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This article was first published in 2008.
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This
material first appeared in the I-CAR Advantage Online, which is published and
distributed free of charge. I-CAR, the Inter-Industry Conference on Auto
Collision Repair, is a not-for-profit international training organization that
researches and develops quality technical education programs related to
collision repair. To learn more about I-CAR, and to subscribe to the free
publication, visit I-CAR
Advantage Online.
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Several vehicle makers use aluminium. Many use
aluminium for various exterior body panels, while on some vehicles, others use
aluminium for the entire structure. Recently, new vehicles with more of a
performance-based attitude have been introduced with aluminium used for the
structure. Let’s look at the reasons why aluminium is used for designing these
vehicles and at some of the vehicles.
There are several reasons vehicle makers use
aluminium. Some of the more common reasons are that aluminium:
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is lightweight. Lighter weight material can help
contribute to quicker vehicle acceleration and shorter stopping distances.
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has excellent corrosion resistance.
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is almost 100% recyclable.
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can be formed multiple ways for part construction.
Aluminium also has excellent strength for being a
lighter weight metal. Part of the strength bonus of aluminium is that it has
high torsional rigidity, or more resistance to twisting. This quality is even
further enhanced in a multi-celled aluminium extrusion. A multi-celled extrusion
with inner reinforcements designed into the part greatly increases the strength
and rigidity. This can contribute to better cornering stability and better
wheel-to-road power distribution.
One of the main reasons for using aluminium in
performance vehicles is safety. Performance vehicles are designed to perform at
higher rates of speed, which may lead to more severe damage to the vehicle in
the event of a collision. Aluminium is very predictable in the way it reacts to
collision forces. Vehicle designers can use this predictability for designing
vehicles that absorb collision energy and transfer collision energy around and
away from the vehicle occupants. Certain vehicle parts, such as front crush
tubes or single-cell, extruded lower rails are designed to compress and absorb
collision energy, while larger, multi-celled extruded inner rockers will
transfer collision energy around the occupants.
There is one common thread with these types of
designs. Parts that are damaged from a collision are often replaced to restore
the structural integrity and safety of these vehicles.
2008 Audi R8
Audi released the new R8 with a space frame
structure built of 69% extruded aluminium. Some of these extrusions are
multi-celled, including a five-celled inner rocker and an eight-celled inner
B-pillar (pictured). Different than previous Audi space frame vehicles, the R8
uses only six castings for construction.
To streamline production, parts that would
typically be made of cast aluminium are made from extruded 6000 series
aluminium.
The R8 has a 4.2 litre V8 engine, capable of
producing 420 horsepower. The R8 engine uses a dry sump oil system with an
external oil tank, similar to conventional race car applications, that holds 15
quarts of engine oil.
The R8 structure is primarily GMA (MIG) welded
together, but does use some rivet-bonding and threaded fasteners for joining.
Audi has complete front and rear structural assemblies available for collision
damage repairs. When replacing damaged structural parts, the factory joining
method is typically duplicated. Welded sectioning is only allowed in a few
areas, such as the outer A-pillar, the outer rocker panel, and select extruded
parts pointed out in the body repair manual. All sectioning joints are made
using inserts. All welding is done using GMA (MIG) welding using pulsed-spray
arc transfer.
Also noteworthy, Audi uses an aluminium/steel
hybrid structure for the 2007- current TT coupe and roadster.
2006-Current Jaguar XK
Jaguar Cars released the redesigned XK with a new
aluminium-intensive structure, replacing the outgoing steel unibody design. The
new advanced monocoque construction of the XK consists of twice as many castings
as the Jaguar flagship model, the XJ sedan, and three times the extruded parts.
The use of more castings and extrusions led to building a vehicle with a more
torsionally rigid structure, with fewer parts.
The rocker panels are an open extrusion design,
which makes them a C-channel shape with mating flanges. The XK uses a
combination of 5000 and 6000 series aluminium, similar to the current XJ
design.
The XK has two engine options available, a 4.2
litre V8 capable of 300 horsepower, or a 4.2 litre supercharged V8 capable of
420 horsepower. The XK is also available as a coupe or a convertible body
style.
The XK has a unique structural design, which
mostly uses rivet bonding and threaded fasteners for joining. The front
structure has a bolted-on front crush tube for low speed impacts. If damage
transfers past the front crush tube, the lower front rail is also attached with
bolts near the cowl (pictured).
Other than threaded connections, the XK coupes and
convertible use mostly rivet bonding for part replacement procedures, while
limiting the amount of welding and sectioning. Rivets used for repairs include
self-piercing rivets, blind rivets, and monobolts. Monobolts differ from blind
rivets in that rather than compressing the rivet body down onto the backside
panel, the stem of the monobolt flares the body out, creating a wedge effect.
2006-Current Chevrolet Corvette Z06
The Corvette Z06 uses an aluminium frame that
consists of two 6000 series extruded main side rails, final shaped using a
hydroforming process. The main side rails measure 4 mm thick in most locations.
Extrusions are also used for bumper reinforcements, A-pillars, and the roof
reinforcement bar. Stamped aluminium is used for B-pillar construction, inner
floor, and tunnel construction. Castings are used for front and rear
suspension-mounting locations.
The Z06 comes with a 7.0 litre V8 engine, capable
of producing 505 horsepower. The Z06 also uses a dry sump oil system.
The Z06 aluminium structure is primarily GMA (MIG)
welded. Self-piercing rivets are used for assembling some stamped pieces
together, for example the B-pillar.
The Z06 side frame rails can be sectioned in five
locations.
General Motors recommends that Z06 repairs
involving GMA (MIG) aluminium welding be done using pulsed-spray arc welding
equipment.
Conclusion
While the vehicles mentioned may have differences
in structural design, they all share one common denominator. Using aluminium for
vehicles capable of high performance is intended to maximize vehicle potential,
while also keeping the occupants safe if a collision takes place.
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