機械外文翻譯---基本加工工序和切削技術

1、<p>　　xxxxxx大學畢業(yè)設計（論文）</p><p><b>　　外文文獻（翻譯）</b></p><p>　　學 院 xxxxxxxxxxxxxxxx </p><p>　　專業(yè)班級 xxxxxxxx </p><

2、p>　　學生姓名 xxxxxxx </p><p>　　指導教師 xxxxx </p><p><b>　　附錄2</b></p><p><b>　　中文翻譯</b></p><p>　　基

3、本加工工序和切削技術</p><p>　　機床是從早期的埃及人的腳踏動力車和約翰·威爾金森的鏜床發(fā)展而來的。它們?yōu)楣ぜ偷毒咛峁﹦傂灾尾⒖梢跃_控制它們的相對位置和相對速度?；旧现v，金屬切削是指一個磨尖的鍥形工具從有韌性的工件表面上去除一條很窄的金屬。切屑是被廢棄的產品，與其它工件相比切屑較短，但對于未切削部分的厚度有一定的增加。工件表面的幾何形狀取決于刀具的形狀以及加工操作過程中刀具的路徑。<

4、;/p><p>　　大多數(shù)加工工序產生不同幾何形狀的零件。如果一個粗糙的工件在中心軸上轉動并且刀具平行于旋轉中心切入工件表面，一個旋轉表面就產生了，這種操作稱為車削。如果一個空心的管子以同樣的方式在內表面加工，這種操作稱為鏜孔。當均勻地改變直徑時便產生了一個圓錐形的外表面，這稱為錐度車削。如果刀具接觸點以改變半徑的方式運動，那么一個外輪廓像球的工件便產生了；或者如果工件足夠的短并且支撐是十分剛硬的，那么成型刀具相對于

5、旋轉軸正常進給的一個外表面便可產生，短錐形或圓柱形的表面也可形成。</p><p>　　平坦的表面是經(jīng)常需要的，它們可以由刀具接觸點相對于旋轉軸的徑向車削產生。在刨削時對于較大的工件更容易將刀具固定并將工件置于刀具下面。刀具可以往復地進給。成形面可以通過成型刀具加工產生。</p><p>　　多刃刀具也能使用。使用雙刃槽鉆鉆深度是鉆孔直徑5-10倍的孔。不管是鉆頭旋轉還是工件旋轉，切削刃與

6、工件之間的相對運動是一個重要因數(shù)。在銑削時一個帶有許多切削刃的旋轉刀具與工件接觸，工件相對刀具慢慢運動。平的或成形面根據(jù)刀具的幾何形狀和進給方式可能產生。可以產生橫向或縱向軸旋轉并且可以在任何三個坐標方向上進給。</p><p><b>　　基本機床</b></p><p>　　機床通過從塑性材料上去除屑片來產生出具有特別幾何形狀和精確尺寸的零件。后者是廢棄物，是由塑

7、性材料如鋼的長而不斷的帶狀物變化而來，從處理的角度來看，那是沒有用處的。很容易處理不好由鑄鐵產生的破裂的屑片。機床執(zhí)行五種基本的去除金屬的過程：車削，刨削，鉆孔，銑削。所有其他的去除金屬的過程都是由這五個基本程序修改而來的，舉例來說，鏜孔是內部車削；鉸孔，攻絲和擴孔是進一步加工鉆過的孔；齒輪加工是基于銑削操作的。拋光和打磨是磨削和去除磨料工序的變形。因此，只有四種基本類型</p><p>　　的機床，使用特別可控

8、制幾何形狀的切削工具1.車床，2.鉆床，3.銑床，4.磨床。磨削過程形成了屑片，但磨粒的幾何形狀是不可控制的。</p><p>　　通過各種加工工序去除材料的數(shù)量和速度是巨大的，正如在大型車削加工，或者是極小的如研磨和超精密加工中只有面的高點被除掉。一臺機床履行三大職能：1.它支撐工件或夾具和刀具2.它為工件和刀具提供相對運動3.在每一種情況下提供一系列的進給量和一般可達4-32種的速度選擇。</p>

9、<p><b>　　加工速度和進給</b></p><p>　　速度，進給量和切削深度是經(jīng)濟加工的三大變量。其他的量數(shù)是攻絲和刀具材料，冷卻劑和刀具的幾何形狀，去除金屬的速度和所需要的功率依賴于這些變量。</p><p>　　切削深度，進給量和切削速度是任何一個金屬加工工序中必須建立的機械參量。它們都影響去除金屬的力，功率和速度。切削速度可以定義為在旋轉

10、一周時速度記錄面相對任何瞬間呈輻射狀擴散的針，或是兩個相鄰溝槽的距離。切削深度是進入的深度和溝槽的深度。</p><p><b>　　在車床中心的車削</b></p><p>　　在機動車床上完成的基本操作已被介紹了。那些用單點刀具在外表面的操作稱為車削。除了鉆孔，鉸孔，研磨內部表面的操作也是由單點刀具完成的。</p><p>　　所有的加工工

11、序包括車削，鏜孔可以被歸類為粗加工，精加工或半精加工。精加工是盡可能快而有效的去除大量材料，而工件上留下的一小部分材料用于精加工。精加工為</p><p>　　工件獲得最后尺寸，形狀和表面精度。有時，半精加工為精加工留下預定的一定量的材料，它是先于精加工的。</p><p>　　一般來說，較長的工件同時被一個或兩個車床中心支撐。錐形孔，所謂的中心孔，兩端被鉆的工件適于車床中心-通常沿著圓柱

12、形工件的軸線。工件接近為架的那端通常由尾架中心支撐，在靠近主軸承的那端由主軸承中心支撐或由爪盤夾緊。這種方法可以牢固的加緊工件并且能順利地將力傳給工件；由卡盤對工件提供的輔助支撐減少切削時發(fā)生的顫振趨勢，如果能小心準確地采用卡盤支撐工件的方法，則可以得到精確的結果。</p><p>　　在兩個中心之間支撐工件可以得到非常精確的結果。工件的一端已被加工，那么工件便可車削了。在車床上加工另一端，中心孔充當精確定位面和

13、承載工件重量和抵制切削力的支撐面。當工件由于任何一原因從車床上移除后，中心孔將準確地使工件回到這個車床上或另一個車床上或一個圓柱磨床上。工件不允許被卡盤和車床中心夾在主軸承上。然而首先想到的是一個快速調整卡盤上工件的方法，但這是不允許的因為在由卡盤夾持的同時也由車床中心支撐是不可能的。由車床中心提供的調整將不能持續(xù)并且爪盤的壓力會損壞中心孔和車床中心，甚至是車床主軸。浮動的爪盤為上述陳述提供了一個例外，它幾乎完全使用在高生產工作上，這些

14、卡盤是真正的工作驅動者并且不為同樣的目的如普通的三爪，四爪卡盤使用。</p><p>　　而大直徑的工件有時裝在兩個中心，它們最好有由面板夾持在主軸承尾部來順利得到能量轉換；許多車床夾頭并不能足量的轉換能量，雖然可以作為特殊的能量轉換。</p><p><b>　　機械加工介紹</b></p><p>　　作為產生形狀的一種方法，機械加工是所有

15、制造過程中最普遍使用的而且是最重要的方法。機械加工過程是一個產生形狀的過程，在這過程中，驅動裝置使工件上的一些材料以切屑的形式被去除。盡管在某些場合，工件無支承情況下，使用移動式裝備來實現(xiàn)加工，但大多數(shù)的機械加工是通過既支承工件又支承刀具的裝備來完成。</p><p>　　小批量，低成本。機械加工在制造業(yè)上有兩個應用。是鑄造，鍛造和壓力工作，產生每一個特殊形狀，甚至一個零件，幾乎總有較高的模具成本。焊接的形狀很大

16、程度上取決于原材料。通過利用總成本高但沒有特殊模具的設備，加工是有可能的；從幾乎任何形式的原材料開始，只要外部尺寸足夠大，由任意材料設計形狀。因此加工是首選的方法，當生產一個或幾個零件甚至在大批量生產時，零件的設計在邏輯上導致鑄造，鍛造或沖壓制品 。高精度，表面精度。機械加工的 第二個應用是基于可能的高精度和表面精度的。如果在其他工序中大批量生產，很多低量零件會產生出低的但可接受的公差。另一方面，許多零件由一些大變形過程產生一般的形狀，

17、并且只在具有很高精度的選定面加工。舉例來說，內線流程是很少產生任何方式以外的其他機械加工并且緊接著壓力操作后零件上的小洞可能被加工。</p><p><b>　　主要的切削參數(shù)</b></p><p>　　在切削時基本工具工作的關系充分描述的方法有4個因素：刀具幾何形狀，切削速度和切削深度。刀具必須由適當?shù)牟牧献龀?；它必須有一定的強度，粗糙度，硬度和抗疲勞度。刀具幾?/p>

18、形狀由面和角度描述，對每一種切削操作都是正確的。切削速度是指切削刃通過工作面的速度，它已每分鐘通過的英尺數(shù)表示。對于加工效率，切削速度相對于特殊工作組合必須具有適當規(guī)模。一般來講，工件越硬，速度越小。進給是刀具進入工件的速率。當工件或刀具旋轉時，進給量的單位是英寸每轉。當?shù)毒呋蚬ぜ鶑鸵苿訒r，進給量的單位是英寸沒次，總的來說，在其他相似情況下進給量與切削速度成反比。切削速度用英寸表示，是刀具進入工件的距離表示的，它是指車削時屑片的寬度或

19、是直線切削時屑片的厚度。粗加工時切削深度比精加工的切削深度大。</p><p>　　切削參數(shù)的改變對切削溫度的影響</p><p>　　在金屬切削作業(yè)中熱量產生于主要和第二變形區(qū)而這些結果導致了復雜溫度遍布于刀具，工件和屑片。一個典型的等溫先如圖所示，它可以看出正如預測的，當工件材料經(jīng)歷主要變形，被減切時，有一個非常大溫度梯度遍布于屑片的整個寬度。當?shù)诙冃螀^(qū)的屑片還有一小段距離就達到了最

20、大溫度。</p><p>　　因為幾乎所有的工作都以金屬切削轉化為熱量而完成，可以預測去除每一單位體積的金屬所增加的能量消耗將會提高切削溫度。因此在所有其他參數(shù)不變，前角變大時，將減少去除每單位體積金屬的能量和切削溫度。當考慮到增加未形成屑片的厚度和速度，情況就更復雜了。增加切削厚度往往會大大影響熱量傳給工件，刀具的多少，而且會使屑片停留在一個固定數(shù)額，同時切削溫度的變化也會很小，可是增加切削速度會減少傳遞給工件

21、的熱量，同時這將增大屑片主要變形的溫升。此外，第二變形區(qū)是比較小的，在這個變形區(qū)會提高溫度。切削參數(shù)的其他變化幾乎不影響去除每單位體積的能量消耗和切削溫度。因此已經(jīng)表明，即使是切削溫度的小規(guī)模變化對刀具磨損率也有重大影響，從切削數(shù)據(jù)來估計切削溫度是恰當?shù)?。檢測高速鋼工具最直接最準確的方法，特倫特給出了高速鋼工具溫度分布的詳細資料。該技術是基于高速鋼刀具的數(shù)據(jù)檢測并與對熱歷史的微觀變化有關。</p><p>　　特

22、倫特已經(jīng)描述了切削溫度的測量和加工大范圍工件時高速鋼工具的溫度分布。使用掃描電子顯微鏡來研究精細尺度微觀結構變化，這項技術已得到了進一步發(fā)展。這項技術也用于研究高速鋼單點車刀和麻花鉆的溫度分布，</p><p><b>　　刀具磨損</b></p><p>　　脆性斷裂已經(jīng)得到了處理，刀具磨損基本上有三個類型。后刀面磨損，邊界磨損和前刀面磨損。刀面磨損發(fā)生在主切削刃和

23、次切削刃。主切削刃負責去除大量金屬，這增加了切削力和溫度，如果任其發(fā)展會導致刀具和工件的振動，這就再不能高效率地切削了。次切削刃決定工件尺寸和表面精度，后刀面的磨損會導致大量產品出現(xiàn)較差的表面精度。根據(jù)實際切削條件，刀具不可用的主要原因在于主刀面先于次刀面的磨損非常大，這導致了一個不可接受部分的產生。</p><p>　　因為刀具的應力分布，剛開始滑動時，滑動區(qū)域的摩擦力在屑片和面之間達到最大，最后摩擦力便為零。

24、因此磨料磨損發(fā)生在這個區(qū)域，在屑片與相離處更多的磨損發(fā)生在與該區(qū)域相鄰處，這比相鄰于這點的更多。</p><p>　　這導致了刀具面的局部點蝕與這面有一定距離，這面通常有一部分是圓弧形的。在許多方面并基于實際切削條件，邊界磨損相比后刀面是一個較不嚴重的磨損，因此刀面磨損是一種較常見磨鈍標準。然后，由于各樣作者表明，伴隨著切削速度的增加面溫度的增加量多于刀面的增加量，而由于溫度變化嚴重影響任一類型的磨損率，邊界磨損

25、通常發(fā)生在較高切削速度的情況下。</p><p>　　刀具與未切削面相接觸的地方，主刀面磨損的尾部的磨損比沿著剩余磨損面的地方更明顯。這是因為局部影響如未切削面是由先前的切削，氧化規(guī)模，局部高溫所形成的加工硬化而造成的。這個局部磨損一般與邊界磨損有關，有時還很嚴重。雖然出現(xiàn)凹口不會嚴重影響刀具的切削性能，凹口是往往比較深，如果繼續(xù)切削刀具很可能斷裂。</p><p>　　如果任何形式的漸進

26、磨損讓其戲劇性的繼續(xù)存在，刀具將面臨災難性的故障，如刀具再不能切割，在好的情況下，工件報廢，最壞時，機械工具可能造成損壞。對于硬質合金刀具和各類型的磨損，在出現(xiàn)災難性故障之前達到最長使用使用壽命的極限。但對于高速鋼切削工具的磨損是不均勻的，目前已發(fā)現(xiàn)當磨損繼續(xù)并甚至出現(xiàn)災難性故障時，便可得到最有意義的和可以復制的結果，當然在實踐中，切削時間遠遠少于故障時間。發(fā)生災難性故障時會出現(xiàn)幾個現(xiàn)象，最常見的是切削力突然增加，工件出現(xiàn)亮環(huán)，噪音顯著

27、增大。</p><p><b>　　表面精整加工機理</b></p><p>　　有五個基本機制對于已加工產品有影響：（1）切削過程的基本幾何形狀，單點車削刀具將軸向前進一個恒定距離，由此產生的面將在它上面，刀具垂直方向進給運動時，一連串的尖點形成切削刀具的基本形狀。（2）切削加工的效率。已經(jīng)提到不穩(wěn)定刀瘤將產生含有硬化刀瘤片段的面。這個片段使表面光潔度降低。也能證明

28、在不利切削條件下引用大進給，小前角和低切削速度，除此以外生產條件也會導致不穩(wěn)積屑瘤產品，切削過程變得不穩(wěn)定而不是在剪切帶連續(xù)切削，發(fā)生破碎，出現(xiàn)不均勻的間斷屑片，表面也不夠光滑。當加工韌性材料時這種情況尤其明顯。（3）機床的穩(wěn)定。根據(jù)某些組合的切削條件，工件尺寸，夾緊的方法和相對機床結構的剛度，不穩(wěn)定性是刀具造成的顫動。在一定條件下，這種顫動將達到并保持一定的振幅，而根據(jù)其它條件的振動也會產生，除非切割阻止了相當大的損壞不然切削刀具和工

29、件都可能發(fā)生顫動。這個現(xiàn)象稱為顫振，而軸向車削的特點是工件上有長螺旋帶，暫加工面上有短節(jié)距起伏。（4）去除切屑的有效性。在間斷切屑生產加工中，如脆性材料的銑削和車削，預計無論是由于重力還是切削液，屑片都將離開切削區(qū)，任何情況下也不會影響切削面。連續(xù)屑片是顯而易見的，如果不</p><p><b>　　極限與公差</b></p><p>　　機械零件被制造因此它們是可互

30、換的。換句話說，每一種機械零件或裝置被制成一定的大小和形狀來適用于其它型號的機器。為了使零件具有互換性，每一個零件都做成一個尺寸來用正確的方法與對應的零件相配。這不僅不可能，而且是許多零件都做成一個尺寸是不切實際的。這是因為機器不是完美的，而工具會磨損。相對于正確尺寸的一點偏差通常是允許的。這個偏差的大小依賴于被制零件的種類，比如一個零件可能是6英寸，上下偏差是0003英寸（三千分之一）。因此這個偏差可以是5997英寸到6003英寸之間

31、并仍能保持正確尺寸。這就是偏差。上偏差和下偏差之差即是公差。</p><p>　　公差是零件尺寸的最大變化量，基本尺寸是允許變動量和公差范圍而衍生的尺寸限制。有時偏差只允許一個方向的變動，它允許公差在孔或軸上變化而不會嚴重影響配合。當公差在兩個方向上都變化時，稱為完全偏差（正和負）。完全偏差是分開的，并且在基本尺寸的每一邊都會有。而極限尺寸只有最大尺寸和最小尺寸。因此，公差是這兩個尺寸之差。</p>

32、<p><b>　　表面精度和尺寸控制</b></p><p>　　產品已經(jīng)完成了應有的形狀和大小，常常需要某種類型的表面精度是它們能夠履行好自己的職能。在某些情況下為了抵抗劃破和擦破，提高表面材料的物理性能是必須的。在許多制造工藝中，產品表面留下污垢，屑片，油脂或其它有害物質。由不同材料組成的混合物，不同方式加工的同種材料，可能需要一些特殊的面處理以提供均勻的外觀。</p

33、><p>　　表面拋光處理有時可能成為一個中間處理程序。舉例來說，先于各種電鍍工藝，清潔和拋光通常是必不可少的。一些清洗程序也用來改善配合零件的表面光滑度，也為了去除毛邊，這些在以后使用中是有害的。表面拋光處理的另一個重要原因是在各種各樣的環(huán)境中的防腐保護。保護程序的類型主要取決于預期暴露，并充分考慮到材料保護和經(jīng)濟因數(shù)。</p><p>　　為了滿足上述目的，因此必須使用表面拋光的主要方法，

34、表面力學的化學變化影響工作面的性能，用各種方法清洗，保護涂料和有機金屬的應用。</p><p>　　在早期的工程中，盡量接近的將配合零件加工到所需尺寸，把配合零件加工到相似尺寸然后完成加工，并不斷地將其它零件與它相配，直到得到理想的關系。如果在加工時不方便將一個零件另一個零件相配，則最后的工作是由鉗工坐在板凳上，刮削配合零件直到理想的配合，因此作為一名鉗工字面意為J，顯而易見，兩個零件仍在一起而M不得不更換，必須

35、再一次去相配合。在這些日子里，我們期望能為壞零件購買一個替代品，而它的功能正常也不需要刮削和其它修改工序。</p><p>　　當一個零件能被用來替換另一個同尺寸和同材料規(guī)格的零件，這時我們稱之為這些零件能互換?；Q系統(tǒng)通?？梢越档蜕a成本，為了一個昂貴的操作是沒有必要的，這有益于客戶在需要時更換磨料零件。</p><p><b>　　自動夾具設計</b></p

36、><p>　　裝配設備的傳統(tǒng)同步夾子有更多的零件與中心線相對，以確保當電弧從傳送帶回升時能在一個眾所周知的地方。然而，在某些應用中，迫使零件與中心線對準，可能會損壞零件和設備。當零件很小并有一些碰撞可導致刮擦，當它的位置被機床主軸或絲杠固定，或公差是很小時，最好使夾子配合零件的位置而不是倒過來。對于這些任務Zaytran公司Elyria已經(jīng)創(chuàng)造了GPN不同步系列，它與夾持兼容。因為力和夾子的同步系統(tǒng)是獨立的，同步系統(tǒng)

37、可以被一個精密的防滑系統(tǒng)取而帶之而不影響夾持力。夾子尺寸范圍從51b夾持力和0.2英寸沖程到40Gb夾持力和6英寸沖程。夾子產品的特點是批量的規(guī)模越來越小并且提供更多元的產品。作為最后一步生產步驟，裝配在批量大小和產品設計時特別容易變化。以前在這種情況下，迫使許多企業(yè)把更多的精力投入到廣泛合理化和自動化裝配上。雖然在以靈活處理系統(tǒng)如工業(yè)機器人的背景下，彈性夾具的發(fā)展在快速下降，但嘗試著增加彈性夾具會成為可能。</p>&l

38、t;p>　　夾具是必需的產品投資，這一事實激化了使夾具更靈活地在經(jīng)濟上的必要性。夾具可以根據(jù)它們的靈活性分為單一夾具，組合夾具，模塊化夾具，高靈活夾具。靈活夾具的特點是對不同工件的高度適應性，較少的變換時間和較低的價格。</p><p>　　在生產任務中工件在夾具里是固定的，固定一個工件有幾個必要步驟。第一步要確定工件在夾具上的位置，考慮未加工面和工作特點。在此之后，固定面必須被選定。工件在確定的位置被固定

39、在固定面上，并添加必要的力和力矩，保證獲得必要的工作特點。最后，必要的調動位置或組合夾具因素都要考慮，調整或組裝，使工件牢牢地固定在夾具上。通過這樣一個程序，工序和工序卡片，夾具的裝配可自動進行。結構造型任務就是要產生若干穩(wěn)定平面的組合，這樣在這些平面上的各夾緊力將使工件和夾具穩(wěn)定。按慣例，這個任務可用人-機對話即幾乎完全自動化的方式來完成。以人-機對話即以自動化方式確定夾具結構造型的優(yōu)點是可有組織有規(guī)劃進行夾具設計，減少所需的設計人員

40、，縮短研究周期和能更好地配置工作條件。簡言之，可成功地達到顯著提高夾具生產效率和經(jīng)濟效益。</p><p>　　Basic Machining Operations and Cutting Technology</p><p>　　Basic Machining Operations </p><p>　　Machine tools have evolved fro

41、m the early foot-powered lathes of the Egyptians and John Wilkinson's boring mill. They are designed to provide rigid support for both the workpiece and the cutting tool and can precisely control their relative posit

42、ions and the velocity of the tool with respect to the workpiece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a rather narrow strip of metal from the surface of a ductile workpiece in the form of a

43、severely deformed chip. The chip i</p><p>　　Most machining operations produce parts of differing geometry. If a rough cylindrical workpiece revolves about a central axis and the tool penetrates beneath its s

44、urface and travels parallel to the center of rotation, a surface of revolution is produced, and the operation is called turning. If a hollow tube is machined on the inside in a similar manner, the operation is called bor

45、ing. Producing an external conical surface uniformly varying diameter is called taper turning, if the tool point trav</p><p>　　Flat or plane surfaces are frequently required. They can be generated by radial

46、turning or facing, in which the tool point moves normal to the axis of rotation. In other cases, it is more convenient to hold the workpiece steady and reciprocate the tool across it in a series of straight-line cuts wit

47、h a crosswise feed increment before each cutting stroke. This operation is called planning and is carried out on a shaper. For larger pieces it is easier to keep the tool stationary and draw the workp</p><p>

48、;　　Multiple-edged tools can also be used. Drilling uses a twin-edged fluted tool for holes with depths up to 5 to 10 times the drill diameter. Whether the </p><p>　　drill turns or the workpiece rotates, rela

49、tive motion between the cutting edge and the workpiece is the important factor. In milling operations a rotary cutter with a number of cutting edges engages the workpiece. Which moves slowly with respect to the cutter. P

50、lane or contoured surfaces may be produced, depending on the geometry of the cutter and the type of feed. Horizontal or vertical axes of rotation may be used, and the feed of the workpiece may be in any of the three coor

51、dinate directions.</p><p>　　Basic Machine Tools </p><p>　　Machine tools are used to produce a part of a specified geometrical shape and precise I size by removing metal from a ductile material i

52、n the form of chips. The latter are a waste product and vary from long continuous ribbons of a ductile material such as steel, which are undesirable from a disposal point of view, to easily handled well-broken chips resu

53、lting from cast iron. Machine tools perform five basic metal-removal processes: I turning, planning, drilling, milling, and grinding. All other </p><p>　　The amount and rate of material removed by the variou

54、s machining processes may be I large, as in heavy turning operations, or extremely small, as in lapping or super finishing operations where only the high spots of a surface are removed. </p><p>　　A machine t

55、ool performs three major functions: 1. it rigidly supports the workpiece or its holder and the cutting tool; 2. it provides relative motion between the workpiece and the cutting tool; 3. it provides a range of feeds and

56、speeds usually ranging from 4 to 32 choices in each case. </p><p>　　Speed and Feeds in Machining </p><p>　　Speeds, feeds, and depth of cut are the three major variables for economical machining.

57、 Other variables are the work and tool materials, coolant and geometry of the cutting tool. The rate of metal removal and power required for machining depend upon these variables. </p><p>　　The depth of cut,

58、 feed, and cutting speed are machine settings that must be established in any metal-cutting operation. They all affect the forces, the power, and the rate of metal removal. They can be defined by comparing them to the ne

59、edle and record of a phonograph. The cutting speed (V) is represented by the velocity of- the record surface relative to the needle in the tone arm at any instant. Feed is represented by the advance of the needle radiall

60、y inward per revolution, or is the differen</p><p>　　Turning on Lathe Centers </p><p>　　The basic operations performed on an engine lathe are illustrated. Those operations performed on external

61、surfaces with a single point cutting tool are called turning. Except for drilling, reaming, and lapping, the operations on internal surfaces are also performed by a single point cutting tool. </p><p>　　All m

62、achining operations, including turning and boring, can be classified as roughing, finishing, or semi-finishing. The objective of a roughing operation is to remove the bulk of the material as rapidly and as efficiently as

63、 possible, while leaving a small amount of material on the work-piece for the finishing operation. Finishing operations are performed to obtain the final size, shape, and surface finish on the workpiece. Sometimes a semi

64、-finishing operation will precede the finishing operati</p><p>　　Generally, longer workpieces are turned while supported on one or two lathe centers. Cone shaped holes, called center holes, which fit the lat

65、he centers are drilled in the ends of the workpiece-usually along the axis of the cylindrical part. The end of the workpiece adjacent to the tailstock is always supported by a tailstock center, while the end near the hea

66、dstock may be supported by a headstock center or held in a chuck. The headstock end of the workpiece may be held in a four-jaw chuck, or i</p><p>　　Very precise results can be obtained by supporting the work

67、piece between two centers. A lathe dog is clamped to the workpiece; together they are driven by a driver plate mounted on the spindle nose. One end of the Workpiece is mecained;then the workpiece can be turned around in

68、the lathe to machine the other end. The center holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to carry the weight of the workpiece  and to resist the cutting forces. After the

69、workpi</p><p>　　While very large diameter workpieces are sometimes mounted on two centers, they are preferably held at the headstock end by faceplate jaws to obtain the smooth power transmission; moreover, l

70、arge lathe dogs that are adequate to transmit the power not generally available, although they can be made as a special. Faceplate jaws are like chuck jaws except that they are mounted on a faceplate, which has less over

71、hang from the spindle bearings than a large chuck would have. </p><p>　　Introduction of Machining </p><p>　　Machining as a shape-producing method is the most universally used and the most import

72、ant of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chip form. Most machining is done with equipment that supports both the work piec

73、e and cutting tool although in some cases portable equipment is used with unsupported workpiece. </p><p>　　Low setup cost for small Quantities. Machining has two applications in manufacturing. For casting, f

74、orging, and press working, each specific shape to be produced, even one part, nearly always has a high tooling cost. The shapes that may he produced by welding depend to a large degree on the shapes of raw material that

75、are available. By making use of generally high cost equipment but without special tooling, it is possible, by machining; to start with nearly any form of raw material, so tong as t</p><p>　　Close accuracies,

76、 good finishes. The second application for machining is based on the high accuracies and surface finishes possible. Many of the parts machined in low quantities would be produced with lower but acceptable tolerances if p

77、roduced in high quantities by some other process. On the other hand, many parts are given their general shapes by some high quantity deformation process and machined only on selected surfaces where high accuracies are ne

78、eded. Internal threads, for example, are se</p><p>　　Primary Cutting Parameters </p><p>　　The basic tool-work relationship in cutting is adequately described by means of four factors: tool geome

79、try, cutting speed, feed, and depth of cut. </p><p>　　The cutting tool must be made of an appropriate material; it must be strong, tough, hard, and wear resistant. The tool s geometry characterized by planes

80、 and angles, must be correct for each cutting operation. Cutting speed is the rate at which the work surface passes by the cutting edge. It may be expressed in feet per minute. </p><p>　　For efficient machin

81、ing the cutting speed must be of a magnitude appropriate to the particular work-tool combination. In general, the harder the work material, the slower the speed. </p><p>　　Feed is the rate at which the cutti

82、ng tool advances into the workpiece. "Where the workpiece or the tool rotates, feed is measured in inches per revolution. When the tool or the work reciprocates, feed is measured in inches per stroke, Generally, fee

83、d varies inversely with cutting speed for otherwise similar conditions. </p><p>　　The depth of cut, measured inches is the distance the tool is set into the work. It is the width of the chip in turning or th

84、e thickness of the chip in a rectilinear cut. In roughing operations, the depth of cut can be larger than for finishing operations. </p><p>　　The Effect of Changes in Cutting Parameters on Cutting Temperatur

85、es </p><p>　　In metal cutting operations heat is generated in the primary and secondary deformation zones and these results in a complex temperature distribution throughout the tool, workpiece and chip. A ty

86、pical set of isotherms is shown in figure where it can be seen that, as could be expected, there is a very large temperature gradient throughout the width of the chip as the workpiece material is sheared in primary defor

87、mation and there is a further large temperature in the chip adjacent to the face as th</p><p>　　Since virtually all the work done in metal cutting is converted into heat, it could be expected that factors wh

88、ich increase the power consumed per unit volume of metal removed will increase the cutting temperature. Thus an increase in the rake angle, all other parameters remaining constant, will reduce the power per unit volume o

89、f metal removed and the cutting temperatures will reduce. When considering increase in unreformed chip thickness and cutting speed the situation is more complex. An incr</p><p>　　The most direct and accurate

90、 method for measuring temperatures in high -speed-steel cutting tools is that of Wright &. Trent which also yields detailed information on temperature distributions in high-speed-steel cutting tools. The technique is

91、 based on the metallographic examination of sectioned high-speed-steel tools which relates microstructure changes to thermal history. </p><p>　　Trent has described measurements of cutting temperatures and te

92、mperature  distributions for high-speed-steel tools when machining a wide range of workpiece materials. This technique has been further developed by using scanning electron  microscopy to study fine-scale micro

93、structure changes arising from over tempering of the tempered martens tic matrix of various high-speed-steels. This technique has also been used to study temperature distributions in both high-speed -steel single point t

94、urning </p><p>　　Wears of Cutting Tool </p><p>　　Discounting brittle fracture and edge chipping, which have already been dealt with, tool wear is basically of three types. Flank wear, crater wea

95、r, and notch wear. Flank wear occurs on both the major and the minor cutting edges. On the major cutting edge, which is responsible for bulk metal removal, these results in increased cutting forces and higher temperature

96、s which if left unchecked can lead to vibration of the tool and workpiece and a condition where efficient cutting can no longer take pl</p><p>　　Because of the stress distribution on the tool face, the frict

97、ional stress in the region of sliding contact between the chip and the face is at a maximum at the start of the sliding contact region and is zero at the end. Thus abrasive wear takes place in this region with more wear

98、taking place adjacent to the seizure region than adjacent to the point at which the chip loses contact with the face. This result in localized pitting of the tool face some distance up the face which is usually referre&l

99、t;/p><p>　　At the end of the major flank wear land where the tool is in contact with the uncut workpiece surface it is common for the flank wear to be more pronounced than along the rest of the wear land. This

100、is because of localised effects such as a hardened layer on the uncut surface caused by work hardening introduced by a previous cut, an oxide scale, and localised high temperatures resulting from the edge effect. This lo