| The interest in magnesium alloys in medical implants is significantly increasing in recent years,due to their degradable performance.However,in the human body environment,easy corrosion performance of magnesium alloy leads to premature loss of mechanical support.Typically,the surface integrity caused by material processing affects the performance and service life of the component.Therefore,the processing of magnesium alloy implants will inevitably affect its corrosion resistance.Ball-end milling is usually used to process some complex surfaces.In view of the low ignition point and easy corrosion of magnesium alloy,the ball-end dry milling was used to avoid surface corrosion by cutting fluid during processing.However,the machining process will still affect the cutting performance(cutting temperature and cutting force)surface integrity,and corrosion resistance of magnesium alloy.In general,ultrasonic-assisted milling can reduce the cutting temperature and cutting force to some extent,improving the surface morphology and corrosion resistance.Therefore,ultrasonic vibration-assisted ball-end dry milling of AZ31B magnesium alloy was studied in this topic.The simulation model for ball-end milling was established to predict cutting force and temperature,to supply a basis for selecting reasonable processing parameters for the ball-end dry milling experiment.The influence of different combinations of process parameters on cutting performance,surface morphology,and electrochemical corrosion characteristics is analyzed via the ball-end dry milling experiment,and the best combination of process parameters is obtained.The main work of this paper includes the following three parts.The first part studies the influences of machining parameters on cutting force,cutting temperature,stress,and strain by ball-end dry milling simulation.First,the geometric model of the ball-end milling cutter is established in Catia V5,the geometric model of the ball-end dry milling is imported into ABAQUS,and the finite element model of the ball-end dry milling is established.Then,the simulation was carried out based on the Johnson-Cook constitutive model.Finally,the analysis of variance(ANOVA)results obtained from the simulation shows the decrease in feed rate and increase in vibration amplitude increases stress,and decrease in spindle speed with increasing in vibration amplitude reduces Strain(PEEQ).The feed rate has the greatest influence on the cutting force.The spindle speed has the greatest influence on the cutting temperature,and the ultrasonic amplitude has little influence on both.The second part studies the influence of machining parameters on cutting force,cutting temperature,and surface integrity by experiments.The Taguchi method is used to design cutting experiments to reduce processing costs and time.Analysis of variance results shows that the feed rate is the most important factor affecting the cutting force in Z-direction and three-dimensional surface roughness Sa.The spindle speed is the most important factor affecting the cutting force in Y-direction and the maximum cutting temperature.The depth of cut is the most significant factor for cutting force in X-direction,three-dimensional surface roughness Sz,and surface hardness.The influence of ultrasonic amplitude is not significant,but the assistance of ultrasonic vibration during the milling process can reduce the cutting temperature to a certain extent when the spindle speed is greater than 5000 rev/min.The third part studies the influence of surface roughness and hardness on corrosion resistance in simulated body fluid(SBF).The corrosion characteristics of the sample with the largest difference in surface roughness and hardness in SBF were studied by electrochemical corrosion experiments.The results show that the surface of the sample with low surface roughness and high hardness has strong corrosion resistance.The corrosion rate of the sample surface processed by UVABM is 25.6%lower than that by conventional milling under the same machining parameters. |
PDF Full Text Request