Abstract
Energy coupling rate during welding of Al-Mg-Si alloy by single and twin spot Nd:YAG laser beams was measured calorimetrically at various input energies. Two beams were aligned parallel to welding direction and the distance was varied from 0.36 to 1.0 mm. The coupling rate in single spot beam welding was higher than that of twin spot beam at same power level. However increasing power, both were saturated in the same level at 80%. Energy coupling rate became larger as the beam distance became smaller. Measured coupling rates fit with modified Couffe-Dausinger model that determine coupling rate by penetration depth and focal spot size calculated from twin spot combined lineally. It is considered that modified focal spot size represents the keyhole opening size affects on reflection loss after multi-reflection in the keyhole.
