| Advanced manufacturing technology has become the core support and basic guarantee for the development and progress of science and technology.And the key to developing advanced manufacturing technology lies in the progress of ultra-precision processing technology.The development of ultra-precision machining technology is one of the important means to improve the national science and technology,economic strength and overall national strength.Grinding and cutting are the most used ultra-precision machining methods in industrial production.Compared with the cutting,the grinding process has higher precision,lower surface roughness,but is likely to cause sub-surface damage and residual stress.Using grinding as the basic form,supplemented by the relevant accuracy protection measures,is an effective way to improve grinding accuracy and processing quality.According to our research team's work on the wear problems on ultrasonic motor contact interface,it is found tha the use of structural surface traveling waves or other forms of elastic waves can effectively remove the workpiece surface material.By means of frequency modulation,phase modulation,amplitude modulation,and change of pre-pressure,the precise control of cutting force,cutting angle,cutting speed and penetration depth can be realized.This novel machining method has great application prospect in the field of hard and brittle material.Accordingly,we proposed a novel machining method which utilize the travelling wave on elastomer surface excited by piezoelectric ceramics to remove the excess materials on workpiece surface so that the controllable processing under low stress condition can be achieved.At the same time,we use piezoelectric ceramics drive mechanism as processing feed device instead of traditional kinematic pairs so as to fundamentally solve the precision loss problems caused by its rotary motion.The content of this paper is divided into the following aspects:1.The working principle of the proposed elastic wave processing method is systematically analyzed as well as the selection principle of the working vibration mode of the cone-shaped piezoelectric vibrators and he processing layer.By utilizing finite element analysis software ANSYS,we can obtain the frequency and displacement response of the first-order longitudinal vibration mode and the second-order bending vibration mode,as well as the frequency and displacement response of the out-of-plane bending vibration mode and in-plane radial vibration mode.Also the dimensions of the cone-shaped vibrators and the processing layer can be obtained.Based on the above theoretical analysis and simulation results,we manufacture and assemble the prototype.A pulley mechanism has been designed to offer pre-contact force between the workpiece and processing layer and is also used to fixed the workpiece.We use the prototype to machine a series of glass optical lenses under different driven voltage parameters,pre-contact force and processing time in order to find the relationship between the input conditions and the machined surface accuracy and quality.Based on the theoretical analysis and experiment research,the correctness and effectiveness of the proposed elastic wave processing method can be verified.2.The electromechanical coupling dynamic model of the cone-shaped piezoelectric vibrator is established,and the vibration equation of the piezoelectric vibrator is deduced in free vibration and under contact force.On this basis,the dynamic model of the force vibration of the processing layer is established,and the vibration equation of the processing layer excited by the longitudinal vibrator and the bending vibratoris obtained.Finally,the motion equation of the surface particles on the processing layer surface can ben calculated.By means of comparing the theoretical solution,the numerical solution of finite element simulation,and the experimental results of modal frequencies,the correctness of the established dynamic models is proved.By utilizing the established dynamic model of the elastic wave machining principle prototype,the parametric analysis of the elastic wave processing tool can be carried out,which is beneficial to the optimize design of the machining tool in further research work,and provide a theoretical basis for exploring the control method of the elastic wave processing.3.The contact model between the processing layer and the workpiece is established,and the relation between the size of the contact area and the pre-contact force is derived.According to the principle of grinding,the formula of the maximum undeformed chip thickness is deduced.Based on the empirical formula of surface roughness of follow-up sharpening by Koichi Ono and the experimental results of the surface roughness of the elastic wave processing method,the prediction formula which is suitable for the elastic wave processing prototype is obtained.Using the principle of ductile domain processing,the applicability of the elastic wave processing method in the field of hard and brittle material processing is analyzed.In order to characterize the quality of the machined surface,the transition layer of the machined surface and the thickness of the deteriorated layer are measured by experiments,which proves that the quality of the machined surface can be changed by changing the input parameters of the elastic wave machining prototype.Through the theoretical calculation and experimental study of the elastic wave processing method in this chapter,it is proved that the control of the precision and quality of the machined surface can be achieved by changing the excitation voltage parameters of the elastic wave machining prototype and the pre-pressure and processing time of the contact interface4.Design and manufacture a 6-DOF positioning platform based on flexible hinge mechanism,which is used for feeding of elastic wave machining.The static analysis model of the flexible hinge mechanism under various degrees of freedom is established,and the expression of the relationship between the excitation voltage and displacement output of each DOF is deduced.Experimental research has been carried out to find the relationship between the input voltage and the platform displacement output,and the positioning accuracy and travel distance of the platform under various degrees of freedom are obtained as well.It proves that the designed 6-DOF positioning platform meets the feed requirements of elastic wave processing tools.5.According to the imaging contrast of the processed optical glasses,the quality of the proposed elastic wave machining method was assessed.The experiment results indicate that the imaging contrast of optical glasses relies on the machining input characteristics.The imaging contrast increases as the processing time increases,and the best contact pressure,excitation voltage,and phase difference are existing to achieve the best imaging contrast.With the excitation voltage of 400 Vpp,the phase difference of 90°,the contact pressure of 6 N,and the processing time of 4 hours,the best surface quality is achieved(surface roughness: 0.027?m,thickness of the metamorphic layer: 3.67 ?m,thickness of the transition layer: 13.59 ?m). |
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