基于子结构耦合法的机床主轴-刀具系统频响函数研究

数控加工过程的稳定性与由频响函数确定的机床主轴-刀具系统的动态特性密切相关,通常,需要进行模态实验以获取数控机床主轴-刀具系统的频率响应函数,为了避免因更换刀具时获取其频响函数的模态实验的重复性,文章研究利用响应耦合法(RCSA)预测主轴-刀具系统刀尖点的频率响应函数,主轴-刀柄基座的频响函数利用实验以及反向RCSA方法获得,并用Timoshenko梁理论计算外伸刀柄和刀具的频响函数,然后将3个子结构的频响函数进行耦合,得到整个系统刀尖点的频响函数,然后利用加入禁忌搜索的粒子群算法识别刀柄和刀具结合面的参数,将预测得到的系统刀尖点的频响函数与实测的频响函数进行对比研究,并通过实验验证了该研究方法的有效性。     

立式数控铣床主轴-刀柄和刀柄-刀具结合面参数辨识方法的研究

以立式数控铣床主轴－刀柄和刀柄－刀具结合面为研究对象,结合Timoshenko梁理论、传递矩阵法,柔度耦合子结构分析RCSA和改进型粒子群优化算法PSO,提出了一种固定结合面参数辨识模型。研究分析表明：该模型采用基于Timoshenko梁理论的传递矩阵法计算刀柄和刀具端点频响函数,避免了复杂的模态分析带来的模态误差,计算精度高;局部搜索与PSO算法相结合的优化算法兼顾PSO强大的全局搜索能力和局部搜索算法的局域搜索能力,能更容易找到全局最优解,实现主轴－刀柄和刀柄－刀具结合面参数的高精度辨识。     

主轴系统建模与刀尖点频响函数预测研究

为了获取稳定性叶瓣图所需要的刀尖点频响函数,基于响应耦合子结构分析法(RCSA)提出一种主轴系统建模方案。根据电主轴系统在实际使用过程中变化与不变化的部分将系统划分成主轴-刀柄基座、刀柄悬伸部分-刀具夹持部分和刀具悬伸部分三个子结构,并利用锤击实验、有限差分法、逆RCSA方法以及Timoshenko梁模型仿真获取各子结构的频响函数。这种模型不仅避免了复杂的结合面建模与参数识别过程,而且能简单、快速、准确地通过刚性耦合预测出不同刀柄-刀具组合下的刀尖点频响函数。以170XDS20Z11型电主轴系统为研究对象,对以上建模方法进行了实验研究,验证了本方法的实用性与准确性。     

基于GA-BP和RCSA的加工空间刀尖频响预测

针对机床主轴加工位置变化和刀具更换引起刀尖频响函数改变的现象，提出了一种基于遗传算法优化的反向神经网络(GA-BP)和子结构响应耦合方法(RCSA)的刀尖加工空间频响函数预测方法。在该方法中，将机床系统划分为刀柄基座、剩余刀柄和刀具3个子结构。采取GA-BP算法构建刀柄基座频响函数预测模型；通过遗传算法辨识刀柄-刀具结合面参数；最后，采用RCSA法预测出不同加工位置和不同刀具的刀尖点频响函数。结果表示，刀尖点频响函数的预测值与实测值基本一致，前二阶固有频率的误差均不超过5%,有效地验证了该方法的可行性和准确性，为不同位置和不同刀具下的频响函数预测提供了有效参考。     

立式铣床刀尖频响函数预测方法研究

由于对机械加工精度和效率影响较大,切削颤振一直是制造领域的研究热点之一。为了避免颤振的发生,通常利用稳定性Lobe图确定合适的加工参数,而机床刀尖频响函数是绘制稳定性Lobe图的先决条件。基于模态叠加法、激振实验和响应耦合子结构耦合方法 (Receptance Coupling Substructure Analysis,RCSA),提出了一种新的机床刀尖频响函数计算方法。首先通过模态叠加法计算刀柄和刀具的各个端点频响函数,通过锤击法得到机床主轴的端点频响函数,最后利用RCSA耦合各个子结构,获取机床刀尖频响函数。对比实验结果,本文作者提出的方法能够得到精确的立式铣床刀尖频响函数。     

基于均布弹簧模型的电主轴有限元建模及动态特性分析

为了研究轴承刚度、结合面刚度等各个参数对电主轴动态特性的影响、验证弹簧模型在电主轴建模中的适用性,基于国产电主轴170XDS20Z11,使用有限元方法,利用Ansys workbench对电主轴单元进行建模。首先分别建立刀具、刀柄和主轴的模型,结合实验进行动静态特性的分析与验证;然后基于均布弹簧的模型对刀柄—刀具结合面、刀柄—主轴结合面和轴承进行建模,通过对实验数据的拟合得到了结合面弹簧的刚度数值,通过预测刀尖点频响函数的方法验证该模型的准确性。研究得出了轴承刚度和结合面刚度的最佳范围,证明了弹簧模型的准确性和实用性。     

主轴-刀柄和刀柄-刀具结合面参数对稳定性Lobe图的影响

为探索主轴-刀柄和刀柄-刀具结合面参数与立铣加工过程稳定性的关系,以主轴-刀柄和刀柄-刀具结合面参数辨识方法和两自由度立铣加工过程动力学模型为基础,研究了主轴-刀柄,以及刀柄-刀具结合面参数等因素对稳定性Lobe图的影响。结果表明:主轴-刀柄和刀柄-刀具结合面的直线刚度对稳定性Lobe图的影响最大,其他结合面参数对稳定性Lobe图均有不同程度的影响;和主轴-刀柄结合面参数相比,刀柄-刀具结合面参数尤其是转动刚度对稳定性Lobe图的影响更大。     

薄壁件铣削系统动态特性及稳定性分析

颤振失稳现象是铣削过程中降低加工表面质量的一种不利因素,针对此问题采用颤振稳定性解析算法建立铣削过程的动态铣削模型,以钛合金ZTC4/42C薄壁件铣削参数作为研究对象,通过仿真绘制出转速和切削深度相关的稳定性叶瓣图;其次,分别对影响铣削稳定性的机床系统的模态因素、刀具几何参数和材料特性进行了分析,研究结果可以为钛合金薄壁件铣削加工提供理论支持。轴承接触点的刚度值与切削稳定性所需的刀尖点频响函数信息密切相关,采用有限元软件对主轴系统进行动态特性研究,借助仿真分析得到刚度与刀尖点频响函数之间的内在关系。     

JKM8凸轮轴磨床头架主轴系统动态特性分析

凸轮轴磨削精度主要受机床主轴系统的自激振动、受迫振动和热变形的影响,模态分析是动力学分析的基础,因此有必要深入分析主轴振型对磨削精度的影响。以JKM8凸轮轴磨床头架主轴系统为研究对象,使用弹性支承单元模拟静压轴承,建立转子-轴承系统有限元模型进行模态分析,获取系统前6阶模态参数,运用参数讨论法,研究系统固有频率随支承刚度的变化规律。结果表明:主轴转速远远低于一阶临界转速,因此不会发生共振;静压轴承的支承刚度对主轴系统的低阶固有频率影响很大,支承刚度大于300 N/μm时,固有频率的增加幅度显著减小。研究结果为磨床主轴系统的优化提供了理论依据。     

机床-刀具-工件系统相对激振方法研究

立式铣床的振动模态,尤其是机床-刀具-工件系统的动态特性直接影响工件质量和加工稳定性。当前,主要通过分析激励刀具和工作台的方法获取刀具和工件系统的频响函数,并通过叠加法计算机床-刀具-工件系统的相对频响函数。该方法能够得到足够精度的幅值谱,但难于实现高精度的相位差。为解决这一问题,提出了一种相对激振方法,该方法可以直接得到高精度的机床-刀具-工件系统的相对频响函数,并对机床-刀具-工件系统的动态特性进行分析。结果表明:机床刀尖频响函数与对应的机床相对动柔度在整体上是一致的;在直接和交叉频响函数G_(xx)和G_(yx)的高频阶段,以及直接与交叉频响函数G_(xy)和G_(yy)的低频阶段差别较大。     

Effect analysis of bearing and interface dynamics on tool point FRF for chatter stability in machine tools by using a new analytical model for spindle–tool assemblies

Self-excited vibration of the tool, regenerative chatter, can be predicted and eliminated if the stability lobe diagram of the spindle–holder–tool assembly is known. Regardless of the approach being used, analytically or numerically, forming the stability lobe diagram of an assembly implies knowing the point frequency response function (FRF) in receptance form at the tool tip. In this paper, it is aimed to study the effects of spindle–holder and holder–tool interface dynamics, as well as the effects of individual bearings on the tool point FRF by using an analytical model recently developed by the authors for predicting the tool point FRF of spindle–holder–tool assemblies. It is observed that bearing dynamics control the rigid body modes of the assembly, whereas, spindle–holder interface dynamics mainly affects the first elastic mode, while holder–tool interface dynamics alters the second elastic mode. Individual bearing and interface translational stiffness and damping values control the natural frequency and the peak of their relevant modes, respectively. It is also observed that variations in the values of rotational contact parameters do not affect the resulting FRF considerably, from which it is concluded that rotational contact parameters of both interfaces are not as crucial as the translational ones and therefore average values can successfully be used to represent their effects. These observations are obtained for the bearing and interface parameters taken from recent literature, and will be valid for similar assemblies. Based on the effect analysis carried out, a systematic approach is suggested for identifying bearing and interface contact parameters from experimental measurements.     

Effects of interface stiffness and delamination on resonant oscillations of metal laminates

In the present study, the effects of the interface stiffness and delamination of the metal laminates were investigated. In the modal analysis, the natural oscillation mode of the laminate consisting of two copper sheets with various interface conditions was analyzed by using a finite element method. The interface delamination decreases the natural frequency for the out-of-plane oscillation mode whereas it has no effect on that for the in-plane mode. The interface stiffness affects the natural frequency for both the out-of-plane and in-plane modes. Its influence was more obvious when the stiffness is lower than that of the matrix for the out-of-plane mode whereas there was an opposite trend for the in-plane mode. In the experiment, the resonant frequency of two copper sheets bonded by the adhesive was measured. As well as the simulation, the lower interface stiffness and the interface delamination decreased the resonant frequencies     

A closed-form approach for identification of dynamical contact parameters in spindle–holder–tool assemblies

Accurate identification of contact dynamics is very crucial in predicting the dynamic behavior and chatter stability of spindle–tool assemblies in machining centers. It is well known that the stability lobe diagrams used for predicting regenerative chatter vibrations can be obtained from the tool point frequency response function (FRF) of the system. As previously shown by the authors, contact dynamics at the spindle–holder and holder–tool interfaces as well as the dynamics of bearings affect the tool point FRF considerably. Contact stiffness and damping values alter the frequencies and peak values of dominant vibration modes, respectively. Fast and accurate identification of contact dynamics in spindle–tool assemblies has become an important issue in the recent years. In this paper, a new method for identifying contact dynamics in spindle–holder–tool assemblies from experimental measurements is presented. The elastic receptance coupling equations are employed in a simple manner and closed-form expressions are obtained for the stiffness and damping parameters of the joint of interest. Although this study focuses on the contact dynamics at the spindle–holder and holder–tool interfaces of the assembly, the identification approach proposed in this paper might as well be used for identifying the dynamical parameters of bearings, spindle–holder interface and as well as other critical joints. After presenting the mathematical theory, an analytical case study is given for demonstration of the identification approach. Experimental verification is provided for identification of the dynamical contact parameters at the holder–tool interface of a spindle–holder–tool assembly.     

Analytical modeling of spindle–tool dynamics on machine tools using Timoshenko beam model and receptance coupling for the prediction of tool point FRF

Regenerative chatter is a well-known machining problem that results in unstable cutting process, poor surface quality and reduced material removal rate. This undesired self-excited vibration problem is one of the main obstacles in utilizing the total capacity of a machine tool in production. In order to obtain a chatter-free process on a machining center, stability diagrams can be used. Numerically or analytically, constructing the stability lobe diagram for a certain spindle–holder–tool combination implies knowing the system dynamics at the tool tip; i.e., the point frequency response function (FRF) that relates the dynamic displacement and force at that point. This study presents an analytical method that uses Timoshenko beam theory for calculating the tool point FRF of a given combination by using the receptance coupling and structural modification methods. The objective of the study is two fold. Firstly, it is aimed to develop a reliable mathematical model to predict tool point FRF in a machining center so that chatter stability analysis can be done, and secondly to make use of this model in studying the effects of individual bearing and contact parameters on tool point FRF so that better approaches can be found in predicting contact parameters from experimental measurements. The model can also be used to study the effects of several spindle, holder and tool parameters on chatter stability. In this paper, the mathematical model, as well as the details of obtaining the system component (spindle, holder and tool) dynamics and coupling them to obtain the tool point FRF are given. The model suggested is verified by comparing the natural frequencies of an example spindle–holder–tool assembly obtained from the model with those obtained from a finite element software.     

Continuous model for analytical prediction of chatter in milling

A novel analytical approach for prediction of chatter in milling process is presented. Existing approaches use lumped-parameter models to define the dynamics of tools/workpieces. In this paper a continuous beam model is employed for prediction of milling operations dynamics. The tool boundary conditions are elastic support at the tool/holder/spindle interface and free support at the other end. Employing the continuous model eliminates the need for tool tip frequency response function (FRF) measurements in tool-tuning practice, especially in micro-milling, where FRF measurement is practically very difficult. Tool/holder/spindle interface parameters, once identified, can be used for other tool lengths. The impact hammer test is used to identify stiffness and damping parameters of the tool/holder/spindle interface. Using the new analytical approach and picking single-frequency solution (SFS), stability lobes are obtained for a slotting operation. The resulting lobes are compared to those obtained by the well-proven lumped-parameter model. In addition to a good general agreement between the two approaches, the continuous model prediction is more conservative for critical depth of cut, which is attributed to its ability to consider all participating modes in the response and so represents a more accurate representation of the system.     

A Modeling Approach for Analysis and Improvement of Spindle-Holder-Tool Assembly Dynamics

The most important information required for chatter stability analysis is the dynamics of the involved structures, i.e. the frequency response functions (FRFs) which are usually determined experimentally. In this study, the tool point FRF of a spindle-holder-tool assembly is analytically determined by using the receptance coupling and structural modification techniques. Timoshenko's beam model is used for increased accuracy. The spindle is also modeled analytically with elastic supports representing the bearings. The mathematical model is used to determine the effects of different parameters on the tool point FRF and to identify contact dynamics from experimental measurements. The applications of the model are demonstrated and the predictions are verified experimentally.     

基于参数优化变分模态分解的滚动轴承微弱故障诊断研究

为了提高变分模态分解(VMD)对滚动轴承微弱故障特征提取的准确性,提出了一种基于参数优化VMD与奇异值分量及其熵相结合的滚动轴承故障诊断方法。该方法通过寻优算法确定VMD的模态数K和二次惩罚因子α;根据余弦-标准差指标提取VMD典型本征模态分量(IMF);计算IMF奇异值及其熵,并利用计算结果分别判断滚动轴承的不同故障状态。结合美国西储大学轴承振动信号数据,实验结果表明:相比经验模态分解奇异值故障诊断方法,基于参数优化VMD奇异值故障诊断方法能更明显地识别滚动轴承的不同故障类型,为区分滚动轴承微弱故障提供了一种可行的诊断思路。     

滚珠丝杠副抗共振可靠性的有限元分析

考虑到轴承刚度的影响,分别计算分析了在刚性支承和弹性支承下的临界转速,利用有限元方法分析计算了轴承刚度对于滚珠丝杠副的动力学特性和抗共振模糊可靠度的影响.结果表明,采用弹性支承时,滚珠丝杠副的第一阶固有频率明显下降;径向刚度主要影响滚珠丝杠副的弯曲模态,而轴向支承刚度主要影响轴向振动;随着径向支承刚度的增加滚珠丝杠副的杭共振模糊可靠度增大.