| TC4 titanium alloy is widely used in aerospace,biomedical and other high-end technical fields because of its excellent properties such as corrosion resistance,heat resistance,fatigue resistance and high specific strength.TC4 titanium alloy,as a typical difficult-to-machinel material,is prone to produce high grinding force,grinding heat and serious wheel adhesion in grinding process,which makes the grinding wheel wear faster.As an excellent ultra-precision machining technology,ultrasonic assisted grinding has the advantages of reducing grinding force,grinding heat and improving workpiece processing quality compared with ordinary grinding.It has gradually become a research hotspot in the field of precision ultra-precision machining of difficult-to-machine materials.Taking TC4 titanium alloy as the research object,and the wear mechanism of wheel in longitudinal-torsional ultrasonic grinding of TC4 titanium alloy was studied from three aspects of theoretical modeling,finite element simulation and experiment.The main contents and conclusions are as follows:(1)Based on the kinematic characteristics of single abrasive particle in longitudinal-torsional ultrasonic grinding,the motion trajectory equation of single abrasive particle in longitudinal-torsional ultrasonic grinding was established.The analysis results show that the introduction of longitudinal-torsional ultrasonic vibration changes the cutting mechanism of single abrasive particle,and makes the grinding trajectory of single abrasive particle longer,which is conducive to the improvement of material removal rate.Based on the longitudinal-torsional ultrasonic grinding arc length model of single abrasive and the tool temperature rise model,the longitudinal-torsional ultrasonic grinding force model and the longitudinal-torsional ultrasonic grinding abrasive surface temperature model were established,the analysis results show that the grinding force and the surface temperature of the grinding grain in the longitudinal-torsional ultrasonic grinding are lower than those of ordinary grinding under the same grinding parameters.Therefore,longitudinal-torsional ultrasonic grinding is helpful to improve the surface quality and machining efficiency of titanium alloy workpiece.(2)Based on the contact theory,the thermal-mechanical coupling model of the abrasive particle-workpiece contact surface during longitudinal-torsional ultrasonic grinding was established,and the stress distribution of abrasive-workpiece contact surface numerical simulation was carried out.The simulation results show that the middle section of the front and rear tool face of the grinding grain forms a compressive stress concentration area in longitudinal-torsional ultrasonic grinding.Therefore,the front and rear tool surfaces in longitudinal-torsional ultrasonic grinding are the main areas where abrasive wear occurs.Based on the wear model and the adhesive wear model,the wheel wear model of longitudinal-torsional ultrasonic grinding was established,and the theoretical analysis was conducted.The analysis results show that the wear rate of wheels in longitudinal-torsional ultrasonic grinding increase with the increase of grinding depth and workpiece feed speed,and decrease with the increase of grinding linear speed and ultrasonic amplitude,and the accuracy of the theoretical model was verified by longitudinal-torsional ultrasonic single factor grinding experiment of TC4 titanium alloy.(3)The finite element model of longitudinal-torsional ultrasonic multi-abrasive particles grinding of TC4 titanium alloy with random distribution of abrasive particles was established by using Deform-3D finite element software.The grinding stress field,temperature field distribution conditions and the wear rate of multiple abrasive grains were analyzed.The simulation analysis results show that the maximum value of Mises stress on the workpiece surface and the maximum value of abrasive surface temperature for longitudinal-torsional ultrasonic grinding are lower than those of ordinary grinding under the same grinding conditions.It indicates that the abrasive grains are subjected to less mechanical and thermal stresses during longitudinal-torsional ultrasonic grinding compared to normal grinding,which contributes to the durability of the grinding wheels.The wear rate of multiple abrasive grains under longitudinal-torsion ultrasonic grinding increase with the increase of grinding depth,and decrease with the increase of ultrasonic amplitude.The wear rate of multiple abrasive grains increase first and then decrease with the increase of grinding linear speed.(4)A synchronous online monitoring experiment platform for grinding force and grinding temperature of longitudinal-torsional ultrasonic grinding was built,and the longitudinal-torsional ultrasonic grinding experiment of TC4 titanium alloy was carried out.The influence of longitudinal-torsional ultrasonic parameters and grinding process parameters on grinding force,grinding temperature and grinding wheel wear rate was studied.The experiment results show that the grinding depth and ultrasonic amplitude have the most significant influence on grinding force and grinding temperature,while the influence of workpiece feed rate and grinding wheel speed are relatively small in longitudinal-torsional ultrasonic grinding of TC4 titanium alloy.For wheel wear rate,grinding depth has the most significant effect,followed by ultrasonic amplitude and grinding wheel speed,and workpiece feed speed has the least effect.With the help of equipment such as super depth-of-field microscope and white light interferometer,the surface wear profile of grinding wheels and the microscopic profile of workpiece surfaces under different grinding wheel wear amounts were observed.The results show that the adhesion and blockage degree of the grinding wheel surface for longitudinal-torsional ultrasonic grinding was significantly lower than that ordinary grinding under the same grinding conditions,which is helpful to improve the service life of the grinding wheel.In addition,the surface roughness of the workpiece machined under L-TUG increase with the increase of grinding wheel wear. |
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