Résumé
Fluid flow motion controls energy transfer in the weld pool and drives solidification process. Experimental investigation of fluid flow during welding is made particularly difficult by unsteady movements in the molten pool. In this paper, proper orthogonal decomposition (POD) based on images during gas tungsten arc welding (GTAW) on thin plates is used to investigate coherent structures revealed by thermal field in the molten pool. The POD method is based on fluctuating gray levels related to surface temperature. Based on this decomposition, two dimensional spatial modes and temporal coefficients are calculated allowing the identification of regions where temperatures are correlated. To explore the potential of POD method, weld beads were performed on 316L stainless steel plate at three welding speeds (2.3, 3.3 and 4.3 mm.s −1) and constant current (80A). These three conditions lead to different sizes of fully penetrated weld pools and different temperature distributions. Spatial modes and temporal coefficients provide information on temperature fluctuations along the free surface. Based on POD first modes, thermal field is reconstructed along the free surface to understand the heat transfer. Combining these results with side-view observations of the arc allows us to derive three dimensional flow patterns within the weld pool.