James Christopher Hansen
Published: 2020
Total Pages: 99
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Aluminum gas metal arc welding (GMAW) uses inert shielding gas to minimize weld pool oxidation and reduce susceptibility to porosity and lack of fusion defects. For aluminum shipbuilding, Naval requirements highly recommend the use of helium – argon mixtures or 100% (pure) helium shielding gas to provide a broader heat field and ensure proper weld fusion, particularly at the weld toes. Pure argon shielding gas can be used but it has proven to be susceptible to lack of fusion and porosity defects, particularly in thick sections that pose a large heat sink where argon’s lower thermal conductivity promotes a narrower arc heat field and poorer weld penetration. The continued use of helium is a concern because it’s a finite resource that costs approximately 5 times argon. In this study, the rotating electrode pulsed gas metal arc welding (REP-GMAW) process was investigated as a way to solve the argon shielding fusion problem, mitigate helium consumption, and provide shipbuilding cost savings. The target application was horizontal and vertical erection butt joints made from 5083 aluminum plate. An advanced REP-GMAW torch was used that permitted the evaluation of a range of electrode spin diameters and frequencies. Compared to torch weaving at a couple hertz, the arc heat field and bead shape can be more effectively changed since the rotation speeds can be up to 5,000 rotations per minute (~83 hertz). A series of bead on plate tests were used to evaluate the relationship between ER5183 electrode rotation parameters and arc power on constant deposit area bead shape. These tests were compared to stringer beads (no oscillation) that were made with argon, helium, and helium-argon shielding gases. Preferred rotating electrode parameter relationships were developed with pure argon for producing weld beads that had underbead fusion profiles that were equivalent to helium-based weld deposits. For preferred deposit sizes for groove welding, preferred bead shape welds were achieved when electrode spin frequency was 50 spins per inch and rotation diameter setting of 2. The second part of the study developed rotating electrode GMA-P welding procedures for 17-mm V-groove butt joints with ceramic backing in both the horizontal and vertical position. The REP-GMAW process was found to improve joint fusion and out of position deposition rate. By distributing the heat, the rotating arc weld pool showed better stability compared to stringer beads, especially in the horizontal position for making the root pass on ceramic, and then multiple fill passes to complete the joint. Deposition rates were up to 5.16 pounds / hour which is very good for aluminum erection welding. Based on this study, REP-GMAW using pure argon shielding gas is a suitable replacement for traditional GMAW of aluminum using pure helium or helium – argon mixtures Future studies with REP-GMAW should investigate bead shape and productivity improvements when welding with other alloys commonly used in shipbuilding. In addition, future studies should explore REP-GMAW arc physics and the interactions between the rotating electrode and the weld puddle.
