Investigation on tool positioning in friction stir lap welding of AA6061 to polycarbonate sheets using force-torque signals

Abstract

The lightweight high-performance thermoplastics are often replaced the metallic parts in aircraft and automobile industries due to high corrosion resistance along with upgraded strength to weight ratio. However, the joining of dissimilar non-ferrous aluminium to amorphous polymers is highly difficult caused by a drastic change in thermal properties which indicates the necessity of solid state welding processes. Therefore, the current work reports the practicality of friction stirred welding unlike AA6061 aluminium alloy and polycarbonate sheets for overlapped conditions by a cylindrical tool having a taper pin of H13 steel. The prime objective was to analyse the influence of tool tilt angle at different plunging depths and tool rotational speeds on the dissimilar weldability using a load-elongation curve. The aluminium to polycarbonate weld interface has also been studied to correlate with mechanical behaviour due to tensile load. The axial thrust force with tool stirring torque signals has been acquired for these parametric conditions for further process monitoring by segregating consecutive stages in the welding cycle. The weld bead profile along welding direction has been monitored using time domain thrust-force signals in the welding phase whose extracted significant features were compared. Finally, a sensitivity analysis was also processed to investigate the degree of parametric impact on thrust-torque as well as weld quality features. The highest joint strength efficiency was found to be 39.4% at higher tool rotational speed (1400 rpm) with reduced plunge depth (0.1 mm) without any tool tilting whereas weld ductility was significantly improved at reversed parametric settings with tool inverted position. The tool plunging force is a better indicator whereas both plunge depth as well as tilt angle were almost equally important for the prediction of lap weld quality.