As with laminations used for aluminum rotors, the laminations used for copper rotors are produced using progressive tooling on the type of stamping press shown here.
Figure 4.1.1: Stamping pressDue to copper's higher electrical conductivity, the optimum slot design for copper rotors differs from that for aluminum rotors. Computer simulations performed by Professor Jim Kirtley at the Massachusetts Institute of Technology have shown that the type of double bar slot design shown in Figure 4.3.1 can provide good running efficiency and provide improved starting performance. Jim Kirtley's work is described in more detail here. Casting trails have demonstrated that there are no problems filling the thin bar between the two slots with copper.
Figure 4.3.1: Double bar slot design for copper rotorsThis double bar slot design has been used for aluminum rotors in the past, and therefore should provide no issues during stamping. It is worth noting that problems have been encountered in the past when this type of design was used with aluminum rotors, as under heavy load conditions melting of the thin bar of aluminum between the two slots has been experienced. However, with copper having a melting temperature more than 400oC higher than aluminum, this will not be a problem with copper rotors.