機械專業(yè)論文外文翻譯

1、英文原文gear manufacturing methodsthere are two basic methods of manufacturing gear teeth: the generating process and the forming process, when a gear tooth is generated, the workpiece and the cutting or grinding tool are in continuous mesh and the tooth form is generated by the tool. in other words, th

2、e work and the tool are conjugated to each other, hobbing :machines, shaper cutters, shaving machines, and grinders use this principle.when a gear tooth is formed, the tool is in the shape of the space that is being machined out. some grinding machines use this principle with an indexing mechianism

3、which allows the gear teeth to be formed tooth by tooth. broaches are examples of form tools that machine all the gear teeth simultaneously.shapingshaping is inherently similar to planning but uses a circular cuttrer instead of rack and the resulting reduction in the reciprocating inertia allows muc

4、h higher stroking speeds: modern shapers cutting car gears can run at 2,000 cutting strokes per minmute. the shape of the cutter is roughly the same as an involute gear but the tips of the teeth are rounded.the generating drive between cutter and workpiece does not involve a rack or leadscrew since

5、only circular motion in involved the tool and workpiece move tangential typically 0.5 mm for each stroke of the cutte匚 on the return stroke the cutter must be retracted about 1 mm to give clearance otherwise tool mb occurs on the backstroke and failure is rapid. the speed on this type of machine is

6、limited by the rate at which some 50kg of cutter and bearings can be moved a distance of 1 mm. the accelerations involved tequire forces of the order of 5000n yet high accuracy must be maintained.are that production rates are relatively high and that itis possible to cut right up to a shoulder. unfo

7、rtunately, for helical gears, a helical guide is required to impose a rotational motion on the stroking motion; such helical guides cannot be produced easily or cheaply so the method is only suitable for long runs with helical gears since special cutters and guides must be manufactured for each diff

8、erent helix angle. a great advantage of shaping is its ability to annular gears such as those required for large epicyclic drives.when very high accuracy is of importance the inaccuracies in the shaping cutter matter since they may transfer to the cut gear. it is obvious that profile errors will tra

9、nsfer but it is less obvious than an eccentrically mounted or ground cutter will give a characteristic "dropped tooth”. there are several causes for "dropped tooth” but it occurs most commonly when the diameter of the workpiece is about half, one and half, two and a half, etc, times the cu

10、tter diamete匚 if the cutter starts on a high point and finishes on a low point during the final finishing revolution of the gear the peak to peak eccentricity errors in the cutter occurs between the last and the first tooth of the final revolution of the cut gear; as the cumulative pitch error of th

11、e cutter may well be over 25 microns there is a sudden pitch error of this amount on the cut gea匚 the next gear cut on the machine may however be very good on adjacent pitch if the final cut happened to start in a favorable position on the cutter.various attempts have been made to prevent this effec

12、t, in particular by continuing rotation without any further cutter infeed but if the shaping machine is not very rigid and the cutter very sharp then no further cutting will occur and the error will not be removed.hobbinghobbing, the most used metal cutting method, uses the rack generating principle

13、 but avoids slow reciprocation by mounting many “racks ” on a rotating cutter. the "racks” are displaced axially to form a gashed worm. the tacks” do not generate the correct involute shape for the whole length of the teeth since they are moving on a circular path and so the hob is fed slowly a

14、long the teeth either axially in normal or in the direction of the helix in "oblique” hobbing.metal removal rates are high since no reciprocation of hob or workpiece is required and so cutting speeds of 40 m/min can be used for conventional hobs and up to 150m/min for carbide hobs. typically wi

15、th a 100mm diameter hob the rotation speed will be loorpm and so a twenty tooth workpiece will rotate at 5 rpm. each revolution of the workpiece will correspond to 0.75mm feed so the hob will advance through the workpiece at about 4mm per minute. for car production roughing multiple start hobs can b

16、e used with coarse feeds of 3mm per revolution so that 100 rpm on the cutter, a two-start hob and a 20 tooth gear will give a feed rate of 30mm/minute.the disadvantage of a coarse feed rate is that a clear marking is left on the workpiece, particularly in the root, showing a pattern at a spacing of

17、the feed rate per revolution. this surface undulation is less marked on the flanks than in the root and is not important when there is a subsequent finishing operation such as shaving or grinding when there are no further operations the feed per revolution must be restricted to keep the undulations

18、below a limit which is usually dictated by lubrication conditions. the height of the undulations in the root of the gear is given by squaring the feed per revolution and dividing by four times the diameter of the hob; 1 mm feed and 100mm diameter gives 2.5 micron high undulations in the root. on the

19、 gear flank the undulation is roughly cos70 as large, ie, about 0.85 micron.accuracy of hobbing is normally high for pitch and for helix, provided machines are maintained; involute is dependent solely on the accuracy of the hob profile. as the involute form is generated by as many cuts as there are

20、gashes on the hob the involute is not exact, but if there are, say, 14 tangents generating a flank of 20 mm radius curvature about 4 mm high the divergence from a true involute is only about half a micron; hob manufacturing and mounting errors can be above 10 microns use of twostart hobs or oblique

21、hobbing gives increased error levels since hob errors of pitching transfer to the cut gear.broachingbroaching is not used for helical gears but is useful for internal spur gears; the principal use of broaching in this context is for internal splines which cannot easily be made by any other method as

22、 with all broaching the method is only economic for large quantities since setup costs are high.the major application of broaching techniques to helical external gears is that used by gleasons in their g-trac machine .this machine operates by increasing the effective radius of a hobbing cutter to in

23、finity so that each tooth of the cutter is traveling in a straight line instead of on a radius. this allows the cutting action to extend over the whole facewidth of a gear instead of the typical 0.75 mm feed per revolution of hobbing. the resulting process gives a very high production rate , more su

24、itable for u.s.a, production volumes than for the relatively low european volumes and so, despite a high initial cost ,is very competitive.broaching give high accuracy and good surface finish but like all cutting processes is limited to "sofv' materials which must be subsequently caseharden

25、ed or heat treated, giving distortion.shavinga shaving cutting cutter looks like a gear which has extra clearance at the root and whose tooth flanks have been grooved to give cutting edges. it is run in mesh with the rough gear with crossed axes so that there is in theory point contact with a relati

26、ve velocity along the teeth giving scraping action. the shaving cutter teeth are relatively flexible in bending and so will only operate effectively when they are in double contact between two gear teeth. the gear and cutter operate at high rotational speeds with traversing of the workface and about

27、 100 mm micron of material is removed cycle times can be less than half a minute and the machines are not expensive but cutters are delicate and difficult to manufacture. it is easy to make adjustments of profile at the shaving stage and crowning can be applied. shaving can be carried out near a sho

28、ulder by using a cutter which is plunged in to depth without axial movement; this method is fast but requires more complex cutter designgrindinggrinding is extremely important because it is the main way hardened gear are machined. when high accuracy is required it is not sufficient to pre-correct fo

29、r heat treatment distortion and grinding is then necessary-the simplest approach to grinding, often termed the orcutt method. the wheel profile is dressed accurately to shape using single point diamonds which are controlled by templates cut to the exact shape required; 6:1 scaling with a pantograph

30、is often used the profile wheel is then reciprocated axially along the gear which rotates to allow for helix angle effects; when one tooth shape has been finished, involving typically 100 micron metal removal the gear is indexed to the next tooth space this method is fairly show but gives high accur

31、acy consistently. setting up is lengthy because different dressing templates are needed if module, number of teeth, helix angle, or profile correction are changedthe fastest grinding method uses the same principle as hobbing but replaces a gashed and relieved worm by a grinding wheel which is a rack

32、 in section. since high surface speeds are needed the wheel diameter is increased so that wheels of 0.5 m diameter can run at over 2000 rpm to give the necessary 1000 m/min. only single start worms are cut on the wheel but gear rotation speeds are high j 00 rpm typically, so it is difficult to desig

33、n the drive system to give accuracy and rigidity. accuracy of the process is reasonably high although there is a tendency for wheel and workpiece to deflect variably during grinding so the wheel form may require compensation for machine deflection effects. generation of a worm shape on the grinding

34、wheel is a slow process since a dressing diamond or roller must not only form the rack profile but has to move axially as the wheel rotates. once the wheel has been trued, gears can be groundrapidly until redressing is required. this is the most popular method for high production rates with small ge

35、ar and is usually called the reishauer method.large gears are usually generated by the maag method which is similar to planning in its approach but uses cup grinding wheels of large diameter to form the flanks of the theoretical mating rack. gears of very large diameter cannot easily be moved so the

36、 gear is essentially stationary while the grinding wheel carriage reciprocates in the direction of the helix. the wheel is only in contact over a small part of the facewidth in helical gears so this is not important when only a few gears of this size are made in a yean as with form grinding, after g

37、rinding a pair of flanks the gear is indexed to the next pai匚a similar method used for medium size gears has stationary wheels, while the rough gear is traversed under the wheels. corresponding rotational movement of the gear is controlled by steel bands unwrapping from a cylinder of pitch circle di

38、ameter so that the motion of gear relative to urack is correct.another method, the nile approach, uses a wheel which is formed to give the "theoretical mating rack instead of using two cup wheels as in the maag method this approach is best suited to medium precision work on smaller gears and is

39、 intermediate in speed between the reishauer and maag methods.all grinding processes are slow and costly compared with cutting processed and so are only used when accuracy is essential a rough rule of thumb is that grinding will increase gear cutting costs by a factor of 10 but the cost of the teeth

40、 is often only a small part of the total cost of a gearbox. the accuracies attainable are surprisingly not very dependent on size of gear ; whether a gear is 5 m or 50 m diameter the pitch involute and helix accuracies attainable are of the order of 5 microns or better and more dependent on the skil

41、l and patience of the operator and inspectors than on any other factors.it is often assumed that grinding will remove all error generated at the roughing stage. unfortunately, grinding machines are relatively flexible and so the grinding wheel has a tendency to follow previous errors. the errors wil

42、l thus be reduced but not completely eliminated unless very many cuts are used; whenever a grinding process is giving in consistent results it is advisable to check the accuracies at the rough-cut stage. the only exception is the form grinding process which will not follow involute errors though it

43、will still allow helix and pitch errors.中文譯文齒輪的加工方法加工齒輪輪齒有対種基木的方法：產(chǎn)生過程和形成過程。當(dāng)一個輪齒產(chǎn)生時， 工件和切削或磨削工具，是不斷嚙合在一起的，輪齒的形式是由刀具決定的。換句 話說，工件和刀具是共軌的。滾齒機，成型切割機，剃齒機，磨床都使用這個原理。當(dāng)一個輪齒形成時，該刀具是星正被加工出來的宇間的形狀的。一些磨床使用 此原理，與一個指示裝置配套在一起使輪齒一個挨一個形成。刀就是同時加工所有 輪齒形成刀具的例子。成型成型本質(zhì)上是與平面圖類似的，但采用了圓形的切削刀具替代了齒條，由此產(chǎn) 生的往復(fù)慣性的減少，允許更高的行程速度：現(xiàn)

44、代的成型切割汽車齒輪可以以每分 鐘2000切割行程運行。切削刀具的形狀大致是與漸開線齒輪相同的，但輪齒的頂端 是圓形的。切削刀具和工件z間的發(fā)電驅(qū)動器z間不涉及機架或連接螺釘，因為只有圓周 運動在涉及的范圍內(nèi)。切割機每走一個行程，工具和工件通常在切線方向移動0.5 毫米。在返回的行程屮，刀具必須被縮進約1毫米留有間隙，否則就會產(chǎn)生摩擦， 馬上發(fā)生故障。這類型機床的速度被限制，保證大約50千克重的切割機和軸承可移 動1毫米的距離。加速度所涉及的扭矩可增加5000n的力，但必須保持高的精度。成型機的優(yōu)點是生產(chǎn)效率相對較高，可能在齒頂上切出直角。不幸的是，對于 斜齒輪，螺旋導(dǎo)向器需耍在直線運動屮施加

45、旋轉(zhuǎn)運動，這種螺旋導(dǎo)向器不容易生產(chǎn), 也不便宜。所以該方法只適合在斜齒輪上的長距離，因為對每個不同的螺旋角就要 生產(chǎn)特殊的刀具和導(dǎo)向器。成型機的一個很大的優(yōu)點，是它可以生產(chǎn)環(huán)形齒輪，例 如那些需要大型epicyclie周轉(zhuǎn)圓的驅(qū)動器。非常高的精確度是十分重要的，而成型切割機的不準確性也是相當(dāng)要緊的。因 為它們可能轉(zhuǎn)移到削減齒輪。很明顯側(cè)面的錯誤將轉(zhuǎn)移，但比起離心機或破碎機給 予的特點，“掉落的輪齒”，是相當(dāng)不明顯的。對于掉齒有兒個原因，但它發(fā)生 最頻繁的是，當(dāng)工件的直徑大約是刀具直徑的一半，15倍或2. 5倍時。如杲刀具 開始在高點，在最后完成漸開線齒輪期間結(jié)束在低點，在刀具上峰與峰的偏心誤弟

46、 發(fā)生在最后的漸開線切割齒輪的第一個和最后一個齒輪z間。當(dāng)?shù)毒叩睦鄯e螺距誤 差可能剛好超過25微米時，切割輪齒時就會有一個突然的這個數(shù)量的螺距誤差。在 機床上切割的下一個齒輪可能在鄰近的節(jié)圓上是好的，如果在切割機上最后的切割 碰巧發(fā)生在一個有利的位置。各種嘗試已經(jīng)作岀，防止這種效應(yīng)，特別是通過連續(xù)旋轉(zhuǎn)，沒有任何進一步的 刀料，但如果成型機是不是很堅固，刀具不是很尖銳，然后沒有進一步的切割發(fā)生, 誤差將不會被消除。滾齒滾齒是最常用的金屬切削方法，使用機架產(chǎn)生的原理，但避免了由在旋轉(zhuǎn)切削 機上增加許多齒條引起的緩慢的往復(fù)運動。齒條在軸線方向上替換為切口蝸桿。齒 條不能為整個輪齒的工作長度產(chǎn)生正確的

47、漸開線形狀，因為他們在圓弧軌跡上移動, 所以滾刀緩慢地沿輪齒走刀，在軸向或法向或傾斜的滾齒機螺旋線方向上。金屬去除率高，因為螺旋銃刀或工件沒有做往復(fù)運動的需要，所以40m/min的 切割速度可用于傳統(tǒng)的滾刀,切割速度高達150m/min的用于硬質(zhì)合金滾刀。通常一 個宜徑為100毫米的滾刀轉(zhuǎn)速達到loorpm , w 20個齒的工件以每分鐘5轉(zhuǎn)的速 度旋轉(zhuǎn)。工件的每個旋轉(zhuǎn)運動將對應(yīng)于0. 75毫米的進給量，所以滾刀會提前通過工 件約每分鐘4毫米。對于汽車生產(chǎn)，近似多頭開始的滾刀，可用于每轉(zhuǎn)3毫米的粗 糙進給量，以便在切割機上達到loorpm的速度，一個兩頭開始的滾刀和20個齒的 齒輪可提供每分鐘

48、30毫米的進給速率。粗糙進給速率的缺點是在工件上會留卜明顯的標(biāo)志，尤其是在齒根，每轉(zhuǎn)在進 給速率的空間顯示一種圖案。齒側(cè)標(biāo)記的表面波紋比齒跟要少，當(dāng)有一個隨后的整 理操作時，如剃齒或磨削，這一點就不重要了。當(dāng)沒有進一步的操作時，每轉(zhuǎn)的進 給量必須加以限制，保證粗糙度在一個界限以下，通常這決定于潤滑條件。齒根上 波紋的高度指定乘以每轉(zhuǎn)的進給量，然后除以滾刀直徑的4倍。1毫米的進給量和 100毫米的直徑可產(chǎn)生2. 5微米高的波紋。對齒側(cè)波紋大約跟cos70 一樣人，即約 0. 85微米。滾齒機的精度對齒距和螺旋線來說，通常很高，假設(shè)機床維持不變，漸開線單 單決定于滾刀齒廓的精度。漸開線的形式隨著滾

49、刀的切入產(chǎn)生，在滾刀上留有裂痕 時，漸開線是不真實的。但是，如果說有14條切線產(chǎn)生在曲率半徑約20毫米的齒 側(cè)，從真實的漸開線分離，僅僅人約0.5微米。滾刀的制造和安裝誤差可以超過10 微米。使用兩頭開始的滾刀或斜滾齒機可增加誤差水平，因為滾刀的齒距誤差的轉(zhuǎn) 移到切割齒輪上。拉削拉削不被用于斜齒輪，但對內(nèi)齒直齒輪時十分有用的。聯(lián)系全局來看，拉削的 最重要的用途是用任何其他的方法都不容易加工的內(nèi)花鍵。跟所有的拉削方法一樣, 這種方法對批量生產(chǎn)是經(jīng)濟的，因為安裝成本較高。拉削技術(shù)對內(nèi)齒斜齒輪主要的應(yīng)用是由g1 easons在其g-trac機床上。這臺機器的 運作，增加滾齒切割機的有效半徑至無限遠，使刀具的每一個齒都能在一條直線上 轉(zhuǎn)動，而不是對在一個半徑上。這使得切割行為延長超過齒輪的整個端面寬度，替 代了傳統(tǒng)的滾刀每轉(zhuǎn)0.75毫米的進給量。由此產(chǎn)生的過程中提供了非常高的生產(chǎn) 率，更適合于美國，美國的產(chǎn)量在整個歐洲來說，相對較低，盡管初始成本高，但 非常具有競爭力。拉削提供了較高的精確度和良好的表面光潔度，但象所有切削過程一樣，僅限 于“軟”材料，必須隨后進行表面淬火