Numerical and Experimental Investigations on the Loads Carried by the Tool During Friction Stir Welding

Abstract

A computational fluid dynamics (CFD) model is presented for simulating the material flow and heat transfer in the friction stir welding (FSW) of 6061-T6 aluminum alloy (AA6061). The goal is to utilize the 3-D, numerical model to analyze the viscous and inertia loads applied to the FSW tool by varying the welding parameters. To extend the FSW process modeling, in this study, the temperature-dependant material properties as well as the stick/slip condition are considered where the material at the proximity of the FSW tool slips on the lower pressure regions. A right-handed one-way thread on a tilted FSW tool pin with a smooth, concaved shoulder is, additionally, considered to increase the accuracy of the numerical model. In addition, the viscous and frictional heating are assumed as the only sources of heat input. In the course of model verification, good agreements are found between the numerical results and the experimental investigations.

Modelling of friction stir welding of DH36 steel

“…2a. Previous work by Schmidt et al [15] and Atharifar et al [12] showed experimentally that sticking conditions are closer to the real contact situation between the tool and workpiece. Cox et al [16] carried out a CFD model on FSW and assumed pure sticking conditions at the tool/workpiece contact area.…”

“…25 [25]. Atharifar et al [12] also reported a decrease in torque with increasing tool rotational speed and decreasing travers speed as a result of a low viscosity field resulting from an accumulation in thermal energy. From this discussion, it is expected that torque increases with increasing traverse speed at a constant tool rotational speed.…”

“…They also found that there was more asymmetry in temperature under the shoulder compared to the regions away from it. Moreover, Atharifar et al [12] proved numerically and experimentally (using thermocouple readings) that the maximum temperature in FSW of aluminium was at the advancing side. This was attributed to the high relative velocity at the advancing side causing more viscoplastic material shearing and consequently the higher heat generation through plastic deformation and viscous heating.…”

“…This is because the heat affected region in FSW is very small compared to the whole length of the workpiece [3,[12][13][14]. The tool and the plate were considered in the fully sticking condition.…”

“…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]. Some of the mention assumptions have been used in previous publications for the authors [18] to model the same grade of steel with two differences -a-fully sticking conditions so the material velocity is equal to tool rotational speed -b-heat generated is totally from viscose heating instead of frictional and plastic heat source.…”