New Automated Tandem Process for Agile Fillet Welding of Ship Structures

Abstract

New ship designs are calling for complex, lightweight panels made of thinner steel (as thin as 3 mm) for weight and structure optimization. For stiffener welding on ship panels, thin steel demands small, precision fillet welds in order to reduce panel distortion and improve downstream processes. The existing panel welding systems in most shipyards use flux-cored arc welding with mechanical seam tracking and cannot cope with the complexity and precision required. Tandem gas metal arc welding (T-GMAW) has shown an increase in deposition rate of up to three times that of single-electrode GMAW while offering process robustness. However, when T-GMAW was combined with through-the-arc (TTA) seam tracking by weaving, the travel speed was limited to 1 m/min (40 in./min) and the minimum fillet weld size was 5 mm. Rotating electrode (RE) GMAW utilizes TTA seam tracking by rotating the contact tip and electrode around a small diameter at 10 to 100 Hz. This method results in capabilities to seam track while making welds as small as 2 mm at travel speeds as high as 2.5 m/min (100 in./min). RE-GMAW is also a robust process with enhanced bead shape characteristics ideal for horizontal fillet welds. However, because RE-GMAW is a single-electrode process, it cannot match the deposition rates of T-GMAW. This project developed rotating lead tandem (RLT) GMAW, which is a new process that offers deposition rates comparable to T-GMAW with the seam-tracking capability of RE-GMAW. An objective was to develop the preferred torch setup and electrode conditions that provide a complete range of fillet weld sizes for agile processing of ship structures. Procedures were developed for 3-, 4-, 6-, and 8-mm fillet welds with RLT-GMAW using the ARCWISE (EWI, Columbus, OH) procedure development method on a seam-tracking T-joint test. Process robustness was assessed by evaluating fusion quality, leg size, convexity, process stability, and spatter susceptibility. A preferred torch setup was determined that met the project objective. RLT-GMAW was shown to offer deposition rates that were near or equal to standard tandem GMAW, especially on smaller 3and 4-mm fillets. While offering high deposition rates, it also demonstrated high-resolution seam tracking at travel speeds up of 2.3 m/min on 3-mm fillets.