機(jī)械論文外文文獻(xiàn)翻譯精鏜中摩擦阻尼器

1、中北大學(xué)信息商務(wù)學(xué)院 外文翻譯精鏜中的摩擦阻尼器學(xué)生： 學(xué)號： 12020143X01 系 別： 機(jī)械工程系專 業(yè)： 機(jī)械設(shè)計制造與其自動化指導(dǎo)教師： 職稱： 副教授 2016年6月2日Stabilization of high frequency chatter vibration in fine boring by friction damperAbstractMachining performance such as that of the boring process is often limited by chatter vibration at the tool-workpiece

2、 interface. Among various sources of chatter, regenerative chatter in cutting systems is found to be the most detrimental. It limits cutting depth (as a result, productivity), adversely affects surface finish and causes premature tool failure.The new damper is characterized by simple structure that

3、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 tunin

4、g, 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 experim

5、ental 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.1. Introduction Chatter in metal c

6、utting process, in general, is the result of both forced and self-excited vibrations. Forced vibration is due to the unbalance of rotating members, such as unbalanced driving system, a servo instability, or impacts from a multi-tooth cutter. In practice, the forced vibration sources can be traced by

7、 comparing the frequency of chatter with the frequency of the possible force functions. Corresponding measures can then be taken to reduce/eliminate such vibration sources. Self-excited vibration consists of two types, namely primary (or non-regenerative type) and regenerative type. The primary/non-

8、regenerative type of self-excited vibration occurs when theses is no interaction between the vibratory motion of the system and the adulatory surface produced in the revolution of the work piece, such as that in threading. Hence if is inherently related to the dynamics of the cutting process. While

9、the regenerative type of self-excited vibration is due to the interaction of the cutting force and the work piece surface undulations produced by previous tool passes. The regenerative type of self-excited vibration is found to be the most detrimental phenomena in most machining process.Effective ch

10、atter prevention during cutting operations may be achieved by increasing the damping capacity of cutting tool system. Damping capacity is generated through (i) micro-slip at certain interfaces included in the tool system, (ii) slip at the grain boundary within a vibrating body by material damping (i

11、nternal 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 o

12、f 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 eithe

13、r 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

14、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 shou

15、ld 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

16、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 hig

17、h frequency chatter problem in the plant, as well as theoretical and experimental analyses of energy dissipation of the proposed damper.2. System modelMachining systems, in general, can be modeled as one-dimensional distributed structures with various boundary conditions. For a non-rotating boring p

18、rocess, the work piece is much stiffer than the boring bar itself. And typically boring bars are much stiffer in torsion than in bending. Hence it can be modeled as a cantilevered rod in bending. Using Euler-Bernoullis bending model for one-dimensional uniform distributed structure, the equation of

19、motion is as follows: (1) where x is the distance along the beam, t the time, f(x,t) the external force, E the Youngs modulus, I the cross-sectional area moment of inertia, the mass density and A the area of cross section of the boring bar.The solution to the classical partial differential equation

20、is usually found using Eigen function expansions. The response can be expressed as a sum of an infinite number of modal components as (2)Where and (i=1,2, ) are the mode shapes and modal coordinates of the system , respectively. The mode shapes are in general, mass-normalized such that (3) where L i

21、s the length of the structure andthe Dirac delta function. The equations of motion can be written in terms of the model coordinates as (4) where is the i th emodal force given by (5)It should be pointed out that in practice. Only a finite number of modes are excited, as a result, the number of modal

22、 components is in general n instead of .In the case of one dominating mode, n=1.Now considering the dynamic interaction of the cutting force and the work piece surface undulations produced by previous tool passes during the cutting process, Eq.(1) then becomes 1 (6a)Where is cutting stiffness determ

23、ined by work piece material and tool geometry, B the depth of cut and T the tooth passing period, is the so-called overlap factor, which accounts for the overlapping of successive cuts. The value of varies between 0 and 1. Considering the worst-case scenario (where=1), then the above equation become

24、s (6b)The corresponding equations of motion in terms of the modal coordinates, by following the same procedures as that of Eqs.(1)-(4),are (7)Where b= is the cutting depth-related dimensionless parameter and the natural frequency of the Ith mode.Eq.(7) describes an undammed structure. Since no purel

25、y undammed structures exist in reality, assuming viscous damping in the structure, the equation of motion is then rewritten as (8)Usually is a small positive number between 0 and 1, with most common values of 0.05. .3.Boring tools tested and the proposed damper structureThe boring tool under study t

26、hat 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 t

27、he 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 fre

28、e 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 as other boring tools that have been prepared for comparison.One of the comp

29、arison 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.Ba

30、sic 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 b

31、etween 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.4. Method of experimentTo validate the effectiveness of the damper in view of controlling the chat

32、ter, 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 functio

33、n 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

34、25mm outer diameter, 14.72±0.05mm 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

35、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

36、 -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

37、 a baseplate on the machine table of vertical machining center. The ring workpiece is mounted and rotated by the machine spindle.5. Analysis of friction damper mechanism5.1 Theoretical analysisDuring the development of chatter, once the vibration reaches certain threshold amplitude, the damper will

38、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.5.2 Experimental analysisIn order to ascertain validity of the two theoret

39、ical 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

40、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 structu

41、re 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 frequenc

42、y 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

43、 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.6. ConclusionIn

44、this paper, a control from wave point of view designed to absorb vibrational energy in a broad frequency range is applied in the control of regenerated chatter in non-rotating boring cutting process, Though it was found that the first mode dominates the response, the rest of the modes more or less c

45、ontribute to the chatter of the system. Furthermore, when designing a controller based on the consideration of only single dominating mode, it is likely to induce control spillover(that is , the control force designed to control the first mode will adversely excite some or all the rest of the modes

46、of the system), as observed in the experimental results of Boring .In this study, with the controller designed based on a broad frequency range, damping is added to all the modes in the frequency range of interest, but also greatly reduces the chatter caused by not only the dominating first mode but

47、 also that by the rest of the modes.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 damper mass and the main vibrating structure has been evaluated by cutting

48、and excitation experiments.The new damper consists of a piece of mass attached to the main structure by permanent magnet. It has been confirmed by the present study that both Coulomb and viscous frictions are occurring at the sliding interface.Due to the Coulomb friction, there occurs threshold ampl

49、itude where the mass starts sliding with respect to the main structure and dissipates a certain amount of vibration energy, which is approximately in linear proportion to the vibration amplitude.When the energy dissipation at this condition is sufficient, the vibration is suppressed to this threshol

50、d amplitude.The damper has been found to be more effective for tools that generate chatter vibration at higher frequencies. From the physical size limit of the damper mass for attachment to the main structure, friction damper is practical for tools which vibrate at frequencies higher than 5,000Hz.Du

51、e to simple structural design and no need of tuning, the proposed damper is a viable solution for the high frequency chatter vibration of continuous cutting operations such as fine boring.AcknowledgementsThis research was supported by NT-Engineering Inc. that has provided materials including workpie

52、ces, some of the boring tools and instruments by care of Mr. Y. Komai, Executive Director of Engineering,and Mr. M. Nakagawa.14 / 17精鏜中的摩擦阻尼器摘要：鏜削的加工性能經(jīng)常受加工中振動的影響。在各種振動來源中,再生顫振是最不利的。它不僅限制了切削深度，對表面質(zhì)量也有不利的影響，同時也會損害工具壽命。盡管加工系統(tǒng)是一種分布式的系統(tǒng)，通用的控制器是根據(jù)一個簡化后的單自由度切削過程模型來設(shè)計的。這是因為大部分切削過程只存在著一個主導(dǎo)模式。然而，簡化后就會出現(xiàn)一些問題。

53、首先，因為系統(tǒng)本身是分布式系統(tǒng)，理論上它是由無數(shù)個振動模型組成，當(dāng)控制器僅僅控制主要的模型，被用來控制主導(dǎo)模型的能量會激起原本靜止的機(jī)構(gòu)的振動，即引起所謂的溢流問題。第二、單自由度控制器設(shè)計的成功依賴于有效的精確的模型參數(shù)（如質(zhì)量當(dāng)量，剛度，阻尼），但不幸的是獲取這些參數(shù)非常困難。新阻尼器結(jié)構(gòu)簡單，它由一個聯(lián)接在主振動結(jié)構(gòu)上的附加質(zhì)量與一小塊永久磁鐵構(gòu)成。其原理是簡單的，利用庫侖力和粘性摩擦將振動能量消散在阻尼器和主振動結(jié)構(gòu)的接口之間。阻尼器對高頻也有效，因此無需調(diào)諧，本文首先介紹了一種在精鏜中消除高頻顫振的摩擦阻尼器的典型設(shè)計，其有效性由切削試驗得以證明，并保證刀尖的正常壽命。對這種新型阻尼

54、器基本原理的理解在理論和實驗分析中得以介紹。在鏜削過程中這種新型阻尼器能夠有效的防止超過5000赫茲的顫振。關(guān)鍵詞 ：高頻振動 , 摩擦阻尼器 , 精鏜1、 引言 金屬切削中的振動總體上是受迫振動和自激振動引起的。受迫振動是由回轉(zhuǎn)件的失衡引起的，比如失衡的驅(qū)動系統(tǒng)，伺服不穩(wěn)定或者多齒零件的撞擊。受迫振動可以認(rèn)為是由振動頻率和受迫力頻率對比引起的，但相應(yīng)的措施可以被用來減小或消除這些振動來源。自激振動包括兩部分：基本類型（不可再生類型）和再生類型。不可再生式自激振動出現(xiàn)在回轉(zhuǎn)件的波動表面對系統(tǒng)的振動沒有相影響的時候，如車螺紋。因此它只和切削過程中受到的力有關(guān)。再生式自激振動是因為工具通過時，系統(tǒng)

55、的振動和回轉(zhuǎn)件的波動表面相互作用產(chǎn)生的，再生式自激振動對加工過程的影響最為不利。先前有研究報告稱精鏜中出現(xiàn)超過10000赫茲的高頻顫振。這種頻率首先發(fā)現(xiàn)于留在切削表面的振紋上，然后在切削實驗中直接使用激光位移計測量得到進(jìn)一步的證實。從鏜刀的自然彎曲振動以與自我激發(fā)的切削過程中的動力學(xué)再生效果、調(diào)制虛部的影響和x-y方向的循環(huán)發(fā)現(xiàn)了這種顫振。本研究的目標(biāo)是防止這種顫振振動的發(fā)生。預(yù)防切削顫振的有效措施可能是通過提高刀具系統(tǒng)的阻尼能力。阻尼能力是通過以下方面產(chǎn)生的：（1）包含在刀具系統(tǒng)接口處的某些微量滑動；（2）在晶界滑移部振動引起的阻尼損耗（耗）；（3）在主振動結(jié)構(gòu)和振動阻尼器接口處的摩擦。許多

56、研究人員對不同類型的用以防止顫振振動，并提高鏜刀或其他切削操作穩(wěn)定性的阻尼器進(jìn)行了研究。該阻尼器已不是傳統(tǒng)阻尼器的動態(tài)特性或沖擊特性了，動態(tài)阻尼器包括額外的彈簧質(zhì)量子系統(tǒng)，通過調(diào)節(jié)系統(tǒng)的固有頻率，使之與主體結(jié)構(gòu)相匹配。一般動態(tài)阻尼器設(shè)計包括任意方向的滑動或部摩擦耗能的彈性材料。彈性阻尼器由一個或多個的自由移動機(jī)構(gòu)組成，其原理是利用自由移動體撞擊主體結(jié)構(gòu)來耗散顫振能量。阻尼器受一定的速度影響才能有效的發(fā)揮其功能，因此不能適用于抑制低頻振動。近來有報道一種動力與摩擦混合阻尼器，并發(fā)現(xiàn)它能有效地抑制低頻振動。本文中所設(shè)計的阻尼器必須能有效地抑制高達(dá)10000赫茲的高頻率顫振，而且它的設(shè)計受到鏜刀本身

57、的工作空間與其自身大小的限制。它最完美的地方就是不需要調(diào)整。該阻尼器在本研究提出一個大規(guī)模隸屬永磁結(jié)構(gòu)的概念。本研究的目的是為了分析抑制高頻振顫阻尼器的有效性與其阻尼特性。為了實現(xiàn)這一目標(biāo)，已進(jìn)行一個類似于抑制精鏜中高頻顫振的切削試驗以與理論和實驗的能源阻尼耗能分析。2、鏜刀測試和阻尼器結(jié)構(gòu)的構(gòu)想根據(jù)研究，在精鏜中原本有一個高頻顫振問題，鏜刀本身包括一個直徑分別為13毫米和20毫米的長懸臂桿和法蘭。在桿的一端有一直徑為5.5毫米的小孔，以適應(yīng)5毫米或孔徑更小的阻尼器。該孔的位置選擇在徑向方向，因為我們已經(jīng)知道高頻振動在X-Y方向循環(huán)。當(dāng)鏜刀空轉(zhuǎn)時，阻尼器被孔壁的離心力推動但可以再徑向方向自由移

58、動。上限用以保護(hù)運行中的阻尼器。該阻尼器的有效性已經(jīng)通過了檢測并準(zhǔn)備和其他鏜刀做比較。用作比較的工具之一具有一樣直徑的長懸臂桿即直徑為13毫米，但其延伸超出了前沿10毫米并產(chǎn)生約5000赫茲的顫振振動。其他與之比較是16毫米直徑懸臂式鏜刀，將以更大的長徑比產(chǎn)生較低頻率的顫振振動。新型摩擦阻尼器的基本結(jié)構(gòu)是一個附加質(zhì)量和永久磁鐵的組合，其中質(zhì)量平面平行于主結(jié)構(gòu)的振動方向。磁鐵可以是不可分割的或者是可分割的都行。另一部件，墊片，可以插入到永久磁鐵和主要結(jié)構(gòu)之間，其目的是控制電磁力的大小。新型摩擦阻尼器在抑制高頻振動的有效性已得到積極評價。3、系統(tǒng)模型加工系統(tǒng)通常可以被模擬成帶有邊界圍的一維分布式結(jié)構(gòu)。對于一個不回轉(zhuǎn)的鏜削加工，工件比鏜刀本身還硬。典型鏜刀的扭轉(zhuǎn)硬度比彎曲硬度要大，因此它可以被模擬成一種懸臂梁。使用一維分布式結(jié)構(gòu)的彎曲歐拉梁，動力學(xué)平衡方程式如下：