Papers by Author: Bo Yan Song

Abstract: This paper mainly makes comparative analysis on four main types of blade in stirred bioreactor by Computational Fluid Dynamics(CFD) simulation. Firstly we establish simulation method suited for stirred bioreactor, then simulate the velocity and shear force of flow field in the bioreactor. No matter from flow field mixing or shear force aspect, Elephant Ear blades is the most suitable for cell large scale culture. At last, it optimizes the installation method and angle of Elephant Ear blades. It concludes that anticlockwise rotation and 45°installation angle is the optimum.

Abstract: The powder mixed electro-discharge machining (PMEDM) technologies of silicon carbide particle reinforced aluminium matrix composites (SiCp/Al) are researched in this article. SiCp/Al is widely acknowledged as one of the most competitive varieties of metal matrix composites, firstly applied in the aviation, aerospace and military fields, and gradually extended. Because of the hard and brittle SiC particles contained in this material, mechanical machining is difficult, but EDM does have some advantages. To the same kind of moderate volume fraction (45%) SiCp/Al material, a comparative test was conducted using two kinds of processing methods, traditional EDM (the former) and PMEDM (the latter). Effects of the electrical parameters of both processing methods on the material removal rate (MRR) were analyzed and compared. After processing, the surface roughness value of the former is Ra1.386μm while the latter is Ra0.406μm which is only 29.3% of the former. The surface hardness was also tested by the MTS nano indenter: the former is about 1.7GPa, and the latter is about 2.2GPa which is 1.3 times of the former. Finally, to the machined surface, the micro-topography and the component of ‘white point’ were observed and analyzed by using scanning electron microscope (SEM) and energy spectrum respectively. Experiments and investigation results show that the PMEDM has a better performance compared with traditional EDM in improving the roughness, hardness and so on. So PMEDM will have a great potential in the processing of aluminium matrix composites.

Abstract: During the whole process of cell culture, it needs enough air, especially oxygen supply. Therefore, the research about air sparger became significant. There are many influence factors of air sparger are important, including air sparger structure, installation location, ventilation rate. In order to solve these problems, the finite element numerical calculation is used to set a numerical model of air-liquid two-phase flow. This analysis makes clear that the distance between air vent and the bottom of bioreactor has little effect on the air voids, and the air voids is higher by adopting the structure of single air vent compared with the one of distribution ring structure. But the ventilation structure of big distribution ring avoids flooding effectively. The air voids of bioreactor increased with the velocity of ventilation is increased within limits. However, it causes air incomplete dispersion in bioreactor, overflowing from head top of the liquid, flooding and low air voids, if the ventilation velocity is over speed.

Abstract: In this paper a kind of architecture for an energy-saving EDM supply composed of three serial stages in the topology and its practical design are discussed. Various special controllers and its assisted circuits are introduced in the each of the three serial stages. The PFC controller UC3854 placed on the front stage provides satisfactory input power factor of the system. The PWM controller UC3875 mounted on the middle stage realize the closed control of the current of the inductance limiting machining current. An embedded controller PIC16F877 on the final stage is chosen to setting such machining variables as peak current, discharge duration and pulse interval. The communication with host PC is also realized by the same embedded controller. The architecture based on model of multi-controller parallel working guarantees capacity of the system real-time process. The prototype of the energy-saving EDM pulse supply using MOSFET power device is developed. A lot of experiments have demonstrated the feasibility and stability of the practical design.

Abstract: The silicon carbide particle reinforced aluminium matrix composite (SiCp/Al) which is acknowledged as one of the most competitive metal matrix composites is now widely applied in aviation, aerospace and military fields, and its application is extending gradually. As a result of the hard and brittle SiC particles contained, mechanical machining of the material is difficult, but the method of electric discharge machining (EDM) has certain prominent advantages. In this paper, SiCp/Al was machined using micro-EDM. First, a Ф40μm × 4.1mm micro tool electrode of which the aspect ratio is up to 100 was made; and then, through experiment, the impact of open-circuit voltage and electrode material on processing speed and electrode wear was analyzed; finally, 28μm wide micro slits, micro square platform of 34μm long on each side and other micro three-dimensional structure were machined. Research and experimental results show that the use of appropriate micro-machining parameters and reasonable processing methods can improve processing performance to better achieve the micro-EDM of SiCp /Al.

Abstract: The performance and stability of output of electrical discharge machining (EDM) are determined by the output of EDM pulse power supply. In order to resolve disadvantages of conventional pulse power supply, such as undesirable efficiency and low power factor, the prototype design of energy-saving EDM pulse power supply is developed. It is composed of such three stages as a single-phase active power factor correction (PFC) pre-regulator, a full-bridge phase shift zero voltage switching (FB-PS-ZVS) converter based on complex control paralleled of machining current closed-loop and voltage closed-loop at period of spark gap insulation, and a pulse generator based on machining sequence control. The PFC pre-regulator contributes to a great increase to about 0.95 in its power factor. The efficiency of the new system is considerably increased to about 70% due to design of ZVS. The pulse generator contributes to the pulse machining current without a tail. Experiment results demonstrates that the prototype is capable of low electrode wear, high speed, stable machining.

Abstract: Their efficiency and their power factor of conventional independent electrical discharge machining (EDM) pulse power supplies with the current-limiting-resistor circuit is so low that they do not meet the need of advanced EDM technologies. The design of highly efficient EDM pulse power supply based on switching circuit pulse width modulation current closed-loop principle has been initiated. It is composed of such three stages as a single-phase active power factor correction preregulator, a full-bridge phase shift resonant converter based on machining current closed-loop control and a pulse generator based on machining sequence control. Therefore, the efficiency of the new system is considerably increased to about 70%, its weight and size is decreased much. Its power factor is a great deal increased to about 0.95. Experiment results have demonstrated that the highly efficient EDM pulse power supply is capable of low electrode wear, high speed, stable machining.