Friction stir spot welding thin acrylonitrile butadiene styrene sheets using pinless tool

In this paper, pinless tool was utilized in the friction stir spot welding (FSSW) of acrylonitrile butadiene styrene (ABS) sheets. ABS gaskets were added to the through-hole of the clamping plate before FSSW in order to avoid upper sheet thickness reduction. The influence of different combinations of plunge rate (PR) and gasket thickness (GT) on joint morphology and mechanical behavior was investigated. Results showed that low PR and GT caused incomplete connection at the center of the bonded area, and straight and sound bonding interface was formed under the moderate PR and GT. Apparent material flow occurred in the vicinity of the lap interface when PR and GT were large. With the increase of PR and GT, bonded area diameter enlarged while joint fracture load increased first and then slightly decreased. Joints produced with and without thickness reduction failed with different fracture modes, and the removing of upper sheet thickness reduction was beneficial to the promotion of the joint strength.