Page 376 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

356 Chapter 14 Metal-Forging Processes and Equipment

CASE STUDY l4.2 Suspension Components for the Lotus Elise Automobile

The automotive industry increasingly has been Lotus group investigated the use of steel forgings
subjected to a demanding set of performance, cost, fuel instead of extruded-aluminum suspension uprights in
efficiency, and environmental regulations. One of the order to reduce cost and improve reliability and
main strategies in improving vehicle design with respect performance. Their development efforts consisted of
to all of these possibly conflicting constraints is to two phases, shown in Fig. 14.20. The first phase
reduce vehicle weight while using advanced materials involved the development of a forged-steel component
and manufacturing processes to preserve performance that can be used on the existing Elise sports car; the
and safety. Previous design optimization has shown second phase involved the production of a suspension
that weight savings of up to 34% can be realized on upright for a new model.
suspension system components-a significant savings, A new design was developed using an iterative
since suspensions make up approximately 12% of a process with advanced software tools to reduce the
car’s mass. These weight savings could be achieved number of components and to determine the optimum
largely by developing optimum designs, utilizing geometry. The material selected for the upright was an
advanced analytical tools, and using net-shape or air~cooled forged steel, which gives uniform grain size
near-net-shape steel forgings instead of cast-iron and microstructure and uniform high strength without
components. In addition, significant cost savings have the need for heat treatment. These materials also have
been demonstrated in many parts when optimized steel approximately 20% higher fatigue strengths than
forgings are used, as opposed to aluminum castings and traditional carbon steels, such as AISI 1548-HT, which
extrusions. is used for similar applications.
The Lotus Elise is a high-performance sports car The revised designs are summarized in
designed for superior ride and superior handling. The Table 14.5. As can be seen, the optimized new forging

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FIGURE l4.2G (a) The Lotus Elise Series 2 automobile. (b) illustration of the original design for the vertical suspension
uprights, using an aluminum extrusion. (c) retrofit design, using a steel forging. (d) optimized steel forging design for new
car models. Source: (a) Courtesy of Fox Valley Motorcars. (b) through (d) Courtesy of Lotus Engineering and the
American Iron and Steel Institute.