Friction stir spot welding ABS using triflute-pin tool: Effect of process parameters on joint morphology, dimension and mechanical property

A triflute-pin tool and a clamping plate with a circular hole were utilized to friction stir spot weld acrylonitrile butadiene styrene sheets. The influences of rotational speed, plunge depth and dwell time on the joint morphology, dimension and mechanical performance were investigated. Joint micromorphology was analyzed by the optical microscope and lap-shear tensile tests were conducted to assess the joint quality. Results showed that excessive rotational speed and plunge depth resulted in linearly distributed pores and gaps, and long dwell time caused the formation of cavities. With the increase of rotational speed, bonded area diameter increased first and then decreased. Plunge depth slightly affected joint dimension while dwell time had a positive effect on it. Four failure modes, namely shear fracture, pull lower nugget, pull upper nugget and the mixed shear and pull nugget, were observed in the tests. The fracture load of the joints varied significantly with the variation of welding parameters. Joints produced with the least tool stirring showed the maximum shear strength of 20.7 MPa, which was 92.8% of the base material. In addition, triflute pin was advantageous to produce joints with higher strength than the cylindrical pin.