Jian Cheng Fang

Influence of In-Flight Particle Characteristics on the Forming Quality

There are many technical parameters influencing on the coating quality in plasma spray forming which has become an important technology in materials processing. In this study, the relationships between the melting state, in-flight property of particles injected into plasma jet and the forming quality have been investigated. The experimental results show that the temperature field distributions of plasma jet are mainly affected by plasma generator power though CCD imaging and gray-scale processing. The velocity of in-flight particle is directly determined by the flow rate of work gas, and the surface temperature of in-flight particle is obviously affected by assisted gas rate. It is clear that the energy coupling and momentum transferring between plasma and particle have a significant influence on deposition efficiency, porosity, microhardness and microstructure of spray-formed parts, and it also provides a good idea to control the forming quality on-line.

FGM Mould with Fine Veins Rapidly Manufactured by Plasma Spraying

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.

Arc Spray Forming of Stainless Steel Mould

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.

A Basic Study on Precision in Electrochemical Abrasive Lapping of Plate

Taking plate as the example, this paper studies the effect of tool’s shape and movement on the electrochemical as well as mechanical lapping characteristics in Electrochemical Abrasive Lapping (ECAL). It is assumed that the removal size of electrochemical action at a random point is in direct proportion to the electrical amperage through this point and the removal size of the lapping action is in direct proportion to the relative frictional distance. Based on the assumption above, electrochemical and mechanical lapping characteristics with different tools shape are studied theoretically. The results show that the diameter of the tool should be larger than the width of the workpiece when a discal tool is used and the inner diameter of the tool should be larger than the width of the workpiece when a ringed tool is used, on the other hand the ratio of the revolving radius of the tool to the diameter of the tool as larger as possible avails to improve the precision and so does the ratio of the angular velocity of the workpiece to the rotating angular velocity of the tool.

Near Net Forming of Metal-Ceramic Parts by Plasma Spraying

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.

Model of Heat and Mass Transfer in Atmospheric Pressure Plasma Arc (APPA) Cleaning Metal Surface

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.

Electrochemical Magnetic Abrasive Compound Finishing

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.

Application of Neural Network in Plasma-Arc Flexible Forming

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.

Magnetic Abrasive Finishing of Non-Ferromagnetic Tube

A new technology of magnetic abrasive finishing (MAF) by applying rotating magnetic field generated pulse circuit was presented. The finishing mechanism was investigated, and the generation device of rotating magnetic field was designed and analyzed to finish the inner surface of non-ferromagnetic tube. The experimental results show: (1) The quality of the finishing is related to the magnetic pole structure: the NSSN structure brings out the highest quality, while the NSNS structure brings out the lowest quality. (2) The supplied weight of magnetic abrasive affects directly on the stock removal and the surface roughness, and it has an optimum value. (3) The finishing efficiency and the surface roughness can be improved effectively when magnetic abrasives are mixed with reasonable mesh-size iron powders in rational weight percent. The technology provides a good basis to spread the application in practical manufacturing. Introduction The principle of magnetic-abrasive finishing (MAF) is that magnetic-abrasives (MA) are attracted by magnetic field in the machining zone, and joined each other along the line of magnetic force, forming flexible MA brushes, which push against workpiece with a certain stiffness to realize cutting by relative motion. It is very suitable to finish the workpiece in plane, rotator, free surface and internal tube. In recent, the MAF for inner surface by employing rotating magnetic field generated by the rotational motion of permanent magnet has been presented, and some satisfactory results have been obtained [1]. The shortcoming of this procedure is that it is difficult to adjust the magnetic induction intensity in finishing. In this paper, a device of rotating magnetic field generated by pulse circuit is designed, which is easy to change the pole structure, for finishing inner surface of non-ferromagnetic tube. Finishing Device Rotating magnetic field can be generated by many methods, such as: 1) by the system of magnetic pole which made of permanent magnet rotating around the tube; 2) by electric magnet using brush control. The former is suitable to finish long-thin tube because of the simple equipment, but an additive device must be supplied to help the rotation of magnetic pole, and the magnetic induction intensity is difficult to be adjusted. The latter overcomes the disadvantage of the former in a certain degree, but the magnitude of magnetic force generated by this equipment could not meet the need of finishing, therefore the mechanical contact of brush results in yielding over resistance, which decreases the current of coil. According to this condition, a new generation device of rotating magnetic field by pulse circuit is designed, which is easy to debug, facile in control, and the rate of rotation is adjusted by controlling the frequency of pulse circuit. The control chart of experimental system is shown in Fig.1, the design chart of generation device of rotating magnetic field is shown in Fig.2, and the structure of the magnetic circuit is shown in Fig.3. The tap of coil winding is set in the midst; the generation device of rotating magnetic field with various structures of pole can be obtained according to the different mode of connection. If initial pole 1 is N, and pole 2 is S; then pole 2 is N, and pole 3 is S; and pole 3 is N, Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 530-534 doi:10.4028/www.scientific.net/KEM.259-260.530

Numerical Simulation of Magnetic Field Distribution in MAF

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.