Recent advances in friction stir welding/processing tools

Friction Stir Welding (FSW) is a popular technique for solid-state joining metals and polymers, as it overcomes many challenges associated with fusion welding. However, the widespread application of FSW to harder alloys, such as titanium and steel, depends on developing cost-effective and long-lasting tools that consistently produce structurally sound welds. Additionally, friction stir processing (FSP) is gaining attention for microstructural modification, improving surface quality, and manufacturing parts of composite materials. Tool materials and design greatly affect FSW and FSP performance, quality, and cost. Recent advances in these areas enhance material flow, reduce force and torque, and improve tool durability. These advances rely on new technologies like numerical models, machine learning, and data-driven optimizations of mechanical and microstructural properties. This review also examines various crucial aspects of FSW/FSP tools, including geometry, material selection, and mechanisms of tool degradation. The review analyzes three FSW techniques: Conventional Friction Stir Welding (CFSW), Bobbin Tool Friction Stir Welding (BTFSW), and Stationary Shoulder Friction Stir Welding (SSFSW). It also covers FSP alternatives like multipin FSP and Fed Friction Stir Processing (FFSP). The analysis covers various parameters, including tool geometry, process variables, heat generation patterns, joint characteristics, and joint performance.