Adaptive Control for Laser-GMAW Hybrid All-Position Root Pass Welding

All-position welding is essential for pipeline installation, yet dynamic variations in butt gaps, groove mismatches, and welding positions challenge weld quality. To address these issues, this study developed an innovative adaptive control system for all-position root pass welding. The system integrated an innovative laser-GMAW hybrid all-position welding with copper liner coordinated control, offering robust process stability and a wide process window. It enables high-quality welding under dynamic fluctuations in work conditions while providing parameter adjustment margins for adaptive control. Furthermore, a particle swarm optimization-back propagation (PSO-BP) neural network was employed to establish an adaptive process database. Additionally, an improved gray centroid method was proposed for U-groove, achieving accuracies of 0.10 mm (0.00394 in.) for butt gaps and 0.07 mm (0.00276 in.) for groove mismatches. Validated on Φ 800 × 12 mm (31.5 × 0.472 in.) pipelines, the system produced welds with 3~4 mm (0.118~0.157 in.) backside reinforcement width and 0.50~0.80 mm (0.0197~0.0315 in.) height. This research provides theoretical and technical foundations for pipeline welding from double-sided to single-sided processes. Future work will focus on weld seam tracking and path planning to develop a comprehensive, all-position adaptive welding control system that integrates root, filler, and capping passes.