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New optical modules to make laser surface treatment ten times faster

The continuously adjustable piezoelectric deformable mirror (PDM) will help dramatically increase the speed of thin layer polishing and processing. (Image: Fraunhofer ILT)

The Fraunhofer Institute for Laser Technology ILT is developing two new optical modules for the near-infrared range that will increase the speed of laser polishing, coating and surface structuring applications by a factor of 10 while reducing their cost by half.

The optics are being developed as part of UltraSurface, an EU research project that has been running for two years and is set to be completed by the end of 2018.

The project partners – consisting of 10 companies and institutes from Germany, Belgium, the Netherlands, Israel and Switzerland – have together been researching and developing ‘Ultra dynamic optical systems for high-throughput laser surface processing’, in order to address demands for faster surface finishing technologies, which while currently being both highly precise and high quality, are also notoriously slow.

One of the optical modules being developed is designed specifically for the polishing and processing of thin layers. To accomplish this, the research team are using a continuously adjustable piezoelectric deformable mirror (PDM), which ensures that the laser beam adapts to the processing situation with switching intervals of less than five milliseconds. 

With the integrated PDM, the laser beam is adapted to the processing situation with switching intervals of less than five milliseconds. (Image: Fraunhofer ILT)

‘The laser beam is reshaped depending on the angle of incidence so that its projection on the work piece surface always has the same shape and the intensity remains constant,’ explained graduate physicist Judith Kumstel, an expert in laser polishing at Fraunhofer ILT. 

This manipulation is important in order to maintain consistent processing results – even with complex component shapes and constantly changing angles of incidence – which are only possible if the three-dimensional beam is continuously adapted at high processing speeds and is hitting the surface with constant intensity. On the other hand, if the laser beam projection deforms on slanted surfaces, the quality of the processed 3D surface also deteriorates.

The second optical module, developed for laser structuring, increases processing speed and productivity by instead enabling four beams to be used in parallel. By using a diffractive optical element (DOE), the module splits the laser beam into a square beam of four partial beams. In conventional multi-beam concepts of this kind, the focusing optics, as well as the shape of the component lead to a distortion of the projected beam. The UltraSurface researchers have addressed this by developing a special system with which each individual partial beam can be adjusted in its position within milliseconds, so that there is always a square beam for processing.

Set-up for laser-based surface processing with the technologies developed in ultraSURFACE. (Image: Fraunhofer ILT)

The UltraSurface team will be testing the two new optical modules in a new laser system for various applications until the end of 2018. In the meantime, a Swiss company is building an industrial-grade machine that can be used to polish, structure and coat flexibly, cost-effectively and with unrivalled speed thanks to the quickly interchangeable optical modules.

‘With the concepts developed in this project, surfaces will soon be processed just as well as with conventional systems,’ Kumstel remarked. ‘Thanks to the new optics and the new machine, processing will be ten times faster than before, so that laser-based surface finishing will offer a cost-effective alternative to conventional surface finishing for many companies from various industries – even for small job shops’.

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