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A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 8 1 8 first car launched in 1990, the fenders, hood, trunk lid, and door panels were made of tough yet lightweight compos- ite material. As some had feared, the Lincoln Town Car hood switched to steel for the 1985 model year as a cost saving mea- sure. CAFE-driven weight class issues would see aluminum return for the 1987 model year. One year later, the Town Car hood remained the only aluminum closure panel in U.S. production. OPTIMIZING HOOD DESIGNS At this time, Alcoa decided tomake another attempt to find a solution that could convince Ford to move away from 2036. Ford’s hood designs were tailored to a styling language with roots in the late 1960s, large and relatively flat pan- els with prominent power domes. The outer panel was spot welded to the in- ner on all four sides, on large down- standing flanges in the front and fender sides, and on a pinch flange hidden un- der a molding at the windshield (Fig. 3). Because they avoided hemming, which required a 180° bend, such de- 1988 Pontiac Fiero. GM’s 1983 Fiero launch signaled the company’s move away from aluminum and into composites. signs suited alloys 2036 or 6010. But styling was moving away from the hatch type hood, and the flow-through hood designs that had first appeared on imports were becoming mainstream (Fig. 4). Alcoa set three goals for the new alloy: It had to be more formable than 6009, capable of flat hemming, and provide a yield strength comparable to 6009 after paint bake. The result was a lean 2xxx alloy that was registered as 2008 (see Table 4) in 1987 [6] . However, some at Alcoa felt that the current designs were simply steel designs converted for aluminum. They initiated a clean sheet study to optimize hood designs for aluminum, with two objectives—lowest overall weight and lowest possible cost. Using finite ele- ment analysis, the team settled on a revolutionary design that abandoned the beam network of the contemporary designs. Instead, the new concept fea- tured an outer skin hemmed and adhe- sively bonded over a thin gauge inner membrane that supported the skin with relatively flat cones. Each cone was topped with a mastic drop. Once cured, such assemblies exhibited exception- al torsional stiffness and good bending performance. The concept was part of the 2008 selling package. TABLE 4 — 2008-T4 AND 2010-T4 DEVELOPMENT Alloy Year Producer Si Fe Cu Mn Mg Cr 2036 1970 RMC 0.50 0.50 2.2 - 3.0 0.10 - 0.40 0.30 - 0.6 0.10 2038 1980 RMC 0.50 - 1.3 0.6 0.8 - 1.8 0.10 - 0.40 0.40 - 1.0 0.20 2008 1987 Alcoa 0.50 - 0.8 0.40 0.7 - 1.1 0.30 0.25 - 0.50 0.10 2010 1990 RMC 0.50 0.50 0.7 - 1.3 0.10 - 0.40 0.40 - 1.0 0.15 6009 1976 Alcoa 0.6 - 1.0 0.50 0.15 - 0.6 0.20 - 0.8 0.45 - 0.8 0.10 6010 1976 Alcoa 0.8 - 1.2 0.50 0.15 - 0.6 0.20 - 0.8 0.60 - 1.0 0.10 6111 1982 Alcan 0.6 - 1.1 0.40 0.50 - 0.9 0.10 - 0.45 0.50 - 1.0 0.10 Fig. 3 — 1987 Lincoln Town Car hood with downstanding flanges at front and fender lines. Fig. 4 — From left, hatch vs. flow-through style hoods.