高速铣削再生颤振稳定性预测与验证

再生型颤振是制约高速铣削加工效率和零件加工质量的主要因素。以高速铣削加工为研究对象,建立了考虑再生效应的高速铣削动态铣削力模型和颤振稳定域解析模型,通过模态实验获得机床-刀具系统的频响函数,在此基础上综合使用铣削稳定性判据进行数值分析,获得了高速铣削颤振稳定域的解析解。最后,进行了零件颤振稳定性铣削加工实验,实验得到的结果与仿真结果吻合良好,由此验证了建立的颤振系统动力学模型和颤振稳定性解析模型的正确性。     

基于数值模型的数控加工中切削力与稳定域仿真

针对数控铣削加工工艺参数选择存在的问题,以球头铣刀高速铣削过程为研究对象,建立了考虑机床-刀具-工件系统振动的非线性动力学模型,分析了铣削力中的动态分量对切削颤振的影响,在考虑再生颤振的基础上建立非线性动力学模型.基于动态铣削力建模和颤振稳定域分析计算,提出了机床切削系统稳定性极限预测方法,并对其进行仿真分析,为铣削加...     

高速铣削稳定性的不确定性建模及实验预测

高速铣削加工过程的颤振不稳定性是制约刀具寿命和加工效率的主要因素。传统的颤振稳定性预测模型都假设系统参数是恒定的,但是在实际的高速铣削过程中,影响加工稳定性的参数会随着高主轴转速、高系统动态特性而发生变化。为提高铣削加工精度,以高速铣削加工稳定性为研究对象,考虑参数不确定性的影响,应用棱边定理和排零准则,建立高速铣削变参数稳定性预测数学模型。在此基础上,通过模态测试和辨识铣削力系数获得固有频率及切削系数的变动范围,然后采用数值分析和铣削实验相结合的方式,验证了建立的高速铣削变参数稳定性模型的正确性。     

模具平面铣削加工动态仿真研究

在平面铣削颤振产生机理的基础上,简单论述了一种更精确有效的动态铣削力理论模型的建立过程,该模型充分考虑瞬态切屑的厚度及有效前角对动态铣削力的影响。在此基础上,运用数字仿真技术在频域内建立起动态铣削力和刀具-工件系统的相对振动位移的计算机仿真模型。利用该仿真模型,可以实时显示不同工艺参数和加工参数状态下动态铣削力的数值及其功率谱密度图形以及刀具-工件系统的动态振动位移图形。仿真结果将为预测和消除铣削过程的颤振现象,保证加工质量和加工效率,延长刀具使用寿命提供可靠的依据。     

永磁型电主轴多频率振动的主动控制

为了有效抑制由砂轮质量不平衡及外部干扰引起的永磁型电主轴转子系统砂轮端的多频率成分振动,在无轴承永磁电机径向磁悬浮力产生原理的基础上,提出了一种基于最小方差快捷分块(FBLMS)的自适应滤波的永磁型双绕组电主轴柔性转子系统砂轮端多频率成分振动的主动控制方案。首先研究了双绕组永磁型电主轴结构及工作原理和径向控制力的模型,借助有限元法建立了永磁型电主轴柔性转子系统的动力学模型,分析了控制电流的不同成分对永磁体涡流损耗及电机定子铁损的影响,设计了永磁型电主轴柔性转子系统砂轮端多频率成分振动的主动控制系统,结果表明,提出的永磁型电主轴柔性转子系统砂轮端多频率成分振动控制方案具有明显的控制效果。     

薄壁零件铣削加工稳定性极限分析

针对薄壁零件铣削加工颤振稳定性问题进行了分析研究。综合考虑刀具子系统和工件子系统动态特性,采用三自由度弹性-阻尼系统,建立了适合薄壁零件的三维动态铣削力模型,求出了高速铣削稳定性极值解析解。根据模态锤击实验获得的频率响应函数(FRF frequency response function),绘出了铣削加工颤振的稳定性图形,并通过实验证实了稳定性图的有效性和准确性。     

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。     

内圆角铣削加工几何分析及铣削力预测

为实现内圆角加工瞬时铣削力预测,提出了工件轮廓和刀具路径的参数化表示方法,依据圆弧角大小不同将内圆角铣削分为两类,分析了其铣削过程。建立了瞬时铣削力模型,采用等参数间隔法,推导了刀具瞬时位置和位置角计算公式。针对不同铣削阶段,给出了实际径向切深计算模型,提出了基于实际径向切深的瞬时未变形切屑厚度计算方法。对内圆角加工的铣削力预测,并进行试验验证。仿真结果与试验结果在变化趋势和幅值方面均具有良好的一致性,仿真耗时显著减小,表明提出的铣削力模型具有较高的精度和计算效率,从而为恒负载铣削和颤振抑制提供了理论基础。     

轧机牌坊修复抱壁铣削机器人结构研究

针对当前轧钢行业面临的轧机牌坊与轧辊轴承座接触面易磨损,且在线修复困难的实际问题,提出了一种可实现在线修复的抱壁铣削机器人。对该机器人在实际铣削作业中的铣削力等参数进行了分析与计算,依据计算结果对铣削执行器高速电主轴进行了选型,为抱壁铣削机器人滑台控制伺服系统的合理选型及机构优化提供了参考。     

模具淬硬钢高速铣削加工的有限元模拟

研究了高速铣削加工数值模拟所涉及的切削层等效简化铣削加工模型,分析了工件材料的流动应力模型与刀屑接触面的摩擦模型和热传导控制方程等关键技术.并根据等效简化模型平面应变特征的特点,建立了铣削加工数值模拟的2-D有限元模型.基于此模型对高速铣削加工淬硬钢P20的切削力、应力和温度进行了有限元模拟.通过铣削力切削加工实验测得了相同条件下的铣削力值.结果表明:实验铣削力值与数值模拟在一定的误差范围内结果一致.由此可见,采用具有平面应变特征的有限元模型进行应力和温度的模拟切削过程是可信的.高速铣削加工有限元模拟研究为淬硬钢切削加工的工艺参数优化、刀具的优选和工艺规划奠定了基础.     

基于开放式控制器的铣削颤振在线抑制

为实现在线抑制铣削颤振,对颤振领域常用的传感器监控技术,尤其是三向切削力和振动加速度传感器的各向分量在颤振监控过程中的时域和频域敏感信号特征进行试验研究。针对监控的颤振敏感信号频域特性,研究快速傅里叶变换技术对信号有效信息的在线提取技术。对自激颤振的机理进行分析,建立颤振频率与主轴转速间的关系模型,为实现变主轴转速抑制自激颤振提供理论基础。对集成在线参数采集、反馈控制的全软件型模块化铣削控制器进行设计,将在线抑制颤振的相关变主轴转速算法嵌入开放式控制器中,并设计控制参数数据流在控制器模块间的实现流程。对连续变切削深度铝合金工件进行在线颤振抑制加工试验,试验验证开放式智能铣削控制器在线抑制颤振相关技术的正确性。     

基于主动磁轴承的切削颤振稳定性分析及控制

提出了基于主动磁轴承的铣削颤振主动控制技术。用有限元法分析了主动磁轴承等效刚度与等效阻尼对铣削稳定性区域的影响,并对铣削过程中的颤振进行了主动控制。结果表明:主动磁轴承的等效刚度能够改变电主轴转子的临界转速,但对铣削的临界切削宽度影响很小;相反,主动磁轴承的等效阻尼能够较大幅度地增大铣削的临界切削宽度,但对电主轴转子的临界转速影响不大。颤振的控制效果表明,调节主动磁轴承的等效刚度和等效阻尼能够减小铣削过程中颤振的振幅。     

Chatter vibration surveillance by the optimal-linear spindle speed control

The paper concerns self-excited chatter vibration during high speed slender ball-end milling. Non-stationary cutting process, with inclusion of various approaches towards dynamic characteristics of the process, is described. Dynamic analysis of the milling process is performed and dynamics of controlled closed loop system with time-delay is presented. In order to reduce vibration level, instantaneous change in the spindle speed appears as a control command, and thus—the method of vibration surveillance by the spindle speed optimal-linear control is developed. Presented cutting models have been applied for the proposed method and procedure of the chatter vibration surveillance with a use of variable spindle speed has been developed. Computer simulations are performed for selected cases of ball-end milling at constant and variable spindle speed. The results of them are successfully confirmed by experimental investigations on the Alcera Gambin 120CR milling machine equipped with the S2M high speed electrospindle.     

The investigation of unbalanced vibration in flexible motorized spindle-rotor system

Unbalance is a significant concern for spindle-rotor dynamic systems and an important problem in high-speed machining. An active control scheme with built-in force actuator is proposed for unbalanced vibration of flexible motorized spindle-rotor, which is to improve the performance of high-speed machining system. At first, the motorized spindle motor with built-in force actuator and flexible motorized spindle-rotor are designed and then the experiment setup based on digital signal processor for controlling actively the unbalanced vibration of flexible spindle-rotor is tailored. Finally, the active vibration control scheme is investigated experimentally based on previous theoretical studies. The experimental results prove the feasibility of the active control scheme.     

Chatter reliability prediction of side milling aero-engine blisk

Reliability analysis of a dynamic structural system is applied to predict chatter of side milling system for machining blisk. Chatter reliability is defined as the probability of stability for processing. A reliability model of chatter was developed to forecast chatter vibration of side milling, where structure parameters and spindle speed are regarded as random variables and chatter frequency is considered as intermediate variable. The first-order second-moment method was used to work out the side milling system reliability model. Reliability lobe diagram (RLD) was applied to distinguish reliable regions of chatter instead of stability lobe diagram (SLD). One example is used to validate the effectiveness of the proposed method and compare with the Monte Carlo method. The results of the two approaches were consistent. Chatter reliability and RLD could be used to determine the probability of stability of side milling.

     

Chatter prevention for milling process by acoustic signal feedback

This paper presents how real-time chatter prevention can be realized by feedback of acoustic cutting signal, and the efficacy of the proposed adaptive spindle speed tuning algorithm is verified as well. The conventional approach to avoid chatter is to select a few appropriate operating points according to the stability lobes by experiments and then always use these preset cutting conditions. For most cases, the tremble measurement, obtained by accelerometers or dynamometers, is merely to monitor spindle vibration or detect the cutting force, respectively. In fact, these on-line measures can be more useful, instead of always being passive. Furthermore, most of these old-fashioned methodologies are invasive, expensive, and cumbersome at the milling stations. On the contrary, the acoustic cutting signal, which is fed into the data acquisition interface, Module DS1104 by dSPACE, so that an active feedback loop for spindle speed compensation can be easily established in this research, is non-invasive, inexpensive, and convenient to facilitate. In this research, both the acoustic chatter signal index (ACSI) and spindle-speed compensation strategy (SSCS) are proposed to quantify the acoustic signal and compensate the spindle speed, respectively. By converting the acoustic feedback signal into ACSI, an appropriate spindle speed compensation rate (SSCR) can be determined by SSCS based on real-time chatter level. Accordingly, the compensation command, referred to as added-on voltage (AOV), is applied to actively tune the spindle motor speed. By employing commercial software MATLAB/Simulink and DS1104 interface module to implement the intelligent controller, the proposed chatter prevention algorithm is practically verified by intensive experiments. By inspection on the precision and quality of the workpiece surface after milling, the efficacy of the real-time chatter prevention strategy via acoustic signal feedback is further examined and definitely assured.     

Counterbalance of cutting force for advanced milling operations

The goal of this work is to concurrently counterbalance the dynamic cutting force and regulate the spindle position deviation under various milling conditions by integrating active magnetic bearing (AMB) technique, fuzzy logic algorithm and an adaptive self-tuning feedback loop. Since the dynamics of milling system is highly determined by a few operation conditions, such as speed of spindle, cut depth and feedrate, therefore the dynamic model for cutting process is more appropriate to be constructed by experiments, instead of using theoretical approach. The experimental data, either for idle or cutting, are utilized to establish the database of milling dynamics so that the system parameters can be on-line estimated by employing the proposed fuzzy logic algorithm as the cutting mission is engaged. Based on the estimated milling system model and preset operation conditions, i.e., spindle speed, cut depth and feedrate, the current cutting force can be numerically estimated. Once the current cutting force can be real-time estimated, the corresponding compensation force can be exerted by the equipped AMB to counterbalance the cutting force, in addition to the spindle position regulation by feedback of spindle position. On the other hand, for the magnetic force is nonlinear with respect to the applied electric current and air gap, the characteristics of the employed AMB is investigated also by experiments and a nonlinear mathematic model, in terms of air gap between spindle and electromagnetic pole and coil current, is developed. At the end, the experimental simulations on realistic milling are presented to verify the efficacy of the fuzzy controller for spindle position regulation and the capability of the dynamic cutting force counterbalance.     

Electromagnetic actuator for determining frequency response functions of dynamic modal testing on milling tool

Machine tools are the main driving forces of industrialization of a country. However, poor machinability because of chatter vibration results in poor surface quality, excessive noise, and reduced material removal rate. Modal testing is a useful method to investigate dynamic properties of a cutting tool system and improve material removal rate. However, at present, modal testing using impact hammer is limited by certain problems. This paper developed a non-contacting electromagnetic actuator (EMA) to determine frequency response functions (FRFs) under amplitude and speed dependencies of cutting milling tools. The geometry was designed using magnetic circuit analysis and generalized machined theory before finite element analysis was conducted using magnetostatic-ansys software. Next, EMA was used as a contacting and non-contacting exciter of a conventional milling machine to determine the FRFs and dynamic properties of milling tool with amplitude and speed dependencies including comparison with static FRFs. Subsequently, dynamic properties and FRFs are used to establish stability lobe diagram. Stability lobe diagram also shows an improvement of up to 5% of depth of cut at lower spindle speed. In conclusion, by generating force that applies to static and dynamic modal testing, an EMA can determine dynamic properties and stability lobe diagram for increasing material removal rate and production rate.     

ESPRIT- and HMM-based real-time monitoring and suppression of machining chatter in smart CNC milling system

Suppression of machining chatter during milling processes is of great significance for surface finish and tool life. In this paper, a smart CNC milling system integrating the function of signal processing, monitoring, and intelligent control is presented with the aim of real-time chatter monitoring and suppression. The algorithm of estimation of signal parameters via rotational invariance techniques (ESPRIT) is adopted to extract the frequency characteristics of acceleration signals, and then, cutting state is categorized as stable state, chatter germination state, and chatter state based on amplitude-frequency characteristics of identified acceleration signals. The model of chatter identification is acquired by training a hidden Markov model (HMM), which combines acceleration signals and labeled cutting state. To implement real-time chatter suppression, the algorithm of fuzzy control is integrated into a smart CNC kernel to determine the relationship between cutting force and spindle speed. Furthermore, spindle speed of machine tool could be adjusted timely in the presented system once the chatter is identified. Finally, the effectiveness of the proposed real-time chatter monitoring and suppression system is experimentally validated.     

STUDY ON ELECTRORHEOLOGICAL FLUID DAMPER FOR APPLICATION IN MACHINING CHATTER CONTROL

The electrorheological fluid(ERF)is a kind of intelligent material with bright prospects for industry applications, which has viscoelastic characteristic: under the applied electric field. The dynamic model of a milling system with an ERF damper is established, and the chatter suppression mechanism of the ER effect is discussed theoretically. Both the theoretical study and the experimental investigation show that the additional damping and additioaal stiffness produced by the ERF increase with the rise in the strength of electric field E, but their influence on the cutting stability is different. Only when both additional damping and additional stiffress cooperate, the milling chatter can be suppressed quickly and effectively. In additional, an ERF dumper used on the arbor of horizontal spindle milling machine is developed, and a series of milling shatter control experiments are performed. The experimental results show that the milling chatter can be suppressed effectively by using the ER damper.