Analysis of welding load reduction in ultrasonic vibration-enhanced friction stir welding

A novel process variant of friction stir welding (FSW), i.e., ultrasonic vibration-enhanced FSW (UVeFSW), has been developed to improve the joint quality and lower the welding loads. To elucidate the underlying mechanism of the UVeFSW process, an integrated 3D model is developed to analyze the effects of ultrasonic vibration on welding loads quantitatively. The predicted traverse force and tool torque agree well with the experimental measured ones. It is found that superimposing ultrasonic vibration in UVeFSW can reduce the traverse force and tool torque, and the reduction percentage of welding loads decreases with an increase of tool rotation speed. Analytic formulae are developed to calculate the traverse force and tool torque in UVeFSW under different levels of welding speed and rotation speed. The predicted welding loads from the analytic formulae fit well with both experimentally measured data and the numerically simulated data by using the validated integrated 3D model. The work lays the foundation for optimizing the process parameters in UVeFSW in order to efficiently use the ultrasonic vibration energy.