increased travel speed used to produce the equivalent levels of penetration when using alternating shielding gases, will also have beneficial effects with regards to weld induced distortion. The model has also shown that the application of alternating shielding gases results in a shorter leg length, Figure 8, thus confirming the experimental results and is a consequence of the concentrated arc column that helium produces [25]. The effective throat thickness is shown to increase with the use of alternating shielding gases, Figure 9, this is primarily linked to the added convexity of the weld metal and increased penetration with the addition of helium. Figure : Effect of Shielding Gas Configuration on Predicted Leg Length Figure : Effect of Shielding Gas Configuration on Predicted Effective Throat The macro images, Figure 10, show that a typical alternating shielding gas weld produces a narrower weld with increased convexity, this along with the results generated by the ANN model show that there is a trend between the shielding gas and the weld geometry. As reported by Kang et al. [3], alternating shielding gases creates complex flow vectors within the molten weld pool whereas constant gas flows produce a steady flow vector. It was reported that helium produces a flow vector which circulates inwards, which will result in a narrower, more convex, weld profile. This is most probably due to the Marangoni effect in that the shielding gas configuration affects the surface tension of the weld, resulting in a thermo-capillary convection phenomenon. As the Marangoni effect is governed by the temperature gradient on the weld pool surface and the temperature coefficient of the surface
increased travel speed used to produce the equivalent levels of penetration when using alternating shielding gases, will also have beneficial effects with regards to weld induced distortion. The model has also shown that the application of alternating shielding gases results in a shorter leg length, Figure 8, thus confirming the experimental results and is a consequence of the concentrated arc column that helium produces [25]. The effective throat thickness is shown to increase with the use of alternating shielding gases, Figure 9, this is primarily linked to the added convexity of the weld metal and increased penetration with the addition of helium. Figure : Effect of Shielding Gas Configuration on Predicted Leg Length Figure : Effect of Shielding Gas Configuration on Predicted Effective Throat The macro images, Figure 10, show that a typical alternating shielding gas weld produces a narrower weld with increased convexity, this along with the results generated by the ANN model show that there is a trend between the shielding gas and the weld geometry. As reported by Kang et al. [3], alternating shielding gases creates complex flow vectors within the molten weld pool whereas constant gas flows produce a steady flow vector. It was reported that helium produces a flow vector which circulates inwards, which will result in a narrower, more convex, weld profile. This is most probably due to the Marangoni effect in that the shielding gas configuration affects the surface tension of the weld, resulting in a thermo-capillary convection phenomenon. As the Marangoni effect is governed by the temperature gradient on the weld pool surface and the temperature coefficient of the surface
Galloway_AM_Pure_Artifical_neural_network_prediction_of_weld_geometry_performed_using_GMAW_with_alternating_shielding_gases_12_Apr_2011.docx