Adaptive feedback beam shaping of the CO 2 welding laser

Abstract

The depth of penetration is probably the most important factor that influences the quality of a laser weld. The depth strongly depends on the focus of the welding beam. The sublimating material forms plasma vapors, that act as a lens and defocus the laser beam. Our contribution presents a method to compensate this phenomenon using an adaptive mirror - a mirror with flexible surface that can adjust the shape of the welding beam. The mirror is regulated by a feedback control loop so that the focus of the laser beam and the penetration depth remain in an optimal range. Since the only possibility to state the penetration depth is to monitor outer effects to estimate desired parameters. a sensor unit is used to monitor the optical emissions of the plasma vapors and the measured data are inputs to an algorithm that estimates the penetration depth. We have done several experiments that study the relation of the adaptive mirror focus and the laser beam shape and how it influences the penetration depth. The estimation results are compared with material samples from test welds. On the basis of these experiments, a preliminary version of a control system was developed and a tested. The tests has shown that the implementation of the control system has positive influence on the quality of the resulting weld.