Active optimal scanning control in thermal processing of materials

Scan thermal processing, enabled by active guidance of the heat source motion during fabrication, combines the flexibility of sequential methods to the productivity of parallel thermal processes. For cylindrically symmetric parts, this is performed by their rapid revolution under a radially or axially translated torch, with its power modulated so as to implement a specified thermal distribution as it sweeps the product surface, and thus to generate desirable material features. An analytical description of the thermal field, based on superposition of Green´s fields, was developed for off-line analysis, as well as a multivariable linearized model with least-squares identification of its varying parameters, for real-time compensation of the process efficiency. This model is embedded in an active thermal control scheme, driving the scanned torch motion and power by a simulated annealing optimization strategy, using temperature feedback from sampled surface locations by an infrared pyrometer. The thermal regulator is validated by computation and experiment and its applicability to other scanned processes is examined