Indirect measurement of keyhole pressure oscillations during laser deep penetration welding

Abstract

The laser deep penetration welding process is highly dynamic. Besides melt pool oscillations the keyhole geometry as well as the pressure inside the keyhole oscillate at high frequencies. Those keyhole oscillations are assumed to support the unwanted process pore formation. Due to limited technological possibilities a direct method for observing the pressure and radius oscillations inside the keyhole is not state of the art. Based on an existing indirect measuring system by observing the exiting keyhole gas flow during the first few milliseconds of welding a new approach of indirectly measuring keyhole pressure oscillations during welding is presented. As the vapor exits the keyhole at varying angles an air gas stabilization is used leading the vapor in a defined direction. The combined gas flow of keyhole vapor and stabilization gas is deviated by a known additional rectangular applied air gas flow. The angle oscillation of the deviated gas flow is a measure of the pressure oscillations in the keyhole. The time signal of the angle oscillation has been recorded and examined for frequency analysis. Typical frequencies for the welding process at varying process parameters could be found. An increase of pressure frequencies could be observed when changing the beam profile from a Gaussian-like to a top hat beam.The laser deep penetration welding process is highly dynamic. Besides melt pool oscillations the keyhole geometry as well as the pressure inside the keyhole oscillate at high frequencies. Those keyhole oscillations are assumed to support the unwanted process pore formation. Due to limited technological possibilities a direct method for observing the pressure and radius oscillations inside the keyhole is not state of the art. Based on an existing indirect measuring system by observing the exiting keyhole gas flow during the first few milliseconds of welding a new approach of indirectly measuring keyhole pressure oscillations during welding is presented. As the vapor exits the keyhole at varying angles an air gas stabilization is used leading the vapor in a defined direction. The combined gas flow of keyhole vapor and stabilization gas is deviated by a known additional rectangular applied air gas flow. The angle oscillation of the deviated gas flow is a measure of the pressure oscillations in the keyhole. T...