| According to Alcan Automotive, the increased
use of aluminium is now a significant part of every carmaker’s lightweight
design strategy. With its high specific strength, wide range of forming
options and unique design advantages, aluminium is playing an essential
role in car construction.
Bumper beam on the Mercedes-Benz
SL – the bumper’s crash optimised design effectively
protects the vehicle against damage during low-speed front
and rear end collisions, thus resulting in lower repair costs
and less time in the repair shop |
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In 2000, aluminium passed plastics in terms of content per vehicle to
become the third most used material in cars and it remains the fastest
growing materials in cars today. Aluminium shipments to car and light
truck markets in North America totalled 2.43 million tonnes in 2002, a
10 per cent increase over 2001. In 2003, aluminium content per vehicle
was an estimated 128 kg which Alcan forecasts will rise to 159 kg by 2010.
European carmakers used more than 1.9 million tonnes of aluminium in 2003
with around 1,000,000 tonnes being used in powertrain applications, 560,000
tonnes in chassis and suspension applications and 370,000 tonnes in body
applications according to a study by Knibb, Gormezano and Partners.
According to a study conducted by the European Aluminium Association (EAA),
the total aluminium content on a typical compact car could increase to
367 kg in the next five to 10 years, reducing the overall weight of the
vehicle by 445 kg and cutting CO2 emissions by around 31 per cent.
Carmakers are adopting different approaches to the use of aluminium for
competitive design and production reasons, as well as to shave weight.
Lightweight aluminium panels provide the ability to optimise the panels
to individual application and production strategies including the development
of advanced alloys.
Mercedes-Benz, for example, employs three distinct aluminium alloys for
the bonnet, wings and liftgate of the current E-Class. The first is designed
for excellent formability, the second for high flangeability while the
third is designed to meet recycling requirements and is used for interior
parts. To meet these three separate demands, Alcan is developing an alloy
that will cover a broad range of applications that it expects to bring
to volume production next year.
Enhancing safety with lightweight structural solutions
Side-impact beams, bumper beams and crash boxes play a key role in safety
concepts for contemporary passenger vehicles because they are the components
that usually take the first hit in a traffic accident. Alcan has developed
advanced design extruded aluminium components that initially behave more
rigidly than steel, but later converts more energy through deformation.
Aluminium side-impact beams not only exhibit better crash behaviour than
shaped-steel beams, they are also lighter and resistant to corrosion.
Aluminium instrument panel
support for various VW models – a multi-material solution
combining aluminium sheet, extrusions, castings and forgings.
The central beam consists of two deep-drawn sheet metal shells
that are electron-beam welded along their length |
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Today’s aluminium bumper systems typically consist of a curved
aluminium crossmember – ideally a hollow, multi-chambered section
– with a frontal foam block. In some cases, aluminium or steel crash
boxes, which are mounted on longitudinal members, can be attached. In
a collision, the foam block initially absorbs the energy of the impact
in line with pedestrian protection requirements. Then, the bumper beam
undergoes elastic deformation. On further intrusion of the barrier, the
curved beam first straightens out and then the hollow chambers of the
extruded section deform. Only then does the crash box begin to buckle,
absorbing the kinetic energy through controlled deformation. The design
and configuration of these elements ensure that the kinetic energy of
an impact under 15 km/h (10 mph) is fully channelled into a controlled
process of deformation, preventing any damage to the longitudinal member.
At the rear of the vehicle, the system may be used without the use of
crash boxes as less energy has to be absorbed. The curved multi-chambered
extruded bumper can be attached directly to the longitudinal members.
Because it is a crash-relevant body component, the instrument panel support
must meet stringent requirements. It is not only the ‘backbone’
of the entire cockpit module, it also is becoming an increasingly important
factor in vehicle safety.
The instrument panel crossmember reinforces the vehicle in the transverse
direction, absorbs the impact forces of airbags in the event of a frontal
collision, and prevents upward movement of the steering wheel. To fulfil
these requirements, a corresponding materials concept is needed. Aluminium’s
specific properties make it particularly suitable for this purpose. Relative
to its weight, the static and dynamic stiffness of the aluminium design
is higher than that of comparable steel solutions. This has a positive
effect on crash behaviour.
Steadily rising production numbers confirm the attractiveness of the Alcan
solution, claims the company. Over one million instrument panel supports
are produced each year for Volkswagen’s small platform alone. A
lightweight aluminium and magnesium component has also been developed
for the Mercedes-Benz A-Class, consisting of a multi-chambered section
that exhibits the same level of stiffness as tubular steel while taking
up only slightly more space. It serves as the structural member for the
whole construction and guarantees optimum transverse reinforcement of
the vehicle body above the knee area.
Aluminium side-impact beams, bumper systems and instrument panel supports
permit lighter automotive solutions than steel, but also contribute to
an increase in passenger safety and a reduction in vehicle operating costs.
Alcan’s Gottmadingen plant in Germany produces all three of these
structural products, supplying the automotive industry with around 20,000
tonnes of aluminium components. On the assumption that these aluminium
systems are 20 per cent lighter than conventional material, this provides
a weight reduction of some 3,750 tones. Based on an annual 15,000 km of
travel, this alone provides fuel savings of more than 2.5 million litres
a year.
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