Papers by Author: Bo Zhao

Abstract: In this paper, the natural frequency and the vibration mode of the lapping tool in ultrasonic vibration lapping are analyzed, the resonance mechanism of the lapping tool is researched by establishing its mechanical model and displacement equation, and the experimental study is carried out in ultrasonic vibration lapping of engineer ceramics. The conclusions include: 1) The natural frequency of the designed lapping tool is ; 2) The acoustic system in ultrasonic vibration lapping is simplified to equivalent many-degrees of freedom system, while the damp is ignored, the lapping tool is resonant with itself-natural frequency, the joint of the horn and the lapping tool is a displacement node, and the whole system is in resonant condition. 3）While the experimental condition is no-load and ultrasonic, the vibration frequency of the lapping tool is 21.3125 , which is further closed to the calculated natural frequency, at that time the amplitude of the lapping tool is maximal and the system is in resonant condition. Moreover, while the resonance frequency of the horn and the lapping tool is different, the good vibration effect of the lapping tool can be obtained by adjusting the excitation frequency of generator.

Abstract: With the rapid development of aviation at home, particle reinforced metal matrix composites (PRMMCs) has been widely applied recently. But at the same time, the difficult machining has gradually been one of the most outstanding bottle-necks that restrict the rapid enhancement of productivity. Here, in virtue of the self-developed ultrasonic drilling equipment, hole-making experiments of common and ultrasonic vibration drilling are performed on SiC particle reinforced aluminum-matrix composites （SiCp/Al）with different content of SiC by using two types of tungsten carbide drill. Drilling characteristics of machining composites with ultrasonic vibration are analyzed from such respects as the composites crush, drilling force, drill wear and hole surface quality. Studies show that, during the ultrasonic vibration drilling process, SiC particle in the composites is prone to break along the crystal connection boundary or suffer ductile fracture under the dynamic ultrasonic impulse, in which the cutting resistance could be reduced and the tool edge could be protected. Thereby, drilling locating precision and hole surface quality could be enhanced, wear of the drill chisel edge effectively improved, and the drilling torque reduced about 30%.

Abstract: Particle-reinforcement aluminum-based metal matrix composites (MMCs) are widely applied in the aviation, aerospace and military fields due to their excellent physical and mechanical properties. But the further application of the materials is hampered owing to its difficultly machining characteristics. There are unique advantages while cutting hard and brittle materials with ultrasonic vibration. The ultrasonic vibration high-speed milling (ultrasonic milling) is a reasonable cutting method in which combined the advantages of high-speed milling (conventional milling) and ultrasonic milling. The machining performances of high volume SiCp/Al MMCs were studied by conventional milling and ultrasonic milling in this paper. The influences of the milling parameters on the milling force were investigated in the experiment. In addition, the wear and mechanism of tool were analyzed in ultrasonic milling. The results show that the cutting force, abrasive wear were reduced, and tool lives were increased effectively during ultrasonic milling of SiCp/Al MMCs.

Abstract: The scheme design process for four–axis machining centers is proposed based on analysis of main kinematic chain, topological and tool changing motion characteristics of machine tool in this paper. All possible kinematic schemes of four-axis machining centers with tool change mechanisms up to eight links are generated. And the number of that is 74 with mechanisms of tree graph considered only. Further more, several schemes can be derived from each one of schemes with characteristics of tool change directions and types of tool magazine considered. The results of this work provide references for new multi-axis machining center’s development and layout design.

Abstract: A study of the fracture phenomenon of zirconia-toughened alumina (ZTA) ceramics was carried. It analyzes the mechanisms of crack propagation of ZTA ceramics, and constructs fracture experiments of ZTA ceramics, so the propagation behavior on fracture in ZTA ceramics was investigated according to the experiment. By contrast, intercrystalline fracture happed in V-shaped groove of ceramic specimen under normal load without ultrasonic vibration during ceramic fracture, and transcrystalline fracture happed in V-shaped groove of ceramic specimen under normal load with ultrasonic vibration during ceramic fracture. Furthermore, the loading force of ceramic specimen under normal load with ultrasonic vibration is smaller than that under normal load without ultrasonic vibration all other conditions being equal. The results of fracture experiment prove that ultrasonic vibration assisted is good for the fracture of ceramic specimen, and it also proves that ultrasonic vibration assisted grinding may raise the working efficiency and improve surface integrity of ceramics from the standpoint of the fracture.

Abstract: In this paper, the stepped horn node position and its deviation with the theoretical value were analyzed. And the main reason which leads to the difference between the real position and its theoretical position was also discussed. Because of the existence of Poisson’s ratio, the longitudinal ultrasonic vibration will induce horizontal vibration, and this will affect the velocity of ultrasonic vibration, finally lead to the deviation of the node position. The optimal node position was analyzed by finite element method. The numerical analysis shows that offsetting node position to the small end of horn can reduce longitudinal vibration of the support plate.

Abstract: Engineering ceramics have been widely used in recent years because of its excellent performances. However, the high hardness and brittleness make it very difficult to process with high efficiency and good quality, especially in precision and ultraprecision machining. Therefore, a method of ultrasonic drilling and grinding is provided to the hole machining of Al¬2O3 engineering ceramics. In the paper, with different machining parameters, the surface roughness of micro hole in ultrasonic and traditional drilling and grinding is compared and analyzed. Moreover, the surface micro profile and the wear condition of drilling-grinding tool in ultrasonic and traditional drilling and grinding are observed through SEM. Finally, it is concluded that ultrasonic drilling and grinding is a kind of high efficient processing method adapting to micro holes of hard - brittle materials etc.

Abstract: Composite materials have good mechanical properties. In order to solve the difficult process of composite materials, this paper proposes to use a method of ultrasonic milling on the composite materials processing, we mainly studies the effect of the length of the arbor, arbor diameter and arbor end milling platform on the acoustic resonant frequency, amplitude, and anti-resonance frequency. With the decreased in the length of the tool bar, tool bar's resonant frequency increased，and the oscillation amplitude also obviously increased. In the vicinity of 35 KHz amplitude of vibration are largest. Along with tool bar diameter's increasing, the resonant frequency is increases gradually. Milling platform has little effect on the resonant frequency and amplitude.

Abstract: In order to investigate the influence of dressing methods on grinding temperature, two kinds of diamond grinding wheels dressed by traditional dressing(TD) and elliptic ultrasonic vibration dressing(ED) respectively were used to grind the same nano-ceramic material. Through grinding experiments, the comparative analysis of the grinding temperature was conducted. The results show that diamond grinding wheel dressed by elliptical ultrasonic vibration method can decrease the grinding temperature.

Abstract: The effects of multiple ultrasonic frequencies on grinding surface quality of Al2O3-ZrO2 nano-composite ceramics are researched to provide optimization laws for ultrasonic grinding parameters. Some SEM photographs of ultrasonic grinding surface with different frequencies are provided to research the surface quality. The enhanced surface quality of ceramics with ultrasonic grinding is explained as the transition of single abrasive particle removal mode from brittle to ductile, which is resulted from the reduction of equivalent rigidity on surface under ultrasonic vibration. And this phenomenon becomes more evident as frequency increases. Through the XRD experiment, the phase transition from tetragonal phase t-ZrO2 to monoclinic phase m-ZrO2 becomes increasingly obvious by the action of ultrasonic vibration. The compressive stress generated during this phase transition can suppress the initiation and expansion of microcracks on the processing surface. The research shows that, the grinding surface quality with ultrasonic vibration is superior to that without ultrasonic vibration, and increasing ultrasonic frequency can contribute to the improvement of the surface quality.