detailset DESIGN
Case 3: Front Truck Cab Support Bracket As-cast cored holes eliminate drilling.
• Careful design of the tooling and cores allows the use of as-cast cored holes with high preci- sion tolerance and reproducibility. As-cast holes in iron castings reduce mass and provide better properties around the cored hole, as opposed to holes drilled afterward. Some cores can be oriented perpendicular to the parting plane with careful core design by casting engineers.
• T e minimum cored hole diameter is driven by section thickness and molding process. Typically for green sand casting, the minimum diameter is 0.5 in., with the section thickness not in excess of 1 in.
Case 4: Auxiliary Drive Casting Casting-in features is often economical, but sometimes drilling them in later is more cost-effi cient.
• Depending on the feature size (diameter and depth) and section wall thickness in the vicinity of a hole, the design engineer must make a call to design it as-cast or cast solid and then drill.
• In highly automated molding processes, cores should be minimized for increased cycle times, better dimensional accuracy and a clean casting.
• For the auxiliary drive casting, engineers made as-cast vs. drilled hole decisions on the following sections: • Deep, cored pockets needed higher draft angles.
• Mounting holes on the vertical surface are cast solid and drilled later. • Mounting lugs are cast solid.
Jiten Shah is president of Product Development & Analysis (PDA) LLC (
www.pda-llc.com), Naperville, Ill., and a 25-year casting design and manufacturing veteran.
Mar/Apr 2016 | METAL CASTING DESIGN & PURCHASING | 19
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