Structural Design And Dynamic Characteristics Analysis Of Ultrasonic Motorized Spindle

Because of the advantages of ultrasonic machining,it is an inevitable trend for the development of ultrasonic machining equipment to integrate ultrasonic machining technology and machining center into a machining center with ultrasonic.As the most important part of the machining center,the study of ultrasonic motorized spindle is of great practical value.In this paper,HSK tool holder is designed as a part of the ultrasonic horn,and the ultrasonic vibration device is combined with the structure of the motorized spindle to form an ultrasonic motorized spindle.Theoretical analysis,finite element analysis and experimental verification are used to design the whole structure,and amplitude of ultrasonic horn is measured.The main research contents are as follows:The overall layout of the ultrasonic motorized spindle is designed.The structural parameters of the spindle are calculated,and the motor and bearings are selected according to the working conditions.The static stiffness of the spindle is calculated according to the bearing pre-load,and the deformation of spindle under stress is calculated by finite element analysis.The influence of bearings pre-load on the static stiffness of spindle is analyzed.It is shown that when the preload of the front bearing increases by 1800 N,the static stiffness of the spindle increases by about 123 N/μm.The preload of the rear bearing increases by 1800 N,and the stiffness of the main shaft only increases by 6 N/μm.The variation of spindle static stiffness with bearing position is analyzed.It is found that when the spindle suspension a=55 mm and the support span L=250 mm,the static stiffness of the spindle reaches the maximum 326.8 N/μm.In order to adapt to automatic tool changer,HSK tool holder was used as a part of the composite half-wavelength ultrasonic horn.Dimension parameters and working frequency of the horn were calculated based on the theory of four-end network.Modal analysis and harmonious response analysis shows the horn generates a longitudinal vibration of 19.5 k Hz while the horn was subjected to clamping force.The first-six order of natural frequency and mode shapes of the spindle were calculated by ANSYS Workbench.According to the modal frequencies,the critical speeds of the spindle were obtained to be 57895.2 rpm,which is higher than the maximum speed of the motor.The influence of bearing pre-load on the natural frequency of spindle is analyzed.When the modal shapes of spindle is radial vibration,the natural frequency of spindle increases with the increase of bearing pre-load.The harmonic response analysis of the motorized spindle shows that the dynamic stiffness of the spindle decreases to 288.9 N/μm when subjected to cutting force,which was in line with the service conditions.When the spindle is subjected to ultrasonic vibration,the maximum response displacement of the spindle appears in the middle of the spindle,which is 0.039μm,and has little effect on the spindle.A sample of the horn is made and its impedance and amplitude are measured.The results show that the tool end produces a stable periodic vibration of up to 5 μm.Meet the requirements of ultrasonic machining.