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Fraunhofer Institute for Laser Technology ILT Laser remelting yields structured metallic surfaces

Editor: Eric Culp

Surface effects on plastic moulded products can be created using mould inserts treated by a laser process more efficient than ablation.

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This mould tool surface with variable structures was produced by laser remelting.
This mould tool surface with variable structures was produced by laser remelting.
(Source: Fraunhofer ILT)

The Fraunhofer Institute for Laser Technology ILT has developed a method of structuring the metallic surfaces of tool inserts by means of laser remelting. This method makes it possible, for the first time, to structure mould materials without having to resort to ablation, and also to polish them to a brilliant gloss finish.

This process innovation not only gives tool manufacturers greater scope to adapt their production processes so as to incorporate novel structures and design elements; it also saves them time and money. Through the use of another new technique developed by the Fraunhofer ILT, mould makers can provide tools and products with a dual-gloss effect.

Surface structuring

The surface of a part or product strongly influences its properties and functions—everything from abrasion resistance to how it feels to the touch and visual appeal. Therefore, many plastic parts have structured, or textured, surfaces. From steering wheels to toothbrush handles, we have become accustomed to the distinctive look and feel of deliberately structured surfaces on items we encounter in numerous areas of our lives. Injection moulding tools made from metal are often the means by which moulded products are given their surface structure.

One technique commonly used to produce the desired structure on tools is photochemical etching. Here, specific regions of the tool insert are structured to produce the desired texture by etching away unwanted regions. This is a costly and time-consuming process, however, which requires the use and disposal of large amounts of environmentally hazardous acids.

See: Lasers cut into traditional materials processing

A more environmentally friendly alternative is the technique of laser structuring by ablation, which has been used successfully for more than 10 years. This method can achieve ablation rates of 1 to 10 mm3/min in processes designed to create structures greater in feature dimension than 10 μm. However, in many cases the workpiece requires subsequent treatment to remove the melt residue that accumulates during ablation. In addition, the laser requires some 10 passes to achieve a structure depth of 200 μm. All of this means that the laser-based structuring of large surfaces through ablation is generally not a cost-effective option for tool manufacturers.

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