Product Code: ICA12_802

Impact of Thermal Focal Shift on Laser Cutting Processes with High Brightness Lasers
Authors:
Sasia Eiselen, Bayerisches Laserzentrum GmbH; Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander Univ. Erlangen-Nuremberg; Erlangen Germany
Heiko Zapf, Bayerisches Laserzentrum GmbH; Erlangen Germany
Eugenia Mantel, Bayerisches Laserzentrum GmbH; Erlangen Germany
Lukas Hofmann, Chair of Photonic Technologies, Friedrich Alexander Univ. Erlangen-Nuremberg; Erlangen
Michael Schmidt, Bayerisches Laserzentrum GmbH; Erlangen Graduate School in Advanced Optical Technologies (SAOT), Chair of Photonic Technologies, Friedrich-Alexander Univ. Erlangen-Nuremberg; Erlangen Germany
Presented at ICALEO 2012

The increasing use of high brightness lasers with output powers in the kilowatt range for laser fusion cutting processes leads to big advantages concerning yield and quality. Conversely, these laser sources are very susceptible to external disruptions and therefore tend towards instabilities. This becomes noticeable in the thermal focal shift which can be influenced by many different factors during the process and can easily extend the rayleigh range. The authors report on investigations of influences on the thermal focal shift at different optic configurations in laser cutting with singlemode and multimode high power fiber lasers. Changes of the beam caustic could be observed due the optical components in the laser processing head including the fiber end block. In consequence of the measured drift of up to four rayleigh ranges (singlemode laser) , the focal shift has a high impact on the cutting results. We investigated the impact of this drift on fusion cutting processes at metal sheets with thicknesses of 0.1 mm to 1.5mm and show a feasible technique for experimental determination of the temporal focal shift. The authors gratefully acknowledge the funding of the Erlangen Graduate School in Advanced Optical Technologies (SAOT) by the Deutsche Forschungsgemeinschaft (German Research Foundation - DFG) within the framework of the German Initiative for Excellence.