A numerical comparison of the flow behaviour in Friction Stir Welding (FSW) using unworn and worn tool geometries

Abstract

The tool is a key component in the friction stir welding (FSW) process, but the tool degrades and changes shape during use, however, only a limited number of experimental studies have been undertaken in order to understand the effect that worn tool geometry has on the material flow and resultant weld quality. In this study, a validated model of the FSW process is generated using the CFD software FLUENT, with this model then being used to assess the detail of the differences in the flow behaviour, mechanically affected zone (MAZ) size and strain rate distribution around the tool for both unworn and worn tool geometries. Comparisons are made at two different tool rotational speeds using a single weld traverse speed. The study shows that there are significant differences in the flow behaviour around and under the tool when the tool is worn. This modelling approach can therefore be used to improve understanding of the effective limits of tool life for welding, with a specific outcome of being able to predict and interpret the behaviour when using specific weld parameters and component geometry without the need for experimental trials.

Modelling of friction stir welding of DH36 steel

“…The interior material of the plate was allowed to move by assigning an inlet velocity at one side. The other side of the plate was assigned with zero constant pressure to ensure there was no reverse flow at that side [17]. All plate walls were assumed to move with the same speed of the interior (no slip conditions) with zero shear stress at the walls.…”

“…Convergence in FLUENT also occurs once the velocity and continuity residual fall below 0.001 and energy residual below 10 −6 . A pressure-velocity coupling algorithm was used to solve the energy and the flow equations (solving the continuity and momentum equations in a coupled manner) to effectively cover the non-linear physical model [17]. Gravitational forces were neglected here due to the very high viscous effect of the material [12].…”

The Application of Friction Stir Processing to the Fabrication of Magnesium-Based Foams

“…As can be seen in figures 1-3, in all the specimens, some large pores were found in the bottom of the stir zone. According to previous studies on the FSP [20], the material flow is lower in the bottom of the stir zone than near the surface, which Fig. 1.…”

Thermo-Mechanical Effect on Poly Crystalline Boron Nitride Tool Life During Friction Stir Welding (Dwell Period)

“…Previous workers [26] have suggested to represent the backing plates effects by a convection heat condition with a higher coefficient of heat transfer values (500-2000 W/m 2 K). In the current model a value of 2000 W/m K has been used as it was found to give a suitable distribution for temperature at workpiece bottom.…”