Papers by Author: Qing Hua Kong

Abstract: A new dressing device for dense type diamond grinding wheel, whose elliptic vibration was prompted by single longitudinal vibration, was designed using a local resonance method. It was employed to dress the metallic bond super-abrasive grinding wheel and the dressing force characteristics were analyzed. The results indicate that the thrust force decreased to 1/7-1/10 of that of conventional method, and the main cutting force decreased by 70%. Compared to other dressing parameters, the dressing force in elliptic ultrasonic vibration was more sensitive to grinding speed. Thrust force and main cutting force increased rapidly when rotation speed beyond 72rpm. But when the ultrasonic power was higher than 50W, dressing force decreased very slowly. It was observed that the new dressing method is contribute to better surface finish such as more even surface, less crush abrasives, more uniform abrasive abscission and so on than the conventional method.

Abstract: Nano-ceramics possessed ascendant mechanical property and physical characteristics contrast with traditional engineering ceramics, and its machining with ultrasonic assistance has been considered one of the most efficient methods. In the present paper a novel ultrasonic grinding vibration device has been developed and the theoretical model of grinding force has been created for ultrasonic vibration grinding. The influences of grinding parameters on grinding forces were tested with self-designd acoustic system based on local resonance. According to the test data, the effect of depth of cut and wheel velocity on the grinding force with/without ultrasonic assistance was analyzed. Both in common and ultrasonic grinding the normal grinding force and tangential grinding force descend against the wheel velocity, while ascend along with the depth of cut. In any case the grinding force in ultrasonic grinding was not more that that in common grinding.

Abstract: As one of the key factors grinding heat has a significant effect on the ground surface quality in grinding engineering ceramics using diamond grinding wheel. Differences between mechanical and physical performances of ceramic materials and grinding parameters have important influences on the surface temperature distribution. In the present research, experiments with/without ultrasonic assistance were carried out to study the temperature characteristics in the grinding field by thermocouple in grinding ZrO2 and Al2O3 engineering ceramics respectively. Moreover, the theoretical analysis and the experiment confirmation for the relationship between grinding parameters and temperature have been discussed. The results show that the further the heat source keeps against grinding surface, the lower the peak value of temperature, and the surface temperature increases with the grinding depth, grinding speed and work table speed. According to the results of orthogonal experiments on grinding parameters, the grinding depth is the most important factor affecting the grinding temperature on the workpiece surface.

Abstract: Based on the machining pattern, mechanics of material removal and theory of micro-indentation, in previous studies the models of material removal rate of hard-brittle materials was discussed through the relatively influencing factors of machining parameters from various aspects, reflecting the research advances on mechanics of material removal of hard-brittle materials. However, those models of material removal rate have limitations, which results from impercipient theory of fracture of new kinks of materials, randomicity of practical machining process, inappropriate assumptions and simplification of the machining conditions and so on. In this work firstly, previous models of material removal rate of hard-brittle materials machining with ultrasonic assistance were reviewed briefly. Subsequently, the models of material removal rate of complex ceramics machining with two-dimensional ultrasonic vibration assistance were established based on fracture theory of micro- indentation in fracture regime and plastic removal mechanics in ductile regime respectively. The material removal rate is affected not only by the properties of material and machining parameters, but also by the character of grinding wheel and parameters of ultrasonic vibration.

Abstract: Experiments on surface features were carried out in honing zirconia engineering ceramics using fine grains. In ultrasonic honing, the surface fracture ratio increased quickly when the depth of cut is more than 3 μm, while in common honing it performed an ascending trend from depth of cut 1.5 μm. The value of surface roughness in ultrasonic honing increased along with the depth of cut; while it descends contrast to the depth of cut when the honing velocity is less than 0.58 m/s in traditional honing. As for honing velocity over 0.74 m/s, it deceased firstly to the minimal value for depth of cut 1μm, then began to ascend along with depth of cut. The value of surface roughness descended to minimum value for the range of honing velocity 0.41-0.58 m/s in traditional honing, while the optimized honing velocity ranged 0.58-0.75 m/s in ultrasonic machining. The surface roughness in ultrasonic honing was superior to that in traditional honing.