Dow Automotive says it has introduced a new bonding system for the roof of the new BMW 7 Series.

In addition to plastic technologies for reducing weight of car bodies, Dow Automotive has developed a new bonding system for the structural bonding of aluminium roofs with steel car bodies which was applied on the new BMW 7 Series.

It says the new system demonstrates the effectiveness of bonding as an assembly technology for both lightweight constructions and mounting processes, crucial factors for the hybrid construction of materials where significant weight reduction advantages only come into play through use of a combination of materials.

In addition to specific assembly requirements such as a steel/aluminium combination that does not allow for any welding, the different thermal expansion coefficient of both materials is another crucial factor to take into account.

"Here, Dow Automotive's new bonding system provides a sustainable solution in two respects," says Orhan Imam, Dow Automotive market development manager for 2K PU adhesives.

"Compared to currently available adhesive systems, it is flexible enough to offset the different expansion coefficients while simultaneously guaranteeing the necessary structural system stability at even higher temperatures." Dow Automotive achieves this due to the improved glass transition temperature (Tg) of it its new 2-component (2K) PU adhesives, which it claims demonstrate unique properties for this kind of adhesive system.

Together with BMW, which uses the steel/aluminium material mix in the production of its new 7 Series, Dow Automotive developed an improved 2K technology based on its BETAMATE 2K PU adhesive range. This is the first time a 2K bonding system has been directly used on the assembly line to assemble an aluminium roof module.

In addition to its technological advantages with regard to flexibility and simultaneous stability, the solution developed for BMW also presents advantages during the assembly process and therefore also provides an economically attractive solution for OEMs, Dow says.