As is known to all, grinding force is one of the most important parameters to evaluate the whole process of grinding. Generally, the grinding force is resolved to three component forces, namely, normal grinding force ...As is known to all, grinding force is one of the most important parameters to evaluate the whole process of grinding. Generally, the grinding force is resolved to three component forces, namely, normal grinding force F n, tangential grinding force F t and a component force acting along the direction of longitudinal feed which is usually neglected because of insignificance. The normal grinding force F n has influence upon surface deformation and roughness of workpiece, while the tangential grinding force F t mainly affect power consumption and service life of grinding wheel. In order to study deep into the process of the unsteady state grinding, we set up a measurement system to monitor the change of grinding force during the course of grinding and try to find some difference in the change of grinding force between the steady state grinding and unsteady state grinding. In the test, the normal and tangential grinding forces, F n and F t were measured by using a set of equipments including sensor, amplifier, oscilloscope and computer monitor. From the results, we can conclude that: 1) In the unsteady state grinding process, the values of the grinding forces are much lower than those of the steady state grinding process and the grinding force ratio showed a nonlinear fluctuation. 2) The tendency of the grinding forces in the process of the unsteady state grinding proved the existence of the cutting and micro-cutting actions. 3) Because the grinding force signals of the unsteady state grinding are much weaker than those of the steady state grinding, to obtain accurate value of the grinding forces, wave filtering is needed to be done. The whole process to filter the perturbation wave can be separated into three steps in order, changing the grinding force signals from analog signals into digital signals, FFT (fast Fourier transform) treatment to the digital signals, and IFFT(inversion fast Fourier transform) treatment to the digital signals after spectrum limitation.展开更多
Single grit grinding is the simplified model to abstract the macro scale grinding.Finite element analysis is a strong tool to study the physical fields during a single grit grinding process,compared to experimental re...Single grit grinding is the simplified model to abstract the macro scale grinding.Finite element analysis is a strong tool to study the physical fields during a single grit grinding process,compared to experimental research.Based on the dynamic mechanical behavior of 2Cr12Ni4Mo3VNbN steel and the mathematical statistics of abrasive grit,modeling of the single grit grinding process was conducted by using commercial software AdvantEdge.The validation experiment was designed to validate the correctness of the FEA model by contrast with grinding force.The validation result shows that the FEA model can well describe the single grit grinding process.Then the grinding force and multi-physics fields were studied by experimental and simulation results.It was found that both the normal and tangential grinding forces were linearly related to the cutting speed and cutting depth.The maximum temperature is located in the subsurface of the workpiece in front of the grit,while the maximum stress and strain are located under the grit tip.The strain rate can reach as high as about 106 s–1 during the single grit grinding,which is larger than other traditional machining operations.展开更多
The purpose of this study is to develop a twin wheel creep-feed grinding machine using continuous dressing to machine precise axisymmetric turbine blades that have been difficult to machine using a conventional creep-...The purpose of this study is to develop a twin wheel creep-feed grinding machine using continuous dressing to machine precise axisymmetric turbine blades that have been difficult to machine using a conventional creep-feed machine.In order to develop such a machine,3D-modeling and machine simulations were performed and a twin wheel creep-feed grinding machine was manufactured.Furthermore,the axisymmetric precision of the machined workpieces through practical machining was evaluated and the quality of the continuous dressing effect of the developed machine was established.In addition,experimental considerations for a proper dresser-to-wheel speed ratio and proper feed rate of the dresser were carried out.As a result,a twin wheel creep-feed grinding machine with continuous dressing is developed through machine simulation,manufacturing and performance evaluation.Optimum condition for the dresser feed rate is 0.3μm/rev.In cases of large dressor-to-wheel speed ratio,grinding efficiency can be enhanced,but the surface roughness shows a conflicting trend.Developed twin wheel creep-feed grinding machine has satisfactory appraisal with regard to surface roughness,flatness,and parallelism.Satisfactory surface roughness below 0.1μm can be obtained for the blade of aircraft.However,in order to perform precise machining,it is necessary to improve the structure of the twin wheel creep-feed grinding machine.展开更多
To meet the increasing demand on the quality and co st of precision components for the semiconductor industries, extensive studies on high efficiency and precision machining of ceramic materials have been conducted ov...To meet the increasing demand on the quality and co st of precision components for the semiconductor industries, extensive studies on high efficiency and precision machining of ceramic materials have been conducted over the past several years. It is found that the effects of grinding pressure and rotational speed of spindle in the machining for the ceramic materials are v ery significant on the quality of the grinding process. In order to achieve stab le grinding conditions for improved performance, a new grinding control scheme i n which the grinding pressure is maintained constant throughout the grinding pro cess was carried out in the present study. The surface quality of ground ceramics depends on the mechanism of material remo val in the vertical grinding process. For grinding of Si 3N 4 and glass under the condition of constant pressure, increasing pressure enhances material remova l rate, and at the same time causes more machining-induced microcracks on the g round surfaces. Along with the analysis of tangential forces, specific grinding energy, and the micro observations on ground surfaces, it can be found that low pressure and high wheel speed should be selected to high efficiently remove cera mics in ductile mode in the vertical grinding. From the theoretically analytical and measured grinding temperatures in the vert ical grinding of ceramics, it is found that the analytical temperature profile w ithε= 55% has the same trend with the measured one. The measured temperature is higher that the analytical one at the beginning stage of grinding process, whic h might be contributed to the unstable grinding condition of this stage. The gri nding temperatures in the vertical grinding of ceramics under a constant are not high enough for glassy phase formation, and may not reduce surface fracture as expected. However, the temperature in dry grinding may cause thermal damage to t he resin bond diamond wheel, thereby resulting in low quality workpiece surface.展开更多
文摘As is known to all, grinding force is one of the most important parameters to evaluate the whole process of grinding. Generally, the grinding force is resolved to three component forces, namely, normal grinding force F n, tangential grinding force F t and a component force acting along the direction of longitudinal feed which is usually neglected because of insignificance. The normal grinding force F n has influence upon surface deformation and roughness of workpiece, while the tangential grinding force F t mainly affect power consumption and service life of grinding wheel. In order to study deep into the process of the unsteady state grinding, we set up a measurement system to monitor the change of grinding force during the course of grinding and try to find some difference in the change of grinding force between the steady state grinding and unsteady state grinding. In the test, the normal and tangential grinding forces, F n and F t were measured by using a set of equipments including sensor, amplifier, oscilloscope and computer monitor. From the results, we can conclude that: 1) In the unsteady state grinding process, the values of the grinding forces are much lower than those of the steady state grinding process and the grinding force ratio showed a nonlinear fluctuation. 2) The tendency of the grinding forces in the process of the unsteady state grinding proved the existence of the cutting and micro-cutting actions. 3) Because the grinding force signals of the unsteady state grinding are much weaker than those of the steady state grinding, to obtain accurate value of the grinding forces, wave filtering is needed to be done. The whole process to filter the perturbation wave can be separated into three steps in order, changing the grinding force signals from analog signals into digital signals, FFT (fast Fourier transform) treatment to the digital signals, and IFFT(inversion fast Fourier transform) treatment to the digital signals after spectrum limitation.
基金Projects(U1537202,51575305)supported by the National Natural Science Foundation of ChinaProject(61328302)supported by National Security Major Basic Research Program of China
文摘Single grit grinding is the simplified model to abstract the macro scale grinding.Finite element analysis is a strong tool to study the physical fields during a single grit grinding process,compared to experimental research.Based on the dynamic mechanical behavior of 2Cr12Ni4Mo3VNbN steel and the mathematical statistics of abrasive grit,modeling of the single grit grinding process was conducted by using commercial software AdvantEdge.The validation experiment was designed to validate the correctness of the FEA model by contrast with grinding force.The validation result shows that the FEA model can well describe the single grit grinding process.Then the grinding force and multi-physics fields were studied by experimental and simulation results.It was found that both the normal and tangential grinding forces were linearly related to the cutting speed and cutting depth.The maximum temperature is located in the subsurface of the workpiece in front of the grit,while the maximum stress and strain are located under the grit tip.The strain rate can reach as high as about 106 s–1 during the single grit grinding,which is larger than other traditional machining operations.
基金Work supported by the Second Stage of Brain Korea 21 Project
文摘The purpose of this study is to develop a twin wheel creep-feed grinding machine using continuous dressing to machine precise axisymmetric turbine blades that have been difficult to machine using a conventional creep-feed machine.In order to develop such a machine,3D-modeling and machine simulations were performed and a twin wheel creep-feed grinding machine was manufactured.Furthermore,the axisymmetric precision of the machined workpieces through practical machining was evaluated and the quality of the continuous dressing effect of the developed machine was established.In addition,experimental considerations for a proper dresser-to-wheel speed ratio and proper feed rate of the dresser were carried out.As a result,a twin wheel creep-feed grinding machine with continuous dressing is developed through machine simulation,manufacturing and performance evaluation.Optimum condition for the dresser feed rate is 0.3μm/rev.In cases of large dressor-to-wheel speed ratio,grinding efficiency can be enhanced,but the surface roughness shows a conflicting trend.Developed twin wheel creep-feed grinding machine has satisfactory appraisal with regard to surface roughness,flatness,and parallelism.Satisfactory surface roughness below 0.1μm can be obtained for the blade of aircraft.However,in order to perform precise machining,it is necessary to improve the structure of the twin wheel creep-feed grinding machine.
文摘To meet the increasing demand on the quality and co st of precision components for the semiconductor industries, extensive studies on high efficiency and precision machining of ceramic materials have been conducted over the past several years. It is found that the effects of grinding pressure and rotational speed of spindle in the machining for the ceramic materials are v ery significant on the quality of the grinding process. In order to achieve stab le grinding conditions for improved performance, a new grinding control scheme i n which the grinding pressure is maintained constant throughout the grinding pro cess was carried out in the present study. The surface quality of ground ceramics depends on the mechanism of material remo val in the vertical grinding process. For grinding of Si 3N 4 and glass under the condition of constant pressure, increasing pressure enhances material remova l rate, and at the same time causes more machining-induced microcracks on the g round surfaces. Along with the analysis of tangential forces, specific grinding energy, and the micro observations on ground surfaces, it can be found that low pressure and high wheel speed should be selected to high efficiently remove cera mics in ductile mode in the vertical grinding. From the theoretically analytical and measured grinding temperatures in the vert ical grinding of ceramics, it is found that the analytical temperature profile w ithε= 55% has the same trend with the measured one. The measured temperature is higher that the analytical one at the beginning stage of grinding process, whic h might be contributed to the unstable grinding condition of this stage. The gri nding temperatures in the vertical grinding of ceramics under a constant are not high enough for glassy phase formation, and may not reduce surface fracture as expected. However, the temperature in dry grinding may cause thermal damage to t he resin bond diamond wheel, thereby resulting in low quality workpiece surface.
