This project application, devoted to the simulation of metal fusion with a laser beam and electric arc, continues the NAISS projects 2023/5-575 (Medium Compute) and 2023/6-389 (Medium Storage). This last one resulted in two manuscripts being finalized for submission to international scientific journals. The proposed project aims to elucidate the causes of metal transfer instability in laser metal fusion when depositing metal alloys (Ti-64, Ni-718) from a resistively heated wire (LDED-w). These causes are poorly known. The gained knowledge will support improving process control. To investigate the causes of instability, the CFD model for LDED-w developed in OpenFOAM during our previous NAISS projects will be applied for each studied alloy to compute: 1) a reference case (with ‛complete´ physical model), 2) a case inhibiting ‛artificially´ the Rayleigh-Plateau instability and 3) a case inhibiting ‛artificially’ the thermocapillary instability. These cases will be run at three different values of electric resistivity. The mesh study was already performed in our earlier project with Ti-64. The proposed project therefore involves a total of nine cases with the alloy Ti-64, plus a mesh study and nine cases with Ni-718. A conference paper and at least one journal manuscript will be prepared. In addition, the proposed project resumes the SNIC projects 2022/5-593 and 2022/6-347 for metal fusion using an arc heat source with a non-refractory electrode. The model included free surface tracking with a volume of fluid (VOF) method. The heat source was set through a boundary condition rather than predicted. To predict it, our objective is to model the thermal plasma arc, the non-refractory electrode, and the electrode-plasma sheath coupling. Such a model does not exist yet due to the incompatibility between the VOF method and the sheath model for non-refractory electrodes. As a result, today’s models rely on adjustable coupling parameters. For about one year, we are generalizing a model we developed in earlier studies for refractory electrodes, implementing our electrode-plasma-coupling sheath model in the novel unified Multiphysics framework for multi-region coupled continuum-physical problems, that was developed in foam-dev by Holger Marschall’s group. This framework enables the sheath coupling to operate at a deforming interface characteristic of non-refractory electrode. To test this first level of generalization, simulations planned in this project consist of an arc discharge lamp case with available measurements for model validation. The computations will be made using the newly developed model and our older model to perform a comparative study. A manuscript for publication in international scientific journal will also be prepared. Based on the former projects, it is evaluated that to conduct the proposed project, in total, a minimum computational time of 80 000 core hours per month and storage for at least 11 250 GiB and 10 million files for a duration of 1-year will be needed.