  Laser beam shaping offers remarkable possibilities to control and optimise
process stability and tailor material properties and structure in laser-based
welding and additive manufacturing. However, little is known about the
influence of laser beam shaping on the complex melt-pool behaviour, solidified
melt-track bead profile and microstructural grain morphology in laser material
processing. A simulation-based approach is utilised in the present work to
study the effects of laser beam intensity profile and angle of incidence on the
melt-pool behaviour in conduction-mode laser melting of stainless steel 316L
plates. The present high-fidelity physics-based computational model accounts
for crucial physical phenomena in laser material processing such as complex
laser-matter interaction, solidification and melting, heat and fluid flow
dynamics, and free-surface oscillations. Experiments were carried out using
different laser beam shapes and the validity of the numerical predictions is
demonstrated. The results indicate that for identical processing parameters,
reshaping the laser beam leads to notable changes in the thermal and fluid flow
fields in the melt pool, affecting the melt-track bead profile and
solidification microstructure. The columnar-to-equiaxed transition is discussed
for different laser-intensity profiles.

Materials Science;Fluid Dynamics