The friction stir welding procedure to seal copper canisters requires variable power input throughout the 45 minute long weld cycle to keep the welding temperature within the process window. This is due to variable thermal boundary conditions throughout the weld cycle which, together with fast disturbances in the spindle torque, requires control of both the power input and the welding temperature to achieve a stable and robust process. By using a cascaded loop that determines the power input requirement, the regulator will not be dependent on repeatability in the necessary power input between weld cycles. As a result, a more accurate and reliable closed-loop control of the welding temperature is acquired.

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