Experimental analysis of laser post-processing of additive manufactured metallic parts

This work focuses on laser-assisted surface finishing and modification of metallic parts produced by means of the selective laser melting (SLM) process. The combination of additive manufacturing (AM) and subsequent laser polishing is a technical approach with high flexibility in comparison to conventional processes. AM parts often present the need of post-processing due to surfaces with roughness higher than the admissible for most applications. The laser polishing process is based on ablation and melting of a small amount of surface material, through laser energy absorption. The affected surface material is redistributed in order to create a homogenous layer with reduced roughness and probably new functionalities. Besides the flexibility, laser polishing provides high processing speed and capability for localized surface treatment. In the presented study, post-processing is realized by different types of lasers in terms of pulse duration, continuous wave (cw), short (ns) and ultrafast (ps, fs) pulses. Ultrafast laser radiation induces almost no heat to the surrounding material during ablation, while nanosecond and especially continuous wave lasers are used to generate a molten film at the surface, resulting in modified material properties of the re-solidified layer in comparison to the bulk material. ... mehrWith different laser operating modes, one achieves different surface qualities (roughness) and functionalities. Besides the pulse duration, the influences of the scan speed, repetition rate and average laser power are investigated. The resulting characteristics of AM parts irradiated by laser sources with these different technical features are examined and a suitable combination of laser processing sequences is discussed. The material under analysis is the 18Ni Maraging steel (300 grade). The samples present simple prismatic geometry. The different surfaces resulting from the AM process present varying roughness Ra in the range of 2 to 6 µm due to particularities of the process, such as powder attached to the surface or porosity. For that reason, both the side and top surfaces of the samples are analysed. To evaluate the impact of laser processing on the material, the surface roughness and microstructure are presented and correlated to the process parameters.