Experimental measurements of load distributions on friction stir weld pin tools

An understanding of the forces acting on the pin of friction stir weld tools is critical to appropriate design, especially in materials with limited toughness such as polycrystalline cubic boron nitride. This article describes a study to measure the longitudinal force distribution on a friction stir weld pin tool. Total longitudinal forces were recorded on a dynamometer while welding 6061 aluminum with pins that varied in length and diameter. A model was developed that characterizes the pin force as a function of pin length and diameter. As the pin length approaches zero, the longitudinal force reaches an asymptote, which is apparently the longitudinal force due to the shoulder. The force due to the pin increases with pin length, but appears not to vary significantly with pin diameter. The force distribution on the pin appears to increase linearly with distance from the shoulder. Unexpected force variation was found at large pin lengths, a result which has yet to be explained.