High-Speed Tandem Gas Metal Arc Welding of Sheet Metal

The pursuit of productivity improvements in competitive manufacturing environments drives the development and optimization of cutting-edge technologies. One such technology is tandem gas metal arc welding (T-GMAW). T-GMAW is a version of gas metal arc welding (GMAW) that uses two power supplies, two wire feeders, and a specialized torch to establish two electrically isolated welding arcs with a common weld pool. While T-GMAW has been available for decades, recent developments in pulse-synchronization technology have greatly improved process stability by significantly reducing the detrimental effects of arc interaction. Among the advantages of T-GMAW are significant increases in deposition rate and travel speed, as well as a reduction in heat input. While T-GMAW is commonly used in heavy fabrication, recent research at EWI has investigated a number of different high-speed welding applications. T-GMAW has additional benefits when compared to other high-speed joining processes such as high-speed laser and hybrid-laser systems. Among these are significant reductions in equipment cost and complexity, as well as a higher tolerance to part fit-up variation.

Previous work at EWI has demonstrated high-speed welding of steel sheet at travel speeds up to 4.5 m/min (177.2 ipm) using conventional T-GMAW with solid steel wire, as well as tandem gas metal arc braze welding (T-GMABW) with silicon-bronze wire. The focus of this study was to identify and investigate specific applications of T-GMAW and T-GMABW of interest to industry and further develop EWI’s high-speed T-GMAW expertise.

To increase the value of this study to industry, EWI consulted with stakeholders to identify applications of interest. The first application identified was low-cost fabrication of tailor-welded blanks. The equipment costs associated with laser welding blanks are very high, and expensive precision-shearing equipment is required as part fit-up is critical. T-GMAW offers significantly lower equipment costs and a higher tolerance for part fit-up variation. In this application, 1.0-mm (0.040-in.) -thick 980-MPa (142-ksi) uncoated steel sheet was welded to 1.4-mm (0.055-in.) -thick 590-MPa (86-ksi) uncoated steel sheet in a square-butt joint configuration.

Based on the results of welding trials, it was concluded that T-GMAW is a viable option for manufacturing TWBs. Full-penetration square-groove welds were made at travel speeds up to 4.5 m/min (177.2 ipm), with the most consistent results observed at 3.5 m/min (137.8 ipm). Test welds were made using rough-sheared coupons with gaps up to 0.3 mm (0.011 in.), demonstrating an increased tolerance to fit-up variation when compared to laser welding, where the maximum recommended fit-up variation for the material thicknesses used is approximately 0.004 in. (0.1 mm).

In the second application T-GMABW was used for fillet welding of lap joints of 0.7-mm (0.0275-in.) -thick 270-MPa (39-ksi) 45/45 galvanealed steel sheet and 0.75-mm (0.030-in.) -thick 270-MPa (39-ksi) 45/45 galvanealed steel sheet. While this joint configuration was selected due to its use in “gutter” welds common to auto-body construction, it is widely used in industry for sheet metal fabrication. Silicon-bronze filler was used as these joints are non-structural and the lower heat-input required for the T-GMABW process was expected to result in minimized degradation of the galvanealed coating.

T-GMABW trials successfully demonstrated the use of silicon-bronze wire to join galvanealed steel sheet in a lap-joint configuration at travel speeds up to 3.5 m/min (137.8 ipm). Parameters were developed that resulted in minimal spatter and minimal backside coating degradation.

Future work will include further development of starting and stopping parameters to provide a consistent bead shape for TWB welds as well as the development of pulse waveforms specifically for T-GMABW with silicon-bronze wire.

For more information, please contact Marc Purslow at mpurslow@ewi.org or call 614.688.5150, or Menachem Kimchi at mkimchi@ewi.org or call 614.688.5153.