Basic Research On Turn-milling Of Damage-tolerant Titanium Alloy

At present,damage-tolerant titanium TC21 as a kind of high strength and toughness titanium alloy in China,has excellent integrated mechanical properties,such as high strength,high toughness,high damage-tolerant performance(i.e.lower fatigue crack growth rate and higher threshold),better fatigue performance than medium strength titanium alloy such as TC4 and TA15,simple heat treatment process,good forgeability,and excellent welding performance.For above reasons,titanium alloy TC21 is suitable for manufacture of large integral forging and welding components.Now TC2 is widely used for manufacturing important and key components of the new generation aircraft,which need high strength and durability such as middle and back fuselage,wing,and undercarriage.Damage-tolerant titanium TC21 has some physical and chemical properties such as low material thermal conductivity,little chip contact area with rake face,high chemical activity for titanium and small deformation coefficient.So some problems exist in cutting process such as high cutting temperature,large tool tip stress,fast tool wear,and difficult guaranteeing processing quality.Especially for some rotary typeparts with typical mechanical structures by using TC21 such as slender rod,undercarriage and etc,the poor cutting machinability of TC21 and weak rigidity of the structures cause that some problems exist in cutting process such as easier machining deformation,more difficult guaranteeing processing quality,and lower machining efficiency.Ultimately,the above situations restrict promotion and the application of TC21 in aerospace.To solve the prominent problems during machining of titanium TC21 such as shorter tool life,lower machining efficiency and more difficult guaranteeing processing quality,the orthogonal turn-milling is adopted to cut TC21.By researches of critical questions such as turn-milling surface topography,cutting layer geometry simulation and modeling of orthogonal turn-milling,and cutting force and chatter stability modeling of orthogonal turn-milling.The specific research contents as follows:(1)The surface profile of orthogonal turn-milling was researched to provide theoretical bases and detailed guidances for cutting parameter optimization,while maintaining reasonable surface profile and surface roughness.First,the selected rules of offset distance,axial feed of tool,rotate speed ratio and teeth number were confirmed.Second,based on the constructor of cross section pattern for orthogonal turn-milling finished surface,the curve contour mathematic model of orthogonal turn-milling macro-profile was built,simulation algorithm of macro-profile was determined,and the influences of some cutting parameters on orthogonal turn-milling macro-profile were analyzed.Second,the mathematic model of bottom cutting edge in tool coordinates and workpiece coordinates were established to determine simulation algorithm of micro-profile,the influences of some cutting parameters on orthogonal turn-milling micro-profile were explored,and finished surface roughness was forecasted.(2)The simulation and modeling of cutting layer geometry were studied to provide quantitative analysis bases of cutting layer geometry change and theoretical bases of cutting force simulation for orthogonal turn-milling.Based on of motion law of orthogonal turn-milling with software NX8.5,the simulation algorithm of orthogonal turn-milling cutting layer geometry was set up to analyze the influences of some cutting parameters on cutting layer geometry by experimental verification.From the location of turn-milling tool bottom blade,the judgment method of orthogonal turn-milling cutting layer geometry was generalized.According to forming process of chip,mathematic models of orthogonal turn-milling cutting layer geometry were set up.(3)The cutting force and chatter stability were simulated and analyzed to optimize cutting parameters from the point of reducing cutting force and enhancing tool life.On the one hand,the mathematic models of orthogonal turn-milling cutting forces were built based on mathematic models of cutting layer geometry,the cutting forces were simulated and verified,and the influencs of some cutting parameters on orthogonal turn-milling cutting force were discussed.On the other hand,based on the regeneration chatter theory,the dynamic cutting force mathematic models of orthogonal turn-milling were established,the chatter stability of orthogonal turn-milling was modled and simulated by using complete discretization method,the lobe graphs of orthogonal turn-milling chatter stability were drawn,and the influencs of axial tool feed on orthogonal turn-milling chatter stability were analyzed.(4)The cutting machinability of orthogonal turn-milling on titanium TC21 was researched to verify the machining advantages of orthogonal turn-milling on difficult-to-machine materials marked by TC21.The turn-milling parameters were optimized by tool life experments,and wear mechanisms of tool were researched by observation of scanning electron microscope and analysis of SEM.In addition,turning and orthogonal turn-milling on TC21 were contrasted and analyzed in three major areas: tool life,machining efficiency and workpiece surface integrity.