Improved process stability during friction stir welding of 5 cm thick copper canisters through shoulder geometry and parameter studies

Abstract

The spent nuclear fuel from Swedish power plants will be placed in copper canisters that are sealed with friction stir welding and the stability and robustness of this process is now being optimised in three steps: first, the shoulder geometry was identified that produced the most stable weld cycle, then the welding parameters were optimised for that geometry with regards to stability, and finally, the chosen geometry and welding parameters were verified and evaluated during multiple weld cycles. The shoulder study showed that stable welds could be produced repeatedly with a convex scroll geometry which proved more stable than various concave and flat scroll geometries. In the subsequent parameter study, not only were the most stable values for the welding parameters derived, but a clear relationship was shown between power input and tool temperature. This relationship can be used to more accurately control the process within the parameter windows, not only for this application but for other applications where the welding temperature needs to be kept within a specified range. Similarly, the potential of the convex scroll shoulder geometry for use in applications with other metals and thicknesses is evident.