In-process Control of Rotational Speed in Friction Stir Welding of Sheet Blanks with Variable Mechanical Properties

In the present work, an adaptive control constraint system was applied in the friction stir welding of AA6082 aluminum alloy with the aim of tailoring the mechanical properties of the sheet blank to the subsequent forming processes. To this purpose, blanks in the solution heat-treated and artificially aged (T6), and in the annealed (O) conditions were welded according to a well defined layout. Such in-process control strategy was based on the variation of the controlled variable (rotational speed of the pin tool) in order to keep the measured one (vertical force) constant during the welding stage of the process. To this end, a preliminary investigation on the effect of the rotational speed, varying from 1000 to 2500 rpm, on the vertical force during FSW was performed. The capability of the proposed approach in friction stir welding sheet blanks with variable mechanical properties along the welding line was proven.