Influence of Bobbin tool design on Quality of welds made by FSW of Aluminium Alloys

Friction Stir Welding (FSW) an Eco-friendly process developed by The Welding Institute (TWI), UK, in 1991. Since its inception, sufficient developments have taken place in this area which we call as conventional or standard friction stir welding (CF SW). But the area of double shoulder or self-reacting tool is very lean in the literature and has a potential to explore it further. There is a need to understand the causality to study the effect of tool design parameters on weld quality. The heat developed in case of Bobbin Friction Stir Welding (BFSW) is different than CFSW due to two shoulders; and hence care must be taken in designing the tool. In general, FSW considered to be defect free solid state joining process, but it is not always true. Root canal, surface tunnel, joint line remnant, voids are some of the defects observed. The present paper will throw some light in the direction of development of bobbin tools, so that an idea will be conceived regarding design requirements and limitations in the fabrication of fixed gap bobbin tools. The tools developed were validated by actual experimental investigations and characterization for different aluminium alloys. A square pin fixed gap bobbin tool was found to be suitable for defect free welding of Al alloys. (C) 2019 Elsevier Ltd. All rights reserved.