Experimental Study On Surface Quality And Fatigue Properties Of Milling Titanium Alloy TC11 Under Different Cooling Conditions

Titanium alloy has excellent characteristics such as high specific strength,high thermal strength,corrosion resistance and fatigue resistance,as well as low thermal conductivity and low elastic modulus.On the one hand,it can meet the light weight of structural components,high reliability,widely used in aerospace,medical equipment,marine ships and other fields,on the other hand,it is difficult to cut,easy to wear,low machining surface quality,So typical hard-to-machine materials for titanium alloys.In order to improve the machinability of titanium alloy,Cryogenic minimum quantity lubrication and liquid nitrogen cryogenic cooling technology to meet the green machining concept,reduce contact friction,reduce cutting heat and assist chip removal.In this paper,the surface quality of milling titanium alloy TC11 under different cooling conditions is studied,and its influence on fatigue performance is explored.Firstly,the cutting test of titanium alloy TC11 was completed.The white light interferometer was used to detect the characteristic machining surface of the specimen,the three-dimensional morphology,the three-dimensional roughness value and the data matrix were extracted.The influence of cooling conditions,spindle speed and feed per tooth on the three-dimensional roughness value was obtained.At the same time,the wavelet transform was used to decompose and reconstruct the surface morphology,and the influence of different processing conditions on the surface morphology of different decomposition frequency bands was analyzed.Secondly,the plastic deformation mechanism was analyzed.The micro images of the surface layer and the material matrix after milling were taken by scanning electron microscope.The micro phase transformation and grain refinement of the surface layer were studied based on the image processing method.Vickers microhardness tester was used to measure the hardness of the specimen,and the work hardening values under dry,Cryogenic minimum quantity lubrication and Liquid nitrogen cryogenic cooling were compared.At the same time,the influence of spindle speed and feed per tooth on work hardening under the same cooling environment was analyzed.Then,the X-ray stress equipment was used to detect the residual stress of the fatigue specimen,and the residual stress values under dry,cryogenic minimum quantity lubrication and liquid nitrogen cryogenic cooling conditions were compared and analyzed.At the same time,the effects of spindle speed and feed per tooth on the cutting residual stress under the same cooling conditions were studied.The esidual stress generated by the milling test of TC11 titanium alloy was simulated by ABAQUS finite element simulation,and the simulation results were compared with the test results.Finally,the electro-hydraulic servo fatigue testing machine was used to carry out the fatigue test of the fatigue specimen after cutting,and the sensitivity of the fatigue property of the specimen to the surface quality parameters was analyzed,including the three-dimensional surface roughness,the surface working hardening and the cutting residual stress,and the fatigue fracture of the specimen was analyzed.