AKL e.V.


ELI

3D micro-structuring of large scale metal surfaces for embossing and printing applications with high

Dr. Stephan Brüning
Dr. Stephan Brüning

R&D Laserapplication Schepers GmbH & Co. KG, Vreden, Germany

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Members of the Project Team
  • Dr. Stephan Brüning, R&D Laserapplication, Schepers GmbH & Co KG, Vreden (Team Representative)
  • Dr. Gerald Jenke, R&D Department, Saueressig GmbH + Co. KG, Vreden
  • Dieter Hüls, R&D Department, Saueressig GmbH + Co. KG, Vreden
  • Dr. Ralf Knappe, Director of R&D, LUMERA LASER GmbH, Kaiserslautern
  • Dr. Sergey Naumov, R&D Department, LUMERA LASER GmbH, Kaiserslautern
  • Dr. Daijun Li, Manager Optic, EdgeWave GmbH, Würselen
  • Dipl.-Phys. Marco Höfer, Group Manager Solid State Lasers, Fraunhofer-Institut für Lasertechnik ILT, Aachen
  • Dipl.-Phys. Stephan Eifel, Group Micro and Nano Structuring, Fraunhofer-Institut für Lasertechnik ILT, Aachen
  • Dr. Arnold Gillner, Competence Area Manager Ablation and Joining, Fraunhofer-Institut für Lasertechnik ILT, Aachen

Areas of Application
Major sectors of industry which are profiting from the innovation:
  • Roto-Gravure printing industry: packing-, security- and electronic-printing, intaglio printing
  • Industrial sectors that use micro-embossing technologies for functional surfaces or security applications

Technological Impact
  • Reduced manufacturing costs for existing products
  • Improved quality in existing products
  • New product features
  • Reduced process costs
  • Improved working conditions
  • Improved quality assurance

Abstract
Laser ablation with ultrashort pulses allow a superior machining quality, compared to laser machining with longer pulses. The high precision and resolution of the structures achievable with ultrashort pulse laser systems are of major interest in the printing, gravure and embossing industry (i.e. security printing, electronic printing, display and smartphone manufacturing). Finest three dimensional structures can be generated directly and melt-free by lasers into copper, nickel, aluminium and steel surfaces. However for surface structuring of large embossing rolls with diameters of 100 mm and larger and lengths exceeding 1m, high structuring speeds and high laser ablation rates are needed to allow an economically production. With currently available picosecond-laser systems using pulse repetitions rates below 1 MHz the ablation rate is limited to ~1 mm3/min. New high-power laser systems with high repetition rates in the multi MHz area offer the possibility to significantly increase the laser ablation rate. However with current laser scanning devices only spot movements in the range of 5 m/s at small spot sizes can be achieved, which results in a large pulse overlap at high laser repetition rates. This leads to a high local thermal accumulation and a pulse-plasma interaction on the metal surface with a low machining quality that can be classified between ps- and ns-pulse regimes. As a consequence, new high speed scanning techniques are required to use the full potential of high power ultrashort pulsed lasers for high machining quality.

In order to enable fast and economic surface structuring of large rotating cylinders, with less thermal effects several innovations had to be developed in combination:
  • A high power amplifier to boost the ps-pulses to an average power of 400 W
  • A material selection and process strategy that enables use of such high power
  • A fast scanning technology
  • A machine and software control that can combine and synchronize these components
Within the public funded BMBF-project PIKOFLAT, Schepers GmbH and the entire project team developed new scanning and ablation techniques that allow scan speeds of up to 50 m/s. Using a rotating cylinder as fast moving workpiece and an additional fast beam scanning device based on acousto optic deflectors, picosecond laser pulses of 10 MHz and higher could be used for high quality micro machining. The project team has built a 400 W picosecond MOPA laser system based on a 10.6 MHz laser seeder and a slab based laser amplifier. The laser system and the new scanning system was integrated in the Digilas machine technology and forms a new type of machine which exceeds all current rotational gravure systems in matters of machining quality. With this system, for the first time ablation rates in metals of up to 20 mm³/min can be realized using ultrashort pulsed lasers.


3D surface of a leather and calotte
embossing tool structured with
picosecond lasers.
(Photo: Schepers GmbH & Co KG,
Vreden, Fraunhofer-Institut für
Lasertechnik ILT, Aachen)

With picosecond-laser 3D structured printing cylinder (Ø 100 mm).
(Photo: Schepers GmbH & Co KG, Vreden, Fraunhofer-Institut für Lasertechnik ILT, Aachen)
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