In-situ characterization and quantification of melt pool variation under constant input energy density in laser powder bed fusion additive manufacturing process

Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

“…Sometimes Equation (1) is slightly modified when referring to a linear specimen (IED = P/v) [106,107]. While similar properties are expected when IED is fixed but its variables change [9,32,[108][109][110], Guo et al [20] showed that the effect of laser power and scan speed should be evaluated differently since they could lead to different laser-powder interaction results. In order to account more for the process parameters which lead the LPBF process, energy density can be defined as volumetric and calculated as a function not only of the laser power (P) and scan speed (v), but also of the layer thickness (t) and hatch spacing (h), as outlined in Equation (2) [9,42].…”

“…Metals 2019, 9, x FOR PEER REVIEW 8 of 21 [20] showed that the effect of laser power and scan speed should be evaluated differently since they could lead to different laser-powder interaction results.…”

“…This instability results in a vertical deformation of the melt pool close to process conditions which are known to generate keyholes in LPBF [33]. A dynamic melt pool [20] given by fluid instability (Marangoni convection [112]) is due to the comparable size between size of the powder particles and laser spot and dominated by spatially varying absorptivity and vapor recoil [93,113].…”

“…It is worth noting that LPBF has more similarities with laser welding rather than casting, since the two laser-based techniques have some common features (i.e., melt-pool formation, moving heat source) [18]. However, process parameters are, in general, quite different in terms of laser power and scan speed, and the laser-matter interaction is much more complicated in LPBF processes, since the powder feedstock is inherently unstable and the solidified material undergoes multiple thermal cycles corresponding to the fusion of subsequent layers during the additive process [19][20][21][22]. Furthermore, owing to the similarities with welding and to the complicated interaction between laser and metal particles, when comparing laser powder bed fusion with other metal forming processes, it is evident that the range of processable alloys is very limited and the number of high-productivity commercially available alloys is even smaller [23].…”

A modified volumetric energy density–based approach for porosity assessment in additive manufacturing process design

“…4 Processed images for the porosity amount assessment (samples obtained with: a power = 375 W, exposure time = 30 μs; b power = 300 W, exposure time = 30 μs) Fig. 3 Scanning strategy (a); spot-to-spot fabrication process, where 's' is the point distance, 'Φ' is the laser beam spot and h is the hatch distance (b) depression induced by the recoil pressure on the melt pool and thus the heat absorption [35,36]. However, this phenomenon would complicate the use of the E d,eff as design parameter; therefore, in this work, it is ignored and the value of β as well as α are kept constant.…”