【作者】 王晓琴；

【导师】 艾兴；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 高效率、高精度、高柔性和绿色化是现代制造技术的发展方向。高速、高效切削加工技术近20年来以其独特的优势成功应用于钢铁及铝合金的切削加工,但是在高温合金的加工中应用并不广泛。论文主要针对Ti6A14V高效切削加工过程中刀具摩擦磨损特性及其热-力耦合作用对刀具磨损与刀具寿命的影响规律展开研究,为钛合金加工刀具材料选择、刀具结构设计及切削参数优化提供理论依据和技术支撑。研究了Ti6A14V-硬质合金的摩擦学行为。摩擦过程中,摩擦系数随摩擦温度变化呈近似线性的规律。硬质合金的磨损率随滑动速度的升高而增加,磨损机理主要是粘着、扩散、氧化、剥落磨损及破损,几种磨损机理是相互影响的,粘结剂Co元素的扩散是导致硬质合金刀具基体弱化剥落的重要因素。在Ti6A14V直角切削刀具-切屑(前刀面)、刀具-工件(后刀面)接触面的摩擦特性试验研究基础上,建立了前、后刀面的摩擦模型,刀具-切屑、刀具-工件接触以粘结为主,接触区分为紧密粘结和非紧密粘结两个区域,非紧密粘结区的成因为刀具表面不平整所致,接触区上主应力及摩擦应力服从负指数分布,摩擦系数为平均温度的函数。在刀具-切屑、刀具-工件、刃口区接触面主应力及相对滑动速度有限元分析的基础上,建立了直角切削前、后刀面及刃口区应力及速度连续性分布模型。为全面分析Ti6A14V加工过程中的刀具-切屑、刀具-工件接触面的摩擦特性及热-力耦合现象奠定了基础。建立了直角切削刀具前、后刀面及刃口区的热-力耦合作用解析模型,计算并分析了切削参数、刀具几何角度、后刀面磨损量对刀具-切屑接触长度、应力分布、切削温度、切削力等变量的影响,为进一步研究刀具磨损规律提供了理论依据。建立了热-力耦合作用下以扩散磨损为主要磨损机理的前刀面月牙洼磨损模型。计算并分析了切削参数及Co含量对硬质合金刀具前刀面磨损率的影响,结果显示硬质合金磨损率与Co含量成正比,为钛合金切削加工硬质合金刀具材料的选择提供了理论依据。建立了以扩散、磨粒、粘结磨损为机理的硬质合金刀具后刀面磨损解析模型。计算结果显示切削速度及后刀面磨损量对各种磨损机理所占比例有重要影响,切削速度及后刀面磨损量增大,扩散磨损比例大大增加。分析了刃倾角及主偏角对Ti6A14V车削过程的影响。刃倾角较小时(-15°～15°),其对前刀面切削温度和切削力影响不大。主偏角对刀具寿命有明显影响,减小主偏角可提高刀具寿命。因此,适当的速度、大切深、小主偏角是硬质合金刀具车削钛合金提高效率的优化方向。试验研究了非涂层硬质合金刀具、涂层硬质合金刀具及PCBN刀具车削Ti6A14V的切削力、切削温度、刀具磨损及寿命随切削参数的变化规律。并以表面粗糙度、刀具寿命及切削效率为优化目标对上述三种刀具切削参数进行了优化。Ti6A14V车削中,刀具的使用性能依次为非涂层硬质合金＜涂层硬质合金＜PCBN,PCBN刀具的应用将使Ti6A14V高速车削成为可能。对Ti6A14V铣削加工过程进行了数值模拟(DEFORM 3D)。铣削过程中的热-力耦合现象与车削显著不同,在断续的机械冲击和热冲击共同作用下,铣削刀具的磨损规律与车削不同。并对铣削可转位非涂层及涂层刀具进行了试验研究,分析了涂层、切削参数及冷却液对刀具切削力、切削温度、刀具寿命等影响。低速下,涂层刀具的寿命高于非涂层刀具,高速下两种刀具的寿命差别不大。冷却液在切削过程中可以使刀具寿命显著提高。最后,分析了刀具寿命与切削效率的关系,并对铣削参数进行了优化。更多还原

【Abstract】 High efficiency, high accuracy, flexibility and greenization are the development directions of modern manufacturing technologies. In the last two decades years, High Speed/Performance Machining (HSM/HPS) is successfully applied in cutting steel, cast iron and alumina alloy, due to its unique advantages. However, it is not yet prevalent in high temperature alloy machining. This dissertation focuses on Ti6A14V HPM, systematically analyzes the tribological behaviors of tool-chip interface (rake face), tool-workpiece interface (flank face), the thermo-mechanical coupling effect and its influence on tool wear and tool life in Ti6A14V machining, finally provides theoretical and practical support for tool materials selection, tool geometries and cutting parameters optimization.Tribological behaviors of Ti6A14V-tungsten carbide (WC-6%Co) were studied. In friction process, friction coefficient is approximately linear with friction temperature. Wear rate of carbide increased with sliding speed, wear mechanism was adhesion, diffusion, oxidation, flaking and fracture, several wear mechanisms is interactive. Diffusion of carbide binder Co is the key factor for carbide substrate weakening and flaking.The friction models in tool-chip (rake face) and tool-workpiece (flank face) interface was constructed, based on friction characteristics analysis in Ti6A14V orthogonal cutting tests. Adhesion is the main contact morphology at tool-chip, tool-workpiece interface, which consist of tight adhesion region and non-tight adhesion region. The principal stress and frictional stress were a negative exponential distribution in whole contact length; friction coefficient is a function of average cutting temperature. The stress and sliding speed continuity hypothesis at tool-chip, tool-workpiece interface and edge area were assumed in visco-plastic material cutting process, base on DEFORM 3D finite element simulation and experimental analysis. It is a foundation for complete research on tribological behaviors and thermo-mechanical coupling effect of tool-chip, tool-workpiece interface in Ti6A14V machining process.Thermo-mechanical coupling analytical models of tool-chip and tool-workpiece interface were constructed; their computation results showed that the contact length, stress distribution, cutting force, cutting temperature at rake face contact area is influenced by cutting parameters and tool geometries, as well as flank wear value in machining process. These models provide the theoretical foundation for the research of tool wear laws in Ti6A14V machining.Diffusive crater wear model was established, based on tool wear mechanism and the thermo-mechanical coupling analysis in Ti6A14V machining. And its computation result showed that diffusion of Co element from tool into workpiece material at elevatated cutting temperature is the key factor of tool wear. The wear rate is proportional to Co content, and these results provide the theoretical foundation for tool material selection in Ti6A14V machining. The flank wear model was also constructed, base on diffusion, adhesion and abrasion wear mechanisms in Ti6A14V machining, its computation results showed that the proportion of three wear mechanisms was affected by cutting speed and flank wear value VB, the proportion of diffusion wear severely increase with VB and cutting speed increase in total wear value.The influence of tool geometries on turning process were analyzed, influence of inclination angle on cutting temperature and cutting force is not significant, when it changes from -15°to 15°. But, the influences of lead angle is remarkable, the smaller lead angle is more favorable for tool life in Ti6A14V turning. Therefore, appropriate cutting speed, lager depth of cut, smaller lead angle are the optimal direction for Ti6A14V high efficiency turning. The Ti6A14V turning cutting experiments with different materials, such as uncoated carbide, coated carbide (TiAlN) and PCBN were conducted, to analyze the influence of cutting parameters on cutting force, cutting temperature, tool wear and tool life. Finally, cutting parameters were optimized for three tools, based on tool life-cutting efficiency relationship analysis. The cutting performances of three tools are uncoated carbide < coated carbide < PCBN. The use of PCBN tool will be capable of Ti6A14V high speed turning.DEFORM 3D milling process simulation results showed that the milling process is different from turning, in which the intermittently mechanical impact and thermal shock result in tool wear and fracture. The Ti6A14V milling test was performed for uncoated carbide and coated carbide (TiAlN), the influences of coating, cutting parameters, coolant on cutting force, cutting temperature and tool life were analyzed. The cutting performance of coated carbide is more excellent than uncoated carbide at lower cutting speed, but it has no remarkable difference in higher cutting speed. The coolant can significantly improve the tool-chip, tool-workpiece interface contact situation and prolong the tool life. Finally, cutting parameters of both tools were optimized, based on tool life-cutting efficiency relationship analysis. This work is sponsored by the National Natural Science Foundation of China (50575126) and National Basic Research Program of China (973) (2009CB724401 and 2009CB724402).更多还原