Fraunhofer Institute for Laser Technology ILT

Laser remelting yields structured metallic surfaces

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Remelting as alternative

The Fraunhofer ILT has completed development of a method of structuring tool inserts via a different form of applied laser radiation: laser remelting. In this technique, the laser beam travels over the workpiece and the heat input from the moving beam melts the metal surface as it goes. At the same time, the laser power is modulated continuously in order to change the size of the melt pool at defined points.

“This modulation causes the material to be redistributed, creating mountains and valleys,” says André Temmler, project manager at the Fraunhofer ILT. “Half of the resulting structure lies above its initial level, while the other half lies below it.” Whereas both photochemical etching and laser ablation are based on the removal of metal, laser remelting is fundamentally different: in the latter process, material is not removed but rather reallocated while molten.

Thanks to surface tension, when the uppermost layer of the molten material solidifies, it exhibits uniformly low roughness. Thus, the surface is left with a brilliant polished finish. Unlike laser structuring via ablation, laser structuring by means of remelting can directly produce finished surfaces that do not require any postprocessing. This ability is the technique’s novelty.

At a structure depth of approximately 200 μm, this method can achieve processing speeds as high as 75 mm2/min, which makes possible the attainment of a volume redistribution rate of 15 mm3/min per pass.

A further advantage of laser remelting is that it consumes less energy and fewer resources than conventional laser-based structuring by ablation. Less energy is required for melting than for sublimation, for one thing. Also, the process requires significantly fewer passes with the laser beam, and there is no loss of workpiece material.

See: Better control of laser material deposition

Depending on the mould material and batch size, these benefits can yield considerable time and cost savings for tool manufacturers.

The laser technique of structuring by remelting is already available for industrial use in applications involving flat surfaces and single-curved component geometries. Temmler and his team are now working on applying the method to free-form surfaces.

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