The periodic undulation of a molten track's height profile in laser-based powder bed fusion of metals (PBF-LB/M) is a commonly observed phenomena that can cause defects and building failure during the manufacturing process. However a quantitative analysis of such instabilities has not been fully established and so here we used Rayleigh-Plateau theory to determine the stability of a single molten track in PBF-LB/M and tested it with various processing conditions by changing laser power and beam shape. The analysis discovered that normalized enthalpy, which relates to energy input density, determines whether a molten track is initially unstable and if so, the growth rate for the instability. Additionally, whether the growth rate ultimately yields significant undulation depends on the melt duration, estimated by dwell time in our experiment.
Laser polishing is widely employed to reduce the surface roughness of products with complex geometries. Traditional laser polishing techniques use a single high-power Gaussian beam to melt and smooth a thin layer of surface material. However, the reliance on high power lasers can present practical challenges such as minimizing surface evaporation or reducing overall cost. In this work, we combined two identical low-power laser beams with a spatial offset in between them to construct an elliptical beam. By changing the spatial offset, combined beams with different lengths along the major axis can be created. We observe over 20% improvement in line roughness reduction using this approach compared to a single Gaussian laser beam with the same total power. Additionally, both experiment and simulation results suggest such improvement is because this dual-laser set-up can create a longer molten pool compared to a single laser.
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