Researchers at the University of Missouri-Rolla are patenting a process that makes metal stronger, more efficient and more cost effective — by making it flow like chewing gum. The result could be manufacturing improvements for the aircraft industry.
"The materials flow like chewing gum at high temperature and then when it returns to room temperature it is a very strong metallic component," says Dr. Rajiv Mishra, associate professor of metallurgical engineering and director of the Center for Friction Stir Processing at UMR.
"We are taking metals to high temperatures and changing the microstructure of the material and after it becomes very superplastic — stretchy and formable — we can give it any shape we want to without the material failing," says Mishra.
Chewing gum does not stretch before it is chewed, but after it has been chewed for a while, it easily stretches and elongates, Mishra says. In the same way, metals treated with this process gain new properties.
In collaboration with Boeing, UMR has a patent pending on this process, known has friction-stir superplasticity (FSS). This process is a variation of friction-stir welding (FSW), which is a new joining method for aluminum alloys, Mishra says.
In FSW, aluminum alloys are joined in a way that is energy efficient, environmentally sound and versatile, Mishra says. A rotating tool is inserted into the metal to be joined, and moved along the joining area. Localized heat is generated by friction between the tool and the work piece.
UMR has received $100,000 from the Defense Advanced Research Projects Agency through a subcontract from Rockwell Scientific of Thousand Oaks, Calif., and more than $500,000 from the National Science Foundation over two, three-year periods to conduct this research. FSS creates very fine grain microstructures in the heated area. Boeing researchers are interested in this process variation because it allows the forming of thicker metal plates than previously possible, Mishra says. This would enable Boeing to manufacture complex components needed in fighter jets as well as commercial planes, using one piece of metal instead of five. "It builds a unitized structure by reducing the number of components and making it more cost effective," says Mishra.
Lucie Johannes, a UMR Ph.D. student in metallurgical engineering from Topeka, Kan., is working with Mishra on this research.
The UMR Center for Friction Stir Processing is investigating several other variations of friction-stir welding, including friction-stir channeling, which builds channels for heat exchange in a solid plate; friction-stir microforming, which makes miniature components that are equal to, or better than existing components; friction-stir surfacing, which enables the surface to be modified for different properties; friction-stir casting modification, which reduces defects by embedding stronger regions into the cast component; and friction-stir powder processing, which makes the metal’s composition more consistent with fewer flaws. All of these processes are based on the friction-stir welding principle but altered slightly to obtain a different end result for the manufacturer.
UMR has filed for patents on friction-stir channeling and microforming. "We are trying to create, using this principle (FSW), a new set of technologies that we can market as our capabilities. The basic concept remains the same, but the way we are applying it is new," says Mishra. "We are coming up with ways of making components and modifying the micro-structure that has not been done before."
Mishra hopes manufacturers find these techniques not only less harmful to the environment, but also more cost effective, resulting in stronger materials.