Active compensation for portal machines

The cutting performance of a machine tool is mainly determined by its static and dynamic behavior. During a cutting process high static and dynamic forces may occur, which result in instabilities of the cutting process. Especially, long protruding structure components, such as z-slider of a portal machine, represent a distinct weak spot concerning their structural behavior. The structure integrated compensation modules represent a new approach to compensate static and dynamic deformations of slider structures and help to achieve a considerable improvement of their compliancy behavior.     

Implementation of a process and structure model for turning operations

The consideration of the dynamic interaction between the machine tool structure and the cutting process is a prerequisite for the simulative prediction and optimization of machining tasks. However, existing cutting force models are either dedicated to already examined manufacturing operations or require extensive measurements for the determination of cutting coefficients. In this context this paper outlines a modular, analytical cutting force model applicable to common turning processes. It takes into account the dynamic material behavior, nonlinear friction ratios on the rake face as well as heat transfer phenomena in the deformation zones. On the part of the machine tool structure a parametric model based on the Finite Element Method (FEM) is implemented. Both models are coupled for the simulation of process and structure interactions, whereas the influence of the control system is considered as well. The simulation results were verified experimentally on a turning center.     

Vibration analysis and cutting simulation of structural nonlinearity for machine tool

The dynamic behavior of a machine tool is affected by the forces applied to the structure. However, cutting processes have been analyzed considering the linear systems in most of the studies so far. In this study, a machine tool structure was excited by using an electromagnetic shaker and the force-dependant frequency response characteristics were measured. Based on the measured result, the nonlinear characteristics of the machine tool structure was identified, and a machine tool with the nonlinear characteristics was mathematically reproduced, which enabled to analyse the nonlinear frequency response characteristics and simulate cutting processes.     

Estimation of CNC machine–tool dynamic parameters based on random cutting excitation through operational modal analysis

Dynamic properties of the whole machine tool structure including tool, spindle, and machine tool frame contribute greatly to the reliability of the machine tool in service and machining quality. However, they will change during operation compared with the results from static frequency response function measurements of classic experimental modal analysis. Therefore, an accurate estimation of the dynamic modal parameters of the whole structure is of great value in real time monitoring, active maintenance, and precise prediction of a stability lobes diagram.Operational modal analysis (OMA) developed from civil engineering works quite efficiently in modal parameters estimation of structure in operation under an intrinsic assumption of white noise excitation. This paper proposes a new methodology for applying this technique in the case of computer numerically controlled (CNC) machine tools during machining operations. A novel random excitation technique based on cutting is presented to meet the white noise excitation requirement. This technique is realized by interrupted cutting of a narrow workpiece step while spindle rotating randomly. The spindle rotation speed is automatically controlled by G-code part program, which contains a series of random speed values produced by MATLAB software following uniform distribution. The resulting cutting produces random pulses and excites the structure in all three directions. The effect of cutting parameters on the excitation frequency and energy was analyzed and simulated. The proposed technique was experimentally validated with two different OMA methods: the Stochastic Subspace Identification (SSI) method and the poly-reference least square complex frequency domain (pLSCF or PolyMAX) method, both of which came up with similar results. It was shown that the proposed excitation technique combined successfully with OMA methods to extract dynamic modal parameters of the machine tool structure.     

Development of a modular dynamometer for triaxial cutting force measurement in turning

Accurate and reliable measurement of cutting forces in turning is essential for tool geometry, tool trajectory and cutting parameters optimization, as well as for tool condition monitoring and machinabilty testing. In this work, an innovative dynamometer for triaxial cutting force measurement in turning, specifically designed to be applied at a milling-turning CNC machine tool endowed with an indexable head, is presented. The device is based on a piezoelectric force ring integrated into a commercial toolshank, and its modular design allows the easy change of the cutting insert without altering sensor preload. The prototype device was assembled and experimentally tested by means of static calibration and dynamic identification, which evidenced good static and dynamic characteristics. Eventually, the sensor was tested in operating conditions by machining a benchmark workpiece.     

Dynamic modeling of cutting acoustic emission via piezo-electric actuator wave control

The fundamental understanding of the dynamic behavior of acoustic emission signals in relation to machining process parameters plays an important role in the automation monitoring and control of metal cutting operations. This paper presents an analytical model for acoustic emission dynamics in orthogonal cutting with chip thickness variation. An analytical expression for acoustic emission generated in turning is established as an explicit function of the cutting parameters and tool/workpiece geometry. Based on the theoretical static cutting acoustic emission model, the generation of the RMS acoustic emission is formulated as the function of three process parameters, namely tool displacement, cutting speed, and rake angle. The incremental change of the RMS acoustic emission is related to the chip formation process in an elemental cutting area and it is characterized by the dynamic variation of these process parameters. The analysis of the RMS acoustic emission is then extended into the dynamic transfer function between tool displacement and RMS acoustic emission. Experimental results via simultaneous tool displacement control by piezo-electric actuator and measurement of RMS AE generated during cutting confirm the validity of the analytical acoustic emission model in orthogonal cutting process.     

Modeling the machining stability of a vertical milling machine under the influence of the preloaded linear guide

The prediction of machining stability is of great importance for the design of a machine tool capable of high-precision and high-speed machining. The machining performance is determined by the frequency characteristics of the machine tool structure and the dynamics of the cutting process, and can be expressed in terms of a stability lobe diagram. The aim of this study is to develop a finite element model to evaluate the dynamic characteristics and machining stability of a vertical milling system. Rolling interfaces with a contact stiffness defined by Hertz theory were used to couple the linear components and the machine structures in the finite element model. Using the model, the vibration mode that had a dominant influence on the dynamic stiffness and the machining stability was determined. The results of the finite element simulations reveal that linear guides with different preloads greatly affect the dynamic behavior and milling stability of the vertical column spindle head system. These results were validated by performing vibration and machining tests. We conclude that the proposed model can be used to accurately evaluate the dynamic performance of machine tool systems designed with various configurations and with different linear rolling components.     

基于有限元分析技术的VK50数控床身铣机床底座设计

介绍了基于有限元优化分析技术的VK50数控床身铣机床底座的开发设计过程,通过CAE技术对开发过程的支持,对机床底座结构进行了其动静态特性的计算机仿真及优化设计,实验表明改进后的机床底座具有良好的动静态特性,同时证明了CAE技术改造传统机床制造业的有效性及科学性.     

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.     

高速精密数控立式铣床本体结构动态特性测试

对某企业装机生产的高速高精密数控立式铣床结构动态特性进行实验测试,特别针对机床不同位置结构开展一系列动态特性测试工作,得到频率和振型等模态参数,最终结合测试结果得到整机的薄弱环节主要是鞍座与底座的结合位置,并且机床整体布局不合理,重心偏高。从两个方面阐述机床本体结构系统动态特性测试的方法和过程,分别是实验模态分析测试和机床切削振动测试。     

Mechatronic Systems for Machine Tools

This paper reviews current developments in mechatronic systems for metal cutting and forming machine tools. The integration of mechatronic modules to the machine tool and their interaction with manufacturing processes are presented. Sample mechatronic components for precision positioning and compensation of static, dynamic and thermal errors are presented as examples. The effect of modular integration of mechatronic system on the reconfigurability and reliability of the machine tools is discussed along with intervention strategies during machine tool operation. The performance and functionality aspects are discussed through active and passive intervention methods. A special emphasis was placed on active and passive damping of vibrations through piezo, magnetic and electro-hydraulic actuators. The modular integration of mechatronic components to the machine tool structure, electronic unit and CNC software system is presented. The paper concludes with the current research challenges required to expand the application of mechatronics in machine tools and manufacturing systems.     

The feasibility of eigenstructure assignment for machining chatter control

The eigenstructure assignment algorithm is proposed for controlling machining chatter by changing the response of the machine tool structure to dynamic cutting forces through the change of its modal properties so that the interaction between the tool and workpiece can be altered. The determination of the desired modal shapes is derived from a concept similar to gain scheduling in adaptive control system theory. By using computer simulations, the desired eigenstructure of the machine tool structure for different cutting conditions is determined and used to form the scheduling table. The gain matrix is adjusted according to the scheduling table and cutting conditions. It was found from experimental results that by changing the principal direction of the machine tool structure, the machining system could be stabilized and that the use of the proper eigenstructure to suppress machine tool chatter could significantly increase the material removal rate. Simulations have shown that the responses of the controlled machining system have been altered from unstable to stable, proving the feasibility of the proposed chatter control concept.     

数控机床切削过程中的动态特性测量方法

针对高速高精度切削加工过程中机床动态特性分析较为困难的问题,提出一种快速扫频正弦切削法来测量数控机床切削过程中的动态特性。该方法采用车削过程中的切削力作为激振力进行试验模态分析,主要通过以恒定的进给量切削正弦轮廓的圆柱形工件,并线性增加主轴转速,从而将切削力转化为数控机床频率响应函数的激励输入。结果表明：与传统的冲击测试方法对比,快速扫频正弦切削测试的共振峰柔度和频率均有所降低,分别降低了约6.7%和16.7%。此外,通过希尔伯特变换分析,观察到冲击测试和快速扫频正弦切削测试之间有很大的区别。在快速扫频正弦切削测试中,可以直接识别出切削过程中非线性的影响,为准确测量机床切削过程中的动态特性提供了理论依据。     

Modeling of spindle-bearing and machine tool systems for virtual simulation of milling operations

This paper presents a general, integrated model of the spindle bearing and machine tool system, consisting of a rotating shaft, tool holder, angular contact ball bearings, housing, and the machine tool mounting. The model allows virtual cutting of a work material with the numerical model of the spindle during the design stage. The proposed model predicts bearing stiffness, mode shapes, frequency response function (FRF), static and dynamic deflections along the cutter and spindle shaft, as well as contact forces on the bearings with simulated cutting forces before physically building and testing the spindles. The proposed models are verified experimentally by conducting comprehensive tests on an instrumented-industrial spindle. The study shows that the accuracy of predicting the performance of the spindles require integrated modeling of all spindle elements and mounting on the machine tool. The operating conditions of the spindle, such as bearing preload, spindle speeds, cutting conditions and work material properties affect the frequency and amplitude of vibrations during machining.     

XK2425/5L五轴龙门铣床主体结构有限元分析

为提高五轴龙门铣床的整机结构性能指标,提出了机床关键零部件与整机并行优化设计的思想。运用CAE工程分析软件,建立了五轴龙门铣床关键零部件及整机的有限元模型,并对其主体结构进行了重力、切削力载荷下的静刚度分析以及关键零部件和整机的动态刚度仿真分析,找出了结构中的薄弱环节,并在此基础上对机床中关键零部件的结构参数提出了改进方案。分析结果表明,改进后的结构方案在整机自重降低632Kg的情况下,静刚度由50.2N/μm提高到68.4N/μm,一阶固有频率由30Hz提高到42Hz,整机性能指标得到显著提高。     

基于结合面特性的机床整机精度设计系统研究

阐述了基于结合面特性的机床整机精度设计系统结构以及4大关键模块,并利用VB开发工具实现了基于结合面特性的机床整机精度设计系统。利用该系统实现了机床结合面特性参数的分析与管理,并基于多体系统理论建立了三轴数控机床静态几何精度模型,可对机床在整个加工空间的几何误差进行预估并对误差源进行敏感性分析;同时集成ANSYS软件,基于结合面特性可对机床整机动态性能进行分析。另外,通过有效管理机床设计过程中的设计经验以及动静态精度分析的知识,将有效地支持机床设计。     

Characteristics of a spindle bearing system with a gear located on the bearing span

The spindle bearing system is the main source of the total cutting point compliance of machine tool structures. In this work, the static and dynamic characteristics of a spindle bearing system driven by a gear located on the bearing span were investigated using the analytical and finite element methods. Based on the calculated results, a prototype spindle bearing system was manufactured and its static and dynamic characteristics were measured. From the comparison of the experimental results with the calculated results, it was found that the finite element method predicted well the static and dynamic characteristics of the spindle bearing system.     

在机床上检测表面粗糙度的试验研究

介绍了在机床上用光纤传感器检测表面粗糙度的原理和一系列试验结果,探讨了检测仪的设计要点以及在线检测技术存在的问题,如光纤探头的结构、传感器的装夹与定位、仪器的元器件选择、仪器的标定、切削液和测量距离变化的影响等,提出了解决或改进的办法,研究结果表明,该检测系统具有结构简单、工作效率高、抗干扰能力强等特点,适用于机床上静态条件下的快速检测和动态条件下的实时监测,有利于提高加工质量和生产效率.     

高速旋转刀具系统动平衡技术的研究

高速切削时，由于刀具系统的转速很高，刀具系统的不平衡会影响刀具寿命、加工精度和效率。论文从理论上分析了高速加工刀具系统产生动平衡的影响因素，运用ANSYS软件对其进行了静力学分析，并提出了改善刀具系统动平衡的技术方案。     

New standardized procedure for the measurement of the static and dynamic properties of forming machines

The geometrical accuracy and the surface quality of sheet metal parts as well as the tool wear are influenced by process parameters and by static and dynamic interactions between the press and the tool. Therefore the qualitative characterization of the machine behavior is of high importance for both press manufacturers and press operators. Within research project (Behrens et al. in Entwicklung und Erweiterung standardisierter Messverfahren zur statischen und dynamischen Pressenvermessung. Final Report of the AiF Research Project 13742 N, 2005), a procedure for the measurement of the static machine behavior has been developed, which for the first time allows the standardized measurement of the ram deflection and the bolster plate deflection along with previously standardized characteristic values. The determination of the procedure as measurement directions and the automated evaluation of the measurements ensure not only reproducible results but also easy comparison of two machines. Additionally a new procedure for the measurement of the dynamic press behavior has been standardized which allows the comparison of the static and the dynamic characteristic values. The project [1] was funded under number AiF 13742 N by the Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. with budget funds from the German Federal Ministry of Economics.