Operational characterization of the serial plasma-GMAW hybrid process for thick-section welding

Abstract The growing industrial demand for high-productivity welding solutions for thick sections has stimulated the development of hybrid arc processes capable of combining high deposition rates with enhanced penetration. In this context, the present study investigates the serial Plasma-GMAW hybrid process with emphasis on its operational behavior, parameter mapping, and applicability to thick steel joints. A systematic experimental program was conducted by varying plasma current and plasma gas flow while maintaining constant GMAW parameters. Process behavior was analyzed through electrical signal monitoring, high-speed imaging, and macrographic evaluation of weld bead geometry, including penetration depth, bead width, and reinforcement characteristics. The results indicated two distinct operating regimes of the plasma arc. Under lower plasma energy levels, a melt-in mode was observed, promoting improved bead wettability and stable weld pool behavior. At higher plasma energy levels, a keyhole mode developed, producing a significant increase in penetration, with strong sensitivity to plasma gas flow rate. Excessive plasma pressure, however, led to weld pool instability and burn-through conditions. Based on the mapped parameter window, circumferential welding trials on 12.7 mm thick steel pipes demonstrated full penetration in a single pass at a travel speed of 60 cm/min with limited joint preparation. Under the evaluated conditions, the process also showed productivity potential when compared with reference SAW procedures. The findings demonstrate that the serial Plasma-GMAW process is a promising alternative for thick-section fabrication from an operational and productivity standpoint. Further studies involving microstructural characterization and mechanical performance are recommended for full industrial qualification.