. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DESIGN DETAILS
Casting Heavy on Looks, Short on Parts Jiten Shah, Product Development & Analysis CASTING PROFILE
Casting Process: Nobake sand casting. Material: 356 aluminum with T6 heat treat Application: Polaris concept motorcycle. Myth: Castings don’t offer smooth fi nish and always require expen- sive secondary operations like machining, hand grinding, etc. Reality: By careful selection of alloy, molding process, orienta- tion in the mold, and design of the process parameters and gating and risering, metalcast- ers can produce castings with smooth as-cast surface fi nish, which can be further enhanced by polishing, blasting, plating, coating and/or buffi ng.
he Polaris motorcycle structural frame one-piece casting, winner of the 2009 Casting of the Year Competition, incorporates the gas tank, air inlet, air intake box, electrical routing, and seat and motor mounts. It was converted from a steel fabrication of more than 30 parts. The 12 x 18.75 x 454.5-in., 51-lb. casting reduced the weight of the assembly by 35%.
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Wall thickness can be optimized using fi nite element analysis and casting process modeling. • Gradually increasing wall thickness promotes smoother fi lling and directional solidifi cation, leading to better soundness and structural integrity. The key is to integrate the overall risering and gating scheme with the parting plane and orientation during the conceptual design stage to take advantage of the process fl exibility and capabilities.
• Heavy sections or hot spots should be kept closer to the risers so they can be fed.
Cored holes support a long core and vent the core gas. • To support the long body core and provide the venting for the core gases to produce better internal soundness, dimensional tolerance and surface fi nish, the cored hole features are essential.
22 METAL CASTING DESIGN & PURCHASING
JANUARY/FEBRUARY 2010
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