D.H. Lammlein PhD Dissertation - Vanderbilt University

Figure 106: Dynamometer data for a butted configuration, sphere weld (1000rpm,
10.4ipm, 0.095” depth) using a 100º conical tool (snub-cup). The weld is a full
circumferential weld and the eccentricity of the setup can be seen in the lower frame,
which shows the vertical position of the tool relative to the machine stage. The
eccentricity was generally around 0.02” but varied in its manifestation from weld to
weld. The desired torque is closely maintained. From approximately 159 to 203 seconds
the spinning tool is being gradually lowered (plunged) into the material at approximately
0.002” per second. From 203 to 209 seconds the vertical and rotary (traverse) motors
are stopped during a brief dwell period prior rotary motor engagement. Reductions in
axial force from 188 to 203 seconds are due to material softening [27].
Accounting for system eccentricity in the experimental setup for the cupped
shoulder, threaded probe tool was done by mapping the eccentricity prior to the weld via
a series of auto-zeroing procedures as both force and torque control proved to be
inconsistent for this particular tool. The relative height of the butted hemisphere surface
to the system was obtained at 60° intervals for each weld sample prior to the weld and a
vertical position path was programmed into the computer for welding at the desired
depth. The tool was brought from the current vertical position to the desired vertical
position (moving from calibration point to calibration point around the sphere) via a
linear function with parabolic blends as described in Chapter 7 of Craig [28]. In these
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