Laser remelting yields structured metallic surfaces

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Fraunhofer-Institut für Lasertechnik

Dual-gloss effect

Another approach to enhancing the appearance of surfaces by design is selective laser polishing, which is useful for creating an effect based on areas of the surface having different degrees of gloss.

In applications where such a dual-gloss effect is called for to distinguish the end product, whether by creating decorative elements or by targeting the whole product surface, the first step is to apply a matte finish to the entire surface of the mould tool. This is generally achieved through blasting with glass beads or sand. Selected regions are then remelted with a laser beam. These regions solidify from the melt with the naturally occurring polished finish. In other words, the process of selective laser polishing generates a contrast between the untreated matte areas and the brilliant, laser-polished areas resulting from the physics of laser remelting.

Depending on the intensity of the gloss created, this method can even produce a 3D effect in which the eye perceives the polished points as protruding from the product surface. One familiar example of how selective laser polishing can be employed is in the moulding of plastic items that have a surface meant to suggest leather grain. The mould tool surface is appropriately structured for the dual-gloss effect by selective laser polishing, and the treated surface transfers the “leather” texture to the plastic end product during the moulding process.

This selective polishing technique is now available for application to both flat and free-form surfaces on an industrial scale.

Visitors to the Fraunhofer booth at EuroMold 2011 had an opportunity to see both components produced from mould tools that were laser structured by remelting and others that were moulded from plastic by selectively laser-polished tools. Readers interested in the science behind these techniques can read a technical paper written by three developmental researchers at RWTH Aachen University and the Fraunhofer ILT.

Fraunhofer Institute for Laser Technology

Aachen, Germany

www.ilt.fraunhofer.de

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