Periodic variation of torque and axial force of tubular aluminum alloy at constant downward and rotational speed

The periodical torque and axial force is obtained by an innovative mockup experiment for modeling the torque and forward force of pin during friction stir welding(FSW). The result shows that the cycle is equal to the time of one rotation. It can be obtained that sliding friction contributes more heat than that of sticking friction, and sliding friction power is greater than the actual average thermal power by calculating, which is the reason for the periodic variation of torque and axial force. The sliding friction accumulates heat more quickly than that of sticking friction so that the material beneath the tool is softened, now the torque and axial force are lowest. However, because lower heat production efficiency of sticking friction cannot keep the material being softened beneath the tool, the softened material will be extruded out. The tool contacts the elastic material, now the axial force and torque are highest, which lead to the sliding friction for softening the material.