【作者】 孙涛；

【导师】 傅玉灿；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2017， 博士

【摘要】 TC21损伤容限型钛合金是目前我国高强韧钛合金综合力学性能匹配优异的钛合金材料。由于具有强度高、韧性高、损伤容限性能高(较低的疲劳裂纹扩展速率值和较高的疲劳裂纹扩展门槛值)、疲劳性能优良(优于普通TC4、TA15等中强度钛合金)、热处理工艺简单、锻造性好和焊接性能优异等综合性能,使得钛合金TC21适合制造大型整体锻造零件和大型焊接整体构件。目前,TC21钛合金已广泛应用于新一代战机的中后机身、机翼和起落架等对强度及耐久性要求高的重要或关键承力部件。TC21损伤容限型钛合金具有材料热导率低、切屑与前刀面接触面积小、钛的化学活性高和变形系数小等物理和化学性质,这就使其在切削时存在切削温度高、刀尖应力大、刀具磨损快和加工质量难以保证等问题。尤其对于采用此类材料的细长杆、起落架等一些具有典型结构特性的回转类零件,材料本身较差的切削加工性加上其结构的弱刚性,造成此类零件的加工一直存在加工易变形、加工精度难以保证和加工效率低等问题,制约了其在航空航天行业中的推广和应用。针对TC21钛合金加工过程中存在刀具耐用度和加工效率不高以及加工表面质量难以保证等突出问题,本文采用正交车铣方式对其切削加工性进行研究。通过对正交车铣加工表面形貌、正交车铣切削层几何形状仿真与建模、正交车铣切削力及加工稳定性等关键性问题的研究,深入开展了TC21钛合金正交车铣的切削加工性研究。具体研究内容如下:(1)正交车铣加工表面形貌的研究。确定了偏心量、铣刀轴向进给量、转速比和齿数的选定规则。通过正交车铣加工表面的横截面图形构造函数,建立了正交车铣加工表面宏观形貌的曲线轮廓解析模型,确定了宏观形貌的仿真算法,分析了切削参数对宏观形貌的影响规律。在建立刀具坐标系下刀刃的解析模型以及工件坐标系下工件、刀刃的解析模型的基础上,确定了微观形貌的仿真算法,进行了试验验证和仿真分析,预测了正交车铣微观形貌和加工表面粗糙度的变化。该研究内容在保证合理表面形貌和表面粗糙度的前提下,为正交车铣切削参数的优选提供了理论依据和指导。(2)正交车铣切削层几何形状仿真与建模的研究。根据正交车铣的运动规律,结合NX 8.5软件提出了正交车铣切削层几何形状的仿真方法,并进行了试验验证和仿真分析。根据刀具底刃的位置,提出了正交车铣不同切削层几何形状类型的判断方法。根据正交车铣不同类型切削层几何形状的形成过程,建立了相应切削层几何形状的解析模型。该研究内容为正交车铣切削层几何形状的变化提供了定量分析依据,为正交车铣切削力的仿真提供了理论基础。(3)正交车铣切削力及加工稳定性仿真与分析。基于正交车铣切削层几何形状的解析模型,建立了正交车铣切削力解析模型,对正交车铣切削力进行了仿真和验证,分析了切削参数对正交车铣切削力的影响规律。基于再生颤振理论,建立了正交车铣动态切削力解析建模,采用完全离散法进行了正交车铣颤振稳定性建模与仿真,绘制了正交车铣加工过程的稳定性叶瓣图,分析了轴向进给量对正交车铣加工稳定性的影响。该研究内容从降低切削力和切削力波动、提高刀具耐用度的角度出发,优选了正交车铣切削参数。(4)TC21损伤容限型钛合金正交车铣的切削加工性研究。通过刀具磨损试验,确定了TC21钛合金正交车铣的优化参数。通过扫描电镜和能谱分析的手段,分析了正交车铣刀具的磨损机理。从刀具耐用度、加工效率和加工表面完整性三方面,对TC21车削和正交车铣的结果进行了对比和分析,探讨TC21正交车铣的切削加工性。该研究内容分析和验证了正交车铣在以TC21为代表的高强韧性难加工材料上的加工优势。更多还原

【Abstract】 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.更多还原