Yu Kui Wang

Micro-Hole Drilled by EDM-ECM Combined Processing

A new method for drilling micro-hole called EDM-ECM combined processing is proposed in this paper. This method consists of EDM shaping and ECM finishing, and they are carried out in sequence on the same machine tool with the same electrode but different dielectric medium. Micro-hole drilling experiment was done by micro-EDM, micro-ECM and EDM-ECM combined processing. The results show that the machining efficiency is improved by 9.2 times compared to conventional micro-ECM, and machining precision and shape accuracy of micro-hole are much better. The surface quality and mechanical property of the workpiece are improved, since the recast layer and surface defects generated by EDM are removed completely by ECM finishing. It proves that this combined machining method is possible and useful in the field of micro-hole drilling.

Electrochemical Machining of Micro Slots Using Shaped Electrode

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.

Optimze the Structure of Impeller for Stirred Bioreactor

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.

Optimization and Analysis for Surface Roughness of SiCp/Al Metal Matrix Composite by Micro-WEDM

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.

The Contact Resistance and Arc Erosion Behavior of Separable CP-Nb-Cr/Cu-Cd Electrical Contact Material

CP-Nb-Cr/Cu-Cd electrical contact material, which contains 1.7wt.% of Cd, 0.5wt.% of CP (man-made diamond particles), 2.0 wt.% of Nb and 0.7 wt.% of Cr, was fabricated by powder metallurgy process. The contact material was installed in different ac contactors covering current range from 40 to 630A. While tested under AC-4 electrical load, the electrical contact material was worn out gradually by repeated electrical arc, and microstructure of the arc-affected surface layer changed dramatically. Mechanism of arc erosion process and contact resistance fluctuation was discussed by corresponding microstructure observation and chemical composition analysis of the surface layer. CP-Nb-Cr/Cu-Cd electrical contact material is capable to be used in 63~250A ac contactors under AC-4 working conditions.

Design and Fabrication of an Aerodynamic Micro-Air Journal Bearing Using Micro-Wire Electrical Discharge Machining

This paper proposed a removal analysis and a contouring strategy of accurate micro-WEDM processing for an aerodynamic micro-air journal bearing for micro-gas turbine engine. It is designed based on aerodynamic theory and can be self-acting by the compressed air pressure. The rotor is stably rotated in a relatively low speed which is below one hundred thousand revolutions per minute, and is much lower than other references. The extended and trimmed tool path is adopted in this paper, and the cusp at the corner of the micro-air journal bearing is obtained by this method which is better than the common arc tool path. The inner and outer diameter of the micro-air journal bearing with a satisfactory shape and good surface quality is 1.068mm and 1.165mm, respectively. The minimum radius at the bottom of wedged-structure is 15.9μm. The kerf of the blanking is 43μm, and the machining discharge gap is 18μm under this machining conditions. The MRR calculated by experimental data is 0.00144mm2/min.

A Coupled Thermal Structural Finite Element Analysis of a Single Pulse Micro-EDM Process

A three-dimensional coupled thermal structural model for micro electrical discharge is presented in this paper. Temperature field and thermal stress field of a single spark discharge process are analysed using this model by indirect coupling method. Temperature field is firstly solved which acts as the foundation of solving thermal stress field. To make the simulation results more reliable, these important elements are also taken into account, such as temperature-dependent properties of material, the phenomenon of plasma channel radius expanding, the percentage of discharge energy transferred to the workpiece and Gaussian distribution of heat flux. The results can explain the formation of cracks around the discharge crater. The thickness of the white layer and residual stresses can be predicated using this model.

CAD/CAM System of Micro-WEDM for a Micro-Air Journal Bearing Fabrication

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.

Numerical Simulation of Cathode Erosion in EDM Process

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.

Analysis of Elastic Deformation of Axial Foil Hydrodynamic Thrust Bearing Used in Turbine Generator

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.