A Semi-Analytical Nonlinear Regression Approach for Weld Profile Prediction: A Case of Alternating Current Square Waveform Submerged Arc Welding of Heat Resistant Steel

Abstract

The complexity in weld profile caused by abrupt change in polarity in square waveform welding is investigated through the development of a model capable to accurately predict weld profile. A semi-analytical model is conceived wherein characteristic attributes of a composite parabolic–elliptic function, which represent the weld profile, are obtained through nonlinear regression (NLR). The proposed model is demonstrated for its efficacy in the prediction of weld profile over a wide range of welding parameters, vis-à-vis, welding current, frequency, electrode negative (EN) ratio, and welding velocity. The investigation suggests that the center and outer cores of welding arc remains more active during positive and negative polarity, respectively, that leads to distinct macroscopic zones in weld cross section and thus, necessitates a composite profile for representation of weld profile. The intersection of the zones forms a metallurgical notch which the investigation offers a method to estimate and thus control. Unlike the convention continuous arc welding, the waveform arc welding caters welding at higher velocity without compromising the weld penetration and almost abolishing the metallurgical notch as well.

Performance Evaluation of Alternating Current Square Waveform Submerged Arc Welding as a Candidate for Fabrication of Thick Welds in 2.25Cr-1Mo Heat-Resistant Steel

“…The results obtained for change in current and welding speed agree with those of Lee et al [22] and Chandel [24]. This outcome further establishes the utility of square waveform arc welding as it is known to support weld penetration, even at very high welding speeds [8].…”

“…Toma et al [6] recommended the AC square waveform over DCEP for better toughness in low-temperature environments. The practical advantages of the AC square waveform encouraged scientific studies using advanced tools, like three-dimensional computational fluid dynamics simulations [7], semi-analytical nonlinear models for weld profile prediction [8], and high-speed videography of metal transfer [9]. The higher heating while a negative electrode increases the melting rate that results in a higher frequency of metal droplet detachment.…”

“…The higher heating while a negative electrode increases the melting rate that results in a higher frequency of metal droplet detachment. The AC square waveform can maintain penetration at higher welding speeds [8]. In combination with DCEP (at the lead wire), the trailing electrode with the AC square waveform in tandem welding enhances the deposition rate [10].…”

Parametric Models and Process Map for Alternating Current Square-Waveform Welding of Heat-Resistant Steel

“…In combination with DCEP (lead wire), the trailing wire with the AC square waveform in tandem welding improves the deposition rate. The waveform control offers a distinct weld bead shape with a bay area (as shown in the later part) that can be computed by composite penetration profile functions depending on materials such as ellipse-ellipse for steel [24] and parabola-ellipse for heat-resistant steel [19].…”

“…Square waveform welding has not been extensively investigated for process models as it is one of the latest technologies for SAW. The main areas of investigation for square-waveform welding have been limited to performance evaluation [18], weld bead shape prediction [19], signal processing [20], and thermal modelling [21]. Studies on process models and maps available for conventional submerged arc welding [22] are not reported for square-waveform arc welding.…”