D.H. Lammlein PhD Dissertation - Vanderbilt University

CHAPTER IV
THE FRICTION STIR WELDING OF HEMISPHERES – A TECHNIQUE FOR
MANUFACTURING HOLLOW SPHERES
D.H. Lammlein, W.R. Longhurst, D.R. DeLapp, P.A. Fleming, A.M. Strauss, G.E. Cook.
The Friction Stir Welding of Hemispheres - A technique for Manufacturing Hollow
Spheres. International Journal of Pressure Vessels and Piping, Submitted August 4,
2010.
Abstract
In this work, thin walled, small radius, aluminum 6061 hemispheres are joined using
friction stir welding (FSW). Hollow spheres are used extensively and in a wide range of
applications, primarily as pressure vessels. FSW of spheres presents challenges
associated with tooling, system eccentricity, internal support, and the method of weld
termination. FSW is an improvement on fusion welding in terms of strength, reliability,
and surface finish. Additionally, a welded solution is preferred for weight considerations
to joining by flange, gasket, and fasteners; this is particularly true in aluminum alloys
selected for their low density. Here, FSW is adapted to the joining of small diameter
hemispheres using two separate approaches. The first approach assumes the use of an
interior supporting anvil is acceptable and a series of full penetration welds are made
using a cupped shoulder, threaded probe tool. A second approach assumes the use of
internal support is unacceptable because this anvil cannot be retrieved. Here, unsupported
welds are made with a shoulder-less, conical tool at partial penetration. For analysis,
lateral macrosections, tensile tests, process force data, and computational fluid models
(CFD) are presented.
Introduction
Friction stir welding (FSW) is a proven solid state joining technology with a
growing range of application [1]. To accommodate a wider variety of engineering
structures, FSW must be adapted to highly curved surfaces and surfaces with dual
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