Impact of fume particles in the keyhole vapour

Abstract

During laser material processing, the energy of the laser beam needs to be efficiently and constantly transported to the processing zone to guarantee constant processing. However, spatters or ejected particles from the keyhole can absorb and scatter the laser energy leading to inhomogeneous heat input and can initiate defect occurrence like pore formation. The impact of ejected particles from the keyhole on the energy transport of the laser beam is not completely understood since they are difficult to observe due to the small size and high speeds of the ejections. In this work, the particle characteristics were derived from a simulation of the keyhole wall movement. The behavior of the calculated particles in a side shielding gas jet was calculated to derive the height, at which the particles leave the laser beam and are not interrupting the laser energy transfer to the processing zone. Low impulse values of the particles were calculated e.g., at defocusing positions slightly underneath the material surface, where also highest melt pool sizes were found. These observations indicate that the fume particles can be one reason to limit the energy delivery. An efficiency increase can be achieved by adjusting the keyhole parameters to a more stable keyhole.