Laser bonding advances thermoplastic composites

Fraunhofer researchers have developed a method for crafting and bonding fiber-reinforced composites with lasers, obviating tradition matting and resin infusion steps. Fraunhofer will unveil the technology at the JEC Composites Show 2010 (April13-15; Paris) showing a method to fully automate production of components from fiber-reinforced thermoplastics. In a traditional multi-step composite manufacture process, forming tools are lined with glass or carbon fiber matting, a pump siphons off air to eliminate bubbles, and fluid resin is injected to saturate the matting. Once this is completed, parts must then be cured in large ovens.

Researchers at Fraunhofer Institute for Production Technology (IPT) have devised a new process where the ingredients for tape placement are fully contained in the roll, with carbon fibers integrated into kilometer-long strips of meltable thermoplastic resin. To produce components from these tapes, multiple laminate layers are stacked on top of each other and then compressed into a compact structure. All the while, a laser rapidly emits precisely measured doses of energy in a targeted manner onto the material, and the tape strips fuse with each other and cool off quickly, minimizing the expenditure of energy and time. Fraunhofer says that compared to prior manufacturing processes, like those where tapes are joined with hot air, the laser-assembled quality is better.

"The infrared laser melts the surface of the plastic components," explains Wolfgang Knapp of the Fraunhofer Institute for Laser Technology (ILT). "If you compress them when they are still fluid and then let them harden, the result is an extraordinarily stable bond." The key to the development has been in the process control, specifically determining the gap between laser head and surface and then controlling the amount of time the laser hits the substrate, and finally calibrating the pressure. —[email protected]