D.H. Lammlein PhD Dissertation - Vanderbilt University

Figure 111: (Unsupported, conical tool) A plot of axial (z-direction) force showing an
inverse relationship with rotation rate and a direct relationship with traverse speed.
Figure 112 and Figure 113 show the weld moment about the vertical, z-axis
plotted against rotational speed for each weld. The torque input consistently increased
with increasing traverse speed for the cupped tool and the opposite relationship held for
the conical tool, somewhat inexplicably. The relationship between torque and rotational
rate for the cupped tool and supported setup was not consistent but shows a general
tendency towards reduced torque at higher rotational speeds. For the conical tool this
relationship was seen more reliably. Figure 113 shows that torque reduced in all cases
with increased rotational speed for the conical tool. The reduction in measured torque is
due to material softening at higher rotational speeds but this is mitigated somewhat by the
fact that were the tool spun in a medium of constant viscosity, higher rotational speeds
would result in a larger moment on the tool.
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