Papers by Author: Zhen Long Wang

Abstract: In this study, an ultrafine WEDM (wire electrical discharge machining) of micro-channel mold is proposed. It could be divided into two parts, rough machining and finish processing. In rough machining procedure, high machining voltage is adopted to improve machining efficiency. In finish machining procedure, extended and trimmed tool path is adopted to obtain the cusp at the corner, low electrical parameters is adopted to improve surface quality and dimensional precision. By conducting finish machining of 40V, a better surface-quality with Ra of 0.32μm and high aspect ratio of 20:1 was fabricated.

Abstract: Phase change cooling technology is based on the boiling of refrigerating medium to absorb the heat generated by the electronic chip. It provides higher heat flux dissipation, reduces the refrigerating medium flux and consumes a lower pumping power, compared with single-phase liquid cooling. It also has good temperature uniformity and higher working temperature, which is ideal for energy reuse. Experimental system was designed for phase change cooling of R123 to analyze the basic conditions required for boiling vaporization. The chip temperature was 70 °C or less when the heat flux was 100 W·cm^-2, with the 0.6 mm rectangular micro-channel evaporator. Experiments were conducted to analyze the effects of heat flux, channel dimension, throttling action on the heat transfer effect.

Abstract: The material removal process of SiC/Al particulate (SiCp/Al) metal matrix composite by micro-wire electrical discharge machining (micro-WEDM) is influenced by many factors interaction, which makes the mathematical model of surface roughness (SR) be difficult to obtain effectively. To solve this problem, experimental study method is conducted under the constraint conditions. In this paper, a central composite design (CCD) testing with 3-factor and 5-level is carried out and SiCp/Al metal matrix composite machining test scheme is designed, and then second-order relational model is established between SR and main power parameters (open-circuit voltage, capacitance, and pulse duration) by using response surface methodology. Through multiple quadratic fitting, the quadratic regression mathematical model of SR is obtained. Constrains of actual machining condition upon the parameters are analyzed further. With the goal of reducing SR of SiCp/Al metal matrix composite by micro-WEDM, the parameters optimization model is established. Particle swarm optimization (PSO) algorithm and its procedure are designed to solve the model. Test proves that the algorithm could achieve optimized process parameters which satisfy multiple constraints rapidly and effectively.

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 fabrication of a micro air journal bearing for micro gas turbine engine is investigated based on CAD/CAE and CAM in this paper. Numerical simulation of the aerodynamic micro air bearing is conducted to investigate the bearing load capacity. Then, a removal analysis and contouring strategy of accurate micro-WEDM processing for the air bearing is conducted based on CAM postprocessor. The extended and trimmed tool path is adopted for micro-WEDM. The inner and outer diameter of the bearing is 1.068mm and 1.165mm, respectively. The radius of the bearing corner is 15.9µm, and the height is 53µm.The satisfactory workpiece shape illustrates that the CAD/CAM integrated system is accurate and useful in micro-structures machining.

Abstract: In this paper electrochemical machining of micro slots using a shaped electrode instead of the traditional cylindrical electrode is presented. By applying shaped electrode the flow state of processing can be improved. An electrochemical machining (ECM system for meeting the requirements of the ECM process was established and a shaped electrode was fabricated by BEDG (Block Electrical Discharge Grinding). A set of experiments were carried out to investigate the influence of shaped electrode on machining efficiency and shape precision. The results show that the side gap and frontal gap of the micro slots can be reduced and machining speed will be improved when the shaped electrode was used compare with cylindrical electrode.

Abstract: A numerical model of cathode erosion in EDM process using finite element method is presented. Using this model, numerical simulation of the single spark of EDM process has been carried out with parameters such as conduction, convection, the latent heat of phase change, thermal properties of material with temperature and gauss distribution of heat flux to predict the temperature distribution in the discharge point of cathode as a result of single discharges in EDM process. The simulation result shows the trend of dynamic temperature distribution of heat -affected zone and well explains mechanism of material removal in EDM process.

Abstract: In this paper an electrochemical drilling method for machning micro holes using a flatted electrode instead of the traditional cylindrical electrode is presented. Both electrochemical drilling processes, in which the cylindrical electrode and the flatted electrode were used respectively, were introduced under same machining conditions. The taper of the micro holes between entrance and exit was reduced and machining speed was improved when the flatted electrode was used compare with cylindrical electrode. The flow field simulation was taken out to investigate the reasons for micro holes electrochemical drilling has advantage in taper reducing and machining speed increasing with flatted electrodes.

Abstract: A micro air journal bearing for micro gas turbine engine is designed in this paper. 2D simulation of the aerodynamic micro air bearing is conducted to investigate the effect of the main parameters of the air bearing on the load capacity, including the clearance between the air bearing and shaft, the gear number and height of the air journal bearing, the rotational speed of rotor. The optimum value of the important parameters are explored and presented. The time correlation method is used to solve the RANS (Reynolds Averaged Navier-Stokes) equations. Requirements both from load capacity and motion stability is considered and compromised for a better and stable performance of the air journal bearing. The shaft is stably rotated in a relatively low speed of 1.18×105rpm, which is much lower than other researches and can be achieved easily.

Abstract: In this paper, an elastic deformation of the axial foil hydrodynamic thrust bearing used in 100KW gas turbine generator is studied. The finite element model of the foil hydrodynamic thrust bearing was established using Solidworks and ANSYS. The foil hydrodynamic thrust bearing which considered foil deformation was analyzed and calculated based on the results of the approximate calculation. The FEA model considered the interaction of plane foil deformation and wave foil. The wave foil was not hypothesized as the linear distributed spring when set up the finite element model. The ANSYS results have demonstrated that the deformation of foil bearing designed based on the result of numerical calculation can meet the requirement of minimal film thickness of bearing lubricant layer.