D.H. Lammlein PhD Dissertation - Vanderbilt University

eccentricity, the method of interior support, and the method of tool disengagement must
be addressed. In this work, the significance of these issues are determined based on
experimental and numerical results, and solutions are presented with applications to
manufacturing.
It is apparent that the contact condition between a traditional, flat shoulder tool
and small diameter cylindrical work differs significantly from that of butted plate
welding. Figure 140 shows the experimental tool and cylindrical work. The flat, circular
shoulder cannot be sit flush with the work surface and, at a reasonable plunge depth, the
shoulder must hang over the front of the cylinder, over the back of the cylinder, or both
depending on the tool’s offset from the work axis of rotation. This creates potential
problems for the shoulder in its material containment role. It must be demonstrated
experimentally that this issue is not significant in pipe welding if a traditional shoulder is
to be used. In this work, the tool is offset 6.0mm forward of the work to create the
plowing effect common in FSW. This effect means the trailing edge of the shoulder is the
portion deepest in the work. This plowing effect is achieved on flat work by tilting the
tool and creating a so called angle of attack. The method presented in this work results in
a similar contact condition and acceptable results.
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