Study On Activating Flux For Gas Metal Arc Welding

Because of high production efficiency,low welding cost,and good welding quality,CO2 gas shielded welding is widely used in automobiles,construction machinery,and construction.In order to improve production efficiency of CO2 gas shielded arc welding,it is necessary to increase welding speed and welding current,which is accompanied by the problem of increased spatter.Splash cleaning has no production value and consumes a lot of manpower and material resources.In welding process,the use of 20%CO2 +80%Ar instead of CO2 gas can effectively improve the stationarity and arc stability of the droplet transfer of gas metal arc welding,leading to reduction of the amount of splashing and proportion of large splashing.However,due to the use of 20%CO2 +80%Ar mixed gas shielded welding instead of CO2 gas shielded welding,the weld penetration becomes smaller and roots become narrower.With same welding parameters,undercuts root is easily produced at the weld spot of the root tack weld..In this paper,the activating flux gas metal arc welding is researched and developed to solve the problem that the depth of 20%CO2+80%Ar gas mixed shielded welding melting pool is shallow and is easy to produce root undercut.Firstly,the effect of single composition activating flux on weld formation was studied.In this paper,14 common flux SiO2,TiO2,MgO,Cr2O3,B2O3,BaO,CaO,Al2O3,Fe2O3,MoO3,MnO,MoS2,CaF2,and K2CO3 were used.The single composition activating flux is applied to 20%C02+80%Ar mixed gas shielded welding,and 14 kinds of single composition activating flux are tested to determine weld surface appearance,shape of the weld pool,the weld depth,weld width,the ratio of depth to width and reinforcement.The mechanism of the increase of weld penetration by oxides is discussed.It is considered that the increase of weld depth by oxide activating flux is the result of the combination of "surface tension gradient theory" and "arc constriction theory".At the same time,the influence of the welding process parameters on the increase of the depth of the activating flux was studied,and the reason why the increase of the depth of the activating flux in the high current welding rate of the gas shielded arc welding was not obvious was analyzed.The results show that with the increase of welding current,the effect of increasing the depth of TiO2 and K2CO3 gradually decreases,and the effect of increasing the depth of CaF2 increase first and then decrease.With the increase of welding speed,effect of TiO2,K2CO3 and CaF2 to increase weld depth is reduced.It is considered that effect of increasing depth of the activating flux in gas shielded metal arc welding is not obvious because the current is too large and the welding speed is too fast,which results in less depth with activating flux such as TiO2,CaF2 and K2CO3.Secondly,in order to obtain better weld depth with activating flux,the multi-component activating flux formulation was designed by using the mixture uniform design method.The experimental data on the influence of the activating flux composition on depth was obtained through welding test,and the quadratic polynomial stepwise regression method was used.The mathematical model of the relationship between the composition of the activating flux and the depth was established.With the goal of maximum depth,the formulation of the multi-component activating flux was optimized to be 31.91%Al2O3,0.94%MgO,1.25%K2CO3,64.71%TiO2,and 1.19%MnO.The welding test was carried out with this formulation,and the depth of the weld was increased significantly.The percentage increase in weld depth was 33.52%,which was in good agreement with the model predictions.Finally,in order to facilitate the engineering application of the activate flux,the effect of the addition of activate flux to flux-cored wire powder on the weld formation was studied.The test results show that the activating flux-cored wire increases the depth of the weld,and the test formula increases the percentage of weld depth to 66.67%.At the same time,it was found that the optimum amount of activate flux is 40%.The use of low-melting point NaF in the activating flux partially or completely replaces the high-melting fluorite,which can effectively reduce the weld crown value of fillet welds and improve the weld formation of fillet welds.