Experimental Investigation and Optimization of Welding Speed, Root Face and Arc-Mode Distribution in TWIN Tandem GMAW

TWIN Tandem gas metal arc welding (GMAW) combines two independently controlled wires in a common weld pool and offers high deposition rates and welding speeds. The present study experimentally investigates the combined influence of welding speed, root face, and arc-mode distribution between the leading and trailing wires on weld penetration in 12 mm S355J2+N steel. A total of 44 experimental runs were performed by robotic welding, each welded in triplicate (132 specimens). Welding speed and root face were treated as numerical factors, while the leading and trailing wire arc modes were varied between pulsed arc and spray arc. Cross-sections of the welded specimens were prepared, and the weld geometry was measured. Design-Expert was used to establish the relationship between the process parameters and penetration, to evaluate model adequacy, to analyse influential observations, and to perform numerical optimization, in which penetration was the primary response, while weld width and excess weld metal height, modelled from the same 44 runs, were included as range constraints. The response surfaces indicated a pronounced interaction between welding speed, root face, and arc-mode distribution. Numerical optimization identified a solution at a welding speed of 54.39 cm/min and a root face of 1.34 mm with pulsed arc operation on both wires. For this condition, the model predicted a penetration of 12.00 mm, a weld width of 18.02 mm, and an excess weld metal height of 1.22 mm, with an overall desirability of 1.000. A confirmation weld verified the predicted penetration. The results show that the selection of arc mode cannot be considered independently from welding speed and joint preparation, and that response-surface-based optimization provides a practical route for defining TWIN Tandem GMAW parameters for full-penetration welding.