Characterisation of periodic variation in torque occurred in friction stir welding process

Friction stir welding was physically simulated to study torque variation by a rotational friction process under constant axial pressing speed. The results indicated that the torque accurately reproduce the same periodic characteristics as the friction stir welding torque, i.e. the torque cycle is equal to the time of one tool rotation. The periodic variation intensity of torque, which was obtained at a constant rotational speed ω and a constant axial pressing speed v, was characterised by non-dimensional amplitude of the torque Γ*. Moreover, a semianalytical model, which describes Γ* as a function of ω² /v in Arrhenius form, was established. In this model, Γ* exponentially increases with ω²/v, and low ω²/v suppresses the variation intensity of torque.