Plastic Parts That Retain The Shapes

Plastic Parts That Retain The Shapes

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It is inevitable that in today’s traffic conditions, the bodywork of a car will get small dents. If there is a minor collision, the dent may be not large enough to justify the high cost of repairing and repainting (and you never really get the same shade again) so many motorists have to live with the unsightly scars.

With the new Peugeot 307, this will not longer be the case for some sections of the bodywork, in particular, the front wings over the wheels. The plastic used for these parts is a special type which is strong and has a ‘memory’ of its shape. They are designed to withstand all aspects of daily conditions, be they minor collisions or impacts of a supermarket trolley. Even a kick from a vandal will not leave a lasting dent.

“But that’s not all,” says Philippe perrot, head of the structural engineering centre at PSA Peugeot-Citroen which designed and developed the plastic wing. “The main advantage of the plastic wing lies in its contribution in repairability.”

Minor collisions at low speeds – the sort that are frequent in urban driving – generally damage the bumpers, headlamps and wings. They are costs that motorists try to avoid and therefore the engineers looked for a solution.

What they designed was a system of fusible clips to attach the wing to the steel body of the car. The wing is no longer screwed on, as in conventional assembly methods, but simply fixed by three plastic clips which cannot be pulled off but will break on impact.

“The wing is not fragile; it is held in position firmly,” assures Perrot. “We have done tests with the car running at speeds as high as 200 km/h and the wing has stayed in place, even when one clip has been broken.”

Continuing the story of the plastic wing, Henri Mueller (who helped draw up the specifications) says work on plastic parts had been going on for some time but there were few practical applications. “They were first used for interior trim in 1955 and some years later, thermoplastic bumpers and bonnets appeared with the Citroen BX. Injected plastics were used for some more technical items like the fuel manifold of the Peugeot 104 and the door handles and rearview mirrors of the Peugeot 305 in the early 1980s.”

Today’s average car contains almost 120 kgs of plastic parts. These are found inside as well as on the exterior of the car, and also in the engine compartment. However, the front wing of the 307 is a new ‘species’ of flexible and ‘intelligent’ thermoplastic whose prime asset is light weight.

The plastic wing of the 307 is no more than 1 kg, compared to 3 kg or 4 kg for a conventional wing. Furthermore, being a thermoplastic, it can be remelted and recycled to reduce waste, another noteworthy quality.

It was not an easy task working with this new material. Mueller drew us specifications which were stringent and detailed things like visual appearance, feel, and above all, resistance to extreme temperatures. It had to be capable of withstanding 160 degree C. in the paintshop during the baking process and yet cope with temperatures way down to -30 degrees C.

“In the past, our main worry concerned the ageing properties of plastic,” recalls Mueller. “The first plastics of this kid became brittle after a few years.”

The high-tech plastic of the 307 has overcome this problem and is designed to retain its initial properties for at least 15 years. It is also a precision part which is flexible and can be moulded into complex shapes with points and angles. Such shapes would not be possible to stamp with sheet steel.

The greatest challenge with plastic is the problem of dilation. Though a high-performance plastic, it is still susceptible to deformation by heat. But even though the part dilates by 10 mm during the paint baking process, our plastics experts have found a way to ensure that it remains flush with the neighbouring parts.

For those who are more interested in the actual plastic, it is known as ‘Noryl GTX 964’ and was first developed in North America. PSA Peugeot-Citroen is not the only automaker using it as it is also used for the wing areas of the Mercedes-Benz A-Class, VW Beetle, Smart and Renault Clio. However, the unique thing about the wings of the 307 is their repairability: the others do not have the fusible clips which have been patented by PSA Peugeot-Citroen.

Future Peugeot models will use the plastic wings but for reasons of cost, the material is unlikely to be used for too many other body parts. Mueller hints that there will soon be plastic taillights and outer door panels but if the part has a structural function that involves safety, then plastic is not suitable.

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