Project: Reflective Diffractive Optical Elements for Industrial Cutting Applications with High-Power CO2 Lasers

The REDOECUT project develops reflective diffractive optical elements (DOEs) for industrial high-power CO2 laser cutting processes. Generally two different laser cutting processes must be distinguished: fusion cutting and oxygen cutting. Since oxygen cutting is mostly affected by the exothermic reaction and less by the laser, the Ps focus on the fusion cutting process which is COly laser-influenced. For sheet metal cutting applications the most interesting thickness range is between 4 and 10 mm, as envisaged in REDOECUT. Regarding the feed rate, the current benchmark is set by a machine equipped with a 6 kW CO2 laser reaching cutting speeds up to 4.0 m/min. The REDOECUT project aims for increasing the cutting speed by at least 50% through optimising the melt flow on the cutting front by adapted laser intensity distributions._x000D__x000D_At present, transmitting DOEs for CO2 laser radiation are mostly made of zinc selenide (ZnSe) substrates provided with an anti-reflection coating due to its high refraction index of ˜ 2.4. Since the coating damage threshold prohibits an irradiation with laser intensities higher than 3.5 kW/cm², common transmitting DOEs are generally not suitable for high-power CO2 applications. Moreover, no information is available about the use of DOEs for high-power CO2 laser applications in industrial environments at all. In addition to the relatively low damage threshold, a health hazard originates from the toxic zinc selenide substrates as well as from the – often used – radioactive thorium fluoride coating in case of lens damage. Consequently, extensive cleaning of the contaminated laser cutting system is necessary._x000D__x000D_By developing reflective components with new diffractive surfaces and process technologies with optics for high-power cutting applications, REDOECUT improves the competitiveness of CO2 laser cutting processes substantially. The optimisation of the focused beam concerning its profile when using these optical components results in coupling the laser power into the work piece more efficiently. For example, by elongating the Rayleigh length of the laser beam the cutting edge shows a more rectangular geometry, which leads to an increased cutting speed for thicker sheet metal going along with reduced production time and costs._x000D__x000D_The CO challenge in this project is to identify and to understand the impact of laser beam shaping enabling higher speed and edge quality for metal cutting processes or for increasing process stability. Therefore, the optimum laser material interaction using shaped laser beams (e.g. multi foci, top hat) is analysed via numerical simulation by LZH. SILIOS develops the reflective DOEs on mirror substrates corresponding to the calculated optimised beam shape by using high-precision manufacturing technologies like photolithography, etching or layer deposition to process high-tech free-space optical components with µm resolution. Using an optic design and simulation software, the reflective DOE can be calculated from the raw laser beam profile together with the envisaged beam profile for the industrial cutting processes. _x000D__x000D_REDOECUT provides, for the first time, DOEs for higher laser powers up to 6 kW with the capability to correct spherical aberrations by a diffractive correction layer. Effective cooling of these mirror components from the backside prevents thermal focus shift. With these reflecting and focussing optical elements, common ZnSe focussing optics for CO2 laser cutting machines are substituted. LZH develops robust and faster processes for cutting of metals with the manufactured reflective DOEs. Hence, sustainable process strategies lead to an improved cutting process regarding the use of higher material thickness and higher processing speed during constant edge quality according to the industrial demands. Finally, TRUMPF and HOEDTKE integrate the reflective DOEs into their commercial laser cutting stations and demonstrate the progress on industrial applications together with possible customers.

Acronym REDOECUT (Reference Number: 5248)
Duration 16/09/2010 - 15/09/2013
Project Topic By developing novel reflective diffractive optical elements (DOEs) for beam shaping of high-power CO2 laser radiation and the according laser cutting process, REDOECUT enables a doubling of the energy efficiency and a 50% increase in cutting speed along with an enhanced cutting quality.
Project Results
(after finalisation)
Realisation of first reflective DOEs for CW high power CO2 lasers._x000D_Realisation of 3D numerical simultations of cutting process._x000D_Increase of knowledge on laser beam / cutting process interaction._x000D_Increase of knowledge on simulations tools and use of them._x000D_Improvement of measurement accuracies of the etched diffractive structures (clean room micro-technologies)
Network Eurostars
Call Eurostars Cut-Off 3

Project partner

Number Name Role Country
4 Trumpf Werkzeugmaschinen GmbH+CO.KG Partner Germany
4 Laser Zentrum Hannover e.V. Partner Germany
4 Hoedtke Kiel GmbH & Co KG Partner Germany
4 SILIOS Technologies Coordinator France