Cold extrusion of copper fillings in slots-shaped cut outs in sheet metal stacks

• Applicant: Professor Dr.-Ing. Mathias Liewald
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Production Automation and Assembly Technology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 550346872

Due to radical changes in the mobility sector the demand for electrical machines is increasing rapidly. As a result, efficient and economic manufacturing technologies are required for the production of efficient electric machines. Currently, the production of efficient squirrel-cage rotors for asynchronous machines is energy and/or assembly-intensive. Most commonly, squirrel-cage rotors are manufactured by die casting of aluminium or copper into rotor lamination stacks which consist of many thin sheet metals. Asynchronous machines with copper squirrel-cages have a significantly higher efficiency in comparison towards aluminium cages. However, production of such today appear very expensive due to high tool wear that occurs using copper die-casting. Another manufacturing method of today is to assemble preformed bars separately into the grooves of the rotor lamination stacks and subsequent welding of the bar face sides with rings. Nevertheless, this process is very assembly-intensive. The proposed project focuses on a fundamentally novel manufacturing approach in which copper fillings are formed into the grooves of a non-hardened rotor lamination stack by cold forging. In an initial experimental trial, the feasibility of the process was shown using an uncoated stack of sheet metal. However, this prove of feasibility also revealed the challenges which have to be solved, such as the damage of the top layers of the stack. The novel process offers the potential of efficient insertion of a copper filling into a rotor lamination stack due to lower assembly efforts and energy requirements compared to commonly used processes. The aim of the proposed project is the determination of the process limits and the identification of the properties of the joined assembly. The rotor lamination stack consisting of several individual sheets is positioned in a die and subsequently a semi-finished copper billet is forged at room temperature into the cut-out of the rotor lamination stack. Thereby, the rotor lamination stack operates as a die for the copper filling. Thus, the copper filling is joined positively and/or frictionally with the rotor lamination stack. The main research topics are the determination of appropriate geometric and process parameters considering the low-strength die material as well as the determination of mechanical properties of the joined assembly.

• DFG Programme: Research Grants