September 2007 Mechanical Engineering Departments: Tech Focus, Pt. 2

This section was written by Associate Editor Alan S. Brown.

Technology Focus part 2:
Materials and Assembly

Stiffer Than Diamond
by Jeffrey Winters

Tin is a fairly malleable substance—the tinsmiths of old used to hammer sheets of the metal into household objects. Barium titanate is crystal that is only half as stiff as steel, used mainly as a piezoelectric element in microphones. One wouldn't expect much in the way of stiffness out of a combination of the two of them together.

"If you mix sugar and coffee, it will never be sweeter than pure sugar and it will never be more bitter than coffee," said Roderic Lakes, professor of engineering physics at the University of Wisconsin in Madison.

That's what renders Lakes's recent work so unusual. He and his colleagues found a way to turn a composite of barium titanate and tin into the stiffest known material, stiffer even than diamonds.

Lakes and his colleagues have been looking at composites for decades, with an eye toward creating new materials that have unique physical properties. One material they studied, microscale tubes that are buckled or kinked, has an extraordinarily high level of mechanical damping.

Barium titanate was recognized for its strange ability to contract as it changes from one solid phase to another. Lakes wanted to see what would happen if tiny crystals of barium titanate were embedded in another material in a way that impeded its ability to change phase. If the properties were set against one another in just the right way, he thought, the new material could resist the change with an incredible amount of force.

Dust-size flakes of the crystal were mixed in molten tin. When the composite cooled, small cantilevers were cut out and subjected to a bend- ing force.

The results were striking. The stiffness of the material changed with temperature. At approximately 55°C, the material began to stiffen and between 57° and 59°C, the composite became almost 10 times as rigid as diamond.

Lakes, for one, doesn't know yet what one could do with this type of material. "This is opening the door to new developments," Lakes said, "but it's a long way from practical applications."

One possible application is to create a composite that exhibits this sort of stiffness at room temperature. No matter how exotic barium titanate may sound, it is less expensive than diamonds.

Some day, then, a superstiff compound might be available for applications such as cases for computer hard drives or even golf clubs.

Going Up
by Alan S. Brown

Walk into most factories and look up. You're likely to see lots of unused space. Now, a new wave of vertical automated storage and retrieval systems is using that space to improve worker productivity.

The concept is simple. Instead of sending workers running down aisles of racks for parts and components, facilities store everything vertically in a compact location. This improves producti-vity by bringing a broad range of parts to workers right where they stand. It also saves capital in facilities approaching capacity, since they can boost storage capacity without having to knock down walls for expansion.

The first vertical storage units were vertical carousels. They work in a fashion similar to the horizontal carousels that hold clothing at a dry cleaner. Workers punch in a code and the carousel rotates until the part comes up.

Vertical lift modules store racks of parts vertically, using an elevator-like shuttle to bring trays to assemblers working nearby.

Vertical lift modules go one giant step further. They consist of two parallel columns of shelves that are separated by an empty shaft that contains an elevator-like shuttle. When a worker punches in the code or scans a bar code, the automated picking device moves up to the shelf, pulls the tray or tote bin, and shuttles it down to the picking location.

"They're not terribly expensive," said Dick Ward, vice president of the Material Handling Industry of America, a trade association. He said common applications range from machine shops that use a wide variety of tools to assembly facilities that require many different parts and components.

Vertical lift modules have grown increasingly sophisticated. Some systems optimize tray and tote locations to maximize storage space. Many feature vertical shuttle speeds of several feet per second, while others enable users to reduce elevator speeds for fragile items. At least one company offers rack-and-pinion drive for improved precision, while several other companies specialize in systems for such heavy parts as dies and molds.

The Material Handling Industry of America has collected a number of case studies that attempt to quantify productivity improvements. They are on the organization's Web site at www.mhia.org.