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by Janice Hamilton
Many people are able to satisfy their desire to grow things by digging in their gardens -- not Mechanical Engineering Professor Joseph Pegna. He is researching ways of growing man-made structures that could range from parts for tiny micro-mechanical devices to blocks of concrete and satellite parts.
He is fascinated by the way nature manufactures structures like shells, as opposed to the way we do it.
"For eons, people have made things by taking a piece of material and carving it out," he said in an interview. "We don't have the technology to make a hand, for example, with its integrated muscles, nerves and bones. The only way we could achieve this type of integration would be if we could deposit the material within a structure exactly where we need it."
For about 10 years now, researchers have been working on techniques to make simple devices by doing just that: depositing material wherever it is needed. Pegna, with the help of a group of undergraduate students here, has come up with an innovative approach that borrows on the ancient and low-tech art of sand painting.
Pegna started his career studying robotics in his native France, and worked there as a research engineer before doing a PhD at Stanford University. He taught at the Rensselaer Polytechnic Institute in Troy, N.Y., where he won a curriculum innovation award, and moved to Concordia in 1997.
He explained that there are a number of ways of depositing material. One of the first successful approaches was to build a cross-section of an object by scanning a laser across a light-sensitive liquid, turning it into a solid wherever it is exposed. Another approach is to start with a powdered material that melts and hardens when the laser scans across it. The object is built up in layers this way. A third process uses an ink-jet printer to glue powders together. However, a common drawback of all these techniques is that they are quite slow, and can only be used to make small objects, since the material has to be deposited one thin layer at a time.
Pegna has been exploring several other approaches. In 1995, he used sand, powdered cement mix and high-pressure steam to make a convoluted cement object big enough to be exposed to some stresses and strains. When he tested it, he discovered this cement has unique strength properties.
His latest research focuses on another method of depositing powders to form patterns. He and his students were inspired by the sand painting practised by Navaho Indians and Tibetan monks. They use coloured sand to make intricate patterns, controlling the flow with little hoppers.
Pegna experimented with hoppers but modified them to use vibration to control the flow of material coming out the nozzle. "We scavenged all over the place to find an old computer and build an apparatus that shakes the powder into place, and then we measured the powder flow," Pegna said, noting that flow is an extremely complex phenomenon. He is currently seeking a patent for this device, and is discussing ways of commercializing it.
Another project close to his heart, but on the back burner until he can get the $25,000 he needs to put together his lab equipment, involves gases and lasers to grow structures shaped like braided rods. This technique can be used with materials like carbon that can exist both as gaseous compounds and as solids.
Pegna has also had success depositing iron on a nickel base. Although the material is deposited almost atom-by-atom, Pegna has found the process is so speedy that it could be used to grow large objects, and could be ideal for building structures in space. Pegna has been working on this research during the summer at the Institute for Micromanufacturing in Louisiana, but hopes to get a lab going here also.
Professor Joseph Pegna (far right) and two doctoral students, Myriam Terrier and Yann Quinsat, flow-test a nozzle.
