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Two wire tandem submerged arc welding process facilitates high rate of joint filling with little increase in the overall rate of heat input due to the simultaneous deposition from two electrode wires. Since the lead wire is usually connected to a DC welding arc and the trail wire to a pulsed AC arc, the tandem process requires appropriate selection of a large number of process variables. A quantitative understanding of the effect of the welding conditions on weld joint dimensions and weld thermal cycle is difficult through experimental studies only. Here we present a three-dimensional heat transfer analysis based on finite element method using two independent volumetric heat sources to account for heat input from two welding arcs. The shapes of the heat sources are estimated based on the original joint geometry and welding conditions. The results show that the trail wire current pulses significantly influences the reinforcement height and weld width while lead wire current affects the depth of penetration. For a constant trail wire effective current, increase in the negative pulse time results in greater reinforcement height and reduced weld width with very little influence on the cooling rate and weld strength. In contrast, increase in trail wire negative current pulse increases both reinforcement height and weld width while reduces cooling rate and weld strength.KEY WORDS: tandem submerged arc welding; numerical modeling; heat transfer analysis.

Two wire tandem submerged arc welding (SAW-T) involves application of two electrode wires to form a single weld pool with one wire leading the other along the weld interface. Realisation of the influences of the lead and trail wire currents on the weld bead morphology and the weld strength are important in SAW-T. The authors here present an experimental and computational investigation on SAW-T process. The concept of central composite rotatable design is followed for designing the experimental trials. The final weld width and the reinforcement height showed greater sensitivity to trail current while the penetration was influenced primarily by lead current. A three-dimensional heat transfer analysis is carried out using finite element method. The computed weld profiles were validated with the corresponding measured results. The computed cooling rates showed a decline with higher welding current and, the corresponding sample welds showed reduced acicular ferrite percentage and lower weld strength.

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