PLASTICS, FROM PLAIN,
TO BEAUTIFUL AND FUNCTIONAL, WORLDWIDE, RAPRA, BERLIN 2005
The Art of Plastics Design
Conference 18th -19th October 2005, Berlin, Germany
The strange story of car bodies
There still is a long way to go in many industries, to make plastics
recognized and appreciated as such. The story of car bodies is quite
significant in this respect.
Whole plastic car bodies have been talked about for many years,
without any mass volume production so far, except for an increasing
number of parts. Yet no mass produced car has yet been marketed
that features an all-plastic body.
There are paradoxes. For instance, steel is painted so that it
will not rust, whilst plastics and composites, that do not alter,
are painted so that they will look like painted steel.
Car salesmen prefer not to mention plastics in car bodies, fenders,
front modules, instead of stressing the intrinsic properties of
plastics, or personalizing their look as such. It is a long way
before man-made materials that are more expensive than steel in
a price/weight ratio, that require a longer converting process than
metal stamping, can be substituted to metal, just for being lighter,
when cost is the only rule for material selection.
The main processing costs are in surface finishing, painting, metallizing
that may double the basic cost. Whilst plastics can be bulk colored,
with many effects, little has been explored in this approach for
The second converting processes, such as welding, machining, assembling,
also are an important cost, that plastics molding and function integration
More than 30 years ago, the consensus was that no car could be
sold without a chrome plated bumper. This plating amounted to 70
% of the total bumper cost. Then, Renault launched a composite bumper
that pioneered the success of plastics in bumpers and totally changed
the look of cars ever since. The decision to use the SMC bumper
was made with one voice of majority at Renault. Then the SMC were
replaced by PP and other thermoplastics, but many car manufacturers
continued to paint the plastics, which should not be necessary,
if the design were better thought. As of today, still, the higher
investment cost is not for the stamping presses, but for all the
finishing processes, mainly cataphoresis.
In order for plastics to be selected for car bodies, the key would
be to do without the Class A bright finish for cars, that practically
doubles the cost, whether the part is molded or stamped. There are
two solutions on which to work with clever design, to be accepted
and to become trendy:
Accept matte hues, instead of the brightness of Class A finish,
which is not very functional anyway, with poor reflection in the
sun, and lost brilliance after a few months.
Or, better even, design a completely plastics car body, with new,
made attractive, bulk colored polymers. This would be a win-win
route, with investment gain, lighter cars because of plastics instead
of steel, and no need for about 20 kg of paint per car.
Many solutions exist, like the Smart car, where the body parts
are obtained with just one press stroke, of PC/PBT alloy. For larger
cars, a good solution could be long fiber reinforced thermoset composites,
of the SMC type. Thermoplastics will eventually be better, as they
are more easily recycled. For the moment, one of the advantages
of steel in cars is that steel is more easily recycled.
In order to insure rigidity of car bodies of plastics, there are
at least two routes, the assembly of smaller plastic parts of engineering
plastics, tied on a metal structure that bear the load. Or the direct
molding of a whole hull of plastics on a specific press/mold machine,
that insures function integration and eliminates all the second
processing steps. The latter is the only answer to insure a development
in plastics car bodies in the next few years. However, the molding,
by compression/extrusion, of a complete hull in one piece requires
reinforcement to insure the needed rigidity/modulus, all this with
higher productivity, and mounted on a metal chassis.
It is certain that the shift to plastics car bodies will happen,
because of weight and cost. It is a matter of trend and fashion,
and of mastering the injection molding of long fibers and the end
of life recycling. What it may just take is a new generation
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