details DESIGN
Boosting Power With Good Casting Design
JITEN SHAH, PRODUCT DEVELOPMENT & ANALYSIS, NAPERVILLE, ILLINOIS CASTING PROFILE
Cast Component: Aluminum exhaust manifold.
Process: Semi-perman ent mold casting.
Material: A356.2-T6 aluminum. Weight: 27 lbs. Dimensions: 8 x 18 x 19 in.
with its customer to identify critical performance requirements and fi nd an eco- nomical engineering solution. T e fi nal redesign yielded a 38-lb. weight saving, eliminated a gasket and potential leak, increased the power output and allowed the engine to meet a new emission standard of 5g/kWHr HC plus NOx.
C
asting conversions can provide benefi ts beyond weight and cost savings. In the case of an exhaust manifold for a V8 marine engine, changing a two-piece part to a single part design also reduced emis- sions and increased the power output by 6%. Casting supplier Stahl Specialty Co., Kingsville, Mo., worked
Water jacket core
Nesting the water jacket and exhaust cores in a one-piece design yields better wall thick- ness control for improved thermal performance of the fi nished product.
• T e wall thickness of the manifold is designed to be stable by incorporating a water jacket core nested/pre-assem- bled with the exhaust core, thereby eliminating the potential for the cores’ relative movement. Consistent wall thickness also yields predictable solidifi cation, cooling rate and proper- ties for aluminum castings.
• Along with computational fl uid dynamics, casting process simulation of fi lling, solidifi cation, microstruc- ture and mechanical properties is an important tool for the development of complex castings.
Casting allows complex bends and smooth transitions, driven by the fl uid thermal interaction requirements for manifolds.
• Drafting smooth transitions and generous fi llet and radii are important in the semi-permanent mold casting process to yield better surface fi nish due to streamlined metal fl ow, facilitate easy stripping of the casting from the metal mold, reduce stress concentration in service, and provide a better overall life cycle of the component.
20 | METAL CASTING DESIGN & PURCHASING | Mar/Apr 2015 Exhaust core Water jacket core
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