外文翻譯--機(jī)械專業(yè)機(jī)床基礎(chǔ)

1、<p><b>　　機(jī)床基礎(chǔ)</b></p><p>　　許多情況下，初步進(jìn)行成型加工出來(lái)的工件必須在尺寸和表面光潔度方面進(jìn)一步精整，以滿足它們的設(shè)計(jì)技術(shù)要求。為了滿足精密的公差，需要從工件上去掉小量材料。通常機(jī)床就是用于這種加工的設(shè)備。</p><p>　　在美國(guó)，材料切削業(yè)是一個(gè)很大的企業(yè)——費(fèi)用每年超過(guò)36×109 美元，包括材料，勞動(dòng)力，管

2、理費(fèi)，機(jī)床裝運(yùn)費(fèi)等所花的費(fèi)用。由于60%機(jī)械和工業(yè)工程以及技術(shù)等級(jí)評(píng)定工作都跟機(jī)械加工工業(yè)有某些關(guān)系，或者通過(guò)買賣、設(shè)計(jì)或者機(jī)器車間中操作或在有關(guān)工業(yè)企業(yè)中加工，因此，對(duì)于工程專業(yè)學(xué)生來(lái)說(shuō)，在他的學(xué)習(xí)計(jì)劃中集中一段時(shí)間去學(xué)習(xí)研究材料切削和機(jī)床，那是個(gè)好方法。</p><p>　　機(jī)床通過(guò)切削工具去使工作成型以達(dá)到所需的尺寸提供了手段。機(jī)床通過(guò)其基礎(chǔ)構(gòu)件的功能作用，以控制相互關(guān)系方式支持、夾緊工具和工件，現(xiàn)將基本部

3、件列舉如下：</p><p>　　(a)床身，構(gòu)架即機(jī)架。這是一個(gè)主要部件，該部件為主軸、拖板箱等提供一個(gè)基礎(chǔ)和連接中介，在負(fù)載作用下，它必須使變形和振動(dòng)保持最小。</p><p>　　(b)拖板箱和導(dǎo)軌。機(jī)床部件（如拖板箱）的移動(dòng)，通常是在精確的導(dǎo)軌面約束下靠直線運(yùn)動(dòng)來(lái)實(shí)現(xiàn)。</p><p>　　(c)主軸和軸承。角位移是圍繞一個(gè)旋轉(zhuǎn)軸線發(fā)生的，該軸線的位置必須在

4、機(jī)床中極端精確的限度內(nèi)保持恒定，而且是靠精密的主軸和軸承來(lái)提供保證。</p><p>　　(d)動(dòng)力裝置。電動(dòng)機(jī)是為機(jī)床所普遍采用的動(dòng)力裝置。通過(guò)對(duì)各個(gè)電機(jī)的合適定位，使皮帶和齒輪傳動(dòng)裝置減少到最少。</p><p>　　(e)傳動(dòng)連桿機(jī)構(gòu)。連桿機(jī)構(gòu)是個(gè)通用術(shù)語(yǔ)，用來(lái)代表機(jī)械、液壓、氣動(dòng)或電動(dòng)機(jī)構(gòu)的，這些機(jī)構(gòu)與確定的角位移和線性位移相關(guān)聯(lián)。</p><p>　　加工

5、工藝有兩個(gè)主要組成部分：</p><p>　　(a)粗加工工藝。粗加工，金屬切除率高，因而往往切削力也大，但所要求的尺寸精度低。</p><p>　　(b)精加工工藝。精加工，金屬切除率低，因而往往切削力也小，但所要求的尺寸精度和表面光潔度高。</p><p>　　由此可見(jiàn)，靜載荷和動(dòng)載荷，例如由不平衡的砂輪引起的動(dòng)載荷，在精加工中比粗加工中有著更為重要的意義。任何

6、加工過(guò)程所獲得的精度通常將受到由于力的作用引起發(fā)生的變形量的影響。</p><p>　　機(jī)床座架一般是用鑄鐵制造的，然而有些也可能用鑄鋼或中碳鋼來(lái)制造。選用鑄鐵是因?yàn)樗阋?，剛性好，受壓?qiáng)度高，并且有減弱機(jī)床操作中產(chǎn)生的振動(dòng)的能力。為了避免床身鑄件碩大斷面，精心地設(shè)計(jì)筋條構(gòu)架以便提供最大的抗彎曲和抗扭轉(zhuǎn)應(yīng)力的能力。筋條的兩種基本類型是：箱型結(jié)構(gòu)和片狀斜支撐式。箱型結(jié)構(gòu)便于生產(chǎn)，箱壁上有孔口便于使型芯定位和取出。片

7、狀斜支撐筋條有較大的抗扭剛度亦能使截面上的碎屑掉落。它常常用于車床床身。機(jī)床的拖板箱和導(dǎo)軌是支撐和引導(dǎo)彼此相對(duì)運(yùn)動(dòng)的零部件，通常是改變刀具相對(duì)于工件的位置。運(yùn)動(dòng)一般以直線運(yùn)動(dòng)的方式，但也有時(shí)是轉(zhuǎn)動(dòng)，例如對(duì)應(yīng)于工件的螺紋上的螺旋角方向而使萬(wàn)能螺紋磨床上的砂輪頭轉(zhuǎn)動(dòng)一個(gè)角度。拖板箱構(gòu)件的基本的幾何結(jié)構(gòu)形狀是平的、V型槽形、燕尾槽形和圓柱形的。這些構(gòu)件可根據(jù)用途，以各種方法分別使用或結(jié)合使用。導(dǎo)軌的特性如下：</p><p

8、>　　(a)運(yùn)動(dòng)精確。于此拖板是要按直線移動(dòng)的，這直線必定是由兩個(gè)相互垂直的平面形成而且拖板必定不存在轉(zhuǎn)動(dòng)。機(jī)床導(dǎo)軌的直線度公差是每米0—0.02毫米，在水平面上這個(gè)公差可以進(jìn)行處理，以使得凸形表面，這樣就抵消導(dǎo)軌下凹的作用。</p><p>　　(b)調(diào)整手段。為了便于裝配、維護(hù)精度和在發(fā)生磨損后便于限制移動(dòng)構(gòu)件之間的“竄動(dòng)”，有時(shí)在拖板內(nèi)裝入扁條，這扁條被叫做“鋃條”。通常該鋃條用穿過(guò)長(zhǎng)孔的沉頭螺釘支住

9、，而用平頭螺釘調(diào)整好后用鎖緊螺母上緊。</p><p>　　(c)潤(rùn)滑。導(dǎo)軌可用以下兩種裝置進(jìn)行潤(rùn)滑：1) 間歇潤(rùn)滑，通過(guò)潤(rùn)滑脂嘴或油嘴進(jìn)行。這是一種適于運(yùn)動(dòng)速度低而不頻繁場(chǎng)合的方法。2) 連續(xù)潤(rùn)滑，例如通過(guò)計(jì)量閥和管道將潤(rùn)滑油泵送到潤(rùn)滑點(diǎn)。用這種方法引入兩表面間的油膜必定是很薄的，目的是避免使拖板“浮起”。如果滑移表面似鏡面平滑，油就會(huì)被擠出而導(dǎo)致表面粘貼。因而在實(shí)踐上，拖板滑移表面是用凹面砂輪的刃進(jìn)行磨削或進(jìn)

10、行刮研。兩種工藝都可產(chǎn)生微小的表面凹痕，它就成為存油凹陷，相配合的零件就不會(huì)處處因“浮起”而發(fā)生分離，這樣使拖板確定保持接觸導(dǎo)軌。</p><p>　　(d) 防護(hù)。為了維護(hù)導(dǎo)軌處于良好狀態(tài)，以下條件必須滿足：1) 必須防止外面物質(zhì)，如碎屑進(jìn)入。具有某一形狀的導(dǎo)軌那是所期望的。在這種場(chǎng)合，是不可能進(jìn)入雜物的，例如是倒V形的導(dǎo)軌時(shí)，那就不可能保存碎屑雜物在導(dǎo)軌上。2) 必須保存潤(rùn)滑油。在垂直或傾斜的導(dǎo)軌面上使用的油

11、要有粘性，那很重要。為了這種使用目的已經(jīng)專門研制出多種有用的潤(rùn)滑油。油的粘性也要保護(hù)，以免被切削液沖毀。3) 必須用防護(hù)罩來(lái)防止意外的損壞。</p><p>　　一臺(tái)機(jī)床實(shí)現(xiàn)三個(gè)主要功能：1) 牢固的支持工件或者刀架和刀具；2) 在工件和刀具之間提供相對(duì)運(yùn)動(dòng)；3) 提供一定的走刀和切削速度范圍。</p><p>　　以去除切屑形式來(lái)加工金屬的機(jī)床一般分為四大類：使用單點(diǎn)刀具切削的機(jī)床；使用

12、多點(diǎn)刀具切削的機(jī)床；使用隨機(jī)點(diǎn)刀具切削的機(jī)床（磨削）和考慮用于特殊場(chǎng)合的機(jī)床。</p><p>　　本質(zhì)上，使用單點(diǎn)刀具切削的機(jī)床包括：1) 普通車床；2) 塔式車床；3) 仿形車床；4)單軸自動(dòng)車床；5) 多軸自動(dòng)車床；6) 牛頭刨和龍門刨床；7)鏜床。</p><p>　　使用多點(diǎn)刀具切削的機(jī)床包括：1) 鉆床；2) 銑床；3) 拉床；4) 鋸床；5)齒輪切割機(jī)床。</p>

13、<p>　　使用隨機(jī)點(diǎn)刀具切削的機(jī)床包括：1) 外圓磨床；2)無(wú)心磨床；3)平面磨床。</p><p>　　用特殊的方法進(jìn)行金屬切削的機(jī)床包括：1) 化學(xué)蝕刻銑削機(jī)床；2) 電火花加工機(jī)床；3) 超聲波加工機(jī)床。車床是借助于轉(zhuǎn)動(dòng)的工件對(duì)著刀具來(lái)切去金屬材料，以產(chǎn)生外圓柱面或內(nèi)圓柱面或錐形表面的。它借助端面切削也普遍用于加工平面。在端面切削加工中，工件旋轉(zhuǎn)，而刀具作垂直于回轉(zhuǎn)軸線方向移動(dòng)。</p

14、><p>　　普通車床是基本的旋削機(jī)床，從這點(diǎn)出發(fā)，已經(jīng)研制出其他旋削機(jī)床。驅(qū)動(dòng)電機(jī)裝在床身基礎(chǔ)上并通過(guò)齒輪、皮帶相結(jié)合來(lái)驅(qū)動(dòng)主軸，以提供每分鐘25到1500轉(zhuǎn)的轉(zhuǎn)速。主軸是一根堅(jiān)固的空心軸，裝在重型軸承之間，其前端用來(lái)安裝驅(qū)動(dòng)盤（花盤），以便把確定的運(yùn)動(dòng)傳到工作。</p><p>　　該驅(qū)動(dòng)盤可借助螺紋、凸輪鎖緊機(jī)構(gòu)或借助一個(gè)螺紋墊圈和鍵固定在主軸上。</p><p>

15、;　　車床的床身是鑄鐵件。它提供精確的磨削的滑動(dòng)表面（導(dǎo)軌），其上放有拖板。該車床拖板是H型的鑄件，而刀具就安裝在拖板上的刀架上。溜板箱裝在拖板前面，并裝有移動(dòng)刀具的齒輪機(jī)構(gòu)，而拖板順著導(dǎo)軌或橫過(guò)導(dǎo)軌以提供所希望的刀具的運(yùn)動(dòng)。拖板上面的小刀架能使刀夾回轉(zhuǎn)所要求的任意角度。為使刀具作線性運(yùn)動(dòng)，在小刀架上裝有手輪和絲桿。以手輪和使小刀架垂直于車床導(dǎo)軌移動(dòng)的絲桿來(lái)提供橫向進(jìn)給。溜板箱中的齒輪系可為拖板沿著導(dǎo)軌和橫跨導(dǎo)軌提供動(dòng)力進(jìn)給。進(jìn)給箱齒輪

16、將運(yùn)動(dòng)傳給拖板并控制刀具相對(duì)于工件的運(yùn)動(dòng)速度。典型的車床進(jìn)給范圍是主軸每轉(zhuǎn)從0.002到0.160英寸，大約有50級(jí)轉(zhuǎn)速。由于進(jìn)給箱的移動(dòng)運(yùn)動(dòng)是由主軸齒輪驅(qū)動(dòng)的，因此進(jìn)給量直接與主軸速度有關(guān)。進(jìn)給箱齒輪傳動(dòng)機(jī)構(gòu)也用于加工螺紋并能加工每英寸4到224扣螺紋。</p><p>　　進(jìn)給箱和車床溜板箱之間的連結(jié)軸是光桿和絲桿。許多車床制造商把這兩桿結(jié)合為一桿，實(shí)際上那就以精確的開(kāi)支減少機(jī)器的費(fèi)用。進(jìn)給桿（光桿）用于提供

17、刀具的運(yùn)動(dòng)，它對(duì)于精確的工件和好的表面光潔度是很重要的。螺紋導(dǎo)桿（絲桿）用于提供精確的（螺紋）導(dǎo)程，這對(duì)于螺紋切削是必需的。光桿是通過(guò)摩擦離合器來(lái)驅(qū)動(dòng)的，那樣在刀具切削超載情況下能夠打滑保護(hù)。這一安全裝置不能裝在絲桿上，因?yàn)槁菁y加工是不允許打滑的。由于螺紋全深很難一次走刀加工完成，因此裝設(shè)一螺紋指示盤作為下幾次走刀加工時(shí)重新對(duì)刀用。</p><p>　　車床裝有尾座，它具有一精確的軸，該軸有一錐孔，以便安裝鉆頭、

18、鉆夾、鉸刀和車床頂針。尾座可以沿著車床導(dǎo)軌移動(dòng)以適應(yīng)工件的不同長(zhǎng)度以及加工錐體或錐形表面。</p><p>　　轉(zhuǎn)塔車床基本上是具有某種附加特性的普通車床，提供作為半自動(dòng)加工和減少人工操作誤差的機(jī)會(huì)。轉(zhuǎn)塔車床的拖板設(shè)有T形槽以便在車床導(dǎo)軌兩端安裝夾刀裝置，當(dāng)轉(zhuǎn)塔轉(zhuǎn)入到合適位置時(shí)，要正確地裝設(shè)刀具以便進(jìn)行切削。拖板也裝設(shè)有自動(dòng)停機(jī)裝置以便控制刀具行程和提供良好的切削的再生產(chǎn)。轉(zhuǎn)塔車床的尾座是六角形結(jié)構(gòu)，在六角頭中可

19、以裝六把刀具。雖然裝刀和加工準(zhǔn)備要花大量時(shí)間，但轉(zhuǎn)塔車床一次裝刀以后無(wú)需熟練工人就可以連續(xù)地重復(fù)地操作加工，直到刀具變鈍并需更換為止。這樣轉(zhuǎn)塔車床僅就生產(chǎn)工作在經(jīng)濟(jì)上是可行的、合理的，于此，根據(jù)所制造零件的數(shù)量，為加工準(zhǔn)備需要花一定數(shù)量的時(shí)間是合理的，無(wú)可非議的。</p><p>　　跟蹤、重復(fù)加工車床裝有一個(gè)重復(fù)裝置以自動(dòng)控制單點(diǎn)刀具縱向和橫向的進(jìn)給運(yùn)動(dòng)并可以一次或兩次走刀就生產(chǎn)出所需形狀和尺寸的光潔零件。&l

20、t;/p><p>　　單軸自動(dòng)車床使用一個(gè)立式轉(zhuǎn)塔和兩個(gè)橫向溜板。工件通過(guò)機(jī)床主軸孔被送入卡盤，而刀具是靠凸輪來(lái)自動(dòng)操作控制。</p><p>　　多軸自動(dòng)車床裝有四、五、六或八根主軸，在每根主軸中裝一個(gè)工件。各主軸圍繞著一根中心軸來(lái)轉(zhuǎn)換位置。以主刀具溜板去接近各主軸。每根主軸位上都裝有一側(cè)向可以獨(dú)立操作的刀具滑板。由于各刀具滑板都是靠凸輪操作的，因此加工準(zhǔn)備可能花幾天時(shí)間，因而至少需要500

21、0件的批量生產(chǎn) ，它的使用才是合理的。這種機(jī)床的主要優(yōu)點(diǎn)就是所有的刀具同時(shí)工作，因而一個(gè)工人可以看管幾部機(jī)床。對(duì)于相對(duì)簡(jiǎn)單的零件而言，多軸自動(dòng)車床可以以每五秒一件的速度生產(chǎn)加工出成品來(lái)。</p><p>　　牛頭刨床使用裝在滑枕一端的刀夾上的單點(diǎn)刀具。切削加工通常是以向前的行程來(lái)進(jìn)行。刀具被抬刀架稍稍抬舉，以避免（刀具）劃過(guò)工件表面的嚴(yán)重拖刮。在返回行程中，刀具下面進(jìn)給機(jī)構(gòu)使工件進(jìn)給為下一次切削作準(zhǔn)備。立式箱形床

22、身裝有牛頭刨的操作機(jī)構(gòu)，亦用作安裝支持工件的工作臺(tái)。工作臺(tái)可在與滑枕互相垂直的兩個(gè)方向上移動(dòng)。利用刀具滑塊來(lái)控制切割深度并進(jìn)行手動(dòng)進(jìn)給。它也可以在其法向垂直位置的各側(cè)回轉(zhuǎn)90度角，那樣就允許相對(duì)于工作臺(tái)表面成一個(gè)角度，再使刀具進(jìn)給。</p><p>　　牛頭刨床有兩種類型的驅(qū)動(dòng)機(jī)構(gòu)：修正過(guò)的惠式快回機(jī)構(gòu)和液壓驅(qū)動(dòng)機(jī)構(gòu)。對(duì)于惠式機(jī)構(gòu)，電動(dòng)機(jī)驅(qū)動(dòng)大齒輪，大齒輪驅(qū)動(dòng)曲臂，通過(guò)可調(diào)節(jié)的曲柄銷來(lái)控制行程長(zhǎng)度。當(dāng)大齒輪旋轉(zhuǎn)時(shí)

23、，搖桿臂受力而往復(fù)運(yùn)動(dòng)并把運(yùn)動(dòng)傳遞給牛頭刨滑枕。</p><p>　　在液壓牛頭刨中的電動(dòng)機(jī)，僅僅是用來(lái)驅(qū)動(dòng)液壓泵。牛頭刨的殘余運(yùn)動(dòng)是靠液壓油的流向來(lái)控制。為機(jī)械所驅(qū)動(dòng)的牛頭刨的切削行程只利用了大齒輪旋轉(zhuǎn)的220度。而返回行程利用了140度。這就構(gòu)成切削行程與返回行程之速比為1.6比1。速度圖表明：切削行程中刀具的速度決不是恒定的，而液壓牛頭刨的速度圖表明：對(duì)于大多數(shù)切削行程，切削速度是恒定的。液壓牛頭刨增加了一

24、個(gè)優(yōu)點(diǎn)，即切削速度可無(wú)級(jí)變速。這類機(jī)床的主要缺點(diǎn)是在滑枕沖程的終端缺乏確定的限制。那就可能允許有千分之幾英寸的行程長(zhǎng)度誤差。</p><p>　　使得由薄板型模板來(lái)再制輪廓成為可能的雙套裝置是有效的。薄板模用來(lái)跟液壓控制相配合。</p><p>　　各種規(guī)格和類型的立式鉆床或手搖鉆床是很有用的，并配以有足夠?qū)挿秶闹鬏S速級(jí)，且能自動(dòng)進(jìn)給以滿足大多數(shù)工業(yè)的需要。典型鉆床的速級(jí)范圍是從每分鐘7

25、6轉(zhuǎn)到每分鐘2025轉(zhuǎn)。鉆頭進(jìn)給速度為：主軸每轉(zhuǎn)從0.002英寸到每轉(zhuǎn)0.020英寸。</p><p>　　搖臂鉆床是用來(lái)鉆削那種很笨重以至于不便搬動(dòng)的工件。</p><p>　　具有速度調(diào)節(jié)和進(jìn)給調(diào)節(jié)機(jī)構(gòu)的主軸被裝在搖臂上。通過(guò)將轉(zhuǎn)臂繞立柱的轉(zhuǎn)動(dòng)同主軸組件沿?fù)u臂的移動(dòng)相結(jié)合，可使主軸和鉆頭對(duì)準(zhǔn)機(jī)床可達(dá)范圍內(nèi)的任何位置上。</p><p>　　對(duì)于太大而不便于放在鉆

26、床工作臺(tái)上的工件，可把主軸組件擺到地面上方并擺到放在機(jī)床旁邊地上的工件上方。</p><p>　　普通搖臂鉆床只能使主軸垂直運(yùn)動(dòng)，而萬(wàn)能搖臂鉆床允許主軸圍繞垂直于搖臂的軸線旋轉(zhuǎn)，而搖臂可繞著水平軸線旋轉(zhuǎn)，這樣就可以在任何角度方位下鉆削。</p><p>　　多軸鉆床具有一個(gè)或多個(gè)通過(guò)萬(wàn)向接頭和可伸縮的花鍵軸來(lái)驅(qū)動(dòng)主軸的裝置。所有的主軸通常都由同一部電動(dòng)機(jī)驅(qū)動(dòng)并同時(shí)進(jìn)給以便鉆削出所要求的孔數(shù)

27、。在大多數(shù)鉆床中，每根主軸都被裝夾在一可調(diào)節(jié)盤中，以便它能相對(duì)于其他主軸而移動(dòng)。相鄰主軸所對(duì)準(zhǔn)的區(qū)域部分交疊以便使鉆床可在其范圍內(nèi)任何位置鉆孔。</p><p>　　銑削工藝是以旋轉(zhuǎn)的刀具來(lái)切去金屬。它包括從工件表面上切去金屬，擴(kuò)大孔眼和成形切削，例如螺紋加工和輪齒加工。</p><p>　　升降臺(tái)式的銑床內(nèi)，立柱是為其他零件的主要支乘構(gòu)件，并包括裝有驅(qū)動(dòng)電機(jī)、主軸和刀具的基礎(chǔ)件。刀具裝于

28、主軸的刀桿上，并且通過(guò)懸臂內(nèi)的軸承而被支承在其外端。升降臺(tái)用燕尾槽裝在立柱上，鞍座用燕尾槽固緊到升降臺(tái)上，而工作臺(tái)則被連接座架上。這樣，該升降臺(tái)的建立使立柱式鉆床能提供相對(duì)于刀具的三個(gè)運(yùn)動(dòng)。借助使工作臺(tái)繞著鞍座上的垂直軸線旋轉(zhuǎn)，就可以提供四個(gè)運(yùn)動(dòng)。</p><p>　　床身固定的銑床設(shè)計(jì)的具有比升降臺(tái)和立柱式的更好的剛性。這工作臺(tái)被直接安裝在機(jī)床基礎(chǔ)板上，為了吸收重大切削力，工作臺(tái)具有良好的剛性，那是必要的，而且

29、僅允許相對(duì)工作臺(tái)作縱向運(yùn)動(dòng)。垂直運(yùn)動(dòng)靠移動(dòng)整個(gè)刀頭獲得。</p><p>　　仿型銑床的特點(diǎn)是刀具和跟蹤元件的軌跡運(yùn)動(dòng)的協(xié)調(diào)或同步。在典型仿型銑床中，跟蹤指針跟隨模型的形狀輪廓，而刀頭重復(fù)著仿型運(yùn)動(dòng)。</p><p>　　Fundamentals of Machine Tools</p><p>　　In many cases products from the p

30、rimary forming processes must undergo further refinements in size and surface finish to meet their design specifications.To meet such precise tolerance the removal of small amounts of material is needed.Usually machine t

31、ools are used for such operation.</p><p>　　In the United States material removal is a big business—in excess of ＄36×109 per year,including material,labor,overhead,and machine-tools shipments,is spent.Si

32、nce 60 percent of the machanical and industrial engineering and technology graduate have something connection with the machining industry either through sale,design,or operation of machine shops,or working in related ind

33、ustry,it is wise for an engineering student to devote some time in his curriculum to studying material removal and machin</p><p>　　A machine tool provide the means for cutting tools to shape a workpiece to r

34、equired dimensions;the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic members,which are as follows:</p><p>　　(a)Bed,Structure or Frame.This is t

35、he main member which provides a basis for,and a connection between,the spindles and slides;the distorion and vibration under load must be kept to a minimum.</p><p>　　(b)Slides and Slideways.The translation o

36、f a machine element(e.g. the slide) is normally achieved by straight-line motion under the constraint of accurate guiding surface(the slideways).</p><p>　　(c)Spindles and Bearings.Angular displacement take p

37、lace about an axis of rotation;the position of this axis must be constant within extremely fine limits in machine tools,and is ensured by the provision of precision spindles and bearings.</p><p>　　(d)Power U

38、nit.The electric motor is the universally adopted power unit for machine tools.By suitably positioning individual motors,belt and gear transmissions and reduced to a minimum.</p><p>　　(e)Transmission Linkag

39、e.Linkage is the general term used to denote the mechanical,hydraulic,pneumatic or electric mechanisms which connect angular and linear displacements in defined relationship.</p><p>　　There are two broad div

40、isions of machining operations:</p><p>　　(a)Roughing,for which the metal removal rate,and consequently the cutting force,is high,but the required dimensional accuracy relatively low.</p><p>　　(b

41、)Finishing,for which the metal removal rate,and consequently the cutting force,is low,but the required dimensional accuracy and surface finish relatively high.</p><p>　　It follows that static loads and dynam

42、ic loads,such as result from an unbalanced grindingwheel,are rmore significant in finishing operations than in roughing operations.The degree of precision achieved in any machining process will usually be influenced by t

43、he magnitude of the deflections,which occur as a result of the force acting.</p><p>　　Machine tool frames are generally made in cast iron,although some may be steel casting or mild-steel fabrications.Cast ir

44、on is chosen because of its cheapness,rigidity,compressive strength and capacity for damping the vibrations set-up in machine operations.To avoid massive sections in castings,carefully designed systems of ribbing are use

45、d to offer the maximum resistance to bending and torsional stresses.Two basic types of ribbing are box and diagonal.The box formation is convenient to produce,</p><p>　　The slides and slideways of a machine

46、tool locate and guide members which move relative to each other,usually changing the position of the tool relative to the workpiece.The movement genenally takes the forms of translation in a straight line,but is sometime

47、s angulai rotation,e.g. tilting the wheel-head of a universal thread-grinding machine to an angle corresponding with the helix angle of the workpiece thread.The basic geometric elements of slides are flat,vee,dovetail an

48、d cylinder.These eleme</p><p>　　(a)Accuracy of Movement.Where a slide is to be displaced in a straight line,this line must lie in two mutually perpendicular planes and there must be no slide rotation.The gen

49、eral tolerance for straightness of machine tool slideways is 0—0.02mm per 1000mm;on horizontal surfaces this tolerance may be disposed so that a convex surface results,thus countering the effect of “sag”of the slideway.&

50、lt;/p><p>　　(b)Means of Adjustment.To facilitate assembly,maintain accuracy and eliminate “play” between slideing members after wear has taken place,a strip is something inserted in the slides.This is called a

51、gib-strip.Usually,the grib is retained by socket-head screw passing through elongated slots;and is adjusted by grub-screws secured by lock nuts.</p><p>　　(c)Lubrication.Slideways may be lubricated by either

52、of the following systems:</p><p>　　1)Intermittently through grease or oil nipples,a method suitable where movements are infrequent and speed low.</p><p>　　2)Continuously,e.g. by pumping through

53、a metering value and pipe-work to the point of application;the film of oil introduced between surfaces by these means must be extremely thin to avoid the slide “floating”.If sliding surfaces were optically flat oil would

54、 be squeezed out,resulting in the surfaces sticking.Hence in practice slide surfaces are either ground using the edge of a cup wheel,or scraped.Both processes produce minute surface depresssions,which retain “pocket” of

55、oil,and complete sepa</p><p>　　(d)Protection.To maintain slideways in good order,the following conditions must be met:</p><p>　　1)Ingress of foreign matter,e.g. swarf,must be prevented.Where thi

56、s is no possible,it is desirable to have a form of slideway,which does not retain swarf,e.g. the inverted vee.</p><p>　　2)Lubricating oil must be retained.The adhensive property of oil for use on vertical or

57、 inclined slide surface is important;oils are available which have been specially developed for this purpose.The adhesiveness of oil also prevents it being washed away by cutting fluids.</p><p>　　3)Accidenta

58、l damage must be prevented by protective guards.</p><p>　　A machine tool performs three major functions:1)it rigidly supports the workpiece or its holder and the cutting tool; 2)it provides relative motion b

59、etween the workpiece and the cutting tool; 3)it provides a range of feeds and speeds.Machines used to remove metal in the form of chips are classified in four general groups:those using single-point tools,those using mul

60、tipoint tools,those using random-point tools(abrasive),and those that considered special.</p><p>　　Machines using basically the single-point cutting tools include:1)engine lathes, 2)turret lathes , 3)tracing

61、 and duplicating lathes, 4)single-spindle automatic lathes, 5)multi-single automatic lathes , 6)shapers and planers, 7)boring machines.</p><p>　　Machines using multipoint cutting tools include:1)drilling mac

62、hines, 2)milling machines, 3)broaching machines, 4)sawing machines, 5)gear-cutting machines.</p><p>　　Machines using random-point cutting tools include:1)cylindrical grinder, 2)centreless grinders, 3)surface

63、 grinders.Special metal removal methods include:1)chemical milling, 2)electrical discharge machining, 3)ultrasonic machining.</p><p>　　The lathe removes material by rotating the workpiece against a cutter to

64、 produce external or internal cylindrical or conical surfaces.It is also commonly used for the production of flat surfaces by faing,in which the workpiece is rotated while the cutting tool is moved perpendicularly to the

65、 axis of rotation.</p><p>　　The engine lathe is the basic turning machine from which other turning machines have been developed.The drive motor is located in the base and drives the spindle through a combina

66、tion of belts and gears,which provides the spindle speeds from 25 to 1500 rpm.The spindle is a sturdy hollow shaft,mounted between heavy-duty bearings,with the forward end used for mounting a drive plate to impart positi

67、ve motion to the workpiece.The drive plate may be fastened to the spindle by threads,by a cam lock me</p><p>　　The lathe bed is cast iron and provides accurately ground sliding surfaces(way)on which the carr

68、iage rides.The lathe carriage is a H-shaped casting on which the cutting tool is mounted in a tool holder.The apron hangs from the front of the carriage and contains the driving gears that move the tool and carriage alon

69、g or across the way to provide the desired tool motion.</p><p>　　A compound rest,located above the carriage provides for rotation of the tool holder through any desired angle.A hand wheel and feed screw are

70、provided with a hand wheel and feed screw for moving the compound rest perpendicular to the lathe way.A gear train in the apron provides power feed for the carriage both along and across the way.The feed box contains ge

71、ars to impart motion to the carriage and control the rate at which the tool moves relative to the workpiece.On a typical lathe feeds range</p><p>　　The connecting shaft between the feed box and the lathe apr

72、on are the feed rod and the lead screw.Many lathe manufacturers combine these two rods in one,a practice that reduces the cost of the machine at the expense of accuracy.The feed rod is used to provide tool motion essenti

73、al for accurate workpiece and good surface finishes.The lead screw is used to provide the accurate lead necessary for the thread cutting.The feed rod is driven through a friction clutch that allows slippage in case the t

74、o</p><p>　　The lathe tailtock is fitted with an accurate spindle that has a tapered hole for mounting drills,drill chucks,reamers,and lathe centers.The tailstock can be moved along the lathe ways to accommod

75、ate various lengths of workpieces as well as to advance a tool into contact with the worpiece.The tailstock can be offset relative to the lathe ways to cut tapers or conical surfaces.</p><p>　　The turret lat

76、he is basically an engine lathe with certain additional features to provide for semiautomatic operation and to reduce the opportunity for human error.The carriage of the turret lathe is provided with T-slots for mounting

77、 a tool-holding device on both sides of the lathe ways with tools properly set for cutting when rotated into position.The carriage is also equipped with automatic stops that control the tool travel and provide good repro

78、duction of cuts.The tailstock of the turret la</p><p>　　Tracing and duplicating lathes are equipped with a duplicating device to automatically control the longitudinal and cross feed motions of the single-po

79、int cutting tool and provide a finished part of required shape and size in one or two passes of the tools.</p><p>　　The single-spindle automatic lathe uses a vertical turret as well as two cross slids.The wo

80、rk is fed through the machine spindle into the chuck,and the tools are operated automatically by cams.</p><p>　　The multispindle automatic lathe is provided with four,five,six,or eight spindles,with one work

81、piece mounted in each spindle.The spindles index around a central shaft,with the main tools slide accessible to all spindles.Each spindle position is provided with a side tool-slide operated independently.Since all of th

82、e slides are operated by cams,the preparation of this machine may take several days,and a production run of at least 5000 parts is needed to justify its use.The principal advantage of t</p><p>　　A shapers ut

83、ilizes a single-point tool in a tool holder mounted on the end of the ram.Cutting is generally done on the forward stroke.The tool is lifted slightly by the clapper box to prevent excessive drag across the work,which is

84、fed under the tool during the return stroke in preparation for the next cut.The column house the operating mechanisms of the shaper and also serves as a mounting unit for the work-supporting table.The table can be moved

85、in two directions mutually perpendicular to the </p><p>　　Two types of the driving mechanisms for shapers are a modified Whitworth quick-return mechanism and a hydraulic drive.For the Whitworth mechanism,the

86、 motor drives the bull gear,which drives a crank arm with an adjustable crank pin to control the length of the stroke.As the bull gear rotates,the rocker arm is forced to reciprocate,imparting this motion to the shaper r

87、am.</p><p>　　The motor on a hydraulic shaper is used only to drive the hydraulic pump.The remainder of the shaper motions are controlled by the direction of the flow of the hydraulic oil.The cutting stroke o

88、f the mechanically driven shaper uses 220 deg. of rotation of the bull gear,while the return stroke uses 140 deg..This gives a cutting stroke to return stroke ratio of 1.6 to 1.The velocity diagram shows that the velocit

89、y of the tool during the cutting stroke is never constant,while the velocity diagram f</p><p>　　A duplicating device that makes possible the reproduction of contours from a sheet-metal template is available.

90、The sheet metal template is used in conjunction with hydraulic control.</p><p>　　Upright drilling machines or drill presses are available in a variety of sizes and types,and are equipped with a sufficient ra

91、nge of spindle speeds and automatic feeds to fit the needs of most industries.Speed ranges on a typical machine are from 76 to 2025 rpm.,with drill feed from 0.002 to 0.20 in. per revolution of the spindle.</p>&l

92、t;p>　　Radial drilling machines are used to drill workpieces that are too large or cumbersome to conveniently move.The spindle with the speed and feed changing mechanism is mounted on the radial arm;by combing the move

93、ment of the radial arm around column and the movement of the spindle assembly along the arm,it is possible to align the spindle and the drill to any position within reach of the machine.For work that is too large to conv

94、eniently support on the base,the spindle assembly can be swung out ov</p><p>　　Plain radial drilling machine provide only for vertical movement of the spindle;universal machines allow the spindle to swive ab

95、out an axis normal to the radial arm and the radial arm to rotate about a horizontal axis,thus permitting drilling at any angle.</p><p>　　A mutispindle drilling machine has one or more heads that drive the s

96、pindles through universal joints and telescoping splined shafts.All spindles are usually driven by the same motor and fed simultaneously to drill the desired number of holes.In most machines each spindle is held in an ad

97、justable plate so that it can be moved relative to the others.The area covered by adjacent spindles overlap so that the machine can be set to drill holes at any location within its range.</p><p>　　The millin

98、g operation involves metal removal with a rotating cutter.It includes removal of metal from the surface of a workspiece,enlarging holes,and form cutting,such as threads and gear teeth.</p><p>　　Within an kne

99、e and column type of milling machine the column is the main supporting member for the other components,and includes the base cotaining the drive motor,the spindle,and the cutter.The cutter is mounted on an arbor held in

100、the spindle,and supported on its outer extremity by a bearing in the overarm.The knee is held on the column in dovetail slots,the saddle is fastened to the knee in dovetail slots,and the table is attached to the saddle.T