Gap tolerance allowance and robotic operational window for friction stir butt welding of AA6061

► A process operational window for friction stir welding of AA6061-T6 was determined. ► The gap between abutting joint interfaces was limited to 0.5 mm for this application. ► A robotic scenario was synthesized with an appropriate operational window. ► 1-m-long test articles were produced by robotic friction stir welding. ► Equivalent weld mechanical performance appears to be achievable by robotic FSW.