Experimentelle und modelltheoretische Untersuchungen zum Extremen Hochgeschwindigkeits-Laserauftragschweißen
Aachen / Fraunhofer Verlag (2020) [Book, Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (105 Seiten) : Illustrationen, Diagramme
Extreme High-speed Laser Material Deposition (German acronym EHLA) is a new approach to Laser Material Deposition (German acronym: LA) with powdery additive materials. In this approach, the powdery additive material is melted above, rather than upon contact with the melt pool as with the conventional approach, and is thus supplied to the melt pool in liquid form. This eliminates the time required to melt the particles in the melt pool and allows the achievable feed rate to be increased from a few meters per minute to up to several hundred meters per minute. Up to now, however, there are no tools or methods available to describe the process-relevant factors that influence the process layout of EHLA, such as degree of transmission, particle-heating in the beam path, heating of the substrate and track formation. Consequently, there is no sufficient understanding of the process to estimate the technological limitations of the EHLA process in terms of achievable feed rate or track formation and to shift the process limits in the future to sustainably increase the application range of the process for production. The overall objective of the present work is therefore to develop the fundamentals of the EHLA process, which enable as well as principally limit the scalability of the process. First, the tools for the EHLA, the powder gas jet and the laser radiation, are characterized experimentally and described with a mathematical model. The model’s assumptions are derived from experimental observations. This allows to completely describe the physical process of EHLA for the first time as a function of the settings for powder feed (grain fraction, powder mass flow, etc.), working distance, laser power, and feed rate. Based on this enhanced breakdown of the process, this study demonstrates both experimentally and model-theoretically that the formation of a melt pool prior to contact with the molten particles is not a necessary condition for the production of metallurgically bonded layers. The substrate must be preheated by the transmitted radiation only to the extent that the energy input of molten powder particles is sufficient to form a metallurgical bond on the surface, even in the case of a solid, not yet molten substrate. This new process layout is called “Extreme High-speed Laser Melt Spraying” (MELT-X). Since MELT-X requires lower laser powers than the EHLA process, the achievable feed rate can be further increased, assuming otherwise identical conditions (degree of transmission, particle heating, etc.), and existing limits to the EHLA process can be overcome.