Beyond Volumetric Energy Density: Process-Window Mapping and Density Metrology for Laser Powder Bed Fusion of High-Strength A20X Aluminium and 304L Stainless Steel

The volumetric energy density (VED) is often used to characterise the process window in laser beam powder bed fusion of metals (PBF-LB/M), commonly referred to as laser powder bed fusion (L-PBF). We assessed its explanatory value using an EOS M280 system on two alloys: stainless steel 304L and the TiB2-modified Al–Cu aluminium alloy A20X. The porosity was measured by light optical microscopy. Furthermore, the pore morphology was quantified, and the results were compared with the densities measured using the Archimedes principle. For 304L, the VED explained 71% of the in-sample variance of the logarithmic porosity, compared with 93% for the factorial model. Scan speed dominated, and irregular pores consistent with lack of fusion predominated. For A20X, no monotonic correlation between porosity and VED was detected. A series of tests at constant VED (62.5–64.8 J/mm3) led to an increase in porosity from 0.03% to 1.08%, which was associated with the accompanying increase in line energy; a contribution of the largest hatch distances could not be excluded. At equal scan speed, hatch distances up to 140 µm had no detectable effect, and pores ≥ 20 µm were compact (median aspect ratio 1.15), consistent with keyhole or gas porosity.