Method of casting vehicle wheel

Abstract

The lower mold which forms the external side of the vehicle wheel is water-cooled by water-cooling pipes. The rib-forming portions of the upper mold which forms the internal side of the vehicle wheel are forcibly air-cooled by the air passages provided along the rib-forming portions. Since water-cooling has better cooling capacity than air-cooling, the molten material inside the cavity between the lower mold and the upper mold is solidified from the external side thereof, and no defects such as shrinkage cavities occur on the external side thereof. When the internal side is solidified, the rib portions are solidified not much later than the other portion of the internal side, thereby shortening the casting cycle time. The split molds which form the cavity for forming therein the rim portion of the vehicle wheel are opened earlier than the upper mold, at the time when the surface layer portion of the molten material in the cavity has been solidified. If the split molds are kept clamped, the clearance to be generated between the split molds and the molten material upon contraction thereof due to solidification, restricts the heat dissipation from the molten material to the split molds, resulting in retarded solidification. To the contrary, early opening of the split molds leads to accelerated solidification of the molten material due to cooling of the rim portion by the atmosphere.