A novel energy density model based on empirically-derived laser and powder parameters for directed energy deposition of stainless steel 316 L

In this study, a modified specific energy density (MSED) is proposed to address the limitations of the nominal energy–density model, which fails to reflect actual laser thermal interactions or effective powder behavior in directed energy deposition (DED). The actual heat-affected diameter and powder distribution were parameterized through empirical laser marking experiments and vision-based image analysis of powder flow. The effective energy delivered per unit mass was calculated by integrating the spatial overlap between laser energy and powder concentration. Geometric growth, including width and height, increased with MSED but began to decrease above 150 (kJ/g) s, at which point the dilution rate approached the physical limit of approximately 70 %. Microstructural trends were also qualitatively identified, with fine dendritic structures appearing at low MSED and gradual dendritic coarsening at high MSED. Furthermore, a regression model was developed using laser power, scan speed, and MSED and validated through four-fold cross-validation. This model demonstrated strong generalization, with an average predictive performance R² = 0.956, and the dilution-specific model achieved an R² = 0.912 for the single MSED relationship. These results demonstrate that MSED serves as a physically based indicator representing various qualities and can be used as an optimization indicator in DED manufacturing.