Product Code: ICAL06_101

Analysis of Basic Processes inside the Keyhole during Deep Penetration Nd-Yag CW Laser Welding
Authors:
Remy Fabbro, LALP (CNRS)/GIP GERAILP; Arcueil Cedex France
Sonia Slimani, Air Liquide-CTAS; St OUEN L'AUMNE France
Frederic Coste, LALP (CNRS)/GIP GERAILP; ARCUEIUL France
Francis BRIAND, Air Liquide-CTAS; St OUEN L'AUMNE France
Presented at ICALEO 2006

The keyhole geometry in deep penetration laser welding results of the combination of several complex processes and their relative importance is not really established today. Firstly, we will report several results concerning the geometry of the keyhole where its inclination has been determined as a function of the main operating parameters (incident laser intensity and welding speed) and a dynamical model allows us to recover the observed evolution. Secondly, the reflectivity of the keyhole front has been measured: the rather low observed reflectivity (less than about 30%) can only be consistent with an high degree of deformation of the vapor/liquid interface. Finally, the resulting evaporation process from the keyhole front is very determinant for the melt pool overall stability: by measuring the corresponding ablation pressure, one can understand why the metallic vapors ejected perpendicularly from the keyhole front can perturb the rear melt pool, when the keyhole front inclination is adequate. We also explain the stabilization of the melt pool oscillations and the control of its flow field by using a side gas jet with adequate dynamical pressure. All these different results allow us to elaborate an overall consistent model of the keyhole behavior.