UNDERSTANDING THE INFLUENCE OF THE FOCAL POSITION IN LASER WELDING ON SPATTER REDUCTION

摘要

Particularly the automation and industrialization ofrnthermal material processing with lasers of radiation ofrn1 μm makes high demands on the resulting weldingrnquality. Indeed, current laser systems with strongrnfocusability exhibit a high innovation potential inrnmany application ranges, for example the possibility ofrnadjusting the welding depth to even small materialrnthicknesses. However, at such high focusability therernare also disadvantages observed especially in laserrnwelding of steel expressed in a strong spatteringrngenerated at the rear keyhole wall. This undesiredrninstability mainly occurs by using lasers with radiationrnof 1 μm in contrast to CO_2 lasers which is why it isrnessential to understand its fundamentals to push thernindustrial use of laser systems of 1 μm.rnIn order to improve the spatter behavior, a soundrnknowledge of the interaction between the front keyholernwall inclination and the melt pool is required. In thisrnstudy emphasis is laid on how to manipulate therninclination of the front keyhole wall by changing thernfocal position. In doing so, the keyhole formation isrnobserved by a novel process monitoring system whichrnallows determining the spatial inclination of therncapillary. According to this, a displacement of thernfocal position below the surface yields a reducedrnnumber of spatters due to the steepening of the frontrnkeyhole wall. By using additional high-speed camerasrnit is possible to distinguish the main driving forces forrnspatter generation and to accent the importance of therninclination of the front keyhole wall.