Simulation of material flow during friction stir welding based on the model of interactive force between tool and material

Friction stir welding (FSW) is a solid state joining method invented by TWI in 1991. This method could prevent melting related defects for its character of solid joining. Material flow at elevated temperature played a central role in producing the weld. The resulted microstructure and defects in the weld were also concerned with transient material flow pattern during the process. Numerical simulation could be a powerful tool to study the flow pattern during the process for difficulties in direct observation. Material flow, heat generation and temperature evolution during FSW, were fully coupled with each other. However, interactive forces, existing between the tool and the material, gave rise to both material flow and heat generation. The forces could be a starting point to understand the complex material flow during FSW. In this research, the three-dimensional flow of metals in FSW have been simulated based on computational fluid dynamics (CFD). The conservation equations of mass, momentum, and energy were solved in three dimensions. The interactive force was imposed as boundary conditions on the tool/material boundary in the model. The strain rate and temperature dependent non-Newtonian viscosity was adopted for the calculation of metal flow. The distribution of temperature, velocity, and strain rate were simulated based on the above models. The simulated temperature distribution agreed well with the experimental results. The simulation results showed that the velocity on the pin was much higher than that on the shoulder. From the comparison between the simulation results and the experiments results, the contours line, corresponding to strain rate = 4s(-1), reflected reasonably well the shape of stir zone, especially at the ground portion.