In this article, multiple lumped thermomechanical characteristics of the welding process are regulated by modulation of the welding conditions in real time through feedback control. The controller design is based on three dynamic welding models: a lumped analytical formulation of the weld bead geometry, a numerical simulation of the distributed thermal and phase field, and an experimental linearized model with nonstationary parameters. To account for nonlinearity and thermal drift effects, the weld parameters are identified in-process by the multivariable adaptive controller through surface temperature measurements with an infared pyrometer. Multiple heat inputs, implemented by a single reciprocating, timeshared torch, are employed for simultaneous decoupled control of thermal attributes, such as weld bead size, heat affected zone and cooling rate. The performance of closed-loop controlled welding is tested in setpoint changes and unexpected process disturbances for various welding techniques, materials and geometric arrangements, including new experiments of stainless pipe seam GTA welding.

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