Effect of Gravitational Orientation on Bead Geometry and Position-Dependent Parameter Compensation in Multi-Pass Orbital Gas Tungsten Arc Welding

This study investigated the influence of circumferential welding position and process parameters on bead geometry during multi-pass orbital gas tungsten arc welding (GTAW) of SUS304 stainless-steel pipes. Three-dimensional surface profiles were measured using a laser line scanner at the top (12H, −45° to 45°) and bottom (6H, 135° to 225°) circumferential regions. The incremental bead height and width of Passes 1 and 2 were quantitatively evaluated after excluding the first and last 10% of the measured region to minimize edge effects. Under identical root-pass conditions, the average Pass 1 bead height at 6H was 9.6% greater than that at 12H, whereas the bead width was 3.3% smaller. After Pass 2, the height difference increased to 12.0%, while the width difference remained small at 2.4%. Primary current, wire feed speed, and travel speed exhibited position-dependent effects on bead formation. Primary current affected the balance between vertical buildup and lateral spreading, wire feed speed consistently influenced bead width, and travel speed strongly affected bead buildup through changes in heat input, filler deposition per unit length, and molten-pool residence time. The greater reinforcement at 6H was attributed to gravity-dependent molten-metal accumulation during successive deposition. Interpolation of the primary-current experiments predicted that approximately 173 A at 12H and 175.5 A at 6H would produce comparable Pass 2 geometries of approximately 1.62 mm in height and 6.57 mm in width. These results demonstrate that circumferential bead uniformity can be improved through position-dependent parameter adjustment rather than identical welding conditions around the pipe circumference.