Page 621 - Automotive Engineering Powertrain Chassis System and Vehicle Body

18.2 Chapter 18.2

Materials for consideration

and use in automotive body

structures

Geoffrey Davies

understanding of materials parameters is required if this
OBJECTIVE
enhanced range of properties is to be exploited to the
To review the choice of materials suitable for body maximum advantage. The situation has advanced signif-
manufacture and provide an understanding of salient icantly from the days when ‘mild steel sheet’ was the
manufacturing processes, product parameters and asso- universal answer to most body parts applications.
ciated terminology. This is essential if the limitations of As apparent from the ‘Introduction’ any distinction be-
specific materials are to be appreciated and advantages/ tween grades was then generally made on the basis of
disadvantages of competing materials are to be compared formability and in the case of the few aluminium speci-
prior to the design selection stage. fications, differentiation was by temper (O ¼ annealed,
H ¼ hard, etc.).
The metallurgy of both steel and aluminium alloys
CONTENT
has now advanced significantly offering a wide choice
The range of materials that can be realistically considered of mechanical and physical properties together with
for body structures is reviewed – the critical need for other attributes. The metallics choice can now be
consistency of properties and effect on productivity is widened and it is also necessary to consider plastics,
emphasized, together with the associated advantages of where 20 different types can be used within the motor
continuous production methods – key stages of both steel vehicle. The traditional requirements of the body en-
and aluminium manufacture are described – the signifi- gineer have always been strength, in both static and
cance of the final skin pass is explained and methods used dynamic terms, and elastic modulus, which governs
to vary the texture of work rolls and strip surface are stiffness/rigidity and imparts stability of shape. To
described – types and strengthening mechanisms of high these can now be added drawability and work-
strength steel (HSS) grades in yield stress range 180– hardening parameters which are important with re-
1200 MPa are graphically described and an introduction spect to forming and stretching, respectively, the latter
provided to the relevant polymer types and mode of also having an important effect on energy absorption
manufacture. and impact resistance.
A number of surface parameters are now held to have
considerable tribological (frictional) as well as cosmetic
18.2.1 Introduction significance. Whereas the main requirement could be
specified in terms of surface roughness, R a , a range of
The main materials used in body construction are evident ‘deterministic’ (pre-etched) rather than ‘stochastic’
from Chapter 18.1, and, as indicated, early choices were (random, shot-blasted) finishes are now options. With
governed by the increasing needs of mass production and the advent of CAD systems the design engineer can no
later, during post-war years, availability, as suppliers longer rely on experience from previous models, or on
struggled to resume production. It will also be obvious a dedicated materials engineer for his materials choice.
that nowadays the choice has broadened considerably as Instead he is often confronted with a series of prede-
materials technology has responded to the needs of the termined choices, from which he must make his selec-
automotive engineer and that a far more enlightened tion. For the correct choice at the engineering stage
Materials for Automobile Bodies; ISBN: 9780750656924
Copyright Ó 2003 Elsevier Ltd; All rights of reproduction, in any form, reserved.