Powder-bed fusion additive manufacturing of 316L stainless steel using short-wavelength diode point melting

Diode Point Melting (DPM) is an alternative additive manufacturing powder-bed melting approach that combines multiple low-power, short-wavelength lasers into a single spot that is raster-scanned by an XY gantry to selectively melt deposited powder. In this study, the DPM laser head is composed of eight 450 nm diodes (∼35 W total) focused to ∼100 × 150 μm and is used to fabricate 316L stainless steel. Parts achieve >98% relative density while operating at slower scan speeds and estimated lower cooling rates than Laser Powder Bed Fusion (LPBF) (≈6.66×104 K s-1 vs ∼107 K s-1). The DPM microstructure is distinguished by larger grains (∼18 μm) and larger cellular sub-grains (∼2 μm) relative to the typical LPBF of 316L. It was demonstrated that cellular size decreases with increasing scan speed, evidencing cooling-rate control of the sub-grain structure. Mechanical characterisation shows a modest reduction in elastic modulus and Vickers hardness compared with LPBF-processed 316L, attributed to grain coarsening and slightly higher porosity, while values remain above those of conventionally manufactured 316L. These findings demonstrate potential for DPM to be a low-cost and accessible alternative to LPBF with unique microstructural characteristics.