Development Of Vibration System For Ultrasonic Assisted Grinding Of Trepanning For Hard And Brittle Materials

Hard and brittle materials have excellent properties such as high hardness,high strength and high wear resistance,which are used more and more in high-end manufacturing.However,their mechanical processing performance is poor due to their hard and brittle characteristics.Ultrasonic machining is an effective processing method for hard and brittle materials,in which the ultrasonic vibration system is the key to ensure the processing quality and efficiency.In this paper,according to the characteristics of the hole(bar)with large depth(length)diameter ratio of hard and brittle materials,the vibration system of the ultrasonic assisted grinding sleeve processing was developed.The structure design of the vibration system was carried out based on the local resonance theory by using the composite Bessel amplitude variable bar.Then,genetic algorithm and finite element method are used to optimize the vibration system of ultrasonic,and the optimization process is improved;Finally,the system is tested and verified.The main research contents and achievements of this paper are as follows:(1)The mechanical model of local resonance system is established,and the influence of equivalent mass and stiffness of ultrasonic transducer,horn and cutter on the vibration performance of the system is analyzed.According to the longitudinal vibration theory of slender rod,the working frequency of the system,the size of the transducer and the position of the joint are determined.Bessel curve with strong designability is selected as the bus of the horn,and the basic size of the half wavelength horn is designed according to the connection conditions.(2)The finite element simulation of the system is carried out.By changing the position of Bezier curve control points,it is proved that the shape of the horn will affect the vibration performance of the system,and the influence law is complex.The influence of tool wall thickness and clamping length on the vibration performance of the system is explored,which provides a basis for the selection of tools.(3)Based on the fast non dominated genetic algorithm(NSGA Ⅱ),the multi-objective optimization of ultrasonic assisted grinding sleeve vibration system is carried out.The resonant frequency,output amplitude and vibration speed ratio are taken as the optimization objectives.After several iterations,the final shape of horn is obtained,and the design of ultrasonic assisted grinding sleeve vibration system is completed.Aiming at the problems of unstable results and poor diversity of optimization methods,a harmonic response analysis method of single step excitation under power frequency condition is proposed,which greatly improves the optimization efficiency and provides a new idea for the design of ultrasonic vibration system with complex horn.(4)The impedance analysis and amplitude test of the designed vibration system are carried out,and the results are compared with the simulation results,which proves that the design method is reasonable.Taking quartz glass as the object,the experiment of ultrasonic assisted grinding trepanning was carried out,and the working ability of ultrasonic assisted grinding trepanning vibration system was verified.