Friday, June 8, 2012: 10:00 AM
Sorrell 1 (Hilton Chicago/Indian Lakes Resort)
Friction stir welding (FSW) is a solid state joining method invented by TWI in 1991. This joining method could prevent melting related defects for its character of solid joining. Material flow at elevated temperature plays a central role in producing the weld. The resulted microstructure and defects in the weld are also concerned with transient material flow pattern during the process. Simulation could be a powerful tool to understand the flow pattern during the process for difficulties in direct observation. Material flow, heat generation and temperature evolution during FSW, are fully coupled with each other. However, interactive forces, existing at the interface between material and tool, give 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, three-dimensional flow of metals in FSW have been modeled based on computational fluid dynamics (CFD), considering the interactive force. The conservation equations of mass, momentum, and energy were solved in three dimensions. The interactive force was imposed on the tool/material boundary, by introducing source terms in the conservation equations of momentum and energy. 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 model. Asymmetry of heat generation rate and material flow pattern were observed. Both the temperature field and material flow pattern were validated by experiments. The simulation results corresponded well with the measured temperature and dimension of nugget zone.