Abstract Scope |
Introduction: Aluminum gas metal arc welding (GMAW) routinely requires back gouging and back welding when fabricating erection joints in a shipyard environment. These steps negatively impact both project cost and schedule. Rotating electrode pulse GMAW (REP-GMAW) has been evaluated on ceramic backing to allow for single-sided erection butt joint welding. Previous work involving REP-GMAW has involved increasing productivity through narrow groove welding. This has been found to show negligible increases in productivity. This study is focused on the use of REP-GMAW technology to improve aluminum weld bead shape, particularly on the root pass. The process is being evaluated using 100% argon shielding gas. In a shipyard environment these weldments are normally fabricated with an argon – helium shielding gas mixture. The ability to transition these welds to 100% argon shielding will result in a significant cost savings.
Experimental Approach: The REP-GMAW process is being evaluated for improved bead shape and fusion characteristics on both 17 mm and 32 mm 5083 aluminum plate with a 60- degree included angle bevel. Welding is completed in the 1G, 2G and 3G positions using a multi- position adjustable table and a bug-o tractor that is interfaced with the SpinArc welding torch.
Weld deposit size was controlled by adjusting the wire feed speed to travel speed ratio (WFS/TS ratio). Both torch angle and work angle were varied while filling the joint to allow for appropriate bead placement, particularly in the 2G position where the impact of gravity was significant. Before moving to welding the 60-degree included beveled joints, a bead on plate study was completed to understand the impact of arc rotation frequency and spin diameter on the resulting bead shape. With basic rules surrounding the arc rotation parameters, welding of the beveled joints began.
Weldments fabricated in each position and at each thickness must be verified by radiographic testing to ensure weld soundness. Welds are sectioned, polished and etched to evaluate parameters before preparing assemblies to be evaluated by radiographic testing.
Results and Discussion: The objective of this project is to develop parameters and weld procedure specifications for REP-GMAW in 1G, 2G and 3G positions using 100% argon shielding gas. The initial bead on plate study in the 1G position allowed for the bracketing of welding parameters from lack of fusion defects at low powers, to defects caused by plasma jet at high power levels. The bead on plate study also allowed for an understanding of the impact of spin frequency and spin diameter. As spin frequency was increased, the depth of penetration at the weld toes was notably improved. The ability to improve weld toe fusion is a critical improvement achieved through the SpinArc REP-GMAW technology as it is a common issue when welding aluminum. As spin diameter was increased, the bead diameter was also increased. At the high end of spin diameter an increase in spatter was observed.
Preliminary results have shown that REP-GMAW is quite robust in the 2G position and can achieve high deposition rates of 4.68 lbs/hour. Arc rotation has proven to create a fast freezing puddle that more resistant to the impact of gravity in the 2G position. Arc rotation has proved particularly useful on the root pass on ceramic backing, allowing for improved gap bridigability and sidewall penetration. Arc rotation also assists with sidewall wetting on the root pass creating a smooth bead that assists with the welding of subsequent passes.
Conclusion: The REP-GMAW process has displayed the ability to improve bead shape and fusion characteristics of aluminum particularly on the root pass on ceramic backing. The use of REP-GMAW has allowed the application of increased power, wire feed speed and travel speed with enhanced root bead fusion. Preferred procedures were developed for 1G and 2G positions, and ongoing development is in-progress to develop 3G (vertical-up) procedures.
Acknowledgement: This project was funded by Austal USA, Naval System Warfare Center Carderock Division (NSWCCD) and Lightweight Innovations For Tomorrow (L.I.F.T). |