Automotive case study | materials feature
and colour, hardness and flexibility, the close coopera- tion with BASF in material formulation and application development was a decisive factor for us”, says Bernard Delles, who headed up the Airbump project at Rehau. Development of the Airbump concept was initiated at
Rehau’s French operation at Morhange, near Metz. However, series production is carried out at the company’s production site at Tortosa in Spain, with finished Airbump panels delivered directly to the PSA assembly line in Madrid. Each injection-moulded capsule is mounted on a rigid injection moulded support shell that is fixed to the metal door (the shell moulding is produced in a Pulse PC/ABS blend supplied by Styron). The ability of the Elastollan HPM grade to form a tight assembly is said to be key to creating the resulting impact-absorbing flexible cavities. Aside from the mechanical performance, the Airbump capsules are also used as a styling feature. The Airbump panels are produced in four colours – black, grey, dun(grey-brown) and chocolate – which can be paired up with the 10 different body colours, allowing the owner to personalise their car. The engineering team worked with PolyOne to develop a specialty colour and additive system that allows the panels to meet the stringent UV stability, appearance and durability requirements laid down by Citroën, which says the Airbump panels will not require any special mainte- nance. The additive system was developed from PolyOne’s OnColor Smartbatch product line. “By working with Citroën and its Tier One suppliers,
we were able to develop an advanced solution that provides the panels with uniform, attractive, and durable colour despite exposure to sunlight, heat, and detergents,” says Christopher Palm, general manager for PolyOne’s colour and additives business in EMEA and India. “TPU materials are rarely selected for a vehicle’s exterior, but by working together, we were able to overcome several material-related challenges.” Although much less obvious visually than the side impact panels, Citroën also uses the Airbump technol- ogy in the more highly exposed areas of the C4 Cactus front and rear bumpers (fenders) and in the spoiler system, all of which are manufactured by Faurecia. The automotive components group developed new assembly techniques to handle the Airbump TPU sections, which are incorporated in the exposed corner sections of the components. “The innovation lay not only in the material but also in the mounting,” says Sébastien Bret, Development Manager at Faurecia. “BASF has developed a plastic that required a new assembly technology. We worked closely to meet the requirements for the industrial
www.compoundingworld.com Left: The
Cactus Airbump system is said to be the first large exterior automotive application for a TPU. The Airbump side panels are produced by Rehau for Citroën using a new BASF Elastollan TPU
mass production of these unusual parts.” Citroën says the goal for the Airbump development
team was to help produce a car that is “as good as new after three years on the road.” It says the system has been extensively tested in the laboratory and on the road to establish its resistance to key scratching, impact, thermal cycling, UV exposure, hand and jet-washing, and the car maker claims an improvement of at least 2.5 times over conventional construction materials. Despite the additional protection, the C4 Cactus weighs some 200kg less than the previous C4 model. However, Airbump is not simply a practical addition
to the vehicle. “With their characteristic Elastollan surface, Airbumps embody the philosophy of the Citroen C4 Cactus perfectly – they have style and are multifunc- tional,” says Jérôme Vinot Préfontaine, purchasing general manager for the C4 Cactus programme at PSA Peugeout Citroën. “Together with BASF and the suppliers of the Airbump parts, we have shaped the material develop- ment and manufacturing process in such a way that the two have resulted in models offering the optimum combination of quality, aesthetics and costs,” he said.
Click on the links for more information: ❙
www.basf.com ❙
www.faurecia.com ❙
www.polyone.com ❙
www.rehau.com
February 2015 | COMPOUNDING WORLD 79
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