Cutting edge

German researchers develop an environmentally-friendly way to etch microstructures into free-form surfaces. Siobhan Wagner reports.

A technique that uses a laser beam to burn micrometre-fine patterns into complex-shaped component surfaces promises to be cheaper and more environmentally friendly than traditional etching methods.

For years etching has been the way to create fine microstructures on component surfaces to give them added cosmetic or performance properties. Plastic dashboards, for example, can be made to look like leather and sharkskin ribs on an aircraft’s fuselage reduce air resistance.

Although lasers have been used for a long time to structure flat surfaces, etching techniques have been the only choice for 3D components of complex shape.

‘Many manufacturers want to substitute etching processes because they are very cost intensive and use chemicals that have to be disposed of later,’ said Sascha Bausch, the lead developer of the laser system at the Fraunhofer Institute for Production Technology in Aache, Germany. ‘We thought this process might be improved by using a laser.’

Bausch’s R&D team recently launched a laser that can burn microstructures into free-form surfaces. With the help of industrial partner BMW, the researchers demonstrated a prototype of an injection-moulded car cockpit with a leather-like look.

The development is the result of months of painstaking research work. The laser has to be exactly focused so that the focal point, which is about 10 micrometres wide, works with precision. It is crucial for the laser to hit the surface vertically — otherwise the focus becomes distorted and the sharp microstructure blurs. The challenge was to guide the laser precisely at the same distance along the curves. For this purpose the team used the attributes of a conventional machine tool.

‘We took a milling machine tool, dismantled the milling spindle and integrated a nanosecond pulse laser laser,’ said Bausch. ‘With this machine tool we can produce whatever surface you want, so the designer has more possibilities to create an individual product.’

A scanner controls the precise movement of the laser and lays down the desired pattern on the component.

One of the most challenging tasks for the researchers was learning how to transfer a pattern to uneven surfaces. Bausch compared it to applying wallpaper to a curved surface. The team used special CAD systems to adapt the desired structure to uneven features and developed a software system to convert data into control commands for the laser, the scanner and the machine tool.

In addition to the prototype car cockpit, the team has also used the laser technique to produce prototype female tools for plastic injection moulding.

Although the researchers are now working with a nanosecond laser, Bausch said more advanced lasers could improve the technique’s accuracy.

‘At the moment our laser has an accuracy of about 30 microns,’ he said. ‘There is a new class of laser on the market, called a picosecond laser, which provides a much finer spot. With this we would be able to decrease this structure size to 5-10 microns. It is not possible at the moment, but it’s something we want to accomplish in the next couple of years.’

Lasers with greater accuracy will mean they can be used for optical systems or medical technology, such as on micro-recesses in implants to improve connection with bone. A further aim, said Bausch, is to develop a mass-producible machine tool for everyday industrial use.

In addition to BMW, Siemens was an industrial partner on the project.