Optimisation of welding using two Nd-YAG laser beams combined at workpiecesurface

Two Nd- YAG laser beams were combined at a certain point on the workpiece s urface to increase weld penetration depth. One of the beams was a pulsed la ser beam, and the other was a continuous wave laser beam or a modulated las er beam. Using this combination of laser beams, a wide range of welding con ditions, such as average power, peak power, and power density, could be sel ected. A high peak power pulsed laser beam would play a significant role in forming a keyhole, bur a severe spatter loss problem could be encountered u nder high peak power laser conditions, thus the conditions necessary to pre vent spatter loss were investigated. The greatest penetration depth is obta ined under the critical conditions for spatter loss. Critical conditions fo r spatter loss are controlled by the peak power of a pulsed laser beam, thu s deeper weld penetration is obtained using a pulsed laser beam with higher average power, that is, of longer pulse width and/or a higher repetition r ate within the limit of the oscillator output. Moreover,, spatter loss is r educed under conditions providing large molten zones lit the weld, thus a h igher peak power pulsed laser beam can be employed under such conditions. L ai ge molten zones are obtained using a modulated laser beam of a high aver age power and/or low welding speeds. (C) 2000 IoM Communications Ltd.