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details DESIGN


Made in Hollow Design JITEN SHAH, PRODUCT DEVELOPMENT & ANALYSIS, NAPERVILLE, ILLINOIS CASTING PROFILE


Cast Component: Tesla Motor Co. Model S front steering knuckle.


Casting Process: Vacuum riserless/pressure riserless casting.


Material: A356-T6. Weight: 9.15 lbs. (4.15 kg).


Dimensions: 24.02 x 9.06 x 5.91 in. (610 x 230 x 150 mm)


V


ehicle steering knuckles support and position wheel bearings and spindles, while providing the connection to the control arms and/ or struts. High-end knuckles traditionally are made out of forged steel or aluminum; low-end knuckles tend to be produced in cast iron. Tesla Motor Co. worked with Compass Automotive Group,


Fruitport, Mich., to design fully hollow knuckles produced in cast aluminum for its Model S fully electric car. T e knuckle is the world’s fi rst series production for the long, completely hollow goose neck steering knuckle cast design. Previ- ous incarnations of a hollow aluminum cast steering knuckle, as used by premium German automaker Porsche, incorporated hollow gooseneck areas rather than the entire knuckle. T e fully hollow knuckle, produced via vacuum riserless/pressure riserless casting (VRC/PRC) weighs 65% less than its cast iron counterpart and 25% less than a solid aluminum design, leading to increased driving range for the electric passenger car. For more on the VRC/PRC process and how the hollow casting was produced, see “Improving Structural Effi ciency in Suspension Components” on p. 48.


Cored holes are placed strategically in the low stress, non-critical areas to maintain the structural integrity of the casting and support the internal body core.


• Cores make the interior features of the casting and allow the design fl exibility to make the component hollow with less unit weight, without compromising the structural integrity of the casting.


• The cores have to be supported and secured in the mold properly, so they don’t float or move during filling and solidification of the casting, causing wall thickness variations.


• Cored holes can be left as-cast or plugged by welding in certain weldable alloys.


Smart Choices


Cross hatching aids fl uidity.


• Cross-hatching features on casting surfaces produced in a permanent mold process, such as VRC/PRC, help break the oxide fi lms formed during fi lling so the thin wall cross section area will fi ll better for cleaner, stronger castings.


18 | METAL CASTING DESIGN & PURCHASING | Jan/Feb 2013


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