On the material behavior at tool/workpiece interface during friction stir welding: A CFD based numerical study

The material behavior at the interface between the welding tool and the workpiece in friction stir welding (FSW) is a critical phenomenon governing heat generation and material flow. Previous computational modeling studies tend to simplify the material behavior at the interface, generally assuming simple stick or frictional slip conditions. In this paper, a new approach is developed that allows for dynamic friction between tool and workpiece, based on considerations of relationship between frictional force and material velocity at the interface. This new approach is implemented in a computational fluid dynamics (CFD)-based model to simulate the heat transfer and material flow. The simulated temperature field and velocity distribution are validated by experiments. The simulation results show that material velocity on tool/workpiece interface is significantly different from the tool velocity and increase with the interfacial frictional stress. It is found that when frictional stress is not large enough to enable large extent plastic flow, asymmetrical material flow appears. Material on the advancing side tends to flow at lower velocity than that at retreating side.