C616車床的橫向伺服進(jìn)給單元改造設(shè)計(jì)
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濟(jì)源職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì)（論文）意見
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濟(jì)源職業(yè)技術(shù)學(xué)院
機(jī)電系2008屆畢業(yè)生畢業(yè)設(shè)計(jì)答辯記錄
姓 名
李文成
專 業(yè)
機(jī)電一體化
班 級
機(jī)電0510
答辯時間
2007年12月29日
答辯地點(diǎn)
機(jī)電樓306教室
設(shè)計(jì)題目
基于C616車床的橫向伺服進(jìn)給單元改造
1.什么是脈沖當(dāng)量？
答：脈沖當(dāng)量是指一個進(jìn)給脈沖使車床執(zhí)行部件產(chǎn)生的進(jìn)給量,它是衡量數(shù)控機(jī)床加工精度的一個基本技術(shù)參數(shù).
2.脈沖當(dāng)量是由什么來確定的？
答：脈沖當(dāng)量應(yīng)根據(jù)機(jī)床精度來確定.
3.改造后的機(jī)床有什么好處？
答：機(jī)床改造花費(fèi)少，改造設(shè)計(jì)針對性強(qiáng)、時間短，改造設(shè)計(jì)后的機(jī)床大多能夠克服機(jī)床的缺點(diǎn)和存在的問題，生產(chǎn)效率高。
4. 進(jìn)給伺服系統(tǒng)機(jī)械部分的計(jì)算與選型的內(nèi)容包括？
答：進(jìn)給伺服系統(tǒng)機(jī)械部分的計(jì)算與選型的內(nèi)容包括:運(yùn)動參數(shù)、動力參數(shù)的計(jì)算、傳動比的分配、轉(zhuǎn)動慣量、等效轉(zhuǎn)矩等計(jì)算.
5. 選擇步進(jìn)電動機(jī)時應(yīng)該注意什么？
答：選擇步進(jìn)電動機(jī)時,必須根據(jù)機(jī)械傳動裝置及負(fù)載折算到電動機(jī)軸上的等效轉(zhuǎn)動慣量,分別計(jì)算各種情況下所需要的力矩,再根據(jù)步進(jìn)電動機(jī)最大靜轉(zhuǎn)矩和啟動運(yùn)行頻率特性選擇合適的步進(jìn)電動機(jī),負(fù)載慣量是驅(qū)動系統(tǒng)的主要參數(shù)之一,它對選擇步進(jìn)電動機(jī),設(shè)計(jì)傳動比等都有十分重要的意義,如果該慣量與電動機(jī)的匹配不當(dāng),系統(tǒng)就得不到快速反應(yīng),甚至失效.
記錄教師（簽名）：
附錄1
車削、銑削和磨削
用于車外圓，端面和鏜孔等加工的機(jī)床稱作機(jī)床。車削很少在其他種類的機(jī)床上進(jìn)行，因?yàn)槠渌能嚧捕疾荒芟蜍嚧材菢臃奖愕眠M(jìn)行車削加工。由于車創(chuàng)出了用于車外圓外還能用于鏜孔，車斷面，鉆孔和鉸孔，車床的多功能型可以使工件在一次定位安裝中完成多種加工。這就是在生產(chǎn)中普遍使用各種車床比其他種類的車床都要多的原因。
兩千多年前就已經(jīng)有了車床。現(xiàn)代車床可以追述到大約1797年，那時候亨利*莫德斯利發(fā)明了一種具有絲杠的車床。 這種車床可以控制工具的機(jī)械進(jìn)給。 這位聰明的英國人還發(fā)明了一種把主軸和絲杠相連接的變速裝置， 這樣就可以切削螺紋。
車床的主要部件：床身，主軸箱組件，尾架組件，托板組件，變速齒輪箱，絲杠和光杠。
床身是車床的基礎(chǔ)件。它通常是由經(jīng)過充分正火或時效處理的灰鑄鐵或者球墨鑄鐵制成， 它是一個堅(jiān)固的剛性框架，所有其他主要部件都安裝在床身上。 通常在床身上面有內(nèi)外兩組相平行的導(dǎo)軌。 一些制造廠生產(chǎn)的四個條導(dǎo)軌都采用倒‘v’ 形，而另一些制造廠則將倒 V 形導(dǎo)軌和平面導(dǎo)軌相結(jié)合。 由于其他的部件要安裝在導(dǎo)軌上并（或）在導(dǎo)軌上移動，導(dǎo)軌要經(jīng)過精密的加工，以保證其裝配精度。同樣的，在操作中應(yīng)當(dāng)小心，以避免損傷導(dǎo)軌。導(dǎo)軌上的任何誤差，常常會使整個機(jī)床的精度遭到破壞。 大多數(shù)現(xiàn)代車床的導(dǎo)軌要進(jìn)行表面淬火處理，以減少摩擦和擦傷，具有更大的耐磨性。
主軸箱安裝在床身一端內(nèi)導(dǎo)軌的固定位置上。 它提供動力，使工件在各種速度下旋轉(zhuǎn)。 它基本上由一個安裝在精密軸承中的空心主軸和一系列變速齒輪——類似于卡車變速箱所組成，通過變速齒輪，主軸可以在許多種轉(zhuǎn)速下旋轉(zhuǎn)。 大多數(shù)車床有8—18種轉(zhuǎn)速，一般按等比級數(shù)排列。 在現(xiàn)代車床上只需要搬動2—4個手柄，就能得到全部擋位的轉(zhuǎn)速。 目前發(fā)展的趨勢是通過電氣的或者機(jī)械的裝置進(jìn)行無極變速。
由于車床的精度在很大程度上取決于主軸，因此主軸的結(jié)構(gòu)尺寸較大，通常安裝在緊密配合的重型圓錐滾子軸承或球軸承中。 主軸中有一個貫穿全長的通孔，長棒料可以通過該孔送料。主軸孔的大小是車床的一個重要尺寸，因?yàn)楫?dāng)工件必須通過主軸孔供料時，它確定了能夠加工棒料毛胚的最大外徑尺寸。
主軸的內(nèi)端面從主軸箱中凸出，其上可以安裝多種卡盤，花盤，檔塊。而小型的車床常帶有螺紋截面供安裝卡盤之用。大多數(shù)車床使用偏心夾或鍵動圓錐軸頭。這些附件組成了一個大直徑的圓錐體， 以保證對卡盤進(jìn)行精確的裝配，并且不用旋轉(zhuǎn)這些笨重的附件就可以鎖定或者松開卡盤或者花盤。
主軸由電動機(jī)經(jīng)V帶或者無聲鏈裝置提供動力。大多數(shù)現(xiàn)代車床都裝有5—15 馬力的電動機(jī)，為硬質(zhì)合金和金屬陶瓷合金刀具提供了足夠的動力，進(jìn)行高速切削。
尾座組件主要由三部分組成。 底座與床身的內(nèi)側(cè)導(dǎo)軌相配合，并可以在導(dǎo)軌上作縱向移動， 底座上有一個可以使整個尾座組件夾緊在任意位置上的裝置。尾座安裝在底座上，可以沿鍵槽在底座上橫向移動，使尾座與主軸箱中的主軸對中并為切削圓錐體提供方便。尾座組件的第三部分是尾座套筒，它是一個直徑通常在2—3英寸之間的剛制空心圓柱軸。通過手輪和螺桿，尾座套筒可以在尾座體中縱向移入和移出幾英寸。 活動套筒的開口一端具有莫式錐度，可以用于安裝頂尖或者諸如鉆頭之類的各種工具。通常在活動套筒的外表面刻有幾英寸的刻度，以控制尾座的前后移動。鎖定裝置可以使套筒在所需要的位置上夾緊。
托板組件用于安裝和移動切削工具。托板是一個相對平滑的H形狀的鑄件， 安裝在床身外側(cè)導(dǎo)軌上，并可以在上面移動。大托板上有橫向?qū)к?，使橫向托板可以安裝在上面，并通過絲杠使其運(yùn)動，絲杠由一個小手柄和刻度盤控制。橫托板可以帶動刀具垂直于工件的旋轉(zhuǎn)軸線切割。
大多數(shù)車床的安裝架安裝在復(fù)式刀座上，刀座上有底座，底座安裝在橫托板上，可繞垂直軸和上刀架轉(zhuǎn)動，上刀架安裝在底座上，可用手輪和刻度盤控制一個段絲杠使其前后移動。
溜板箱在大托板前面，通過溜板箱內(nèi)的機(jī)械裝置可以手動和動力驅(qū)動大托板以及動力驅(qū)動橫托板。通過轉(zhuǎn)動溜板箱前的小輪，可以手動操作托板沿床身移動。手輪的另一端與溜板箱背面的小齒輪連接，小齒輪與齒條嚙合，齒輪倒裝在床身前上邊緣的下面。
利用光杠可以將動力傳遞給大托板和橫托板。光杠上有一個幾乎可以貫穿整個光杠的鍵槽，光杠通過兩個轉(zhuǎn)向相反并用鍵連接的錐齒齒輪傳遞動力。 通過溜板箱前的換向手柄可使嚙合齒輪與其中的一個錐齒輪嚙合，為大托板提供“向前”或者“向后” 動力。適當(dāng)?shù)碾x合器或者與齒條小齒輪連接或者與橫托板的螺桿連接，使托板縱向移動或者使其橫托板橫向移動。
對于螺紋加工，絲杠提供了第二種縱向移動的方法。光杠通過摩擦力離合器驅(qū)動托板移動，離合器可能會產(chǎn)生打滑現(xiàn)象。而絲杠產(chǎn)生的運(yùn)動是通過溜板箱與絲杠之間的直接機(jī)械連接來實(shí)現(xiàn)的，對開螺母可以實(shí)現(xiàn)這種連接。通過溜板箱前面的夾緊手柄可以使對開螺母緊緊包合絲杠。對開螺母閉合時，可以沿絲杠直接驅(qū)動托板，而不會出現(xiàn)打滑的可能性。
現(xiàn)代的車床由一個變速齒輪箱，齒輪箱的輸入端由車床主軸通過合適的齒輪傳動來驅(qū)動。 齒輪箱的輸出端與絲杠連接。主軸就是這樣通過齒輪傳動鏈驅(qū)動變速齒輪箱，再帶動絲杠和光杠，然后帶動托板，刀具就可以按照株洲的轉(zhuǎn)速縱向地或者橫向的精確移動。一臺典型的車床主軸每旋轉(zhuǎn)一圈，通過光杠可以獲得從0.002到0.118英寸范圍內(nèi)的48種進(jìn)給量，
而使用絲杠可以車削從1.5到92牙/英寸的48種不同的螺紋。一些老式的或者廉價(jià)的車床為了能夠得到所有的進(jìn)給量和加工出所有的螺紋，必須更換主軸和變速齒輪箱之間的齒輪系中的一個或者兩個齒輪。
銑削是機(jī)械加工的一個基本方法。在這一加工過程中，當(dāng)工件沿垂直旋轉(zhuǎn)刀具軸線方向進(jìn)給時，在工件上形成并除去切屑從而逐漸的銑出表面。有時候，工件是固定的，而刀具處于進(jìn)給狀態(tài)。大多數(shù)情況之下，使用多齒刀具，金屬切削量大，只需一次銑削就可以獲得所期望的表現(xiàn)。
在銑削加工中使用的刀具稱作銑刀。它通常是一個繞其軸線旋轉(zhuǎn)并且周邊帶有同間距齒的圓柱體，銑刀齒間歇性接觸并銑削工件。在某些情況下，銑刀上的刀齒會高出圓柱體的一端或兩端。
由于銑削切削金屬速度快，并且能產(chǎn)生良好的表面光潔度，故特別適合大規(guī)模生產(chǎn)加工。為了實(shí)現(xiàn)這一目的，已經(jīng)制造出了質(zhì)量一流的銑床。然而在機(jī)修車間和工具模具加工中心也已經(jīng)廣泛的使用了非常精確的多功能通用的銑床。 車間里擁有一臺銑床和一臺普通車床就能加工出具有適合尺寸的各種產(chǎn)品。
銑削操作類型
銑削操作可以分為兩大類，每一類又有多種類型。
1圓周銑削 在圓周銑削中， 使用的銑刀刀齒固定在刀體的圓周上，工件銑削表面與旋轉(zhuǎn)刀具軸線平行，從而加工表面。 使用這種方法可以加工出平面和成型表面，加工中表面橫截面與刀具的軸向外輪廓相一致。這種加工過程常被稱為平面銑削。
2端面銑削 銑削平面與刀具的軸線垂直，被加工平面是刀具位于周邊和端面的齒綜合作用形成的。 刀具周邊齒完成銑削的主要任務(wù)，而端面齒用于精銑。圓周銑削和端面銑削的基本概念，圓周銑削通常使用臥式銑床，端面銑削則既可以在臥式銑床又可以在立式銑床上進(jìn)行。
銑削面的形成： 銑削時可以采用兩種完全不同的方法。應(yīng)注意，在銑削時， 銑刀旋轉(zhuǎn)方向與工件進(jìn)給方向相反，而在順銑時候銑刀旋轉(zhuǎn)與工件進(jìn)給方向相同。在逆銑削過程中，當(dāng)銑刀齒剛剛切入工件時候，切削時非常薄的，然后漸漸增厚，在刀齒離開工件的地方，切屑最厚。在兩種銑削方法中，切屑的形成是不同的，逆銑削過程中，道具推動工件并使工件從工作臺上提升的趨勢，這種作用有助于消除銑床工作臺進(jìn)給螺旋桿和螺母的間隙，從而形成平穩(wěn)的切削。然而，這種作用也有造成共建與夾緊裝置之間的松動的趨勢，這是應(yīng)當(dāng)施加更大夾緊力。 此外，銑削平面的平整度主要取決于切削刃的鋒利程度。
順銑時，最大切屑厚度產(chǎn)于靠近刀具與工件的接觸點(diǎn)處。由于相對運(yùn)動趨于把工件拉向銑刀，如果采用順銑法，要消除工作臺進(jìn)給螺桿可能產(chǎn)生的松動。因?yàn)?，對于不能于用于順銑的銑床，不要采用順銑的方法。因?yàn)樵阢姷督Y(jié)束切削時，處于切線方向的被切材料發(fā)生屈服，所以與逆銑削相比，順銑的被加工表面沒有之類的切很。順銑的另一個優(yōu)勢是切削力趨于將工件壓緊在工作臺上，因此對工件的夾緊力可以小于逆銑。這一優(yōu)勢可以用于銑削較薄的工件時或進(jìn)行強(qiáng)力切削。
順銑的弱點(diǎn)是銑刀剛剛一切削每片鐵屑時，刀齒會撞擊工件的表面。如果工件表面堅(jiān)硬，向鑄鐵，就會使刀齒迅速變鈍。
銑刀
銑刀的分類有多種的方法，一種方法是根據(jù)刀具后角將銑刀分為兩大類：
1.仿型銑刀 每個刀齒在切削力的背面磨了一個很小的棱面形成后角，切削刃可以是直線的也可以是曲線的。
2.成型或凸輪型后角銑刀 每個齒的橫截面在切削刃的背面成偏心曲線狀，以產(chǎn)生后角。偏心后角的各面與切削刃平行，具有切削刃的相同形狀。這種類型的銑刀僅需要磨削齒的前刀面就可以變得鋒利，只要切削刃的外形保持不變。
銑刀的另一種分類方法是根據(jù)銑刀安裝的方法進(jìn)行分類。 心軸銑刀帶有一個中心孔以使銑刀安裝在心軸上。 帶柄銑刀有一錐柄或直柄軸，含錐形柄的銑刀可以直接安裝在銑床的心軸上，而直柄軸的銑刀則是夾持在卡盤里。平面銑刀通過常用螺栓固定在刀軸的末端上。
根據(jù)這種分類的方法，通用型的銑刀可分類如下：
心軸銑刀： 圓柱形銑刀 ，角度銑刀，側(cè)刃銑刀 ，嵌齒銑刀，錯齒銑刀，成型銑刀，開槽銑刀，高速切削刀。
帶柄銑刀：端面銑刀， T形槽銑刀， 整體式銑刀，半圓鍵座銑刀 套式銑刀，高速切削刀，空心銑刀。
銑刀的類型 圓柱形銑刀是在圓周上有直的或者螺旋形的齒的圓柱形或者盤形銑刀。他們可以用來銑削平面，這種銑削稱作平面銑削。螺旋形的銑刀上的每個齒是逐漸地接觸工件，在給定的時間內(nèi)，一般有多齒進(jìn)行銑削，這樣可以減少震動，獲得一個比較平滑的表面。因此，與直齒銑刀相比，這種類型的銑刀，通常使用的更多。
側(cè)刃銑刀的齒除了在圓柱刀體的一端或者兩端向徑向延伸之外，與圓柱形銑刀是相似的。側(cè)刃銑刀的刀齒既可以是直線運(yùn)動，也可以是螺旋形的，這種銑刀一般較狹小，具有盤形的形狀。在跨式銑削加工中常常講兩個或更多的側(cè)刃銑刀同時相間的安裝在一個刀桿上同步進(jìn)行切削。
雙聯(lián)槽銑刀是由兩個側(cè)刃銑刀組成，但是在銑槽時，作為一組銑刀進(jìn)行操作。在兩個銑刀之間增加了一些薄 墊片，以調(diào)整之間的間距。錯齒銑刀是較薄的圓柱形銑刀，刀上有互相交錯得刀齒，鄉(xiāng)鄰刀齒具有相反的螺旋角。這種銑削經(jīng)研磨后僅用于周銑，在每個齒突出的一邊，留有供切屑排除的縫隙。 這種類型的銑刀可用于高速切削，在銑削深槽時可以發(fā)揮獨(dú)特的作用。
開槽銑刀是一種薄型的圓柱形銑刀，厚度一般為1/32——3/16英寸。 這種銑刀的側(cè)面呈盤狀，有間隙，可以防止粘連。與圓柱形銑刀相比，這種類型的銑刀每英寸直徑上的齒數(shù)更多，通常用于銑削較深的，狹窄的槽，并可以用于切割加工。
磨削分類與無心磨削
近20年來，人們對磨削加工的研究一直非常的感興趣。 一般來說，磨削是被用來作為精加工工序是產(chǎn)品道刀所要求的表面光潔度，正確的尺寸和精確的外形。但是，近期的研究表明磨削也可以像車削，銑削等加工方法那樣很經(jīng)濟(jì)的利用于大量去除不需要的材料。
磨削的分類
磨削加工可以根據(jù)被磨削工件表面形狀，磨床的類型或者磨削的產(chǎn)品類型進(jìn)行分類，根據(jù)表面的類型和磨床的分類，分類如下：
1 平面磨削 ：用于磨削平面。
2 內(nèi)圓，外圓磨削：用于磨削內(nèi)外圓柱表面。
3 無心磨削: 用于磨削內(nèi)，外圓柱表面，在這一加工過程中，使用的磨床不同于常規(guī)的內(nèi)外圓磨床。
4 成型磨削：包括齒輪的磨削，螺紋磨削和花鍵軸磨削等等。
5磨削切割加工：使用高速旋轉(zhuǎn)的薄型的砂輪加工金屬和非金屬的材料。這種加工方法取決于磨粒的切割作用。在切割過程中，產(chǎn)生的熱量有助于切割。
6 砂帶磨削：這種方法在磨削加工中被看作是一個重要的加工方法。由于砂帶易于粘合零件的形狀，因此，可以用來磨削平滑的，圓柱的和曲面的形狀。
7 手工磨削加工：在這一加工過程中，工件或者砂輪在手中，移動并加工。所用的機(jī)械有臺式磨床，便攜式磨床，模具磨床等。然而，對很多零件已設(shè)計(jì)出專用磨床，如曲軸磨床，凸輪磨床等等。在各種磨削加工中，可以根據(jù)磨制產(chǎn)品的類型，或根據(jù)磨床控制的類型作選擇。例如：在圓柱磨削加工中，可以使用下列各種不同的類型的磨床：
1普通外圓磨床。
2重型平面或軋輥磨床。
3萬能外圓磨床。
4 計(jì)算機(jī)數(shù)控外圓磨床。
5 仿型磨床，如計(jì)算機(jī)控制的凸輪磨床。
6 曲軸磨床。
在現(xiàn)代計(jì)算機(jī)數(shù)控機(jī)床中，已經(jīng)實(shí)現(xiàn)了砂輪自動修整和工件自動控制。
無心磨削
在無心磨削加工中，磨削圓柱時工件既不要像外圓磨床那樣用頂尖住圓柱兩個中心孔，也不要使用卡盤，圓柱形工件被支撐在砂輪，導(dǎo)輪和工件支架上，用于外圓表面的無心磨削。 工件的旋轉(zhuǎn)速度是由導(dǎo)輪的表面速度控制的。通過調(diào)節(jié)工件支架，工件的中心就可以保持在砂輪和導(dǎo)輪的中心連接線上。工件支架表面相對中心線有一傾角，其傾斜度和工件中心的高度時獲得精確的圓柱表面的重要參數(shù)。
外圓無心磨削
為了加工不同外形的產(chǎn)品，工業(yè)上使用4種外圓無心磨削，這4種方法：
1縱向進(jìn)給貫穿式無心磨削。
2橫向進(jìn)給無心磨削。
3縱向定程進(jìn)給無心磨削。
4縱向和橫向進(jìn)給組合無心磨削。
縱向進(jìn)給加工用于普通圓柱形工件?？刂戚嗇S相對對砂輪軸稍有傾斜。這樣工件就可以獲得兩種類型的行動：即：1，繞自身軸的旋轉(zhuǎn)；2 平行于砂輪軸的直線運(yùn)動。由于第二種運(yùn)動，工件可以從一側(cè)進(jìn)給，在磨削過程中，工件會移動到另一側(cè)，因此這一加工過程能夠自動化。
橫向進(jìn)給加工用于階梯圓柱體工件加工，這種工件不能貫穿進(jìn)給，在這種情況下，導(dǎo)輪回退，送進(jìn)工件，然后推進(jìn)導(dǎo)輪，進(jìn)行磨削加工。為了使所有直徑都能夠同步的進(jìn)行磨削，砂輪和導(dǎo)輪應(yīng)該具有類似步驟。
縱向定程進(jìn)給磨削加工用于圓錐形表面或僅僅在末端有一定的長度需要磨削的工件。
橫向和縱向進(jìn)給組合用于階梯軸的加工，其階梯軸長度大于砂輪的寬度。
內(nèi)圓磨削，有兩種加工方法，管狀的工件放置在導(dǎo)輪，支撐輪和壓輥之間，導(dǎo)輪，工件和砂輪的中心全都在相同的一條直線上，這種磨削就稱作同心內(nèi)圓無心磨削。
在第二種加工方法中，工件也是支撐在導(dǎo)輪，支撐輥和加壓輥之間，但是砂輪的中心并不位于導(dǎo)輪中心和工件中心的連接線上。 這種磨削稱作偏心內(nèi)圓無心磨削。
在第一種加工方法中，即使是非常薄的管狀工件，其壁厚也能精確的研磨。
附錄2
Turning, milling and grinding
The basic machines that are designed primarily to do turning, facing and boring are called lathes. Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathe can do boring, facing, drilling, and reaming in addition to turning, their versatility permits several operations to be performed with a single setup of the work piece. This account for the fact that lathes of various types are more widely used in manufacturing than any other machine tool.
Lathes in various forms have existed for more than two thousand years. Modern lathes date from about 1797, when Henry Maudsley developed one with a lead screw. It provided controlled, mechanical feed of the tool. This ingenious Englishman also developed a change gear system that could connect the motions of the spindle and leads crew and thus enable threads to be cut.
Lathe Construction. The essential components of a lathe are depicted in the block diagram of Fig.15. These are the bed, headstock assembly, tailstock assembly, carriage assemble, quick-change gear box, and the leads crew and feed rod.
The bed is the backbone of lathe. It usually is made of well-normalized or aged gray or nodular cast iron and provides a heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, and contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat ways intone or both set. Because several other components are mounted and /or move on the ways they must be made with precision to assure accuracy of alignment. Similarly, proper precaution should be taken in operating a lathe to assure that the ways are not damaged; any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed. The ways on most modern lathes are surface hardened to offer greater resistance to wear and abrasion.
The headstock is mounted in affixed position on the inner ways at one end of the lathe bed. It provides a provides a powered means of rotating the work at various speeds. It consists, essentially, of a hollow spindle, mounted in accurate bearings, and a set of transmission gears---similar to a truck transmission---through which the spindle can be rotated at a number of speeds. Most lathes provide from eight to eighteen speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives.
Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball types, A longitudinal hole extends through the spindle so that long bar stock can be fed through it. The size of this hole is an important size dimension of a lathe because it determines the maximum size of bar stock that can be machined when the material must be fed through the spindle.
The inner end of the spindle protrudes from the gear box and contains a means for mounting various types of chucks , face plates , and dog plates on it .Whereas small lathes often employ a threaded section to which the chucks are screwed, most large lathes utilize either cam-lock or key-drive taper noses . These provide a large-diameter taper that assures the accurate alignment of the chuck, and a mechanism that permits the chuck or face plate to be locked or unlocked in position without the necessity of having to rotate these heavy attachment.
Power is supplied to the spindle by means of an electric motor through a V-belt or silent-chain drive. Most modern lathe has motors of from 5 to 15 horsepower to provide adequate power for carbide and ceramic tools at their high cutting speeds.
The tailstock assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clamping the entire assembly in any desired location. An upper casting fits on the lower one and can be moved transversely upon it on some type of keyed ways. The transverse motion permits aligning the tailstock and headstock spindles and provides a method of turning tapers .The third major component of the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 2 to 3 inches in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a hand wheel and screw. The open end of the quill hole terminates in a Morse taper in which a lathe center, or various tools such as drills, can be held. A graduated scale, several inches in length, usually is engraved on the outside of the quill to aid in controlling its motion in and out of the upper casting. A locking device permits clamping the quill in any desired position.
The carriage assembly provides the means for mounting and moving cutting tools. The carriage is a relatively flat H-shaped casting that rests and moves on the outer set of ways on the bed. The transverse bar of the carriage contains ways on which the cross slide is mounted and can be moved by means of a feed screw that is controlled by a small hand wheel and a graduated dial. Through the cross slide is a means is provided for moving the lathe tool in the direction normal to the axis of rotation of the work.
On most lathes the tool post actually is mounted on a compound rest .This consists of a base, which is mounted on the cross slide so that it can be pivoted about a vertical axis, and an upper casting. The upper casting is mounted on ways on this base so that it can be moved back and forth and controlled by means of a short lead screw operated by a hand wheel and a calibrated dial.
Manual and powered motion for the carriage, and powered motion for the cross slide, is provided by mechanisms within the apron, attached to the front of the carriage. Manual movement of the carriage along the bed is effected by turning a hand wheel on the front of the apron, which is geared to a pinion on the back side. This pinion engages a rack that is attached beneath the upper front edge of the bed in an inverted position.
To impart powered movement to the carriage and cross slide, a rotating feed rod is provided. The feed rod, which contains a keyway throughout most of its length, passes through the two reversing bevel pinions and is keyed to them. Tighter pinion cam be brought into mesh with a mating bevel gear by means of the reversing lever on the front of the apron and thus provide “forward” or “reverse” power to the carriage. Suitable clutches connect either the rack pinion or the cross-slide screw to provide longitudinal motion of the carriage or transverse motion of cross slide.
For cutting threads, a second means of longitudinal drive is provided by a lead screw. Whereas motion of the carriage when driven by the feed-rod mechanism takes place through affrication clutch in which slippage is possible, motion through the lead screw is by a direct, mechanical connection between the apron an the lead screw. This is achieved by a split nut. By means of a clamping lever on the front of the apron, the split nut can be closed around the lead screw. With the split nut closed, the carriage is moved along the lead screw by direct without possibility of slippage.
Modern lathes have a quick-change gear box. The input end of this gear box is driven from the lathe spindle by means of suitable gearing. The output end of the gear box is connected to the feed rod and lead screw. Thus through this gear train, leading from the spindle to the quick-change gear box. Thence to the lead screw and feed rod, and then to the carriage, the cutting tool can be made to move a specific distance, either longitudinally or transversely, of each revolutions of the spindle. A typical lathe provides, through the feed rod, forty-eight feeds ranging from 0.002 inch to 0.118 inch per revolution of the spindle, and, through the lead screw, leads for cutting forty-eight different threads from 1.5 to 92 per inch. On some older and some cheaper lathes, one or two gears in the gear train between the spindle and the change gear box must be changed in order to obtain a full range of threads and feed.
Milling is basic machining process in which the surface is generated by the progressive formation and removal of chips of material from the work piece as it is fed to a rotating cutter in a direction perpendicular to the axis of the cutter. In some cases the work piece is stationary and the cutter is fed to the work .In most instances a multiple-tooth cutter is used so that the metal removal rate is high and frequently the desired surface is detained in a single pass of the work.
The tool used in milling is known as a milling cutter. It usually consists of a cylindrical body which rotates on its axis and contains equally spaced peripheral teeth that intermittently engage a cut the work piece. In semen cases the teeth extend part way across one or both ends of the cylinder.
Because the milling principle provides rapid metal removal and can produce good surface finish, it is particularly well-suited for mass-production work, and excellent milling machine have been developed for this purpose . However, very accurate and versatile milling shop and tool and die work. A shop that is equipped with a milling machine and an engine lathe can machine almost any type of product of suitable size.
Types of milling operations. Milling operations can be classified into two broad categories, each of which has several variations:
1 In peripheral milling a surface is generated by teeth located in the periphery of the cutter body; the surface is parallel with the axis of rotation of the cutter. Both flat and formed surfaces can be produced by this method. The cross section of the resulting surface corresponds to the axial contour of the cutter. This procedure often is called slab milling.
2 In face milling the generated flat surface is at right angles to the cutter axis and is the combined result of the actions of the portions of the teeth locate4d on both the periphery and the face of the cutter . The major portion of the cutting is done by the peripheral portions of the teeth with the face portion of the cutting is done by the peripheral portions of the teeth with the face portions providing a finishing action
The basic concepts of peripheral and face milling are illustrated in fig.16-1.peripheral milling operations usually are performed on machines having horizontal spindles, whereas face milling is done on both horizontal an vertical –spindle machines.
Surface generation in milling. Surfaces can be generated in milling by two distinctly different methods depicted in fig. note that in up milling the cutter rotates against the direction of feed the work piece, whereas in down milling the rotation is the same direction as the feed. A shown in fig16-2, the method of chip formation is quite different in the two cases. In up milling the c hip is very thin at the beginning, where the tooth first contacts the work, and increase in thickness, becoming a maximum where the tooth leaves the work. The cutter tends to push the work along and lift it upward from the table. This acting tends to eliminate any effect of looseness in the feed screw and nut of the milling machine table and results in a smooth cut. However, the action also tends to loosen the work from the clamping device so that greater clamping forcers must be employed. In addition the smoothness of the generated surface depends greatly on the sharpness of the cutting edges.
In down milling, maximum chip thickness occurs close to the pint at which the tooth contacts the work. Because the relative motion tends to pull the work piece into the cutter, all possibility of looseness in table feed screw must be eliminated if down milling is to be used. It should never be attempted on machines that are not designed for this type of milling. Inasmuch as the material yields in approximately a tangential direction at the end of the tooth engagement, there is much less tendency for the machined surface to show tooth marks than when up milling is used. A nether considerable advantage of down milling is thee the cutting force tends to hold the work against the machine table, permitting lover clamping force to be employed. This is particularly advantageous when milling thin work piece or when taking heavy cuts.
Sometimes a disadvantage of down milling is that the cutter teeth strike against the surface of the work at the beginning of each chip. When the work piece has a hard surface, such as casting do, this may cause the teeth to dull rapidly.
Milling cutters. Milling cutters can be classified several ways one method is to group them into two broad classes, based on tooth relief, as follows:
1 Profile-cutters have relief provided on each tooth by grinding a small land back of the cutting edge. The cutting edge may be straight or curved.
2 In form or cam-relieved cutters the cross section of each tooth is an eccentric curve behind the cutting edge, thus providing relief. All sections of the eccentric relief, parallel with the cutting edge, must have the same contour as the cutting edge; cutters of these types are sharpened by grinding only the face of the teeth, with the contour of the cutting edge thus remaining unchanged.
Another useful method of classification is according to the method of mounting the cutter. Arbor cutters are those the have a center hole so they can be mounted on an arbor. Shank cutters have either tapered or straight integral shank. Those with tapered shanks can be mounted directly in the milling machine spindle, w
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