Simulation And Experimental Study Of Ultrasonically-assisted Drilling Of Cortical Bone

With the development of society and the improvement of residents’ living standards,people are paying more and more attention to their own health problems.Due to sports injuries,traffic accidents,increased age and so on,bone fractures become a common disease in daily life.Internal fixation is a commonly used method for treating fractures in medical treatment.Pre-drilling of bones is required during internal fixation so as to implant the fixture.But excessive axial force during bone drilling may cause cracks in the cortical bone or cause damage to the bone tissue.In order to reduce the axial force during drilling,this paper introduced ultrasonic assisted drilling.The mechanism of ultrasonic assisted drilling was studied through theory analysis,and compared the similarities and differences between ultrasonic assisted drilling and conventional drilling through finite element simulation and experimental research.Finally,the axial force of the ultrasound-assisted drilling of the cortical bone was optimized using Minitab software.The detailed research contents are as follows:(1)Through the kinematics analysis of ultrasonic axial assisted drilling,the kinematics equation of axial vibration drilling is established,and the cutting speed,track length and cutting thickness at any point on the cutting edge during ultrasonic vibration drilling are obtained.Then the characteristics,the separation shock characteristics of ultrasonic assisted drilling,the mechanism of vibration friction reduction and chip breaking are analyzed.(2)Based on ABAQUS finite element analysis software,the finite element analysis of ultrasonic assisted drilling of cortical bone was carried out.The three-dimensional drilling model was simplified into a two-dimensional cutting model.The stress field of ultrasonic assisted cutting and conventional cutting was studied and compared.The concept of cutting degree is introduced,and the local stress state changes of cortical bone cutting during conventional drilling and ultrasonic assisted drilling were analyzed.(3)The single factor experiment of cortical bone drilling was designed and carried out.The Kister 9129 AA dynamometer and the Taylor Hobson Talysurf i-Series 5 roughness profiler were used to study the difference between conventional drilling and ultrasonic assisted drilling.The effect of the different drilling method on axial force,chip shape and surface roughness of the cortical bone under different drilling methods were studies.(4)Using Minitab software to design and carry out the central composite test,the effects of drilling speed,feed rate,ultrasonic frequency and amplitude on the axial force were analyzed.Then the ultrasonic assisted drilling cortex was established based on the response surface method.The prediction model of the axial force was established,and the variance analysis of the model was carried out.Finally,the parameters were optimized.