Casting process for producing hermetically sealed housings for hard disk drives

Abstract

An aluminum alloy casting having a globular microstructure forms a housing for a hard disk drive by pouring a molten aluminum alloy with a fine grain and a non-dendritic structure into the shot chamber defined by a shot sleeve of a vertical die cast press. Heat is removed from the molten alloy to produce a semi-solid slurry which is forced upwardly into a die cavity through an offset elongated funnel gate opening positioned to received and merge hotter slurry within the center portion of the shot chamber with cooler slurry adjacent the shot sleeve. The solidified alloy forms a housing that has a gas leak rate that meets the requirements of being hermetically sealed.

What is claimed is: 
     
         1 . A method of producing an aluminum alloy casting having a globular microstructure and adapted to form a hermetically sealed housing for a hard disk drive, the method comprising the steps of forming a molten aluminum alloy with a fine grain and a non-dendritic structure, directing the molten alloy into a shot chamber defined by a shot sleeve of a vertical die cast press, removing heat from the molten alloy within the shot chamber to produce a semi-solid slurry, and forcing the slurry into a die cavity through an offset funnel gate opening positioned to received and merge convection heat from hotter slurry within the center portion of the shot chamber with convection heat from a cooler slurry adjacent the shot sleeve. 
     
     
         2 . A method as defined in  claim 1  and including the step of forcing the molten slurry from the funnel gate opening through a tapered nozzle opening within a lower mold section and extending to the die cavity. 
     
     
         3 . An aluminum alloy casting having a globular microstructure and adapted to form a hermetically sealed housing for a hard disk drive, said casting comprising a body of solidified semi-solid aluminum alloy, and said body having a hermeticity leak rate of about 5×10 e−8 cc/second. 
     
     
         4 . Apparatus for producing a metal part within a die cavity defined by a die set mounted on a vertical die cast press, said press comprising a shot sleeve defining a shot chamber having a generally vertical axis, a shot piston supported for axial movement within said shot sleeve, a coolant passage within said shot piston for cooling a molten metal within said shot chamber to within a predetermined temperature range, a power actuator for moving said shot piston upwardly to transfer molten metal from said shot chamber through a gate opening into the die cavity where the molten metal solidifies to form the metal part, and said gate opening comprising an offset funnel gate opening positioned to receive and merge hotter slurry within a center portion of said shot chamber with cooler slurry adjacent said shot sleeve. 
     
     
         5 . Apparatus as defined in  claim 4  and including a mold plate above said offset funnel gate opening and defining a tapered nozzle opening extending to the die cavity.