Quality assessment of friction-stir-welded aluminum alloy welds via three-dimensional force signals

An online detection technology must be developed for realizing the real-time control of friction stir welding. In this study, the three-dimensional force exerted on a material during friction stir welding was collected synchronously and the relationship between the forces and welding quality was investigated. The results indicated that the fluctuation period of the traverse force was equal to that of the lateral force during the stable welding stage. The phase difference between two horizontal forces was π/2. The values of the horizontal forces increased with welding speed, whereas their amplitudes remained the same. The proposed force model showed that the traverse and lateral forces conformed to an elliptical curve, and this result was consistent with the behavior of the measured data. The variational mode decomposition was used to process the plunge force. The intrinsic mode function that represented the real fluctuation in the plunge force varied at the same frequency as the spindle rotational speed. When tunnel defects occurred, the fluctuation period features were consistent with those obtained during normal welding, whereas the ratio parameter defined in this study increased significantly.