The Effect of Electrode Diameter on Single-Track Morphology and Process Window in Powder-Bed Arc Additive Manufacturing

Powder-bed arc additive manufacturing (PBAAM) is a low-cost alternative powder bed fusion process that uses a TIG arc as heat source. This study systematically investigates the effect of electrode diameter (φ = 0.6, 0.8 and 1.0 mm) on single-track morphology and process window in inclined-bed PBAAM of 316L stainless steel powder. Twenty-seven full-factorial combinations of three current levels (I = 20, 25, 30 A) and three travel speeds (v = 2, 3, 4 mm/s) were evaluated using an image analysis framework based on Otsu thresholding with expert manual correction. Maximum gap length (L_gap) and width coefficient of variation (CV = σ_w/w̄) metrics were compared across six threshold scenarios (S1–S6); S5 (L_gap) = 0.50 mm, CV = 0.15) was identified as the most appropriate combination based on physical justification and literature consistency. Process map analysis revealed travel speed v as the most critical parameter governing the process window: at v = 2 mm/s, 9/9 combinations (100%) produced continuous tracks; at v = 4 mm/s, only 5/9 (56%) were continuous. Multiple linear regression models achieved R² = 0.626 for mean track width w̄ and R² = 0.562 for CV. Electrode diameter φ significantly affects track width (β_φ = 0.762, p = 0.019) but has no significant linear effect on width uniformity CV (p = 0.955); CV is primarily governed by I and v. The φ = 0.8 mm electrode confined all Fragmented/Balling combinations to v = 4 mm/s only and produced approximately 35% lower mean CV (0.184) than the other two electrode diameters for continuous tracks.