Dynamic Molten Pool Behavior And Penetration Control For Wire-filled Pulsed Gas Tungsten Arc Welding Of Pipe In Horizontal Position

In pipe welding production,it is often necessary to use wire-filled pulsed gas tungsten arc welding(GTAW-P)in horizontal(2G)position and controlling the uniformity of weld penetration is the key to ensure the weld quality.At present,most researches on control of weld penetration in GTAW focuses on the autogenous GTAW in the flat position.Due to the influence of gravity and the introduction of filler wire,the dynamic behavior of weld pool in wire-filled GTAW-P of pipe in horizontal position is not clear,and there is a lack of effective means to control the uniformity of weld penetration.The research will explore the interaction mechanism between the dynamic behavior of the weld pool and the penetration degree in fixed-point wire-filled GTAW-P of pipe in horizontal position,find the characteristic signal reflecting the penetration degree from the arc voltage signal,and finally control the backside weld width.Based on the volume of fluid(VOF)method,a numerical model of weld pool in fixed-point wire-filled GTAW-P of pipe in horizontal position is established.The Fluent software is redeveloped with the C language to calculate the temperature field and flow field of weld pool.The dynamic change of the weld pool surface in the welding process and its corresponding relationship with the penetration degree are obtained,and its mechanism is analyzed.When critical penetration occurs,the molten pool will collapse sharply.With the increase in backside molten pool width,the liquid metal flows to the backside molten pool during the peak current period is more and faster,resulting in the greater oscillation amplitude of the topside molten pool during the base current period.Also,the effects of the amount of wire filling and base current on molten pool oscillation are studied.An experimental setup of fixed-point wire-filled GTAW-P of pipe in horizontal position is designed and established.The dynamic behavior of molten pool and penetration degree of the weld are analyzed by visual sensing and electrical signal sensing.The continuous behavior of molten pool surface along with time are obtained,which verified the numerical simulation results.When critical penetration occurs,the collapse of the molten pool will cause the change in average peak voltage(ΔU~*)increasing.With the increase in backside molten pool width,the average base voltage((?)_b)and the fluctuation of base voltage(ΔUb)increase approximately linearly.Also,the effects of the amount of wire filling,base current and the distance between tungsten electrode tip and workpiece on characteristic signals are studied.As per step welding,the penetration control system is established and penetration control strategy is designed.BP neural network is used to model the relationship between characteristic electrical signals and backside molten pool width.The influences of step distance on the characteristic signal are explored,based on which the backside weld width is controlled in real time in the horizontal wire-filled GTAW-P process.The effectiveness of penetration control strategy is verified by variable gap and variable heat dissipation tests.