Laser-induced plume investigated by finite element modelling and scaling of particle entrainment in Laser Powder Bed Fusion (LPBF)
2019
Although metal vaporisation has been observed in several laser processes such as drilling
or welding, vapour plume expansion and its induced side effects are not fully understood.
Especially, this phenomenon is garnering scientific and industrial interest since recent
investigations in laser powder bed fusion (LPBF) have designated metal vaporisation as main
source of denudation and powder spattering. The present study aims to provide a new insight
on the dynamics of laser-induced vaporisation and to assess the potential of different gases
for particle entrainment. A self-consistent finite element model of laser-induced keyhole and
plume is thus presented for this purpose, built from a comprehensive literature review. The
model is validated with dedicated experimental diagnostics, involving high-speed imaging
to measure the ascent velocity of the vapour plume. The transient dynamics of vapour plume
is thus quantified for different laser incident intensities and gas flow patterns such as the
mushroom-like structure of the vapour plume are analysed. Finally, the model is used as a tool
to quantify the entrainment flow expected in LPBF and an analytical model is derived to define
a velocity threshold for particle entrainment, expressed in term of background gas properties.
Doing so it is possible to predict how denudation evolves when the gaseous atmosphere is
changed.
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