D.H. Lammlein PhD Dissertation - Vanderbilt University

often reduced with increasing rotation rate, however, this association is very loose over
the parameter range tested. The highest average axial force occurred at a parameter
setting of 1600rpm and 17.0ipm. This parameter setting should be considered as on the
edge, or outside of, the parameter window which defines acceptable welds as ideal
surface appearance was not be maintained throughout the weld, particularly in the initial
portion of the weld where the weld temperature was the lowest. The abrupt jump in axial
force at this setting indicates both a lack of plastization and that additional heating is
needed to prevent a breakdown of the FSW process.
Computational fluid models (CFD) have been used with some success to predict
the expected axial force encountered during the FSW process based on work material,
tool and work geometry, and process parameters (Atharifar, Lin, & Kovacevic,
Numerical and Experimental Investigations on the Loads Carried by the Tool During
Friction Stir Welding, 2009). Figure 145 shows corresponding axial force values obtained
from the Fluent CFD models presented later. The numerical results provide a reasonable
estimate of the axial force values seen during the experiment.
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