Papers by Author: Wen Ji Xu

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: In this paper, surface topography characteristics of electrochemical mechanical finishing (ECMF) for steel was investigated. The scanning electron microscopy (SEM) was used to observe the surface topography. And the microcosmic geometry parameters were measured by Talysurf SLI2000. Compared with original surface, the surface topography characteristics of the workpiece machined by ECMF have been analyzed with altitude density function (ADF) and auto correlation function (ACF). The results show that there exist periodicity component in surface profile before and after finishing. The auto correlation curves of ECMF surface have a smaller average period compared with grinding surface. The low-frequency component and the mean ripple peak distance of original surface profile are obviously decreased. Furthermore, the ripples and peak density are increased, and the surface roughness Ra is decreased from 0.231μm to 0.023μm. The results indicate that surface quality, material ratio of the profile and wear resistance machined by ECMF are improved obviously.

Abstract: The drilling burr is taken as the research object. A mathematical model of electrochemical deburring (ECD) is established and the effects of main influencing factors, such as inter-electrode gap, applied voltage and deburring time, on burr height have been analyzed. The results show that the deburring time increases with the increase of initial burr height, inter-electrode gap, with the decrease of volume of electrochemical equivalent of the workpiece material, conductivity of electrolyte and applied voltage. The deburring time for various burr heights can be predicted by the mathematical model. The calculated results obtained from the mathematical model are approximately consistent with the experimental results. The results show that initial burr height h0=0.722mm is removed, and the fillet radius R=0.211mm is obtained.

Abstract: Gears’ surface quality and modification characteristic have an important influence on its working performance. Pulse Electrochemical Finishing (PECF) could get excellent surface topography. In this project, PECF with a scanning cathode is used to finishing the cylinder gear. Tooth profile modification is realized by PECF with an uneven interelectrode gap distribution along the tooth profile and tooth lead modification is realized by PECF with a variable moving velocity of the cathode. The experimental results show that the tooth surface roughness could be decreased from Ra 3.9μm to Ra 0.35μm, which means that the PECF process possesses the finishing ability for the raw surface tooth, and the difference of material removal of PECF with an uneven interelectrode gap distribution could be 46μm and the material removal could be controlled by regulating the moving velocity of the cathode, which means tooth profile and lead modification could be realized by PECF.

Abstract: The service properties and lives of mechanical parts and components are closely related to their surface quality and precision, and many of the frictional surfaces are required to be finished thereby improving the surface quality and precision. In electrochemical mechanical finishing (ECMF) processes, the surfaces of metal parts are removed through the electrochemical anodic dissolution to obtain the desirable dimensions and surface finish. ECMF is characterized by the independence of the hardness of workpiece and little wear in tools. As a result, it has received more and more attention in the research area of polishing and finishing for mechanical parts. This article reviews the practical works in ECMF technologies from the aspects of surface quality and precision characteristics. Not only excellent surface quality but also high precision dimensions of parts can be obtained with ECMF. It has wide applications in machining precision mechanical parts and components.

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: 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.

Abstract: Mechanical strength and service life of the coatings manufactured by plasma spray forming are significantly reduced by residual stresses. A 2D finite element model constructed for temperature and residual stress simulation of a single stainless steel splat solidifying and cooling on the carbon steel substrate is presented in this paper. Simulated results show that the temperature of the splat rim is higher than that of the central part during the initial stage of solidification, and the temperature difference between the two parts reverse thereafter. The minimum residual stress locates at the rim of the top surface of the splat, and the maximum residual stress, which decreases when the substrate is preheated to a higher temperature, situates at the rim of the interface. Stresses appear as tensile stresses within the splat and compressive stresses within the substrate. The research can provide quantitative understanding of the temperature and residual stress states at the splat level.

Abstract: Based on a principle of laser drilling size and the roundness copied with respect of laser spatial mode, heat absorbing rate for laser drilling of YG8 is presented in theory and application. The mathematical models are then developed. The relationship of heat absorbing rate compared to the original absorbing rate is thus derived that is A = T +A0. It shows that heat absorbing rate to laser beam increases linearly with drilling temperature. The research outcome is used to optimize preheating process in which the novel method improves laser drilling precision from 0.03mm of primitive laser system to 0.01mm under the condition of heat absorbing.

Abstract: A FEM model, based on the structural characteristics of laminated clad metal sheets (LCMS) containing defects, was developed to study the variations of temperature field in the flexible forming using plasma arc. The typical LCMS Q235A/1Cr18Ni9Ti was selected as the sample, and the effects of different defects in the bonding interface on the temperature field were analyzed. The results show that the peak value of temperature containing defect is 107 oC higher than that without defect under the same processing parameters. The peak values of temperature and temperature difference increase with the increasing of defect size, but decrease when the location of defect is far away from the heating surface of LCMS. Compared with spherical defect, cubic defect has more power to impede heat conduction along the thickness direction of LCMS.