Abstract
<title>Abstract</title> <p>In laser powder bed fusion (LPBF), melt-track width is often compressed into a condition-level mean, but this representation loses local narrowing, sustained drift and clustered fluctuation along the scan path. Here, path-resolved melt-track width, Width(x), was used as the response variable for 72 velocity–orientation conditions at a fixed laser power of 370 W to establish a width-trajectory-based relative spatial-stability analysis. Width(x) records the processed melt-track width as a function of path position rather than a real-time liquid melt-pool width. Seven spatial signatures were extracted and combined into Sspatial, an empirical composite index for relative ranking and review prioritization within the fixed-power, observed-orientation set. Mean Width and Width CV were moderately negatively correlated (Pearson r = − 0.48), indicating that average width cannot replace local within-path fluctuation. Under LOVO, the random forest achieved Spearman ρ = 0.811 and MAE = 0.086; under LOOO, precision for the highest 20% of high-instability conditions decreased to 0.143, indicating good recoverability along the speed dimension but a clear orientation-extrapolation boundary. The index organizes relative path stability as defined by Width(x) and is not equivalent to defect probability, quality certification or a general process window.</p>