ONSERT bolts applied in BMW i3
DELO (adhesive expert) and Böllhoff (assembly specialist) announced a new innovative joining method for light-weight materials like CFRP and GFRP.
Composites, thin sheet metals, plastics or other materials can be equipped with a multi-purpose connection element by using a bonded bolt called ONSERT.
The first electric cars assembled using this method are the BMW i3 and i8.
The adhesive is cured in just four seconds using an LED lamp and the whole process can be automated:
"Böllhoff and DELO have tested this technology in a series of pilot projects. The last one was about fixing of cables, claddings and other components of the BMW i3. After this technique has proven its capabilities in series production, it will now be launched."
"Composite materials, such as CFRP and GFRP, take established joining technologies including welding, screwing and riveting to their limits. This 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."
"The special feature of this technique is its speed. The adhesive is cured within about 4 seconds using an LED lamp. It is possible to fully automate this process. 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. 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."
Here is video of BMW’s automated production process using ONSERT: