D.H. Lammlein PhD Dissertation - Vanderbilt University

CONCLUSION AND FUTURE WORK
Conclusion
The research presented is expected to expand the range of application of the FSW
process. The use of force feedback control of weld seam alignment permits the use of
FSW in an automated, manufacturing setting on blind type t-joints. Experimental and
computational data demonstrated that the vertical member of the t-joint can be followed
based on process force feedback. This will allow a FSW machine tool to follow ribs
under large metal sheets without tedious alignment and tool path determination. In the
case of serpentine ribs, this research will permit the application of FSW to a geometry
which was previously not feasible.
In this work, the FSW was shown for the first time to be capable of welding small
diameter butted hemisphere type joints. It was shown that a cupped shoulder tool in
conjunction with internal support can be used to effectively join two hemispheres at a
high percentage of the parent material strength. Additionally, it was shown that for cases
where internal support is not permissible that a conical type tool can be used to obtain
welds exceeding 50% penetration. In a practical measure of strength where these partial
penetration welds are compared to the strength of the full thickness of the parent material,
these unsupported welds achieved strengths exceeding 25%. These strengths were
achieved using the limited weld parameter permutations attempted experimentally and
can likely be increased. A partial penetration weld of butted hemispheres without the
use of an internal support has applications to external compression vessels. Additionally,
the use of a conical tool in FSW at partial penetration without anvil support applies to
other situations where the underside of the work is inaccessible and the use of an
underside support device is unfeasible.
The joining of butted hemispheres with full weld penetration was demonstrated
successfully with weld strengths exceeding 70% over the limited parameter range tested.
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