Scanned Orbital Welding: Thermal Modeling and Lumped Adaptive Control

Scan orbital welding of cylindrical vessel, flange, and piping parts is performed by their rapid revolution under a radially or axially translated heat source, with its power modulated so as to implement a specified thermal distribution. Thus, the plasma-arc welding torch sweeps the stainless steel surface to generate a desirable temperature field and the concomitant material features. A numerical simulation of the thermal field is developed for off-line analysis. On this basis, a lumped thermal regulator of the heat-affected zone, employing infrared temperature feedback at a single spot, as well as standard PI, gain scheduling, and self-tuning control algorithms is tested. The thermal model is also employed for real-time torch efficiency identification and compensation. The numerical reference model serves as the basis for an in-process adaptive thermal control system to regulate the temperature field, using thermal feedback from the infrared pyrometer. A distributed-parameter control strategy, with guidance of the torch motion and power by a new weighted attraction strategy to randomly sampled points, is tested on scan-welded flanges. The regulator is validated computationally and experimentally, and its applicability to other scanned processing of materials is considered.