At present it is unclear whether it is necessary to pre-heat the lamination stack when die-casting copper rotors. For prototyping trials performed during the ICA/CDA project, sample rotors were cast using both pre-heated and non pre-heated stacks. Pre-heating was typically carried out for about an hour in a convection furnace set to either 260 or 370°C.
A systematic evaluation of the impact of stack pre-heating on rotor quality and performance has not been performed. However, casting trials revealed that porosity concentrations in the end rings can be reduced through the use of extremely high melt superheats. The dies used to produce these rotors samples were only heated to 120-320°C, suggesting that heat loss from the liquid copper to the cooler casting die must be controlled in order to minimize porosity in die-cast rotors. When dies are pre-heated to greater than 600°C, heat loss will become less critical, probably eliminating the need for stack pre-heating. However, should non-fills or excessive porosity becomes a problem during copper die-casting, one approach to eliminating the problem would be to pre-heat the lamination stack.