Modeling of pin shape effects in bobbin tool FSW

Abstract

The Coupled Eulerian-Lagrangian (CEL) technique is used for numerical modeling of the bobbin tool friction stir welding (BTFSW) of magnesium alloy. Temperature and force history curves are used to validate the numerical model. To investigate the impacts of pin shapes, researchers used a variety of tools with square, trigonal, inward conical, hexagonal, and outward conical pin shapes. The material flow data demonstrate that the material goes from the advancing side (AS) to the retreating side (RS) in the pin-driven zone. In contrast, in the shoulder-driven zone, the material moves in the opposite direction. Although the trigonal pin moves a larger volume of material by involving the most extended sweeping lever, the hexagonal pin generates the most uniform material coalescence. The inward conical pin is weak in producing adequate material flow, causing the generation of tunnel cavity defects. On the contrary, a subsidiary material flow made by the outward conical pin enhances the coalescence. The stir zones’ general shapes, resulted from the numerical model, are compared with the empirical observations via the cross-section macro-images along with the microhardness variation curves. The axial force is almost zero in BTFSW; however, the traverse force is very much higher than the regular FSW. In the pins with edges, the traverse force increases by addition of the edges, and the outward conical tool pin generates the highest force value.

Keywords

• Bobbin tool FSW
• AZ91 magnesium
• Pin shape
• CEL model
• Material flow
• Welding force