Optimization of process parameters of friction stir spot welding of polycarbonate sheets and morphological analysis

Abstract

AbstractFriction stir spot welding has a great impact on the joining process of thermoplastics. In this work, effects of varying rotational speed, plunge depth, and dwell time were investigated on polycarbonate sheets and a filler sheet was utilized to reduce the keyhole size of friction stir spot welded joints. The welding parameters were arranged according to Taguchi L9 orthogonal design of experiments to determine the optimum levels of process parameters. Lap shear tests were performed to examine the mechanical properties. Using analysis of variance and signal to noise ratio, influences of each welding parameter on the lap joint shear load were evaluated. According to achieved results, tool rotational speed has the highest effect while plunge depth has minimum effect on the mechanical behavior of friction stir spot welded joints. Optimum process parameters were attained as 1000 min−1 for rotational speed, 10.5 mm of plunge depth, and 40 s of dwell time. Optimized process parameters showed 15 % improvement compared to the initial welding parameters. Cross‐sectional appearances of welded samples which play an important role in determining lap joint shear load were analyzed by morphological and visual comparisons. Failure modes of the fractured samples for lowest, moderate and highest lap joint shear loads were also observed.