Michael Berghaus

Powder bed fusion using a laser beam (PBF-LB/M) is a widely utilized additive manufacturing technique known for its ability to produce complex geometries with high precision. However, there are numerous factors that can influence the properties of components manufactured by this process. One scarcely investigated factor is the laser incidence angle, which refers to the orientation and positioning of a component relative to the direction from which the laser interacts with the layer to be melted. This study examines the effect of the laser incidence angle on surface roughness and fatigue properties of 316L components. Although the laser incidence angle varies during layer-by-layer deposition, two initial part orientations were investigated. IA specimens were oriented toward the laser, while IT specimens were oriented away from it. This initial orientation establishes a trend in the effective incidence angle throughout the build. Results confirmed that the tendency of the laser incidence angle significantly affects surface roughness and can contribute to the formation or reduction of internal defects. Increased surface roughness and internal defects, particularly the latter, adversely impact fatigue strength, with internal defects playing a primary role in crack initiation in this study. Given that the initial part orientation establishes the effective laser incidence angle trend, careful positioning of components on the build plate is crucial for optimizing surface quality and fatigue properties of additively manufactured parts.

Due to its ease of processing, the stainless steel 316L is a widely used material for the laser powder bed fusion (PBF-LB/M) process. Compared to other additive manufacturing technologies PBF-LB/M has a lot of advantages such as design freedom and high resolution of details. However, PBF-LB/M also has some disadvantages, such as a reduced build-up rate. In general, 316L provides a wide range of parameter settings used for PBF-LB/M. In this study, the manufacturing limits were approached allowing a maximum build-up rate along with a high relative density > 99% without compromising the required mechanical properties. Microstructure analyses as well as tensile tests were performed to validate this approach. This article also provides insights on defects and relative density for scanning speed above 3000 mm/s. Furthermore, it was shown that the scanning speed has a major influence on the grain size and on the texture of the specimens. For the first time, the relative density, microstructure and mechanical properties of additively manufactured 316L were determined in relation to each other for high scanning speed. A set of parameters has been found that works best with a laser power of 285 W and a scanning speed of 1250 mm/s which results in a specimen relative density of 99.2%, a yield strength of 425 MPa, a tensile strength of 586 MPa and a build-up rate of 4.64 mm³/s. The findings can be further used to enhance the mechanical properties of PBF-LB/M 316L in terms of high build-up rates.