Papers by Author: Yong Jun Tang

Abstract: Increasing concerns about reliable supplies and envi­ronmental consequences of petroleum-based fuels have made it important to develop sustainable green sources for liquid transportation fuels. One such source is cellulosic biomass. However, high costs associated with transportation and storage of low-density cellulosic biomass has hindered large-scale, cost-effective manufacturing of cellulosic biofuels. Ultrasonic vibration-assisted (UV-A) pelleting can increase biomass density, improve storability, and reduce transportation costs. This paper reviews the state of the art of this technique, covering the effects of different process parameters on pellet quality, pellet charring, pellet crack, and sugar yield. It can be concluded that pellet density increases with an increase in ultrasonic power and pelleting pressure, and with a decrease in biomass moisture content and particle size. However, large ultrasonic power may lead to the charring of cellulosic biomass, which adversely affects the conversion of cellulosic biomass to ethanol. In addition, some problems associated with UV-A pelletingof cellulosic biomass are proposed.

Abstract: In order to resolve the problem of polishing micro-shafts and cavities, a novel technique of Micro-Electrochemical Polishing Mixed with Powder (EPMP) has been presented in this paper. That can be accomplished through high speed spindle driving micro-abrasive to proceed soft-grinding, which can achieve merit of little polishing force. The principle of EPMP has been introduced, and a series of issues have been studied. Finally, experiments of EPMP have been carried out based on above optimized machining parameters, and a micro-screw-shaft of Φ100μm has been polished. Which is near to mirror effect (Ra=0.02μm).

Abstract: In order to obtain well work performance, a new design process and the optimal method are systemically presented during ultrasonic vibrator’s design. Firstly, the general dimensions are calculated according to formula of ultrasonic theory. Secondly, 3D model without flange is established, and the best position setting a flange has been conformed through finite element analysis (FEM). Then constraints are laid on the flange, and the best model of vibration is obtained based on model analysis. The results are benefit to the following control design of ultrasonic vibrator. Finally, an ultrasonic vibration system has been made, and a series of experiments validate the feasibility of the design method.

Abstract: In order to resolve the problem of connecting rod notches machining, a new process of WEDM (Wire Electric Discharge Machine) has been presented, and it is greatly possible that expensive laser process can be replaced by WEDM in virtue of its unique advantages. Firstly, process parameters of notch have been analyzed, and project of machining notch using WEDM has been introduced, including measures to achieve good-quality notch. The relationship between cutting speed and power supply parameters has been investigated, and it is discovered that micro-crackle on bottom of notch are greatly effect to fracture splitting process, also new idea of active controlling micro-crackle has been presented. Finally, fracture splitting machining has been carried out. The cost and entrance standard of fracture splitting process are greatly dropped owing to new breakthrough of machining notch using WEDM.

Abstract: A system of ultrasonic combined with grinding has been designed, and one novel connective method of straight screw combined with taper surface has been applied in spindle, so compact size and high revolving accuracy can be achieved. Modal analysis of ultrasonic vibration system has been implemented by FEM (Finite Element Method), and its optimal dimension has been calculated to find out optimal vibration estate. Full-bridge converter has been applied in driving circuit of ultrasonic vibrator, and auto-frequency tracking has been designed in order that ultrasonic vibration works on resonant or quasi-resonant frequency. Finally, machining experiments have been fulfilled about ultrasonic combined with grinding, and its machining effect has been distinctly improved comparing ordinary grinding machining.

Abstract: A nanosecond pulse power supply for micro-ECM (Electrochemical Machining) has been developed, and the minimum pulse on-time is 50 ns. After the influence of ultra-short pulse on micro-ECM was analyzed, complementary chopper circuit was presented to avoid waveform distortion, which can achieve higher pulse frequency. A fast protect circuit was designed, and its response time is less than 5μs, which can avoid damaging workpiece and electrical components by switching off machining voltage and step motor as soon as a short circuit was detected. A series of ECM experiments using the power supply have been carried out, and results of test have proved that high frequency, short pulse width power supply helps to achieve better quality surface, higher machining accuracy.

Abstract: In order to improve machining accuracy and surface quality effectively in ECM (electrochemical machining), a novel pulse inversion power supply has been presented, which has following merits such as high-frequency short pulse, high-power, and compact size. The scheme of full bridge inversion has been selected in this power supply model, and feedback circuit realizes voltage adjusted automatically, and guarantees to stability of voltage. Protect circuit has designed to avoid the problem of workpiece-burn. Finally, a series of electrochemical mechanical polishing tests using the power supply have been carried out, and the results have proved that it helps to achieve well surface quality processed, and improve machining accuracy, and also verify feasibility of its scheme.

Abstract: In order to operate in narrow space, a novel miniaturized EDM (Electro Discharge Machining) mechanism has been developed. A prototype of miniaturized EDM device based on ultrasonic motor (UM) has been developed, which has its advantage of compact size (70×40×50 mm). The differential driving electrode has been presented, and coaxial forced vibration of electrode is benefit for the evacuation of debris, so it helps to achieve stable and efficient machining. Driving principle of ultrasonic motor is analyzed, and simulation using Finite Element Method (FEM) is accomplished. The auto-frequency tracking has been carried out, in order that the motor work on resonant or quasi-resonant frequency. Finally, EDM experiment has been finished, and holes with figures of circleΦ85μm and Y-typed have been machined.