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開題論證報告
課題名稱：ZH1105柴油機氣缸三面粗鏜組合機床后主軸箱設(shè)計
一、課題來源、課題研究的主要內(nèi)容及國內(nèi)外現(xiàn)狀綜述
課題來源于鹽城市江動集團,課題研究的主要內(nèi)容是設(shè)計ZH1105柴油機氣缸三面粗鏜組合機床，具體進行總體/后主軸箱設(shè)計。主要的內(nèi)容有：
1.總體設(shè)計：
1)制定工藝方案，確定機床的配置型式及結(jié)構(gòu)方案；
2)三圖一卡設(shè)計，包括：a)被加工零件工序圖；(b) 加工示意圖；(c) 機床聯(lián)系尺寸圖；(d) 生產(chǎn)率計算卡。
2．后主軸箱設(shè)計：
1) 后主軸箱總裝圖；
2) 后主軸箱箱體零件圖；
3) 其它零件圖；
4) 有關(guān)計算、校核等。
從機床行業(yè)近5年的情況看，進口強勁，出口乏力，進出口逆差不斷擴大。一方面說明我國機械制造業(yè)固定資產(chǎn)投資增速快，機床需求量大；另一方面也反映了國產(chǎn)機床在品種、質(zhì)量、可靠性以及交貨期、售前售后服務等方面存在著差距和不足。近幾年來，我國機床行業(yè)在調(diào)整結(jié)構(gòu)、研制開發(fā)新產(chǎn)品、營銷服務等方面取得了明顯的成效。但切忌估計過高，要正視差距，迎頭趕上，滿足用戶需要。
機床行業(yè)的進出口狀況，既反映了行業(yè)發(fā)展外向型經(jīng)濟，開展國際經(jīng)濟技術(shù)合作的情況；更重要的是在我國面向經(jīng)濟全球化的過程中，體現(xiàn)行業(yè)本身核心競爭力的水平。從近5年金屬加工機床進出口情況看，面臨的
形勢是十分嚴峻的。近幾年機床行業(yè)的結(jié)構(gòu)調(diào)整已取得初步成效。但產(chǎn)品結(jié)構(gòu)、產(chǎn)業(yè)組織結(jié)構(gòu)、資本結(jié)構(gòu)的不合理狀況，尚未根本改觀。需要繼續(xù)努力，加大改組、改制的力度，淘汰一批經(jīng)營困難、資不抵債的企業(yè)。資源配置向優(yōu)勢企業(yè)傾斜，提高行業(yè)的生產(chǎn)集中度和核心競爭力。在市場競爭中，形成一批具有較高市場競爭力的企業(yè)。
目前，我國制造業(yè)承受著國內(nèi)外市場競爭和產(chǎn)品品質(zhì)的壓力，同時受到資源、環(huán)境、策略和人員素質(zhì)的制約。面臨的主要困難是：
?、佼a(chǎn)品開發(fā)設(shè)計方法和技術(shù)手段落后；②小而全、大而全的莊園式企業(yè)嚴重制約了制造業(yè)的發(fā)展；③管理落后；④產(chǎn)品質(zhì)量有待于進一步提高；⑤制造工藝與技術(shù)裝備陳舊落后。
解決我國制造業(yè)目前的困難，應注重以下幾個方面的問題：
?、兕I(lǐng)導統(tǒng)一認識、高度重視、全面規(guī)劃；②產(chǎn)學研結(jié)合、企業(yè)作為主體、重點抓應用；③加強人員培養(yǎng)和培訓工作；④從企業(yè)實際出發(fā)，采用滾雪球戰(zhàn)術(shù)；⑤抓管理技術(shù)、少硬件投資、向管理要效益；⑥參與國際合作、跟蹤國際研究動態(tài)、引進、消化、創(chuàng)新先進技術(shù)；⑦制定合理政策、促進民族工業(yè)發(fā)展；⑧扶持中小企業(yè)，增加知識投入；⑨促進學科交叉，加強基礎(chǔ)研究。
我國發(fā)展、推動、振興制造業(yè)的出路在于有效地集成企業(yè)體制和機制的改革，生產(chǎn)合理化的改組，以及生產(chǎn)現(xiàn)代化的改造，充分利用并集成分散的、有限的制造資源，集成技術(shù)創(chuàng)新，并以技術(shù)創(chuàng)新和管理創(chuàng)新激活我國制造業(yè)存在的巨大潛力，這是我國制造業(yè)的必然選擇。
二、本課題擬解決的問題
1.制定機床的總體方案的設(shè)計；
2.如何配置機床的結(jié)構(gòu)型式；
3.被加工零件工藝方案的設(shè)計；
4.如何保證機床應運轉(zhuǎn)平穩(wěn)，工作可靠，結(jié)構(gòu)簡單，裝卸方便，便于維修、調(diào)整；5.如何降低機床的制造成本；
6.如何解決機床各動力部件的控制；
7.機床應能滿足加工要求，保證加工精度。
三、解決方案及預期效果
1.解決方案
1)機床盡量能用通用件，以使降低制造成本；
2)各機床部件使用電氣控制；
3)根據(jù)制造要求來選擇立式或臥式；
4)確定它的制造過程、制造工藝、來改善機床的性能；
5)認真閱讀被加工零件的圖樣,研究其尺寸、形狀、材料、硬度、重量、被加工部件的結(jié)構(gòu)及加工精度和表面粗糙度；
6)通過畢業(yè)實習深入到組合機床的制造和使用單位,全面精細地調(diào)查和使用機床的布置,毛坯和制品的流向、工人的技術(shù)水平、刀具制造能力以及單位的技術(shù)能力、生產(chǎn)經(jīng)驗、和設(shè)備狀況等條件；
7)搜索和分析國內(nèi)外的有關(guān)的技術(shù)資料以獲取可靠的設(shè)計依據(jù)；
8)確定零件在組合機床上的工藝內(nèi)容,選擇定位基準和夾緊部位選擇切削用量；
9)確定機床的配置形式、制定影響機床總體布局和技術(shù)性能的主要部件的結(jié)構(gòu)方案
10)確定主軸箱的傳動系統(tǒng)，先把全部主軸中心盡可能分布在幾個同心圓上，在各個同心圓的圓心上分別設(shè)置中心傳動軸，根據(jù)已選定的各中心傳動軸再取同心圓，用最少的傳動軸來帶動這些中心傳動軸，最后通過合攏傳動軸和動力箱驅(qū)動軸連接起來。
2. 預期效果
本課題設(shè)計多孔鉆組合機床保證了大批量生產(chǎn)的ZH1100型柴油機齒輪室蓋的外形、大小、精度，提高了生產(chǎn)效率，目前已經(jīng)基本完成資料收集工作，以及到相關(guān)的行業(yè)也進行了相應的實習，正在進行總體設(shè)計，進度適中，爭取在規(guī)定時間內(nèi)保質(zhì)保量地完成任務。
四、課題進度安排
3月5日～3月17日．畢業(yè)實習階段。
畢業(yè)實習，查閱資料，到多個公司實踐，撰寫實習報告。
3月18日～4月15日．開題階段。
提出總體設(shè)計方案及草圖，填寫開題報告。
4月16日～5月23日． 設(shè)計初稿階段。
完成總體設(shè)計圖、部件圖、零件圖。
5月24日～6月7日． 中期工作階段。
完善設(shè)計圖紙，編寫畢業(yè)設(shè)計說明書，中期檢查。
6月8日～6月10日．畢業(yè)設(shè)計預答辯。
6月11日～6月13日．畢業(yè)設(shè)計整改。
圖紙修改、設(shè)計說明書修改、定稿，材料復查。
6月14日～6月15日．畢業(yè)設(shè)計材料評閱。
6月16日～6月18日．畢業(yè)答辯。
6月19日～6月21日．材料整理裝袋。
五、指導教師意見
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六、專業(yè)系意見
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七、學院意見
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外文翻譯
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外文資料名稱：MACHINE TOOLS
外文資料出處： Computer-Aided Design
附 件：1.外文資料翻譯譯文
2.外文原文
附件1
機 床
摘要：車床用于旋轉(zhuǎn)工件并從生成所需加工表面的所需方向進給切削刀具。最常見的車床形式是以圖解方式顯示的六角車床，它由一個支撐床頭箱、拖板和六角刀架的水平床身組成。工件夾在卡盤或夾頭中，或者安裝在機床主軸端部的花盤上。
關(guān)鍵字：機床 車床
機床基礎(chǔ)
許多情況下，初步進行成型加工出來的工件必須在尺寸和表面光潔度方面進一步精整，以滿足它們的設(shè)計技術(shù)要求。為了滿足精密的公差，需要從工件上去掉小量材料。通常機床就是用于這種加工的設(shè)備。
在美國，材料切削業(yè)是一個很大的企業(yè)——費用每年超過36×109美元，包括材料，勞動力，管理費，機床裝運費等所花的費用。由于60％機械和工業(yè)工程以及技術(shù)等級評定工作都跟機械加工工業(yè)有某些關(guān)系，或者通過買賣、設(shè)計或者機器車間中操作或在有關(guān)工業(yè)企業(yè)中加工，因此，對于工程專業(yè)學生來說，在他的學習計劃中集中一段時間去學習研究材料切削和機床，那是個好方法。
機床通過切削工具去使工件成型以達到所需的尺寸提供了手段。機床通過其基礎(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)將基本部件列舉如下：
a）床身，構(gòu)架即機架。這是一個主要部件，該部件為主軸、拖板箱等提供一個基礎(chǔ)和連接中介，在負載作用下，它必須使變形和振動保持最小。
b）拖板箱和導軌。機床部件（如拖板箱）的移動，通常是在精確的導軌面約束下靠直線運動來實現(xiàn)。
c）主軸和軸承。角位移是圍繞一個旋轉(zhuǎn)軸線發(fā)生的，該軸線的位置必須在機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提供保證。
d）動力裝置。電動機是為機床所普遍采用的動力裝置。通過對各個電機的合適定位，使皮帶和齒輪傳動裝置減少到最少。
e）傳動連桿機構(gòu)。連桿機構(gòu)是個通用術(shù)語，用來代表機械、液壓、氣動或電動機構(gòu)的，這些機構(gòu)與確定的角位移和線性位移相關(guān)聯(lián)。
加工工藝有兩個主要組成部分：
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。
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。
由此可見，靜載荷和動載荷，例如由不平衡的砂輪引起的動載荷，在精加工中比粗加工中有著更為重要的意義。任何加工過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。
機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制造。選用鑄鐵是因為它便宜，剛性好，受壓強度高，并且有減弱機床操作中產(chǎn)生的振動的能力。為了避免床身鑄件碩大斷面，精心地設(shè)計筋條構(gòu)架以便提供最大的抗彎曲和抗扭轉(zhuǎn)應力的能力。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。機床的拖板箱和導軌是支撐和引導彼此相對運動的零部件，通常是改變刀具相對于工件的位置。運動一般以直線運動的方式，但也有時是轉(zhuǎn)動，例如對應于工件的螺紋上的螺旋角方向而使萬能螺紋磨床上的砂輪頭轉(zhuǎn)動一個角度。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。導軌的特性如下：
（a）運動精確。于此拖板是要按直線移動的，這直線必定是由兩個相互垂直的平面形成而且拖板必定不存在轉(zhuǎn)動。機床導軌的直線度公差是每米0～0.02毫米，在水平面上這個公差可以進行處理，以使得到凸形表面，這樣就抵消導軌下凹的作用。
（b）調(diào)整手段。為了便于裝配、維護精度和在發(fā)生磨損后便于限制移動構(gòu)件之間的“竄動”，有時在拖板內(nèi)裝入扁條，這扁條被叫做“鋃條”。通常該鋃條用穿過長孔的沉頭螺釘支住，而用平頭螺釘調(diào)整好后用鎖緊螺母上緊。
（c）潤滑。導軌可用以下兩種裝置進行潤滑：1）間歇潤滑，通過潤滑脂嘴或油嘴進行。這是一種適于運動速度低而不頻繁場合的方法。2）連續(xù)潤滑，例如通過計量閥和管道將潤滑油泵送到潤滑點。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，油就會被擠出而導致表面粘貼。因而在實踐上，拖板滑移表面是用凹面砂輪的刃進行磨削或進行刮研。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處因“浮起”而發(fā)生分離，這樣使拖板確定保持接觸導軌。
（d）防護。為了維護導軌處于良好狀態(tài)，以下條件必須滿足：1）必須防止外面物質(zhì)，如碎屑進入。具有某一形狀的導軌那是所期望的。在這種場合，是不可能進入雜物的，例如是倒V形的導軌時，那就不可能保存碎屑雜物在導軌上。2）必須保存潤滑油。在垂直或傾斜的導軌面上使用的油要有粘性，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滑油。油的粘性也要保護，以免被切削液沖毀。3）必須用防護罩來防止意外的損壞。
車床
一臺機床實現(xiàn)三個主要功能：（1）牢固地支持工件或者刀架和刀具；（2）在工件和刀具之間提供相對運動；（3）提供一定的走刀和切削速度范圍。
以去除切屑形式來加工金屬的機床一般被分為四大類：使用單點刀具切削的機床；使用多點刀具切削的機床；使用隨機點刀具切削的機床（磨削）和考慮用于特殊場合的機床。
本質(zhì)上，使用單點刀具切削的機床包括：（1）普通車床；（2）塔式車床；（3）仿形車床；（4）單軸自動車床；（5）多軸自動車床；（6）牛頭刨床和龍門刨床；（7）鏜床。
使用多點刀具切削的機床包括：（1）鉆床；（2）銑床；（3）拉床；（4）鋸床；（5）齒輪切割機床。
使用隨機點刀具切削的機床包括：（1）外圓磨床；（2）無心磨床；（3）平面磨床。
用特殊的方法進行金屬切削的機床包括：（1）化學蝕刻銑削機床；（2）電火花加工機床；（3）超聲波加工機床。車床是借助于轉(zhuǎn)動的工件對著刀具來切去金屬材料，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。
普通車床是基本的旋削機床，從這點出發(fā)，已經(jīng)研制出其他旋削機床。驅(qū)動電機裝在床身基礎(chǔ)上并通過齒輪、皮帶相結(jié)合來驅(qū)動主軸，以提供每分鐘25到1500轉(zhuǎn)的轉(zhuǎn)速。主軸是一根堅固的空心軸，裝在重型軸承之間，其前端用來安裝驅(qū)動盤（花盤），以便把確定的運動傳到工件。
該驅(qū)動盤可借助螺紋、凸輪鎖緊機構(gòu)或借助一個螺紋墊圈和鍵固定在主軸上。
車床的床身是鑄鐵件，它提供精確的磨削的滑動表面（導軌），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，并裝有移動刀具的齒輪機構(gòu)，而拖板順著導軌或橫過導軌以提供所希望的刀具的運動。拖板上面的小刀架能使刀夾回轉(zhuǎn)所要求的任意角度。為使刀具作線性運動，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軌移動的絲桿來提供橫向進給。溜板箱中的齒輪系可為拖板沿著導軌和橫跨導軌提供動力進給。進給箱齒輪將運動傳給拖板并控制刀具相對于工件的運動速度。典型的車床進給范圍是主軸每轉(zhuǎn)從0.002到0.160英寸，大約有50級轉(zhuǎn)速。由于進給箱的移動運動是由主軸齒輪驅(qū)動的，因此進給量直接與主軸速度有關(guān)。進給箱齒輪傳動機構(gòu)也用于加工螺紋并能加工每英寸4到224扣螺紋。
進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)合成一桿，實際上那就以精確的開支減少機器的費用。進給桿（光桿）用于提供刀具的運動，它對于精確的工件和好的表面光潔度是很重要的。螺紋導桿（絲桿）用于提供精確的（螺紋）導程，這對于螺紋切削是必需的。光桿是通過摩擦離合器來驅(qū)動的，那樣在刀具切削超載情況下能夠打滑保護。這一安全裝置不能裝在絲桿上，因為螺紋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重新對刀用。
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、鉆夾、鉸刀和車床頂針。尾座可以沿著車床導軌移動以適應工件的不同長度以及加工錐體或錐形表面。
轉(zhuǎn)塔車床基本上是具有某種附加特性的普通車床，提供作為半自動加工和減少人工操作誤差的機會。轉(zhuǎn)塔車床的拖板設(shè)有T形槽以便在車床導軌兩端安裝夾刀裝置，當轉(zhuǎn)塔轉(zhuǎn)入到合適位置時，要正確地裝設(shè)刀具以便進行切削。拖板也裝設(shè)有自動停機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)，在六角頭中可以裝六把刀具。雖然裝刀和加工準備要花大量時間，但轉(zhuǎn)塔車床一次裝刀以后無需熟練工人就可以連續(xù)地重復地操作加工，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，為加工準備需要花一定數(shù)量的時間那是合理的，無可非議的。
跟蹤、重復加工車床裝有一個重復裝置以自動控制單點刀具縱向和橫向的進給運動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。
單軸自動車床使用一個立式轉(zhuǎn)塔和兩個橫向溜板。工件通過機床主軸孔被送入卡盤，而刀具是靠凸輪來自動操作控制。
多軸自動車床裝有四、五、六或八根主軸，在每根主軸中裝一個工件。各主軸圍繞著一根中心軸來轉(zhuǎn)換位置。以主刀具溜板去接近各主軸。每根軸位上都裝有一側(cè)向可以獨立操作的刀具滑板。由于各刀具滑板都是靠凸輪操作的，因此加工準備可能花幾天時間，因而至少需要5000件的批量生產(chǎn)，它的使用才是合理的。這種機床的主要優(yōu)點就是所有的刀具同時工作，因而一個工人可以看管幾部機床。對于相對簡單的零件而言，多軸自動車床可以以每五秒鐘一件的速度生產(chǎn)加工出成品來。
附件2
MACHINE TOOLS
Shigley J E, Vicher J J. Theory of machines and mechanisms. New York: MeGraw-Hill Book Company, 2000
Abstract: Lathes are designed to rotate the workpiece and feed the cutting tool in the direction necessary to the required machined surface. The most common form of lathe is the turret lathe it consists of a horizontal bed supporting the headstock,the carriage and the turret.The workpiece is gripped in a chuck or is mounted on a faceplate mounted on the end of the main spindle of the machine.
Keyword: machine tools lathes
Fundamentals of Machine Tools
In many cases products from the primary forming processes must undergo further refinements in size and surface finish to meet their design specifications. To meet such precise tolerances the removal of small amounts of material is needed. Usually machine tools are used for such operation.
In the United States material removal is a big business-in excess of $ 36 X 109 per year, including material, labor, overhead, and machine tool shipments, is spent. Since 60 percent of the mechanical and industrial engineering and technology graduates have something connection with the machining industry either through sale, design, or operation of machine shops, or working in related industry it is wise for an engineering student to devote some time in his curriculum to studying material removal and machine tools.
A machine tool provides the means for cutting tools to shape a workpiece to required dimensions; the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic members, which are as follows:
(a) Bed, Structure or Frame. This is the main member, which provides a basis for, and a connection between, the spindles and slides; the distortion and vibration under load must be kept to a minimum.
(b) Slides and Slideways. The translation of a machine element (e.g. the slide) is normally achieved by straight-line motion under the constraint of accurate guiding surfaces (the slideway).
(c) Spindles and Bearings. Angular displacements take place 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.
(d) Power Unit. The electric motor is the universally adopted power unit for machine tools. By suitably positioning individual motors, belt and gear transmissions are reduced to a minimum.
(e) Transmission Linkage. Linkage is the general term used to denote the mechanical, hydraulic, pneumatic or electric mechanisms, which connect angular and linear displacements in defined relationship.
There are two broad divisions of machining operations;
(a) Roughing, for which the metal removal rate, and consequently the cutting force, is high, but the required dimensional accuracy relatively low.
(b) Finishing, for which the metal removal rate, and consequently the cutting force, is low, but the required dimensional accuracy and surface finish relatively high.
It follows that static loads and dynamic loads, such as result from an unbalanced grinding wheel, are more significant in finishing operations than in roughing operations. The degree of precision achieved in any machining process will usually be influenced by the magnitude of the deflections, which occur as a result of the force acting.
Machine tool frames are generally made in cast iron, although some may be steel casting or mild-steel fabrications. Cast iron 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 used 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, apertures in walls permitting the positioning and extraction of cores. Diagonal ribbing provides greater torsional stiffness and yet permits sward to fall between the sections; it is frequently used for lathe beds.
The slides and slide ways of a machine tool locate and guide members which move relative to each other, usually changing the position of the tool relative to the workpiece. The movement generally takes the form of translation in a straight line, but is sometimes angular 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 and cylinder. These elements may be used separately or combined in various ways according to the applications. Features of slideways are as follows;
(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 general 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.
(b) Means of Adjustment. To facilitate assembly, maintain accuracy and eliminate "play" between sliding members after wear has taken place, a strip is sometimes inserted in the slides. This is called a gibstrip. Usually, the gib is retained by socket-head screws passing through elongated slots; and is adjusted by grub-screws secured by lock nuts,
(c) Lubrication. Slideways may be lubricated by either of the following systems,
1) Intermittently through grease or oii nipples, a method suitable where movements are infrequent and speed low.
2) Continuously, e.g. by pumping through a metering valve 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 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 depressions, which retain ''pocket" of oil, and complete separation of the parts may not occur at all points positive location of the slides is thus retained.
(d) Protection. To maintain slideways in good order, the following conditions must be met.
1) Ingress of foreign matter, e.g. swarf, must be prevented. Where this is no possible, it is desirable to have a form of slideway, which does not retain swarf, e.g. the inverted vee.
2) Lubricating oil must be retained. The adhesive property of oil for use on vertical or 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.
3) Accidental damage must be prevented by protective guards.
Lathes
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 between 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 multipoint tools, those using random point tools (abrasive), and those that are considered special.
Machines using basically the single-point cutting tools include, (1) engine lathes, (2) turret lathes, (3) tracing and duplicating lathes, (4) single-spindle automatic lathes, (5) multi-spindle automatic lathes, (6) shapers and planers, (7) boring machines.
Machines using multipoint cutting tools include: (1) drilling machines, (2) milling machines, (3) broaching machines, (4) sawing machines, (5) gear-cutting machines.
Machines using random-point cutting tools include; (1) cylindrical grinder, (2) centreless grinders, (3) surface grinders. Special metal removal methods include: (1) chemical milling, (2) electrical discharge machining, (3) ultrasonic machining.
The lathe removes material by rotating the workpiece against a cutter to produce external or internal cylindrical or conical surfaces. It is also commonly used for the production of flat surfaces by facing, in which the workpiece is rotated while the cutting tool is moved perpendicularly to the axis of rotation.
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 combination 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 positive motion to the workpiece. The drive plate may be fastened to the spindle by threads, by a cam lock mechanism, or by a threaded collar and key.
The lathe bed is cast iron and provides accurately ground-sliding surfaces (way) on which the carriage 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 carnage along or across the way to provide the desired tool motion.
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 provided on the compound rest for linear motions of the tool. The cross feed is 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 gears 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 from 0.002 to 0.160 in. per revolution of the spindle, in about 50 steps. Since the transmission in the feed box is driven from the spindle gears, the feeds are directly related to the spindle speed. The feed box gearing is also used in thread cutting and provides from 4 to 224 threads per in.
The connecting shaft between the feed box and the lathe apron 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 essential 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 m case the tool is overloaded. This safety device is not provided in the lead screw, since thread cutting cannot tolerate slippage. Since the full depth of the thread is seldom cut in one pass, a chasing dial is provided to realign the tool for subsequent passes.
The lathe tailstock 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 accommodate various lengths of workpieces as well as to advance a tool into contact with the workpiece. The tailstock can be offset relative to the lathe ways to cut tapers or conical surfaces.
The turret lathe 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 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 reproduction of cuts. The tailstock of the turret lathe is of hexagonal design, in which six tools can be mounted. Although a large amount of time is consumed in setting up the tools and stops for operation, the turret lathe, once set, can continue to duplicate operations with a minimum of operator skill until the tools become dulled and need replacing. Thus, the turret lathe is economically feasible only for production work, where the amount of time necessary to prepare the machine for operation is justifiable in terms of the number of part to be made.
Tracing and duplicating lathes are equipped with a duplicating device to automatically control the longitudinal and cross feed motions of the single-point cutting tool and provide a finished part of required shape and size in one or two passes of the tools.
The single-spindle automatic lathe uses a vertical turret as well as two cross slides. The work is fed through the machine spindle into the chuck, and cams operate the tools automatically.
The multispindle automatic lathe is provided with four, five, six, or eight spindles, with one workpiece mounted in each spindle. The spindles index around a central shaft, with the main tool slide accessible to all spindles. Each spindle position is provided with a side tool-slide operated independently. Since cams operate all of the slides, 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 this machine is that all tools work simultaneously, and one operator can handle several machines. For relatively simple parts, multispindle automatic lathes can turn out finished products at the rate of 1 every 5 sec.
Shapers, Drilling and Milling Machines
A shapers utilizes 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 fed under the tool during the return stroke in preparation for the next cut. The column houses the operating mechanisms of the shaper and also serves as a mounting unit for the work-supporting table. The table can be moved in two directions mutually perpendicular lo the ram. The tool slide is used to control the depth of cut and is manually fed. It can be rotated through 90 deg. on either side of its normal vertical position, which allows feeding the tool at an angle to the surface of the table.
Two types of driving mechanisms for shapers are a modified Whitworth quick-return mechanism and a hydraulic drive. For the Whitworth mechanism, the motor drives the hull gear, which drives a crank arm with an adjustable crank pin to control the length of stroke. As the bull gear rotates, the rocker arm is forced to reciprocate, imparting this motion to the shaper ram.
The motor on a hydraulic shaper is used only to drive the hydraulic pump. The remainders of the shaper motions are controlled by the direction of the flow of the hydraulic oil. The cutting stroke of the mechanically driven shaper uses 220 deg. of rotation of the bull gear, while the return stroke uses HO deg. This gives a cutting stroke to return stroke ratio of 1.6 to 1. The velocity diagram shows that the velocity of the tool during the cutting stroke is never constant, while the velocity diagram for a hydraulic shaper shows that for most of the cutting stroke the cutting speed is constant. The hydraulic shaper has an added advantage of infinitely variable cutting speeds. The principal disadvantage of this type of machine is the lack of a definite limit at the end of the ram stroke, which may allow a few thousandths of an inch variation in stroke length.
A duplicating device that makes possible the reproduction of contours from a sheet-metal template is available. The sheet metal template is used in conjunction with hydraulic control.
Upright drilling machines or drill presses are available in a variety of sizes and types, and arc equipped with a sufficien
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