Could lasers be replacing metal bonding adhesives?

The key to better performing vehicles that are also more fuel efficient is to reduce their weight.

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You might think seats would be one of the easier components to shave a pound or two off, but car seats have to perform to exacting safety standards and stand up to strain for years on end. Few office chairs survive as long as car seats.

Composite materials combining metal and plastics are promising in principle, but they don’t readily adhere, nor does carbon fibre readily bond with either. These three materials are chemically and physically very dissimilar.

The PMJoin project

The EU recently financed a research project to see if lasers might offer some alternative approaches. Four million euros were put at the disposal of a team drawn from companies including the Basque R&D centre, Fraunhofer Group, the Armines Centre, Andaltec Foundation, Peugeot-Citro├źn, Lasea, Valeo and Faurecia Automotive.

The method investigated consists of two steps. First, lasers etch microgrooves into the metal surface. Next, the plastic is layered above and the contact area laser-heated. The plastic is transparent to the laser wavelength and melted by contact with the metal. Pressure is applied at the same time to encourage the molten plastic to flood the keyed surface.

A range of samples was produced using different lasers, plastics and scoring patterns, then each was subjected to tensile shear, pull, and peel tests. Adhesion onto laser-etched metal was shown to be twice as effective as adhesion to surfaces roughened by sand-blasting and four times that of untreated metal surfaces.

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The second step was to construct several versions of an actual seat-back rest in which the loads and strengths at critical joint positions could be impact tested.

Modest results

Hybrid backrests failed at 60 per cent of the impact force measured for steel seats in rear impact tests but at close to 90 per cent in front impact tests. This appears to indicate no immediate prospect of replacing traditional metal joints or metal bonding adhesive. Fortunately, there have been steady improvements in metal bonding adhesive like that at http://www.ct1ltd.com/.

Nevertheless, the team views the results as a successful proof of concept and believe further improvements are possible. The technique can still find applications in areas where impact strength is less safety-critical. Questions remain about how laser bonded materials will stand up to humidity and temperature variations.

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