While many supercar enthusiasts have “gone ape” over the Ford 2017 GT, the program development engineers have done the same for a new lightweight glazing solution.
Called “Gorilla Glass,” the three-layer laminate is claimed by its supplier, Corning Inc., to deliver more than five times the strength, pound for pound, of conventional automotive glass while offering significant mass reduction. In the case of the GT, more than 12 lb (5.4 kg) was saved by using Gorilla Glass in three areas: the windshield (first use for a production vehicle), the rear window, and in an acoustic separator in the rear bulkhead. It also helped reduce the car's center of gravity by 3 mm (0.12 in).
Ford engineers are delighted with the performance of the new glass and are looking to increase its vehicle applications beyond the GT.
Introduced in 2007 as a thin, durable screen material for smartphones and tablets, Gorilla Glass is currently used on 4.5 billion mobile devices from a variety of global consumer-electronics brands. Since then Corning has been developing an automotive-grade variant that is produced using a twist on the ion-exchange process used in alumina silica glass manufacturing. PGW (Pittsburgh Glass Works) also played a role in the material's development.
Ford's Fusion MMLV (Multi-Material Lightweight Vehicle) concept car debuted Gorilla Glass in 2014 in its windshield and side windows, delivering a 30% reduction in glazing weight, the companies claim.
The GT windshield is a tri-layer laminate comprised of a 0.7-mm (0.028-in) -thick inner layer of Gorilla Glass for Automotive, a 2.1-mm (0.08-in) outside layer of annealed soda-lime glass, and a 0.76-mm (0.03-in) resin foil interlayer. The Corning product enables the glass layers to be up to 50% thinner than conventional vehicle glass.
Work for the supercar application began in late 2014. “It was an accelerated development program,” observed Paul Linden, Ford's Advanced Mechanisms Body Exterior Lead. “We completed all our application testing in four months. The AR (application readiness) approval process typically takes us up to two years. My boss Ali Jamul put the team together and gave us the budget to build and test the vehicles. We went into this thinking it was a win-win, which it is, so we pulled out all the stops.”
As the GT program itself was also on a fast track, Jamul's team completed its testing regime, including overlap, back-to-back, and rollover, on the vehicle's critical path.
The new lightweight glazing technology offers opportunities across Ford's global vehicle line, noted Hau Thai-Tang, Ford's Group Vice President, Global Purchasing. He said a typical passenger vehicle has about 50 ft2 (4.6 m2)-about 80 lb (36 kg)-of glass. A Ford Explorer with sunroof is laden with about 200 lb (91 kg), so a significant reduction in glazing-system mass has a “cascade” effect on surrounding body structure, such as A-pillar cross section, windshield headers, and the upper cowl.
“The big thing for us in designing bodies is looking at not only static stiffness but also dynamic stiffness,” explained Thai-Tang, a veteran vehicle engineer and accomplished race-car driver. “Dynamic stiffness is the square root of k/m, so the lighter you can make the body-in-white system for the same equivalent torsional stiffness, the more you can drive up the dynamic stiffness. And that's where we're seeing the improvements with this glass technology.”
He said that in the GT application, the advantage of Gorilla Glass comes from more than the stiffer material. “It's also a function of the windshield or window's shape; the GT's windshield has a lot of curvature,” he told Automotive Engineering. “That was part of the answer to the different thicknesses of the laminate. We have some built-in tension in the glass system that adds the stiffness. But the main thing is we're driving the mass down so the dynamic stiffness, the ‘k’ factor, increases.”
Panoramic sunroofs, which place significant glass mass far above a vehicle's center of gravity, “are a huge potential application for this technology,” Thai-Tang said. “It's clearly a big area we're looking at.”
Gorilla Glass for Automotive also provides optical advantages compared with conventional float glass. It has no optical draw lines, making it ideal for extremely “fast” (low angle) windshield applications as in the GT.
“A lot of times we can't execute what our designers want because of the glass distortion,” noted Thai-Tang. “Distortion is also a factor when you introduce HUDs [head-up displays], LiDARs, and radars. As we bring in more autonomous driving technologies, you can imagine a day where we project images and information onto the glass. In an autonomous vehicle the elimination of optical distortion becomes an important factor.”
The GT racecars being prepared by Ford and Multimatic will use Gorilla Glass in the 24 Hours of LeMans in June, he confirmed. While the car's headlamp lens covers will remain polycarbonate initially, Ford engineers are looking at other applications including the interior.
“Instead of just having an information screen you can have a full center console that is a Gorilla Glass surface,” he asserted. “All the things being done in the consumer-electronics space for tablets and phones is applicable in vehicles. We want to pair the Corning technology with not only the exterior guys but also the interior designers. But you won't see us use Gorilla Glass on a refresh-the thinner glass will drive new door and body structures.”
The new exterior-glazing system requires no change to the vehicle assembly process; the Gorilla Glass components are installed using conventional robotics and urethane-bonding system. Corning produces the glass at its Harrodsburg, KY, plant.