Investigation of the roughness influence on the absorption behavior of additively manufactured metals by the Laser speckle photometry

The Laser Powder Bed Fusion of Metals (LPBF-M) is one of the most important methods in additive manufacturing. The process can be used to produce components with a high degree of complexity and design freedom with high mechanical properties. Unfortunately, hundreds of factors influence the quality of process and material, which limits the reproducibility and the economic viability. Therefore, quality control during process as well as the testing of material properties afterward is one of the key development fields. This paper presents the applicability of the Laser-Speckle-Photometry (LSP) for determination of the surface topology of additively manufactured metals. The LSP is a non-destructive testing method, which examines optical interference patterns and changes based on the speckle phenomena. For this purpose, samples with a specific pore structure in the surface were manufactured for optical roughness measurement and correlation to the LSP signal during laser excitation. By the help of an experiment the different absorption behaviour of the 3d printed specimen according to the roughness could be determined based on measured temperatures. With a simple setup of the LSP, the absorption influence due to the varied roughness can also be detected.