Heat Source Characteristics of Ternary-Gas-Shielded Tandem Narrow-Gap GMAW.

Cai Cai,Dong Dong,Lin Lin,Fan Fan,Murphy Murphy,Yang Yang

doi:10.3390/ma12091397

Cai Cai, Dong Dong + Show 4 more

Open Access

https://doi.org/10.3390/ma12091397

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Journal: Materials	Publication Date: Apr 29, 2019
Citations: 11	License type: CC BY 4.0

Affiliation: Harbin Institute of Technology, CSIRO Manufacturing

Abstract

The characteristics of the welding heat source for tandem narrow-gap gas metal arc welding are examined for different ternary shielding gas (Ar-CO2-He) compositions. Results of previous calculations of arc properties for bead-on-plate geometry are adapted to the narrow-gap geometry to predict these characteristics. The heat source concentration factor decreases and the maximum heat flux density increases as the helium content increases, which leads to an increased welding heat efficiency. Addition of CO2 up to around 10% also increases the heat efficiency. When the CO2 content exceeds 10%, the heat source concentration factor increases significantly and the heat efficiency decreases. The shielding gas composition also affects the heat source distribution. The heat source characteristics are applied to a computational fluid dynamic model of the weld pool to predict the weld shape, and the predictions are verified by experiment. The results indicate that the appropriate addition of helium to the shielding gas can increase the heat transferred to the peripheral regions of the arc and increase the sidewall penetration.

Highlights

Narrow-gap (NG) welding is an efficient welding method for thick plates [1], in which a narrow and deep gap is used instead of wide-angle groove
The results indicated that the helium content led to changes to the arcresults properties that using numerical simulation for a standard bead-on-plate
One part of the heat source is distributed on the sidewall where it melts the sidewall metal, and the other part is distributed on the groove bottom to ensure depth of penetration

Summary

Introduction

Narrow-gap (NG) welding is an efficient welding method for thick plates [1], in which a narrow and deep gap is used instead of wide-angle groove. Narrow gap arc welding contains narrow gap tungsten arc welding (NG-GTAW), narrow gap gas metal arc welding (NG-GMAW) and narrow gap submerged arc welding (NG-SAW). Compared with NG-GTAW and NG-SAW, NG-GMAW has a high welding efficiency; heat input is low and the welded joint has good properties, so the NG-GMAW has a better application prospect. The shielding gas composition can modify the arc properties and heat transfer performance, which will affect the final weld formation. It is expected that more heat can be transferred to the peripheral regions of the arc, which leads to the increase of the metal fusion area. Urmston [3] found that a more rounded weld profile could be obtained with the addition of helium to the shielding gas in GMAW.

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Discussion

Conclusion