Numerical simulation of welding fume formation mechanism in gas tungsten arc welding

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In a GTA (Gas Tungsten Arc) welding, large amount of high temperature metal vapor is generated from the melting tip of a welding wire, a droplet and a weld pool. In this process, high temperature metal vapor is cooled rapidly and oxidized during diffusion to the surrounding air. Then a primary particle (nanoparticle), whose size is approximately 1nm～100nm, is formed through a nucleation. Furthermore, a part of these particles condenses and produces a secondary particle whose maximum size is over 1μm. It becomes the form of smoke and rises with the ascending current from the high temperature weld pool. They are called welding fume. For reducing the quantity and controlling the size of the fume, we integrated a fume formation model and visualized the fume formation process. Simulation was calculated changing physical property. Fig. 1 represents a secondary particle. The secondary particles with beaded (chain-like) shape composed of small particles whose sizes are approximately below 100nm were observed. As a result, it was confirmed that the shapes and the sizes of the secondary particles obtained in the simulation approximately agrees with that in the experiment.

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