Study On Ultrasonic Milling Process And Surface Microscopic Characteristics Of Titanium Alloy

Titanium alloy has many excellent properties such as high specific strength,high temperature resistance,and corrosion resistance,and has been widely used in important fields such as aerospace,military defense,and civil manufacturing.However,titanium alloys are typical of difficult-to-machine materials due to their severe cold hardening during processing,small deformation coefficient,and severe tool wear.There is an urgent need to develop new processing technologies to solve the processing problems of titanium alloys in order to achieve good processing results.Ultrasonic-assisted cutting has many advantages.It is of great significance to combine ultrasonic machining with common machining to study the process and results of ultrasonic-assisted milling.The main research contents and results of this article are as follows:The trajectory of the cutting edge during the axial vibration of the tool,the horizontal vibration of the workpiece and the longitudinal torsional vibration of the tool are derived.Regarding the side edge as bevel cutting,the critical derivation speed of the side edge is obtained theoretically.The force and material removal of the tool in different ultrasonic milling stages were analyzed.The cutting force model during ultrasonic milling was established and ultrasonic vibration platforms under different vibration modes were set up to carry out ultrasonic milling titanium alloy machining tests.Orthogonal machining test and single factor machining test were conducted to explore the influence of each machining parameter on the milling force.The combined force in the milling plane is used to characterize the milling force.Tests show that the order of influence of various factors on the combine force in the milling plane is:feed per tooth(f_z)>milling speed(v)>axial depth of cut(a_p)>longitudinal amplitude(A)and the order of influence of various factors on the axial force in the milling plane is:milling speed(v)>longitudinal amplitude(A)>feed per tooth(f_z)>axial depth of cut(a_p).Compared with ordinary machining,the axial ultrasonic vibration can reduce the cutting force and is smaller than the cutting force when horizontal vibration,and the degree of tool wear is reduced.The frequency analysis of cutting force provides a feasible method for measuring the actual vibration frequency in ultrasonic machining.The influence of tool wear on surface morphology and cutting force was studied.The change of surface morphology and the fluctuation of cutting force caused by tool wear increased,and the surface morphology and cutting force could also reflect the tool wear.The variation of chip morphology during ultrasonic milling was studied.When ultrasonic vibration is applied in the axial or horizontal direction,the degree of jaggedness increases with the increase of cutting speed,and decreases with the increase of amplitude.Increasing the axial amplitude of the tool can change the sawtooth chip to the band chip,but the excessive amplitude will reduce the quality of the machining surface.The micro-characteristics of the ultrasonic milling surface were explored,and it was found that the root cause of the surface microtexture generation is the periodic change of the cutting depth.Therefore,compared with the horizontal vibration of the workpiece,the application of axial vibration is more conducive to the generation of microtexture.Due to the Poisson effect,when the workpiece vibrates in the horizontal direction,the processed surface generates a transitional distributed microtexture along the vibration direction.Friction and wear tests show that the surface microtexture enhances the chip storage performance of the workpiece surface and can reach the stable friction stage in a faster time.The fractal theory was used to effectively characterize the regularity of the surface microtexture.The smaller the characteristic fractal dimension,the stronger the regularity of the microtexture,and the shorter the running-in time.