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 the additive manufacturing. This process can be used to produce components with a high degree of complexity and design freedom as well as with material density. Unfortunately, hundreds of factors influence the quality of the processes and thus the material characteristics 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 in additive manufacturing of metals. The LSP is a non-destructive testing method which examines optical interference patterns bases on the speckle phenomena for the defect detection on surfaces. For this purpose, samples with a specific pore structure in the near-surface zone which influences the surface characteristics were manufactured. With the LSP, the surfaces were measured to verify a correlation between the roughness and the LSP signal. Depended on the surface roughness different absorption behaviors of the fabricated specimens were determined during external laser excitation as a part of LSP measurement and simultaneously measured temperature.