details DESIGN
An as-cast water passageway provides smooth surface fi nish for good heat transfer.
• In conventional casting processes, cored features are made by placing a physical core into the mold cavity, which can aff ect the dimensional tolerances and reproducibility. In lost foam, cored features such as holes, water passages and volute areas are incorporated easily as-cast with tighter dimensional tolerances and true positioning. Near-net-shaped features are possible, eliminating machining operations and extra stock.
• T e foam pattern is coated with fi ne refractory coating, which provides a smooth surface fi nish. In most cases, the as-cast surface is adequate and eliminates the secondary machining operation. Actual as-cast surface fi nish depends upon the alloy, process parameters, the overall casting size, wall section thickness and the gating and risering system.
Lost foam allows the placement of a knob appendage.
• T e lost foam pattern is an exact replica of the fi nished casting shape, and typically the pattern is made of out multiple foam subcomponents glued together. T e casting orientation is adjusted for the desired fi lling and solidifi cation pattern, unlike other casting processes where parting plane dictates the casting orientation.
Jiten Shah is president of Product Development & Analysis (PDA) LLC, Naperville, Ill., and a 25-year casting design and manufacturing veteran.
Nov/Dec 2012 | METAL CASTING DESIGN & PURCHASING | 19
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