Quality assurance in pulsed laser welding

Abstract

The growing use of lasers for welding in industrial applications has accentuated the need for effective quality assurance measures. The ability of accurately measure key characteristics such as penetration depth and seam quality for pulsed laser welding are essential to priorily certify and finally guarantee a demanded quality. This paper describes a method to ensure quality by using the physical effect of enhanced absorption in deep keyholes due to multiple reflexions at their walls. To realize this method, it is necessary to measure and to process the signals of a sensor detecting the laser power that is reflected out of the keyhole. The operability of this approach is proved for steel by fundamental experimental investigations with a pulsed Nd: YAG-laser. The presented results that are discussed concerning essential parameters (i.e. peak laser power, pulse duration) show the distinct correlation between measured signals and obtained penetration depths. Further evidence concerning the quality is gained by evaluating the signal shape during each laser pulse. Welding processes causing either high or low quality weld seams can be identified by merely seperating different signal phases that typically correlate with different states while pulsed laser deep welding.The growing use of lasers for welding in industrial applications has accentuated the need for effective quality assurance measures. The ability of accurately measure key characteristics such as penetration depth and seam quality for pulsed laser welding are essential to priorily certify and finally guarantee a demanded quality. This paper describes a method to ensure quality by using the physical effect of enhanced absorption in deep keyholes due to multiple reflexions at their walls. To realize this method, it is necessary to measure and to process the signals of a sensor detecting the laser power that is reflected out of the keyhole. The operability of this approach is proved for steel by fundamental experimental investigations with a pulsed Nd: YAG-laser. The presented results that are discussed concerning essential parameters (i.e. peak laser power, pulse duration) show the distinct correlation between measured signals and obtained penetration depths. Further evidence concerning the quality is gained ...