PSI - Issue 37

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G. Macoretta et al. / Procedia Structural Integrity 37 (2022) 632–643 G. Macoretta, B. D. Monelli / Structural Integrity Procedia 00 (2019) 000 – 000

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= 2 ∙

(3)

where T m is the material melting temperature, n is a numerically evaluated constant, r and l the meltpool radius and length defined in Fig. 1 (a). This approach, preliminarily validated by literature data, was thus employed to predict the SLM feasible region for the Inconel 718, by introducing in the model the material thermal properties at the temperature nearest to the solidification temperature, Agazhanov et al. (2019), and the absorptivity of a laser beam having the same characteristic length of the one employed by the SLM machine, Montgomery et al. (2020); Zhou et al. (2019). The process feasible region is represented by the green hatched area in Fig. 1 (b), where a round marker represents the most widely used set of process parameters present in the more recent literature that report an almost full-dense material, named as a baseline condition. While lack of fusion line can be considered as a boundary geometrically connected with the density of the final part, the aspect ratio, orange dotted, lines only describe meltpool featuring the same aspect ratio ( A r ) and are only indirectly linked to material-dependent defects (i.e. humping or hot tearing cracks), Guo et al. (2020).

Fig. 1. (a) Cross-section and top view of the meltpool geometry predicted by the analytical model for a single scan line, (b) SLM process feasible region for the alloy Inconel 718. The productivity rate of the SLM can be defined as the nominal melted volume per unit of time: = ∙ ℎ ∙ [ 3 ] (4) where t is the layer thickness, h the hatch distance, and v the scan velocity. Two sets of process parameters aimed to significantly increase the process productivity were developed, named A1 and A2 , featuring a similar laser power but different values of scan speed and hatch distance, resulting in a meltpool aspect ratio of 8 and 10, respectively. In order to preserve the nominal vertical resolution of the printing process, the layer thickness was kept constant and equal to 60 μm. The present parameter sets were employed both for the hatching phase of the laser scan and for the external contour of the specimen.