The conical tool design is potentially a simple solution to the problem of closure welding. According to Trapp, Fischer, and Bernath of the Edison Welding Institute(ESI) in U.S. Patent #7234626, the appropriate cone included angle can contain weld material regardless of cone penetration depth and during cone tapered retraction (gradual removal of tool during weld traverse.) The conical tool in conjunction with the tapered retraction procedure could therefore be used to weld closed contours such as cylinders and spheres without leaving a defect where the tool exits the material. The conical tool can furthermore be used for in-process adjustment of penetration depth (i.e. variable thicknesses welds.) The conical tool design is especially attractive because it is very simple and durable design. The conical tool is potentially a simple and elegant solution to the seemingly complex problem closure welding in FSW. The current solution is an exceedingly complex, hydraulically actuated retractable pin tool apparatus.

An experimental weld matrix has been performed on 1/8" thick, butted 6061 alloy aluminum plates. A suitable inclusive angle for FSW with cones was found by testing a range of tool angles (60, 90, and 120 degrees.) Suitable weld parameters were established and a weld parameter matrix was performed. The characteristic weld forces were determined via dynamometer, achievable weld strengths via tensile testing, weld structure and appearance via etching of macrosections, and approximate shoulder edge temperature via thermal camera. The tool tapered retraction procedure is also evaluated.