Molding in fasteners to CFRP parts

 

At the JEC show in Paris this year, one of the project displays in the Automotive World showcase was a molded-in fastener developed by Böllhoff Otalu (La Ravoire, France), the French subsidiary of the German fastener supplier Böllhoff (Bielefeld).

 

Yann Bernard is the product manager for the Böllhoff IMTEC HR, which stands for In-Molding TEChnology High mechanical Resistance fastener. He explains that IMTEC HR was developed with the innovation departments at automotive OEMs. “We were asked to work on heavy structures to reach a high level of performance. We can make very strong composite parts, but the weak point is assembly. The need was for total assemblies such as seats, which must be attached to a floor.” Bernard notes that in typical metal structures, this was achieved using a blind rivet or welded nut set on the floor. “But now floors may be composite. So, how do you fasten to this type of composite structure?”

 

 

For injection molding, the fastener is robotically placed first onto a pin fixed on the mold. The pin locates the fastener and protects the threads inside of it from being coated with resin. Next, the composite material is robotically placed into the mold. The mold is closed, the plastic injected and the part demolded with fastener integrated.

For compression molding, the process is essentially the same except the pin is a plastic screw-off “cap” and also serves to push the material aside for inserting the fastener into the composite, thereby eliminating the need for hole drilling. This not only saves time, it avoids cutting the fibers. The pin cap again protects interior threads during molding and is removed after the part is demolded.

“There are no extra operations once the floor is produced,” notes Bernard. “We believe this technology helps to make composite floors or any other structural parts with an affordable production cost. It replicates the used of blind rivets with metal floors because the fastener is already there in the molded composite part. You now attach the seat with standard methods. This equals the playing field because parts can be attached to a composite floor the same as to a metal floor.”

Böllhoff’s IMTEC HR fastener developed for molding process embeds into the composite part without reducing section thickness. SOURCE: Böllhoff.

A special version of IMTEC® HR has been developed with Cetim which is compatible with the QSP production line. Cetim is the French research organization that has developed the Quilted Stratum Process (QSP) for highly automated production of composite parts.

According to an article published by Cetim, the patent pending IMTEC HR fastener developed for QSP shows a 30-75% increase in pull-through performance and 60-75% improvement in lap-shear performance compared to conventional fasteners.