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 car bodies.

The second converting processes, such as welding, machining, assembling, also are an important cost, that plastics molding and function integration can avoid.

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 of designers.

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