TWI

A control concept for friction stir welding (FSW) of structural steels was developed based on a closed loop architecture that limits the heat input during the welding process according to the continuously monitored value of the magnetic permeability within the thermomechanically affected zone (TMAZ). The control system was based on two premises: thermomechanical processing of steels within the intercritical temperature region, preventing full austenitisation within the TMAZ, and the fact that the significant change of magnetic permeability near the Curie temperature also occurs in the intercritical temperature region. Magnetic permeability variation with temperature was monitored with eddy current sensors. The adjustment of key FSW process parameters (rotational speed, travel speed and welding force) was implemented with respect to a pre-established welding lobe.

11th International Symposium, 17-19 May 2016, Session 6A: Process Control, Paper 03