Effects of Active Gases on Droplet Transfer and Weld Morphology in Pulsed-Current NG-GMAW of Mild Steel

Guoqiang Liu,Haichao Cui,Qi Xu,Xinhua Tang,Fenggui Lu

doi:10.1186/s10033-021-00583-2

Abstract

The current research of narrow-gap gas metal arc welding (NG-GMAW) primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect. However, the high cost and operation difficulty of the methods limit the industrial application. In this study, small amount of active gases CO2 and O2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO2, being added into the pure argon shielding gas, changes from 5% to 25%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O2 is added. Both CO2 and O2 are favorable to stabilizing arc and welding process. O2 is even more effective than CO2. However, O2 is more likely to cause slags on the weld surface, while CO2 can improve the weld appearance in some sense. The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant. This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.

Highlights

Thick and large structural components are widely applied in various fields, such as offshore drilling platforms, shipbuilding, high-pressure vessels, and nuclear industry
Narrow-gap gas metal arc welding (NG-GMAW) is a preferential technology in manufacturing such components owing to its great advantages, such as less filler metal, higher productivity, low heat input and minimal welding distortion [1, 2]
The results revealed that the metal transfer always remained a pulsed spray transfer when C O2 was kept at 10%, no matter how the helium content varied in a certain range [20]

Summary

Introduction

Thick and large structural components are widely applied in various fields, such as offshore drilling platforms, shipbuilding, high-pressure vessels, and nuclear industry. Laser-arc hybrid welding and tandem GMAW are commonly utilized in narrow gap welding processed to eliminate the lack-of-fusion defect and improve the weld formation [8,9,10,11] All of these methods mentioned above can improve the weld bead formation but need specially designed welding torches or additional equipment, which means more investment. The variation of weld bead formation is attributed to that the shielding gas directly determines the arc behavior and surface tension which influence the metal transfer and fluid flow in the welding pool [17,18,19]. A series of welding experiments were carried out to evaluate the effects of varied gas compositions on the arc behaviors, metal transfer, welding process stability and weld morphology in pulsed current NG-GMAW of ferrous metal.

Results and Discussion

Welding Process Stability

Weld Bead Formation

Conclusions