Design features for bobbin friction stir welding tools: Development of a conceptual model linking the underlying physics to the production process.

Highlights: [•] Specific design recommendations for bobbin friction stir welding tools. [•] Pin with four flats feature best for thin plate aluminium. [•] Shoulder gap affects hence vertical flow motion. [•] Clamped side has higher hardness and lower tensile strength. [•] Developed a conceptual model representing the underlying physics. [Copyright &y& Elsevier]