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November 3rd, 2011

‘Pin art’ gadgetry used to make curvy glass sheets

Published on November 3rd, 2011 | By: Eileen De Guire

Flat windows chop up the smooth contours of this Gehry-designed health center. Scientists at the Fraunhofer Institute in Germany have developed an economical process for bending large sheets of glass. Credit: Wikipedia.

The southern elevation of architect Frank Gehry’s design for the Lou Ruvo Center for Brain Health in Las Vegas, Nev., rises and swells in waves of steel and glass crashing over each other as if caught in a confluence of currents going in opposite directions. However, the building’s windows break up the smooth motion of the waves—some are carved out of the curves, some look as if they are tentatively balanced on top of the wave. The viewer’s eye wants the windows assume the contour of the building like a leaf would on a wave.

However, curved glass panels are expensive to manufacture, and even more so when each one is different. The process involves making a mold of the shape, laying a sheet of glass on top of it, loading the mold-glass rig into a furnace and heating it to a temperature where viscous flow of the glass allows it to slump and conform to the mold’s contour. The piece must be closely monitored—remove the glass too soon, and you don’t have the right shape; wait too long, and you get pressure marks at the support points.

Fraunhofer Institute researchers inspect a curved glass panel in fron of the test furnace. Credit: Fraunhofer IWM

Fraunhofer Institute researchers inspect a curved glass panel in front of the test furnace. Credit: Fraunhofer IWM.

Researchers at the Fraunhofer Institute for Mechanics of Materials IWM in Germany have found a way to economically produce bent glass pieces by getting rid of the mold itself. In a press release, scientist Tobias Rist says, “It’s no longer necessary to produce a special steel mold.”

Instead of forcing a sheet to conform down onto a mold, they have found a way to have the form fall away from the sheet so that only the necessary parts of the glass sink into it. The process uses an array of pins or rods, similar to the “pin art” gadgets that make impressions of things pressed into them, like hands, faces, etc. A sheet of glass is slid onto the flat array and rolled into an already hot furnace. The array is programmed to assume the desired geometry after the assembly is in the furnace.

In the press release, Rist says, “Our process is roughly six-times faster than the conventional process, as well as being considerably more energy-efficient and cost-effective.”

Energy is saved because the furnace is held at temperatures slightly below that at which the glass becomes viscous. The additional heat needed to cause viscous flow is applied only to the spots that need to deform. Time and more energy are saved because the furnace can be kept hot between pieces, and additional cost is saved by eliminating job-specific mold forms.

The new approach allows for more precise control of the process. Rist says, “While the conventional process relies a great deal on trial and error, we simulate the process and the material behavior on a computer. We then compare the outcome with the results from physical tests so we can identify and implement the most favorable process conditions.”

The Fraunhofer team has demonstrated the process on sheets of glass measuring approximately one meter square. Those sizes are big enough for a guy like Gehry to work with.


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