Automated production of fibre-reinforced components

Paul Boughton
Fibre-reinforced thermoplastics are fifty to seventy per cent lighter than steel and 15 to 20 per cent lighter than aluminium; their stability and breaking strength are also impressive. Yet until now, processing these materials was considered complicated and cost-intensive: manufacturers of boat hulls, aircraft components and rotary blades had to work with expensive forming tools that were lined with glass- or carbon-fibre matting. In the second process step, a pump drew the air out before fluid resin could saturate the matting (the vacuum prevents air bubbles from accumulating on the fibres and impeding stability). Then, to harden the material, a very large oven is needed to heat the components. And, ultimately, the parts still had to be bonded together. Thankfully, this whole process will soon get easier: at the JEC Composites Show 2010 in Hall 1, Booth T18, Fraunhofer researchers will demonstrate how fibre-reinforced composites can be crafted and then bonded with lasers – with no need to bother with matting and resins.
To facilitate the fully-automated production of components out of fibre-reinforced thermoplastics, engineers and scientists at the Fraunhofer Institute for Production Technology (IPT) devised an entirely new process. Carbon fibres are integrated into kilometre-long strips of meltable thermoplastic resin, which are supplied on tape reels. Despite their very low 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 layers are laminated on top of each other by the laser just before being laid down; they are 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 minimises the expenditure of energy and time. Compared to existing manufacturing processes – for instance, joining tapes with hot air – the quality is even better.
Using laser beams, engineers can even bond components together: at the JEC in Paris, the researchers will present a new joining technology for glass-fibre-reinforced thermoplastics. Wolfgang Knapp of the Fraunhofer ILT states: "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."
Difficult-to-form, bulky components of fibre-reinforced plastic can be joined together in a manner sturdy enough to satisfy the demanding standards enforced by the automotive, aviation and aerospace industries. Knapp explains: "The materials must withstand immense acceleration, vibrations and temperature differences, so a 200 per cent level of safety is required." In conjunction with his colleagues, Knapp optimised 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." One of the advantages of the technology is in its versatility. With the infrared laser, any components made of thermoplastic composites can be welded together – including airplane fuselages, load-bearing structures for cars, components of boat hulls, rocket tanks.
The possible uses of laser beams in the production and processing of fibre-reinforced thermoplastics are said by Knapp to be limitless: "The new joining techniques are suitable for all thermoplastic materials that are subjected to extreme strains. Because fibre 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."
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