Papers by Author: H.Y. Li

Abstract: Plasma spraying has been carried out under different spraying parameters, the particle in-flight behaviors have been measured to analyze the influence of argon flow rate, hydrogen flow rate and electrical current on the particle temperature and velocity. The particle velocity increased remarkably with the increase of the argon flow rate. The particle temperature was mainly influenced by the hydrogen flow rate, and increasing electrical current resulted in the increase of the particle temperature and velocity to some extent.

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.

Abstract: The molybdenum powder doped with rare earth oxide was processed by powder metallurgy method and a new style thin film cathode material was firstly processed by Spark Plasma Sintering (SPS) method in this paper. The secondary emission property of such kind of cathode materials were studied, the maxim secondary emission coefficient after the material was activated at 1600°C reached to 3.84 about double that of traditional cathode materials application in magneto. The microstructure, element analysis and phase constitution of materials before and after the secondary emission property was measured were studied through SEM, EDAX and XRD. The results show that a rare earth layer about 5um thickness was created after the material was activated at 1600°C. The material grain size is about 1 um or even smaller and the distribution of elements in such materials is even.

Abstract: By analysing the change of the anodic surface topography in Electrochemical Abrasive Lapping (ECAL), the influence of the lapping action and the electrochemical action on the anodic smoothening velocity is studied. In electrochemical finishing, the micro-peaks on the anodic surface could be smoothened quickly by electrochemical action and the surface topography presents the profile wave, but in ECAL, the profile wave after electrochemical action could be divided into micro-peaks renewedly by lapping action and the alternation of electrochemical action and lapping action makes the surface topography before electrochemical action present profile micro-peaks, which will increase the anodic smoothening velocity. The influence of machining parameters, such as abrasive grain sizes, tool’s pressure, abrasive content, frictional velocity and current density etc, on the anodic smoothening velocity is discussed in detailed.

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: In order to improve the lifespan and performance of the forming mould with low melting point, arc spray forming of stainless steel mould has been advanced. The technical process of spray mould has been investigated, and the correlations among the spray parameters, in-flight characteristics of molten particle and the forming quality have been analyzed in detail. Meantime, the influence of the preheating temperature of the spray mould and the spray angle on the morphology of the splashing particles has been also investigated. The research results indicate that the atomization pressure greatly influences the velocity and granularity of the in-flight particles. The working current greatly influences the particle temperature, and the spray distance influences the temperature and velocity to some extent. A compact spray layer, with a low porosity, little oxide content, and high microhardness, can be obtained by increasing the atomization pressure. The research has a great significance to optimize and control the forming quality of rapid tooling by arc spraying.

Abstract: In this paper, electrochemical finishing（ECF） is presented. Compared with conventional finishing technology, the characterization of surface topography machined by ECF and its effect on the performance, including friction coefficient, original wear and tear, precision durability, fatigue strength, contact stiffness, corrosion resistance and adhesiveness are analyzed and studied. Experimental results have testified that ECF can observably improve surface quality of parts and finally improve its physical mechanical performances and lifetime to a large extent.

Abstract: In order to find a solution to the problem of inefficiency in magnetic abrasive finishing (MAF), electrochemical finishing (ECF) has been introduced to realize compound finishing. A new idea of integrating a magnetic pole with an electrode pole has been proposed as electrochemical magnetic abrasive finishing (ECMAF). At the same time, the occurrence of broken and dropped magnetic abrasives (MAs) has been discussed from the point of view of probability. Research on stock removal and surface roughness shows that the passive film has been removed continuously with a new substrate material emerging during the process of machining, which accelerates the process of electrochemistry to realize the surface finishing. The finishing efficiency and surface quality have been improved by the combination of MAF with the electrochemistry process, and the various cutting behaviors of MA in ECMAF.