Papers by Author: Hong Jun Xu

Abstract: Heat transfer performance of the heat-pipe grinding wheel (HPGW) is mainly depended on the heat pipe in the wheel. In this paper, a basal body of HPGW was developed and a heat transfer experiment was performed to study the effect of the parameters of the heat pipe such as liquid filling ratio and rotating speed on the heat transfer performance of the HPGW. Results show that the heat transfer performance decreases if the liquid filling rate is too large or too small under the same heat source intensity and the optimal liquid filling rate is about 35% of the volume inside the heat pipe. The heat transfer performance of the HPGW is enhanced with the increasing of the rotating speed. The analysis of the results also shows that the heat pipe in the HPGW can play a great role on enhancing the heat transfer in the grinding zone with suitable processing parameters.

Abstract: This study has developed a new kind of high performance monolayer brazed diamond tool for ceramic grinding. The grit size of the diamond brazed in the grinding wheel surface is 300m, which has never been reported in diamond tools for ceramic precision machining. The experiment has achieved wonderful surface finish of Zirconia workpiece. This does owe to the designed and precision conditioned topography of the new developed grinding wheel. The topography of the grinding wheel before and after dressing has been measured by means of laser triangulation method. Then the Zirconia workpiece has been ground. The obtained Ra value decreases with no spark grinding times and the minimum Ra of the ground surface is 0.11m. The study proved that the brazed large grit diamond tools would realize high efficiency and precision grinding, namely, high performance of ceramic grinding.

Abstract: Conventional grinding of optical glass will normally result in not only much lower material removal rate but also short service life of grinding tools, which causes the high fabrication cost of optical glass. This paper focuses on the precision grinding of optical glass with the indigenously developed monolayer brazed diamond grinding wheel. Before grinding process a precision dressing is conduct. The dressed grinding wheel topography is observed. Through precision dressing the grinding process achieves moderate surface finish as well as ensures certain grinding efficiency. The ground surface of the optical glass workpiece is made up of micro-pits and glazing zones and the obtained surface roughness variation with the process parameters is analyzed. The experiment shows that the developed diamond grinding wheel is suitable to the application of optical glass machining.

Abstract: The monolayer brazed diamond tools have recently been used increasingly in hard-brittle materials grinding because of their excellent grinding performances as long tool life, high material removal rate and large inter-grit chip space, etc. However, they possess an inherent shortcoming of the high roughness of the grinding surface. This work is an attempt to reduce the over-protruded grits of the monolayer brazed diamond wheel so that precision grinding operations can be executed effectively. In this investigation, the monolayer brazed diamond wheels with regular distribution pattern of grit have been dressed by a special conditioning process and used in precision grinding experiments on Li-Ti ferrite. The outcome of this attempt appeared highly encouraging. A substantial improvement of the ground surface roughness could be achieved with the dressed monolayer brazed diamond wheels.

Abstract: Li-Ti ferrite used in aviation occasions needs good surface quality. In conventional grinding it is difficult to meet the surface demand. Accordingly, this paper proposed a new grinding process to change the situation. The process employed graphite grinding wheel which is always used in ultra-precision grinding of steel piece. The process can obtain good surface quality and ensure certain material removal rate. The ground surface appearance is nearly mirror-like. The lowest surface roughness of Ra value of the ground surface is 0.05μm in the experiment. The ground surface morphology is made up of spread glazed area and dispersed minute pits. The ductile regime dominates the material removal mechanism and no surface damage is induced in the process. In consideration of the results in the experiment it can be seen that grinding with graphite grinding wheel is a good finishing procedure in ferrite machining because of its obtained high surface quality.

Abstract: An attempt has been made to investigate the new generational manufacturing technology for multi-layer diamond tools by brazing. A kind of new multi-layer brazed diamond core drills with random grains distribution was made by mixing diamond particles with brazing alloy powders. And a preliminary machining performance experiment was carried out through drilling granite. The testing results show the typical topography of the multi-layer brazed diamond core drills after drilling granite, just like that of multi-layer sintered ones, is that diamond grits drag long tails. Different from multi-layer sintered diamond core drills, no grit pull-outs can be seen during the whole drilling process because of chemical metallurgical effect between diamond grit and brazing alloy, the same as monolayer brazed diamond core drills. The main drawback to this kind of multi-layer brazed diamond tools is each individual particle is not subjected to the same drilling force throughout the drilling operation because of random grain distribution. This leads to premature fracture of the leading particles. Similarly, because large gaps between particles exist, the bond is being exposed to the workpiece, which leads to erosion of the bond. The overall performance is lower tool lives and slower drilling speeds. Therefore, ideally, diamond particles should be evenly distributed throughout the bond, which means they are all subject to the same drilling forces and the multi-layer brazed diamond tool is operated at its optimum efficiency.

Abstract: In order to improve the machining performance of the new type porous metal bond wheel, a new attempt were carried out for fabricating porous metal bond matrix with adjustable and high porosity as well as large pore size by use of pore-forming agent ammonium bicarbonate (NH4HCO3) and a vacuum loose powder sintering process. The porosity, bending strength and microstructure of the as-sintered porous metal bond matrix have been studied. The results show that the pore-forming agent NH4HCO3 with a certain amount can effectively increase porosity and pore size. The porosity of the fabricated porous metal bond matrix increases linearly with addition of ammonium bicarbonate and reaches as high as 67.7%, while the size of pores is larger than 300 μm. Meanwhile, the use of the raw materials were given and the sintering mechanism was discussed.

Abstract: A new type of brazed diamond grinding wheel with a rotating heat pipe is developed to effectively remove the heat generated in the grinding zone meanwhile minimize the pollution and contamination of the environment. A grinding temperature-measurement experiment of titanium alloy was conducted to evaluate enhanced heat transfer effect of the rotating heat pipe on the grinding zone. The experiment results show that, when grinding using the wheel with heat pipe the grinding temperature decreases 30% than that using the wheel without heat pipe.

Abstract: The shear strength samples of brazed single crystal diamond with the (72Ag–28Cu)–xTi (x=2, 4, 7wt.%) active filler metal were prepared, using vacuum brazing methods. Microstructure evolution of interfacial reaction product and shear strength of the brazed diamond and Ag based filler alloy were studied. The results show that there exits a layer of TiC on the surface diamond in different Ti additions, and the thickness of TiC layer increases with the increase of Ti addition. With the increase of Ti addition, the shear strength of the brazed joint decreases due to the increase of TiC layer thickness and amount of intermetallics. From the results, it was seen that mutual diffusion of C and Ti was effective on the morphology of the interface zone that affected the shear strength of the bonds. To achieve a reliable brazed joint, the Ti content must be controlled under 4wt.%.

Abstract: Brazing diamond grits onto steel substrate using a Ni-based filler alloy was carried out by laser beam in an argon atmosphere. The microstructure of the interfacial region among the Diamond grits, the filler layer and the steel substrate, were investigated by means of scanning electron microscopes (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Meanwhile, the formation mechanism of carbide layers was discussed. All the results indicated that the active element chromium in the Ni-based alloy concentrated preferentially to the surface of the grits to form a chromium-rich layer, and the hard joint between the alloy and the steel substrate is established through a cross-diffusion of iron and Ni-based alloy.