减小镗杆颤振的方法

镗杆折悬臂结构决定在镗削时不可避免地产生颤振，颤振降低加工工件的表面质量及几何精度；减小颤振是镗杆设计的重要课题；文中介绍了利用动力吸振器、冲击消振器、调整切削参数等方法减小颤振；并介绍根据这些方法设计的镗杆。     

基于经验模态分解和希尔伯特-黄变换的精密孔镗削颤振特征提取

针对精密孔镗削加工过程中容易出现颤振现象,影响精密孔的表面质量问题,建立了镗削加工的监测系统,对镗削颤振信号进行特征提取,以实现对镗削颤振的快速预报。首先,根据颤振信号的时频特点,将经验模态分解(EMD)和希尔伯特-黄变换(HHT)引入颤振特征提取过程,并介绍了其基本原理及具体实现过程。然后,在线拾取镗杆的振动信号,并对振动信号进行EMD分解和HHT变换。最后,通过对各本征模态函数分量的Hilbert谱分析,提取出了颤振发生的征兆特征。实验结果表明,利用EMD和HHT对镗削振动信号进行特征提取,可以在颤振形成之前0.5s得到颤振爆发的征兆,为后续的颤振抑制工作赢取时间,进而确保精密孔的表面加工质量。     

独特的镗削加工方法

镗削过程中影响加工精度的最不利因素是刀具的刚度、工艺系统的抗振性、切屑的排出等,为了确保所需的加工精度,在加工中必须采用各种手段,其中最主要的是为镗杆建立辅助支承,而且支承应尽可能接近切削刃。 如图1a所示,辅助支承建立在切削区之外。为了减小镗削同轴度误差,镗杆支承配置在主轴1孔中,     

切削参数对内置式减振镗杆振动影响的研究

深孔加工中镗杆的颤振严重影响深孔的表面质量,而切削参数对内置式减振镗杆振动有很大的影响。为解决这一问题,建立基于有限元分析软件ANSYS的内置式减振镗杆仿真模型,加载应力载荷;采用单因素分析法,研究镗削过程切削参数对内置式减振镗杆刀尖最大振动幅值的影响,得到不同切削参数对内置式单减振镗杆刀尖幅频特性曲线;最后由幅频特性曲线归纳出切削参数对内置式减振镗杆切削状态的影响规律。所得结论为内置式减振镗杆在实际镗削精加工中应用提供参考。     

应用电流变材料改变镗杆动态特性的研究

为保证镗削加工切削稳定性,基于电流变材料设计一种智能型镗杆。该镗杆可通过调节施加于电流变材料上的电场强度来改变整个镗杆的动态特性,并借以抑制切削颤振。采用 端部激振方法研究镗杆在不同激振频率和不同电场强度下的动态特性。实验结果表明,在不同的电场强度和振动频率下,电流变材料表现出来的振动特性差异明显,使镗杆的支撑刚度和结构阻尼特性发生显著的变化。     

超声振动改善深孔镗削加工质量

深孔加工在航空发动机制造过程中广泛存在,由于其刚性弱,静态让刀量大,导致加工颤振和刀具磨损严重,使得其加工质量难以得到保证。超声振动切削作为一种特种切削加工手段,具有降低切削力,提高系统刚性和抑制加工颤振等优势。将超声振动应用于深孔镗削,进行了断屑条件验证,孔径误差测量,已加工表面粗糙度测量以及表面形貌观测等试验。试验结果表明,超声振动镗削能够有效缓解深孔镗削过程中的堵屑问题,减小孔径误差和表面粗糙度,抑制切削颤振,从而改善深孔镗削加工质量。     

深孔镗削振动机理研究

介绍深孔镗削加工过程中自激振动产生的原理,分析加工过程中的切削颤振机理,总结出为避免切削颤振,镗杆应安装的合理角度.     

细长孔阻尼抑制深孔镗削颤振的研究

针对深孔镗削加工中的颤振问题,设计了一套具有多个细长孔的双镗杆刀具系统结构,通过细长孔阻尼作用,抑制镗削加工过程中刀具系统的颤振。根据流体力学环形间隙流动以及细长孔阻尼理论,建立双镗杆刀具系统结构的数学模型,利用MATLAB进行数值模拟;利用Fluent软件对双镗杆刀具系统结构的内部流场进行仿真,得出流场域的阻力系数增大;建立镗削过程中的振动模型,运用Simulink对其进行动力学仿真得到振动时域图,直观显示了切削液流经具有多个细长孔的阻尼通道能有效抑制深孔镗削过程中的颤振。     

阶梯孔的精密镗削

阶梯孔的精密镗削为了提高阶梯孔的镗削精度和效率，可采用镗杆（图ａ）或单面切削镗刀（图ｂ）进行加工。单面切削镗刀与镗杆不同之处在于，其每一级上或某一级上装有两个导向件，该导向件同时对被加工表面起熨压作用。加工阶梯孔用的镗仟（ａ）和单面切削镗刀（ｂ）１．...     

高精度微孔镗削加工工艺的优化研究

为解决使用微细切削技术加工微小型孔时存在的钻削孔表面质量差、孔轴线偏斜等问题,将镗削加工方法应用到微小型孔的加工中。通过选取合适的镗削工艺参数,定性地建立了镗刀尺寸、进给速度、转速与表面质量、尺寸精度之间的关系,优化了镗削加工的工艺参数,极大地改善了微小型孔的表面质量与加工精度。在具有较高强度的3J33马氏体时效钢上对钻削出的Ф2.7 mm小孔进行了镗削加工试验,测量并分析了镗削孔表面粗糙度与尺寸数据。实验结果表明,微细孔镗削加工比钻削加工更能够保证零件的尺寸精度、形状精度,并得到更好的表面质量。     

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。      

Parameter optimization of time-varying stiffness method for chatter suppression based on magnetorheological fluid-controlled boring bar

An innovative chatter suppression method based on a magnetorheological (MR) fluid-controlled boring bar for chatter suppression is developed. The MR fluid, which can change stiffness consecutively by varying the strength of the applied magnetic field, was applied to adjust the stiffness of the boring bar and suppress chatter. The cutting dynamic stability under different natural frequencies of the structure was analyzed by an energy method, which shows that cutting dynamic stability depends on both the natural frequency of the structure and the spindle speed. The chatter suppression mechanism with varying natural frequency is analyzed for further parameter optimization. Furthermore, both theoretical analyses and numerical simulations indicate that a square wave exciting current with a large amplitude and a moderate frequency has a better effect on regenerative chatter suppression. Experiments utilizing a MR fluid-controlled boring bar under an exciting current with different waveforms and frequencies were conducted. The experimental results show that the chatter can be significantly suppressed using MR fluid-controlled boring bar under a square wave exciting current with a frequency of 4–6 Hz and an amplitude of 0–2 A.     

Development of a novel boring tool with anisotropic dynamic stiffness to avoid chatter vibration in cutting: Part 1: Design of anisotropic structure to attain infinite dynamic stiffness

This paper presents a novel design method of the anisotropic structure to attain infinite dynamic stiffness to avoid chatter vibration in boring operations. Because a long and slender tool is used for boring operations, the stiffness of the tool holder is likely to decrease, resulting in low chatter stability. Although it is difficult to improve the stiffness of the boring holder itself, the nominal dynamic stiffness for the cutting process can be improved by designing an appropriate anisotropy in the dynamic stiffness of the boring tool. In this study, we formulate a theoretical relationship between the mechanical structural dynamics and chatter stability in boring operation and present the basic concept of tool design with anisotropic structure. In the actual tool design, ideal anisotropy may not be realized because of the influence of design error. Therefore, an analytical study was conducted to clarify the influence of the design error on the vibration suppression effect. Analytical investigations verified that the similarity of the frequency response functions in the modal coordinate system and the design of the compliance ratio according to the machining conditions are important. Furthermore, we designed a boring tool with an anisotropic structure which can achieve the proposed anisotropic dynamics. The frequency response function was evaluated utilizing FEM analysis. The estimated anisotropic dynamics of the proposed structure could significantly improve the nominal dynamics for boring operations.     

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.     

基于电流变材料的切削颤振在线监控技术研究

提出可以利用电流变材料的电控流变特性,通过在线调控切削系统动态特性以提高切削稳定性。并针对镗削系统,开发出一套可根据实时采集的切削振动信号自适应地快速调整系统动态特性以避免颤振发生的颤振智能监控系统。     

Improvement of chatter stability in boring operations with passive vibration absorbers

This paper is focused on the behavior of boring bars with a passive dynamic vibration absorber (DVA) for chatter suppression. The boring bar was modeled as a cantilever Euler-Bernoulli beam and only its first mode of vibration was considered. The stability of the two-degree-of-freedom model was analyzed constructing the stability diagram, dependent on the bar characteristics and on the absorber parameters (mass, stiffness, damping, and position). Two analytical approaches for tuning the absorber parameters were compared. The selection criterion consisted on the maximization of the minimum values of the stability-lobes diagram. Subsequent analysis performed in this work, allowed formulating of new analytical expressions for the tuning frequency improving the behavior of the system against chatter.     

长悬臂铣刀铣削颤振的分析与抑制

长悬臂铣削颤振一直是机械加工工艺难点问题,国内外专家学者长期不懈地对此问题进行了研究,并取得了一定的成果。数控刀具的快速发展为解决此类问题提供了常规方式,比如减振刀杆,但这只是其中的一个方法,并不能保证颤振完全消失。本文对颤振机理、铣削过程进行了分析研究,通过对刀具几何角度的选择和走刀路径的优化,来达到更多地抑制长悬臂铣削颤振的目标,为解决长悬臂铣削颤振问题提供了有效方法。     

超声激振双刃镗刀精密深孔镗削的试验研究

通过切削试验研究了超声激振双刃镗刀镗削深孔的过程和效果,分析了超声激振双刃镗削的切削机理,讨论了切削参数对加工表面粗糙度的影响规律。     

Development of a novel boring tool with anisotropic dynamic stiffness to avoid chatter vibration in cutting: Part 2: Analytical and experimental verification of the proposed method

In this study, we developed prototypes of boring tools with anisotropic dynamic stiffness, and their chatter stability was investigated analytically and experimentally. In Part 1, a novel design of boring tools with an anisotropic structure was proposed to improve the nominal stiffness in boring operation, thus resulting in higher chatter stability in simulation. In this part (Part 2), anisotropic boring tools with a holder length-to-diameter ratio (L/D) of 4 and 10 designed in Part 1 were prototyped, and their frequency response functions were evaluated. Then, the chatter stabilities were evaluated through turning experiments. With respect to a L/D4 boring tool with anisotropic structure, the nominal dynamic stiffness was significantly improved within the range of machining conditions that satisfies the appropriate combination of cutting force ratio and chip flow direction, compared to a conventional tool with isotropic structure. We confirmed that the proposed boring tool with an anisotropic structure increases the critical radial depth of cut by approximately 17 times compared with conventional tools. Even with an L/D10 anisotropic boring tool, a similar effect was observed wherein the dynamic stiffness of the tool was improved. In contrast, the effect of improving the dynamic stiffness was insufficient; thus, chatter free cutting could not be realized. Analytical investigations verified the importance of further improvement of dynamic characteristics. To realize stable boring with L/D10 boring tools, it is necessary to further reduce the system compliance while also improving the similarity of the frequency response function.