Apparatus and method for die casting

The present invention provides a method and apparatus for die-casting copper and other metals that are cost-effective and practical for production use in die-casting, for example, copper motor rotors. In motor rotors, the incorporation of die-cast copper for conductor bars and end rings in place of aluminum is known to result in improvements in motor energy efficiency. Previous attempts to die-cast copper motor rotors in a commercially feasible manner have failed because copper's high melting point places too great a stress on the die material, resulting in cracking and fracturing of the molds. High temperature die materials such as nickel, tungsten and molybdenum based alloys with a high melting point are employed, and a die casting apparatus is provided to pre-heat the molds prior to injection of the molten copper. Pre-heating and high operating temperatures provide extended die life. By preheating, the die materials experience reduced cyclic stresses associated with thermal expansion, because the thermal shock that results from the difference in temperature between the molten copper and the surface of the mold is reduced, ideally below the yield strength of the mold material. Extended die life provides the opportunity for economically viable copper motor rotor die-casting.