Application of FSW to Join Aluminium Foil Winding Coils for Electrical Transformers

Abstract

The technically pure copper is being replaced by aluminium as conductive material in electrical transformers for power systems. This evolution brings new manufacturing challenges. One major difficulty is the limited weld ability and non-acceptable residual deformations of the aluminium, when welded by fusion arc welding processes. The Friction Stir Welding (FSW) was selected for evaluation considering the requisites of the application on mechanical strength, distortion and electrical conductivity. The current work evaluates the feasibility of application of FSW to join successive residual aluminium foil winding coils, into new longer foil winding coils. The residual foil winding coils are made of AA1070 with 1.6 mm thick and 1100 mm wide. The residual foil winding coils are butt jointed by FSW and rewind in one new longer foil winding until the total length of the new bobbin already enables its application in the production of new components for high voltage electrical transformers. This way, the FSW may be used as key technique to add-value and promote a more sustainable industrial production system. Each of the residual foil winding coils had an average weight of about 250 kg, which required the development of dedicated supporting, positioning and clamping systems. The technological conditions to be implemented in real scale are initially developed in 300 mm length welds. The analysis of the results addresses the mechanical resistance, hardness distribution and metallurgical properties of the resulting joint zones. It was demonstrated the technological feasibility of joining by FSW, and rewind, residual winding foils, to produce new coils complying with the requirements for distortion, mechanical strength and electrical resistance properties.