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Shallow Theory Turning Processing of Vibration and Control
The author:Lan Wenqing
【Abstract】In the machine process creation of vibration all have is forced a vibration and from arouse vibration, and tool machine, tongs, knife and work piece the dynamic state characteristic of craft system for constitute relevant.Detailed analysis the car pare to process medium vibration of main type and creation of reason, vibration of endanger, and from the knife, tongs, sliced to pare craft’s etc. to put forward to let up or cancellation vibration of measure.
【Key words】The car pare low frequency vibration;High frequency vibration;Cancellation measure
Preface
In turning process vibrations, not only interfere with the normal cutting process, serious impact on the product's surface quality, still can shorten the machine and tools using life. The resulting noise may even affect the operator to normal work motion, carrying on the negative influence, and bring certain But in order to reduce vibration, often have to reduce the amount of feed processing, which reduces the productivity. I through in the work of this phenomenon continually observing, analysis and practice, the summary, made some effect, this paper discussed some opinions for everybody.
1. The classification of vibration, generally in machining the vibrations have forced vibration and the excitedself vibration, and machine tool, cutting tool and workpiece, fixture of the dynamic characteristic of the process system concerned. In eliminating turn components (such as electric machine, workpiece, etc) and transmission system axis (such as pulley, rolling bearing, hydraulic transmission system pressure pulse, etc.), the vibration of the vibration after turning machining is mainly the change in velocity with turning the excitedself vibration, mainly is the turning process workpiece system (the bending vibration frequency close to the natural frequency of the workpiece low frequency vibration) and the deformation of the tool produced the bending vibration (its vibration frequency close to turning the natural frequency of the high frequency vibration).
2. Vibration analysis of the causes of low frequency vibration frequency low, usually compare low of noise, vibration in the more violent, the vibration of the machined surface traces left deep and wide. Usually in low frequency vibration system and cutter systems workpiece in vibration, they sometimes hasten far, sometimes approach, produce an equal and opposite effect reaction. In vibration process, when the workpiece and tool is far, far and cutting force F hasten workpiece displacement direction is same, wrought for positive system obtain input energy E (+), when the workpiece is approaching the knives cutting force F with workpiece displacement direction opposite approach, wrought negative, system energy consumption E (-), in turning process, by various factors are likely to cause periodic change, cutting force and make F > F is far reaching, E (+) > E (-), namely in each vibration cycle, the workpiece (or cutting force of cutter) of reactive power is always greater than it is (or tool) workpiece of reactive power, thereby negative (or tool) obtain workpiece self-excited vibration energy supplement.
In turning process, the influence periodically change, cutting force and make F > F cut out the situation has the following factors:
2.1 Cutting and tool relative motion produces friction. When in processing toughness steel with radial cutting component F began cutting speed increases, a speed since the beginning, with cutting speed decreases. According to the principle that cutting Fv mainly depends on the radial cutting component of cutting and tool relative motion, namely, the friction produced before cutting and tool the friction sword. Friction varies with the increase of friction velocity decreases characteristics, namely negative friction properties. In mechanical system, which has negative friction properties of the system is easy to stimulate cutting vibration.
2.2 Regeneration of workpiece before cutting in turn left when a trace of vibration caused by cutting thickness cyclical change, thus affecting the cycle of cutting force change. Say commonly, after turn (after the chatter marks cutting times) relative to turn (previous) before cutting of chatter marks will not synchronous, they always have a poor phase in a vibration value phi, in the period of chatter marks, Ycos omega curve Yn = t, Y n (t) on the phase lag in previous Yn - 1 (t) namely 0 < phi < PI, it can be seen in a half cycle of vibration is thicker than the average cutting vibration one half of the cycle, and the average cutting out the thickness of vibration cutting force the work done is greater than cutting force vibration person doing negative power, the system will have energy input, vibration could be maintained. So Yn advance than Yn - 1, then just usually situation and lag contrary.
2.3 Vibration, the relative motion trajectory tip is a shape and position is not very stable, close approximation of the ellipse. This is the case in turning thread or with wide blade knife (blade width less than pitch) turning square teeth when a circular thread, this easy to produce a turn cutting and cutting surface before a turn absolutely no overlap. With the phase difference for elliptic track changes caused periodic changes, thus block, resulting in cutting force cyclical change.
2.4 In cutting tool and workpiece encountered from different levels of metal sclerosis, thus make cutting force in change. In addition, the vibration process tool actual geometry Angle cyclical changes can also cause periodic changes of cutting force.
3. The vibrating measures from the above analysis, we can conclude that system is occurring chatter, already and cutting cutting process with process system and related to the structure stiffness, aiming at the characteristics of vibration related, especially corresponding vibrating measures.
3.1 In the low frequency vibration, mainly because the vibration caused Y direction change of cutting force, he gets F > F is far reaching, which produced vibration. Therefore, in addition to increasing system in the direction of the Y stiffness and damping, try to reduce the Fy and any stop cutting component of the workpiece and along the direction of tool relative displacement of y. factors, usually can weaken or eliminate vibration. Main can adopt the following measures:
(1) Turning time, generally when v = 30 ~ 70m/min speed range, easy to produce the vibration, so choose turning speed cutting force should avoid appear with the slower speed area, or low range in high-speed cutting vibration very not easy the creation,.
(2) Avoid scraps wide and thin, otherwise susceptible to the cutting vibration. In the permission cases (such as machine tools have enough rigidity, enough motor power, surface roughness of workpiece reference when less demanding, etc), suitable enlargement of feeding and reduce cutting depth also help curb vibration.
(3) Suitable enlargement of cutting tools rake Angle gamma can reduce vibration Fy force, thereby deadening. But in cutting speed higher range, the influence of vibration anterior horn, so high speed will weaken the negative rake Angle cutting and not produce strong vibration. Usually adopt double ventral horn vibrating knife, use figure 1 front width f to control tool and cutting contact, can significantly reduce length of cutting force, thus inhibiting vibration. 1 > 0 speed, high speed gamma gamma 0 when < 0, 1 and gamma gamma 2 ° between 15 difference
(4) hen cutting depth and feeding unchanged, as the Lord PianJiao K gamma increases, cutting Fy reduced. Bit Therefore, suitable enlargement PianJiao, can eliminate tool Lord or reducing the vibration.
(5) tool back Angle is too big or too sharp blade, cutting artificially pieces, easy to produce the vibration. When the reduced to 2 ° ~ 3 °, vibration significantly weakened. Behind the tools for a grinding out negative chamfering, as figure2shows, about 0.1-0.3 mm negative chamfering, can reduce the radial vibration cutting force and inhibition.
(6) Cutter system if have negative stiffness brings, easy "chew vibration generation" workpiece. So, as far as possible to avoid the negative stiffness cutting system turning vibrations.
3.2 Workpiece system and cutting system stiffness not produce low-frequency vibration, can adopt the main reason the measures to eliminate or reduce vibration:
(1) use three claws or four claw clamping workpiece as possible to make the work rotary center and the coaxial tolerance spindle center minimum error, avoid workpiece tilt concentres cutting or uneven cutting caused periodic changes of cutting force generated vibration.
(2) processing slightness shaft with cutter, center when worn can increase cutting process stability.
(3) when in turning using elastic and did not use top dead center, avoid excessive jacking force caused by jacking force bending or size of workpiece within less than supporting role to make the work and note the tailstock swinging stretch not too long sleeve suspension.
(4) regular inspection towing plate and big dragging plate, small cutter and dragging plate in the contact between coattails "guide, adjust good inclined set a gap and avoid cutter moves appeared to crawl. In addition, can scrape, enhance the surface grind coupling coupling stiffness method to improve the system of construction ant-vibration sex.
(5) arrange main cutting force direction, such as cutting and cutting, because the workpiece reverse the direction of cutting force and maximum rigidity direction to converge system will increase the stability of the system.
3.3 high frequency vibration frequency is very high, noise, Wilder in surface processing by the traces of fine and dense, vibration, just cutting tools in vibration, and workpiece itself is very stable and machine components. Its causes is due to face after bigger, tool wear sword behind and between the workpiece drop caused friction performance to eliminate or reduce high frequency vibration, the major measures are as follows: (1) the length decreases suspension stretch tools.
(2) strengthening the lathe tool and flexural stiffness of tool rod.
(3) change in time after cutting knife surface wear larger.
(4) installed knives, should guarantee the knife rod and workpiece rotate center to vertical, tighten the insertion force evenly to avoid tool rod imbalance and bending vibration generation.
(5) using damping device.
4. Closing through this a series of aimed at turning process produces different vibration, on the analysis of vibration causes the measures taken after the response, can obviously reduce the vibration, enhances turning process of workpiece surface quality and productivity and prolong the service life of cutting tools.
references
[1]. Turner technicians, skills ChenYu [M].beijing: China's labor and social security press. 2003.
[2] PengDe shadow. Turner technology and skills training [M].beijing: China labor social security press, 2001.
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淺論車削加工中的振動與控制
???作者：蘭文清 ?
【摘要】在機械加工中產(chǎn)生的振動都具有受迫振動和自激振動，與機床、夾具、刀具和工件組成的工藝系統(tǒng)的動態(tài)特性有關(guān)。詳細分析了車削加工中振動的主要類型及產(chǎn)生的原因、振動的危害，并從刀具、夾具、切削工藝等方面提出了減小或消除振動的措施。
?【關(guān)鍵詞】車削低頻振動;高頻振動;消除措施
??????? 前言
? 在車削過程中產(chǎn)生的振動，不僅干擾了正常的切削過程，嚴重影響了加工件的表面質(zhì)量，還會縮短機床及刀具使用壽命。由此產(chǎn)生的噪音甚至可能影響到操作者工作情緒，對正常工作的開展帶來一定負面影響；而為了減少振動，往往不得不減少加工時的進刀量，從而降低了生產(chǎn)率。本人通過在工作中對這一現(xiàn)象不斷觀察、分析、實踐、總結(jié)，取得了一些效果，現(xiàn)提出一些看法供大家探討。
1. 振動的分類一般來講，在機械加工中產(chǎn)生的振動都具有受迫振動和自激振動，與機床、夾具、刀具和工件組成的工藝系統(tǒng)的動態(tài)特性有關(guān)。在消除機床回轉(zhuǎn)組件(如電機、工件、旋轉(zhuǎn)軸等)和傳動系統(tǒng)(如皮帶輪、滾動軸承、液壓傳動系統(tǒng)的壓力脈沖等)的振動后，車削加工中的振動主要是不隨車削速度變化的自激振動，主要是車削過程中工件系統(tǒng)的彎曲振動(其頻率接近工件的固有頻率的低頻振動)和車刀的變形產(chǎn)生的彎曲振動(其振動頻率接近車刀的固有頻率的高頻振動)。
??????? 2. 振動原因分析低頻振動的振動頻率較低，通常發(fā)出的噪音比較低沉，振動較為劇烈，在加工表面留下的振動痕跡深而寬。在低頻振動時通常工件系統(tǒng)和刀架系統(tǒng)都在振動，它們時而趨遠，時而趨近，產(chǎn)生大小相等方向相反的作用和反作用力。在振動過程中，當(dāng)工件與刀具趨遠時，切削力F趨遠與工件位移方向相同，所做之功為正值，系統(tǒng)獲得輸入能量E(+)，當(dāng)工件趨近刀具時，切削力F趨近與工件位移方向相反，所做之功為負值，系統(tǒng)消耗能量E(-)，在車削過程中，由于各種因素的影響都可能引起切削力周期性的變化，并使F趨遠>F趨近，E(+)>E(-)，即在每一振動周期中，切削力對工件(或刀具)所做之正功總是大于它對工件(或刀具)所做之負功，從而使工件(或刀具)獲得能量補充產(chǎn)生自激振動。
??????? 在車削過程中，影響切削力周期性地變化，并使F退出>F切人的情況有以下幾個因素：
??????? 2.1切削與刀具相對運動產(chǎn)生的摩擦力。在加工韌性鋼材時徑向切削分力F開始隨切削速度的增加而增大，自某一速度開始，隨切削速度的增加而下降。據(jù)切削原理可知，徑向切削分力Fv主要取決于切削與刀具相對運動產(chǎn)生的摩擦力，即切削與刀具前刀面的摩擦力。摩擦力具有隨摩擦速度的增加而下降的特性，即負摩擦特性。在機械系統(tǒng)中，具有負摩擦特性的系統(tǒng)容易激發(fā)切削振動。
??????? 2.2再生切削時因工件在前一轉(zhuǎn)時振動留下的痕跡引起切削厚度周期性的變化，從而影響切削力的周期變化。一般說，后轉(zhuǎn)(后次)切削的振紋相對于前轉(zhuǎn)(前次)切削的振紋總不同步，它們在相位上總有一個差值φ，在一個振動周期中，對振紋曲線Yn =Ycosωt，Y n(t)在相位上滯后于前次的Yn-1(t)即0<φ<π的情況，可以看出，在振出的半周期中的平均切削厚度大于振人的半周期中的平均切削厚度，于是振出時的切削力所做的功大于振人時切削力所做的負功，系統(tǒng)就會有能量輸人，振動就有可能得以維持。于是Yn比Yn-1超前φ的情況，則正好和滯后時的情況相反。
??????? 2.3振動時，刀尖相對運動的軌跡是一個形狀和位置都不十分穩(wěn)定的，封閉的近似橢圓。這種情況在車削螺紋或用寬刃刀(刃寬小于螺距)車削方牙螺紋的外圓時易產(chǎn)生，這時后一轉(zhuǎn)的切削與前一轉(zhuǎn)切削表面完全沒有重疊。因橢圓軌跡隨相位差變化而變化，從而引起切削面周期性變化，最終引起切削力周期性的變化。
??????? 2.4刀具在切人和退出工件時所遇到的金屬硬化程度不同，從而使切削力在變化。除此以外，振動過程中刀具實際幾何角度周期性改變也會引起切削力的周期性變化。
??????? 3. 消振措施由上面的分析可知，系統(tǒng)是否發(fā)生切削顫振，既與切削過程有關(guān)，又與工藝系統(tǒng)的結(jié)構(gòu)剛度有關(guān)，針對振動的特點，特提出相應(yīng)的消振措施。
??????? 3.1在低頻振動時，主要是由于Y方向的振動引起了切削力的變化，便得F趨遠> F趨近，而產(chǎn)生了振動。因此，除了增加系統(tǒng)沿Y方向的剛度及阻尼外，設(shè)法減少切削分力Fy及任何阻止工件與刀具沿Y方向的相對位移的因素，通常都能減弱或消除振動。主要可采取下面幾種措施：
(1)車削時，一般當(dāng)v=30～70m／min速度范圍內(nèi)，容易產(chǎn)生振動，因此選擇車削速度時應(yīng)避開出現(xiàn)切削力隨速度下降的中速區(qū)，在高速或低速范圍進行切削，自振極不易產(chǎn)生。
??????? (2)應(yīng)盡量避免寬而薄的切屑的切削，否則極易產(chǎn)生振動。在許可的情況下(如機床有足夠的剛度，足夠的電機功率，工件表面粗糙度參考值要求較低時等)，適當(dāng)增大進給量和減小切削深度也有助于抑制振動。
??????? (3)適當(dāng)增大刀具前角γ可減小Fy力，從而減弱振動。但在切削速度較高的范圍內(nèi)，前角對振動的影響將減弱，所以高速下采用負前角切削，不致產(chǎn)生強烈的振動。通常采用雙前角消振刀，利用圖1前面的寬度f來控制刀具和切削的接觸長度，可顯著減小切削力，從而抑制振動。低速時γ1>0，高速時γ0<0，γ1與γ2之間相差15°
??????? (4)當(dāng)切削深度和進給量不變時，隨著主偏角Kγ增大，切削分力Fy減少。因此，適當(dāng)增大刀具主偏角，可以消除或減小振動。(5)刀具后角太大或刀刃過分鋒利，刀具切人工件時，容易產(chǎn)生振動。當(dāng)后角減小到2°～3°時，振動有明顯的減弱。在刀具后面磨出一段負倒棱，如圖2所示，約0．1-0．3mm負倒棱，可以減小徑向切削力和抑制振動。
(6)刀架系統(tǒng)如果有負剛度是時，容易“啃人”工件產(chǎn)生振動。因此，盡可能避免刀架系統(tǒng)的負剛度對車削產(chǎn)生的振動。
??????? 3.2工件系統(tǒng)和刀架系統(tǒng)的剛度不是產(chǎn)生低頻振動的主要原因，可采取下面的措施來消除或減小振動：
(1)用三爪或四爪夾緊工件時盡可能使工件回轉(zhuǎn)中心和主軸回轉(zhuǎn)中心的同軸度誤差最小，避免工件傾斜而斷續(xù)切削或不均勻切削造成切削力的周期性變化所產(chǎn)生的振動。
(2)加工細長軸時用跟刀架、中心架可以增加切削過程穩(wěn)定性。
(3)在車削時采用彈性頂尖而不采用死頂尖，避免頂力過大造成工件彎曲或頂力大小起不到支承作用使工件擺動，并注意尾座套筒懸伸不能過長。
(4)定期檢查中拖板和大拖板、小刀架與中拖板之間燕尾導(dǎo)軌的接觸情況，調(diào)整好斜鑲條間隙，避免刀架移動時出現(xiàn)爬行。另外，可以用刮研聯(lián)結(jié)表面，增強聯(lián)結(jié)剛度等方法來提高結(jié)構(gòu)系統(tǒng)的抗振性。
(5)合理安排主切削力的方向，比如在切斷和工件反轉(zhuǎn)切削時，由于切削力的方向與系統(tǒng)最大剛度方向趨于一致會提高系統(tǒng)的穩(wěn)定性。
??????? 3.3高頻振動振動頻率很高，產(chǎn)生的噪音尖銳刺耳，在加工件表面留下的痕跡細而密，振動時只是刀具本身在振動，而工件及機床部件卻很穩(wěn)定。其產(chǎn)生的主要原因是由于后刀面磨損較大，刀具后面與工件之間摩擦的下降性能引起的，消除或減小高頻振動的措施主要有：(1)減小車刀懸伸長度。
(2)加強車刀及刀桿的抗彎剛度。
(3)及時更換后刀面磨損較大的刀具。
(4)裝刀具時，應(yīng)保證刀桿與工件旋轉(zhuǎn)中心垂直，緊固時要施力均勻，避免刀桿受力不平衡而彎曲產(chǎn)生振動。
(5)使用減振裝置。
??????? 4. 結(jié)束語通過這一系列針對車削過程中產(chǎn)生的不同振動，在分析產(chǎn)生振動的原因后采取響應(yīng)的措施，可明顯減小車削過程中的振動，提高了工件表面質(zhì)量和勞動生產(chǎn)率，延長了刀具的使用壽命。
參考文獻
［1］陳宇．車工技師、技能［M］．北京：中國勞動和社會保障出版社．2003．
［2］彭德蔭．車工工藝與技能訓(xùn)練［M］．北京：中國勞動社會保障出版社，2001．