Porosity reduction by co-axial laser shock modulation of molten pool in powder-bed selective laser sintering: take widely-used stainless steel as an example

Powder-bed metal additive manufacturing is often troubled by high porosity issue resulted from gas trapping and keyhole instability. Here, this work is the first to propose a breakthrough approach: in-situ molten pool modulation by low-pulse-energy co-axial laser shock. An additional pulsed laser beam is coupled to a selective laser sintering system to achieve low-porosity high-quality manufacturing of metal parts. In-situ monitoring shows that the used laser shock method inhibits severe splashing during sintering, contributing to the achieved low porosity. Computed Tomography (CT) quantifies the volume, diameter, and sphericity of pores. Results show that the porosity of the printed 316L stainless steel block is significantly reduced by 86 percent, achieving less than 0.016%  at an optimal pulsed laser condition. Meanwhile, the shape and size of pores are beneficially controlled.