Study On The Humping Formation In High Speed GMAW And Suppression With The Hybrid Process Of GMAW+TOPTIG

Gas metal arc welding(GMAW) is one of high efficient welding process which is widely used. This process is simple and easy to achieve automation. In recent years, many enterprises have put forward the need to further improve the production efficiency of GMAW. Therefore, high speed welding is one of choice. But for high speed welding, it is easy to produce the appearance of weld defects such as undercutting, humping with the increase of welding speed. In order to avoid forming defects in the process of high speed welding, the principle of forming there defects must be analyzed and then the effective suppression method is found. In this paper, we are mainly focus on the formation mechanism of the humping defects for the process of GMAW and the suppression method is proposed. This study has important significance for engineering application of high speed welding process.This study is focus on humping defects of gas metal arc welding(GMAW) with the higher welding speed of 2m/min. The common phenomenon of humping formation will be observed according to test different welding parameters such as welding speed, arc length and shielding gases. Building of high speed camera system with laser illumination will help understanding the mechanism of humping formation. The test results show that “solid spot” under arc of GMAW is the defect source of humping formation. These “solid spot” are sometimes melted by the thin liquid metal under arc or backfilling molten metal. However, these small “solid spot” is easy to converge and become the bigger solid area. The bigger solid area not only prevents the backfilling of behind portion of the weld pool, but limits the backward flow of molten weld metal of the front portion of the weld pool. So the bigger solid area will form the “valley” and the limited backward flow of molten weld metal of the front portion of the weld pool continuously accumulate and solidify to form a hump. For high speed welding, heat input imposed to the base metal is lower with the increase of welding speed. So melting liquid metal is thinner under the arc. Like “blowing to the water”, when blow the thin film of water, it is easy to appear the solid surface. So the arc force is easy to blow the thin film of melting liquid and form “solid spot”. Therefore, the amount of “solid spot” and the size of “liquid metal film” under the arc as well as the fluidity of backfilling molten metal determine the degree of humping defect.Based on the existing equipments and the analysis of humping formation mechanism, we developed a hybrid welding process of GMAW+TOPTIG in order to achieve high speed welding. The test results show that the hybrid welding process for high speed welding could suppress obviously the humping formation compared to the conventional GMAW process. The arc force of TOPTIG could push the backfilling molten metal to reduce the number of “solid spot” and the size of “liquid metal film” under the arc. The arc heat from TOPTIG could reduce the surface tension of backfilling molten metal and improve the fluidity of backfilling molten metal. In addition, the function of feeding wire of TOPTIG also suppress the additional defect source-“solid spot” which is produce by TOPTIG arc. Through the optimization of welding parameters combination between GMAW torch and TOPTIG torch, we could achieve the good results of 2m/min of welding speed, no humping formation and good weld appearance.