金属切削加工的颤振及避振分析

针对规避切削颤振问题,应用相对切削速度概念,提出了速度型动态切削力表达式以及车削或镗削的振动力学模型。通过对速度型动态切削力分析,解释了切削颤振产生的机理,给出了颤振发生的必要和充分条件。同时指出,在较大的切削速度范围内,存在一个或两个相对稳定的切削速度区域。如果公称切削速度处于该稳定区域,即使背吃刀量较大,系统也不易发生颤振。这种相对稳定的切削速度区域是可以预估的,文中给出了预估公式及预估方法,并由实验分析验证。依据能量原理提出的极限背吃刀量指标是预防颤振发生的有效预估指标,极限背吃刀量的表达式也解释了变速切削技术抑制颤振的原理。     

切削颤振模型及机理研究

提出了同时考虑工件系统和刀具系统对切削颤振影响的２自由度切削系统模型,用此模型解释了双频颤振和单频颤振产生的机理,提出了产生的条件,并进行了试验验证。     

车削Inconel 625锯齿形切屑形成对颤振影响的试验研究

为研究高温合金Inconel 625车削过程中锯齿形切屑的产生对颤振的影响,本文通过有限元软件对车削刀具、机床主轴等部件进行模态仿真,获取对应的模态频率;进行不同切削参数的车削试验,采集加速度信号并进行频域分析以获取其FFT功率谱。通过超景深显微镜观察切屑形态,并计算不同切削参数下的切屑锯齿化频率。对比仿真和试验结果发现:当切屑锯齿化频率接近于车床某部件的主振频率时,产生了较大的颤振峰值,这说明锯齿形切屑的产生会诱导切削颤振发生,对切削过程稳定性产生了不利的影响。     

变速切削方法的减振原理

在深入研究机床加工系统在变频激励力作用下振动响应规律的基础上,系统地论述了变速切削方法的减振原理。理论分析和试验结果表明,变速切削过程的振动响应是机床加工系统在变频激励力作用下的振动响应,它远比在恒频激励力作用下的振动响应小,这是变速切削方法之所以具有显著减振效果的最为本质的减振机理。     

Stability of high frequency machining vibration by extended chatter model

An extended chatter model was proposed in a previous paper [1], which explains the onset of machining chatter at frequencies as high as 10,000 Hz in fine boring operation. The model consists of an equation of energy equilibrium, including two sources of energy supply and other two sources of energy dissipation. The sources of energy supply are by the regeneration and X–Y looping of the tool tip, and the sources of energy dissipation are by the structural damping and the cutting process damping.The present study applies the energy equilibrium equation for predicting the stability borderline in terms of cutting condition. At the cutting condition above the stability borderline where the chatter should occur, some parameters are further predicted by computation to characterize the vibration of the tool tip. The transition from the borderline to the condition above the borderline has been evaluated by the predictive calculation of the time phase between X and Y vibration displacements, the inner to outer modulation phase lag, and the percentage share by mechanisms of the energy supply and dissipation.Validity of the prediction in terms of borderline width of cut, and X to Y amplitude ratio are confirmed by comparison with experimental measurements obtained in cutting tests.     

Proposal of novel spindle speed variation profile with constant acceleration rate for improvement of chatter stability

Spindle speed variation (SSV) is one of the effective methods which suppresses regenerative chatter. However, regenerative chatter can grow even if SSV is applied. In the previous work, the chatter growth characteristics in SSV were clarified. The chatter frequency changes proportionally to the varying spindle speed, and it causes the change of the magnitude of the dynamic compliance. Hence, chatter can be suppressed through SSV since the dynamic compliance usually reduces as the chatter frequency changes. A greater compliance reduction can be obtained by a higher rate of spindle speeds in two consecutive revolutions at the same angular position, i.e., acceleration rate. From the investigations in the previous work, limitation of the conventionally utilized SSV profiles is found as follows: the acceleration rate always fluctuates with speed variation and the chatter vibration grows where the acceleration rate is insufficient for suppression, and hence suppressing chatter in all sections of SSV is difficult. In this paper, a new SSV profile with a constant acceleration rate, namely CAR-SSV, is proposed to overcome the limitation of chatter stability improvement by utilizing conventional SSV profiles. The magnitude of the acceleration rate is kept constant to realize the chatter suppression effect throughout the cutting process. Through time-domain simulation and cutting experiments, the chatter stability of CAR-SSV is investigated based on the previously introduced chatter stability evaluation indices. Influence of the parameters of CAR-SSV on the stability is investigated, and an appropriate strategy for setting SSV parameters to achieve higher stability is discussed. In addition, in order to verify the effectiveness of the proposed profile, the stabilities of conventional SSV profiles and CAR-SSV are compared through time-domain simulations and cutting experiments.     

切削颤振研究的关键技术与进展综述

切削颤振是金属切削加工过程中的一种非常复杂的机械振动现象,影响零件加工质量并限制生产率提高.颤振产生的原因和发生、发展规律与切削过程本身以及切削机床动态特性都有着内在的本质联系,长久以来被众多研究者关注.本文就切削颤振在颤振机理、建模、稳定性分析、颤振识别预报以及颤振控制领域的国内外研究成果进行了详细介绍,讨论和分析了...     

螺旋铣孔工艺的切削稳定性及工艺参数规划

以螺旋铣孔工艺时域解析切削力建模、时域与频域切削过程动力学建模、切削颤振及切削稳定性建模为基础,研究了螺旋铣孔的切削参数工艺规划模型和方法。切削力模型同时考虑了刀具周向进给和轴向进给,沿刀具螺旋进给方向综合了侧刃和底刃的瞬时受力特性;动力学模型中同时包含了主轴自转和螺旋进给两种周期对系统动力学特性的影响,并分别建立了轴向切削稳定域和径向切削稳定域的预测模型,求解了相关工艺条件下的切削稳定域叶瓣图。在切削力和动力学模型基础之上,研究了包括轴向切削深度、径向切削深度、主轴转速、周向进给率、轴向进给率等切削工艺参数的多目标工艺参数规划方法。最后通过试验对所规划的工艺参数进行了验证,试验过程中未出现颤振现象,表面粗糙度、圆度、圆柱度可以达到镗孔工艺的加工精度。     

基于小波包能谱熵的铣削颤振监测方法

针对切削加工过程中容易出现颤振,导致零件表面加工质量降低,本文以铣削加工为研究对象,提出了基于小波包能谱熵的铣削颤振监测方法。信号的采集是一个连续的过程,为避免刀具不参与切削对这种方法的影响,本文提出基于铣削力幅值平方和的方法以识别刀具是否参与切削。试验结果表明,无论对于刀具是否参与切削的识别或者是否出现铣削颤振的监测都能有效的监测。     

机床再生颤振的频率筛分机理及其新的监控策略

本文通过变切宽切削颤振试验,观察到一种有规律的多频现象,其最大特征是各频率成分之间按工件回转频率等间隔排列,分析表明,它产生于再生颤振的频率筛分机理。该机理是由相继走刀波纹在一定切削长度内相移几何约束条件决定的,受到主轴转速的决定性影响。基于此机理可提出新的颤振监控策略,即对感兴趣频带内相隔n/60Hz的有限个成分进行监测,可达到高效准确的目的。     

金属切削过程中自激振动的实验分析

通过实验,分析说明切削颤振的振动频率主要由机床切削系统的模态固有频率决定,摩擦自激振动是导致切削颤振的主要原因。     

基于有限元分析的滚齿SLD构建

针对稳定性耳垂线图(SLD)应用于滚齿颤振预测时存在动力学参数获取困难、切削深度难以确定等问题,建立了考虑滚刀刀杆柔性的三维滚齿系统动力学模型,通过滚刀极限切屑厚度与轴向进给量的关系计算滚齿系统动力学参数,并在此基础上绘制出滚齿SLD。设计了滚齿颤振实验方案,通过采集的实验数据分析平稳切削与颤振切削振动的特征量,确定颤振频率及颤振主体,证实了所建立的动力学模型及SLD的有效性。所提方法为滚齿工艺颤振预测、切削参数选取提供了一种新手段。     

离散隐马尔可夫模型在颤振预报中的应用研究

对于切削过程中颤振孕育的动态模式,提出了基于离散隐马尔可夫模型(DHMM)的模式识别理论预报颤振的新方法。首先对切削过程的振动信号进行FFT特征提取,然后利用自组织特征映射(SOM)神经网络对提取的特征矢量进行冗余信息压缩与预分类编码;再根据多变量DHMM建模理论,对切削颤振孕育的各种过程模式建立相应的DHMM,把矢量编码作为观测序列引入到DHMM中进行机器学习、训练;最后将观测序列引入到DHMM中进行颤振孕育的概率识别尝试。实验表明,该方法对颤振孕育过程识别是十分有效的,颤振预报正确率达93.3%。     

Chatter suppression in micro-milling using shank-mounted Two-DOF tuned mass damper

The tuned mass damper (TMD) has been used in machining processes for reducing forced vibration, suppressing chatter, and improving machined surface quality. In micro-milling process, the tiny size of the cutting tool-tip and the high rotating speed bring challenges in implementing the TMD. Besides, the TMD needs to have two degrees-of-freedom (DOFs) for reducing vibrations of micro-mill in two orthogonal directions. This paper presents the chatter suppression for micro-milling by attaching a two-DOF TMD to the tool shank and rotates with the cutting tool. The frequency response function (FRF) at the tip of the micro-mill clamped by an aerostatic spindle is predicted using receptance coupling analysis. A two-DOF TMD is designed via graphical approach based on the FRF result at the tool-tip. The natural frequencies and damping ratio of the TMD are optimized under different spindle speeds in order to enhance the cutting stability. The chatter stability of micro-milling is predicted considering the gyroscopic and centrifugal effects of the TMD structure. Modal tests and micro-milling experiments are conducted to validate the effect of the TMD on chatter stability. The results show that the TMD is able to improve the critical depth of cut by 13 folds, and satisfy the compact design requirement for micro-milling.     

Unique regenerative chatter in wiper-turning operation with burnishing process Part 2: Experimental verification of predicted generation mechanism,critical stability,and characteristics

In this paper, the predicted generation mechanism, chatter stability, and characteristics of the unique regenerative chatter with the burnishing process in wiper-turning operations are verified experimentally. It was found in the first part of the paper that the vibration regenerates in the burnishing process by the wiper part of the insert causing a novel type of chatter. In this second part, this chatter phenomenon is investigated in an experimental manner to verify its mechanism. The specific burnishing force, which is a gain factor characterizing the burnishing process, is determined by the Hertzian contact law. In addition, the specific cutting force is measured by a cutting test, the compliance of the flexible structure is measured by a hammering test, and the residual compliance is measured by a static indentation test. Then, experiments are conducted where the tilt angle and the feed rate are varied to find the critical stability. The conducted chatter experiments prove that the predicted generation mechanism, critical stability, and characteristics are true.     

平面磨削颤振试验研究

首先,通过平面磨削过程动力学模型,对平面磨削颤振的发生和发展进行分析。然后,设计平面磨削颤振的试验方案,获得磨削颤振和磨削表面波纹度的试验结果,进而研究不同的磨削条件对磨削颤振和磨削表面波纹度的影响,得到与理论分析一致的结果。最后,给出磨削颤振和磨削表面波纹度之间的相互关系,研究表明,在平面磨削过程中,磨削深度是影响磨削颤振和磨削表面波纹度的主导因素;在较大的磨削深度条件下,磨削颤振的幅值和磨削表面的波纹度幅值随着工件速度的增加有显著增大的趋势。     

高速铣削时颤振的诊断和稳定加工区域的预报

给出一种通过测量加工过程中的噪声来诊断高速铣削时颤振的方法.先测量环境噪声,然后测量加工噪声.理论分析和试验结果表明,如果加工噪声的主谐振频率接近其中一个环境噪声主谐振频率或者是齿频的整数倍,那么系统无颤振,否则有颤振.建立系统结构和铣削过程动力学特征参数的数学模型.根据测出的颤振频率,通过所建模型可解出系统的固有频率、阻尼比和过程参数,并计算出稳定极限曲线.试验证明,该方法能较好地预报高速铣削时的稳定加工区域.     

Low-frequency chatter genesis during inclined surface copy-milling with ball-end mill: Experimental study

In this study low-frequency chatter during machining of inclined surfaces with ball-end mills is experimentally investigated. An explanation of genesis of low-frequency vibrations have been proposed for various conditions: cutting direction, lead angle values, spindle speed, depth of cut. As a result, it has been proven that low-frequency chatter has more significant effect on machined surface than usual chatter. Low-frequency chatter occurs during downward milling, rather than upward milling, especially when lead angle increases. Furthermore, low-frequency chatter takes place in the beginning of cutting process, thereafter develops into steady state of usual chatter, which has no such significant effect on machined surface, as it has been shown. The results are in line with the supposition that low frequency vibrations are caused by sudden and irregular nature of shearing process, when magnitude is small.     

Prediction of dynamic cutting force and regenerative chatter stability in inserted cutters milling

Currently, the modeling of cutting process mainly focuses on two aspects: one is the setup of the universal cutting force model that can be adapted to a broader cutting condition; the other is the setup of the exact cutting force model that can accurately reflect a true cutting process. However, there is little research on the prediction of chatter stablity in milling. Based on the generalized mathematical model of inserted cutters introduced by ENGIN, an improved geometrical, mechanical and dynamic model for the vast variety of inserted cutters widely used in engineering applications is presented, in which the average directional cutting force coefficients are obtained by means of a numerical approach, thus leading to an analytical determination of stability lobes diagram (SLD) on the axial depth of cut. A new kind of SLD on the radial depth of cut is also created to satisfy the special requirement of inserted cutter milling. The corresponding algorithms used for predicting cutting forces, vibrations, dimensional surface finish and stability lobes in inserted cutter milling under different cutting conditions are put forward. Thereafter, a dynamic simulation module of inserted cutter milling is implemented by using hybrid program of Matlab with Visual Basic. Verification tests are conducted on a vertical machine center for Aluminum alloy LC4 by using two different types of inserted cutters, and the effectiveness of the model and the algorithm is verified by the good agreement of simulation result with that of cutting tests under different cutting conditions. The proposed model can predict the cutting process accurately under a variety of cutting conditions, and a high efficient and chatter-free milling operation can be achieved by a cutting condition optimization in industry applications.     

用于切削颤振机理分析的在线测量系统

金属切削加工中产生的自激振动对加工质量和表面质量均会产生很大的影响,有时甚至使加工无法进行。利用Delphi,开发出了一套在线测量系统,对切削颤振的机理进行了研究。通过实时采集切削过程中与颤振相关的各种数据,并采用FFT（快速傅立叶变换）技术对切削颤振的频率及功率谱进行计算分析,同时结合李萨如图形对颤振能量消减情况进行跟踪显示,在此基础上对自激振动的谐振频率及主要影响因素进行分析,为寻求相应的消振措施提供必要的理论依据。