Product Code: ICA10_106

Moving Humps at the Capillary Front in Laser Welding
Authors:
Peter Berger, IFSW, University of Stuttgart; Stuttgart Germany
Rainer Schuster, Institut FüR Strahlwerkzeuge (Ifsw); Stuttgart Germany
Helmut HüGel, Institut FüR Strahlwerkzeuge (Ifsw); Stuttgart Germany
Thomas Graf, Ifsw, University of Stuttgart; Stuttgart Germany
Presented at ICALEO 2010

Welding is a widespread application in laser mate-rials processing and the current development of laser systems with high beam quality helps to enhance the number of applications furthermore. However, the weld pool dynamics is still a limit-ing factor leading to weld defects and it seems to be more important for lasers with high focusabil-ity and for radiation around 1 µm compared to the 10 µm radiation.
In the time past a lot of investigations were per-formed to analyse the reasons for those instabili-ties: high speed imaging, X-ray analysis and also modelling. In addition to experiments with real workpieces (iron and aluminium alloys) a set of experiments with transparent materials such as water and ice were performed at IFSW in the last years.
As a result, flow components of the melt parallel to the laser beam were identified to be a major reason of the unwanted behaviour of the melt, driven by humps at the capillary front. Although such humps were discovered in X-ray analyses already in the 1980th and described in some mod-els, they were discussed relatively seldom.
For this contribution, welding with tracer material in the specimen was used to identify typical flow patterns, whereas the welding in transparent material shows directly typical flow structures. Finally, calculations of the beam propagation within the capillary clarify interesting differences for different wavelengths and beam quality. In this context, also the role of the polarisation will be discussed.