Cascade control of the friction stir welding process to seal canisters for spent nuclear fuel

• Published in: Control engineering practice Vol. 20; no. 1; pp. 35 - 48
• Main Authors: Cederqvist, L., Garpinger, O., Hägglund, T., Robertsson, A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 2012; Elsevier
• Subjects: Applied sciences; Canisters; Cascade control; Cascade control Friction stir welding Temperature control Disturbance rejection PI controllers; Computer science; control theory; systems; Control Engineering; Control system synthesis; Control theory. Systems; Disturbance rejection; Electrical Engineering, Electronic Engineering, Information Engineering; Elektroteknik och elektronik; Engineering and Technology; Exact sciences and technology; Fracture mechanics; Fracture mechanics (crack, fatigue, damage...); Friction stir welding; Fundamental areas of phenomenology (including applications); Joining, thermal cutting: metallurgical aspects; Metals. Metallurgy; Physics; PI controllers; Process control. Computer integrated manufacturing; Reglerteknik; Seals; Solid mechanics; Strategy; Structural and continuum mechanics; Teknik; Temperature control; Welding; Cascade control; Disturbance rejection; Temperature control; Friction stir welding; PI controllers; Radioactive waste; Hermetic sealing; Integral proportional control; Process control; Rupture; Control synthesis; Power system stability; Nuclear fuel; Weld; Robust control; Welded joint; Defect; Friction welding; Differential integral proportional control
• ISSN: 0967-0661; 1873-6939
• DOI: 10.1016/j.conengprac.2011.08.009

This article presents the development to reliably seal copper canisters containing the Swedish nuclear waste, using friction stir welding. To avoid defects and welding tool fractures, it is important to control the welding temperature within a span of 790–910 °C. A cascade controller is used to efficiently suppress fast power input disturbances reducing their impact on the temperature. The controller is tuned using a recently presented method for robust PID control. Results show that the controller keeps the temperature within ± 10 ° C during the 40 min long joint line sequences. Apart from the cascaded control structure, good process knowledge and control strategies adapted to different weld sequences have contributed to the successful results.