Fraunhofer ILT heads toward digital photonic production

Its highlights included beam sources and manufacturing processes for ultrashort laser pulses as well as ways to systematically optimize machining processes using computer simulations. There was even a specialist booth at the fair dedicated to the revolutionary technological potential of digital photonic production.

Now in its fortieth year, LASER World of Photonics is still considered the flagship trade fair for the laser and photonics industry, as this year’s event proved. 27,000 visitors from 74 countries came to Munich to see the latest products and developments being displayed by 1,135 exhibitors. Eight Fraunhofer Institutes also had a presence at the fair, this year under the banner of “Customized Solutions”.

Computer simulation optimizes laser machining

Laser machining processes often test the limits of what is technologically possible. Such processes require high beam intensities for working the smallest of surface areas, and yet demand maximum machining speed, precision and reliability. This pushes the technology needed to monitor and control processes to the edge of its capabilities. But computer simulations can help, by keeping time-consuming tests that optimize processes by trial and error to a minimum.

Scientists at Fraunhofer ILT have 20 years of experience when it comes to laser-specific computer simulation and modeling. Since 2010, they have also had access to a high-power computer cluster built as part of the Center for Nanophotonics, all of which has allowed the Aachen-based scientists to make definite progress on various laser-based processes. Industrial partners visiting the fair were shown five sample applications for laser-machined products and process developments, including efficient display glass cutting (TRUMPF laser technology) and the improved water-jet-guided laser cutting system (SYNOVA).

Rapid polygon scanners for efficient use of USP lasers

The big advantage of using ultrashort pulse lasers is that they enable cold ablation, whereby material is removed without causing thermal damage to the surrounding area. But this works only as long as not too many pulses overlap – which is not easy to ensure at pulse frequencies in the MHz range and spot sizes of 20 µm. In fact the spot has to be moved at speeds of over 100 m/s to achieve this.

Experts at Fraunhofer ILT have now developed a polygon scanner with a 20 mm aperture and a focal length of 163 mm that is capable of achieving scanning speeds of up to 360 m/s. It can treat a 100 x 100 mm² area of a workpiece in 3 seconds, and has a scanning action that moves in two directions simultaneously. One plane of movement is the progress of the laser beam as it moves through the scanner, while the high-speed up and down movement of the workpiece along a different axis represents the second dimension. Depending on the positioning of both axes, the laser can be piloted at frequencies of up to 40 MHz. This means that the full power of modern USP sources can be brought to bear on the workpiece with great effect. In order to highlight its machining speed and precision, experts used the polygon scanner to engrave a metallic calling card in a live demonstration.

Kilowatt USP laser with record brilliance

Fraunhofer ILT has already set standards in recent years with the development of its high-performance USP systems. This year for the first time it showcased a femtosecond laser system that is capable of achieving a beam parameter product of under 2 mm*mrad with 1 kW of output power. A similar system was used to set a new world record for generating green short-pulse radiation under laboratory conditions: the system managed to deliver 430 watts at a wavelength of 515 nm.
The USP system developed in Aachen is based on a MOPA amplifier configuration, with an open platform setup that allows different seed sources to be combined flexibly and any given pulse train to be amplified as required. An active beam position control system makes it much easier to combine the beam source and amplifier, while also ensuring the system remains stable in the long term.
The system’s extremely high performance parameters allow correspondingly high machining throughput and lower costs per watt. In keeping with the phrase “Femto goes Macro”, the system is thus ideally suited for working larger surfaces, for instance structuring the surfaces of wind turbines. Scientists have also expressed great interest in using the system as a pump in OPCPA systems for generating few-cycle pulses and tunable pulses.

Digital photonic production is gaining ground

Digital photonic production processes are based on the idea of taking digital data and using it to produce components using laser technology. Unlike in conventional processes, the complexity of the component is almost irrelevant. Another advantage of using light as a tool is that even the smallest batch sizes can be produced cost effectively.

In a joint presentation at the specialist digital photonic production stand at the fair, the Aachen-based Fraunhofer Institutes, the Chair for Laser Technology LLT at RWTH Aachen University and various industrial partners including Concept Laser, Realizer, SLM Solutions, MTU, Bego Medical, Citim and Schepers together showcased various facilities and design software tools for use in industry. The components made using additive laser technology represented a range of different industrial fields. A print roller with a surface structured using short pulse lasers was on display to demonstrate what is possible using ablative processes.

A further example of ablative processes is In-volume Selective Laser Etching (ISLE), whereby specific areas within the volume of the workpiece are modified using a laser. These areas are then removed using wet chemical processes. With this method, complete 3D hollow structures can be made out of materials such as glass, directly from digital data and on an industrial scale.

At the specialist booth at the trade fair, the technology’s enormous potential was demonstrated in collaboration with various industrial partners, using selected examples from the automotive and aerospace industries, the energy technology sector, lightweight construction, and medical and consumer technology.

The next LASER World of Photonics trade fair takes place June 22-25, 2015, and the next World of Photonics Congress June 21-25, 2015.

Contacts

Dr. Jens Schüttler
Modelling and Simulation Group
Phone +49 241 8906-680
jens.schuettler@ilt.fraunhofer.de

Prof. Wolfgang Schulz
Head of the Chair for Nonlinear Dynamics of Laser Processing NLD
Phone +49 241 8906-204
wolfgang.schulz@ilt.fraunhofer.de

Dipl.-Phys. Oliver Nottrodt
Process Control and System Technology Group
Phone +49 241 8906-625
oliver.nottrodt@ilt.fraunhofer

Dipl.-Ing. Peter Abels
Head of the Process Control and System Technology Group
Phone +49 241 8906-428
peter.abels@ilt.fraunhofer.de

Fraunhofer Institute for Laser Technology ILT
Steinbachstraße 15
52074 Aachen, Germany