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.
Numerical Simulation and Analysis on Jet Characteristics of Combined Plasma Arc
A three-dimensional axisymmetric mathematical model, including the influence of the swirl exiting in the plasma torch, was developed to describe the heat transfer and fluid flow within a combined plasma arc. In the model, a mapping method and a meshing method of variable step-size were adopted to mesh the calculation domain and to improve the results precision. To overcome a problem from a coexistence of non-transferred arc and transfer arc and a complicated interaction between electric, magnetic, heat flow and fluid flow phenomena in the combined plasma arc, a sequential coupling method and a physical environment approach were introduced into the finite element analysis on jet characteristics of the combined plasma arc. Furthermore, the jet characteristics of combined plasma arc such as temperature, velocity, current density and electromagnetic force were studied; the effects of working current, gas flow and the distance from the nozzle outlet to the anode on the distributions of temperature, velocity and current density were also revealed. Compared with the collection and diagnosis on the combined plasma arc by CCD, the results show that the simulated value appears to be in good agreement with measured value, and the temperature of combined plasma arc is much dependent on the working current, while is less sensitive to the argon flow rate and the distance from the nozzle outlet to the workpiece anode.
Plasma jet imaging by CCD technology in rapid mold manufacturing
Abstract Plasma spraying, as an important enabling technology, is being applied to rapid mould manufacturing in order to reduce the development time and manufacturing cost. Due to the melting and in-flight states of powders being affected directly by the plasma jet, which ultimately determines the quality of the bulk deposit, there is an increasing interest in research on the diagnostics and control of plasma spray processing. This paper presents a compact, low-cost and practical method for the real-time diagnosis of a plasma jet, which integrates CCD and computer imaging technology. The collecting principle and methods were especially investigated, whilst the fake color processing of the jet image and jet shape under different process parameters were studied also, using an experimental system of real-time data collection by the present method. The current work is of paramount importance for further study of the closed-loop control of plasma spraying processes, which could turn plasma digitized manufacturing into reality.