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details DESIGN


Part Consolidation Makes Lost Foam Attractive for Differential Carrier


JITEN SHAH, PRODUCT DEVELOPMENT & ANALYSIS, NAPERVILLE, ILLINOIS CASTING PROFILE


Cast Component: Differential carrier housing for power transfer on the drive line for a heavy truck.


Process: Lost foam. Material: Ductile iron. Weight: 140 lbs.


Dimensions: 15.7 x 16.9 x 17.5 in.


fi nish. Lost foam off ers design fl exibility by allowing multiple features oriented as required for the form, fi t and functionality compared to conventional sand or permanent mold casting, where parting line and drafting restrict them. Grede Columbiana achieved an approximately 75% machining stock reduction


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on an 11 x 17-in. section of the diff erential carrier. A recessed area incorporated into the design allowed for machining relief, and new features were added at no additional cost that would have been expensive and time consuming to machine. In addition, the design of the casting and the tool allowed for quick-change part geometry. Inserts in the tool could be interchanged, so multiple part numbers were produced from one tool.


Lost foam’s fl exibility in the placement of features, zero draft and detail enables a machining relief area to be incorporated.


• T e lost foam pattern is an exact rep- lica of the fi nished casting shape, and typically the pattern is made of multiple foam sub-components glued together. T e binderless molding substrate has good fl owability that allows for capturing fi ne details in the casting.


An interior water passage with enhanced surface fi nish is produced without a core.


• In conventional casting processes, cored features are made by placing a physical core into the mold cavity, which aff ects the dimensional tolerances and repro- ducibility. In lost foam, holes are incor- porated as-cast with tighter dimensional tolerances.


• T e foam pattern is coated with a fi ne refractory coating that provides a smooth fi nish and details. In most cases, the as- cast surface is adequate and eliminates the secondary machining operation. Actual as-cast surface fi nish depends on the alloy, process parameters, overall size and weight, wall section thickness and the gating and risering system.


14 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2014


onverting to the lost foam casting process allowed for the signifi cant reduction of machining costs for a diff erential carrier produced by Grede Columbiana, Columbiana, Ala. Lost foam is a near-net-shape casting process used to make complex castings with excellent dimensional tolerance and surface


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