Optimization Of Ternary Gas Composition For Tandem Narrow Gap GMAW

In order to solve the problem of low efficiency of thick plate welding,the tandem narrow gap GMAW were chosen for thick plate welding.But the problem of poor sidewall fusion is likely to occur during the narrow gap welding.Therefor,it is further suggested to change the protective gas component?turn the traditional binary protective gas to the Ternary protective gas?to change the arc behavior,so that the sidewall penetration could increase to avoid the problem of poor sidewall fusion.Because of the high thermal conductivity of He,the arc temperature distribution can be uniform,so the Ar + CO₂ + He are chosen as the welding protection gas.First,carry out narrow gap mono-filament welding at flat welding position.The air flow rate was kept as 40 L / min.The content of CO₂?He?was changed by fixed He?CO₂?content,and the remaining parts was filled with Ar.Through the high-speed camera to observe the impact of changes of the arc shape,and take the photo of arc.Observe and summarize the effect of protective gas content on arc root and arc length,And analysis of arc behavior changes in the law to get the appropriate protective gas process window.It is found that when the He content ranges from 5% to 15%,and the CO₂ content ranges from 5% to 15%,you can get a more stable welding process.In addition,the voltage and current values were calculated during the welding process to observe the impact of protective gas content on welding voltage and current value.The droplet transition was observed by using high-speed camera and combining with the welding voltage signal and current signal collected simultaneously with high-speed camera to analyze the droplet transition form during the welding process.So that we could analyze the relationship between weld surface forming and droplet transfer.It is found that with the increase of CO₂ content,the transition form of droplet is changed from jet transition to droplet transition and finally becomes short circuit transition.With the increase of He content,the droplet transition form changes from the droplet transition to the jet transition,and then becomes the droplet transition.the metallographic pieces is cut in the middle of the weld and measure the weld sidewall weld penetration after grinding to summarize the effect of the protective gas content on the weld sidewall penetration.It was found that when the He content was 10%,the weld sidewall was the largest,and when the CO₂ content was 10%,it could also be a good weld.Finally,based on the protective gas process window,the experiment of respond surface method was designed.The CO₂ content and He content were the main factors,and the depth of penetration and longitudinal depth of the main thread were measured.The relationship between the response value and the factors is established,and the influence of the variables of single factor on the weld sidewall penetration and longitudinal penetration is studied,and the effect of the interaction between the two factors on the response value is studied.According to the obtained response surface,the optimal protection gas process has been found,the optimal protection gas process is 10% He and 11% CO₂.The experimental results show that the actual value is not the same as the predicted value.The fitting equation is accurate.