Research On Surface Integrity And Fatigue Property In Machining Of New Titanium Alloy

Titanium alloys have been widely applied in the fields of aviation,aerospace,chemical industry and armarium due to their attractive properties,such as high strength-to-weight ratio,low density,exceptional resistance to corrosion and excellent low temperature performance.However,titanium alloys are generally defined as a difficult-to-machine material.The surface quality of parts after machining is not ideal,which will also directly affect the fatigue property of parts.Therefore,how to improve the surface quality and fatigue property of titanium alloys after machining has been an urgent problem in manufacturing and machining technology.In this paper,new titanium alloy TB17 was taken as experimental object and a systematic research on surface integrity and fatigue property in milling TB17 titanium alloy has been carried out.The main work and the corresponding research results were as follows:1.The single-factor experiment was conducted to study the effect of milling process parameters on surface integrity in machining TB17 titanium alloy.Cutting fluid,milling speed,feed per tooth,axial depth of cut,radial depth of cut,rake angle,clearance angle and helix angle were included in the milling process parameters.Surface roughness,surface work hardening,surface residual stress and surface morphology were taken as evaluation index of surface integrity.The mechanism of milling process parameters on surface integrity was analysed based on related theories of cutting force,cutting heat and tool wear,which could provide basis for subsequent machining of fatigue specimens.2.Two different milling process parameters were chosen to machine fatigue specimens of TB17 titanium alloy,and the effect of surface integrity on fatigue property was investigated through fatigue experiment.The results showed that the larger surface roughness and more surface defects aggravated the stress concentration effect,accelerating the formation of initial crack,and shortened the fatigue life.The fracture and separation of ? phase was the main reason to form inner fatigue crack of TB17 titanium alloy.Besides,the existence of surface residual compressive stress was not only beneficial to fatigue source transferring from machined surface to sub surface,but also reduced the rate of fatigue crack propagation,which improved the fatigue property of material.3.The influence level of milling process parameters on each evaluation index of surface integrity was studied by the analysis of the signal to noise ratio.Meanwhile,the fatigue property of TB17 titanium alloy was optimized by Taguchi method and grey relational analysis based on milling parameters.The results showed that in order to obtain the relatively better fatigue performance under the experimental parameters' levels,milling process parameters could be chosen as follows: the cutting fluid condition of H-1 fine grinding fluid,a milling speed of 100m/min,a feed per tooth of 0.02mm/z,an axial depth of cut of 1mm,a radial depth of cut of 1.5mm,a rake angle of 18°,a clearance angle of 12°,and a helix angle of 60°.In addition,the results of analysis of variance indicated that milling speed was the most significant factor for the fatigue property of TB17 titanium alloy after machining.Finally,the results of confirmation experiment demonstrated that there was a great agreement between the predicted results and experimental results,which proved the reliability of the optimization method used in this paper.