Characterization of the influences of FSW tool geometry on welding forces and weld tensile strength using an instrumented tool

FSW process automation is essential to making consistent and reliable friction stir welds and this requires an understanding of how tool design can influence process parameters, which in turn can provide high joint strength and performance. Tool optimisation hinges on a better understanding of the effect of tool parameters on forces during welding, on the tool torque and tool temperature. Important parameters include flute design (e.g. number, depth, and taper angle), the tool pin diameter and taper, and the pitch of any thread form on the pin. These influences were investigated in this study using a systematic tool profile matrix which considered the influence of four variations of each of these six geometric factors. Forces on the tool, applied torque and temperature were monitored and recorded during welding of 6 mm thick 5083-H321 aluminium alloy. The lateral reaction forces on each tool and the relative angle of orientation of the peak resultant force are described via a bi-lobed polar plot called the “force footprint” (FF). This provides visual information on the interaction between tool profile and the plastic stir zone, which cannot be obtained purely from force magnitude information. Key characteristics of the tool–weld interaction can be extracted, analysed and summarized to provide guidance on optimum tool selection for a given set of weld conditions.