Compacted graphite iron (CGI) has moved out of the laboratory and the academic community and is set to become an increasingly important material for powertrain engineers. Today, the world's top seven vehicle manufacturers are actively pursuing CGI: General Motors, Toyota, Ford, Volkswagen, DaimlerChrysler, PSA-Peugeot Citroen and Hyundai. Unlike some other materials, motor sport has not spearheaded commercial applications - only recently have CGI cylinder blocks penetrated the North American racing engines of GM, Toyota and DaimlerChrysler. CGI is a particular grade of cast iron that offers three main mechanical benefits: 75 per cent higher strength, 45 per cent higher stiffness and 100 per cent higher fatigue life. By using CGI, engine makers can make diesels more compact for the same power, or extract more power for a given envelope. The higher strength of CGI helps engineers meet the increasingly higher peak cylinder pressures necessary for future emissions legislation. On the downside, CGI is more expensive to produce, and it is tough and difficult to machine with lower cutting speeds and shorter tool life - typically 70 per cent of grey iron tool life. The feature that gives CGI its strength is its worm-shaped or vermicular microstructure. It is this coral-like structure that inhibits cracks and leads to superior mechanical properties. However, CGI also includes spheroidal graphite particles, which, while increasing strength and stiffness do so at the expense of castability, machinability and thermal conductivity. To produce CGI therefore is a delicate process, requiring precise control of elements such as magnesium and titanium - titanium aids process stability but makes machining even more difficult.
Iron's in the fire.
Eisen im Feuer
Automotive Engineer ; Mar. ; 31-32
2006
2 Seiten, 1 Bild
Article (Journal)
English
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