Papers by Author: Wen Ji Xu

Abstract: A new method for laser milling of Al2O3 ceramic based on deteriorative layer controlled is presented in which no assistant gas was used during the laser milling. The new milling technology is developed by means of laser scanning of ceramic surface and forming a deteriorative layer directly. Laser milling parameters are determined through crystal phase’s analysis of the deteriorative layer. The laser milling depth, surface quality, and milling mechanism with different milling parameters were studied systematically on an Nd: YAG CNC laser and multi-layer laser milling experiments were also conducted with optimized processes on the surface of Al2O3 ceramic workpiece. Therefore, the practical experimental results are that each depth of layer milling is between 0.35-0.5 mm and the surface roughness of laser milling reaches to Ra 2-3.2μm. The experimental study has thus provided deeper understanding on laser milling technology for Al2O3 ceramic both in theory and application.

Abstract: Zinc-alloy with low melting point can be easily sprayed directly on the production surface to fabricate a mould with high precision by arc spraying. But the zinc-alloy mould has the disadvantage of easy invalidation due to its relatively low hardness and poor anti-wear property. In this paper, the surface modification of zinc-alloy tooling by composite electro-brush plating was researched. The joining mechanism between the plating film and sprayed coating was investigated, and the law of quality control on the unification of rapid tooling and surface modification was revealed. A new modification technology possessing the advantage of economical and high quality surface relating to moulding was developed with independent intellectual property right.

Abstract: During plasma spray forming, the forming quality is directly influenced by the flattening behavior of the droplet impacted onto the substrate, which is determined by the flattening configuration and solidification state of the droplet. In this study, according to the rule of Reynolds number and Peclet number, the flattening behavior of big-size molten droplet impacted onto the substrate with low-speed were experimentally simulated during flattening. The droplets of Sn30Pb70, Zn and ZA12 impacting onto the stainless steel substrate with different velocity were investigated. Splashing degree was introduced to evaluate the flattening profiles of the splats. The relationships between the splashing degree and the impact velocity, Reynolds number and Weber number of the droplet were established. Experimental results show that the flattening and diffusion are impeded by the dynamic viscosity and surface tension of the droplets, and the impeding effects are more remarkable when the impact velocity is lower. The research has a significant ap

Abstract: A three-layer FEM model, based on the characteristics along the thickness direction of laminated composite metal sheets (LCMS), was developed to study the variation rules of transient deformation in the flexible forming of LCMS using plasma arc. Besides, the comparisons of the typical LCMS Q235A/1Cr13 and single layer metal sheet (SLMS) Q235A were performed. It indicates that the displacement of end point of SLMS is 0.076 mm larger than that of LCMS with the same process parameters. Moreover, the differences of X-axis plastic strain, Z-axis plastic strain along the thickness direction of LCMS decide the bending direction, the occurrence of the edge effect of LCMS during linear heating, respectively. Furthermore, Y-axis stresses of LCMS different layers undergo three dramatic changes with the maximum stress difference of 1.420×107 Pa, and the possible failure of interface delamination occurs in the bonding interface of Q235A and transition layer.

Abstract: The surface quality of components has the important influence on the components’ operational performance, characteristic of the geometry topography and statistical Characteristic is the important aspect of the surface quality. This study takes the arithmetic mean deviation of the assessed profile (Ra) to reflect the altitude characteristic of the surface profile, takes the mean width of the profile elements (Sm) to reflect the width characteristic of the surface profile, takes the material ratio of the profile (tp) to reflect the shape characteristic of the surface profile and takes the altitude density function φ(z) and autocorrelation function R(l) to reflect the statistical characteristic. Four groups of experiments are carried out in which 1Cr18Ni9Ti is taken as the material object of the test piece and test pieces with different initial surface roughness are polished. By experiment, the changing rules of the value of Ra, Sm, tp, φ(z) and R(l) after different polishing time are obtained. By analyzing the changing rules of Ra, Sm, tp, φ(z) and R(l), the influence of the Electrochemical Polishing (ECP) process on the surface geometry and statistical characteristic is obtained.

Abstract: From the viewpoint of the change of the anodic surface microtopography in the process of Electrochemical Finishing (ECF), this paper studies the anodic smoothening mechanism of ECF and puts forward the directional issue of the dissolution of anodic surface in the microtopography sense. On condition that the anodic material is dissolved along with the normal direction of the micro-profile on the anodic surface, the influence of wave length of the micro-profile on the smoothening effect is discussed in detail and the mathematical model based on the “lateral direction dissolution” is established. Finally, ECP is taken as the example and the experiment is carried out, the result shows that the smoothening rule obtained by experiment accords with that by calculation.

Abstract: According to analyzing the principle of atmospheric pressure plasma arc (APPA) cleaning metal surface, a model of heat and mass transfer is put forward with using transient-state heat transfer equation about interior heat source and Arrhenius equation of chemical reaction kinetics theory. With finite volume method, the one dimensional control differential equation is transformed into discrete control equation, which is calculated numerically and analyzed with the using of implicit scheme. Taken cleaning lubricant film as an example and analyzed temperature distribution of cleaning film on metal surface, the result indicates that the temperature of film has a strong effect on its removal rate which improves with increasing temperature. In order to both avoid damaging the workpiece surface owing to higher temperature and ensure removal rate of the film, there exists an appropriate temperature under given calculation conditions.

Abstract: This paper researches on the theory of the crown modification of cylinder-roller bearing raceway using electrochemical abrasive belt grinding (ECABG) technology, and establishes relevant experimental device. The range of processing parameters with a better surface roughness can be obtained through experiments. On this basis, a mathematics model of distribution of material removal of electrochemical machining bearing is set up. Considering the controllability of processing parameters and demand of the surface quality, the processing parameters such as interelectrode voltage, electrolyte, interelectrode gap and cathode geometry are invariable in the experiment, and processing time is changed to control the crown value. The experimental results show that ECABG can enhance the surface quality of raceway to a great degree, and obtain the ideal forming crown at the same time under the optimum technological parameters. This paper developed a new method for the crown processing and finishing of bearing raceway.

Abstract: Electrochemical abrasive belt grinding (ECABG) technology, which has the advantage over conventional stone super-finishing, has been applied in bearing raceway super-finishing. However, the finishing effect of ECABG is dominated by many factors, which relationship is so complicated that appears non-linear behavior. Therefore, it is difficult to predict the finishing results and select the processing parameters in ECABG. In this paper, Back-Propagation (BP) neural network is proposed to solve this problem. The non-linear relationship of machining parameters was established based on the experimental data by applying one-hidden layer BP neural networks. The comparison between the calculated results of the BP neural network and experimental results under the corresponding conditions was carried out, and the results indicates that it is feasible to apply BP neural network in determining the processing parameters and forecasting the surface quality effects in ECABG.

Abstract: Top-quality surfaces are obtained by means of pulse electrochemical finishing (PECF) in neutral electrolyte. The machining principles and advantages of PECF are analyzed. Moreover, the technique are applied to some typical cases such as sheeny lettering, fine and deep holes and complex shaped surface finishing, gear surface finishing that all of them are more difficult to be machined by the traditional finishing technologies. The results show mirror-like surfaces could be gained by PECF and the surface roughness values could be reduced from more than Ra 0.8 μm to less than Ra 0.08 μm within 1~2 seconds. It’s hoped that PECF will play an important role in finishing key parts in the modern manufacturing industries.