Friction stir blind riveting (FSBR) is a new process for joining automotive light alloys based on aluminium and magnesium. During FSBR, a blind rivet, rotating at high speed (typically 2000-12000 rpm), is brought in contact with the upper sheet or workpiece of a lap joint. The frictional heat generated between the rivet and the workpieces softens the material and this, in turn, reduces the force required to drive the rivet into the workpieces. Once fully inserted, the blind rivet is upset using the internal mandrel and an appropriate tool, as in conventional blind riveting. The FSBR process thus retains the one-sided accessibility of conventional blind riveting, but eliminates the extra predrilling and any subsequent cleaning steps required for the latter process.
In this paper we investigate the effects of the main process parameters, rotational speed and feed rate, and the rivet design, on rivet insertion force and torque as well as the static tensile shear strength of lap joints produced using various wrought aluminium alloys (AA 5005-H34, AA 6013-T6, AA 6260-T6 and AA 6005A-T5), die cast aluminium alloys (A380 and Aural-2 cast) as well as a twin roll cast magnesium alloy (AZ31B-O), with sheet thicknesses in the range 1.6-3.0 mm. Commercial breakstem steel rivets with hollow mandrel head design resulted in significantly lower rivet insertion force and torque values compared to those with solid mandrel heads. In addition, the hollow mandrel head rivets minimised flash formation and provided a means to accommodate the workpiece material displaced by the plunging rivet within the hollow mandrel head cavity. Tensile shear strengths of lap joints (stack-ups in the range 3.2-6 mm) of the various aluminium alloys and the magnesium alloy were in the range 4-6.5 kN. We also present results on the capability of FSBR for dissimilar materials joining, for example, wrought aluminium alloys to die cast ones and aluminium alloys to magnesium alloys.
