Thixotropic forming process for wheels fashioned in rheocast metal alloy and fitted with pneumatic tires

A thixotropic forming process utilizing metal alloy ingots for forming wheels of rheocast metal alloy and including a disc section, and sections of lesser thickness of a substantially cylindrical lateral surface of a rim having an inside flange and an outside flange, comprising the steps of:

• injecting a metal alloy ingot while in a semisolid thixotropic state with an injection pressure force into a die whose cavity has the shape of the wheel with a section of greater width corresponding to a wheel hub section of greater thickness and a section of lesser width corresponding to a wheel hub section of lesser thickness, the geometry, sectional profile and dimensions of said cavity being substantially the same as the geometry, sectional profile and dimensions of the finished wheel hub;
• thermoregulating the die by maintaining a relatively higher temperature at the cavity section of lesser width and simultaneously maintaining a relatively lower temperature at the cavity section of greater width, thereby to heat the semisolid metal alloy ingot at a relatively higher temperature and decrease the alloy viscosity when flowing in said cavity section of lesser width and to heat the semisolid metal alloy at a relatively lower temperature in said cavity section of greater width-and decrease the alloy viscosity when flowing in said cavity section of greater width;
• varying the velocity at which the ingot is injected to control the rate at which the leading part of the metal alloy ingot in the semisolid state advances within the cavity according to the different cavity sections of greater and lesser width until the cavity is completely filled and in such a manner that the semisolid ingot leading part advances at a slower rate through a die cavity section of lesser width and advances at a faster rate through the die cavity section of greater width, the combination of thermoregulating and varying the velocity providing the semisolid alloy ingot with a more substantially laminar flow in the die;
• and
• subjecting the injected metal alloy solidifying within the cavity to a pressure force greater than the injection pressure force to compact the material internally of the die.