Die-Cast Copper Motor Rotors: Die Materials and Process Considerations for Economical Copper Rotor Production

Abstract

For a high melting temperature metal such as copper (T_m= 1083 °C) to be economically pressure die cast, one or more suitable high temperature die materials must be identified and adapted to the process. This is a meaningful objective in terms of the rotor of the induction motor where aluminum has been the material of choice for the squirrel cage structure because this lower melting metal is readily die cast. A fabrication process other than pressure die casting is difficult to imagine. Because of copper’s higher electrical conductivity, substitution of copper for the aluminum would increase the electrical energy efficiency of the induction motor and potentially provide benefits in manufacturing economics and weight savings, depending on design objective. Copper rotor casting experience and performance of motors equipped with copper rotors are detailed in another paper in this conference. At the 1999 EEMODS conference, a progress report on the die material investigation was presented [1]. This paper updates the results presented in 1999 and elaborates on the die failure mechanism and how die life can be extended. More complete accounts of this work can be found elsewhere [2 3].