Vision-derived stability indicators from melt pool and wire dynamics in laser hot-wire directed energy deposition

Laser hot-wire directed energy deposition (LHW-DED) improves process performance by enhancing wire preheating. Reliable in situ assessment of process stability remains challenging because the melt-pool behavior and wire transfer are commonly evaluated separately. This study develops vision-derived stability indicators by jointly characterizing melt-pool geometry and wire dynamics during the deposition of stainless steel 316LSi under varying laser power and hot-wire power. Optical videos were analyzed using multi-Otsu segmentation for melt-pool area extraction and the Segment Anything Model 2 for temporal wire segmentation. Melt-pool area was used to characterize the energy input, while frame-to-frame Intersection over Union (IoU), IoU volatility, and angle variability were evaluated as indicators of wire stability. Low energy conditions produced smaller melt pools and greater wire flutter, whereas sufficient energy inputs produced larger melt pools and more consistent wire behavior. Parameter-level correlations showed that melt-pool area for single beads was related to penetration depth and total cross-sectional area measured by optical microscopy. Melt-pool area was also associated with wire stability during the single-bead laser-power sweep. These results establish melt-pool geometry and wire dynamics as complementary indicators of LHW-DED stability and support future process qualification and in situ feedback control.