Abstract
Interest in research on the application of variable-polarity cold metal transfer mode in wire-based direct energy deposition has been growing; particularly popular are investigations into the respective influences of polarity, amplitude of the arc current, and polarity variation sequence on the quality of the final product manufactured via additive manufacturing. The application of the electrode-negative phase is more capable of yielding relatively large droplets and increasing the weight of the deposited material. However, the proportions of the electrode positive phase are typically larger than those of the electrode-negative phase because it maintains arc stability and droplet transfer. This discrepancy has prevented the accurate evaluation of the effects of the polarity mode and polarity sequences on the deposition characteristics associated with variable-polarity cold metal transfer. In this study, variable-polarity cold metal transfer was performed using a tuned waveform, and the effects of the electrode-negative pulsing ratio and pulse repetition on the geometrical features and deposition rate were assessed. The weight tended to increase with decreasing welding speed and increasing electrode-negative pulsing ratio. The number of repetitions influenced molten pool behavior, and when sufficiently high, induced ripple formation via droplet accumulation below the electrode. In addition, the effects of the electrode-negative pulsing ratio and repetition on the microstructure formation were analyzed. It was revealed that the average grain size was related to the amount of supplied energy and polarity switching during grain formation.
Highlights
Publisher’s Note: MDPI stays neutralAdditive manufacturing (AM) is a promising alternative for fabricating extremely high buy-to-fly ratio components with complex geometry [1]
The deposition rate of laser or electron beam deposition is in the order of 2–10 g/min [2–4], compared with 50–130 g/min for arc welding-based AM technology [5–7]
Wire arc additive manufacturing (WAAM) using an arc heat source is a promising technology for manufacturing with medium to large size in terms of productivity, cost-competitiveness, and energy efficiency [1,7–9]
Summary
Additive manufacturing (AM) is a promising alternative for fabricating extremely high buy-to-fly ratio components with complex geometry [1]. Wire arc additive manufacturing (WAAM) using an arc heat source is a promising technology for manufacturing with medium to large size in terms of productivity, cost-competitiveness, and energy efficiency [1,7–9]. WAAM typically entails the use of gas metal arc welding (GMAW), plasma arc welding, and gas tungsten arc welding (GTAW) power sources to build parts using a layer-by-layer approach. Among the WAAM arc welding processes, GMAW entails the utilization of a coaxially fed wire and an arc between the end of the wire and the base metal; this setup enables high energy efficiency because anode and cathode heating facilitate the melting of the wire and base metal. GMAW power supplies are designed for constant current, constant voltage, or pulsed current with an electrode-positive (EP) polarity; an electrode-negative (EN) polarity; or a variable-polarity with regard to jurisdictional claims in published maps and institutional affiliations
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