双顶角钻头钻削CFRP复合材料的刀具磨损机制

为了研究碳纤维增强树脂基(CFRP)复合材料切削中刀具在不同部位的磨损机制和规律,以典型的硬质合金双顶角钻头作为研究对象,主要研究对出口分层影响较大的横刃和对最终制孔成型影响较大的第二主切削刃的磨损机制及规律。通过减小磨损测量间隔,并引入切削刃钝圆半径以及后刀面磨损带宽度,表征了横刃和第二主切削刃在加工中的衰变过程。基于显微刃口观测和钝圆半径变化,揭示横刃易崩刃和第二主切削刃磨损后又受到重新刃磨的磨损机制,获得了此类型钻头不同部位的磨损规律。同时,基于上述的磨损表征,研究不同切削部位磨损量对钻削轴向力和力矩的影响,横刃轴向力与横刃钝圆半径变化相关性较小,而钻削最大力矩与第二主切削刃后刀面磨损变化规律相一致。     

细长轴切削颤振的稳定性分析和实验研究

为了对细长轴的加工颤振进行稳定性研究,在对细长轴切削颤振机理的研究基础上,建立了刀具和细长轴耦合振动的两自由度系统的再生型颤振分析模型。利用解析法对时滞的动力学方程进行稳定性分析,得出了关于切削宽度和转速的稳定性切削极限图。从结果中可以得出两自由度系统的极限切削宽度比单自由度系统减小了28.6%。该成果可以为柔性零件的高效稳定加工提供理论切削参数。在车铣复合中心上进行了细长轴的切削颤振实验,通过与稳定性极限图的对比,发现实验结果与理论研究相吻合,并且总结出颤振发生前后刀具和细长轴的振动特性变化规律。这种振动特征的变化过程是对加工颤振进行监测和预警的重要识别指标     

滞后型切削颤振诊断技术的研究

着重讨论了滞后型切削颤振的诊断原理和诊断方法。理论分析和试验结果证明，滞后型切削颤振系统的稳定性和切削力信号Ｆｙ（ｔ）相对于振动加速度信号ｙ（ｔ）的相位差ρ存在某种一一对应的关系。因此，可以通过测量切削过程中切削力信号Ｆｙ（ｔ）相对于振动加速度信号ｙ（ｔ）的相位差ρ的大小来诊断生产现场中发生的颤振是否属于滞后型颤振。试验在普通车床上进行。     

Effect of longitudinal−torsional vibration in ultrasonic-assisted drilling

In general, drilling of aeronautical materials is faced with some difficulties. To improve this process, a variety of methods have been presented by researchers. One of these methods is ultrasonic-assisted drilling (UAD). In this study, performance of longitudinal?torsional (L-T) vibration in UAD of Al 7075-T6 with HSS tool is investigated. Accordingly, a vibration tool with ability of producing L-T vibration was designed. After modal analysis and achievement of desired resonance frequency, it was fabricated and some experimental tests were conducted. A dynamometer with six degrees of freedom was utilized to measure torque and thrust force during the cutting process. As a result, it was revealed that this kind of vibration significantly reduces cutting forces compared with the conventional drilling (CD). Furthermore, this reduction was clarified by investigation of generated chips and tool rake angle. Moreover, effect of ultrasonic vibration on drill skidding and surface quality has been studied.     

Delay induced canards in a model of high speed machining

We consider here a model from Stone and Askari [Nonlinear models of chatter in drilling process, Dyn. Syst. 17 (2002), pp. 65–85] for regenerative chatter in a drilling process. The model is a nonlinear delay differential equation where the delay arises from the fact that the cutting tool passes over the metal surface repeatedly. For any fixed value of the delay, a large enough increase in the width of the chip being cut results in a Hopf bifurcation from the steady state, which is the origin of the chatter vibration. We show that for zero delay the Hopf bifurcation is degenerate and that for a small delay this leads to a canard explosion. That is, as the chip width is increased beyond the Hopf bifurcation value, there is a rapid transition from a small amplitude limit cycle to a large relaxation cycle. Our analysis relies on perturbation techniques and a small delay approximation of the DDE model due to Chicone [Inertial and slow manifolds for delay differential equations, J. Diff. Eqs 190 (2003), pp. 364–406]. We use numerical simulations and numerical continuation to support and verify our analysis.     

基于似然比检验原理的机床切削颤振早期监测

根据似然比检验原理提出了一种新的机床切削颤振监测统计量，能识别切削过程中产生的信噪比为０．１５的微弱振动成份。文章还就颤振监测工作特性、颤振监测门限值设置等有关问题进行了分析讨论。颤振监测考证试验在一台数控车床上进行。     

基于动力学及切削特性耦合的数控机床结构设计

切削性能是评价数控机床好坏的重要指标之一,在结构设计阶段必须加以考虑。以提高实验室自主研发的立卧转换四轴联动数控机床的切削性能为目的,研究基于动力学特性与切削特性耦合的机床结构设计优化方法。首先结合切削加工中的颤振稳定域理论,通过实验获取机床刀尖频响函数和切削力系数,预测切削加工时的三维颤振稳定域图(主轴转速-切宽-切深)及颤振频率图(主轴转速-切宽-频率)。其次采用实验模态技术对整机进行结构动力学测试及分析,在获取可视化振型的基础上,分析引起机床发生颤振,并导致切削性能降低的结构设计上的缺陷。在此基础上,改进主轴头结构并比较刀尖频响函数,结果表明系统动刚度约增加28.2%,机床抵抗切削颤振的能力得到明显加强。     

机床速度型切削颤振的非线性研究

本文建立了由刀架弹性子系统、工件弹性子系统在非线性动态切削力耦合下的多自由度非线性系统的速度型切削颤振理论模型,通过数值模拟显示,此系统存在内共振现象,从而解释了速度型切削颤振发生的振动机理。为解决切削颤振问题提供了一种新的技术途径。     

钻柱内外沿轴向流动的钻井液对钻柱横向振动的影响

本文讨论了钻柱内外沿轴向流动的钻井液对钻柱横向振动的影响，讨论了钻柱与钻井液的耦合振动问题，并引入附加质量系数来描述在钻柱与井壁之间的环形空间中向上流动的钻井液对钻柱振动的影响。数值算例表明这种环形空间中存在并流动着的钻井液对钻柱的横向振动有很大的影响。     

Integrated approach for prediction of stability limits for machining with large volumes of material removal

High-speed machining of thin-walled structures is widely used in the aeronautical industry. Higher spindle speed and machining feed rate, combined with a greater depth of cut, increases the removal rate and with it, productivity. The combination of higher spindle speed and depth of cut makes instabilities (chatter) a far more significant concern. Chatter causes reduced surface quality and accelerated tool wear. Since chatter is so prevalent, traditional cutting parameters and processes are frequently rendered ineffective and inaccurate. For the machine tool to reach its full utility, the chatter vibrations must be identified and avoided. In order to avoid chatter and implement optimum cutting parameters, the machine tool including all components and the work piece must be dynamically mapped to identify vibration characteristics. The aim of the presented work is to develop a model for the prediction of stability limits as a function of process parameters. The model consists of experimentally measured vibration properties of the spindle-tool, and finite element calculations of the work piece in (three) different stages of the process. Commercial software packages used for integration into the model prove to accomplish demands for functionality and performance. A reference geometry that is typical for an aircraft detail is used for evaluation of the prediction methodology. In order to validate the model, the stability limits predicted by the use of numerical simulation are compared with the results based on the experimental work.     

Prediction of machining chatter in milling based on dynamic FEM simulations of chip formation

Chatter vibration is a major obstacle in achieveing increased machining performance. In this research, a finite element model of chip formation in a 2D milling process is used to predict the occurrence of chatter vibrations, and to investigate the effects of various machining parameters on this phenomenon. The dynamic properties of the machine tool at the tool tip are obtained based on experimental modal analysis, and are used in the model as the cutter dynamics. The model allows for the natural development of vibration as the result of the chiptool engagement, and accounts for various phenomena that occur at the chip-tool interface ultimately leading to stable or unstable cutting. The model was used to demonstrate the effects of the machining parameters, such as the axial depth of cut, radial immersion, and feed rate, on the occurrence of chatter. Additionally, the phenomenon of jumping out of the cut region could be observed in this model and its effect on the chatter process is demonstrated. The numerical model is verified based on comparisons with experimental results.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0228-7.pdf     

切削颤振的在线监测与控制研究现状分析

切削颤振是切削过程中，工件和刀具之间自发产生的振荡，它严重影响机床加工性能。因此，多年来国内外学者针对切削颤振的机理、在线监测和在线控制进行了大量的研究。本文介绍了切削颤振在线监测与控制技术国内外研究现状，分析了现有方法的优缺点，总结了研究中存在的问题，展望了机床颤振的在线监测与控制技术的发展趋势。     

扭转振动工具滑模控制降黏分析

在深部硬地层钻井领域,扭转振动工具具有破岩效果明显和抑制钻头黏滑的作用,但其相应的降黏机理和控制机理研究还不完善。为此,在现有通过扭转振动工具解决黏滑问题的基础之上,建立了钻柱系统的扭转振动方程,提出U1和U2两种滑模控制降黏方法,并在有工具作用时,结合理论方程、给定参数对两种控制方式的降黏效果进行了分析。结果表明:当存在参数摄动时,钻柱系统处于黏滑状态附近,参数的变化会导致钻柱系统的脆弱性,钻柱系统需要加以控制;两种滑模控制方式均能有效对钻柱的黏滑振动进行控制;通过对在不同条件下各控制器的控制性能、鲁棒性的对比可知,滑模控制方式U2整体控制性能较好,且滑模控制方式U2具有更强的鲁棒性,有利于提高钻柱系统的稳定性和可靠性。     

对再生型切削颤振模型的试验分析

一个专门设计的切削颤振试验揭示了颤振发生和发展的全过程.在连续增加切深的条件下,颤振会在一个特定的切深下突然发生,其特征是某一频率上的振幅突然大幅度增加;切深继续加大,振幅也继续增大但颤振频率几乎不变;最后,颤振频率向下漂移并保持颤振.随后进行的激振试验,确认了本次颤振试验中出现的两个颤振频率分别属于工件系统和刀具系统.从颤振能量补充和质量效应的角度分析,颤振应发生于两个最终执行部件之一的固有频率上.以此为基础建立了一个具有两个颤振主动体的颤振模型,新的模型可以用来合理解释本试验的现象,也更适合颤振监测和抗颤振结构改良的需要.     

Tool wear monitoring using acoustic emission in the existence of chatter

A method using an acoustic emission (AE) technique to monitor automatically a tool wear was examined. A flank wear is calculated using a statistical model which uses RMS value of AE signal and cutting speed as variables. The investigation reveals that the AE signal is influenced by tool vibration, specially during chatter. This contradicts the theory that the AE signal is not susceptible to mechanical vibration. The paper discusses the mechanism that explains the effect of the tool vibration on the AE signals.     

岩屑床破坏器在水平井斜井段的清洁效果研究

针对水平井斜井段岩屑堆积成床易造成钻柱摩阻、扭矩增大及卡钻等问题，对斜井段中岩屑床破坏器的影响规律和清洁效果进行评估分析。首先，基于CFD （computational fluid dynamics，计算流体动力学）技术，对岩屑床破坏器的清洁机理进行研究，并通过对比分析得到岩屑床破坏器的清洁效果。然后，分析了不同井斜角、钻井液排量和钻柱转速下岩屑床破坏器对水平井斜井段岩屑床的影响规律，并对岩屑床破坏器的工况参数进行优选，以更好地发挥其清洁作用。最后，通过岩屑床破坏器的现场应用来验证其清洁效果。结果表明，岩屑床破坏器对水平井斜井段井眼的清洁效果非常明显，使用后可减小钻柱的摩阻和扭矩，有效防止钻进过程中卡钻事故的发生。研究结果可为岩屑床破坏器的使用提供指导。     

灰铸铁和球墨铸铁前托架钻削性能评价

从导热系数、铁屑形貌、钻孔内表面粗糙度、钻头顶部温度、钻削负载(扭矩、进给力)等方面,评价了QT450和HT250材质拖拉机前托架的钻削性能,并分析了钻削性能与微观组织的关系。结果表明,对HT250和QT450前托架钻削加工时,两者钻削负载没有明显差别;与HT250相比,QT450的石墨对基体的分割作用小,其基体组织中较多的铁素体,造成钻削加工时断屑和排屑困难,导致钻孔内表面粗糙度大;QT450导热系数低、铁屑与钻头摩擦严重,使得钻头温度较高;QT450有较小的切削力和铁屑对钻头较大的摩擦力,在这2个力作用下,QT450钻削负载与HT250基本相同。     

圆锯片横向再生颤振模型及计算

通过分析圆锯片切割工件横向振动情况,得出横向再生切削力表达形式。基于Kirchhoff线弹性板理论建立圆锯片横向再生颤振方程式。利用伽辽金法对横向颤振方程进行变换,得出以各阶振型分量为变量的延迟微分方程组,并用状态变量形式表示延迟微分方程组。通过延迟微分方程组状态变量表达形式编写MATLAB函数来描述圆锯片切割系统横向再生颤振的动态模型,调用dde函数求解各阶振型分量随时间的变化关系,从而得出圆锯片横向再生颤振响应。     

强研磨性地层中PDC钻头井底热-流-固三场耦合研究

PDC（polycrystalline diamond compact， 聚晶金刚石复合片）钻头在强研磨性地层中破岩时，其钻齿在刮切破碎岩石的同时与岩屑、岩石剧烈摩擦，产生的局部高温加快了钻齿的磨损失效，这会极大地缩短整个钻头的使用寿命。因此，探究温度对PDC钻头磨损的影响并改进其水力结构对提升单个钻头的进尺深度和降低钻井经济成本有显著意义。为此，通过钻齿切削实验来验证其温度与磨损之间的关系，并在考虑井底钻井液流动状态及其与钻齿之间对流换热的基础上，建立了PDC钻头井底热?流?固三场耦合模型，分析了井底钻井液与PDC钻头之间的相互作用，同时针对原有的PDC钻头水力结构提出了优化措施。结果表明：1）在钻齿切削过程中温升现象十分明显，说明温度是影响PDC钻头磨损的重要因素；2）PDC钻头井底流场呈热?流?固耦合状态，且钻井液流动状态对其钻齿换热的影响大，这为钻头水力结构的优化提供了方向；3）通过调整喷嘴的流量及角度等水力结构，降低了钻齿的平均温度，可有效改善PDC钻头的磨损情况。研究结果对强研磨性地层中钻头的优化设计有重要指导意义。     

超精密车削单晶硅刀具振动频谱分析

为了在线监测单晶硅超精密车削的脆塑转变现象及分析单晶硅车削过程中材料的微纳去除方式,采用圆弧刃金刚石刀具对单晶硅（100）晶面进行了超精密车削,研究了单晶硅超精密车削时刀具振动频谱分布与切削参数的关系,并对刀具振动频谱的变化规律及其演变机理进行了分析.结果表明,刀具振动频谱分布与刀具和单晶硅接触方式、单晶硅微纳去除模式密切相关.当单晶硅的去除模式从脆性域过渡到塑性域时,材料由崩碎状脆性去除方式转变为以剪切滑移变形为主的塑性去除方式,刀具振动频谱高频段信号增多,且振动总能量增大;塑性域车削时,切削速度越小、切削深度越大、进给量越大,材料微观剪切变形区内位错滑移数量越多,刀具振动频谱高频段信号越多,刀具振动主总能量越大.切削速度、进给量、切削深度对刀具振动频谱分布的影响依次减小,采用合理的切削参数,可以降低切削系统的总体振动.