Key Engineering Materials Vols. 304-305

Abstract: Wheel structure has a critical influence on grinding performance especially active cuttingedge density. Experiments were carried out to find out the relationshipbetween active and staticcutting edge density. It was found that there are many more active cutting edges in grinding thanexpected based on chip thickness formulae mainly due to wheel deflection in grinding.

Abstract: Optical surface finish below Ra 10nm can be achieved on a ‘Tetraform C’ grinder of ultra-high stiffness, when grinding a low alloy steel with or without the help of ELID (electrolytic in process dressing). Surface roughness generation modelling has been carried out to predict thepossible surface roughness values. Efforts have been made to transfer the process knowledge to different grinding mode using a rigid 5-axis Edgetek CNC grinder. The effects of material removal rate and grit size and also that of spark out passes on the surface roughness generated have been investigated.

Abstract: The paper presents a method that identifies and extracts features of chips on loading grinding wheel using image processing technology. The Sobel operator is adopted to detect chips edge. The segmenting threshold was obtained by applying Otsu's method. Image dilation connects the discontinuous segments to yield continuous and close shapes of chips. Erosion removes the noise from the image. The different optical characters between metal chips and abrasive grains are analysed. The ratios of chips are calculated and displayed to monitor the wheel surface working status. The toolbox of the MATLAB is used for image processing.

Abstract: Manufacturing of vitrified bond CBN wheels for internal precision grinding of the air-conditioner compressor piston hole is still big challenge to all of the domestic manufacturers. Recently, by choosing pre-melting mixed CBN abrasives and a proper sintering process, a cost-effective method was conceived to produce grinding wheels of comparative quality. The grinding performance of wheels was evaluated with a series of internal precision grinding of compressor piston hole. Experimental results show that the vitrified bond CBN grinding wheel produced by this method has better grinding performance, and can be substitute to the same type of grinding wheels imported. But the manufacturing cost is only 60% of the wheel imported according to estimation.

Abstract: Laser processing of abrasive grinding wheels is paying a great role in a truing technique to complement mechanical methods. An energy balance model was adopted that took into account the space modes of laser energy absorbed/scattered by the wheel (circular profile). Both geometric and mathematic models were developed to reveal laser processing mechanism and predict various processing parameters, such as incident position, focal offset, and incident power, to perform material removal during laser processing a cylindrical grinding wheel. Moreover, the incident angle for laser processing of small-vitrified CBN grinding wheels was optimized. Further theoretical analysis and experiments determined the focal position of the incident beam with respect to the wheel profile. Experimental studies were carried out using different processing parameters and grinding wheels to test the effects of laser space properties on processing quality. The experimental results were shown to be in reasonable agreement with predicted results.

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.

Abstract: A kind of new monolayer brazed diamond wire saw with both chemical bonding at the interface between diamond grits and brazing alloy and optimum grits distribution was made. And a machining performance comparative experiment was carried out between the sintered diamond saw from Italy and the brazed one mentioned above. The sawn material is marble with middle hardness. The testing results show that the wire saw with a brazed bonding diamond grid can achieve two to three times the working efficiency of conventional sintered diamond saw, and the corresponding service life can do 3~4 times. Furthermore, the grits of the brazed diamond wire fail mainly in micro fracture modes other than pull-out ones of the sintered diamond saw grits, indicating the strong retention of brazing alloy to the diamond grits. Almost no grits pulling out for brazed diamond wire saw is the key factor of its longer service life, and the optimum distribution and micro fracture of the brazed diamond wire grits raise the machining efficiency.

Abstract: Nanocrystalline diamond compact possesses not only the advantageous performance of polycrystalline diamond but also the high strength and the high toughness of nano-ceramics. However, single-phase nanocrystalline diamond compact is very difficult to sinter because of a huge amount of oxygen-containing and nitrogen-containing functional groups absorbed on the surface of nanocrystalline diamond. In this paper, atomic layer deposition (ALD) method has been used to coat nanocrystalline diamond with titanium, which will promote the bonding of nanocrystalline diamond as the bond in polycrystalline diamond. In vacuum, the H2 and TiCl4 reactants were employed alternately in an ABAB… binary reaction sequence to achieve Ti layer, which reacted with diamond matrix and formed TiC in the coating, realizing strong chemical bonding between the coating and the diamond. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized to study the structure and the morphology of the coating. The results confirmed the formation of titanium carbide at the depositing temperature 500°C. The darker spots and strips observed on nanocrystalline diamond particles by TEM were proved to be TiC and the nucleation and subsequent growth of TiC preferentially occurred in the defects as twin zones and dislocation areas on diamond surfaces.