Gravitational effects on the weld pool shape and surface deformation during GTAW and LBW

An analytical and experimental study was conducted to investigate the effects of gravitational orientation on the weld pool shape during gas tungsten arc welding (GTAW) and laser beam welding (LBW) for 304 stainless steel. Welding was conducted by varying scan velocity and gravitational orientation, e.g., welding upward opposing gravity (parallel-up or vertical-up weld), welding downward with gravity (parallel-down or vertical-down weld), and welding perpendicular to gravity (perpendicular weld). The behavior of the weld pool shape associated with degree of convection was analyzed in light of the weld surface deformation. As the translational velocity (Va) decreased and the weld pool size increased under the constant arc power, more significant effects of gravitational orientation were observed on both weld pool shape and surface deformation. The ll-D weld displayed maximum mass accumulating ahead of the arc due to gravity and the ll-U weld showed deepest surface depression. This will cause a smaller arc diameter (d_a) for ll-D as compared with the ll-U case, resulting in a more hemispherical shape of the weld pool in the ll-D case. As V_a increased to 4 mm s^-1, the weld pool shape did not vary significantly as a function of gravitational orientation. At 8 mm s ^-1, the weld pool shape for the ll-D showed more convexity in the weld pool bottom than the ll-U case. For 1.6-2.6 kW laser beam welding (LBW), however, insignificant effect of gravitational orientation was observed because beam diameter was mostly constant within a range of weld surface deformation.