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DELO and Böllhoff launch ONSERT joining method for light-weight materials; used in BMW i3, i8

The assembly specialist Böllhoff and the adhesive expert DELO have developed an innovative joining method for light-weight materials using a bonded bolt called ONSERT. With ONSERT, composites, thin sheet metals, plastics and other materials are equipped with a multi-purpose connection element. Böllhoff and DELO have tested this technology in a series of pilot projects, the last one of which was to secure cables, claddings and other components of the BMW i3. The partners are now launching the technique commercially.

Composite materials, such as CFRP and GFRP, take established joining technologies including welding, screwing and riveting to their limits. This new technology, based on stud welding, combines bonding and screwing by equipping fastening elements, such as threaded metal bolts, with a transparent plastic base and bonding it to fiber composite materials. The threaded rod of the ONSERT can be screwed and—when necessary—removed again.

ONSERT bolt. ONSERT bolts applied in BMW i3.

The special feature of this technique is its speed. The adhesive is cured within about 4 seconds using an LED lamp; the process can be fully automated. The bonded connection can be loaded immediately. Bonded bolts with a base diameter of 25 mm achieve a pull-off strength up to 2,000 N on CFRP.

Third-party video of BMW i8 production. Installation of ONSERT bolts is seen at 2:15.

When applying higher forces, a predetermined breaking point in the base ensures that the laminate of the composite material remains intact and no fibers are torn out. Nevertheless, the ONSERTs are robust as shown by salt spray and VDA climate tests.

In addition, ONSERTs excel due to their flexibility in design and production. First, the structural shape can be defined by the user to a great extent, particularly in terms of rod length and base diameter. Second, they provide much freedom in production as bonded bolts can be attached to the raw body and prior to final assembly of lacquered elements.

ONSERTs are suitable for a broad variety of tasks where components must be fixed. Possible applications include cable harnesses, control units, sensor retainers, brake lines, claddings or exterior attachment components. Cover plates, insulating materials or floor panels in airplanes are also imaginable. Finally, white goods also open up multiple application possibilities.


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