Purdue NewsPurdue News
September 1995
The new technique, which controls how parts are cooled after they've been formed from hot metal, also may lead to lighter, stronger planes and cars, more fully recyclable autos and more efficient electric vehicles, says Issam Mudawar, professor of mechanical engineering at Purdue University.
"The aluminum industry is in dire need of more cost-effective methods for fabricating complex-shaped, high-strength aluminum alloy parts," says Mudawar, who developed the method with doctoral student David D. Hall of Crown Point, Ind. "Cooling the part after it has been formed is one area in the fabrication process that contributes a great deal to high production costs and poor part quality."
Funded in part by the Aluminum Company of America, the research was described in a recent issue of the International Journal of Heat and Mass Transfer. Additional details of the work will appear in an upcoming issue of the same journal.
In addition to aluminum alloys, Mudawar also is working to incorporate the same methodology in the fabrication of aluminum-based composite materials.
He says the system can be implemented by companies now with little investment and modification to existing setups.
To form aluminum parts, manufacturers heat the metal to a high temperature and extrude it through a die, like toothpaste from a tube, or stamp it in dies in a press. When a part comes out, it has the desired shape for a particular application, such as a support beam for an airplane wing or the frame of an automobile.
The part then must be cooled in a process called heat-treating, of which quenching is the most crucial step. Most manufacturers quench a part by spraying it simultaneously with several sprays of water. But if a part has a very complex shape, or is very thick in one section and thin in another, the part cools unevenly, which can cause it to warp. Also, because the rate at which a part cools affects its metallurgical properties, improper quenching can result in structural imperfections that severely reduce its strength, hardness and durability, causing the part to fail, Mudawar says.
Manufacturers use trial and error to determine the best configuration of spray nozzles to cool a part. They often produce several test parts before finding the proper settings. This process not only can result in inferior parts and wasted materials, it also wastes production time, Mudawar says.
Mudawar's system uses computers to optimize the quenching process. He and Hall have developed computer software that determines the precise configuration of spray nozzles and the amount of water needed on each area of any given part shape in order to cool it uniformly.
"Using this system, all the structural properties of a part can be determined in advance, before the part is even produced," Mudawar says. "A manufacturer does not have to spend two or three weeks producing junk in order to optimize cooling. This process eliminates virtually all the scrap generated from trial and error methods and guarantees that the part will be cooled evenly for optimal strength, hardness and durability."
Mudawar and several graduate students set out 10 years ago to understand how sprays cool surfaces and to predict precisely what happens to the mechanical properties of a part, such as strength and hardness, as it is quenched. Hall quenched parts experimentally and then compared the parts' actual properties with his predictions, which were based on metallurgical information.
"Our experiments demonstrated the accuracy of our models," says Hall, who has worked on the project since he was an undergraduate. "The last step was developing the computer software. We can now predict the strength and hardness of a part point by point using the models that are implanted in the software."
The result is the first system capable of predicting the mechanical properties of any size or shape of quenched part from knowledge of only the spray nozzle configuration, Mudawar says.
The system is not yet being used by any company, but Mudawar says it's ready to be implemented. Here's how it would work in a plant: The operator of a heat-treating system enters the aluminum alloy's composition and part geometry into a computer. After consulting an extensive computer data base, the computer system determines the nozzle configuration and the pressure in each water nozzle needed to achieve optimal cooling and the desired mechanical properties.
With a little more development, Mudawar says, his system could be adapted to send the information directly to an automated nozzle-positioning and control system, similar to the robot systems used to spray-paint cars. "There already are robots that can maneuver around a contoured surface, and as they do so they can reduce or increase the flow rate of the spray, which is precisely what we need for cooling," he says. "It wouldn't require much modification or be a major investment, because spray-painting technology is very mature. For companies that are interested, we feel implementation of a fully automated system is just around the corner, maybe only a year or two."
One industry that would benefit from Mudawar's system is aerospace.
"Aluminum alloy parts are used extensively in airplanes, from the structures that hold the wings together to the brackets that hold the engines in place," Mudawar says. "By incorporating this technology, companies could expand to the point where instead of just surviving on the making of one bracket for a particular type of plane, they could meet other aerospace or auto industry needs as well. That's particularly important for the growing number of smaller manufacturers in the United States."
Mudawar's system also could make electric and aluminum-intensive vehicles more feasible.
"In Europe, automakers are responsible for melting or scrapping a car when the consumer is finished with it," Mudawar says. "With aluminum, you can recycle virtually every gram, while with steel there's a lot of scrap left."
For the United States, aluminum car parts will become important when manufacturers start producing more electric vehicles, Mudawar says. "One of the problems is that electric vehicles have giant batteries that work for only about an hour or two. But if you have a light vehicle made from aluminum alloys, power consumption goes way down."
An all-aluminum vehicle would cost more to produce now than a steel one, because it would mean a whole new process for the manufacturer, Mudawar says. "Obviously you can't justify suddenly switching every car to aluminum, but for electric vehicles it becomes a big advantage. They may provide a transition to producing cars with more aluminum parts."
Source: Issam Mudawar, (765) 494-5705; home, (765) 447-5278; Internet, mudawar@ecn.purdue.edu
Writer: Amanda Siegfried, (765) 494-4709; home, (765) 497-1245; Internet, amanda_siegfried@purdue.edu
NOTE TO JOURNALISTS: Color photo of Issam Mudawar in the lab is available from Purdue News Service, (765) 494-2096.
