【作者】 王宝林；

【导师】 艾兴； 刘战强；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 钛合金材料具有优异的力学性能、低密度以及良好的耐蚀性,是航空航天工业最主要的消费材料。然而,由于具有导热系数低、高温化学活性高和弹性模量小特点,钛合金又是一种典型的难加工材料。在切削加工过程中,容易产生很高的切削温度,导致刀具磨损加快、表面质量难以控制,而低的切削速度导致加工效率难以提高。同时,由于航空钛合金零部件的整体结构件设计特点,大量的材料需要从整块坯料中去除,造成切削成本较高。因此,实现钛合金材料的高效、高速加工成为航空航天制造业亟需解决的问题。本文针对航空钛合金TC17,基于其动态力学性能特征研究,结合切削实验,对钛合金TC17的切屑形貌特征、切削力、切削温度、刀具寿命及磨损机理和表面粗糙度等切削加工特性问题及其影响规律进行系统研究,为生产实际中高效、高速切削加工提供理论与技术支持。材料在快速变化载荷作用下的动态响应,对于分析材料的切削机理具有很重要的作用。论文通过准静态压缩实验及分离式霍普金森压杆实验,获得应变率10-3/s～104/s,温度25℃～800℃范围内,钛合金TC17的塑性变形特征。实验表明在高温下TC17材料表现出明显的温度软化特征,随着温度的升高,流动应力减小。温度在700℃以上,准静态条件下钛合金TC17表现出明显的流变软化。通过高加载率下的冲击压缩实验表明,TC17材料的屈服强度和流动应力随着应变率增大而增大,TC17材料的动态响应是应变强化、应变率强化和温度软化三种效应的耦合作用。同时拟合回归得到TC17合金材料在比较宽的温度和应变率范围内的本构方程。通过直角切削获得不同切削参数下的TC17材料的切屑形貌,基于热粘塑性材料本构失稳条件,建立材料流变参数Ψ与切削速度vc,进给量f间的关系,获得切屑由连续带状切屑向锯齿状转变的临界切削条件,及材料的临界流变参数Ψ的值。采用锯齿形切屑的齿距、切削比、锯齿化程度和剪切带倾角来表征锯齿状切屑的几何特征,研究切削参数对切屑几何特征的影响,结果表明：随着切削速度和进给量的增大,锯齿状切屑的齿距和锯齿化程度增加,剪切带带倾角减小；随着切削速度增大,剪切带内的显微硬度增大。建立了基于材料本构关系的切削力理论预测模型,通过三因素三水平的正交回归实验极差分析,发现斜角切削加工TC17中,切削深度对切削合力影响最大,其次是切削速度,进给量对切削合力的影响最小。切削速度vc对切削温度的影响最显著,进给量f的影响次之,切削深度αp对切削温度的影响最小。研究了PVD TiAlN涂层硬质合金刀具车削加工钛合金TC17的刀具寿命随切削参数的变化规律,表明切削速度vc对刀具寿命具有显著性影响,其次是进给量f,而切削深度影响较弱。建立了刀具寿命经验模型,分析了刀具寿命与切削效率间的关系,借助SEM观察和能谱分析EDS等手段,对钛合金TC17切削加工刀具的磨损机理进行分析。研究表明钛合金TC17切削加工刀具磨损和失效的主要机理是粘结磨损,同时伴随有磨粒磨损、氧化磨损、扩散磨损。通过正交回归实验法得到车削和面铣加工钛合金TC17的表面粗糙度经验公式。基于表面粗糙度的经验模型,进行表面粗糙度对各个切削参数响应的灵敏度分析,获得得到平稳表面粗糙度的切削参数区间,并结合刀具寿命-切削效率间的关系获得高效车削加工TC17材料切削参数区间。(?)本课题得到国家基础研究发展计划(973)(2009CB724401)的资助。更多还原

【Abstract】 Titanium alloys have been widely used in aircraft industry due to their high specific strength and excellent corrosion resistance. However, titanium alloys are typical difficult-to-machine materials due to their poor thermal conductivity, low elastic modulus and high chemical activation. High cutting temperature generated in titanium alloy machining usually leads to rapid tool wear and poor surface quality. On the other hand, most materials need to be removed from roughcast due to the design characteristics of components used in the aircraft industry. Therefore, the improvement of the efficiency of material removal for titanium alloy machining has been an urgent problem to be solved in aerospace manufacturing. The response of TC17alloy under dynamic loading with different strain rates and temperatures is investigated in this dissertation. The characteristics during machining TC17alloys, systematically analyzes the chip morphology, cutting forces, cutting temperature, tool life and wear mechanism, and surface roughness, using the method of combining theoretical analysis and experimental research, are focused in order to provide theoretical and practical support in high efficiency and high speed machining TC17.This study has investigated the mechanical response of TC17alloy under quasi-static and dynamic loading with different strain rates and temperatures. The results have shown that the stress-strain response of TC17is highly sensitive to both the strain rate and the temperature. TC17has evident heat softening effect, strain rate strengthening effect and strain hardening effect. The flow stress decreases while temperature increases. Flow softening behavior has been observed above700℃under quasi-static loading. The constitutive model of TC17has been established, which has high precision in forecasting material flow stress. It is a foundation for research on deformation mechanism in TC17machining process.The serrated chip formation in orthogonal cutting TC17is studied. A flow localization parameter is expressed in terms of associated cutting conditions and properties of TC17. The effect of cutting conditions on the formation of sawtooth chip in TC17machining is investigated. It is found that the critical value during machining TC17is0.0032m2/min, at which the serrated chip is observed. Intervals of segments, cutting ratio, degree of serrated chip and the inclination angle of shear band are used to characterize the geometric characterization. Microhardness of shear band is used to characterize the mechanical properties characterization. By orthogonal cutting experiments, the relationship among cutting parameters, geometric characterization, and mechanical properties characterization are explored. It is found that, intervals of segments, degree of serrated chip and microhardness of shear band increase with the increase of the cutting speed and feed rate, the inclination angle of shear band decreases with the cutting speed and feed rate increasing.Cutting force and temperature are influenced by the mechanical properties of workpiece. Based on Oxley cutting theory, the mathematic models of stress, strain, strain rate, temperature in shear zone and orthogonal cutting forces are proposed, which is tenable under cutting condition. From the view point of controlling of cutting forces and cutting temperature, appropriate cutting speed, larger depth of cut, medium feed rate are preferred.Systematic researches have been conducted on tool wear patterns and wear mechanisms with TiAlN coated carbides. Adhesive wear is the main failure mechanism, accompanied by abrasive wear, oxidation wear, and diffusion wear. The empirical formula of tool life when turning TC17using coated carbide tool has been founded. The results show that cutting speed and feed rate have a great influence on the tool life. Finally, tool life-cutting efficiency relationship is developed.The effects of cutting conditions on surface roughness when turning and face milling TC17are researched by experiments. The empirical formula has been founded. The sensitivity analysis for the cutting parameters show that the surface roughness is most sensitive to the feed rate, and less sensitive to the cutting speed and cutting depth for turning operations. The surface roughness in face milling process is most sensitive to cutting speed, and less sensitive to the feed per tooth and cutting depth.更多还原