Apr. 9, 2001 John DuPont, assistant professor of materials science and engineering at Lehigh University, remembers Star Trek programs in which objects materialized at the push of a button. Fantasy? Maybe not any more. DuPont is studying ways that complex metal objects and parts are made to materialize almost by the flick of a switch. It's not as simple a process as that portrayed in Star Trek, but there are similarities.
DuPont's project is called LENS, for Laser Engineered Net Shaping, in which the computer-aided drawing of an object is transferred from the computer to a specialized laser machine, and the object is constructed from metal powders laid down on a substrate. DuPont has constructed simple prototypes with the LENS process to demonstrate its effectiveness.
The heart of the process is the laser machine that has four nozzles positioned around a laser beam. The beam melts the surface of the substrate and the nozzles deposit powdered metallic material that goes down layer by layer into a molten "liquid." As the material solidifies the object slowly takes shape. The laser remains stationary while the substrate turns on a special table.
The process has tremendous advantages because the object can be made from just about any kind of metallic powder and its composition and properties can be changed subtly or drastically, as needed, during fabrication. The process also allows for the creation of objects in nearly unlimited shapes. The laser simply follows the directions of the computer.
DuPont says LENS will fill a substantial niche in the manufacturing sector and can be used to create a vast number of products. He cites, for example, the production of prototype dies, or molds, used in the manufacture of plastics. With current technology, a prototype die is machined and welded in a multi-step process. It must then be ground and polished and dipped in special anti-corrosive coatings. The entire process can take up to six months and cost hundreds of thousands of dollars.
With the LENS process, however, the die is made in one step and the laser has the capacity to create "nearly all possible shapes," DuPont says. And because LENS can deposit different metals, the coating is laid down as the object is fabricated.
Also, DuPont notes, dies used in the fabrication of plastic objects come with drilled channels through which water passes to cool the mold during the manufacturing process. But the machining process allows only for straight channels. Yet curved channels of many shapes and sizes are desired because they provide more surface area in which to dissipate heat. LENS allows intricately curved channels to be fabricated while an object is being made.
The Lehigh professor says products made with LENS would be relatively small - no more than three feet by three feet - and the process is useful primarily for limited production runs of high-performance parts. But this still encompasses a vast number of products.
Restoration of a jet engine is another application. The tips of the blades wear as they rub against a shroud and eventually must be repaired. Currently, tips are restored by conventional welding and then machined back into shape. With LENS, the restoration would be completed in one process and the amount of machining would be greatly reduced.
### Dupont is collaborating on LENS with scientists at Sandia National Laboratory in New Mexico, who developed the LENS machine. His work focuses on improving the layering process. "We're trying to perfect the process by developing models and parameters that instruct people how to select materials so they can go from one material to another. If you go too sharply from one to the other you build up the stresses. You want to go gradually and we have to come up with ways to make the process work. We're trying now to get the exact mix of metals on the right spot," DuPont says.
Dupont's research is supported by two National Science Foundation awards totaling $860,000. He was recently selected as one of 20 young scientists and engineers for a 2000 Presidential Early Career Award for Scientists and Engineers by former President Clinton.
A graduate of Ohio State University who received his Ph.D. in materials science and engineering from Lehigh, DuPont collaborates on LENS with Herman Nied, professor of mechanical engineering and mechanics, and Scott Hummel, who earned his Ph.D. in mechanical engineering in 1998 from Lehigh and is now an assistant professor of mechanical engineering at Lafayette College.
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