Papers by Author: Hong Jun Xu

Abstract: A new segmented grinding wheel of the brazed monolayer diamond was developed with a defined grains pattern on the wheel surface. Results of grinding zirconia using brazed segmented diamond wheel were presented. The experiment results showed that the grinding forces ratio becomes higher with the increasing of the specific material removal rate and the specific energy falls with the increasing of the maximum undeformed chip thickness during grinding zirconia process. In this investigation, brazed diamond wheels with defined distribution patterns was conditioned by touch-dressing method so that grit tips get micro-conditioned and allow the underlying grits to participate and consequently improve the quality of finish. All the ground surfaces of zirconia were generated by the combined removal modes of brittle and ductile.

Abstract: The wear resistance samples of brazed single crystal diamond with Ni-Cr filler alloy were prepared, using high frequency induction brazing and vacuum brazing methods. By wear test of brazed single crystal diamond, the wear performance of the samples with different brazing processes was studied. The test result indicates that the wear performance of the high frequency induction brazed diamond samples is better than that of the vacuum brazed diamond samples. Because of different brazing processes, the wearing pattern of diamond varied; the wear course of the vacuum brazed diamond samples in the initial wear period were abnormal and the failure modes is different.

Abstract: The temperature, time and cooling rate are key factors in the hardening process using the grinding heat instead of the high frequency induction heat source. Thus, this paper established the mathematical model estimating the grind-hardening temperature, experimentally determined the grinding temperature and the cooling rate of different grinding parameters for 48MnV microalloyed steel using the conventional aluminum grinding wheel on a surface grinder, and investigated the grind-hardening effects and the forming mechanism of grind-hardening layer. The results show that the estimating temperatures are comparatively close to the measuring ones and hence the model could be utilized to optimize the processing parameters, and the satisfactory grind-hardening temperature and cooling rate could be achieved under the optimized processing parameters. The microstructure of the grind-hardening layer, the fine needlelike martensite in the entirely hardened zone, the martensite and ferrite in the transitional region is similar to that acquired through the high frequency induction technique. Especially, the average hardness of the entirely hardened zone is 740HV and the depth of the hardened layer is adjacent to 1.5mm, which indicate that the grind-hardening effects are very excellent. Different from the forming mechanism of the high frequency induction hardened layer, higher grind-hardening temperature is needed to compensate shorter time austenitization, and because of thermo-mechanical loading induced during grinding, from surface to inside, the morphology of martensite changes from fine to thicker, then to finer, other than from thick to finer.

Abstract: This paper introduces the new technology of ultrasonic vibration honing, and analyzes the cutting principle of ultrasonic honing in terms of cutting motion, grain performance and cutting quantity. Then, the applied effect used in the cast-iron cylinder of DY90 is introduced. The principle and the structure of this device are discussed. This new technology can further be used in micro-car’s cylinder, can provides a high-productivity, high-quality for cast-iron cylinder.

Abstract: The Ti-coated diamond and the uncoated diamond were brazed with Ni-based filler alloy by high-frequency induction under argon atmosphere at 1050°C within 15 seconds. The interfacial microstructures between brazed diamond and the filler alloy were analyzed by scanning electron microscopy (SEM), energy dispersion spectrometer (EDS) and X-ray diffraction (XRD). It is surprisedly found that Cr-carbides forms normally and compactly on the surface of Ti-coated diamond brazed, whereas Cr-carbide forms tangentially and loosely on the surface of uncoated diamond brazed. The abrade experiment results for the brazed diamonds show that the bond strength between the normally formed Cr-carbide and the diamond is higher than that between Cr-carbide and uncoated diamond brazed. Furthermore, the cause that Ti changes the morphology of Cr-carbides on the surface of Ti-coated diamond brazed is discussed by the further tests specially designed.

Abstract: Measurement of the grinding wheel topography and its change in machining process is important for revealing the grinding principle of high-temperature brazed mono-layer super-abrasive grinding wheel. A new approach of measuring grinding wheel topography based on binocular stereovision is presented. Firstly, the binocular images are achieved while the optical axes of the two cameras are parallel, and a corner reflection function algorithm is applied to detect corners. Secondly, in order to get matching corners, optimal matching template is obtained by matching curves. The experimental results show that the sequential similarity matching operation with optimal template has advantages of high accuracy, and less error matching. Finally, the height of the corners is obtained by calculating their parallax on left and right image, and the height error is less than 5%.

Abstract: A kind of brazed monolayer diamond grinding wheel was developed with a relatively regular distribution of grains on the wheel surface. Grinding performances of this kind of brazed wheel in the surface grinding of cemented carbide were studied. The experiment results show that the grinding forces ratio becomes higher with the increasing of the maximum undeformed chip thickness and the specific energy falls with the material removal rate during grinding cemented carbide process. Under certain grinding conditions, the material was removed almost through plastic deformation and good surface quality is gained. Furthermore, the grits of the brazed diamond grinding wheel fail mainly in attritious wear modes other than pull-out ones in conventional electroplated and sintered diamond tools, which indicates that the strong retention of brazing alloy to the diamond grits and longer service life of this kind of wheel.

Abstract: An experimental study on induction brazing diamond grinding wheel with Ni-Cr filler alloy was carried out. Brazing trial was conducted at the temperature range of 1020-1080 oC and the brazing time were 10, 20, 30 and 40 seconds in a flowing argon environment with a flow rate of 5000cm3/min. The scanning electron microscopic (SEM) results indicate that good wetting existed between the brazing alloy and diamond. The element distribution of C, Cr, Si and Ni were examined by energy dispersive spectrometer (EDS), the results demonstrated an intermediate layer rich in the chromium formed between the filler metal and diamond. Kinds of compounds formed in the interface were detected by means of x-ray diffraction (XRD), and the graphitization of the brazed diamond grits was determined by Raman spectroscopy. The monolayer induction brazing diamond grinding wheels were used in grinding of nature granite, experimental results show that induction brazing wheels performed better than vacuum brazing diamond wheels, and no pullout of diamond grits or peeling of the filler metal layer took place.

Abstract: Although the porous metal bonded diamond grinding wheel, which has recently been developed, had an excellent grinding performance for hard-brittle materials, its applications were only in precision grinding in past study. A new method for fabricating the new porous metal bonded diamond grinding wheel by Ni-Cr alloy as bond and vacuum loose powder sintering was proposed in this paper. The morphology of cross section of the segments and microstructure of interface between diamond grits and bond were analyzed. The wetting mechanism between Ni-Cr alloy bond and diamond is reacting wetting. Machining performance experiments about grinding ratio and surface roughness have been carried out. The testing results show that the porous Ni-Cr alloy bonded diamond grinding wheel has certainly fine machining performance in high grinding force occasion, and the maximal grinding ratio and best surface roughness were 6660 and 1.08
m, respectively.

Abstract: Ceramic coating materials own some advantages, for example high-rigidity, good abradability and good performance under high temperature. At the same time, ceramic coating materials are also difficult-to-machine materials. High machining precision and efficiency can be obtained in grinding WC-Co coating by cup wheel. The affection of grinding temperature is very important for grinding processing. But there is no research on grinding temperature of WC-Co coating by cup wheel. So in this paper, grinding temperature by cup wheel is researched on theory, the new concept, which is effectiveness width of arc moving heat source, is presented, and theoretical formula of grinding temperature is also built. Then experimental research on grinding temperature of WC-Co coating by cup wheel is done by use of thermocouple temperature measurement technology. The experimental results show the validity and effectivity of the theoretical formula. The affection of grinding parameters to grinding temperature is researched also.