D


riving the portion of the steel market that includes the very smallest castings (between only a few ounces and 20 lbs.) is a process, rather than a specifi c application. “The investment castings have been going gangbusters,”


said Raymond Monroe, executive vice president of the Steel Founders Society of America, Crystal Lake, Ill. “Under 20 lbs., they can do lots of interesting things to eliminate machining.” Monroe said much of the advantage of investment casting


steel parts comes from the ability to hold tight tolerances and achieve fi ne detail (wall thicknesses can be as low as 30 thousandths of an inch) with a material that has lesser fl uid life and lower viscosity than other ferrous metals.


Investment Casting Steel


“They fi re their shell [molds] at 1,800F and pour into


the shell hot,” he said. “By having a hot mold, you get much better surface fi nish and reproducibility of fi ne de- tail, whereas in sand casting, anything under about 30-40 thousandths, you can’t see the detail.”


The Design Is in the Details When designing small steel parts for investment casting,


it is important to work with your metalcaster to ensure the metal is located only where it should be and the design in- corporates all of the secondary processing that can be cast-in. And don’t be afraid to go low on those wall thicknesses. METAL


This latch housing (5.4 x 0.6 x 3-in.) in stainless steel maintains a high strength to weight ratio by in- corporating pockets in the side walls where no metal is used. The design was selected by the customer over a bar stock hog- out for its reduced cost and lead time.


This hollow commercial cam casting (1 lb.) includes cast-in cam tracks and splining. Producing the casting to near- net-shape eliminated machining, broach- ing and assembly steps. The casting process allowed an overall reduction in weight from a billet machining because metal was put only where the design required it.


This small cleaning mesh holder was developed as a prototype that incorpo- rated four pieces into one casting. The prototype proved the fi ne detail of the tines could be cast to near-net-shape.


44 METAL CASTING DESIGN AND PURCHASING JANUARY/FEBRUARY 2011


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