基于摩擦耗能原理的抑振镗杆

讨论了摩擦耗能镗杆的原理,建立了有非线性库仑干摩擦环节的力学模型,并以摩擦参数为变化量,通过数值分析的方法考察了模型的吸振效果。研制了一种基于摩擦减振的新型镗杆,结合颤振发生的机理与切削稳定性理论,分析了不同摩擦条件下镗杆的抑振效果。将不同摩擦条件下的镗杆切削实验结果与理论模型仿真结果进行对比,发现在既定的摩擦阻尼器中,有滑动摩擦与粘接两个状态,而且存在一个最优正压力使得滑动摩擦消耗能量达到最大值又不处于粘接的状态,此时系统抑振效果达到最佳。切削实验发现基于摩擦减振原理的镗杆有良好的颤振抑制效果。      

CONTINUITY AND BREAK OF CHATTER VIBRATION STATUS

By turning a specifically designed conical part, complete process of metal cutting, in which the chatter occurs and expands, is recorded and analyzed. This process exposes that chatter vibration has two characters called continuity and break. The continuity character means that vibration extent enlarges continuously while chatter frequency is almost changeless as the cutting depth extends downwards continuously. The break one is that chatter frequency moves rapidly downwards to a lower level while chatter remains after the cutting depth reach another given value. It is confirmed through an exciting test that the two chatter frequencies obtained in chatter test belong to the natural frequencies of workpiece system and cutting tool system respectively. From the viewpoints of chatter energy supplying and chatter mass effect, the. chatter should occur on one of the two final executive components in its natural frequency. On this basis, a new chatter model with two chatter active bodies is proposed. This new model can better explain the above phenomenon, and adapt to chatter monitoring and improvement of component structure well.     

电流变液减振器在抑制深孔切削颤振上的研究

针对深孔机床切削中的颤振问题,设计了一套基于流动模式的电流变液减振器,分析了电流变液减振器的阻尼力并得出其表达式;又通过对切削颤振产生原因的分析,推导出瞬时动态钻削力的表达式;并在研究了深孔机床切削过程的基础上,建立了切削系统动力学模型,得出安装电流变液减振器后的动力学方程。在给定动力学方程中的参数值后,通过计算机仿真,对比安装和未安装电流变液减振器后的振动时域图,时域图表明电流变液减振器能有效地抑制深孔机床的切削颤振。     

切削颤振研究的关键技术与进展综述

切削颤振是金属切削加工过程中的一种非常复杂的机械振动现象,影响零件加工质量并限制生产率提高.颤振产生的原因和发生、发展规律与切削过程本身以及切削机床动态特性都有着内在的本质联系,长久以来被众多研究者关注.本文就切削颤振在颤振机理、建模、稳定性分析、颤振识别预报以及颤振控制领域的国内外研究成果进行了详细介绍,讨论和分析了...     

超磁致伸缩致动器抑制车削加工颤振实验研究

切削颤振会降低加工质量与切削效率,降低刀具、机床的使用寿命,超磁致伸缩致动器是利用稀土-铁超磁致伸缩材料Terfenol-D在外加磁场作用下发生形变这一特性,实现电磁能向机械能转换的一种新型转换器。笔者建立以超磁致伸缩致动器为执行元件的微位移刀架切削系统,通过给微位移刀架加振动切削信号,实验研究抑制切削颤振。     

超声振动干式车削尺寸精度实验研究

采用超声振动干式车削方法对钨基合金材料进行了车削加工实验,研究了切削参数、振动参数对零件加工尺寸精度的影响。结果表明,在切削深度一定的前提下,对于加工圆度影响的主次关系为:进给量>振动振幅>切削速度;而对锥度影响的主次关系为:振动振幅>切削速度>进给量。在低速低进给加工方式下,振动车削的抑振效果不明显,但随着切削速度、进给量的增大,振动切削抑振效果显著。本实验条件下,当振动振幅为3μm时,对工艺系统具有较佳的抑振效果。     

Analysis of regenerative chatter suppression with adding the ultrasonic elliptical vibration on the cutting tool

A method is proposed to suppress regenerative chatter in turning operation, in which the ultrasonic elliptical vibration is added on the cutting tool. It results in the fact that the cutting tool is separated periodically from the chip and the workpiece, and the direction of the frictional force between the rake face of the cutting tool and the chip is reversed in each cycle of the ultrasonic elliptical vibration. The experimental investigations show that the regenerative chatter occurring in ordinary turning operation can be suppressed effectively by applying the ultrasonic elliptical vibration on the cutting tool. In order to clearify the reason of the regenerative chatter suppression, theoretical analysis and computer simulation are performed on turning with ultrasonic vibration. There is a good agreement among the experimental investigations, theoretical analysis and the computer simulation.     

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。     

金属切削加工的颤振及避振分析

针对规避切削颤振问题,应用相对切削速度概念,提出了速度型动态切削力表达式以及车削或镗削的振动力学模型。通过对速度型动态切削力分析,解释了切削颤振产生的机理,给出了颤振发生的必要和充分条件。同时指出,在较大的切削速度范围内,存在一个或两个相对稳定的切削速度区域。如果公称切削速度处于该稳定区域,即使背吃刀量较大,系统也不易发生颤振。这种相对稳定的切削速度区域是可以预估的,文中给出了预估公式及预估方法,并由实验分析验证。依据能量原理提出的极限背吃刀量指标是预防颤振发生的有效预估指标,极限背吃刀量的表达式也解释了变速切削技术抑制颤振的原理。     

一种基于振动信号处理的颤振预报方案研究

针对切削过程中产生的颤振现象,通过对机床的在线监测,将采样出的振动加速度信号进行数据处理,提出一种以方差和互相关系数作为综合判据的方法来判别颤振是否发生,并在MATLAB环境下仿真证明该方法的可行性。     

基于阻尼减振器的铣削过程稳定性研究

针对薄壁件铣削加工中出现的颤振现象采用外置式阻尼减振器。该减振器与刀杆过盈配合联接为一体,铣削过程中可以吸收刀杆受到的振动,通过安装阻尼减振器和未安装阻尼减振器两个铣削对比试验,以阻尼材料、阻尼减振器安装位置为变量,探究该阻尼减振器对铣削抑振和加工稳定性的影响程度及变化规律。试验结果表明,安装该阻尼减振器后系统铣削稳定性得到提高,切削深度平均提高2.5倍。     

高速铣削用机械阻尼器铣刀模型的建立及其减振规律的分析

高速铣削加工过程中,刀具颤振会对机床、刀具和工件表面产生不良影响。提出增加机械阻尼器来抑制铣刀颤振的方法;通过对建立的铣刀模型进行理论分析,讨论了阻尼耗散功率随着刀指内径、刀指数目、刀指初始安装角变化而变化的规律。     

Influence of flank texture patterns on the suppression of chatter vibration and flank adhesion in turning operations

In this paper, we propose a practical texture design on the tool flank face for suppressing chatter vibration and flank adhesion. To avoid chatter vibration during cutting, the process damping phenomena can be utilized, where the tool flank face contacts the surface of a finished workpiece to provide a damping effect. As a new technology for an effective process damping, the tool flank texture-assisted technique has been proposed, and its excellent performance in suppressing chatter vibration has been demonstrated. However, issues that can lead to adhesion and tool damage pose challenges from a practical viewpoint. To overcome such issues, this paper proposes new texture geometries that improve the practical performance: parallel line type, vertical line type, and dot type. The results of a series of finite element analyses showed that the effectiveness of process damping depends on the vibration amplitude and wavelength. The proposed flank textures were fabricated on tool flank faces, and turning tests were carried out. The experimental results showed that the proposed tool is stabler than the conventional untextured tool and that it can more effectively improve the critical cutting speed, reduce the vibration amplitude, and decrease the surface roughness after cutting. With the appropriate design of the texture distance, adhesion and tool damage were hardly observed, and a stable and practical cutting could be realized.     

切削颤振模型及机理研究

提出了同时考虑工件系统和刀具系统对切削颤振影响的２自由度切削系统模型,用此模型解释了双频颤振和单频颤振产生的机理,提出了产生的条件,并进行了试验验证。     

基于电流变材料的车削切断颤振抑制研究

应用电流变材料的特殊性能——对电信号的快速响应能力和连续可变的阻尼，研制了一种智能切削颤振抑制结构(刀座刚度可变部分)，并将其附加在车床刀架上，建立了机床车副颤振实时监控系统，实现了机床车削切断过程的颤振抑制。实验结果表明，利用电流变材料智能切削颤振抑制结构可以对机床车削振动进行有效控制，刀具的振动幅值减小50％以上，且工件表面的加工质量有较大提高。     

Integration of cutting force control and chatter suppression control into automatic cutting feed adjustment system design

Abstract

This study designed an automatic cutting feed adjustment system for computer numerical control (CNC) turning machine tools, which integrate the operational characteristics of cutting force control and chatter suppression control to shorten the machining time and maintain the quality of workpieces. The setting of appropriate machining conditions (such as cutting feed, spindle speed and depth of cut) to consider both machining quality and efficiency often causes difficulties for machine tool operators. Therefore, this study uses cutting force control to design an automatic cutting feed adjustment method for cutting tools, and then, the chatter suppression control design is used to modify the cutting force command to suppress cutting chatter. The experimental results of the CNC turning machine tool show that the use of the cutting force control to adjust the cutting feed can shorten the machining time; however, the cutting chatter results in larger surface waviness on the workpiece surface. When the cutting force command is properly modified by actuating the chatter suppression control, the workpiece shows better surface roughness with prolonged machining time. Therefore, the cutting tests demonstrate that the proposed system is feasible for satisfying the machining requirements of the manufacturing processes of mechanical parts for high speed and high accuracy.     

Time domain coupled simulation of machine tool dynamics and cutting forces considering the influences of nonlinear friction characteristics and process damping

A higher machining ability is always required for NC machine tools to achieve higher productivity. The self-oscillated vibration called “chatter” is a well-known and significant problem that increases the metal removal rate. The generation process of the chatter vibration can be described as a relationship between cutting force and machine tool dynamics. The characteristics of machine tool feed drives are influenced by the nonlinear friction characteristics of the linear guides. Hence, the nonlinear friction characteristics are expected to affect the machining ability of machines. The influence of the contact between the cutting edge and the workpiece (i.e., process damping) on to the machining ability has also been investigated. This study tries to clarify the influence of the nonlinear friction characteristics of linear guides and ball screws and process damping onto milling operations. A vertical-type machining center is modeled by a multi-body dynamics model with nonlinear friction models. The influence of process damping onto the machine tool dynamics is modeled as stiffness and damping between the tool and the workpiece based on the evaluated frequency response during the milling operation. A time domain-coupled simulation approach between the machine tool behavior and the cutting forces is performed by using the machine tool dynamics model. The simulation results confirm that the nonlinear frictions influence the cutting forces with an effect to suppress the chatter vibration. Furthermore, the influence of process damping can be evaluated by the proposed measurement method and estimated by a time domain simulation.     

动态切削力对切削颤振的影响

以外圆车削实验为依据,建立加工过程中刀具振动的非线性动力学模型,并采用数值分析方法,研究切削力中的动态分量对切削颤振的影响.结果表明,随速度变化的切削力分量对颤振幅值影响较小,而且会在短时间内被系统内的结构阻尼所衰减.而与加速度成非线性关系的切削力分量对颤振的影响却很显著,而且加速度系数有临界值存在,当超过这个临界值后,颤振的理论幅度将急剧增大.     

Stabilization of high frequency chatter vibration in fine boring by friction damper

Friction damper has been found successful to prevent high frequency chatter occurring at more than 10,000Hz, and causing problem of reduced tool life in fine boring operation. The new damper is characterized by simple structure that consists of an additional mass attached to the main vibrating structure with small piece of permanent magnet. The principle is straightforward in which Coulomb and viscous frictions dissipate vibration energy at the interface between the damper and main vibrating structure. The damper needs no tuning, and is effective at high frequency. The paper first introduces a typical design of the friction damper with experimental proof by cutting tests of its effectiveness in eliminating the high frequency chatter in fine boring, and assuring normal tool life of the cutting edge. Theoretical and experimental analyses are introduced for understanding the fundamental principle and characteristics of the new damper. The new damper is effective for boring tools, which vibrate at frequency more than 5,000Hz.     

Chatter suppression in micro-milling using shank-mounted Two-DOF tuned mass damper

The tuned mass damper (TMD) has been used in machining processes for reducing forced vibration, suppressing chatter, and improving machined surface quality. In micro-milling process, the tiny size of the cutting tool-tip and the high rotating speed bring challenges in implementing the TMD. Besides, the TMD needs to have two degrees-of-freedom (DOFs) for reducing vibrations of micro-mill in two orthogonal directions. This paper presents the chatter suppression for micro-milling by attaching a two-DOF TMD to the tool shank and rotates with the cutting tool. The frequency response function (FRF) at the tip of the micro-mill clamped by an aerostatic spindle is predicted using receptance coupling analysis. A two-DOF TMD is designed via graphical approach based on the FRF result at the tool-tip. The natural frequencies and damping ratio of the TMD are optimized under different spindle speeds in order to enhance the cutting stability. The chatter stability of micro-milling is predicted considering the gyroscopic and centrifugal effects of the TMD structure. Modal tests and micro-milling experiments are conducted to validate the effect of the TMD on chatter stability. The results show that the TMD is able to improve the critical depth of cut by 13 folds, and satisfy the compact design requirement for micro-milling.