D.H. Lammlein PhD Dissertation - Vanderbilt University

When the measured temperature exceeded the desired temperature the weld
controller would adjust the tool rotational velocity or traverse rate based to reduce heat
input. Alternatively the weld controller could trigger a heat dissipation system when the
measured temperature exceeded the desired temperature. This heat dissipation system
could be a heat exchanger in the tool or work. It has also been suggested that a jet of
compressed air could be focused on the work behind the traveling tool during rotary
welding to eliminate the secondary heating effect.
A temperature based feedback control system for controlling thermal conditions
in conjunction with an axial force or torque based feedback control system for controlling
axial force would be effective methods of controlling weld quality in FSW. The
temperature based controller would likely adjust tool rotational velocity to control the
weld temperature while the force based controller adjusted tool vertical position to
control axial force and the downward pressure excreted by the tool. The FSW is sensitive
to axial force and the temperature in the vicinity of the tool. Although FSW can be done
without feedback control, control systems reduce the necessary preparation time, increase
the tolerance error, and increase the reliability of the system. In a manufacturing
environment where a robust and flexible process is required, these feedback control
systems are likely necessary.
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