Papers by Author: Xiao Juan Dong

Abstract: The theory of Least Squares Support Vector Machines was applied to metal surfaces cleaning by atmospheric pressure plasma arc. An intelligent predictive model of the non-linear relationship between cleaning quality and process parameters was established with the k-fold cross training of sample data. An orthogonal experiment was conducted to assess the effect of processing parameters on surface quality. The experimental results and predicted values show that the atmospheric pressure plasma arc (APPA) cleaning is effective in reducing considerably the amount of lubricant. Furthermore, it is feasible to apply LS-SVM in forecasting the cleaning quality and determining processing parameters, and the mean absolute percent error e_MAPE between predictive value and experimental value of water contact angle is 6.09%. Otherwise, the e_MAPE of working current is 4.46%.

Abstract: A theoretical analysis was carried out to investigate the characteristics of atmospheric pressure plasma arc injected transverse to a transverse alternating magnetic field and a mathematical model was developed to describe the heat flux density distribution of the plasma arc. The effect of processing parameters, such as flow rate of working gas, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the heat flux density distribution of plasma arc were also analyzed. The results show that it is feasible to adjust the heat flux density of the plasma arc by the transverse alternating magnetic field, which can expand the region of plasma arc thermal treatment and flatten the heat flux density upon the workpiece. With the magnetic flux density enhancing, the heat flux density gradient upon the workpiece decreases. Under the same magnetic flux density, the more gas flow rate and arc current, the more heat flux density peak increase. Contrarily, more distance from nozzle outlet to workpiece descends the heat flux density peak.

Abstract: A mathematical model was established to describe the electromagnetic, heat flow and fluid flow phenomena within a combined plasma arc. In the development of the model allowance is made for the conservation of mass, momentum, energy and the Maxwell equations. With the ANSYS finite analysis software, specific calculations were presented for a pure argon system, operating in a laminar mode. The distributions of the current density, temperature and velocity of combined plasma arc were gotten. In addition, the influences of process parameters, including arc current, argon gas flow rate and the distance from the nozzle outlet to the anode workpiece, on the temperature distributions along the axial and radial direction were evaluated, respectively. The results shows that 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.

Abstract: 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 this model, a mapping method and a meshing method of variable step-size were adopted to mesh the calculation domain and to improve the computational precision. To overcome the problem issuing 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 the behaviors of combined plasma arc. Furthermore, the characteristics of combined plasma arc such as temperature, velocity, current density and electromagnetic force were studied.

Abstract: A mathematical model was developed to describe the oscillating amplitude of the plasma arc injected transverse to an external transverse alternating magnetic field. The characteristic of plasma arc under the external transverse alternating magnetic field imposed perpendicular to the plasma current was discussed. The effect of processing parameters, such as flow rate of working gas, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the oscillation of plasma arc were also analyzed. The results show that it is feasible to adjust the shape of the plasma arc by the transverse alternating magnetic field, which expands the region of plasma arc thermal treatment upon the workpiece. Furthermore, the oscillating amplitude of plasma arc decreases with decrease of the magnetic flux density. Under the same magnetic flux density, more gas flow rate, more arc current, and less standoff cause the oscillating amplitude to decrease. The researches have provided a deeper understanding of adjusting of plasma arc characteristics.

Abstract: The beam form has a direct effect on the quality and efficiency of flexible forming using a combined plasma arc. But it is difficult to directly measure relative parameters of combined plasma arc for its characteristics of high temperature and high energy density. In this paper, an image collection system was designed with a lens, a neutral filter, an interference filter and a CCD camera. And then, the acquired digital image of diagnostic face of plasma arc was implemented pre-processing such as removing noises, edge extraction, histogram equalization, contrast enhancement, enhancing morphological features. Furthermore, based on spectral diagnostics of plasma arc, the effects of working current, gas flow and the distance from the nozzle outlet to the anode on temperature distribution of combined plasma arc were also investigated. The results show that 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.