Berlin 2001 – wissenschaftliches Programm

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K: Kurzzeitphysik

K 5: Laser material processing

K 5.3: Vortrag

Donnerstag, 5. April 2001, 18:05–18:20, EB107

Modeling of melt pool flow for laser drilling with short pulses — •Andreas Ruf, Peter Berger, Friedrich Dausinger, and Helmut Hügel — IFSW Universität Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart

In the case of laser drilling with longer pulselengths melt ejection often represents an efficient method of material removal. On the other hand, for precision drilling solidified melt layers on the crater walls are undesirable and hence one usually applies shorter pulses for these applications to avoid a thick melt layer. Nevertheless, also in this case melt can never be avoided completely. As to high process quality and stability, this liquid layer should preferably be ejected entirely. This contribution deals with the question up to what extent this is possible for nanosecond pulses. To clarify this question, several models have been applied ranging from simple analytical estimations to complex numerical FEM simulations. These approaches demonstrate that the resulting high process pressures in principle can lead to high ejection velocities but these are usually only reached after long acceleration periods on the order of 100 ns. For shorter pulses the pulse duration limits the melt dynamics considerably since the accelerating vapor pressure drops very fast after the end of the pulse. Still, melt can be ejected long after the laser heating without further acceleration as the surface remains molten at least for some microseconds. With increasing hole depth melt expulsion becomes more and more difficult and a high pressure within the crater is necessary to keep the capillary opened.