Research On Welding Procedure And Technology Of High Speed P-GMAW+GMAW

To increase the welding speed of P-GMAW+GMAW greatly,welding current must be increased properly,which may lead to weld defects such as humping and undercutting.In order to solve this problem effectively,the double wire GMAW is usually used to improve the welding speed and efficiency.At present,the research of the double wire GMAW is mainly focused on Tandem P-GMAW,but the welding characteristics and application prospects of P-GMAW+GMAW,a new double wire GMAW welding method,are still lack of comprehensive and in-depth research.Based on the synchronization acquisition system of images and electrical parameters,the arc shape and fluid flow process of GMAW welding process at high welding speed,with different welding modes,were compared and analyzed.It was found that the formation of humping bead was caused by liquid flow at high speed leading by large current,cyclic occurring liquid thin layer,premature solidification of liquid thin layer.The leading current and trailing current of the Tandem P-GMAW must be same.When high current parameter and high welding speed was adopted in Tandem P-GMAW,the trailing arc would hinder the backward flow of liquid metal with high speed,caused by leading arc,and give rise to a new backward liquid flow with high speed.Although there was no typical humping in the weld formation,there were a lot of undercutting.There was no phase relation between the two wires of P-GMAW+GMAW.So high current parameter was allowed for leading wire to ensure sufficient penetration and deposited metal.And the trailing wire adopted small current parameter pulse current to hinder the backward flow of liquid flow with high speed and improve the heat distribution of molten pool and the fluidity of liquid metal.The arc shape,fluid flow process and weld formation of P-GMAW+GMAW were analyzed,when wire distance and trailing current and welding speed were all changing.The arc interruption of trailing arc only occurred when the wire distance and trailing current were too small.As the trailing current increased,the influence of the trailing arc on the backward flow of liquid with high speed increased,which could decrease the backward flow velocity of liquid and improve the quality of the weld formation.But when the trailing current reached a certain level,the trailing arc would give rise to backward flow of liquid with high speed.At this point,increasing the trailing current would aggravate the turbulence of the weld pool,which was not conducive to the weld formation.And increasing the wire distance could decrease the electromagnetic attraction between leading arc and trailing arc,and increase the stability of welding process.When the wire distance was too large,the heating and insulation effect on the tail area of weld pool,by two arc,would be decreased.At the same time,temperature gradient increased and fluidity of liquid metal decreased,which would lead to the occurrence of undercutting easily in weld formation The increase of welding speed would aggravate the phenomenon of backward dragging of two arcs,which would cause the droplets to fall backward and improve the flow velocity of the backward liquid flow.At this time,the welding defects such as undercutting were more likely to occur in the weld formation.