In laser powder bed fusion (LPBF) the surface layer temperature is continually changing throughout the build process. Variations in part geometry, scanned cross-section and number of parts all inuence the thermal eld within a build. Process parameters do not take these variations into account and this can result in increased porosity and dierences in local microstructure and mechanical properties, undermining condence in the structural integrity of a part. In this paper a wide-eld in-situ infra-red imaging system is developed and calibrated to enable measurement of both solid and powder surface temperatures across the full powder bed. The inuence of inter-layer cooling time is investigated using a build scenario with cylindrical components of diering heights. In-situ surface temperature data are acquired throughout the build process and are compared to results from porosity, microstructure and mechanical property investigations. Changes in surface temperature of up to 200°C are attributed to variation in inter-layer cooling time and this is found to correlate with density and grain structure changes in the part. This work shows that these changes are signicant and must be accounted for to improve the consistency and structural integrity of LPBF components.
Melt ejection is the dominant material removal mechanism in long, ms, pulse laser drilling of metals, a process with applications such as the drilling of cooling holes in turbine blades. Droplets of molten material are ejected through the entrance hole and, after breakthrough, through the exit hole. High speed filming is used to study the ejected material in order to better understand how this debris may interact with material in the immediate vicinity of the drilled hole. Existing studies have quantified various aspects of melt ejection, however they usually focus on ejection through the entrance hole. This work concentrates on rear melt ejection and is relevant to issues such as rear wall impingement. A 2kW IPG 200S fibre laser is used to drill mild steel. High speed filming is combined with image analysis to characterise the rearward-ejected material. Particle size and velocity data is presented as a function of drilling parameters. It is concluded that high speed filming combined with image analysis and proper consideration of process limitations and optimisation strategies can be a powerful tool in understanding resultant debris distributions.
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