Effects of Transverse Magnetic Field with Different Alternating Currents on Heat Flux Density Distributions of Plasma Arc
An external transverse-alternating magnetic field with sinusoidal and triangular alternating currents was applied to a combined plasma arc to create a plasma arc for expanding the cross section of arc column and flatting the distributions of arc temperature. Two mathematical models were developed to describe the heat flux density distributions of the combined plasma arc driven by a transverse-alternating magnetic field with sinusoidal and triangular alternating currents. The behavior of plasma arc under the external transverse-alternating magnetic field imposed perpendicular to the plasma current was discussed theoretically and experimentally by changing various parameters such as working gas flux, arc current, magnetic flux density including its wave form and the standoff from the nozzle to the workpiece. The analytical results show that it is feasible to adjust the shape and heat flux density of the combined plasma arc by the transverse- alternating magnetic field, which expands the region of combined plasma arc thermal treatment and uniforms the heat flux density upon the workpiece. Changing the waveform of the alternating current can also control the heat flux density distribution. As well as, calculated heat flux density distributions of combined plasma arc driven by the external transverse-alternating magnetic field show a good agreement with experimental data. The magnetic field with triangular alternating current can flat the heat flux density distribution on the anode rather than sinusoidal one. This approach to flat the heat flux density distribution on the anode surface will give an effective controllability to the combined plasma arc application.
Surface modification of stainless steel using an atmospheric pressure plasma arc driven by an external transverse-alternating magnetic field
An experimental cleaning system for surface modification was developed. It consisted of a plasma torch with a DC power supply to generate an atmospheric pressure plasma arc, two field coils with an AC power supply to generate an external transverse-alternating magnetic field, a moving system for the plasma arc cleaning stainless steel samples. The external transverse-alternating magnetic field was applied to the atmospheric pressure plasma arc to widen its cross section and uniform its energy density distribution. Effects of process parameters, such as arc currents, gas flow rates, distances from the torch nozzle to the substrate, scanning velocities, and magnetic flux densities on the cleaning quality were investigated. The experimental results demonstrate that it is feasible to improve cleaning quality of the atmospheric pressure plasma arc with the external transverse-alternating magnetic field, which can expand the cleaning area and uniform the energy density distribution upon the substrates. As well as, the experimental results show that the cleaning region and cleaning quality of plasma arc are significantly influenced by the process parameters.
Analysis of TIG Welding Arc Using Boundary-Fitted Coordinates
The characteristics of argon arc in tungsten inert gas (TIG) welding have been studied by considering the electrode shape which has an effect on the current density distribution near the electrode tip. For including the electrode surface configuration into the solution domain, the boundary-fitted coordinate system was employed. Then, a non-rectangular computational region in the physical domain was transformed into a rectangular area with uniformly spaced grids in the computational domain using the second-order central difference method. With the geometric transformation coefficients, the finite difference equations were derived in the computational transformed domain. As the most critical boundary condition, the normal current density distribution entering an electrode surface was postulated by the Gaussian distribution in consideration of the geometry of the electrode shape. For examining the simulated results, the temperature profile was compared with the experimental measurement of the previous research. The transferring phenomena on the base plate, such as current density, heat flux, arc pressure and drag force, were also calculated, because they are necessary data for analysing the molten pool during welding.