Product Code: ICA11_308

Understanding the Influence of the Focal Position in Laser Welding on Spatter Reduction
Authors:
Jan-Philipp Weberpals, Institut fuer Strahlwerkzeuge (IFSW); Stuttgart Germany
Philipp Krueger, Institut fuer Strahlwerkzeuge (IFSW); Stuttgart Germany
Peter Berger, Institut fuer Strahlwerkzeuge (IFSW); Stuttgart Germany
Thomas Graf, Institut fuer Strahlwerkzeuge (IFSW); Stuttgart Germany
Presented at ICALEO 2011

Particularly the automation and industrialization of thermal material processing with lasers of 1 micrometer-radiation makes high demands on the resulting welding quality. Indeed, current laser systems with strong focusability exhibit a high innovation potential in many application ranges, for example the possibility of adjusting the welding depth to even small material thicknesses. However, at such high focusability there are also disadvantages observed especially in laser welding of steel expressed in a strong spatter behavior generated at the rear keyhole wall. This undesired instability mainly occurs by using lasers with 1 micrometer-radiation in contrast to CO2-lasers which is why it is essential to understand its fundamentals to push the industrial use of 1 micrometer-laser systems.
In order to improve the spatter behavior which requires the knowledge of the interaction between keyhole and melt pool the inclination of the front keyhole wall plays an important role. This study shows how to manipulate the inclination of the front keyhole wall by changing the focal position. In doing so the keyhole formation is observed by a novel process monitoring system which allows determining the spatial inclination of the capillary. According to that a displacement of the focal position below the surface yields a reduced number of spatters due to the straightening of the front keyhole wall. By using additional high-speed cameras it is possible to distinguish the main driving forces for spatter generation and to accent the importance of the inclination of the front keyhole wall.

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