Reduction of spatter formation by superposition of two laser intensities

By using laser light as energy source for material processing, high intensities on the work piece surface can be achieved enabling high processing speeds and thus high productivity. In case of laser beam welding this advantage also leads to a small welding seam as well as a small heat affected zone. The past developments in the field of laser system technology result in a reduction of the investment costs and systems with increased power outputs at better beam quality which further increases the achievable intensity, processing speed and productivity. However, available laser power cannot always be transferred to increasing processing speed since imperfections such as the formation of spatters occur, especially in the range of 5 m/min to 20 m/min. The occurrence of spatters is strongly connected to conditions in and around the keyhole in laser deep penetration welding.This paper shows an experimental approach to reduce the spatter formation by using an adapted intensity distribution. An increase of the melt pool width close to the work piece surface is achieved by superimposing two laser spots resulting in a significantly reduced spatter formation. The assumption is that the increased area of the melt pool leads to a reduction of the flow velocity of molten material and therefore its momentum decreases. Finally, the droplet escape condition is not being fulfilled. The experimental tests were executed with high alloyed austenitic steel sheets using a high power disk laser and a diode laser. The mass loss was reduced significantly using this approach in comparison to the process with a standard intensity distribution. The high speed camera footage shows a different behavior of the weld pool due to the additional laser spot. Moreover, metallurgical cross-sections demonstrate the influence of the approach on the shape of the melt pool and the resulting weld seam.