Jeremy D. Webb and Dr. Russell Daines, Mechanical Engineering

Friction Stir Welding (FSW) is a semi-solid state joining process. The process utilizes a threaded pin tool “stirring” two aluminum plates together as it “sews” the seam together. One application of this process would replace the use of rivets to join aluminum paneling on commercial aircraft.

Several simplifications and assumptions were made to begin the modeling process. A nonthreaded pin rotating in a stationary plate was chosen making the shear stress inversely proportional to the radial distance from the pin. In place of a mechanical deformation model, a Bingham Plastic (non-Newtonian fluid) was utilized. It is assumed that a friction factor similar to that found in extrusion processes will eventually need to be incorporated at the interface between the pin and the semisolid aluminum (1). Steady state conditions were also assumed for this initial model.

Two experiments were undertaken to establish velocity (strain rate) and temperature profiles. Thermocouples embedded at radial distances from the center of the pin were used to establish isotherms. The second experiment has not yet been complete. A standard torsion-testing machine is being adapted to turn the pin tool at three different rates while the aluminum plate will be held at constant temperatures of 300°F, 350°F, 400°F, 450°F and 500°F. From the observed deformation, strain rates at various temperatures can be calculated and applied at the corresponding isotherms.

Once the model of the non-translating pin has been tested it can be further modified to include translation. The first step is to verify the assumed boundary conditions. Equipment preparation and background information is complete. Computing tools have been examined for feasibility. “Fluent” is available on campus and will be sufficient for the preliminary model. “DEFORM” is suggested for the final model. This commercially available software has been used to model other semisolid processes such as extrusion (2) and may be useful as the project progresses.

References

• S. Turenne, N. Legros, S. Laplante, and F. Ajersch. April 1999 Metallurgical & Materials Transactions. pp.1137-1146. Mechanical Behavior of Aluminum Matrix Composite during Extrusion in the Semisolid State.
• E.M. Herba and H.J. McQueen. 1998. The Institute of Materials. pp. 1057-1064. Extrusion modeling of 6061 aluminum alloy and particle reinforced MMCs.