Papers by Author: Ming Jun Chen

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Authors: Ming Jun Chen, Qi Long Pang, Jing He Wang, Kai Cheng
Abstract: 3Dfractal dimension and 2D profile fractal dimension distribution of the surfaces made by brittle or ductile grinding are calculated. From the calculated results of 3D fractal dimension, it can be found that the microtopograhpy of ductile ground surface is more exquisite than brittle ground surface and 3D fractal dimension Ds has inverse relation with the roughness parameter Rq. Through the analysis of 2D profile fractal dimension distribution in different ground surfaces, it is revealed that the topography of ground surface is changed with grinding parameters such as ground surfaces may have weakly or strongly anisotropic even isotropic features when different grinding parameters are adopted. Using fractal method to analyze the topography of ground surface is helpful to understand the generating mechanism of surface topography.
Authors: J.Z. Zhang, Dan Li, Ming Jun Chen, Shen Dong
Authors: Ming Jun Chen, Ziang Li, Kang Jun Luo, Ying Chun Liang, Zhen Fang, Bo Yu
Abstract: Fused silica glass is widely used on the manufacture of optical apparatus and resonators due to it’s interesting optical and vibration properties. In order to machining the complex structures in the resonators and optical apparatus, grinding process with inclined ball-headed diamond wheel is discussed. Analytical model of the grinding process with inclined ball-headed diamond wheel was built firstly. Afterwards grinding experiments were conducted by varying the feed speed, the rotation speed, the cutting depth and the average grain size of the ball-headed diamond wheel. The machining surfaces were characterized by surface profiler to investigate the effect of the grinding parameters on the surface roughness. The measurement result shows the average grain size of the diamond wheel has important influence on the machining surface and the surface roughness at the groove bottom is better than the groove edge due to the wheel axis tilt angle.
Authors: Ming Jun Chen, Wen Bin Jiang
Abstract: Indentations on the three main crystallographic planes (100), (110), and(111) of CaF2 were analyzed. Appropriate material parameters were obtained by experimental load-displacement curves. The results show a value in the range of 70–110 MPa for the initial shear yield strength. The submicron-level orthogonal cutting process of CaF2 had been investigated by the finite element approach, and the effects of tool rake angle on cutting stress and chip formation were investigated. The results indicate that increasing the tool rake angle causes a significant increase in stress and a decrease in chip thickness. The simulation results from the present study show the optimal tool rake angle to the ultra-precision cutting of CaF2 is -20°.
Authors: Ming Jun Chen, Jing He Wang, X.M. Chen, Ying Chun Liang
Abstract: In order to study mechanical property with different crystal-plane and different crystal orientation of the crystal KDP, nano-indentation experiments are first done. The mechanical properties of crystal KDP, such as elastic modulus, yielding stress, are obtained from the analysis of the experimental curve. To obtatin the stress-strain curves of crystal KDP, by using the spherical tip can get characteristic of continuous strain, the spherical indentation experiments is proposed firstly and carried out. According to obtained parameters, A finite element cutting model of crystal KDP is established. The cutting process of crystal KDP is simulated by the model, and the influence of rake angle and depth of cut on chip and surface quality is studied. The theory shows that when the cutter’s rake angle is in the range of -40° to -45°, an perfect super-smooth KDP crystal surface will be obtained. Finaly, the experiments is carried out on special ultra-precision machine tool for crystal KDP by ourself devoloping. Experiment results show that when the cutter’s rake angle is about -45°, an super-smooth surface (rms: 6.521nm and Ra: 5.151nm )is obtained on the plane (001), and this experiment certified correctness of theory analysis.
Authors: Jing He Wang, Ming Jun Chen, Shen Dong, H.X. Wang, J.H. Zhang, Wen Jun Zong
Abstract: In this paper, mechanical characteristics of KDP crystal anisotropy are analysed theoretically. Vickers indentation experiments are adopted to validate the variation rule of hardness and fracture toughness in different orientation of KDP crystal plane (100), and a model to calculate critical cutting thickness of brittle-ductile transition is proposed for the KDP crystals. The result shows that, on the crystal plane (100), the minimum value of critical cutting thickness of KDP crystal in brittle-ductile transition appears in the direction [110], but the maximum appears in the direction [010]. Finally, the ultra-precision machining of KDP crystal is performed, and the results agree well with the theoretical conclusions. Super-smooth surface with a roughness RMS of 6.6nm is reached as machined in the crystal direction [010], and 11.2nm to the direction [110].
Authors: Jing He Wang, Ming Jun Chen, Shen Dong, Shi Qian Wang
Abstract: In the ultra-precision machining of KDP crystal, there are many factors affecting the surface quality[1-3]. The experiments show that the rake angle and back angle of the tool have significant effects on machined surface roughness. Therefore, an efficient way to improve the surface roughness is to select a proper negative rake angle. In this study, the ANSYS static analysis method was employed to analyze the stress field distribution within the whole cutting region. A finite element simulation model was set up to calculate the residual stresses variation with tool’s angles, which can be considered to select optimal rake and back angles in the ultra-precision machining of KDP crystal. Results show that the optimal tool rake angle and back angle are -49° and 7°, respectively. Finally, by using different tool angles to process KDP crystal and utilizing AFM to analyze the surface roughness, it can be found that the measurement results agree well with what are deduced from theoretical calculation.
Authors: Yin Rui Su, Dan Li, He Nan Liu, Ming Jun Chen, Hui Peng
Abstract: In order to resolve the difficulty in polishing work of complex shape, a new magnetorheological finishing (MRF) technology with a small permanent magnet ball-end tool is developed. Rotary symmetrical magnetic field generated by the small permanent ball-end tool, stiffen a magnetic fluid which is delivered by a slender needle tubing, in contact with a workpiece. The permanent magnet tool is hold by a slender cylindrical shank, so it won’t interfere with workpiece when polishing deep concave cavity. A prototype apparatus is established to study the processing characteristics of this polishing method. MRF spots are taken on stationary workpiece to study the influence of several processing parameters on the material removal function, such as, spindle speed, included angle and minimum gap between polishing tool and finishing-surface. A 3×3mm square on a fused quartz (FS) is polished and the surface roughness decrease from 81nm Ra to 1.5nm Ra after polishing for 100min.
Authors: Jing He Wang, Shen Dong, H.X. Wang, Ming Jun Chen, Wen Jun Zong, L.J. Zhang
Abstract: The method of single point diamond turning is used to machine KDP crystal. A regression analysis is adopted to construct a prediction model for surface roughness and cutting force, which realizes the purposes of pre-machining design, prediction and control of surface roughness and cutting force. The prediction model is utilized to analyze the influences of feed, cutting speed and depth of cut on the surface roughness and cutting force. And the optimal cutting parameters of KDP crystal on such condition are acquired by optimum design. The optimum estimated values of surface roughness and cutting force are 7.369nm and 0.15N, respectively .Using the optimal cutting parameters, the surface roughness Ra, 7.927nm, and cutting force, 0.19N, are obatained.
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