車(chē)門(mén)玻璃升降器的設(shè)計(jì)及運(yùn)動(dòng)仿真開(kāi)題報(bào)告

1、開(kāi)題報(bào)告題目：車(chē)門(mén)玻璃升降器的設(shè)計(jì)及運(yùn)動(dòng)仿真課題來(lái)源江蘇省蘇州奧杰汽車(chē)技術(shù)科學(xué)依據(jù)(包括課題的科學(xué)意義；國(guó)內(nèi)外研究概況、水平和開(kāi)展趨勢(shì)；應(yīng) 用前景等)(1)課題科學(xué)意義正在開(kāi)發(fā)中的某車(chē)型的滑門(mén)需要一款玻璃升降器作為車(chē)門(mén)附件，用來(lái)控制滑門(mén)車(chē) 窗的開(kāi)啟和關(guān)閉。本課題主要著重負(fù)責(zé)玻璃升降器的逆向設(shè)計(jì)，運(yùn)用UG軟件建立玻璃 升降器的三維數(shù)模，通過(guò)運(yùn)動(dòng)仿真模塊校核玻璃升降器在滑門(mén)上的布置和干涉情況， 從而優(yōu)化結(jié)構(gòu)，方便汽車(chē)配件廠盡快實(shí)現(xiàn)數(shù)控加工，加快汽車(chē)新產(chǎn)品上市。我國(guó)電動(dòng) 玻璃升降器的開(kāi)展很快，它不但在轎車(chē)中大量配套，而且開(kāi)始在輕型客車(chē)中大量配套。 目前國(guó)內(nèi)外很多主機(jī)廠和汽車(chē)配件廠實(shí)現(xiàn)了基于原有設(shè)計(jì)平

2、臺(tái)的逆向設(shè)計(jì)，加快了產(chǎn) 品開(kāi)發(fā)的過(guò)程，將來(lái)將會(huì)實(shí)現(xiàn)產(chǎn)品系列參數(shù)化設(shè)計(jì)，只需對(duì)三維數(shù)模某些結(jié)構(gòu)尺寸修 改參數(shù)，就能實(shí)現(xiàn)產(chǎn)品的快速開(kāi)發(fā)。隨著汽車(chē)工業(yè)的開(kāi)展，電動(dòng)玻璃升降器將呈現(xiàn)智 能化、模塊化的開(kāi)展趨勢(shì)。體。通過(guò)手輪和螺桿，尾座套筒可以在尾座體中縱向移入和移出幾個(gè)英寸。車(chē)床的規(guī)格用兩個(gè)尺寸表示。第一個(gè)稱(chēng)為車(chē)床的床面上最大加工直徑。這是在車(chē)床上 能夠旋轉(zhuǎn)的工件的最大直徑。它大約是兩頂尖連線(xiàn)與導(dǎo)軌上最近點(diǎn)之間距離的兩倍。第二個(gè) 規(guī)格尺寸是兩頂尖之間的最大距離。車(chē)床床面上最大加工直徑表示在車(chē)床上能夠車(chē)削的最大 工件直徑，而兩頂尖之間的最大距離那么表示在兩個(gè)頂尖之間能夠安裝的工件的最大長(zhǎng)度。普通車(chē)床是生產(chǎn)

3、中最經(jīng)常使用的車(chē)床種類(lèi)。它們是具有前面所敘的所有那些部件的重 載機(jī)床，并且除了小刀架之外，全部刀具的運(yùn)動(dòng)都有機(jī)動(dòng)進(jìn)給。它們的規(guī)格通常是：車(chē)床床 面上最大加工直徑為305610mm （1224英寸）；但是，床面上最大加工直徑到達(dá)1270mm （50英寸）和兩頂尖之間距離到達(dá)36581nm的車(chē)床也并不少見(jiàn)。這些車(chē)床大局部都有切屑盤(pán) 和一個(gè)安裝在內(nèi)部的冷卻液循環(huán)系統(tǒng)。小型的普通車(chē)床一車(chē)床床面最大加工直徑一般不超過(guò) 330mm （13英寸）一被設(shè)計(jì)成臺(tái)式車(chē)床，其床身安裝在工作臺(tái)或柜子上。雖然普通車(chē)床有很多用途，是很有用的機(jī)床，但是更換和調(diào)整刀具以及測(cè)量工件花費(fèi) 很多時(shí)間，所以它們不適合在大量生產(chǎn)中應(yīng)用

4、。通常，它們的實(shí)際加工時(shí)間少于其總加工時(shí) 間的30%。此外，需要技術(shù)熟練的工人來(lái)操作普通車(chē)床，這種工人的工資高而且很難雇到。 然而，操作工人的大局部時(shí)間卻花費(fèi)在簡(jiǎn)單的重復(fù)調(diào)整和觀察切屑過(guò)程上。因此，為了減少 或者完全不雇用這類(lèi)熟練工人，六角車(chē)床、螺紋加工車(chē)床和其他類(lèi)型的半自動(dòng)和自動(dòng)車(chē)床已 經(jīng)很好地研制出來(lái)，并已經(jīng)在生產(chǎn)中得到廣泛應(yīng)用。.數(shù)字控制先進(jìn)制造技術(shù)中的一個(gè)基本的概念是數(shù)字控制（NC）。在數(shù)控技術(shù)出現(xiàn)之前，所有的 機(jī)床都是由人工操縱和控制的。在與人工控制的機(jī)床有關(guān)的很多局限性中，操作者的技能大 概是最突出的問(wèn)題。采用人工控制是，產(chǎn)品的質(zhì)量直接與操作者的技能有關(guān)。數(shù)字控制代表 了從人工控制

5、機(jī)床走出來(lái)的第一步。數(shù)字控制意味著采用預(yù)先錄制的、存儲(chǔ)的符號(hào)指令來(lái)控制機(jī)床和其他制造系統(tǒng)。一個(gè) 數(shù)控技師的工作不是去操縱機(jī)床，而是編寫(xiě)能夠發(fā)出機(jī)床操縱指令的程序。對(duì)于一臺(tái)數(shù)控機(jī) 床，其上必須安有一個(gè)被稱(chēng)為閱讀機(jī)的界面裝置，用來(lái)接受和解譯出編程指令。開(kāi)展數(shù)控技術(shù)是為了克服人類(lèi)操作者的局限性，而且它確實(shí)完成了這項(xiàng)工作。數(shù)字控 制的機(jī)器比人工操縱的機(jī)器精度更高、生產(chǎn)出零件的一致性更好、生產(chǎn)速度更快、而且長(zhǎng)期 的工藝裝備本錢(qián)更低。數(shù)控技術(shù)的開(kāi)展導(dǎo)致了制造工藝中其他幾項(xiàng)新創(chuàng)造的產(chǎn)生：電火花加工技術(shù)、激光切割、電子束焊接數(shù)字控制還使得機(jī)床比它們采用有人工操的前輩們的用途更為廣泛。一臺(tái)數(shù)控機(jī)床可以自動(dòng)生產(chǎn)很

6、多類(lèi)的零件，每一個(gè)零件都可以有不同的和復(fù)雜的加工 過(guò)程。數(shù)控可以使生產(chǎn)廠家承當(dāng)那些對(duì)于采用人工控制的機(jī)床和工藝來(lái)說(shuō)，在經(jīng)濟(jì)上是不劃 算的產(chǎn)品生產(chǎn)任務(wù)。同許多先進(jìn)技術(shù)一樣，數(shù)控誕生丁麻省理工學(xué)院的實(shí)驗(yàn)室中。數(shù)控這個(gè)概念是50年代 初在美國(guó)空軍的資助下提出來(lái)的。在其最初的價(jià)段，數(shù)控機(jī)床可以經(jīng)濟(jì)和有效地進(jìn)行直線(xiàn)切 割。然而，曲線(xiàn)軌跡成為機(jī)床加工的一個(gè)問(wèn)題，在編程時(shí)應(yīng)該采用一系列的水平與豎直的 臺(tái)階來(lái)生成曲線(xiàn)。構(gòu)成臺(tái)階的每一個(gè)線(xiàn)段越短，曲線(xiàn)就越光滑。臺(tái)階中的每一個(gè)線(xiàn)段都必須 經(jīng)過(guò)計(jì)算。在這個(gè)問(wèn)題促使下，于1959年誕生了自動(dòng)編程工具（APT）語(yǔ)言。這是一個(gè)專(zhuān)門(mén)適用 于數(shù)控的編程語(yǔ)言，使用類(lèi)似于英語(yǔ)的語(yǔ)

7、句來(lái)定義零件的幾何形狀，描述切削刀具的形狀和 規(guī)定必要的運(yùn)動(dòng)。APT語(yǔ)言的研究和開(kāi)展是在數(shù)控技術(shù)進(jìn)一步開(kāi)展過(guò)程中的一大進(jìn)步。最初 的數(shù)控系統(tǒng)下今天應(yīng)用的數(shù)控系統(tǒng)是有很大差異的。在那時(shí)的機(jī)床中，只有硬線(xiàn)邏輯電路。 指令程序?qū)懺诖┛准垘希ㄋ髞?lái)被塑料帶所取代），采用帶閱讀機(jī)將寫(xiě)在紙帶或磁帶上的 指令給機(jī)器翻譯出來(lái)。所有這些共同構(gòu)成了機(jī)床數(shù)字控制方面的巨大進(jìn)步。然而，在數(shù)控發(fā) 展的這個(gè)階段中還存在著許多問(wèn)題。一個(gè)主要問(wèn)題是穿孔紙帶的易損壞性。在機(jī)械加工過(guò)程中，載有編程指令信息的紙帶 斷裂和被撕壞是常見(jiàn)的事情。在機(jī)床上每加工一個(gè)零件，都需要將載有編程指令的紙帶放入 閱讀機(jī)中重新運(yùn)行一次。因此，這個(gè)問(wèn)

8、題變得很?chē)?yán)重。如果需要制造100個(gè)某種零件，那么應(yīng) 該將紙帶分別通過(guò)閱讀機(jī)100次。易損壞的紙帶顯然不能承受?chē)?yán)配的車(chē)間環(huán)境和這種重復(fù)使 用。這就導(dǎo)致了一種專(zhuān)門(mén)的塑料磁帶的研制。在紙帶上通過(guò)采用一系列的小孔來(lái)載有編程 指令，而在塑料帶上通過(guò)采用一系列的磁點(diǎn)瞇載有編程指令。塑料帶的強(qiáng)度比紙帶的強(qiáng)度要 高很多，這就可以解決常見(jiàn)的撕壞和斷裂問(wèn)題。然而，它仍然存在著兩個(gè)問(wèn)題。其中最重要的一個(gè)問(wèn)題是，對(duì)輸入到帶中指令進(jìn)行修改是非常困難的，或者是根本不 可能的。即使對(duì)指令程序進(jìn)行最微小的調(diào)整，也必須中斷加工，制作一條新帶。而且?guī)ㄟ^(guò) 閱讀機(jī)的次數(shù)還必須與需要加工的零件的個(gè)數(shù)相同。幸運(yùn)的是，計(jì)算機(jī)技術(shù)的實(shí)際應(yīng)

9、用很快 解決了數(shù)控技術(shù)中與穿孔紙帶和塑料帶有關(guān)的問(wèn)題。在形成了直接數(shù)字控制（DNC）這個(gè)概念之后，可以不再采用紙帶或塑料帶作為編程 指令的載體，這樣就解決了與之有關(guān)的問(wèn)題。在直接數(shù)字控制中，幾臺(tái)機(jī)床通過(guò)數(shù)據(jù)傳輸線(xiàn) 路聯(lián)接到一臺(tái)主計(jì)算機(jī)上。操縱這些機(jī)床所需要的程序都存儲(chǔ)在這臺(tái)主計(jì)算機(jī)中。當(dāng)需要時(shí), 通過(guò)數(shù)據(jù)傳輸線(xiàn)路提供給每臺(tái)機(jī)床。直接數(shù)字控制是在穿孔紙帶和塑料帶基礎(chǔ)上的一大進(jìn) 步。然而，它敢有著同其他信賴(lài)于主計(jì)算機(jī)技術(shù)一樣的局限性。當(dāng)主計(jì)算機(jī)出現(xiàn)故障時(shí)，由 其控制的所有機(jī)床都將停止工作。這個(gè)問(wèn)題促使了計(jì)算機(jī)數(shù)字控制技術(shù)的產(chǎn)生。微處理器的開(kāi)展為可編程邏輯控制器和微型計(jì)算機(jī)的開(kāi)展做好了準(zhǔn)備。這兩種技

10、術(shù)為 計(jì)算機(jī)數(shù)控（CNC）的發(fā)打下了基礎(chǔ)。采用CNC技術(shù)后，每臺(tái)機(jī)床上都有一個(gè)可編程邏輯 控制器或者微機(jī)對(duì)其進(jìn)行數(shù)字控制。這可以使得程序被輸入和存儲(chǔ)在每臺(tái)機(jī)床內(nèi)部。它還可 以在機(jī)床以外編制程序，并將其下載到每臺(tái)機(jī)床中。計(jì)算機(jī)數(shù)控解決了主計(jì)算機(jī)發(fā)生故障所 帶來(lái)的問(wèn)題，但是它產(chǎn)生了另一個(gè)被稱(chēng)為數(shù)據(jù)管理的問(wèn)題。同一個(gè)程序可能要分別裝入十個(gè) 相互之間沒(méi)有通訊聯(lián)系的微機(jī)中。這個(gè)問(wèn)題目前正在解決之中，它是通過(guò)采用局部區(qū)域網(wǎng)絡(luò) 將各個(gè)微機(jī)聯(lián)接起來(lái)，以得于更好地進(jìn)行數(shù)據(jù)管理。.車(chē)削加工普通車(chē)床作為最早的金屬切削機(jī)床的一種，目前仍然有許多有用的和為人要的特性和 為人們所需的特性?，F(xiàn)在，這些機(jī)床主耍用在規(guī)模較小的

11、工廠中，進(jìn)行小批量的生產(chǎn)，而不 是進(jìn)行大批量的和產(chǎn)。在現(xiàn)代的生產(chǎn)車(chē)間中，普通車(chē)床已經(jīng)被種類(lèi)繁多的自動(dòng)車(chē)床所取代，諸如自動(dòng)仿形車(chē) 床，六角車(chē)床和自動(dòng)螺絲車(chē)床?，F(xiàn)在，設(shè)計(jì)人員已經(jīng)熟知先利用單刃刀具去除大量的金屬余 量，然后利用成型刀具獲得外表光潔度和精度這種加工方法的優(yōu)點(diǎn)。這種加工方法的生產(chǎn)速 度與現(xiàn)在工廠中使用的最快的加工設(shè)備的速度相等。研究?jī)?nèi)容.玻璃升降器設(shè)計(jì)局部：.適合該車(chē)型的玻璃升降器方案選擇;.逆向設(shè)計(jì)玻璃升降器的機(jī)械結(jié)構(gòu)。.玻璃升降器的運(yùn)動(dòng)仿真.玻璃升降器運(yùn)動(dòng)校核局部：.運(yùn)動(dòng)行程校核；.傳動(dòng)動(dòng)力校核；.結(jié)構(gòu)干涉校核。擬采取的研究方法、技術(shù)路線(xiàn)、實(shí)驗(yàn)方案及可行性分析分析國(guó)內(nèi)外電動(dòng)玻璃升降

12、器市場(chǎng)各種電動(dòng)玻璃升降器的特點(diǎn)以及適應(yīng)性、電動(dòng)玻 璃升降器開(kāi)發(fā)中的問(wèn)題、各種電機(jī)性能、各部件機(jī)構(gòu)及工作原理、機(jī)械設(shè)計(jì)過(guò)程，通 過(guò)對(duì)升降器各部件的性能分析，最終開(kāi)發(fā)出一款適合該車(chē)型的電動(dòng)玻璃升降器。運(yùn)用UG軟件進(jìn)行逆向設(shè)計(jì)，分析玻璃升降器總成及各部件的位置結(jié)構(gòu)和功能，建 立三維數(shù)模，對(duì)總成進(jìn)行運(yùn)動(dòng)仿真，分析運(yùn)動(dòng)數(shù)據(jù)，優(yōu)化結(jié)構(gòu)布置。江蘇省蘇州奧杰汽車(chē)技術(shù)在汽車(chē)設(shè)計(jì)領(lǐng)域，運(yùn)用當(dāng)今汽車(chē)工業(yè)最先進(jìn)的 計(jì)算機(jī)輔助造型(CAS)、計(jì)算機(jī)輔助工程(CAE)、計(jì)算機(jī)輔助設(shè)計(jì)(CAD)和計(jì)算機(jī)輔助 制造(CAM)軟件進(jìn)行設(shè)計(jì)開(kāi)發(fā)，至今已積累了數(shù)十個(gè)車(chē)型，整車(chē)平臺(tái)及零部件開(kāi)發(fā)經(jīng)驗(yàn)。 在玻璃升降器方面具備很強(qiáng)的設(shè)計(jì)開(kāi)

13、發(fā)能力，同時(shí)國(guó)內(nèi)外市場(chǎng)對(duì)電動(dòng)玻璃升降器的需 求不斷擴(kuò)大，對(duì)電動(dòng)玻璃升降器的智能化、模塊化越來(lái)越高，具備很大的市場(chǎng)可行性。研究計(jì)劃及預(yù)期成果研究計(jì)劃：2012年11月12日-2012年12月25日：按照任務(wù)書(shū)要求查閱論文相關(guān)參考資料，填寫(xiě) 畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告書(shū)。2013年1月11日-2013年3月5日：填寫(xiě)畢業(yè)實(shí)習(xí)報(bào)告。2013年3月8日-2013年3月14日：按照要求修改畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告。2013年3月15日-2013年3月21日：學(xué)習(xí)并翻譯一篇與畢業(yè)設(shè)計(jì)相關(guān)的英文材料。2013年3月22日-2013年4月11日：CAD繪圖。2013年4月12日-2013年4月25 0： UG設(shè)計(jì)。2013年4

14、月26日-2013年5月21日：畢業(yè)論文撰寫(xiě)和修改工作。預(yù)期成果：到達(dá)預(yù)期的實(shí)驗(yàn)結(jié)論：使用CAD設(shè)計(jì)繪制車(chē)門(mén)玻璃升降器裝配圖，并用UG繪制 三維圖像，制作PPT文件，以及仿真。特色或創(chuàng)新之處玻璃升降器的整個(gè)機(jī)構(gòu)、功能、性能都可通過(guò)UG逆向設(shè)計(jì)得以實(shí)現(xiàn)，實(shí)現(xiàn)了產(chǎn)品 的快速設(shè)計(jì)；通過(guò)運(yùn)動(dòng)仿真可以校核是否存在結(jié)構(gòu)干涉情況，降低了樣品試制的本錢(qián) 和風(fēng)險(xiǎn)。交叉臂式電動(dòng)玻璃升降器適用負(fù)載較大車(chē)門(mén)玻璃，結(jié)構(gòu)簡(jiǎn)單，制造本錢(qián)低，使用 壽命長(zhǎng)，采用高防護(hù)電機(jī)驅(qū)動(dòng)，實(shí)現(xiàn)車(chē)門(mén)玻璃的自動(dòng)升降，乘員操作方便靈活，提高 了車(chē)型的整體舒適度和豪華感。已具備的條件和尚需解決的問(wèn)題已具備的條件：電腦；相關(guān)開(kāi)發(fā)軟件；局部技術(shù)資料。

15、尚需解決的問(wèn)題：學(xué)習(xí)UG軟件；確定產(chǎn)品的結(jié)構(gòu)尺寸和技術(shù)要求；逆向設(shè)計(jì) 建立三維數(shù)模；總成運(yùn)動(dòng)仿真校核。指導(dǎo)教師意見(jiàn)指導(dǎo)教師簽名:教研室（學(xué)科組、研究所）意見(jiàn)教研室主任簽名:系意見(jiàn)主管領(lǐng)導(dǎo)簽名:英文原文Machine design theoryThe machine design is through designs the new product or improves the old product to meet the human need the application technical science. It involves the project technology each

16、 domain, mainly studies the product the size, the shape and the detailed structure basic idea, but also must study the product the personnel which in aspect the and so on manufacture, sale and use question.Carries on each kind of machine design work to be usually called designs the personnel or mach

17、ine design engineer. The machine design is a creative work. Project engineer not only must have the creativity in the work, but also must in aspect and so on mechanical drawing, kinematics, engineerig material, materials mechanics and machine manufacture technology has the deep elementary knowledge.

18、If front sues, the machine design goal is the production can meet the human need the product. The invention, the discovery and technical knowledge itself certainly not necessarily can bring the advantage to the humanity, only has when they are applied can produce on the product the benefit. Thus, sh

19、ould realize to carries on before the design in a specific product, must first determine whether the people do need this kind of productLathesLathes are machine tools designed primarily to do turning, facing and boring, Very little turning is done on other types of machine tools, and none can do it

20、with equal facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the work piece. Consequently, more lathes of various types are used in manufacturing than any other machine tool.The essential components of a lathe ar

21、e the bed, headstock assembly, tailstock assembly, and the leads crew and feed rod.The bed is the backbone of a lathe. It usually is made of well normalized or aged gray or nodular cast iron and provides s heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel,

22、longitudinal ways, inner and outer, are 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 way in one or both sets, They are precision-machined to assure accuracy of alignment. On most modern lath

23、es the way are surface-hardened to resist wear and abrasion, but 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 headstock is mounted in a foxed position on the inner

24、ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists 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 num

25、ber of speeds. Most lathes provide from 8 to 18 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 th

26、e 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. The spindle has a hole extending through its length, through which long bar stock can be fed. The size of maximum size of bar stock th

27、at can be machined when the material must be fed through spindle.The tailsticd 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 casti

28、ng fits on the lower one and can be moved transversely upon it, on some type of keyed ways, to permit aligning the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76mm(2to 3 inches) in diameter, that can be moved several inches longitudinally in and out of the u

29、pper casting by means of a hand wheel and screw.The size of a lathe is designated by two dimensions. The first is known as the swing. This is the maximum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the near

30、est point on the ways, The second size dimension is the maximum distance between centers. The swing thus indicates the maximum work piece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of work piece that can be mounted between centers.Engine

31、 lathes are the type most frequently used in manufacturing. They are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest. They commonly range in size from 305 to 610 mm(12 to 24 inches)swing and from 610 to 121

32、9 mm(24 to 48 inches) center distances, but swings up to 1270 mm(50 inches) and center distances up to 3658mm(12 feet) are not uncommon. Most have chip pans and a built-in coolant circulating system. Smaller engine lathes-with swings usually not over 330 mm (13 inches ) -also are available in bench

33、type, designed for the bed to be mounted on a bench on a bench or cabinet.Although engine lathes are versatile and very useful, because of the time required for changing and setting tools and for making measurements on the work piece, thy are not suitable for quantity production. Often the actual ch

34、ip-production tine is less than 30% of the total cycle time. In addition, a skilled machinist is required for all the operations, and such persons are costly and often in short supply. However, much of the operators time is consumed by simple, repetitious adjustments and in watching chips being made

35、. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw machines, and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing.Numerical ControlOne of the most fundamental concepts in the area

36、of advanced manufacturing technologies is numerical control (NC). Prior to the advent of NC, all machine tools ere manually operated and controlled. Among the many limitations associated with manual control machine tools, perhaps none is more prominent than the limitation of operator skills. With ma

37、nual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first major step away from human control of machine tools.Numerical control means the control of machine tools and other manufacturing systems through the use o

38、f prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes a program that issues operational instructions to the machine tool. For a machine tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programm

39、ed instructions, known as a reader.Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs a

40、re lower. The development of NC led to the development of several other innovations in manufacturing technology:Electrical discharge machining,Laser cutting,Electron beam welding.Numerical control has also made machine tools more versatile than their manually operated predecessors. An NC machine too

41、l can automatically produce a wide of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled mac

42、hine tolls and processes.Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U.S. Air Force. In its earliest stages, NC machines were able to made straight cu

43、ts efficiently and effectively.However, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter the straight lines making up the steps, the smoother is the curve, Each line segment in the steps h

44、ad to be calculated.This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the n

45、ecessary motions. The development of the APT language was a major step forward in the fur ther development from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reade

46、r was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development.A major problem was the fragility of the punched pap

47、er tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instructions had to be

48、 rerun through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate tines. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use.This led to the

49、 development of a special magnetic plastic tape. Whereas the paper carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than the paper tape, which solved the problem of

50、 frequent tearing and breakage. However, it still left two other problems.The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To made even the most minor adjustments in a program of instructions, it was necessary to interrupt machining

51、operations and make a new tape. It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape.The development of a co

52、ncept known as direct numerical control (DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control, machine tools are tied, via a data transmission link, to a host c

53、omputer. Programs for operating the machine tools are stored in the host computer and fed to the machine tool an needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as a

54、ll technologies that depend on a host computer. When the host computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control.TurningThe engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirab

55、le attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered.The engine lathe has been replaced in todays production shops by a wide variety of automatic lathes such as automatic of single-point tooling for maximum metal removal, and the use of form tools for finish on a par with the fastest processing equipment on the scene today.Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be careful in using tolerances of an ex