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

• 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.

The effects of different pin features and dimensions of scrolled shoulder bobbin friction stir welding were tested for welding marine grade aluminium, Al6082-T6. Welds were created in longitudinal and transverse plate extrusion directions in thin plate aluminium clamped and supported at one side. Measured outcomes included visual inspection, plate distortion, mechanical properties, metallurgical examination, and hardness test. This study shows that tool features cannot be directly transferable from conventional friction stir welding technology without comprising process variables and tool part functionality. Process setting such as clamps, support arrangements, shoulder gap and welding direction create compression, vibration and heat distribution hence influence the weld quality. The best joint was produced by four flats tool pin followed by threaded tool pin with three flats. These findings were used to develop a conceptual theory representing the underlying physics of the friction stir welding process. The effects of pin features, specifically threads and flats, are identified. This model is useful for direct linking welding factors towards the expected consequences.

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