Papers by Author: Dao Hui Xiang

Abstract: Nano-ceramics possessed ascendant mechanical property and physical characteristics contrast with traditional engineering ceramics, and its machining with ultrasonic assistance has been considered one of the most efficient methods. In the present paper a novel ultrasonic grinding vibration device has been developed and the theoretical model of grinding force has been created for ultrasonic vibration grinding. The influences of grinding parameters on grinding forces were tested with self-designd acoustic system based on local resonance. According to the test data, the effect of depth of cut and wheel velocity on the grinding force with/without ultrasonic assistance was analyzed. Both in common and ultrasonic grinding the normal grinding force and tangential grinding force descend against the wheel velocity, while ascend along with the depth of cut. In any case the grinding force in ultrasonic grinding was not more that that in common grinding.

Abstract: Large advancements have been achieved in understanding nucleation and growth of CVD diamond, but adhesion of diamond film to substrates is poor and there is no good methods about how to quantitative evaluation of the adhesive strength. The blister test is a method appropriate for measuring the adhesion of CVD diamond. In this test a pressure difference is applied across a thin film and the pressure when the film separates from substrate is measured, and the adhesive strength of diamond thin film was calculated using analytical model. Using the finite element model, the deflection at the center of a free-standing window sample of diamond thin films is calculated as a function of applied pressure and the adhesive strength is obtained using the FEM. The result indicates that finite element method-based prediction of the total energy release rate is in good agreement with that obtained from analytical expressions and experimentally observed values.

Abstract: Despite great advancements in diamond thin film growth and deposition techniques, determination of the residual stress and Young’s modulus for diamond films has continued to be a challenge. The bulge test is a potentially powerful tool for characterizing the mechanical properties of diamond film. In a bulge tester, pressure is applied on a thin membrane and the out-of-plane deflection of the membrane center is measured. The Young’s Modulus and the residual stress are simultaneously determined by using the load-deflection behavior of a membrane. By means of electron-enhanced hot filament chemical vapor deposition (HFCVD), a diamond film was deposited on silicon slice (100), and the free-standing window sample of diamond thin films was fabricated by means of photolithography and anisotropic wet etching. The deflection of the membranes is measured using a laser interferometry system. The elastic modulus and residual stress were measured using a self-designed bulge equipment. In addition, the distortion of diamond thin films under different pressure was simulated using finite element analysis and the contrast was made with experimental data. The research indicated that the Young’s Modulus of diamond thin films is 937.8GPa and the residual stress is -10.53MPa. The elastic modulus and the residual stress coincide with the report in the literature and the value tested by X-ray diffraction, respectively. This method uses a simple apparatus, and the fabrication of samples is very easy, and it has provided an effective means for precise measure the mechanical properties of other thin films.

Abstract: Nanocrystalline diamond film with smooth surface and uniform grains was deposited successfully on Co-cemented carbide using the bias-enhanced hot filament chemical vapor deposition (HFCVD). The surface morphology and chemical quality of film were estimated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. Comparative experiments of tribological and wear performances of conventional and nanocrystalline diamond films were carried out by pin-on-disc tester. The research results show that nanocrystalline diamond film with good tribological performance and high quality can be deposited by regulating the deposition parameters on Co-cemented carbide. The film not only has high adhesive strength but also has smooth surface, low surface roughness, low friction coefficient. The work done in this paper provide the wide application of diamond on complex shape tools, drawing dies and other wear resistant device with experimental reference.

Abstract: Nano ceramics possesses excellent mechanical property and physical characteristics in contrast to conventional engineering ceramics, so it has tremendous application prospect. Adopting ultrasonic composite processing we describe the influences of grinding speed, grinding depth, wheel granularity and no-spark grinding times on the surface roughness of nano ZrO2 ceramics. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics in the condition of conventional and ultrasonic grinding are also discussed. At last, the residual stress of surface and crystalline phase transformation under the condition of conventional grinding and ultrasonic vibration grinding were analyzed by X-ray diffraction. The research indicated that ultrasonic vibration grinding could obtain nano finished surface with high efficiency. The residual stress of nano ZrO2 ceramics surface is determined much by different grinding styles.

Abstract: The crack extension course and ductile removal mechanism of nano ZrO2 ceramics were analyzed in this paper. On the basis of contrast tests with or without ultrasonic vibration, the influences of critical ductile grinding depth on grinding forces and surface quality were studied by dynamometer, SEM and AFM in different grinding condition. The reason for the increase of the critical grinding depth was discussed based on the analysis of grinding force and ultrasonic vibration course. At last, the formation mechanism of surface topography observed by AFM in ductile domain was analyzed. The research indicated that ultrasonic machining could obtain nano finished surface with high efficient.

Abstract: Due to the large difference in thermal properties of the resin and the abrasive grits, the laser-assisted dressing technology is of great interest for grinding wheel preparation. From a viewpoint of thermal induced material removal mechanism, a numerical method was presented to simulate the laser dressing process. The numerical simulation results could reveal the relations between the laser parameters and the groove formation. The overlap coefficient was introduced for practical application. Simulation for the variation of the number of active grinding points was also made for non-uniform wheel topography. Based on the numerical modeling, the suitable grinding^wheel surface topography can be achieved through the laser-assisted dressing technology. The comprehensive researches on the laser-assisted dressing process control, grinding wheel topography reconfiguration by 3D laser scanning technology and analyses of grinding temperature were made. A series of grinding tests with the laser-assisted dressed grinding wheel and mechanically dressed grinding wheel were conducted for comparison. The results proved the feasibility of laser-assisted dressing for resin bonded superabrasive grinding wheels and revealed the importance of choosing appropriate laser dressing parameters.