Zhi Yu Zhao

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.

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.

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.

Study on the Composite Technology of Electro-Brush Plating and Arc Spraying

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.

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.

Plasma-Particle Interaction in Spray Forming

The quality of spray-formed parts is the most important research field in plasma spraying, which has been developed in rapid forming the materials of difficult processing such as ceramics, high melting point alloy and composite materials in recent years. It is insufficient to research the forming quality affected by the plasma-particle interaction based on the plasma characteristics. The temperature field distributions of plasma jet have been investigated under the different conditions by imaging and processing, and the experimental measurements of surface temperature for in-flight particle have been carried out by the principle of two-wavelength pyrometer. At the same time, the mathematical models of momentum and energy transfer have been established to analyze the motion laws and temperature distribution of in-flight particles during spraying. The results show that the temperature field distribution of plasma jet is obviously affected by the components of working gas, the forming quality is significantly influenced by the flight time and melting state till arriving at the spray mould, in which the mechanical behavior and the heating characteristic of plasma-particle interaction in spraying system should be properly matched with each other. The mathematical simulations of temperature are in a good agreement with experimental results.