外文翻譯--高速銑削鋁合金工件腹板的走刀策略

1、<p><b>　　中文3428字</b></p><p>　　畢業(yè)設計(論文)外文資料翻譯</p><p>　　學院 (系)： 機械工程學院 </p><p>　　專 業(yè)： 機械工程及自動化 </p><p>　　姓 名：

2、 </p><p>　　學 號： </p><p>　　外文出處：S.Smith&D.Dvorak. Tool </p><p>　　Path strategies for high speed mill

3、ing</p><p>　　Aluminum workpieces with thin webs. </p><p>　　Mechatronics, 1998 (8) :291-300 </p><p>　　附 件： 1.外文資料翻譯譯文；2.外文原文。</p><p>　　注：請將該封面與附件裝訂成冊。</p><

4、;p>　　附件1：外文資料翻譯</p><p>　　高速銑削鋁合金工件腹板的走刀策略</p><p>　　S Smith, D Dvorak</p><p><b>　　摘 要：</b></p><p>　　本論文描述了關于高速銑削有薄壁彈性框架的鋁合金結構件方法的研究?？蝮w腹板是在銑刀的端面產(chǎn)生的薄壁結構，而與之

5、相對的側壁是在端銑刀的外圍產(chǎn)生的薄壁結構。高速加工實體工件中帶有薄壁腹板和側壁的零件是一種快速發(fā)展中的制造技術。采用了高速加工，現(xiàn)在可以經(jīng)常用功能相等的，比較輕且便宜的整體結構來取代復雜而貴重的金屬片組合。然而，生產(chǎn)這樣的整體結構所需的刀具定位和路徑卻不是很明顯。而且使用現(xiàn)有的商業(yè)數(shù)控程序也不容易得到刀具路徑。</p><p><b>　　正 文</b></p><p&g

6、t;　　本論文描述了關于高速銑削有薄壁彈性框架的鋁合金結構件的方法研究?？蝮w腹板是在端銑刀的面產(chǎn)生的薄壁結構,就像相對的側壁是在端銑刀的外圍產(chǎn)生的薄壁結構。為了生產(chǎn)更強的，更輕的，更便宜的零部件，高速加工實體工件中帶有薄壁腹板和側壁的零件的方法正在迅速取代原來的裝配工序。原來被用做裝配的薄壁部分零配件的部件現(xiàn)在可以使用高速加工而做成更廉價，且功能相等的整體結構。整體結構可以更強，更輕, 比與他們同等功能的裝配更精確。由于列入清單的零配件

7、的減少，以及零配件裝配工序的去除和鉆模，夾具，檢查樣板等后續(xù)裝配時間的減少（盡可能的高精度），整體零配件就會比金屬片組合更便宜。市場的競爭也需要高速加工技術和高的金屬去除率。</p><p>　　高速加工薄壁零配件被廣泛使用的一個主要限制就是加工操作的安全性。顯而易見的是，當側壁和腹板變得越來越薄時，剛性將會減少，而且顫動也會變得更棘手。在這些部件加工中的顫動能對零件造成毀壞 (特別是切斷薄壁結構) 或者至少對需

8、要手動清理的表面質(zhì)量造成損傷。這篇論文就是描述依托于不加工件來進行薄壁腹板加工的策略的發(fā)展。</p><p><b>　　前期工作</b></p><p>　　在薄壁加工中涉及的問題已經(jīng)被 Tlusty ，Smith和 Winfough 所描述[1]，</p><p>　　正如 Fig.1 所示，,他們指出在一系列的軸向路徑中薄壁應該用怎樣的刀

9、具來加工,刀桿的上面部分較下面更細。這樣，加工只在側壁剛性最好的下面進行,而上面易曲部分就不會有在側壁和刀具刃口之間的無端接觸。一些其他的作者已經(jīng)研究了加工腹板中的問題。Kline[2]用有限元分析方法模擬了薄板和梁的端銑,但卻靜態(tài)地考慮了問題,Altints[3]為易曲板的外圍銑削呈現(xiàn)了一個動態(tài)模型結構，但是他的實驗被很小的主軸速度范圍所限制。Rao[4]指出支撐薄框架的加工是相對簡單的。一個支撐的薄框架直接對著工作臺或一個夾具。一個

10、這樣的腹板在遠離刀尖方向是非常堅硬的。腹板也由于一個流體薄膜(典型如油)的流體靜力學作用而不會碰到刀尖部分。另外，本報告還研究了無支撐薄腹板在加工中遇到的問題。Fairman[5] 設計了一個更加任意的測試零件進行了一系列的加工測試。他通過主軸速度、刀具、軸向切深和徑向切深的組合變化進行切削試驗, 但卻沒能成功加工出一個無顫動零件。就像下面的內(nèi)容所描述的,后來的研究表明了他的測試零件比目標產(chǎn)品的薄壁結構更易曲。</p>&

11、lt;p><b>　　一個典型零件的測試</b></p><p>　　為了要進行一個典型零件的測試，五個航空器零配件產(chǎn)品被用做抽樣進行模態(tài)測試來收集動態(tài)數(shù)據(jù)，自然頻率以及模態(tài)形狀的數(shù)據(jù)。Fig 2 展示了一個在1.3毫米厚的矩形鋁框架體上測定的典型的頻率響應函數(shù) (FRF)。這個矩形框架體源自一個防水壁，面積254毫米*184 毫米。如表1所示，可以看出在這個測量中的模態(tài)動剛性從 10

12、-106 m/ MN 。標準的阻尼比從1-2%。航空器零件的產(chǎn)品抽樣全部展現(xiàn)了 10-120 m/MN 范圍的動剛性，而且比1500赫茲低5到10個自然頻率。所有腹板的阻尼比在次序上為0.5-3.0%。</p><p>　　鋁7050-T7451的一個總體的測試環(huán)節(jié)設計了一個不斷重復的程序，將不同的腹板和側壁結構用來實驗并運用有限元方法分析預測自然頻率和模態(tài)形狀。在標準的數(shù)據(jù)范圍中假定阻尼比，并計算動剛性。在Fi

13、g3中顯示的結構預見了7個1500Hz</p><p>　　時的振動模態(tài)，它們的動態(tài)剛性范圍在150-160m/MN。 Fig4表示了這個測試零件中心附近的一個節(jié)點計算的頻率響應函數(shù) (FRF)。當不特別針對任何一個檢測的產(chǎn)品零配件時,這個結構所表現(xiàn)的自然頻率和動剛性與零配件產(chǎn)品足夠接近而成為一個代表性的測試零件。</p><p><b>　　切削策略研究</b>&l

14、t;/p><p>　　在加工薄側壁時使用堅硬的不加工件來支撐正在切削中的易曲部分的技術已經(jīng)被Tlusty，Smith和Winfough所發(fā)展[1]。這種一般性的原則也能被應用到加工薄腹板，但有個最重要的區(qū)別就是后者在確定刀具方位時更多的取決于切削刀具。相比于加工側壁，當工件最明顯的變形沿著加工刀具的徑向時，腹板最明顯的變形將沿著刀具的軸方向。</p><p>　　圖5表示了在加工時工件怎樣才能

15、被用來支撐腹板。在這張圖中，刀具進給方向在頁面外。加工側壁時, 切削的寬度被刀具的直徑限制，軸向的進刀深度被傳統(tǒng)顫動理論限制。由于軸向的進刀深度被限制，需要一些軸向的走刀去完成腹板加工以達到所需的厚度。</p><p>　　為了準備總體的測試部分，及腹板加工的測試，測試零件的整個第一面和第二面的外圍腹板一起被加工到最終尺寸。然后只加工第二面的中心腹板。不切削腹板的最易曲位置被標記為“第一切痕”。見Fig 6中(a

16、)。這一個區(qū)域被用直徑19毫米</p><p>　　的刀具加工到最后深度，端銑刀的刀具路徑見Fig6(b)，加工了有全切深的一個槽孔。在槽孔加工過程中發(fā)現(xiàn)，接近腹板的自然頻率即418Hz時產(chǎn)生了顫動。</p><p>　　在槽孔加工完成之后，在Fig 6(c)中顯示的刀具路徑用來加工中心腹板的剩余部分。Y向的加工路徑長度等于刀具直徑的75%。不僅除去了在腹板內(nèi)部上的尖端，并且允許了刀具軸向

17、的自由進給, 而不是在切削中。大約75%的腹板不需要顫動就能被加工。由于顫動是在第二面上的槽孔加工期間產(chǎn)生，而不是在第一面的槽孔加工期間出現(xiàn)的，我們就可以看出顫動是由逐漸增加的工件變形所引起的。</p><p>　　為了要在槽孔加工時改良安全性，一個更小的12.7毫米直徑的端銑刀被用來加工測試零件的腹板。另外, 在易曲的位置中去除任意的徑向切削 , 一個U形的“內(nèi)</p><p>　　部槽

18、孔”從測試零件的中心腹板加工作為第一個階段，如Fig 7 所示，加工內(nèi)部槽孔時刀具在點A (見Fig 7) 鉆進, 從工件的最堅硬部分的附近進入, 而并非沿一條斜線或是直接進入易曲端。第二個測試腹板，采用直徑12.7毫米，零角半徑的端銑刀和剛剛描述的刀具路徑加工，不需要任何的顫動就可以被加工出來。然而，在刀尖圓角半徑的缺乏造成了在側壁--腹板的連接點的一個尖角。因此在側壁和腹板之間需要一個光滑的內(nèi)圓來減少應力并且避免部件的損壞。<

19、/p><p>　　為了要在側壁和腹板之間的產(chǎn)生圓弧，下一個測試零件使用一個直徑12.7 毫米，角半徑3 毫米的端銑刀以及相同的刀具路徑加工。刀具變化的結果是在周圍腹板最后切削和內(nèi)部槽孔的第一次切削上帶來顫動,( 見Fig 7)。當然，原因是切削力方向的改變,如Fig8 所舉例。角半徑使切削力在軸向方向產(chǎn)生了一個分量，這足夠影響工件引起顫動。</p><p>　　當在側壁和腹板之間的一個光滑內(nèi)圓

20、必需一個角半徑時，無法進行大量的金屬去除。事實上，使用這樣的刀具可通過減少兩次角半徑的長度在距離允許時減少金屬品的去除率(為了避開尖端)。為了用必需的光滑內(nèi)圓生產(chǎn)一個無顫動零件，一個新的測試零件用直徑12.7毫米，角半徑為零的刀具進行加工。腹板和薄壁之間的一個內(nèi)圓留下充足的加工尺寸，走刀分成四個“步驟”，0.76毫米寬的和0.76毫米高的刀具部分被留在腹板的底部，如Fig9所示，在腹板被用零角半徑刀具加工之后，用直徑12.7 毫米，角半

21、徑3 毫米的刀具來加工進一個光滑內(nèi)圓。為了使角半徑刀具避免顫動，主軸速度范圍被設定得足夠小來利用阻尼進程的優(yōu)勢。Tlusty[6]表示，當振動的波長短于3毫米時，阻尼進程就會變得活躍。產(chǎn)生的主軸速度是1629轉/分。產(chǎn)生的角半徑是無顫動的, 而且還有完美的表面質(zhì)量。</p><p>　　以不切削工件作支撐來加工的技術也可能被應用到其他不同的位置，一個略微不同的腹板設計被第七個測試零件用到。這是一個設計有1毫米厚鑄

22、造壁的雙面腹板，面積191毫米 *191毫米, 類似于沒有側壁的整體測試零件，腹板被附近的一個0.5毫米厚的鑄造壁所支撐，測試零件以15,000個轉/分的主軸速度加工，用刀具直徑12.7 毫米，角半徑3毫米的端銑刀完成加工。在加工完測試零件第一面之后，第二面從一個腹板開始切出槽孔直到最終的腹板厚度如Fig10 (a)所示，另外的四個斜坡從第一個小角度腹板開始被切出來，如Fig 10(b)所示，接下來，腹板通過同心直徑切削繼續(xù)加工。加工這

23、個測試零件時有沒有顫動是檢測的標準。</p><p><b>　　結論</b></p><p>　　為了總是切削在不加工工件的支撐架附近的底板，選擇刀具路徑來切削薄壁框架零配件是可行的。這與薄側壁加工的策略類似。在兩種情況下指導原則是選擇刀具路徑以便正在被加工的區(qū)域盡可能地被更多不加工區(qū)域支撐。對于腹板，使用一個沒有角半徑的刀具進行大部份的加工是有利的。如果在側壁和腹

24、板之間需要一個內(nèi)圓, 內(nèi)圓應被慢慢走刀接近。在操作結束的時候, 需要有角半徑的刀具來完成內(nèi)圓并用一個足夠小的主軸速度范圍產(chǎn)生阻尼進程來避免顫動。</p><p>　　不幸地是，使用現(xiàn)有的數(shù)控軟件難以實現(xiàn)采取的刀具路徑。使用者一定要進行新軟件的手動編程。</p><p><b>　　附件2：外文原文</b></p><p>　　Tool path

25、 strategies for high speed milling aluminum workpieces with thin webs</p><p>　　This paper describes an investigation into methods for high speed end milling of aluminum parts with thin, flexible webs. Webs a

26、re the surfaces created by the face of the end mill as opposed to the surfaces creted by the periphery of an end mill,which we will call ribs .in the effort to produce stronger,lighter,cheaper components,high speed machi

27、ning of parts with thin ribs and webs from a solid workpiece is rapidly replacing previous assembly operations Parts which were previously made as assem</p><p>　　A major limitation to the widespread use of h

28、igh speed machining for the production of thin components is the stability of the machining operation .It is easy to see that as the ribs and webs become thinner, the stiffnesses will decrease, and chatter will become mo

29、re problematic. Chatter during the machining of such parts can result in damage to the part (even cutting through the thin structure) or at least poor surfaces which require hand finishing. This work describes the develo

30、pment of a stra</p><p>　　Previous work</p><p>　　The problems involved in the machining of thin ribs have been described by Tlusty, Smith and Winfough [1]. As shown in Fig.1, they indicate that t

31、hin ribs should be</p><p>　　machined using relieved shank tooling, in a series of axial passes, roughing and finishing on every pass, or not finishing at all. In this way, the machining happens at the base o

32、f the rib, where it is stiffest, and the motion of the upper, flexible portion of the rib does not result in unintended contact between the rib and cutting edges of the tool. A few other authors have examined the problem

33、 of machining thin ribs. Kline[2] used the finite element method to model the plate and beam theory f</p><p>　　Development of a representative test part</p><p>　　In order to develop a representa

34、tive test part, a sampling of five production aircraft parts were subjected to modal testing to gather data on the dynamic flexibilities, natural frequencies, and mode shapes of real webs. Fig 2 shows a typical Frequency

35、 Response </p><p>　　Function (FRF) measured on a 1.3 mm thick rectangular aluminum web measuring 254 mm *184 mm on a bulkhead. As shown in Table 1,the dynamic stiffnesses of the modes </p><p>　　

36、evident in this measurement ranged from 10-106 m/MN . The measured damping ratios ranged from 1-2%. The sampling of production aircraft parts all exhibited typical dynamic stiffnesses in the range of 10-120 m/MN. and had

37、 between 5 and 10 natural frequencies below 1500 Hz. Damping ratios for all the webs were on the order of 0.5-3.0%.</p><p>　　A generic test part in aluminum 7050-T7451 was designed through an iterative proce

38、ss using finite element analysis to predict the natural frequencies and mode shapes while different web and rib configurations were tried. The damping ratios were assumed in the range of the measured data, and dynamic st

39、iffnesses were calculated. The configuration shown in Fig 3 was predicted to have 7 vibration modes under 1500 Hz with dynamic flexibilities in the range of 150-160 m/MN. Fig 4 shows a computed FRF </p><p>　

40、　Cutting strategy development</p><p>　　The technique developed by Tlusty .Smith and Winfough [1] for machining thin ribs essentially uses the stiff uncut portion of the workpiece to support the flexible sect

41、ion being cut. This general principle can also be applied to thin webs; there is a major difference in the orientation of the most significant flexibility with respect to the cutting tool. In contrast to machining thin r

42、ibs, where the most significant workpiece flexibility is oriented radially with repect to the tool, the most sig</p><p>　　Figure 5 shows how the workpiece can be used to provide support for the web during ma

43、chining. In this figure, the tool feed direction is out of the page. As with machining thin ribs, the width of cut is limited by the diameter of the tool and the axial depth of cut is limited by traditional chatter theor

44、y .As a result of the axial depth of cut limitation, several axial steps are required to finish the web to its desired thickness.</p><p>　　To prepare the generic test part, for web machining tests, the entir

45、e tests, along with peripheral web of the second side of the test part was machined to final dimension. The only machining remaining then was the center web of the second side. The most flexible location of the uncut web

46、 was the area labeled “first pass” in Fig 6(a). This region was machined to final depth using a 19 mm dia. end mill in ramp-down tool path as shown in Fig 6 (b), creating a slot to the full depth. Chatter was obs</p&g

47、t;<p>　　Following completion of the slot, the tool path shown in Fig 6(c) was used to machine the remainder of the center web. The motions in the direction were equal in length to 75% of the tool diameter. This el

48、iminated the cusp on the inside of the rib, and also allowed the axial feed to happen in air, rather than in the cut. Approximately 75% of the web was machined without chatter. Because the chatter was present during the

49、production of the slot on the second side, but was not present during the s</p><p>　　In order to improve the stability during the slot, a smaller, 12.7 mm dia end mill was used to machine the webs of subsequ

50、ent test parts. Additionally, to eliminate any unintentional axial cutting in a flexible location, a U-shaped “interior slot” was removed from the center web of subsequent test parts as a first step, as shown in Fig 7 Th

51、e interior slot involved a plunge at point A (see Fig 7), near the stiffest part of the workpiece, rather than a ramp-down or plunge at the flexible end. The </p><p>　　To produce a fillet between the rib and

52、 the web, the next test part was machined using the same tool path with a 12.7 mm dia 3 mm corner radius end mill. The result of this tool change was chatter on the last cut of the peripheral web, and on the very first c

53、ut of the interior slot (see Fig 7). Of course, the reason is the change in the orientation of cutting forces, as illustrated in Fig 8. The corner radius produces a component of the cutting force in the axial direction w

54、hich is enough to exc</p><p>　　While the corner radius is necessary to produce a smooth fillet between ribs and webs, there is no reason to use one for bulk metal removal. In fact, using such a tool decrease

55、s the metal removal rate by reducing the allowable step over distance between passes by twice the length of the corner radius (in order to avoid the cusp). To produce a chatter-free part with the required smooth fillet,

56、a new test part machined almost entirely with a 12.7 mm dia zero corner radius tool. To leave enough mat</p><p>　　low enough to take advantage of process damping. Tlusty [6] showed that process damping becom

57、es active when the wavelength of vibration is shorter than about 3 mm. The resulting spindle speed was 1629 rpm. The resulting corner radius was chatter-free, and had an excellent surface finish.</p><p>　　To

58、 demonstrate that the technique of using the uncut workpiece as a supporting structure could also be applied to different geometries, a slightly different web design was used for the seventh test part. This design consis

59、ted of one double-sided web 1 mm thick wall and measuring 191 mm * 191 mm, the web was supported all around by a 0.5 thick wall, similar to the generic test part without the rib. The test part was completely machined usi

60、ng 12.7 mm dia 3 mm corner radius end mill at 15,000 rpm. </p><p>　　CONCLUSIONS</p><p>　　It is possible to cut thin web parts by choosing the tool path so as to always cut the floor near the sup

61、port of the uncut workpiece .This is similar to the thin rib machining strategy. The guiding principle in both cases is to choose the tool path so that the area being machined currently I supported by as much unmachined

62、workpiece as supported area. For thin webs, it is advantageous to perform most of the machining using a tool with no corner radius (minimizing the force component normal to th</p><p>　　Unfortunately, the sug

63、gested tool paths are difficult to implement using exising </p><p>　　C programming software. The user typically must resort to manual programming of the generation of new software.</p><p>　　Ackn

64、owledgments</p><p>　　The authors gratefully acknowledge the support of the National Science Founcation through grant #DDM-9114588, and McDonell Douglas Aerospace in the completion of the reported work.</p