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Proceedings Paper

Aerodynamic window for high precision laser drilling
Author(s): Steffen Sommer; Friedrich Dausinger; Peter Berger; Helmuth Hügel
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Paper Abstract

High precision laser drilling is getting more and more interesting for industry. Main applications for such holes are vaporising and injection nozzles. To enhance quality, the energy deposition has to be accurately defined by reducing the pulse duration and thereby reducing the amount of disturbing melting layer. In addition, an appropriate processing technology, for example the helical drilling, yields holes in steel at 1 mm thickness and diameters about 100 &mgr;m with correct roundness and thin recast layers. However, the processing times are still not short enough for industrial use. Experiments have shown that the reduction of the atmospheric pressure down to 100 hPa enhances the achievable quality and efficiency, but the use of vacuum chambers in industrial processes is normally quite slow and thus expensive. The possibility of a very fast evacuation is given by the use of an aerodynamic window, which produces the pressure reduction by virtue of its fluid dynamic features. This element, based on a potential vortex, was developed and patented as out-coupling window for high power CO2 lasers by IFSW1, 2, 3. It has excellent tightness and transmission properties, and a beam deflection is not detectable. The working medium is compressed air, only. For the use as vacuum element for laser drilling, several geometrical modifications had to be realized. The prototype is small enough to be integrated in a micromachining station and has a low gas flow. During the laser pulse, which is focussed through the potential flow, a very high fluence is reached, but the measurements have not shown any beam deflection or focal shifting. The evacuation time is below 300 ms so that material treatment with changing ambient pressure is possible, too. Experimental results have proven the positive effect of the reduced ambient pressure on the drilling process for the regime of nano- and picosecond laser pulses. Plasma effects are reduced and, because of the less absorption, the drilling velocity is increased and widening effects are decreased. So the process is more efficient and precise. Furthermore, the necessary pulse energy for the drilling of a certain material thickness is reduced and so laser power can be saved.

Paper Details

Date Published: 26 April 2007
PDF: 7 pages
Proc. SPIE 6346, XVI International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, 634625 (26 April 2007);
Show Author Affiliations
Steffen Sommer, Forschungsgesellschaft für Strahlwerkzeuge (Germany)
Friedrich Dausinger, Univ. Stuttgart (Germany)
Peter Berger, Univ. Stuttgart (Germany)
Helmuth Hügel, Univ. Stuttgart (Germany)

Published in SPIE Proceedings Vol. 6346:
XVI International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers
Dieter Schuöcker, Editor(s)

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