Process parameter effects on melt pool dimensions along the build height and multi-criteria optimization in LPBF of M300 maraging steel

Laser powder bed fusion (LPBF) involves a wide range of process parameters that critically influence the final quality, microstructure, and mechanical performance of fabricated parts. Key factors such as energy input, melt pool geometry and stability, cooling rates, residual stresses, defect formation, and surface characteristics determine both the robustness of the process and the resulting material properties. This study investigates the evolution of melt pool dimensions and their variation along the build height, while introducing a new multi-criteria evaluation approach for identifying robust parameter sets. A full-factorial Design of Experiments (DoE) was conducted on M300 maraging steel (EN 1.2709, 18Ni-300), with systematic variations in laser power (210–240 W), scan speed (700–840 mm/s), and hatch distance (80–96 µm). The influence of these parameters on porosity, hardness, melt pool geometry, and melt pool stability was analyzed. An interim evaluation focusing on porosity and melt pool variation identified five promising parameter sets for further investigation, including tensile testing and detailed melt pool analysis along the build height (0.04–60 mm). Finally, a multi-criteria evaluation approach, the Porosity–Variation–Strength Score (PVS Score), was introduced. This method enabled the identification of an optimal parameter set for M300 maraging steel that simultaneously ensured nearly zero porosity, high tensile strength, and low mean melt pool variation.