MODELLED DEPENDENCY OF THE DIRECT ABSORPTION ON THE KEYHOLE WALL WAVINESS DURING 1 MICRON- AND 10 MICRON-LASER WELDING

摘要

During keyhole mode laser welding the absorption ofrnthe laser beam at the vapour capillary, the keyhole,rntakes directly place by Fresnel absorption. From ultrarnhigh speed imaging it was observed that waves streamrndown the keyhole front. By introducing a wavy surfacernto the modelled keyhole front, the dependency of thernabsorption on the slope of the waves was studied. Evenrnwaves of low roughness rapidly cause shadowing,rnparticularly at low welding speed. For 1 μm-lasers therndirect absorptance increases for higher waviness whilernCO_2-lasers follow the opposite trend. The CO_2-laserrnoperates close to the Brewster-maximum for smoothrnkeyholes, while waves introduce reflective domains.rnThe sensitivity to waviness decreases with increasingrnspeed for the 1 μm-wavelength lasers.