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The submerged arc welding (SAW) process can achieve high productivity and deep penetration, making it an important process for joining large diameter and/or thick-walled components. SAW typically uses direct current electrode positive (DCEP) polarity because of power source availability, good arc stability, and deep penetration. Greater deposition rates are possible with direct current electrode negative (DCEN) polarity, but can result in reduced penetration and arc stability.
Heat input (Eq. 1) is typically used to monitor energy supplied for a given weld length. It incorporates current, voltage and travel speed, but does not address waveform variables such as balance or offset that can be controlled with squarewave alternating current (AC-SQ). A series of welds were produced using the same nominal heat input variables (recorded heat input ranged from 1.4 to 1.7 kJ/mm) but with different waveform settings. As heat input increases (Fig. 1), wire feed speed (WFS) generally increases, but with significant scatter.
Equations 2 and 3 can be used to estimate heat input supplied by the DCEP and DCEN phases of the AC cycle. It is then possible to determine relationships of polarity-specific heat input values on various weld outputs (e.g., WFS) by using Equation 4 and normalizing the data. Figure 2 shows clear trends between normalized heat input and WFS.
Additional AC-SQ welds were performed using different waveform settings. WFS values and bead profile measurements were compared with traditional, instantaneous and polarity-specific heat inputs. Waveform analysis was performed to confirm the effects of waveform variables, and to further refine polarity-specific heat input formulas.
Figure 1 - The effect of traditional heat input on WFS
Figure 2 - The effect of polarity-specific heat input on normalized WFS