Investment casting in one form or another has been in use for thousands of years now – and for good reason. Even though there are plenty of other ways to mold, cast and machine metals, this casting process excels at producing parts with tight tolerances, complex features and desirable metallurgical properties. With expensive or tough-to-machine metals in particular, this near-net-shape process can also offer significantly lower costs than machining. All of these benefits were on display during the Investment Casting Institute’s 2006 Casting Contest, which drew its winners and finalists from aerospace, military, electrical, oil-and-gas and sports applications. Here’s a closer look at the contest’s three top winners:
Titanium Takes Flight
A 10 x 12 x 14-inch flight control manifold produced by Alcoa Howmet’s Ti-Cast facility for Parker Hannifin took top honors in the aerospace category. Manifolds were machined from block in the past. Yet casting offered both economic and functional advantages. From an economic standpoint, investment casting enabled a more efficient material utilization than machining – or what’s called the “buy-to-fly” ratio in the aerospace business. According to Michael Pepper, vice president and general manager of Howmet Products and Services, the investment casting process enabled more than 95 percent of the titanium alloy (Ti6-4) to be used in the finished casting. In terms of function, investment casting was able to produce the part’s serpentine hydraulic passageways with gentle, flow-friendly radii that would have been difficult or impossible to machine. Then again, it wasn’t easy to cast either. “The manifold has one of the most complex geometries ever manufactured using the investment casting process,” Pepper says.
Casting Away Extra Parts
An aluminum alloy (A356T6) fan housing used in military expeditionary vehicles won in the contest’s military category. Cast by Uni-Cast for Fairchild Controls, the housing consolidates into one part what would have been multiple machined parts. Salim Khan, a Uni-Cast manager, estimates that a comparable machined and assembled component would have required five to 10 separate parts and cost about 50 percent more than the investment cast housing. “Investment casting was the only cost effective way to make the part,” he says. Measuring roughly 15 x 14.75 x 12.25-inches, the part posed a number of manufacturing challenges. Among them were transitions between the part’s relatively thin nominal walls and its many thick sections. What’s more, there’s a complex set of blades within the part.
Design for Casting
The winner in the contest’s electronics category, an optical bench for a laser target-acquisition system, highlighted the importance of designing parts specifically for the casting process. Manufactured by Precision Castings of Tennessee Inc. this 8 x 6 x 6-inch stainless steel (17-4PH) component acts as a carrier for the system’s optical components. “It has to pack a lot of mirrors and electronic components into a limited space,” says Clay Cooper, Precision Casting’s director of engineering. He recalls the part had been well-designed in CAD from a functional standpoint. “But it was nearly un-manufacturable as drawn,” he says, explaining that it had many isolated thick sections and lacked suitable gating locations. Precision Casting’s engineers helped revamp the initial design to make it more casting-friendly. “Now, it’s a really good casting,” Cooper says.
Get more information on the Investment Casting Institute’s Technical Conference, Exposition and Casting Contest.