外文翻译--在精镗中提供稳定高频振动的摩擦阻尼器

附件 在精镗中提供稳定高频振动的摩擦阻尼器 Evita Edhi, Tetsutaro Hoshi 摘要 在精镗过程中防止发生超过 10000Hz的高频振动而造成刀具寿命降低问题的摩擦阻尼器已研制成功。新阻尼器结构简单，它由一个联接在主振动结构上的附加质量与一小块永久磁铁构成。 其原理是简单的， 利用库仑力和粘性摩擦将振动能量消散在阻尼器和主振动结构的接口之间。阻尼器对高频也有效，因此无需调谐，本文首先介绍了一种在精镗中消除高频颤振的摩擦阻尼器的典型设计，其有效性由切削试验得以证明，并保证刀尖的正常 寿命。 对这种 新型阻尼器基本原理的理解在理论和实验分析中得以介绍。在镗削过程中这种新型阻尼器能够有效的防止超过 5000赫兹的 颤振。 关键词 高频振动 摩擦阻尼器 精镗 1、引言 先前有研究报告称精镗中出现超过 10000赫兹的高频颤振。这种频率首先发现于留在切削表面的振纹上，然后在切削实验中直接使用激光位移计测量得到进一步的证实。从镗刀的自然弯曲振动以及自我激发的切削过程中的动力学再生效果、内调制虚部的影响和 x-y方向的循环发现了这种颤振。本研究的目标是防止这种颤振振动的发生。 预防切削颤振的有效措施 可能是通过提高刀具系统的阻尼能力。阻尼能力是通过以下方面产生的：（ 1）包含在刀具系统接口处的某些微量滑动；（ 2）在晶界滑移内部振动引起的阻尼损耗（内耗）；（ 3）在主振动结构和振动阻尼器接口处的摩擦。许多研究人员对不同类型的用以防止颤振振动，并提高镗刀或其他切削操作稳定性的阻尼器进行了研究。 该阻尼器已不是传统阻尼器的动态特性或冲击特性了，动态阻尼器包括额外的弹簧质量子系统，通过调节系统的固有频率，使之与主体结构相匹配。一般动态阻尼器设计包括任意方向的滑动或内部摩擦耗能的弹性材料。弹性阻尼器由一个或多个的自由 移动机构组成，其原理是利用自由移动体撞击主体结构来耗散颤振能量。阻尼器受一定的速度影响才能有效的发挥其功能，因此不能适用于抑制低频振动。近来有报道一种动力与摩擦混合阻尼器，并发现它能有效地抑制低频振动。 2 本文中所设计的阻尼器必须能有效地抑制高达 10000赫兹的高频率颤振，而且它的设计受到镗刀本身的工作空间及其自身大小的限制。它最完美的地方就是不需要调整。该阻尼器在本研究提出一个大规模隶属永磁结构的概念。 本研究的目的是为了分析抑制高频振颤阻尼器的有效性及其阻尼特性。 为了实现这一目标，已进行一个类似于抑制精 镗中高频颤振的切削试验以及理论和实验的能源阻尼耗能分析。 2、镗刀测试和阻尼器结构的构想 根据研究，在精镗中原本有一个高频颤振问题，镗刀本身包括一个直径分别为 13毫米和 20毫米的长悬臂杆和法兰。在杆的一端有一直径为 5.5毫米的小孔，以适应 5毫米或孔径更小的阻尼器。该孔的位置选择在径向方向，因为我们已经知道高频振动在 X-Y方向循环。当镗刀空转时，阻尼器被孔壁的离心力推动但可以再径向方向自由移动。上限用以保护运行中的阻尼器。 该阻尼器的有效性已经通过了检测并准备和其他镗刀做比较。 用作比较的工具之一具有相同直径 的长悬臂杆即直径为 13毫米，但其延伸超出了前沿 10毫米并产生约 5000赫兹的颤振振动。其他与之比较是 16毫米直径悬臂式镗刀，将以更大的长径比产生较低频率的颤振振动。 新型摩擦阻尼器的基本结构是一个附加质量和永久磁铁的组合，其中质量平面平行于主结构的振动方向。磁铁可以是不可分割的或者是可分割的都行。另一部件，垫片，可以插入到永久磁铁和主要结构之间，其目的是控制电磁力的大小。新型摩擦阻尼器在抑制高频振动的有效性已得到积极评价。 3. 实验方法 为了验证该阻尼器控制颤振的有效性，并保证正常的刀具磨损和表面粗糙度，切削试 验将与其设计尺寸一样，与 13毫米直径的钻孔工具配合使用。这样的话，镗刀安装在一个卧式加工中心的主轴上，通过设置调整孔直径以自动控制刀尖径向位置。 将内表面是由旋转刀具镗加工的环型工件准备好。工件的材料是 SCM420H合金钢，淬火至硬度为 313 332HBS，外径为 25mm，内径为 14.72 0.05mm，长度为 15mm。工件由专门设计的具有足够硬度的夹具装夹。 切削试验是在标准条件下进行的，切削速度为 130m/min，进给量为 0.03mm/rev,背吃刀量为 0.14mm，切削过程中不使用任何切削液。一种新的 尖端技术在加工过程中不断调整加工条件。每个试验重复两次，其中一次在镗刀系统中安装阻尼器，而另一次不安装。刀具材料用的是非涂层 TiC金属陶瓷，其轴向前角为 -50，径向前角为 -150，刀尖圆弧半径为 0.4mm。 对于直径为 16毫米的工件振动的测量，准备用另一个安装程序将环行工件的外表面固定。这样的话，工件被夹紧使测试在一对立式加工中心机床基板上举行。环行工件和机床主轴一同旋转。 3 4.摩擦阻尼器的机理分析 4.1 理论分析 振动的产生，一旦达到一定的振动幅度，阻尼器将开始滑动，由此引起阻尼器的主体结构和界面的 摩擦，从而耗散振动能量，并防止振幅不断增大甚至超出极值振幅。 实验分析 为了确定该假设库仑力和粘性摩擦的区别，一个主体结构模型振动的两个理论模型的有效性监测了二者的不同状况，并激发了电动式激振器外部。用作主体结构的是一直径为 16毫米的悬臂钢梁，它和原长为 170mm的镗刀具有相似的设计，其二阶弯曲频约能达到 5700Hz。在检测梁的端部振动时将使用微型加速度测量计。阻尼器主体结构的顶部有一磁铁，并通过此处与油管口相接。 首先采用随机激励确定主体结构的固有频率。然后是应用在正弦激励变幅的动力输入 f至 z微调周围随机 激励确定固有频率。与此同时，用 FFT分析仪分析振幅在主体结构出的响应差异。 激发各周期能源供应量的正弦振动是从测量 f时开始的，计算如下 当 x是降低阻尼器或与供油接口相连接时，主体结构的振幅也降低了。当使用阻尼器时，激励由 0.3N增至 0.6N时，振幅 x将不会增大。对于较低的频率，虽然也能有一定大的抗振效应，但效果并不明显。 5、结论 为了控制频率高达 10000Hz的高频颤振，正如以前报道的精镗过程一样，利用一种新的阻尼器与主体结构之间的摩擦效应，削弱振动能量而达到减振目的。 新的阻尼器 由一个联接在主振动 结构上的附加质量与一小块永久磁铁构成。 据目前的研究已证实了库仑力和粘性摩擦在滑动界面的产生。由于库伦摩擦力，发生在主体结构处的滑移就能抵消一部分颤振能量，而且它们之间大致是呈线性关系的。如果在此条件下能够充分的消耗颤振能量，则就可以抑制颤振了。 在抑制高频颤振时，该阻尼器显得更为有效。由于受到阻尼器主体结构自身条件的限制，在精镗中该阻尼器能抑制的最高颤振频率只能略高于 5000Hz。 由于简单的结构设计，也无需经常调整，使用拟阻尼器抑制连续切削高频率颤振（如精镗等）是一种可行性方法。 致谢 本研究得到了 NT工 程公司的大力支持。他们提供了大量的研究材料和工具，得到了 4 Y. Komai先生和 M. Nakagawa先生 的大力支持和帮助。 附件 II 英文文献原文 Stabilization of high frequency chatter vibration in fine boring by friction damper Evita Edhi*, Tetsutaro Hoshi Abstract 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. Keywords: High frequency chatter； Friction damper； Fine boring. Introduction A previous study reported fine boring tools exhibiting chatter at high frequency, more than 10,000Hz . The frequency was first identified from the chatter mark left on the surface, then further confirmed in cutting test by direct measurement using the laser displacement meter. The chatter was found attributable to bending natural vibration of the boring tool, self-excited by cutting process dynamics that include the regenerative effect, the imaginary part effect of inner modulation, and X-Y Looping. Prevention of such chatter vibration is the target of the present study. Effective chatter prevention during cutting operations may be achieved by increasing the damping capacity of cutting tool system. Damping capacity is generated through (i) micro-slip 5 at certain interfaces included in the tool system, (ii) slip at the grain boundary within a vibrating body by material damping (internal friction), (iii) friction at an interface between the main vibrating body and the damper structure . Studies on various kind of damper to prevent chatter vibration, and to improve stability of boring tools or other cutting operation have been carried out by many researchers. Practical types of damper have been conventionally either dynamic or impact damper . Dynamic damper consists of additional spring-mass sub-system, and needs tuning of natural frequency of the sub-system to match that of the main structure. The dynamic damper is usually designed to include energy dissipation by either sliding or internal friction of the spring material. Impact damper consists of one or more of free moving bodies, and the principle mechanism is to dissipate energy by the impact of free moving body with the main structure. Impact damper needs certain velocity to effectively function, thus cannot be applied to suppress vibration at low frequency. A hybrid design of dynamic and impact dampers has been reported recently, and found to be effective to suppress the low frequency vibration . In the present study, the damper is required to be effective at frequencies as high as 10,000Hz, and it should be designed within size limitation of the boring tool to accommodate space for seating the tool insert, chip pocket and the damper itself. It is also preferable that the damper needs no tuning. The damper proposed in the present study consists of a piece of mass attached to the main structure by permanent magnet. The objective of the present study is to analyze the effectiveness and characteristics of the proposed damper in preventing chatter vibration that occurs at high frequency. To achieve the objective, cutting tests have been conducted in boring operation analogues to the one having high frequency chatter problem in the plant, as well as theoretical and experimental analyses of energy dissipation of the proposed damper. Boring tools tested and the proposed damper structure The boring tool under study that originally had a problem of high frequency chatter consists of a 13mm diameter and 20mm long cantilevered steel bar integral with a base flange. A small diameter hole, 5.5 mm, is prepared at the end of the bar to accommodate the damper mass of which diameter may be 5mm or less. The position of the hole is selected in radial orientation om1, because the high frequency vibration due to X-Y looping has been known to occur dominantly in the orientation om2 as depicted. When the tool is rotated in boring operation, the damper is pushed to the wall of the hole by the centrifugal force, but is free to move in the orientation of the vibration om2. A cap is provided to protect the damper from chips removed during the operation. The effectiveness of the damper has been tested for the tool as shown in the figure, as well 6 as other boring tools that have been prepared for comparison. One of the comparison tools has the same diameter 13mm, but extended 10mm beyond the cutting edge, and generates chatter vibration at about 5,000Hz. Other comparisons are 16mm diameter cantilever type boring tools, designed with greater length (L) to diameter (D) ratios that exhibit chatter at lower frequencies. Basic structure of the new friction damper is the combination of a mass and permanent magnet, which anchors the mass to the main structure on a flat surface parallel to the direction of vibration. The magnet may be either integral or separated with the mass. A third member, a spacer, may be inserted between the permanent magnet and the main structure whose purpose is to control magnitude of magnetic force. Effectiveness of the friction dampers in suppressing high frequency chatter has been evaluated. 3. Method of experiment To validate the effectiveness of the damper in view of controlling the chatter, and to assure normal tool wear and surface roughness generated, cutting tests have been performed with the 13mm diameter boring tool rotated as it is in production site. In this case,the boring tool is mounted on the main spindle of a horizontal machining center via a setting head whose function is to adjust the radial position of the tool tip for automatic control of the hole diameter in production. Ring type workpieces have been prepared whose inner surface is to be machined by the rotating boring tool. Rings are made of SCM420H alloy steel, hardened to 313 to 332 Brinnell hardness with 25mm outer diameter, 14.720.05mm inner diameter, and 15mm length. A milling chuck clamps the ring on a specially designed fixture with sufficient stiffness. The standard condition for cutting test is set to 130m/min cutting speed, 0.03mm/rev feed rate, 0.14mm depth of cut, and using no cutting fluid. A new cutting edge is prepared for each set of cutting tests in which workpieces are continuously machined. The cutting test is repeated twice for each boring tool system with and without the damper. Tool insert material used for the boring tool is TiC Cermet non-coated, with axial rake angle -5, radial rake angle -15, and nose radius 0.4mm. For measuring vibration of the 16mm diameter tool, another setup was prepared with the tool held stationary, and used to machine outer surface of the rotating ring workpiece. In this setup, the tool is clamped by a milling chuck staged on a baseplate on the machine table of vertical machining center. The ring workpiece is mounted and rotated by the machine spindle. 4. Analysis of friction damper mechanism 7 4.1 Theoretical analysis During the development of chatter, once the vibration reaches certain threshold amplitude, the damper will start sliding, therefore introducing friction at the interface between the damper mass and the main structure. The friction dissipates the vibration energy, and prevents the chatter from growing beyond the threshold amplitude. 4.2 Experimental analysis In order to ascertain validity of the two theoretical models assuming Coulomb and viscous friction respectively, vibration of a main structure model has been monitored with and without the damper mass attached, and excited externally by an electro-dynamic exciter. A cantilevered steel beam 16mm diameter, having similar cutting edge design with the original boring tool and 170mm length, has been used as the main structure whose second order bending mode was excited around 5,700Hz frequency. The vibration at the end of the beam is detected by micro size accelerometer pickup. A damper with an integral magnet is attached on top of the main structure via cleaned and dried interface as well as oiled interface. Random excitation is first applied to identify the natural frequency of the main structure. Then sinusoidal excitation is applied at variable amplitude f of the input dynamic force F at frequency Z finely tuned around the natural frequency identified by random excitation. At the same time, amplitude x of response vibration X of the main structure, and the phase difference between input dynamic force and response vibration , are measured by the FFT Analyzer. Amount of energy supplied Es per vibration cycle by the sinusoidal excitation is computed from the measured f,as follows: vibration amplitude x of the main structure is reduced when the damper is attached on either dried or oiled interface. When the damper is used, the amplitude x exhibits a stagnant step during the excitation force increment from 0.3 to 0.6N. 5. Conclusion To control chatter vibration occuring at frequencies as high as 10,000Hz, as previously reported in fine boring operation, performance of a new damper mechanism utilizing friction between a