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Material of the Future: 3-D Printed Molds Improve Titanium Casting’s Potential

Researchers developed molding methods and materials to provide exceptional design flexibility while simplifying production. SAIRAM RAVI AND JERRY THIEL, UNIVERSITY OF NORTHERN IOWA, CEDAR FALLS, IOWA


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itanium alloys continue to remain some of the most ver- satile alloys available with high strength to weight ratios and excel-

lent resistance to corrosion. Titanium’s use as an engineering material in cast components has been limited due to its high cost, some of which results from the casting process. Because of strong reactivity with oxygen, current methods for producing titanium castings include rammed graphite molding and invest- ment casting. Both involve multiple steps and require extensive equipment. Recently, three dimensional (3-D)

printing equipment has become a read- ily available technology possessing the

ADDING IT ALL UP Breaking down the latest research is as easy as 1-2-3.

“Three Dimensional Printed Molds for Titanium Casting Applications,” Sairam Ravi and Jerry Tiel, University of Northern Iowa, Cedar Falls, Iowa

Background—The researchers developed a system that provides exceptional design flexibility while reducing the time, steps and complexity of produc- ing titanium castings. It was designed to address the high reactivity of liquid titanium with molding materials and to minimize alpha case depth.

Procedure—First, the researchers studied the formulation and characteriza- tion of a suitable nonreactive coating for titanium casting applications. Trial cylindrical mold metal reactivity molds were produced, preliminary titanium casting trials were held and the alpha case layer formed was measured. Finally, titanium casting trials at the Rock Island Arsenal used silica sand molds and the newly developed refractory coating. The alpha case layer of titanium was measured and correlated to the preliminary trials.

Results and Conclusions—Using rapid prototyping technology to produce silica sand molds and using an effective refractory coating such as a water based Alumina coating, the alpha case layer defect in titanium castings can be reduced to a large extent in sand casting. Also, 3-D printed molds proved to have the quality and integrity required to pour titanium castings, as long as the surface was protected with a nonreactive refractory coating.

32 | MODERN CASTING April 2015

accuracy required to produce high qual- ity molds and cores for castings. Te University of Northern Iowa, Cedar Falls, Iowa, with funding provided by the U.S. Department of Defense, has developed molding methods and mate- rials to enable casting titanium in 3-D printed (binder-jet printed) molds. Tis system provides exceptional design flexibility while reducing the time, steps and complexity of produc- ing titanium castings. It was designed to address the high reactivity of liquid titanium with molding materials and minimize alpha case depth. Although the scope of this research was limited to 3-D printed molds, the technol- ogy developed also could be used with conventional molds.

internal geometric features at a fraction of the cost of competing technologies. It is commonplace for conventional ferrous and nonferrous materials to be cast in intricate shapes in sizes from ounces to hundreds of tons. But because of titanium’s reactivity with oxygen in the atmosphere or vessels that contain the liquid metal, its use as a casting material has been limited. Titanium is as strong as steel but more than 40 percent lighter. It is only 60 percent heavier but over four times stronger than aluminum and with high temperature characteristics not pos- sible with other alloys. Currently, titanium components


are predominantly used in ultra-high performance applications includ- ing aerospace. Increasingly stringent regulations on fuel efficiency and lower greenhouse gas emissions has focused interest on weight reduction and improving performance. Titanium has great potential to be the designer’s material of the future, because of its unique combination of metallurgical properties such as high strength-to- weight ratio in the temperature range from sub-zero to 1,004F (540C). Another remarkable property of titanium and its alloys is their excel- lent corrosion resistance to a range of acids, alkalis and chemicals. Tis attribute makes them ideal for applica- tions in power plants and the chemical industry. Titanium is the only struc- tural metal having corrosion fatigue behavior in saltwater that is practi- cally identical to that in air, making it ideal for all sea water-based applica-

Background Casting remains the single

most versatile metal forming technology. No other process has the ability to form intricate

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