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本科生畢業(yè)設(shè)計(jì) (論文)
外 文 翻 譯
原 文 標(biāo) 題
An intelligent fixture design method based on
smart modular fixture unit
譯 文 標(biāo) 題
基本的加工工序—切削，鏜削和銑削
作者所在系別
機(jī)電工程學(xué)院
作者所在專(zhuān)業(yè)
機(jī)械設(shè)計(jì)制造及自動(dòng)化
作者所在班級(jí)
B13113
作 者 姓 名
牛從從
作 者 學(xué) 號(hào)
20134011305
指導(dǎo)教師姓名
丁紅軍
指導(dǎo)教師職稱(chēng)
講師
完 成 時(shí) 間
2017
年
3
月
北華航天工業(yè)學(xué)院教務(wù)處制
譯文標(biāo)題
基本的加工工序—切削，鏜削和銑削
原文標(biāo)題
Basic Machining Operations—Turning ,Boring and Milling
作 者
B. W. Nile
譯 名
本.沃.聶邇
國(guó) 籍
加拿大
原文出處
Modern Manufacturing Process Engineering
譯文：
基本的加工工序
機(jī)床是從早期的埃及人的腳踏動(dòng)力車(chē)床和約翰.威爾金森的鏜床發(fā)展而來(lái)的。它們用于為工件和刀具兩者提供剛性支撐并且可以精確控制它們的相對(duì)位置和相對(duì)速度。一般來(lái)說(shuō)，在金屬切削中用一個(gè)磨尖的楔形工具以緊湊螺紋形的切屑形式從有韌性工件表面上去除一條很窄的金屬。切屑是廢棄的產(chǎn)品，與其工件相比，它相當(dāng)短但是比未切削的部分厚度有相對(duì)的增加。機(jī)器表面的幾何形狀取決于刀具的形狀以及加工過(guò)程中刀具的路徑。
不同的加工工序生產(chǎn)出不同幾何形狀的部件。如果一個(gè)粗糙的柱形工件繞中心軸旋轉(zhuǎn)而且刀具穿透工件表面并沿與旋轉(zhuǎn)中心平行的方向前進(jìn)，就會(huì)產(chǎn)生一個(gè)旋轉(zhuǎn)面，這道工序叫車(chē)削。如果以類(lèi)似的方式加工一根空心管的內(nèi)部，則這道工序就叫鏜削。制造一個(gè)直徑均勻變化的錐形外表面叫做錐體車(chē)削。如果刀具尖端以一條半徑可變的路徑前進(jìn)，就可以制造出象保齡球桿那種仿形表面；如果工件足夠短而且支撐具有足夠的剛性，仿形表面可以通過(guò)用一個(gè)垂直于旋轉(zhuǎn)軸的仿形刀具來(lái)制造。短的錐面或柱面也可以仿形切削。
常常需要的是平坦的或平的表面。它們可以通過(guò)徑向車(chē)削或端面車(chē)削來(lái)完成，其中刀具尖端沿垂直于旋轉(zhuǎn)軸的方向運(yùn)動(dòng)。在其他情況下，更方便的是固定工件不動(dòng)，以一系列直線方式往復(fù)運(yùn)動(dòng)刀具橫過(guò)工件，在每次切削行程前具有一定橫向進(jìn)給量。這種龍門(mén)刨削和牛頭刨削是在刨床上進(jìn)行的。大一些的工件很容易保持刀具固定不動(dòng)，而像龍門(mén)刨削那樣在其下面拉動(dòng)工件，再每次往復(fù)進(jìn)給刀具。仿形面可以通過(guò)使用仿形刀具來(lái)制造。
也可以使用多刃刀具。鉆削使用兩刃刀具，深度可達(dá)鉆頭直徑的5-10倍。不管是鉆頭轉(zhuǎn)動(dòng)還是工件轉(zhuǎn)動(dòng)，切削刃與工件之間的相對(duì)運(yùn)動(dòng)都是一個(gè)重要因素。在銑削作業(yè)中，有許多切削刃的旋轉(zhuǎn)銑刀與工件相接合，這種工件相對(duì)銑刀運(yùn)動(dòng)緩慢。根據(jù)銑刀的幾何形狀和進(jìn)給的方式，可以加工出平面和仿形面?？梢允褂盟交虼怪毙D(zhuǎn)軸，工件可以沿三個(gè)坐標(biāo)方向中的任意一個(gè)進(jìn)給。
基本的機(jī)床
機(jī)床用于以切屑的形式從韌性材料上去除金屬來(lái)加工特殊幾何形狀和精密尺寸的部件。切屑是廢品，其變化形狀從像鋼這樣的韌性材料的長(zhǎng)的連續(xù)帶狀屑到鑄鐵形成的易于處理、徹底斷掉的切屑，從處理的觀點(diǎn)來(lái)講，不想要長(zhǎng)的連續(xù)帶狀屑。機(jī)床完成5種基本的金屬切削工藝：車(chē)削、刨削、鉆削、銑削和磨削。其他所有金屬切削工藝都是這5種基本工藝的變形。例如：鏜削是內(nèi)部車(chē)削；鉸削、錐體車(chē)削和平底锪孔則修改鉆孔，與鉆削有關(guān)；滾齒與切齒是基本銑削作業(yè)；弓鋸削和拉削是銑削和磨削的一種形式；而研磨、超精加工、拋光和磨光是磨削和研磨切削作業(yè)的各種變化形式。因此，僅有4種使用專(zhuān)用可控幾何形狀的刀具基本機(jī)床：1、車(chē)床，2、刨床，3、鉆床，4、銑床。磨削工藝形成碎屑，但是磨粒的幾何形狀不可控制。
不同加工工藝切削的材料的數(shù)量和速度卻不相同。可能極大，如大型車(chē)削作業(yè)；或者極小，如磨削和超精加工作業(yè)，只有表面高出的點(diǎn)被去除。
機(jī)床完成3種主要功能：1、剛性支撐工件或工件夾具以及切削刀具；2、提供工件與切削刀具之間的相對(duì)運(yùn)動(dòng)；3、提供了一定范圍的速度進(jìn)給，通常每種有4-32種選擇。
切削速度和進(jìn)給
切削速度、進(jìn)給量和切削深度是切削加工的3個(gè)主要變量，其他變量還有工件和工具材料、冷卻劑以及切削刀具的幾何形狀。金屬切削的速率和加工所需的功率就決定于這些變量。
切削深度、進(jìn)給量和切削速度是任何金屬切削作業(yè)中必須都建立的變量。它們都影響切削力、功率和對(duì)金屬切削的速率?？梢酝ㄟ^(guò)把它們與留聲機(jī)的唱針和唱片相比較給出定義。切削速度（V）由任意時(shí)刻唱片表面相對(duì)于拾音器支臂內(nèi)部的唱針的速度來(lái)表示；進(jìn)給量由唱針每圈徑向向內(nèi)的前進(jìn)量或者由兩個(gè)相鄰槽的位置差來(lái)表示。切削深度是唱針進(jìn)入的量或者是槽的深度。
切削
那些在外表面上用單刃刀具完成的工序叫車(chē)削。除鉆削、鉸削和錐體車(chē)削外，在內(nèi)表面的作業(yè)也由單刃刀具完成。
包括車(chē)削和鏜削在內(nèi)的所有加工工序都可以分為粗加工、精加工和半精加工。粗加工工序的目的是盡可能迅速且高效地去除大量的材料，在工件上只留下少量的材料給精加工工序。精加工工序用以獲得工件最終的大小、形狀和表面粗糙度。有時(shí)，在精加工工序前進(jìn)行半精加工作業(yè)以便在工件上留下少的、預(yù)定的和均勻量的原材料供精加工去除。
通常，較長(zhǎng)的工件是在一個(gè)或兩個(gè)車(chē)床頂尖的支撐下進(jìn)行的。用于安裝車(chē)床頂尖的錐形孔叫做頂尖孔，它是在工件的端部鉆出的——通常沿著柱形部件的軸心。與尾架鄰近的工件端部總是由尾架頂尖支撐，而挨著主軸箱的一端則由主軸箱頂尖支撐或裝在卡盤(pán)內(nèi)。工件的主軸箱一端可以裝在一個(gè)四爪卡盤(pán)或套爪卡盤(pán)內(nèi)。這種方法牢固地夾持工件并且把功率平穩(wěn)地傳送到工件上；由卡盤(pán)提供的額外支撐減少了車(chē)削作業(yè)時(shí)發(fā)生震動(dòng)的傾向。如果仔細(xì)地將工件精確的固定在卡盤(pán)上，用這種方法將獲得精密的結(jié)果。
通過(guò)將工件支撐在兩個(gè)頂尖之間可以獲得非常精確的結(jié)果。一個(gè)車(chē)床夾頭夾在工件上；然后由安裝在主軸前端的撥盤(pán)一起帶動(dòng)。先加工工件的一端，然后可以在車(chē)床上將工件掉頭加工另一端。工件上的頂尖孔是用作精確定位面以及承受工件重量和抵抗車(chē)削力的支撐面。在工件被拆下后，頂尖孔可以精確地將其裝回機(jī)床。工件千萬(wàn)不要同時(shí)通過(guò)卡盤(pán)和頂尖安裝在主軸箱一端。雖然這樣似乎是一種快捷方法，但是這樣做使得工件受力不均勻，頂尖的對(duì)正作用不能維持，而且爪的壓力可能損壞頂尖孔、車(chē)床頂尖甚至車(chē)床主軸。幾乎被獨(dú)自用在大量生產(chǎn)工件上的補(bǔ)償或浮動(dòng)爪式卡盤(pán)是上述的一個(gè)例外。這些卡盤(pán)是自動(dòng)偏心夾緊卡盤(pán)不能起到普通三爪或四爪卡盤(pán)同樣的作用。
直徑非常大的工件雖然有時(shí)安裝在兩個(gè)頂尖上，但是最好用花盤(pán)把它們固定在主軸箱端以獲得流暢的動(dòng)力傳輸；此外，可以把它們制造成專(zhuān)用部件，但是一般不能提供足夠大的車(chē)床夾頭來(lái)傳輸動(dòng)力。除非是安裝在花盤(pán)上，其主軸軸承上的外伸要比大卡盤(pán)上的少一些。
鏜削
在車(chē)床上鏜孔的目的是：
1、擴(kuò)孔；
2、把孔加工到所需直徑；
3、精確的為孔定位；
4、在孔內(nèi)獲得好的表面粗糙度。
當(dāng)?shù)毒邚较蛄锇蹇v向移動(dòng)而工件繞車(chē)床的軸線旋轉(zhuǎn)時(shí)，鏜刀的運(yùn)動(dòng)平行于車(chē)床上的軸線。當(dāng)兩種運(yùn)動(dòng)結(jié)合起來(lái)鏜孔時(shí)，就會(huì)與車(chē)床的旋轉(zhuǎn)軸同心。通過(guò)把工件固定在車(chē)床上可以精確定位孔的位置以使待加工孔所環(huán)繞的軸與車(chē)床的旋轉(zhuǎn)軸一致。當(dāng)鏜削工序與用于車(chē)削和刮削工序的設(shè)置相同時(shí)，實(shí)際上可以達(dá)到理想的同心與垂直。
鏜刀固定在一根通過(guò)刀具徑向溜板進(jìn)給的鏜桿上。根據(jù)待做的工作來(lái)使用這一設(shè)計(jì)的變化形式。如果有的話(huà)，所用的倒角總是應(yīng)該小些。而且，鏜刀前端的半徑一定不能太大。用于鏜孔的切削速度可以等于車(chē)削速度。但是，在計(jì)算車(chē)床主軸速度時(shí)，應(yīng)當(dāng)使用完成后的或最大的孔徑。鏜削的進(jìn)刀速度通常比車(chē)削的小一點(diǎn)以補(bǔ)償鏜桿剛性的不足。
鏜削工序一般分兩步完成，即粗鏜和精鏜。粗鏜工序的目的是快速、高效地去除多余的金屬；而精鏜工序的目的是獲得所需的尺寸、表面粗糙度和孔的位置?？椎某叽缤ㄟ^(guò)試切來(lái)獲得?？椎闹睆娇梢杂脙?nèi)卡尺和千分尺測(cè)量。測(cè)量?jī)x表或內(nèi)千分卡尺直接測(cè)量直徑。
型心孔和要鉆的孔有時(shí)相對(duì)于車(chē)床的旋轉(zhuǎn)是偏心的。當(dāng)鏜刀進(jìn)入工件時(shí)，鏜桿在孔的一邊切口比另一邊深，當(dāng)采用這深切口時(shí)就會(huì)更偏斜，結(jié)果鏜的孔與工件旋轉(zhuǎn)不同心。這一影響通過(guò)利用淺切口在整個(gè)孔加工中進(jìn)行幾次加工來(lái)糾正。因?yàn)槊總€(gè)淺切口形成的孔比使用深切口形成的孔更加同心。在完工前，進(jìn)行精加工，孔應(yīng)該與工件的旋轉(zhuǎn)同心以確保完工時(shí)孔能精確定位。
肩、溝槽、輪廓、錐度和螺紋也應(yīng)該在孔內(nèi)鏜出。內(nèi)槽是用與外部開(kāi)槽工具相似的工具切削。鏜削內(nèi)槽的步驟非常類(lèi)似于車(chē)削肩部的步驟。大的肩部使用前導(dǎo)裝置定位的鏜刀進(jìn)行刮削，使用橫向滑板進(jìn)給工具。內(nèi)部輪廓使用車(chē)床上的描摹附件加工。仿行板附件安裝在橫向滑板上，靠模指跟隨標(biāo)準(zhǔn)剖面板的輪廓線運(yùn)動(dòng)。這使刀具對(duì)應(yīng)于標(biāo)準(zhǔn)剖面樣板的輪廓線的路徑進(jìn)行移動(dòng)。這樣標(biāo)準(zhǔn)剖面樣板的輪廓就在孔內(nèi)得到復(fù)制。標(biāo)準(zhǔn)剖面樣板精確安裝在一個(gè)專(zhuān)用的滑板上，滑板可以在兩個(gè)方向上進(jìn)行精確調(diào)整以使刀具與工件以正確的關(guān)系對(duì)正。這臺(tái)車(chē)床有一個(gè)偏心夾型的主軸前端，允許在任意一方向旋轉(zhuǎn)時(shí)進(jìn)行切削。正常的車(chē)削是在主軸逆時(shí)針轉(zhuǎn)動(dòng)時(shí)進(jìn)行的；鏜削切削是在主軸順時(shí)針?lè)较蚧颉跋蚝蟆鞭D(zhuǎn)動(dòng)時(shí)進(jìn)行的。這允許在孔的“后側(cè)”進(jìn)行鏜削切削，在車(chē)床前面，從操作者的位置易于看到后孔。在具有螺紋主軸前端的車(chē)床上不應(yīng)這么做，因?yàn)榍邢髁Φ淖饔脮?huì)旋松卡盤(pán)。
銑削
銑削是一種通過(guò)工件與多刃旋轉(zhuǎn)銑刀間的相對(duì)運(yùn)動(dòng)去除材料的加工工藝。在一些應(yīng)用中，工件固定而旋轉(zhuǎn)的銑刀以一定進(jìn)給速度移過(guò)工件（橫向進(jìn)給）；在其他應(yīng)用中，工件與銑刀既彼此相對(duì)運(yùn)動(dòng)，又相對(duì)銑床運(yùn)動(dòng)。但是，更常見(jiàn)的是工件以一個(gè)相對(duì)較低的運(yùn)動(dòng)速度或進(jìn)給速度朝正在高速旋轉(zhuǎn)的銑刀前進(jìn)，而銑刀軸保持在一個(gè)固定位置。銑削工藝特有的性能是每個(gè)銑刀齒都以小的單個(gè)切屑的形式切去一部分原料?？梢栽谠S多不同的機(jī)器上進(jìn)行銑削作業(yè)。
由于工件和銑刀都可以彼此相對(duì)運(yùn)動(dòng)，銑削可以獨(dú)立的或以組合方式完成各式各樣的作業(yè)。各種應(yīng)用包括平面或仿行面、窄槽、槽、退刀槽、螺紋和其他外形的加工。
銑削是一種最為通用而又復(fù)雜的加工方法。該工藝比任何其他基本加工方法在所用機(jī)器的種類(lèi)、工件運(yùn)動(dòng)以及加工工具種類(lèi)方面都具有更多的變化。利用銑削去除材料的重要優(yōu)點(diǎn)包括原料切削速度高，能形成相對(duì)光滑的表面粗糙度以及可應(yīng)用的刀具更為多樣。刀具的切削刀刃可以仿行以形成任何復(fù)雜的表面。
主要的銑削方法有周銑和端銑，此外，還有許多相關(guān)方法，他們屬于這2種方法的變化形式，這些變化形式取決于工件或刀具的類(lèi)型。
周銑
在周銑（有時(shí)也叫平面銑削）中，由位于銑刀主體外周上的尺或刀片銑削的面一般在一個(gè)與銑刀軸平行的平面上。使用鏟齒銑刀和成形銑刀完成的銑削工序包括在這一類(lèi)。銑削面的界面與所使用的銑刀或刀具組合的輪廓線或輪廓相符。
周銑作業(yè)通常在帶有水平定位主軸的銑床上進(jìn)行。但也可以在帶有端面銑刀的主軸銑床上進(jìn)行。銑刀安裝在心軸上，尤其是由于設(shè)置的條件，銑刀或者若干銑刀位于距主軸前端一定距離處時(shí)，心軸一般在外端得到支撐來(lái)提高剛性。如果部件可以端銑，一般不應(yīng)進(jìn)行周銑。
端銑
端銑在臥式銑床和立式銑床上進(jìn)行。由位于銑刀外周和端面的切削刃聯(lián)合銑削所形成的銑削面一般與銑刀軸成直角。除了在肩部銑削時(shí)外，銑削面是平的，與齒的輪廓形狀無(wú)關(guān)。一般來(lái)講，無(wú)論何時(shí)何地，只要可能就應(yīng)使用端銑。
傳統(tǒng)（上）端銑中切屑厚度是變化的，在銑刀齒進(jìn)入和退出處最薄，而在沿水平直徑處最大。銑削面由齒和專(zhuān)屬轉(zhuǎn)速痕跡表現(xiàn)其特征，這與周銑銑刀情況相同。這些痕跡的起伏度由齒的端面切削刃的磨削精度或由刀體/刀片在可以指標(biāo)化的刀具內(nèi)組合精度以及刀具安裝精度來(lái)控制，以使刀具在主軸上精確運(yùn)動(dòng)。起伏度還由機(jī)器及工件本身的剛性來(lái)控制。當(dāng)端面切削刃的長(zhǎng)度短于每轉(zhuǎn)的進(jìn)給量（或銑刀每轉(zhuǎn)一圈工件的移動(dòng)量）時(shí)，在銑面上就會(huì)形成一系列的環(huán)形凹槽或環(huán)紋。當(dāng)后齒在工件的銑面上拖動(dòng)時(shí)，也會(huì)產(chǎn)生類(lèi)似的標(biāo)記，這叫齒根拖動(dòng)。
在端銑中，如果想獲得最佳結(jié)果，重要的是選擇銑刀具有適于所建議的切削寬度的直徑。如果可能，應(yīng)避免切削寬度等與銑刀外徑相同，因?yàn)樵邶X的入口處，薄的銑屑界面會(huì)由于研磨加上銑屑有焊或粘到齒或刀片上并被帶來(lái)帶去或再次切削的趨向而導(dǎo)致齒的加速磨損。這對(duì)表面粗糙度是有害的。好的銑刀直徑與工件或提議的切削路線寬度之比是5：3。
原文：
Basic Machining Operations
Machining tools have evolved from the early foot –powered lathe Egyptians and John Wilkinson’s boring mill. They are designed to provide rigid support for both the workpiece and the cutting tool and cutting tool and can precisely control their relative positions 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 from of a severely deformed chip. The chip is waste product that is workpiece in the from of a severely deformed chip is a waste product that is considerably shorter than the workpiece from which it came but with a corresponding increase in thickness of the uncut chip. The geometrical shape of the machine surface depends on the shape of the tool and its path during the machining opration.
Most machine operations produce parts of differing geometry. If a rough cylindrical workpiece revolves about a central axis and tool penetrates beneath its surface 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 on the machined on the inside in a similar manner, the operation is called boring. Producing an external conical surface of uniformly varying diameter is called taper turning. If the tool point travels in a path of varying radius, a contoured surface like that of bowling pin can be produced; or, if the piece is short enough and the support is sufficiently rigid, a contoured surface could be produced by feeding a shaped tool normal to the axis of rotation. Short tapered or cylindrical surfaces could also be contour formed.
Flat or plane surface are frequently required. They can be generated by radial turning or facing, in which the tool point moves normal to the axis of rotation. In other cases, it is more convenient to hole the workpiece steady and reciprocate the tool across , it is series of straight-line cuts with 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 workpiece under it as in planning. The tool is fed at each reciprocation. Contoured surfaces can be produced by using shaped tools.
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 drill turns or the workpiece rotates, relative 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. Plane 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 work piece may be in any of the three coordinate directions.
Basic Machine Tools
Machine tools are used to part of a specified geometetrical shape and precise size by removing metal from a ductile material in the form chips. The latter are a waste product and vary from long continuous ribbons of a disposal point of view, to easily handed well-broken chips resulting from cast iron. Machine tools perform five basic metal-remove processes: turning, planning, drilling, milling, and grinding. All other metal-removal processes are modifications of these five basic processes. For example, boring is internal turning; reaming, tapping, and counter boring mollify drilled holes and are related to drilling; hobbling and gear cutting are fundamentally milling operations; hack sawing and broaching are a from of planning and honing; lapping, super finishing, polishing, and buffing are variants of grinding or abrasive removal operations. Therefore, there are only four types of basic machine tools, which use cutting tools of specific controllable geometry. The grinding process forms chips, but the geometry of the abrasive grain is uncontrollable.
The amount and rate of material removed by the various machining processes may be large, as in heavy turning operations, or extremely small, as in lapping or superfinishing operations where only the high spots of a surface are removed.
A machining tool performs three major functions: 1. it rigidly supports the workpice or its holder and the cutting tool; 2. it provides relative motion between the workpice and the cutting tool; 3. it provides a range of feeds and speeds usually ranging from 4 to32 choices in each case.
Speed and Feeds in Machining
Speeds, feeds, and depth pf cut are the three major variables for economical machining. 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.
The depths of cut, feed, and cutting speed are machine setting 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 needle 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 radially inward per revolution, or is the difference in position between two adjacent grooves. The depth of cut is the penetration of the needle into the record or the depth of the grooves.
Turning on lathe centers
The basic operations operations performed on an engine lathe are illustrated in fig. 11-3. those operations performed on external surfaces with a single point cutting tool are called turning. Except for drilling, reaming, and tapping, the operations on internal surfaces are also performed by a single point cutting tool.
All machining operate, 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 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-finishing operation will precede the finishing operation to leave a small predetermined and uniform amount of stock on the work-piece to be removed by the finishing operation.
Generally, longer workpieces are turned while supported on one or two lathe centers. Cone shaped holes, called center holes, which fit the lathe centers are drilled in the end 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 end near the headstock 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 in a collet type chuck. This method holds the workpiece firmly and transfers the power to the workpiece smoothly; the additional support to the workpiece provided by the chuck lessens the tendency for chatter to occur when cutting. Precise result can be obtained with this method if care is taken to hold the workpiece accurately in the chuck.
Very precise results can be obtained by supporting the workpiece between two centers. A lathe dog is clamped to the workpiece; together they are driven by the driver plate mounted on the spindle nose. One end of the workpiece is machined; then the workpiece can be turned around in the lathe to machine to 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 workpiece has been remove from the lathe for any reason, the center holes will accurately align the workpiece back in the lathe or in another lathe, or in a cylindrical grinding machine. The workpiece must never be held at the headstock end by both a chuck and a lathe center. While at first thought this seems like a quick method of aligning the workpiece in the chuck, this must not be done because it is not possible to press evenly with the jaws against the workpiece while it is also supported by the center. The alignment provided by the center will not be maintained and the pressure of the jaws may damage the center hole, the lathe center, and perhaps even the lathe spindle. Compensating or floating jaw chucks used almost exclusively on high production work provide an exception to the statements made above. These chucks are really work drivers and cannot be used for the same purpose as ordinary three or four-jaw chicks.
While very large diameter workpiece are sometimes mounted on two centers, they are preferably held at the headstock end by faceplate jaws to obtain the smooth power transmission; moreover, large 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 overhang from the spindle bearings than a large chuck would have.
Boring
The objective of boring a hole in a lathe is:
1．To enlarge the hole
2．To machine the hole to the desired diameter
3．To accurately locate the position of the hole
4．To obtain a smooth surface finish in the hole
The motion of the boring tool is parallel to the axis of the lathe when the carriage is moved in the longitudinal direction and the work piece revolves about the axis of the lathe. When these two motions are combined to bore a hole, it will be concentric with the axis of rotation of the lathe. The position of the hole can be accurately located by holding the work piece in the lathe so that the axis about which the hole is to be machined coincides with the axis of rotation of the lathe. When the boring operation is done in the same setup of the work that is used to turn and face it, practically perfect concentricity and perpendicularity can be achieved.
The boring tool is held in a boring bar which is fed through the hole by carriage. Variations of this design are used, depending on the job to be done. The lead angle used, if any, should always be small. Also, the nose radius of the boring tool must not be too large. The cutting speed used for boring can be equal to the speed for turning. However, when the spindle speed of the lathe is calculated, the finished, or largest, bore diameter should be used. The feed rate for boring is usually somewhat less than for turning to compensate for the rigidity of the boring bar.
The boring operation is generally performed in two steps; namely, rough boring and finish boring. The objective of the rough-boring operation is to remove the excess metal rapidly and efficiently, and the objective of the finish-boring operation is to obtain the desired size, surface finish, and location of the hole. The size of the hole is obtained by using the trial-cut procedure. The diameter of the hole can be measured with inside calipers and outside micrometer calipers. Basic Measuring Instrument, or inside micrometer calipers can be used to measure the diameter directly.
Cored holes and drilled holes are sometimes eccentric with respect to the rotation of the lathe. When the boring tool enters the work, the boring bar will take a deeper cut on one side of the hole than on the other, and will deflect more when taking this deeper cut, with the result that the bored hole will not be concentric with the rotation of the work.. This effect is corrected by taking several cuts through the hole using a shallow depth of cut. Each succeeding shallow cut causes the resulting hole to be more concentric than it was with the previous cut. Before the finale, finish cut is taken, the hole should be concentric with the rotation of the work in order to make certain that the finished hole will be accurately located.
Shoulders, grooves, contours, tapers, and threads are also bored inside of holes. Internal grooves are cut using a tool that is similar to external grooving tool. The procedure for boring internal shoulder is very similar to the procedure for turning shoulders. Larger shoulders are faced with the boring tool positioned with the nose leading, and using the cross slide to feed the tool. Internal contours can be machined using a tracing attachment on a lathe. The tracing attachment is mounted on the cross slide and the stylus follows the outline of the master profile plate. This causes the cutting tool to move in a path corresponding to the profile of the profile plate. Thus, the profile on the master profile plate is reproduced inside the bore. The master profile plate is accurately mounted on a special slide which can be precisely in two directions, in order to align the cutting tool in the correct relationship to the work. This lathe has cam-lock type of spindle nose which permits it to take a cut when rotating in either direction. Normal turning cuts are taken with the spindle rotating counterclockwise. The boring cut is taken with the spindle revolving in a clockwise direction, or “backwards”. This permit the boring cut to be taken on the “back side” of the bore which is easier to see from the operator’s position front of the lathe. This should not be done on lathes having a threaded spindle nose because the cutting force will tend to unscrew the chuck.
Milling
Milling is a machining process for removing material by relative motion between a workpiece and a rotating cutter having multiple cutting edges. In some applications, the workpiece is held stationary while the rotating cutter is moved past it and a given feed rate (traversed). In other applications, both the workpiece and cutter are moved in relation to each other and in relation to the milling machine. More frequently, however, the workpiece is advanced at a relatively low rate of movement or feed to a milling cutter rotating at a comparatively high speed, with the cuter axis remaining in a fixed position, a characteristic feature of the milling process is that each milling cutter tooth takes its share of the stock in the form of small individual chips. Milling operations are performed on many different machines.
Since both the workpiece and cutter can be moved relative to one another, independently or in combination, a wide variety of operations can be performed by milling. Applications include the production of flat or contoured surfaces, slots, grooves, recesses, threads, and other configurations.
Milling is one of the most universal, yet complicated machining methods. The process has more variations in the kinds of machines used, workpie