Development of manufacturing technology for a hybrid induction rotor

Abstract

General Motors is developing designs and manufacturing processes for new generations of electric motors intended for use in electric vehicles. There is interest in replacing the aluminum traditionally used in induction motor rotors with copper to improve motor capability. This work explored the use of casting aluminum end-rings to copper conducting bars (spokes) in the fabrication of copper rotors. Gravity casting trials were carried out in experimental foundry. Pure aluminum end-rings were overcast and interlocked over C101 copper conductor bars encapsulating a laminate stack of highly magnetic steel. Steel permanent mold was designed and constructed specifically for the project. The mold was capable of casting one end-ring of the rotor at a time and allowed for the assembly to be reoriented for casting of the opposite end-ring. The objective of this work is to investigate the effects of intermetallic compound (IMC) formation at the interfaces of cast-bonded Cu-Al bars on the rotor mechanical integrity and electrical resistance. The Cu-Al bonding strength was measured by tension tests, and the influence of IMC layer variation on the tension load and electrical resistance were analysed. This research phase showed that sufficient bonding and interlocking were achieved among the aluminum and copper by using a special feature and/or flux at the bar ends in the permanent mold casting process. The paper reviews the data collected for evaluation of the quality of hybrid rotor cage.