Automotive
Rover and Land Rover were among the first users of aluminium in Europe, the
ubiquitous Defender models using the 3xxx series alloys for flatter panels with the
Al–Mg 5xxx series being used in other applications, a wealth of experience being
gained in pressing, assembly and paint pre-treatment and finishing. Although the
chassis was cumbersome it was – and still is – ideal for mounting the extensive range
of Land Rover Defender body variants. Until this day the hot rolled grades of steel
are used (typically HR 4) but it is easy to see why efforts are being made to downscale
these relatively massive ladder frames with consideration being given to using newer
material in thinner gauges, e.g. high strength steels up to 300 N/mm2 (TRIP steels up
to 590 N/mm2 are now being used for 80 chassis parts on the Mitsubishi Paquera).
Design modifications must be made to accommodate the thinner gauges and
consideration has already been given to alternative material forms such as hydroformed
sections (described later), as referenced by the ULSAB process, which could be used
to bolster stiffness and crashworthiness. Although better suited to more conventional
car body design, the incorporation of tailored blanks again offers an alternative
approach giving the engineer strengthening exactly where required and a further
opportunity for parts consolidation/reduced weight. This enduring type of rugged
and versatile design has persisted as it answers the diverse needs of military purchasers
but it is not surprising that as fleet average economy targets are considered more
critically the monocoque is now becoming more stringent for the more volumeoriented
4 × 4 vehicles – as featured by the Land Rover Freelander. Durability is
satisfied by the use of hot-dip or iron–zinc alloy coating as steel substrates replace
the use of expensive aluminium for outer panels (see Chapter 7) and the model
features another material innovation in the selection of polymer front wings.
Before leaving body-on-chassis design it should be mentioned that other types of
chassis include the steel backbone type used by Lotus and the designs featuring
triangular sectional arrays as shown in Fig. 2.4. These were steel square or tubular
sections, and later Lotus adopted another chassis configuration termed the ‘punt’,
also shown.
Materials for Automobile Bodies
Geoff Davies F.I.M., M.Sc. (Oxon)
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