Numerical Simulation And Experimental Study On Surface Integrity For Ultrasonic Assisted Milling Titanium Alloy

Ti-6Al-4V titanium alloy is an indispensable structural material widely used in aerospace field for its outstanding characteristics such as excellent specific strength and thermal stability,good corrosion and oxidation resistance.Nevertheless,resulting from high friction coefficient,low thermal conductivity,low modulus of elasticity,and high chemical activity of titanium alloy,several problems including high cutting temperature,tool chatter and tool wear occur during processing,which directly affect the production cost,processing quality and efficiency.To some extent,the difficult-to-machine characteristic of titanium alloy has brought challenges to the development of aerospace industry,so it is of great significance to explore the processing technology applicable to titanium alloys.Ultrasonic assisted milling technology changes the tool trajectory by introducing ultrasonic vibration and the high-frequency impact also affects the material removal mechanism.Studies have shown that ultrasonic assisted milling technology has obvious effects on reducing milling force and milling temperature,and improving the machined surface quality of alloy materials and hard-brittle materials.However,the current research on ultrasonic assisted milling titanium alloy has not been yet mature.In this paper,the study on ultrasonic assisted milling Ti-6Al-4V was carried out.The thermo-mechanical characteristics,surface formation mechanism,and surface integrity of ultrasonic assisted milling titanium alloys were studied by combining numerical simulation and experiment.The main research contents are as follows:(1)This paper studies the thermo-mechanical characteristics of ultrasonic assisted milling titanium alloy.Conventional milling and ultrasonic assisted milling experiments were carried out,and the effects of ultrasonic amplitude,cooling method,spindle speed,feed per tooth and milling depth on the milling force were explored.Research shows that ultrasonic vibration and wet cutting are beneficial to reduce the milling force,which increases with the increase of the feed per tooth and the milling depth.Moreover,the simulation results gained by Abaqus show that ultrasonic vibration can reduce milling temperature and equivalent stress,promote chip breaking.(2)This paper carried out the simulation study on the topography of ultrasonic assisted milling titanium alloy.Cnsidering the influence of cutting parameters,ultrasonic parameters and system geometric errors,the movement trajectory equation of the cutting edge with time was established in the workpiece coordinate system based on kinematic analysis.By the boolean operation,the coordinate information of the milled surface topography was obtained,and the prediction model of ultrasonic assisted milling surface topography was established,whose effectiveness was verified through experiments.Moreover,the effects of vibration frequency,ultrasonic amplitude,feed per tooth,axial runout and tool eccentricity on the surface topography were studied based on the model.(3)This paper investigated the surface integrity of titanium alloy machined by conventional milling and ultrasonic assisted milling.The influence of processing parameters,ultrasonic parameters and cooling methods on surface roughness,residual stress,surface microhardness and surface microstructure are explored.Studies show that the high-frequency impact during ultrasonic assisted milling cause the surface roughness and surface microhardness increasing.Compared with conventional milling,residual stress and plastic deformation also has been changed significantly.