Laser remelting produces structured surface designs

Ashley N. Paddock, ashley.paddock@photonics.com

Structuring the metallic surfaces of tool inserts by laser remelting allows manufacturers to more quickly and cost-effectively adapt their production processes to incorporate novel structures and design elements.

Unlike laser structuring by ablation, remelting can produce finished surfaces that do not require postprocessing. For a structure depth of ~200 µm, this method can achieve processing rates of up to 75 mm in 2 min in a single pass. The ablation method achieves only 1 to 10 mm in 3 min and requires about 10 passes to achieve the 200-µm structure depth.

A laser-remelting technique can produce surfaces with variable structures. Courtesy of Fraunhofer Institute for Laser Technology ILT.

In laser remelting, a technique developed by researchers at Fraunhofer Institute for Laser Technology ILT, a laser beam travels over the workpiece, melting the metal surface. Modulating the laser power continuously changes the size of the melt pool at defined points, causing the material to be redistributed at those points and creating valleys and mountains.

When the top layer of the molten material solidifies, surface tension gives it uniformly low roughness, leaving it with a polished finish. The laser remelting is already available for industrial use on flat surfaces and single-curved component geometries. The researchers are investigating how to apply the technique to free-form surfaces.

Dual-gloss effect: A molded plastic component can be created using a selectively laser-polished tool insert.

Sometimes an additional dual-gloss effect is required for end products such as decorative elements or an entire product surface. In these cases, FIX the first step is to apply a matte finish to the whole surface of the tool, generally achieved through blasting with glass beads or sand. Selected regions are then remelted using a laser beam. These regions solidify from the melt with a polished finish so that there is a contrast between the untreated matte areas and the shiny laser-polished areas. Depending upon the intensity of the dual gloss, a 3-D effect can arise in which the polished points appear to protrude from the surface. This selective polishing technique now can be applied on an industrial scale for both free-form and flat surfaces.