Papers by Author: Wen Zhuang Lu

Abstract: A series of grinding experiments were carried out with CBN wheel to focus on the surface integrity of titanium alloy TC4-DT in high speed grinding . In order to get the proper process parameters to control the surface integrity of the TC4-DT, surface roughness, subsurface morphology and microhardness variations have been studied. In addition to the use of CBN wheel, scanning electron microscopy (SEM), 3-d contour instrument and microhardness tester was applied. The results show that the surface roughness is decreased obviously when grinding wheel linear velocity rises from 60m/s to 80m/s. While the grinding speed rises from 80m/s to 100m/s, the surface roughness value increases slightly. Moreover, the surface roughness value increases with the grinding depth and the increasing trend is obvious in the process of machining. The microstructure analysis shows that during high speed grinding with CBN wheels, good quality surface with 10μm grinding depth can be obtained. Table feed rate has weak influence on the grinding surface topography. The microhardness analysis indicates that surface microhardness increases sharply with the increasing of grinding wheel linear velocity in high speed grinding.

Abstract: Chemical vapor deposition nanocrystalline diamond (NCD) film has numerous unsurpassed properties, among them, bulk modulus, hardness; abrasion resistance and thermal conductivity are notable ones like polycrystalline CVD diamond film. The super mechanical properties have made NCD film to be an effective way to improve the resistance performance of the ceramic bearing and extended its life. The contact stress of bearing ball with NCD coating in elastic contact was analyzed. Factors such as substrate material, thickness of NCD coating, load and interlayer material which affect the shear stress distribution of NCD coating on bearing ball were investigated. The results show that substrate with low elastic modulus and heavy load will enlarge the difference of equivalent stress value at NCD/substrate interface. Thick film will make the stress distribution at the interface uniform. Soft interlayer should be inhibited to avoid extra stress in contact status.

Abstract: The size and accuracy of the micro-structure is determined by the performance of micro-milling tool. To reduce the tool vibration and improve the machining quality, research on the mechanical characteristics of micro-milling tool is necessary. Finite element method was used to research the mechanical characteristics of micro-milling in this paper. By Mode and Static Analysis, the natural frequencies and mode shapes of various structure of micro-milling cutter was studied. The stress and deformation characteristic, including the influence, was also studied. Finally, the suggestion of optimal structure was supplied.

Abstract: The performance of Atomic Force Microscope (AFM) is greatly determined by the quality of its probe. Nowadays, probes of diamond tips have become more and more popular than silicon ones, and have been widely used in industries. In this paper, research about the fabricating of nanocrystalline diamond (NCD) coated AFM probe has been done using Hot-Filament Chemical Vapour Deposition (HFCVD) technique. The results showed that NCD films have been grown on the probe. Problems about the growth of NCD on the tips have been discussed. The optimum parameters have also been proposed. This research can provide reference for the further experiments on the fabrication of NCD coated tips.

Abstract: The performance of CVD diamond coated cemented carbide cutting tool in comparison with K10 uncoated cemented carbide tool in the dry turning of Al-20wt%Si aluminum-silicon hypereutectic alloy was investigated. The obtained results showed a better cutting performance for CVD diamond coated tool in machining Al-20wt%Si, particularly in terms of cutting force, tool wear, surface roughness, when compared with K10. The cutting forces are lower with CVD diamond coated tool and the depth of cut promotes a great increment of the cutting force. The tool wear processes taking place in the tool tips in all cutting conditions. The tool life of CVD diamond coated tool is longer than that of the uncoated K10. The surface roughness Ra increases obviously with the increase of feed rate using a CVD diamond coated cutting tool. A higher feed rate produces surface rougher. The chip morphology in machining of Al-20wt%Si alloy by CVD diamond coated tool is continuous. The tests showed that the CVD diamond coated tool can be applied on the K10 tool at low feed rate to produce high quality surfaces.

Abstract: The contact stress of cemented carbide with NCD coating in elastic contact was analyzed using ANSYS. Factors such as elastic modulus and thickness of NCD film and elastic modulus of interlayer which affect the shear stress distribution of NCD film on cemented carbide substrate were investigated. The results show that the maximum shear stress point moves towards the interface with the increase of film elastic modulus. Film thickness has a significant effect on shear stress distribution of NCD film. High shear stress develops in the film layer with the increase of film thickness. Interlayer with low elastic modulus will cause shear stress concentration in NCD film.

Abstract: The magnitude and the uniformity of the substrate temperature are the most important factors that affect the quality and the growth rate of diamond films deeply. In this paper, the model of the swing substrate temperature field is established according to the heat transfer theory in Miniature EACVD System, the effects of the hot-filament parameters and the substrate swing parameters on the magnitude and uniformity of the substrate temperature were discussed. The calculated results show that the hot-filament parameters have great influence on the magnitude of the substrate temperature , the results also show that the hot-filament number , the substrate swing angle and the distance between the hot-filament and the substrate affect the uniformity of the substrate temperature field deeply. All the results provide a basis for optimizing the parameters of deposition in Miniature EACVD System.

Abstract: The thermal blockage and thermal round flow in HFCVD system for CVD diamond growth will lead to un-stability of product quality. Finite element method has been used to simulate the gas flow field around the cutting tool substrate within a HFCVD diamond reactor. Experiments have been done to prove the simulation results. Excellent agreement between simulation and experiment was obtained by depositing of CVD diamond coated cutting tool. The thermal blockage and thermal round flow in HFCVD system decrease by using a hollow substrate holder. High quality CVD diamond coating can be obtained using a hollow substrate holder.

Abstract: Ice fixed abrasives (IFA) polishing is a novel ultra-precision machining method. The motion tracks of abrasives during IFA polishing have an important effect on the quality of the machined silicon wafer. Firstly, the motion tracks of IFA polishing are theoretically analyzed in this paper. It is founded that the paths of any point in the IFA polishing pad relative to the wokpiece are a group of cycloids. Then, the motion tracks of single abrasive and multiple abrasives in the IFA polishing pad are simulated respectively. The results show that increasing the eccentricity is beneficial to the enlargement of the size range of polishing process. With the increasing of the speed ratio between the IFA polishing pad and the workpiece, the abrasive at higher speed can leave longer tracks on the workpiece than that at lower speed at the same time. The more the abrasives, the more uniform the mark density under the influence of more abrasives.

Abstract: Chemical vapor deposited (CVD) diamond film has a series of outstanding properties. However, it can not be easily machined by conventional technologies available currently for its high hardness and stability. Laser processing diamond film method can be an efficient way to process diamond film because of its high energy density. The mechanisms of laser processing diamond film are thermal oxidation, graphitization and evaporative ablation of graphite. Temperature distribution is of great importance to understand these complex phenomena taking place during the process because different temperatures lead to different physical and chemical changes of diamond. In this paper, the finite element method (FEM) software ANSYS is applied to calculate the temperature distribution. The relation between etching depth and laser machining parameters (laser power and scanning speed) is presented. The proper parameter ranges of laser power and scanning speed for a certain etching depth is also investigated with this method.