机床相对动柔度劣化对稳定性Lobe图的影响分析

在机床各种形式的振动中,再生颤振具有最小的稳定极限切削宽度,换言之,机床抵抗再生颤振的能力最差。品质系数(Coefficient of Merit,COM)是切削力和切削表面法向相对位移之间的交叉频响函数最小负实部的函数,其大小直接反映机床抵抗再生颤振的能力。此外,在机床的连续使用过程中,品质系数COM会逐渐减小,进而影响机床再生颤振抗振能力。基于相对激振方法和四自由度立铣加工过程动力学模型,重点分析了机床相对动柔度劣化过程中品质系数COM的变化趋势,以及对加工过程稳定性Lobe图的影响。研究表明:随着机床相对动柔度的劣化,轴向极限切深ap逐渐减小,并有加速递减的趋势,这和机床品质系数的劣化趋势一致。因此,考虑机床相对动柔度对稳定性Lobe图的影响,才能确定更合适的工艺参数,保证切削过程的稳定性,提高加工效率。     

基于广义马尔科夫链模型的动柔度预测

动柔度对机械加工的稳定性和精度有重要的影响。对动柔度进行预测能为机床加工精度补偿和稳定性分析提供实际的指导作用。由于不确定性的存在会降低结果的可靠性与可信度,传统的马尔科夫链预测方法没有考虑不确定性问题。为了提高预测结果的可靠性与可信度,在马尔科夫链模型的基础上提出了一个广义马尔科夫链模型,并通过广义马尔科夫链模型对动柔度进行了预测。结果表明：提出的预测方法有一个好的预测性能。     

基于熵特征与HMM的滚动轴承退化状态识别

为准确识别滚动轴承的性能退化状态,提出一种基于熵特征与隐马尔科夫模型(Hidden Markov Model,HMM)的轴承退化状态识别方法。该方法提取轴承振动信号的多尺度模糊熵和VMD能谱熵作为退化特征向量,利用全寿命数据样本的退化特征向量训练不同退化状态下的HMM模型,最后通过建立的HMM模型库并根据最大对数似然概率原则识别轴承退化状态。其中,针对人为划分轴承退化阶段的不足,采用GG聚类方法实现全寿命数据在时域上的退化阶段划分。实测数据分析结果表明,所提方法能够达到90%以上的识别率,优于常用退化指标下的识别效果。     

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。     

基于小波包-隐马尔科夫模型的机床加工状态识别

机床加工状态对加工工件质量有很大的影响,因此识别机床加工状态有重要的意义.依据采集的机床加工数据,通过FFT频谱分析,划分出机床加工的3种状态.利用小波包分解,分别求出各种状态在不同频带节点上的能量分布百分比,并把它作为隐马尔科夫模型的输入特征向量.按照隐马尔科夫模型模式识别方法,建立3种标准状态的训练优化模型库,把测试样本代入优化模型库中,依据最大对数似然值对机床的加工状态进行了识别.计算结果表明,状态识别结果正确.     

机床运转状态下相对激振的动态性能研究

阐述了在机床运转状态下进行相对激振试验的方法及其原理,并利用此方法测定了K360A数控车床的动态特性,分析了机床的薄弱模态及其对机床性能的影响。同时,通过机床运转和静止两种不同状态下试验结果的对比分析,得出旋转状态下的动态测试能更准确地揭示影响机床加工性能的动力学本质。     

滚齿机床振动对齿轮几何精度的影响

滚齿机床切削加工过程中,刀刃成排轮流从切入到切出,切削力由小逐渐变大,再逐渐变小,在工件和刀具之间产生周期性的激振力,使刀刃和工件加工表面产生相对位移,对加工齿轮的几何精度产生影响。研究机床结构振动与被加工齿轮精度的关系,建立滚刀和工件加工表面产生的相对位移对齿轮几何精度影响的理论模型,定量推导出了由此相对位移产生的齿廓误差;通过大量实验,对滚刀和工件加工表面产生相对位移对应的齿轮齿廓误差进行在线精密测量;使用此齿廓误差减法运算新方法,对两组实验数据进行对比分析。结果表明:提出的运算新方法能够准确地处理数据,实验数据很好地验证了建立的理论模型的正确性,误差小于2%。     

XK713数控镗铣床整机静动态特性分析

为了更准确地预测和分析机床整机的静动态特性,建立的机床整机有限元模型必须包含各结合面特性参数.以XK713数控镗铣床为例,运用有限元法将各结合面特性参数融合到整机模型中,建立包含结合部特性的机床整机动力学模型.在此基础上,利用谐响应分析法计算刀具与工件之间的相对刚度.与同类机床相比,XK713数控镗铣床三向静刚度都较高,但y向静刚度相对较小;x向刀具与工件相对振幅较大,y向的谐响应频率最丰富.因此在使用中要注意避开优势固有频率,在改进设计时要注意提高y向静刚度和x向动刚度.     

基于新陈代谢灰色马尔科夫 ARMA模型的航空公司能耗预测

航空公司能耗的预测直接影响能源需求的规划与节能的决策.针对航空公司能耗数据既有趋势性又有波动性的特点,提出了新陈代谢灰色马尔科夫-ARMA的能耗组合滑动预测模型.该模型利用灰色马尔科夫方法描述了能耗的变动趋势,通过ARMA模型捕捉残差序列的相关性来描述波动性,用新陈代谢的方法剔除模型中失去时效性的旧数据,解决了常规预测模型不足以完全描述航空公司能耗运动趋势的问题,提高了模型预测精度.仿真结果表明:提出模型精度优于传统ARMA模型和灰色马尔科夫模型,能够实现月度能耗的有效预测,为航空公司能耗监测和节能工作的优化开展提供了有力支持.     

基于新陈代谢灰色马尔科夫-ARMA模型的航空公司能耗预测（英文）

航空公司能耗的预测直接影响能源需求的规划与节能的决策。针对航空公司能耗数据既有趋势性又有波动性的特点,提出了新陈代谢灰色马尔科夫-ARMA的能耗组合滑动预测模型。该模型利用灰色马尔科夫方法描述了能耗的变动趋势,通过ARMA模型捕捉残差序列的相关性来描述波动性,用新陈代谢的方法剔除模型中失去时效性的旧数据,解决了常规预测模型不足以完全描述航空公司能耗运动趋势的问题,提高了模型预测精度。仿真结果表明:提出模型精度优于传统ARMA模型和灰色马尔科夫模型,能够实现月度能耗的有效预测,为航空公司能耗监测和节能工作的优化开展提供了有力支持。     

Analysis of compliance between the cutting tool and the workpiece on the stability of a turning process

Chatter is a common vibration problem that limits productivity of machining processes, since its large amplitude vibrations causes poor surface finishing, premature damage and breakage of cutting tools, as well as mechanical system deterioration. This phenomenon is a condition of instability that has been classified as a self-excited vibration problem, which shows a nonlinear behavior characterized by the presence of limit cycles and jump phenomenon. In addition, subcritical Hopf and flip bifurcations are mathematical interpretations for loss of stability. Regeneration theory and linear time delay models are the most widely accepted explanations for the onset of chatter vibrations. On the other hand, models based on nonlinearities from structure and cutting process have been also proposed and studied under nonlinear dynamics and chaos theory. However, on both linear and nonlinear formulations usually the compliance between the workpiece and cutting tool has been ignored. In this work, a multiple degree of freedom model for chatter prediction in turning, based on compliance between the cutting tool and the workpiece, is presented. Hence, a better approach to the physical phenomenon is expected, since the effect of the dynamic characteristics of the cutting tool is also taken into account. In this study, a linear stability analysis of the model in the frequency domain is performed and a method to construct typical stability charts is obtained. The effect of the dynamics of the cutting tool on the stability of the process is analyzed as well.     

A review of tool wear estimation using theoretical analysis and numerical simulation technologies

A thorough understanding of the material removal process in cutting is essential in selecting the tool material and in design, and also in assuring consistent dimensional accuracy and surface integrity of the finished product. Tool wear in cutting process is produced by the contact and relative sliding between the cutting tool and the workpiece, and between the cutting tool and the chip under the extreme conditions of cutting area. This paper presents the information on development of study on theoretical analysis and numerical simulation of tool wear in all over the world. Hidden Markov models (HMMs) were introduced to estimate tool wear in cutting, which are strongly influenced by the cutting temperature, contact stresses, and relative strains at the interface. Finite element method (FEM) is a powerful tool to predict cutting process variables, which are difficult to obtain with experimental methods. The objective of this work focuses on the new development in predicting the tool wear evolution and tool life in orthogonal cutting with FEM simulations.     

A new receptance coupling substructure analysis methodology to improve chatter free cutting conditions prediction

The cutting process stability depends on machine tool dynamics that is strongly influenced by the tool. Receptance coupling substructure analysis (RCSA) can be used to estimate the tool tip dynamic compliance and consequently the chatter free cutting conditions when the machine is equipped with a tool that has not been previously tested. This methodology can be particularly useful on real shop–floors where a lot of different tool–tool holder configurations are generally used. RCSA typically combines experimental dynamic compliance measurements performed on a machine equipped with a selected tool and the finite element (FE) models of both the already tested tool and the new ones. This paper presents a new receptance coupling substructure analysis (RCSA) approach that overcomes the drawbacks in the estimation of the receptances that contain rotational and moment contributes. This indeed often limits the accuracy of the RCSA techniques presented in other scientific works. The proposed formulation allows to better estimate both the matrices of receptances of the spindle–tool holder assembly and the tool–tool holder connection stiffness. Those quantities are used, together with the FE model of the new tool, to predict the unknown tool tip dynamic compliance. Some useful guidelines to implement the proposed RCSA are also defined: they allow to manage the procedure accuracy considering the experimental methodology typically used to measure dynamic compliances. The proposed innovative RCSA is experimentally tested and validated.     

基于自适应响应面法的数控铣床尺寸优化

为了能够更加有效地改善数控铣床的动静态特性,采用试验设计与数理统计相结合的方法对XK719数控铣床进行了结构尺寸优化。对数控铣床整机采用拉丁超立方试验设计方法进行采样,在此基础上运用移动最小二乘法对采样点进行拟合,以构造近似函数;对近似函数采用自适应响应面法进行优化;通过25次迭代,在数控铣床整机质量变化不超过3%的情况下,实现了整机1阶固有频率提高16.3%,2阶固有频率提高13%。结果表明:该方法能够实现机床的快速优化设计。     

PC3S技术注塑模具制造

传统门板中部插件为获得柔软效果,通常采用手工包覆及低压注塑工艺。手工包覆工序繁杂、不环保;低压注塑工艺面料利用率低,同时需要低压注塑设备,设备投入大。针对以上2种工艺的缺点,开发了面料尺寸与制件大小相当,且使用常压注塑机预裁软质小面料常压合模注塑技术(Precutting small soft skin close mould technology,PC3S)制备门板中部插件。介绍了PC3S工艺的注塑模具材质要求和模具结构特点。实践表明,该工艺可以制备手感与传统手工包覆相似的软化效果的门板中部插件,生产成本大大降低,且生产工艺节能环保。     

Virtual Machine Tool

This paper presents current state of Virtual Machine Tool Technology and related ongoing research challenges. The structural analysis of machine tools using Finite Element models and their experimental calibration techniques are presented. The kinematic analysis and optimisation of machine tool elements are discussed with sample examples. The interaction between the control of the feed drives, cutting conditions and machine tool structure is presented. Multi-body dynamic models of the machine, which allow integrated simulation of machine kinematics, structural dynamics and control techniques, are discussed. The interaction between the machine tool, controller and cutting process disturbances are discussed with sample examples. The simulation of machining operation and its impact on the dynamics of the machine tool and CNC are elaborated. The paper presents both the summary of current and past research, as well as research challenges in order to realise a fully digitised model of the machine tool.     

基于STL分解的平均故障间隔时间组合预测

由于影响数控机床刀架系统平均故障间隔时间的因素较多,采用单一的模型作预测无法充分提取已知数据中的隐含信息,导致预测困难。应用基于STL进行时间序列分解的组合模型预测算法,将原始故障数据分解为趋势项、季节项和随机项,应用指数平滑法和支持向量机回归分别对前两项数据进行预测,根据时序分解的加法模型将其结合,得到组合模型预测结果,并将组合模型与单一的预测模型进行对比分析。实例证明:组合模型预测优于单一模型预测。此方法应用于MTBF的预测,有助于工作人员针对故障发生时间点提前采取措施,同时为数控机床可靠性评估提供了新的研究方法。     

基于细化谱和隐马尔科夫模型的齿轮故障分类方法

为了快速准确地对齿轮故障作出分类,结合隐马尔科夫模型（HMM）高效的模式分类能力,提出了基于细化谱（ZOOMFFT）和隐马尔科夫模型的故障分类方法。采用时域同步平均法从复杂信号中提取目标齿轮的啮合信号作为分析对象,对其进行细化谱分析,提取基频、倍频及其边频带幅值作为特征量输入到HMM中训练和识别,再通过对比对数似然概率值来确定齿轮故障类型。试验结果表明该方法可以有效地对齿轮故障进行分类。