Friction stir spot welding (FSSW) is a solid-state joining technique which is used to weld alloys that has a low weldability such as the 2000 and 7000 series aluminum alloy. The marine, automotive and aerospace industry benefits using this method as the need for weight reduction and fuel economy make the use of aluminum and other light metals necessary. The purpose of this study is to find the optimum parameters and the ultimate failure load for FSSW welded specimens in a basic lap configuration. Two coupons of AA7075-T6 with a dimension of 210×30×0.8 mm and 210×30×1.6 mm were welded using a self-made FSSW machine rebuild for the purpose of this project. The experiment was performed using engineering robust design approach to investigate the optimal parameter combinations that provides optimal joint performance. Experiments has been carried out using the Taguchi L9 orthogonal arrays with 4 factors and 3 levels. The factors and levels were chosen as follows: pin length in the interwall 1.2 mm to 1.6 mm, shoulder depth 0 to 0.4 mm, dwell time I sec to 2.5 sec and tool rotation speed 1800 rpm to 2600 rpm. The joint performance has been evaluated considering the ultimate tensile load. Tensile testing of weldments was carried out using an Instron Universal Testing Machine. To estimate the error variance for the factor effects and variance of the predicted error analysis of variance (ANOVA) was performed. The mathematical framework anticipated an ultimate failure load of 3286N, and the verification run confirmed the predicted result by an average of 3215N. The optimum parameters were found to be a pin length of 1.4 mm, shoulder depth of 0.4 mm, dwell time at 2.5 sec and a rotational speed of 2200 RPM. The ANOVA showed that the shoulder depth was the dominant factor influencing 87.9 % of the variation of the signal-to-noise ratio (S/N).
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