BMW 7 Series Betaforce Dow Automotive

The BMW 7 Series relies on Dow Automotive Systems’ BETAFORCE™ bonding adhesives to bond CFRP parts to metal ones, such as in side-frame applications. Photo Credit: BMW

A case in point is the injection bonding technique Dow developed for its BETAFORCE™ bonding adhesives. The company describes this development as an example of the customizing capabilities of BETAFORCE to address customers’ specific production requirements, such as open times and cycle times, without affecting the adhesive’s mechanical properties. By adjusting parameters on a case-by-case basis, Dow Automotive aims to promote the wider use of CFRP parts in mixed-material assembly.

The injection bonding has been used to bond carbon fiber parts to metal in side-frame applications along the roof of the BMW 7 series. In this application, the carbon fiber component sits within a steel housing that runs along the A-pillar into the roof and down the D-pillar. According to Dow, this combination of materials, bonded by BETAFORCE structural adhesives, ensures the stability of the passenger compartment in the case of a side-pole impact or rollover, while also increasing vehicle stiffness and improving ride-handling and minimizing NVH (noise, vibration and harshness) at the lowest mass.

The challenge of integrating such long CFRP composite parts comes in managing the differential coefficient of linear thermal expansion during both assembly and the operative life of the vehicle. BETAFORCE technology helps address that challenge.

BETAFORCE, based on a two-component polyurethane structural adhesive technology, is characterized by a high modulus for needed stiffness and a high elongation factor that enables a high level of energy absorption and flexibility. This combination helps manage different levels of thermal expansion, according to Dow.