surface roughness and the larger particles.

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One of the factors that most affects surface roughness is the angle of incidence of the laser with respect to the platform, which varies across the platform. However, to make the L-PBF process a competitive technology, several parts must be manufactured on the same platform, using maximum building volume. Nevertheless, due to this angle of incidence, even if identical parameters and geometries are used, the surface finish of the parts varies considerably depending on the positioning of the part on the platform. Throughout this work, the effect that this angle of incidence has on the surface of parts manufactured in the different positions of the platform is presented. For this purpose, first the angle of incidence on the whole platform was determined. Then, based on these results, the distortion of the melt pool was analyzed analytically, with the aim of relating the poor surface finish, seen by different technologies such as infinite focus microscope or SEM, with the distortion of the melt pool generated by the angle of incidence.