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Creating Bonds with Lasers

Photonics.com
Apr 2010
MUNICH, Germany, April 5, 2010 – In what was once considered a complicated and cost-intensive process, fiber-reinforced composites are now being crafted and bonded with lasers, eliminating the need for matting and resins.

Fiber-reinforced thermosplastics, for example, are ideal because they are fifty to seventy percent lighter than steel, fifteen to twenty percent lighter than aluminum and still maintain impressive strength and durability.


Components made of fiber-reinforced straps are bonded with a laser. (Image: Fraunhofer IPT)

Until now, manufacturers had to work with expensive forming tools that were lined with glass or carbon fiber matting. In the matting process, a pump siphoned off the air before fluid resin could saturate the matting – the vacuum prevented the accumulation of air bubbles on the fibers, which impede stability. Then, to harden the material, a gigantic oven is needed – an oven big enough to accommodate the components. And ultimately, the parts still had to be glued together.

Components made of strips

To facilitate the fully-automated production of components out of fiber-reinforced thermoplastics, engineers and scientists at the Fraunhofer Institute for Production Technology IPT devised an entirely new process.

Carbon fibers are integrated into kilometer-long strips of meltable thermoplastic resin. Despite their negligible weight, these strips have above-average resilience. To assemble sturdy components from these tapes, multiple laminate layers are stacked on top of each other by the laser just before being laid down and then compressed into a compact structure. This way, the tape strips fuse with each other and cool off quickly, too, because the laser rapidly emits precisely measured doses of energy in a targeted manner onto the material. This minimizes the expenditure of energy and time. Compared to prior manufacturing processes – for instance, joining tapes with hot air – the quality is even better. Even though it is still in the prototype phase, the researchers say there is already an industry demand for the process.

Using laser beams, engineers can even glue components together. At the JEC Composites Show in Paris, Fraunhofer researchers presented the new joining technology for glass- fiber-reinforced thermoplastics.

"All we need for this is a laser that emits infrared light," explained Wolfgang Knapp of the Fraunhofer Institute for Laser Technology ILT. "The infrared laser melts the surface of the plastic components. If you compress them when they are still fluid and then let them harden, then the result is an extraordinarily stable bond."

Difficult-to-form, bulky components of fiber-reinforced plastic can be joined together in a manner sturdy enough to satisfy the demanding standards enforced by the automotive, aviation and aerospace industries.

"The materials must withstand immense acceleration, vibrations and temperature differences, so a 200-percent level of safety is required," said Knapp, who in conjunction with his colleagues optimized the laser joining process. "The know-how sticks in the process control: in determining the gap between laser head and surface; in controlling the time which the laser beam lingers on substrate; in calibrating the pressure."

The magic of the technology is in its versatility. With the infrared laser, any components made of thermoplastic composites can be welded together – airplane fuselages, load-bearing structures for cars, components of boat hulls, rocket tanks.

Materials for the extreme case

The possible uses of laser beams in the production and processing of fiber-reinforced thermoplastics are absolutely limitless, according to the researchers.

"The new joining techniques are suitable for all thermoplastic materials that are subjected to extreme strains," concluded Knapp. "Because fiber composites are not only stable, they are also lightweight and they save energy with any type of acceleration – no matter if by land, sea, in the air or in space."

For more information, visit: www.ilt.fraunhofer.de  

carbon fibersEuropefiber opticsfiber-reinforced compositesforming toolsFraunhofer Institute for Laser Technology ILTGermanyindustrialinfrared laserJEC Composites Showlaminate layerslaser-joining processlasersmattingResearch & Technologyresinsthermoplastic resin

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