Abstract
Development, optimisation and qualification of welding and additive manufacturing procedures to date have largely been undertaken on an experimental trial and error basis, which imposes significant costs. Numerical simulations are acknowledged as a promising alternative to experiments, and can improve the understanding of the complex process behaviour. In the present work, we propose a simulation-based approach to study and characterise molten metal melt pool oscillatory behaviour during arc welding. We implement a high-fidelity three-dimensional model based on the finite-volume method that takes into account the effects of surface deformation on arc power-density and force distributions. These factors are often neglected in numerical simulations of welding and additive manufacturing. Utilising this model, we predict complex molten metal flow in melt pools and associated melt-pool surface oscillations during both steady-current and pulsed-current gas tungsten arc welding (GTAW). An analysis based on a wavelet transform was performed to extract the time-frequency content of the displacement signals obtained from numerical simulations. Our results confirm that the frequency of oscillations for a fully penetrated melt pool is lower than that of a partially penetrated melt pool with an abrupt change from partial to full penetration. We find that during transition from partial to full penetration state, two dominant frequencies coexist in the time-frequency spectrum. The results demonstrate that melt-pool oscillations profoundly depend on melt-pool shape and convection in the melt pool, which in turn is influenced by process parameters and material properties. The present numerical simulations reveal the unsteady evolution of melt pool oscillatory behaviour that are not predictable from published theoretical analyses. Additionally, using the proposed simulation-based approach, the need of triggering the melt-pool oscillations is expendable since even small surface displacements are detectable, which are not sensible to the current measurement devices employed in experiments.
Highlights
Molten metal behaviour during fusion-based welding and additive manufacturing affects energy transport in melt pools, which in turn influences their geometrical evolution [1,2]
The oscillation frequencies obtained from the numerical simulations agree fairly well with the experimental measurements reported by Li et al [19] and Yu et al [27] and theoretical approximations reported by Xiao and den Ouden [12], 15] for stationary gas tungsten arc welding (GTAW)
The spatial distribution of arc power-density and forces imposed on the melt pool change with surface deformations that can affect the temperature distribution over the melt-pool surface, and flow instabilities that are often dominated by Marangoni flow
Summary
Molten metal behaviour during fusion-based welding and additive manufacturing affects energy transport in melt pools, which in turn influences their geometrical evolution [1,2]. Melt pool behaviour appears to substantially determine the properties, structure and quality of weldments or additively-manufactured products [3]. Limitations of experimental methods in detecting molten metal flow in melt pools coupled with excessive costs of trial-and-error experiments, which are commonly applied in industry to date, pose additional challenges to understanding the melt pool behaviour, and to developing effective melt pool control. A promising alternative to trial-and-error experiments is to utilise a simulation-based approach to predict and describe the melt pool behaviour [5], which results in a decrease in the number of experiments required for process development and optimisation
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