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which is now produced as one lost foam casting produced by CNC machining the foam patterns. Subtractively CNC machin- ing sand molds offers advantages when producing a very large part. “Many of the RP systems


can’t handle a very large enve- lope. And if they can handle it, it takes a long time to additively build up layers,” said Gustafson. “If you have a part that’s 10 or 15 inches tall, it takes a lot of time and there’s a cost there.” Sand mold and core material


composition is more flexible with subtractive methods. “We can tweak the binder levels and the type of sand we use to the production process,” Gustafson said. “So if we can get the process sheets from a produc- tion foundry, we can mimic that exactly. For instance, a magnesium foundry might make a sand mold with all the inhibitors or other things that might


Shown is an example of foam billet CNC cut for a lost foam prototype pattern.


be metered into the sand as the molds are made, give us the block and we can machine it.” A single company probably won’t


have all of the available technology, choosing instead to specialize in one or two areas. But, there is a tendency


toward collaboration among casting suppliers providing rapid solutions, as well as jobbing out to one another.


The Benefit for Buyers For original equipment


manufacturers (OEMs) buying castings, rapid manufacturing offers a variety of benefits. Design and engineering ideas that were not always possible can be realized. Te precision of additive methods in particu- lar enables feats of draft and wall thickness that have not been possible in the past.


“We see the importance of these design issues in aeronautics and space components,” Murray said. “People wonder why those parts cost so much. Well, it’s because of the engineering requirements. But now things that make jet engines more efficient don’t


28 | MODERN CASTING April 2014


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