The die-cast copper motor rotor – a new copper market opportunity

Induction motor manufacturers have long known that substitution of copper for diecast aluminum in the rotor squirrel cage would significantly reduce motor losses and improve the electrical energy efficiency. Aluminum is readily die-cast to produce the complex squirrel cage within and around the iron laminations of the rotor. Copper is much more difficult to die-cast due to its high melting temperature which leads to premature die failure. The work reported here addresses the die life problem in die casting electrical grade copper. A number of candidate high temperature die materials were surveyed. Computer simulation of the cyclic thermal and stress gradients in dies provided insight into the “heat checking” failure mechanism and how it could be minimized or avoided. A nickel-base alloy die system preheated to and operated at ~625°C has been developed and shown to greatly extend die life compared to die steels operated conventionally. A die insert heating and insulation system was developed to make extended runs possible. Copper motor rotors were die cast over a range of machine operating parameters in joint effort with several motor manufacturers. Motor test results showing the predicted 15 to 20% reduction in motor losses and reduced motor operating temperatures are presented.