Numerical simulation of vortex- friction stir welding based on internal friction between identical materials

A novel modification of friction stir welding (FSW), namely vortex-friction stir welding (VFSW), is recently developed. It utilizes a tool made of identical materials as workpieces to avoid tool wear and break in conventional FSW. New phenomena in heat generation (mainly produced by plastic deformation) and material flow (self-adaptation of penetration) are essentially different from those in conventional FSW. It is urgent to investigate the underlying mechanism of heat and mass transfer in VFSW to promote its maturity and application. In this study, the spatial heat transfer and three-dimensional visco-plastic flow in VFSW have been modeled in a computational fluid dynamics (CFD) analysis. The equations of conservation of mass, momentum, and energy were solved in three dimensions to describe the spatial heat transfer and plastic material flow. The calculated results show that the heat for welding mainly comes from the plastic deformation work of the material, which is greatly influenced by the tool's rotating speed. The gradient of heat generation rate is very large in the workpiece thickness direction. The high-temperature region in VFSW is much larger than that in FSW due to the larger stir bar used. The diameter of the rotational flow zone (RFZ) is almost the same or even larger than that of the stir bar near the workpiece top surface. It decreases with the distance from the workpiece top surface, which produces the characteristic shape of a vortex. The risk of incomplete penetration defect can be predicted according to whether the vortex intersects with the workpiece bottom surface. The numerically predicted temperature profile and thermo-mechanically affected zones agreed well with the independently determined experimental ones. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The underlying mechanism of heat and mass transfer in vortex-friction stir welding (VFSW), which utilizes a tool made of identical materials as workpieces, was investigated in this study. Computational fluid dynamics analysis was used to model the spatial heat transfer and three-dimensional visco-plastic flow in VFSW. The results showed that the heat for welding mainly comes from plastic deformation work and is greatly influenced by the tool's rotating speed. The high-temperature region in VFSW is larger than that in conventional friction stir welding (FSW), and the vortex shape decreases in size as the distance from the workpiece surface decreases.