Research On Weld Formation Of Narrow-gap GMAW With Swing Arc System In Horizontal Position

With rapid development of nuclear power, shipbuilding and otherheavy equipment manufacturing industries, an increasingly demand forsteels is becoming larger and larger, the thickness is also growing thicker.However, limited to the production capacity of forging equipment, themajority of the plates are thinner than250mm by one rolling process. Forthose thicker than that, a practicable manufacturing method is twice rollingwith two superimposed steel billets which need to be welded in thesurrounding connections. Base on this rolling method to produce largethicker steel, a newly swing arc welding system is introduced for narrowgap gas metal arc welding (NG-GMAW) in the horizontal position in thispaper, and the pre-research experiments have got good welds.In this research, the original NG-GMAW torch is optimized for betterperformance and improvement by replacing the drive motor, gas protectivecover, contact tip, etc., so that it could meet the welding requirements inthe horizontal position. The Q345D steel is selected as the base material,and the welding parameters were investigated to gain an optimal range inthe situation of single-layer welding through orthogonal experiments, inwhich the points are focused on the effects of arc swing amplitude andfrequency on the final weld formation. Then sagging molten pool andincomplete sidewall penetration existing in the multilayer welding arestudied and solved through the regulation of welding procedure, the weldsget good shapes and without defects. Finally, with the help of high-speedphotography system, the images of droplet transfer and swing arc motionduring welding are captured, which show a direct view of the droplettransfer mode and the variation range of arc heating region and their effects on the final weld bead formation.Experimental results show that the narrow gap welding torch canmeet the need for deep gap welding that deeper more than60mm in thehorizontal position, and there are steady arc burning and excellent weldappearance in the welding process. The swing arc enlarges the force areaof the arc on the molten pool and the arc force effectively suppresses thesagging pool. And swing motion increases the arc heating range andimproves uneven heating situation along sidewalls, complete penetrationcan be seen from the cross-sections of horizontal welds. There exist bothspray transfer and projected transfer modes, and swing arc reaches uniformheating on both the upper and lower sidewalls. The Z-direction tensile testsof the welds show that all fractures occur in the base metal, indicating thatthe weld quality meets tensile requirements. Comparing the three kinds ofmultilayers welding, hybrid welding with unilateral groove has theassembly simplicity and is more suitable for the actual welding needs.