Abstract: An attempt was taken to simulate the bending strength of diamond impregnated segments in three point bending tests by using a discrete element method (DEM). The influences of main bond matrix components (Fe and Cu), the porosity in the matrix, the coefficient of friction among the matrix particles, and the connection strength between abrasive particles and matrix particles on the bending strength were investigated through simulation. It is found that the bending strength increases with the proportion of Fe but decreases with the increase of porosity. An increase in both the friction coefficient of the matrix particles and the bonding strength between the diamond grains and metal matrix particles can also lead to the increase of bending strength.
Abstract: This study was focused on the theoretical modeling and numerical simulation about the dynamic characteristics of spindle system of ultra-high speed grinder. Based on the rotor dynamics and structural system dynamics, a dynamic model was established using the transfer matrix method and the overall transfer matrix method. The critical speeds of first three orders, the modes of variation and other dynamic characteristic parameters of the spindle system were analyzed and calculated. The results showed that the working speed of the spindle system is much lower than the primary critical speed and can therefore stay away the resonance range effectively. Furthermore, the span of the fulcrum bearing and the overhang had significant influences on the critical speed within a certain range, and the study provided the basis and guidance for the structural design and performance optimization of the spindle system.
Abstract: Abrasive machining is widely used as final machining process. It is still challenged to investigate the fundamental knowledge on the formation mechanism of groove and pile-up in single abrasive particle cutting. A 3D finite element analysis model to simulate single abrasive particle scratching on bearing steel (52100) workpiece with low cutting speed is proposed. An adaptive meshing technique is applied to handle large mesh deformation problem of the scratching process. The formation process of groove and pile-up for workpiece material is indentified qualitatively. The simulated results show that cutting speed has little effect on lateral profile. The height and area of pile-up increase with increase of depth of cut.
Abstract: In order to predict fatigue life of hybrid ceramic ball bearing (HCBB) by Ioannides and Harris (IH) theory, the contact subsurface stress field is needed. The contact surfaces of ball and race groove are compatible. The closed-form analytical solution of compatible contact problem is hard to be obtained. The Finite Element Method (FEM) together with submodel technology is adopted to accurately and efficiently calculate the contact deformation and subsurface stress of ball–race groove contact. The result indicated that, the FEM with submodel technology considers the real contact deformation of ball-race groove, and can accurately and efficiently calculate the subsurface stress field. It is believed that the calculated subsurface stress field can be used in IH theory to predict fatigue life of HCBB.
Abstract: Relief valves used in the coal liquefaction equipment are running in an extremely harsh environment with extraordinarily high temperature, high pressure differential, high fluid velocity as well as the intensely slurry flow erosion. The lifetime of relief valves is critically important to the reliability and running cost of the coal liquefaction equipment. Diamond film is potentially used as wear-resistant and protective coating for the relief valve components in coal liquefaction equipment due to its outstanding mechanical and tribological properties. In present study, a layer of high-quality diamond films are deposited on the working surface of conventional WC-Co cemented carbide relief valve components, using the hot filament chemical vapor deposition (HFCVD) technique. Two different types of hot filament arrangements are respectively adopted for depositing diamond films on the interior surface of valve seat and outer surface of valve spool. The fabricated CVD diamond coated relief valve components are characterized using Scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), and Raman spectroscopy. The results exhibit that working surfaces of both valve seat and spool are covered by a layer of continuous, homogeneous diamond films on which well-faceted diamond grains with grain size of ~2-3 μm distribute. Furthermore, the fabricated relief valve components are equipped on a coal liquefaction facility and their performance is evaluated in real production. The results present that the working lifetime is largely elongated up to ~1200 hours, as more than three times as that of conventional tungsten carbide valve components.
Abstract: Quasi atomic layer deposition method has been successfully used to coat detonation nanodiamonds with ultrathin silicon film from decomposition of gaseous monosilane. Transmission electron microscopy observation indicates a continuous silicon coating could be obtained on every individual particle of nanodiamonds. The changes in the microstructural property of silicon thin films deposited at the temperatures of 400, 450, 500, 550, and 600 °C have been characterized by Raman spectroscopy, X-ray diffraction and Energy dispersive spectroscopy techniques. The results show the phase transition of as-deposited silicon from a crystalline to an amorphous then to a crystalline phase with the temperature increase.
Abstract: Micro/nano-crystalline multilayered ultra-smooth diamond (USCD) films are deposited on the interior-hole surface of conventional WC-Co drawing dies with a combined process consisting of the hot filament chemical vapor deposition (HFCVD) method and polishing technique. Scanning electron microscopy (SEM), surface profilemeter, Raman spectroscopy and X-ray diffraction (XRD) are employed to provide a characterization of as-deposited USCD films. The results exhibit that as-deposited USCD films present an ultra-smooth surface, its surface roughness values (Ra) in the entry zone, drawing zone and bearing zone are measured as 25.7 nm, 23.3 nm and 25.5 nm respectively. Furthermore, the working lifetime and performance of as-fabricated USCD coated drawing dies are examined in producing copper tubes with hollow sinking, fixed plug and floating plug. The results show that the lifetime of USCD coated drawing is as more than 30 times as that of WC-Co drawing dies in the drawing process with hollow sinking, 7 times in the fixed plug drawing and 10 times in the floating drawing.
Abstract: Carbon fiber reinforced plastics (CFRP) have been widely used for manufacturing spacecraft, aircraft and automobile structural parts in aerospace and automotive industries. However, CFRP is a kind of hard machining materials and conventional tungsten carbide drills always experience severe tool wear, and thus short lifetime in the CFRP drilling process. In this paper, the CVD diamond films are deposited on the surface of cobalt cemented tungsten carbide (WC–Co) drills using hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscope (SEM) is adopted to investigate the surface morphology of as-fabricated CVD diamond coated drills, additional analysis using Raman spectrum also indicates the high purity of sp3 phase of as-deposited diamond film. Furthermore, the machining performance of as-fabricated CVD diamond coated drills is examined in drilling the CFRP, comparing with the uncoated WC-Co drills. The chisel edge and primary cutting edge wear of drills are studied using the tool microscope. The results show that as-fabricated CVD diamond coated drills exhibit a much elongated lifetime than that of uncoated WC-Co drills, and also smoother surface finish of machined holes, which is supposed to be attributed to the excellent wear resistance and satisfied adhesive strength between the as-deposited diamond films and drills.
Abstract: . High quality diamond film wafers with different thickness are prepared by high power DC arc plasma jet CVD (DCPJ CVD) method using a CH4/Ar/H2 gas mixture. The effect of substrate temperature on the quality of diamond film was studied with theoretical analysis and experimental investigation. The results indicate that different structures in diamond film may grow with different substrate temperatures. The temperatures of 800°C, 900°C and 1000°C were tested in the experiments. The quality of diamond film showed the best at the temperature of 900°C. Characterization by X-ray diffraction, Raman spectroscopy and SEM analysis are also carried out.
Abstract: Slicing the wafers with diamond wire saw is recently paid much attention. This study proposes a novel method for developing a kind of diamond wire saws with ultraviolet curing resin and spraying technique. The process of wire saw manufacturing and the selection of optimal parameters are introduced. The experiments of the slicing marble are carried out using different diamond wire saws. The effects of wire saw running speed, work-piece in-feed speed, work-piece rotation frequency on the material removal rate, and surface roughness were investigated. Result shows that new method for development of diamond wire saw is feasible.