Abstract Scope |
There is a continual effort to develop welding systems that address the skills gap and welder shortage. Decades ago, pulsed spray transfer was developed, which shortened the learning curve and allowed less skilled welders to deposit sound weld metal. Subsequently, welding waveforms were developed to address specific applications such as open root pipe welding or sheet metal welding. More recently, systems have come into play that match welding waveforms, wire feed systems and welding electrodes to further enhance ease of use and improve productivity. One example is a welding system comprised of multiple electrodes that are controlled by welding waveforms and physical spacing to achieve a single arc to the workpiece.
A study was undertaken to evaluate the properties of mild and low-alloy steel weld metal deposited using this single-arc, multi-wire, waveform-controlled system with both flux cored arc welding (FCAW) and gas metal arc welding (GMAW) processes. These welds were compared to their equivalent single wire welds using standardized joints welded with solid and flux-cored electrodes. Control variables were heat input, welding position and electrode design. Deposited weld metal was evaluated for productivity, soundness, mechanical properties and chemical composition.
Based on the observed results, select welds and electrodes were further evaluated physically, chemically and metallurgically to gain an understanding of the operability differences and failure modes. Among the findings, it was determined that increasing heat input affected the weld metal toughness in a similar manner to those deposited with single electrodes. The larger weld nugget that resulted from higher heat input and higher deposition rates left weld metal that was not fully refined by the subsequent weld passes. The mild steel and low alloy weld metals in this study exhibited similar overall trends, yet some designs and alloy systems were less influenced by these changes.
Single-arc, multi-wire processes delivered filler metal at a faster rate and with fewer defects than comparable single wire processes. An arc cone-to-puddle ratio concept (Ař:Př) was developed to quantify an important relationship. Higher Ař:Př ratios made arc manipulation easier, improved sidewall fusion, and lowered defect generation. This modified arc shape was found to be especially important with less skilled welders. Productivity increases exceeding 30% were documented when comparing this welding system to equivalent single wire GMAW and FCAW processes on typical fillet and multi-pass groove welds. Mechanical properties were comparable or better than traditional single wire processes.
Single-arc, multi-wire waveform controlled welding can have a positive impact on both ease of use and productivity. However, specific guidelines must be followed to achieve optimal results. In particular, it is important to select electrodes that will maintain good arc stability and weld metal properties at the higher heat input rates associated with this welding system. The diameter and surface of the electrodes, the amount of preheating, their physical spacing and the welding waveforms were all shown to influence the arc transfer and deposition rates. The optimal combination of these factors resulted in high quality and high productivity semiautomatic welding.
Keywords:
Gas Metal Arc Welding - GMAW
Flux Cored Arc Welding – FCAW
Deposition Rate
Mechanical Properties
Waveform Controlled Welding
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