چكيده به لاتين
In this research, an attempt has been made to investigate plasma arc welding with the help of computer simulation to determine the effect of the size of the nozzle orifice on the electric arc. In this regard, the factors affecting the quality of welding resulting from this process, such as the shape and size of the nozzle, the speed and current of welding, the rate and composition of the flow of shielding gas and the orifice, and the characteristics of the electrode, were stated. Numerical simulation of plasma arc during welding was presented to predict the behavior of the arc, as well as comparing the results for three geometries with different diameters of the orifices, to investigate the effect of the orifice diameter on the arc resulting from this welding. Numerical simulation was done using Ansys Fluent software. The first step was to simulate the design of the studied geometry or computational domain. In the next step, the designed geometry was meshed. At this stage, all the assumptions of the problem, including the investigated models (governing equations including mass continuity equation, velocity equations, energy equation, electric potential equation and magnetic field equation), boundary conditions for each equation and changes in density, viscosity, specific heat capacity, thermal and electrical conductivity of flowing fluid (pure argon gas) were determined in the calculation range with temperature as plasma gas and shielding gas. After setting the method of solving the problem (solution method, number of consecutive solutions and the expected residual for the convergence of the answer) and performing calculations with the help of the software, the results of solving the problem for all equations, for comparison the arc obtained from three nozzles with the orifice diameter of 1.8 mm, 2.4 mm and 3 mm were provided. The results regarding temperature, velocity, pressure, magnetic force, current density and electric potential for all three nozzles with different diameters were presented as separate contours. According to the obtained results, the design of the nozzle orifice has a direct effect on the electric arc in such a way that by reducing the diameter of the nozzle orifice, the electric arc becomes more contracted and due to the direct effect of all the features of the arc on each other, it affects. The contraction of the arc causes an increase in the arc pressure and a reciprocal increase in the plasma flow rate during the arc, as well as an increase in temperature.
