Fully coupled thermo-mechanical modelling of a friction stir welding process using finite elements analysis

Abstract

Friction Stir Welding (FSW) is a relatively new developed solid state joining technique. FSW process was invented by Wayne Thomas at The Welding Institute (TWI) in December 1991, and since its invention, it has shown to be viable for joining many kinds of materials of various thicknesses, including hard-to-weld materials. The main feature of FSW is that the weld takes place in a solid phase below the melting point of the material to be joined. In the present study a finite element model of the FSW process is built and a FSW butt weld of two aluminium alloy 2024-T3 plates is simulated using a fully coupled thermo-mechanical analysis. Besides the welded panels, the model includes the backing plate and the welding tool as physical bodies, which makes the simulations more realistic. The model also includes conductive heat transfer between the contact surfaces of the FSW tool, the aluminium plates and the backing plates, heat generation due to friction between the tool and the welded plates and heat loss to the ambient air due to convection. The simulated model makes it possible to analyse and check several aspects of this welding technique. It is proved that tool geometry has a vital importance in the FSW process. The influence of using instantaneous or ramped velocity at the beginning of the simulations is also studied. Moreover, it is seen that the mesh used in the finite element analysis and the adjustment of the inelastic heat fraction have a great influence on the obtained results.