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Product Code: ICA13_1901

High-Efficiency Laser Processing of CFRP
Authors:
Rudolf Weber, IFSW, University of Stuttgart; Stuttgart Germany
Volkher Onuseit, Ifsw, University of Stuttgart; Stuttgart
Simon Tscheulin, Ifsw, University of Stuttgart; Stuttgart
Thomas Graf, Ifsw, University of Stuttgart; Stuttgart
Markus Grafried, Ifsw, University of Stuttgart; Stuttgart
Presented at ICALEO 2013

Industrial large-volume application of CFRP requires efficient and high-quality processing. Laser processing of carbon fibres is very promising but highly energy consuming due to the large sublimation enthalpy of graphite. In contrast, the sublimation enthalpy of the embedding plastic matrix is lower by about a factor of ten and is often the reason for unwanted thermal damage caused by heat conduction along the fibers.
However, choosing appropriate laser parameters and processing strategies this effect can be utilized to realize a very efficient ablation of CFRP: In the first step only small kerfs are created by sublimating the carbon material. By producing two close kerfs perpendicular to the fibre orientation fibre fragments are created which can be removed in a second step by just sublimating the matrix material.
This can be achieved with three methods: I) In the case of fragment lengths in the range of a few hundred microns, heat conduction of the heat deposited during the processing of the kerfs themselves is sufficient to delaminate the fiber fragments. For larger fragments, additional heating of the matrix around the fragments might be necessary. II) In the case of laser wavelengths between about 400 nm and 1 µm, where the matrix is almost transparent, the fiber fragments are heated above the evaporation temperature of the matrix causing delamination. III) In the case of highly absorbed laser wavelength, e.g. at 10 µm, the matrix is directly removed.
The detached fiber fragments are either removed by the ablating material pressure or by an additional process gas jet.
The present paper compares the required absorbed energy densities for the different processing strategies of CFRP. The basic mechanisms are discussed as well as their influence on the extent of matrix damage in the surrounding of the processed region caused by heat conduction and heat accumulation. The theoretical considerations will be compared with experimental results achieved with ns-drilling of blind holes and ns-cutting of different CFRP materials.

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