Switching to aluminum, magnesium, or composites can slash weight, but automakers must assess manufacturing risks. After having built steel parts for decades, each time automakers decide to use any new material, they face uncertainties like these: Does the material have the necessary dimensional integrity? Can it be machined satisfactorily? Will it shorten tool life? Are process cycle times fast enough? Can the extra costs be justified? With a raw material cost of less than 40 cents a pound and a long list of proven attributes, steel is ideal for most situations. Automakers need compelling reasons not to choose it. Aluminum has, apart from weight, another advantage over steel - significantly extended tool life. Aluminum's primary manufacturing weakness is that it is slightly trickier to cast. But after more than 8 years of experience with lost-foam casting, Saturn manufacturing engineers of Saturn, Springhill, TN, say the problems are negligible. With densities just 66 % that of aluminum and 22 % that of steel, magnesium alloys offer a potential for weight reduction matched by few other materials. But its price is, on a weight basis, about twice as much as aluminum and, on a volume basis, about 30 % higher than that of aluminum. Automakers are looking at a process called thixo-molding that would help eliminate much of the machining now required by magnesium components. Engineers of the Northwest Alliance for Transportation Technology (NATT), Richland, WA, are testing aluminum metal matrix composites (MMCs) in automotive applications. Like magnesium, aluminum MMCs provide light weight at high cost; researchers hope to lower the price to 1 dollar per pound. MMCs are, however, difficult to machine. Nevertheless, steel surges back into contention. A steel body-in-white has been developed (in a project which cost 22 million dollars and spanned four years) that weighed 36 % less than a conventional steel auto body. Several key technologies were used, among them hydroforming and the use of tailored blanks. In the end, the move to alternatives to steel such as aluminum, magnesium, and MMCs boils down to an issue of risk management.
Steel still rules automobile manufacturing
Manufacturing Engineering ; 120 , 6 ; 42-49
1998
6 Seiten, 2 Bilder
Article (Journal)
English
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