Fraunhofer Researchers Develop Process for Laser Forming and Bonding of Fiber-Reinforced Composites; Marine, Automotive and Aerospace Applications

Components made of fiber-reinforced straps are bonded with an infrared laser. Click to enlarge.

Researchers at Fraunhofer-Gesellschaft in Germany have developed a process that crafts and bonds fiber-reinforced composites with lasers. Fraunhofer will demonstrate the process at the JEC Composites Show 2010 in Paris, 13-15 April.

Fiber-reinforced thermoplastics are 50-70% percent lighter than steel and 15-20% percent lighter than aluminum; their stability and breaking strength are impressive, making their use attractive in marine, automotive and aerospace applications. However, processing these materials can be complicated and cost-intensive.

Manufacturers of boat hulls, aircraft components and rotary blades have had to work with expensive forming tools that were lined with glass or carbon fiber matting. In the second process step, 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 big enough to accommodate the components is needed. And ultimately, the parts still had to be glued together.

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. The ingredients for tape placement come from within the roll: carbon fibers are integrated into kilometer-long strips of meltable thermoplastic resin.

Despite their negligible weight, these strips have above-average resilience; in this regard, engineers measure and evaluate the impact and tensile strength and tear resistance. To assemble sturdy components from these tapes, multiple laminate layers are stacked on top of each other and then compressed into a compact structure.

In this process, the tape strips fuse with each other and cool off quickly, 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, according to Fraunhofer.

Using laser beams, 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.

All we need for this is a laser that emits infrared light. 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. The materials must withstand immense acceleration, vibrations and temperature differences, so a 200-percent level of safety is required.

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 new joining techniques are suitable for all thermoplastic materials that are subjected to extreme strains.

—Wolfgang Knapp of the Fraunhofer Institute for Laser Technology ILT