Effect of leading ultrasonic vibrations on the welding forces of friction stir lap welding

Influence of leading ultrasonic vibrations on the process forces in the friction stir lap welding of AA 6061-T6 with and without ultrasonic vibrations is investigated at varied welding speeds. The axial force, traverse force, and tool torque in the processes are determined by adopting a recently developed method that uses electrical signals of the servo motors and main spindle AC motor of the friction stir welding machine during the welding process. It is found that the exerted ultrasonic vibrations decrease the welding forces without compromising the mechanical properties of welds. The effect of ultrasonic vibrations on traverse force is more pronounced than that on the tool torque and axial force. Force measurements at different welding speeds indicated that the axial force and traverse force varied significantly with travel speed of tool. Not much difference is found in the tool torque variation. With ultrasonic vibrations, the reduction in welding force in different directions is affected differently by welding speed. The ultrasonic effect on welding forces is found to be governed by the travel speeds of both the tool and workpiece.