薄板件铣削颤振稳定性的非线性判据实验研究

铣削过程中非线性动力学行为一直伴随整个切削过程,为准确地判定和预测加工过程的颤振稳定性,基于实验方法,研究了两端固定薄板件铣削颤振稳定性的非线性判据。实验中以薄板件振动信号为研究对象,基于相平面法、庞加莱法和频谱分析了不同加工参数时的振动信号,绘制并讨论了最大Lyapunov指数与主轴转速和铣削深度的变化关系。最后以最大Lyapunov指数作为判据,通过等高线法确定铣削颤振稳定域,并和基于全离散法得出的铣削颤振稳定域进行比较分析,实验得出了航空铝合金7075-T6薄板件颤振稳定域的非线性判据。     

高速车铣加工三维颤振的稳定性分析与试验研究

针对立铣刀高速车铣加工,基于其切削原理采用解析法建立三维颤振稳定域的理论模型。在立铣刀四轴车铣加工模态试验基础上,仿真分析了颤振稳定域叶瓣图,结果表明立铣刀高速车铣加工产生颤振的条件与铣刀几何形状、工件材料、铣刀转速、切削深度和机床结构的频率响应函数等密切相关。在进行车铣切削颤振稳定域试验时,其切削力频谱分析的结果表明:当刀齿切入频率起主导作用时,切削过程是无颤振和稳定的;当系统模态频率起主导作用时,将产生颤振并测得切削力和表面粗糙度值都大于或高于无颤振情况。因此该理论模型及仿真结果对立铣刀车铣加工零件的加工效率和加工精度可提供相应的理论指导。     

切削加工稳定图中相邻不稳定叶瓣间的控制规律

本文研究了切削加工稳定图中相邻两个不稳定叶瓣之间的控制规律。经理论和实验分析给出的规律表明,颤振振幅和切宽的关系在切宽较大时,由右边不稳定叶瓣的左侧控制;而在切宽较小时,由左边不稳定叶瓣的右侧控制。该规律能全面描述机床双频颤振现象和颤振过程主频带移动的原因。     

基于隐式Adams方法的螺旋曲面铣削系统稳定性预测研究EI北大核心CSCD

针对螺杆转子铣削过程中的铣削系统稳定性进行研究。首先通过模态试验获取刀具的模态参数。其次,根据盘铣刀铣削螺杆转子曲面原理建立三自由度铣削力模型和以线性时滞微分方程表示再生型颤振影响的铣削加工动力学模型,并对刀齿铣削周期进行离散。然后,提出基于隐式Adams对螺旋曲面铣削系统稳定性进行预测的方法,在利用隐式Adams方法对动力学方程进行数值求解的基础上,依据Floquet理论判断系统的稳定性,获得螺旋曲面铣削系统的稳定性叶瓣图。最终,根据稳定性叶瓣图选取加工参数进行试验,验证隐式Adams方法在螺旋曲面铣削系统的适用性。试验结果表明:数值求解结果与试验结果吻合程度较高,即采用的隐式Adams方法适用于螺旋曲面铣削系统的稳定性预测。     

基于隐式Adams方法的螺旋曲面铣削系统稳定性预测研究

针对螺杆转子铣削过程中的铣削系统稳定性进行研究。首先通过模态试验获取刀具的模态参数。其次,根据盘铣刀铣削螺杆转子曲面原理建立三自由度铣削力模型和以线性时滞微分方程表示再生型颤振影响的铣削加工动力学模型,并对刀齿铣削周期进行离散。然后,提出基于隐式Adams对螺旋曲面铣削系统稳定性进行预测的方法,在利用隐式Adams方法对动力学方程进行数值求解的基础上,依据Floquet理论判断系统的稳定性,获得螺旋曲面铣削系统的稳定性叶瓣图。最终,根据稳定性叶瓣图选取加工参数进行试验,验证隐式Adams方法在螺旋曲面铣削系统的适用性。试验结果表明：数值求解结果与试验结果吻合程度较高,即采用的隐式Adams方法适用于螺旋曲面铣削系统的稳定性预测。     

基于径向基函数的AL2A12薄壁件铣削稳定性研究

在薄壁件铣削过程中,颤振对工件表面质量有很大影响,在实际加工之前进行铣削稳定性预测,便于获取无颤振的加工条件。基于径向基函数逼近理论,提出一种铣削稳定性预测方法。通过试切法和锤击法获得了AL2A12薄壁件的切削力系数和模态参数,并基于所提出的方法推导了系统的状态转移矩阵,通过Floquet定理来判定系统的稳定性,从而获得了AL2A12薄壁件铣削过程的稳定性图。为了验证所提方法的计算效率,采用相同的系统参数来进行计算。通过与零阶半离散法和全离散法相比,表明在获得的铣削稳定性图一致的前提下,所提方法的计算效率最高。在预测的稳定性图中选择4个参数点,利用参数点所对应主轴转速和轴向切深来加工AL2A12薄壁件,将实际加工结果与稳定性预测结果进行比较,验证了所提预测方法的有效性。通过实际切削表明,在AL2A12薄壁件的加工过程中,当轴向切深相近时,较高的主轴转速可以获得更好的加工表面,同时也可以避免黏刀现象的产生。     

预测铣削稳定性的Hamming线性多步法

针对铣削加工过程中产生的振动现象,提出了一种Hamming线性多步法(HAMM)来预测铣削加工过程中的稳定性。考虑再生颤振的铣削加工动力学方程可以表示为时滞线性微分方程,将刀齿周期划分为自由振动阶段和强迫振动阶段,对强迫振动阶段进行离散,运用HAMM方法构建状态传递矩阵,利用Floquet理论,判定系统的稳定性,获得系统的稳定性叶瓣图。Matlab软件仿真结果表明,HAMM方法是预测铣削稳定性的一种有效方法。随着离散数的增加,HAMM方法的收敛速度要快于一阶半离散法(1st-SDM)和二阶全离散法(2nd-FDM),离散数较少的HAMM方法能达到和离散数较多的1st-SDM方法和2nd-FDM方法的局部离散误差。此外,在单自由度和双自由度动力学模型下,由三种方法的稳定性叶瓣图可以看出,HAMM方法预测铣削稳定性的精度均好于1st-SDM方法和2nd-FDM方法,计算效率远远高于1st-SDM方法和2nd-FDM方法。实验结果表明,HAMM方法是一种有效的预测铣削稳定性的方法。     

包含刀具-工件多重交互与速度效应的铣削颤振稳定性分析

为研究刀具-工件多重交互与速度效应对铣削颤振稳定性的影响,建立了包含刀具-工件多重交互与速度效应的铣削动力学模型,阐明了无刀轴倾角状态下再生效应、过程阻尼、刀具结构模态耦合与速度效应的耦合作用对铣削颤振稳定性的影响规律,研究了不同径向浸入比下刀具-工件交互与速度效应对铣削稳定性的影响。结果表明,与只考虑再生效应的铣削动力学模型相比,当同时考虑再生效应、过程阻尼与刀具结构模态耦合时,得到的稳定性叶瓣图中颤振区域发生明显变化;当主轴转速较低时,刀具-工件之间的多重交互效应是影响铣削颤振稳定性的主要因素,速度效应对极限切深的影响可忽略不计;随着主轴转速升高,速度效应对极限切深的影响逐渐增大,稳定性叶瓣图中稳定区域呈逐渐减小趋势;在一定范围内,随着铣刀后刀面磨损带的增加,铣削极限切深逐渐增大;主轴转速一定时,径向浸入比相对较小的情况下过程阻尼对铣削稳定性的影响更加明显。采用铣削试验进行验证,结果表明,与传统动力学模型相比,构建的铣削动力学模型能够更加可靠地预测实际铣削状态。     

基于瞬时频率估计与Vold-Kalman滤波的铣削颤振识别

颤振严重制约了高速铣削加工效率。动态铣削力信号具有非线性、非平稳的特点,常规的信号分解方法难以处理该类信号。提出了一种基于瞬时频率估计和Vold-Kalman滤波的多分量信号分解方法,并运用该信号分解方法识别颤振。基于频谱集中性指标估计信号的瞬时频率参数;用Vold-Kalman滤波器提取对应参数的各信号分量;由于颤振时铣削力信号的能量分布在频域发生变化,由此引入能量熵的定义。采用分解得到的子信号能量熵变化来识别颤振。实验分析表明该方法有效可行。     

数控机床切削稳定性分析及实验研究

针对因机床结构的复杂性及零件加工轨迹不确定性,刀尖频响函数切削中难以保持恒定易造成稳定域图变化,导致机床切削参数选择不确定性问题,结合模态实验分别研究数控机床沿不同进给方向及机床主轴处于不同位置的颤振稳定域图预测;对同型号两台数控机床的切削稳定性进行对比分析。由实验采集切削中声音信号验证机床沿不同进给方向的切削稳定性存在差别。研究结果对实际加工中避免切削颤振及工艺参数选择具有指导意义。     

Determination of optimal geometrical parameters of peripheral mills to achieve good process stability

This paper focuses on optimization of the geometrical parameters of peripheral milling tools by taking into account the dynamic effect. A substructure synthesis technique is used to calculate the frequency response function of the tool point, which is adopted to determine the stability lobe diagram. Based on the Taguchi design method, simulations are first conducted for varying combinations of tool overhang length, helix angle, and teeth number. The optimal geometrical parameters of the tool are determined through an orthogonal analysis of the maximum axial depth of cut, which is obtained from the predicted stability lobe diagram. It was found that the sequence of every factor used to determine the optimal tool geometrical parameters is the tool overhang length, teeth number, and helix angle. Finally, a series of experiments were carried out as a parameter study to determine the influence of the tool overhang length, helix angle, and teeth number on the cutting stability of a mill. The same conclusion as that obtained through the simulation was observed.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0226-9.pdf     

Efficient determination of stability lobe diagrams by in-process varying of spindle speed and cutting depth

The experimental determination of stability lobe diagrams (SLDs) in milling can be realized by either continuously varying the spindle speed or by varying the depth of cut. In this paper, a method for combining both these methods along with an online chatter detection algorithm is proposed for efficient determination of SLDs. To accomplish this, communication between the machine control and chatter detection algorithm is established, and the machine axes are controlled to change the spindle speed or depth of cut. The efficiency of the proposed method is analyzed in this paper.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0225-x.pdf     

Chatter prediction for uncertain parameters

The occurrence of chatter in milling processes was investigated in this study. The prediction of the stability lobes of metal cutting processes requires a model of the cutting force and a model of the dynamic machine tool behavior. Parameter uncertainties in the models may lead to significant differences between the predicted and measured stability behavior. One approach towards robust stability consists of running a large number of simulations with a random sample of uncertain parameters and determining the confidence levels for the chatter vibrations, which is a time-consuming task. In this paper, an efficient implementation of the multi frequency solution and the construction of an approximate solution is presented. The approximate solution requires the explicit calculation of the multi frequency solution only at a few parameter points, and the approximation error can be kept small. This study found that the calculation of the robust stability lobe diagram, which is based on the approximate solution, is significantly more efficient than an explicit calculation at all random parameter points. The numerically determined robust stability diagrams were in good agreement with the experimentally determined stability lobes.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-018-0230-0.pdf     

基于犹豫模糊决策的铣削参数优化

为提升铣削加工质量，研究一种基于犹豫模糊决策的数控铣削参数优化方法。根据铣削过程机理和实验数据建立铣削参数优化的数学模型，将犹豫欧氏距离与模糊逻辑推理相结合，对铣削过程中多响应系统进行简化，既避免了传统模糊测度方法中权重的设置，也充分提取了各响应之间相关性的有效信息，最后通过对实验中可控因子与模糊推理过程输出值进行主效应分析，得到铣削过程控制因子的最佳参数组合：当进给量为0.01 mm/tooth，铣削深度为0.064 mm、铣削速度达到396 m/min，铣削宽度达到12.26 mm时，加工零件的表面粗糙度R_a和R_t可以得到整体优化，从而提升加工零件的质量。该方法首次将犹豫模糊决策理论方法应用于铣削过程工艺参数优化，避免了均值处理法带来的信息损失，可增加实验设计的鲁棒性。与满意度函数法相比，研究的基于犹豫模糊决策的铣削参数优化方法不受权重大小制约，能够同时使过程的两个响应得到优化，具有实用的有效性和可操作性。     

一种基于多步回溯算法的铣削稳定性预测方法

在加工过程中,由于薄壁件的弱刚性易发生加工颤振,从而对工件表面质量和刀具寿命等造成不良的影响,对铣削过程的稳定性进行预测是至关重要的。通过提出一种多步回溯算法来预测铣削过程的稳定性,将铣削过程离散化成时滞周期方程,在每个时间间隔上采用多步回溯的方法来近似时间周期及时滞项。通过构建状态转移矩阵,根据Floquet理论获得了铣削稳定性边界参数。最后,通过仿真对比实例验证了算法的计算精度和收敛率。结果表明,多步回溯算法具有快速收敛及高计算精度等特点,尤其在低速铣削的稳定性预测中具有良好的应用前景。     

A pseudospectral tau approximation for time delay systems and its comparison with other weighted‐residual‐type methods

This paper presents a method which applies pseudospectral tau approximation for retarded functional differential equations (RFDEs). The goal is to construct a system of ordinary differential equations, which provides a finite dimensional approximation of the original RFDE. The method can be used to determine approximate stability diagrams for RFDEs. Thorough numerical case studies show that the rightmost characteristic roots of the ordinary differential equation approximation converge to the rightmost characteristic roots of the original RFDE. Application of the method to time‐periodic RFDEs is also demonstrated, and the convergence of the stability boundaries is verified numerically. The method is compared with recently developed highly efficient numerical methods: the pseudospectral collocation (also called Chebyshev spectral continuous‐time approximation), the spectral Legendre tau method, and the spectral element method. The comparison is based on the stability analysis of three linear autonomous RFDEs. The efficiency of the methods is measured by the convergence rate of stability boundaries in the space of system parameters, by the convergence rate of the rightmost characteristic exponent and by the computation time of the stability charts. Copyright © 2016 John Wiley & Sons, Ltd.     

孔底起爆孔网参数优化的多目标灰色决策

地下矿山中深孔爆破孔网参数优化研究对于改善爆破效果、提高铲装效率、降低采矿成本至关重要。但是影响爆破质量的因素很多，参与试验的技术经济指标缺乏公度性，加之现场试验条件和实验次数的限制，在孔底起爆孔网参数优化选择时有一定的随机性和模糊性。本文结合杨家坝铁矿具体矿岩条件，在孔底起爆孔网参数优化试验的基础上，运用多目标灰色决策理论，建立了孔网参数决策模型，从而确定了最优孔网参数。工程实践表明是合理的，并对同类矿山有一定的参考价值。     

主轴运行状态下机床刀尖点动力学行为分异特征辨识

刀尖点动力学特性直接影响切削稳定性和加工表面的质量。现阶段对主轴运行状态下刀尖点动力学特性的理论研究和实验研究分别存在着建模复杂和设备昂贵等局限性。为此,提出一种基于半理论法的主轴运行状态下刀尖点动力学行为分异特征辨识方法。该方法将分异特征辨识转化为一类优化设计问题,即以不同转速下刀尖点动力学特性参数为变量、以极限切深和颤振频率的实验标定值与理论预测值的偏差之和最小为目标构建优化模型,并借助粒子群退火优化算法进行求解,从而获得在不同转速下刀尖点动力学行为的分异特征及规律。以某型立式加工中心为平台,通过变切深铣削实验,对所提出的辨识方法进行验证,结果显示极限切深预测值与标定值吻合度较高。在不需复杂建模和昂贵实验设备的条件下,利用所提出的方法能够准确预测运行状态下刀尖点动力学行为分异特征,实现切削稳定性的精准预测,为进一步提高铣削加工质量和效率提供理论基础和数据支撑。     

Chatter stability prediction in high-speed micromilling of Ti6Al4V via finite element based microend mill dynamics

High-speed micromilling (spindle speeds 100 000 r/min) can create complex three-dimensional microfeatures in difficult-to-machine materials. The micromachined surface must be of high quality, to meet functional requirements. However, chatter-induced dynamic instability deteriorates the surface quality and can be detrimental to tool life. Chatter-free machining can be accomplished by identifying stable process parameters via stability lobe diagram. To generate accurate stability lobe diagram, it is essential to determine the microend mill dynamics. Frequency response function is required to determine the tooltip dynamics obtained by experimental impact analysis. Note that application of impact load at the microend mill tip (typically 100-500 μm) is not feasible as it would invariably end with tool failure. Consequently, alternative methods need to be developed to identify the microend mill dynamics. In the present work, the frequency response function for the microend mill is obtained by finite element method modal analysis. The frequency response function obtained from modal analysis has been verified from the experimentally obtained frequency response function. The experimental frequency response function was obtained by impacting the microend mill near the taper portion with an impact hammer and measuring the vibration of the tool-tip with a laser displacement sensor. The fundamental frequency obtained from finite element method modal analysis shows a difference of 6.6% from the experimental fundamental frequency. Microend mill dynamics obtained from the finite element method is used for chatter prediction in high-speed micromilling operations. The stability lobe diagram predicts the stability boundary accurately at 60 000 r·min^-1 and 80 000 r/min; however, a slight deviation is observed at 100 000 r/min. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0210-4     

Milling performance of stone-plastic composite with diamond cutters

In order to meet the requirements of cutting efficiency and economy in the processing of stone plastic composite, milling tests of the stone plastic composite were conducted using straight tooth diamond tools. Cutting forces and temperature were measured under different cutting parameters. Response surface methodology was used to analyze the variation of cutting forces and temperature and to determine the significant contribution of each variable and its two-level interaction. The correlation between actual and predicted results was found by building mathematical models of cutting forces and temperatures, which can be used to make accurate predictions. At last, the optimal cutting parameters for stone plastic composite straight-tooth milling with low cutting forces and cutting temperatures were found to be 10° front angle, 37.9 m/s cutting speed, 0.32 mm feed per tooth, and 0.5 mm milling depth. It is possible to improve processing efficiency and reduce production costs by using these parameters in industrial processing.