Papers by Author: Zhi Yu Zhao

Abstract: Pulse electrochemical polishing is an important method to improve the surface quality of metal sheet. The reasonable control of process parameters is the key to obtain high-quality polishing. In this paper mechanism of pulse electrochemical polishing of stainless steel were studied using the stainless steel sheets of SUS201, SUS202, and SUS304. The influence of the current density, pulse frequency, duty cycle, and other factors on surface roughness were examined, and the optimal parameters was determined. The research results have directional meaning to the scale polishing of stainless steel-based in manufacturing enterprise.

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: The quality of coatings is directly influenced by the flattening and solidification of many individual molten droplets in plasma spray forming, so many properties such as thermal, electrical, mechanical etc are strongly linked to the real contact between the “piled-up” splats. The research on the transient temperature of impacting droplets and the heat transfer between droplets and substrate plays an important role in improving the quality of coatings. Because of complexity and high cost of temperature measurement systems for molten droplet during flattening in plasma spray forming at present, this paper presents a new kind of simulation measurement system for transient temperature of spray droplets when impacting on substrate based on LabVIEW, which could display the real-time changes of the temperature by waveform graph. Finally, the experiments were carried out on Pb-Sn alloy molten droplets to reveal the close connection between the impacting droplets temperature changes and the coatings quality, and the heat transfer between droplets and substrate was discussed.

Abstract: The main factors that influence the deposition efficiency and forming quality are the state of in-flight particles, which are directly effected by process parameter during plasma spray forming. In this study, plasma spraying of ZrO2 powder was employed according to the method of orthogonal experiments, and the relationship between spray parameters and characteristics of in-flight particles, which were monitored by an optical monitoring system of CCD camera, were investigated. Radial basis function (RBF) neural network model had been designed to forecast the temperature and velocity of in-flight particles, and optimized spray parameter. The comparison of the simulations with the experimental results shows the validity of the model.

Abstract: A novel technology of metal-ceramic parts with special functions formed by plasma spraying has become an important research trend. In this paper, the technical characteristics and spray parameters have been analyzed in detail based on the experiments of metal-ceramic near net forming, and some important techniques such as spray mould fabricating, backing and demoulding have been researched and summarized. Furthermore, the microstructure and property have been analyzed to forecast the quality of spray-formed parts. The research results show that plasma spraying is suitable for the production of metal-ceramic parts of any size with special mechanical and thermomechanical properties, which can realize the contemporary integration of forming and machining. Therefore, this technology with simple process and low cost is a method of metal-ceramic fabrication with a broad and brilliant prospect.

Abstract: Magnetic field distribution (MFD) plays an important role in magnetic abrasive finishing (MAF). The mathematical models of the MFD in MAF have been established, and forced behavior of magnetic abrasive (MA) in the magnetic field has been analyzed in this paper. The MFD characteristics of the grooved poles have been numerically simulated, and the distribution law of magnetic force, interaction force and interface pressure have been investigated based on a single particle. The calculated results show that the MFD in the finishing zone is directly affected by the pole structure and working gap. The mapping function of interaction force and interface pressure corresponds to corner-effect in the peak point of the pole, and the magnetic brush stiffness is changed by the diameter and magnetization characteristics of MA, and the magnetic flux intensity (MFI). The numerical simulations are in a good agreement with the experiments. All of results mentioned above will offer an important method to study further on the finishing mechanism.

Abstract: Flexible forming using plasma arc (FFUPA) is a newly developed method of sheet metal forming. It makes the forming by means of thermal stress and thermal strain without mould and die, and is recognized as a promising forming method in developing new products. But the forming effect of FFUPA is determined by many factors, which compose a highly nonlinear system due to their complicated interact. As a result, it is difficult to predict the forming results and choose the processing parameters in FFUPA. In this paper, BP neural network is applied to solve this problem. After introducing the mechanism of FFUPA and analyzing the influence of processing parameters on the forming result, BP neural network is established, which include an input layer, an output layer and a hidden layer. When inputs and outputs are properly chosen, the BP neural network can be used to predict the forming results and to select the forming parameters. To verify the validity of this network, the results obtained by the BP neural network are compared to those obtained by experiments, and the results show that the former is close to the later, which indicates it is feasible to apply BP neural network in determining the processing parameters and forecasting the bending effects in FFUPA.

Abstract: There is the advantage of continuity in organic structure and mechanical property for functionally gradient materials (FGMs), but it is unable to be used in the mould industry for the difficulty of the second machining up to now. In this study, a novel technology of FGM mould with fine veins fabricated by plasma spraying has been developed, which can easily realize the integration of FGM forming and deep machining of the mould. According to applied characteristic of plastic injection mould, WC-12%Co/NiCrAl powders are selected and the reasonable FGM coating has been prepared. Spraying processes have been investigated, such as fabrication of spray mould with fine veins, FGM forming, backing and demoulding, etc. At the same time, the metallography, porosity and microhardness of the spraying layer have been analyzed. The results show that the service performance of the FGM mould is much more excellent than that of the traditional mould, and the life span can also be greatly improved. The research will have a significant influence on the material development in the mould industry.