基于ProE的二級(jí)圓柱齒輪減速器實(shí)體設(shè)計(jì)
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信息時(shí)代的機(jī)械工程
在80年代的初期,工程師們?cè)?jīng)認(rèn)為要加快產(chǎn)品的研制開(kāi)發(fā),必須進(jìn)行大量的研究工作。結(jié)果是實(shí)際上只進(jìn)行了較少的研究工作,這是因?yàn)楫a(chǎn)品開(kāi)發(fā)周期的縮短,促使工程師們盡可能地利用現(xiàn)有的技術(shù)。研制開(kāi)發(fā)一種創(chuàng)新性的技術(shù)并將其應(yīng)用在新產(chǎn)品上,是有風(fēng)險(xiǎn)的,并且易于招致失敗。在產(chǎn)品開(kāi)發(fā)工程中采用較少的步驟是一種安全的和易于成功的方法。
對(duì)于資金和人力都處于全球性環(huán)境中的工程界而言,縮短產(chǎn)品研制開(kāi)發(fā)周期也是有益的。能夠設(shè)計(jì)和制造各種產(chǎn)品的人可以在世界各地找到。但是,具有創(chuàng)新思想的人則比較難找.對(duì)于你已經(jīng)進(jìn)行了6個(gè)月的研制開(kāi)發(fā)工作,地理上的距離已經(jīng)不再是其他人發(fā)現(xiàn)它的障礙。如果你的研制周期較短,只要你仍然保持領(lǐng)先,這種情況并不會(huì)造成嚴(yán)重后果。但是如果你正處于一個(gè)長(zhǎng)達(dá)6年的研制開(kāi)發(fā)過(guò)程的中期,一個(gè)競(jìng)爭(zhēng)對(duì)手了解到你的研究工作的一些信息,這個(gè)項(xiàng)目將面臨比較大的麻煩。
工程師們?cè)诮鉀Q任何問(wèn)題時(shí)都需要進(jìn)行新的設(shè)計(jì)這種觀念很快就過(guò)時(shí)了.在現(xiàn)代設(shè)計(jì)中的第一步是瀏覽因特網(wǎng)或則其他系統(tǒng),看其他人是否已經(jīng)設(shè)計(jì)了一種類似于你所需要的產(chǎn)品,諸如傳動(dòng)裝置或者換熱器等。通過(guò)這些信息系統(tǒng),你可能發(fā)泄有些人已經(jīng)有了制造圖紙,數(shù)控紙帶和制造你的產(chǎn)品所需要的其他所有東西。這樣,工程師們就可以把他們的職業(yè)技能集中在尚未解決的問(wèn)題上。
在解決這類問(wèn)題時(shí),利用工作站和進(jìn)入信息高速公路可以大大增強(qiáng)工程小組的能力和效率。這些信息時(shí)代的工具可以使工程小組利用大規(guī)模的數(shù)據(jù)庫(kù)。數(shù)據(jù)庫(kù)中有材料性能,標(biāo)準(zhǔn),技術(shù)和成功的設(shè)計(jì)方案等信息。這些經(jīng)過(guò)驗(yàn)證的設(shè)計(jì)可以通過(guò)下載直接應(yīng)用,或者通過(guò)對(duì)其進(jìn)行快速,簡(jiǎn)單的改進(jìn)來(lái)滿足特定的要求.將產(chǎn)品技術(shù)要求通過(guò)網(wǎng)絡(luò)送出去的遠(yuǎn)程制造也是可行的。你可以建立一個(gè)沒(méi)有任何加工設(shè)備的虛擬公司。你可以指示制造商,在產(chǎn)品加工完成后,將其直接送給你的客戶。定期訪問(wèn)你的客戶可以保證你設(shè)計(jì)的產(chǎn)品按照設(shè)計(jì)要求進(jìn)行工作。盡管這些研制開(kāi)發(fā)方式不可能對(duì)每個(gè)公司都完全適用,但是這種可能性是存在的。
過(guò)去客戶設(shè)計(jì)的產(chǎn)品通常是由小公司來(lái)制造。大公司不屑于制造這種產(chǎn)品,
他們討厭與特殊定向產(chǎn)品市場(chǎng),或者是客戶設(shè)計(jì)的小批量產(chǎn)品打交道。"這就是我的產(chǎn)品”,一家大公司這樣說(shuō):"這是我們能夠制造出來(lái)的最好產(chǎn)品,你應(yīng)該喜歡它。如果你不喜歡,順這條街走有一家小公司,它會(huì)按你的要求去做。”
今天,因?yàn)榭蛻魝冇休^大的選擇余地,幾乎所有的市場(chǎng)都是特殊定向產(chǎn)品市場(chǎng).如果你不能使你的產(chǎn)品滿足某些特定客戶的要求,你將失去你市場(chǎng)份額中的一大部分,或者失掉全部份額。由于這些定向產(chǎn)品市場(chǎng)是經(jīng)常變化的,你的公司應(yīng)該對(duì)時(shí)常的變化作出快速的反應(yīng)。
定向產(chǎn)品市場(chǎng)和根據(jù)客戶要求進(jìn)行設(shè)計(jì)這種現(xiàn)象的出現(xiàn)改變了工程師研究工作的方式。今天,研究工作通常是針對(duì)解決特定問(wèn)題進(jìn)行的。現(xiàn)在許多由政府資助或者由大公司出資開(kāi)發(fā)的技術(shù)可以在非常低的成本下被自由使用,盡管這種情況可能是暫時(shí)的。在對(duì)這些技術(shù)進(jìn)行適當(dāng)改進(jìn)后,它們通常能夠被直接用于產(chǎn)品開(kāi)發(fā),這使得許多公司可以節(jié)省昂貴的研究經(jīng)費(fèi)。在主要的技術(shù)障礙被克服后研究工作應(yīng)該主要致力于產(chǎn)品的商品化方面,而不是開(kāi)發(fā)新的,有趣的,不確定的替換產(chǎn)品。
采用上述觀點(diǎn)看問(wèn)題,工程研究應(yīng)該致力于消除將已知技術(shù)快速商品化的障礙。工作的重點(diǎn)是產(chǎn)品的質(zhì)量和可靠性,這些在當(dāng)今的顧客的頭腦中是最重要的。很明顯,一個(gè)質(zhì)量差的聲譽(yù)是一個(gè)不好企業(yè)的同義詞。企業(yè)應(yīng)該盡最大的努力來(lái)保證顧客得到合格的產(chǎn)品,這個(gè)努力包括在生產(chǎn)線的終端對(duì)產(chǎn)品進(jìn)行嚴(yán)格的檢驗(yàn)和自動(dòng)更換有缺陷的產(chǎn)品。
研究工作應(yīng)該著重考慮諸如可靠性等因素對(duì)成本帶來(lái)的益處。當(dāng)可靠性提高時(shí),制造成本和系統(tǒng)的最終成本將會(huì)降低。如果在生產(chǎn)線的終端產(chǎn)生了30%的廢品,這不僅會(huì)浪費(fèi)金錢(qián),也會(huì)給你的競(jìng)爭(zhēng)對(duì)手創(chuàng)造一個(gè)利用你的想法制造產(chǎn)品,并將其銷售給你的客戶的良機(jī)。
提高可靠性和降低成本這個(gè)過(guò)程的關(guān)鍵是深入,廣泛地利用設(shè)計(jì)軟件。設(shè)計(jì)軟件可以使工程師們加快每一階段的設(shè)計(jì)工作。然而,僅僅縮短每一階段的設(shè)計(jì)時(shí)間,可能不會(huì)顯著地縮短整個(gè)設(shè)計(jì)過(guò)程的時(shí)間。因而必須致力于采用并行工程軟件,這樣可以使所有設(shè)計(jì)組的成員都能使用共同的數(shù)據(jù)庫(kù)。
隨著我們步入信息時(shí)代,要取得成功,工程師們?cè)诩夹g(shù)開(kāi)發(fā)和技術(shù)管理方面都應(yīng)該具有一些獨(dú)特的知識(shí)和經(jīng)驗(yàn)。成功的工程師們不但應(yīng)該具有寬廣的知識(shí)和技能,而且還應(yīng)該是某些關(guān)鍵技術(shù)或?qū)W科的專家,他們還應(yīng)該在社會(huì)因素和經(jīng)濟(jì)因素對(duì)市場(chǎng)影響方面有敏銳的洞察能力。將來(lái),花在解決日常工程問(wèn)題上的費(fèi)用將會(huì)減少,工程師們將會(huì)在一些更富有挑戰(zhàn)性,更亟待解決的問(wèn)題上協(xié)同工作,大大縮短解決這些問(wèn)題所需要的時(shí)間。我們已經(jīng)開(kāi)始了工程實(shí)踐的新階段。計(jì)算機(jī)和網(wǎng)絡(luò)工程師們具有了越來(lái)越強(qiáng)的解決問(wèn)題的能力,這也給他們的工作帶來(lái)了很大的希望和喜悅。為了確保成功,我們所使用的工具的性能和對(duì)更好的產(chǎn)品與系統(tǒng)的不斷追求應(yīng)該與標(biāo)志著在過(guò)程方面所有巨大努力的創(chuàng)新工作所帶來(lái)的喜悅相適應(yīng)。機(jī)械工程是一個(gè)偉大的行業(yè),在我們盡可能多地利用了信息時(shí)代所提供的機(jī)遇后,它將變得更加偉大。
許多工程師的職責(zé)是進(jìn)行產(chǎn)品設(shè)計(jì),而產(chǎn)品是通過(guò)對(duì)材料的加工制造而生產(chǎn)出來(lái)的。設(shè)計(jì)工程師在材料選擇——制造方法等方面起著關(guān)鍵的作用.一個(gè)設(shè)計(jì)工程師應(yīng)該比其他的人更清楚地知道他的設(shè)計(jì)需要達(dá)到什么目的。他知道他對(duì)使用載荷和使用要求的假設(shè),產(chǎn)品的使用環(huán)境,產(chǎn)品應(yīng)該具有的外觀形貌。為了滿足這些要求,他必須選擇和規(guī)定所使用的材料。通常,為了利用材料并使產(chǎn)品具有所期望的形狀,設(shè)計(jì)工程師知道應(yīng)該采用哪些制造方法。在許多情況下,選擇了某種特定材料就可能意味著已經(jīng)確定了某種必須采用的加工方法。同時(shí),當(dāng)決定采用某種加工方法后,很可能需要對(duì)設(shè)計(jì)進(jìn)行修改,以使這種加工方法能夠被有效而經(jīng)濟(jì)地應(yīng)用。某些尺寸公差可以決定產(chǎn)品的加工方法?？傊?在將設(shè)計(jì)轉(zhuǎn)變?yōu)楫a(chǎn)品的過(guò)程中,必須有人做出這些決定.在大多數(shù)情況下,如果設(shè)計(jì)人員在材料和加工方法方面具有足夠的知識(shí),他會(huì)在設(shè)計(jì)階段做出最為合理的決定。否則,做出的決定可能會(huì)降低產(chǎn)品的性能,或則使產(chǎn)品變得過(guò)于昂貴。顯然,設(shè)計(jì)工程師是制造過(guò)程中的關(guān)鍵人物,如果他們能夠進(jìn)行面向生產(chǎn)(即可以進(jìn)行高效率生產(chǎn))的設(shè)計(jì),就會(huì)給公司帶來(lái)效益。
制造工程師們選擇和調(diào)整所采用的加工方法和設(shè)備,或者監(jiān)督和管理這些加工方法和設(shè)備的使用。一些工程師進(jìn)行專用工藝裝備的設(shè)計(jì),以使通用機(jī)床能夠被用來(lái)生產(chǎn)特定的產(chǎn)品。這些工程師們?cè)跈C(jī)床,工藝能力和材料方面必須具有廣泛的知識(shí),以使機(jī)器在沒(méi)有過(guò)載和損壞,而且對(duì)被加工材料沒(méi)有不良影響的情況下,更為有效地完成所需要的加工工序。這些制造工程師們?cè)谥圃鞓I(yè)中也起到重要作用。
少數(shù)工程師們?cè)O(shè)計(jì)在制造業(yè)中使用的機(jī)床和設(shè)備。顯然,他們是設(shè)計(jì)工程師。而且對(duì)于他們的產(chǎn)品而言,他們同樣關(guān)心設(shè)計(jì),材料和制造方法4之間的相互關(guān)系。然而,他們更多地關(guān)心他們所設(shè)計(jì)的機(jī)床將要加工的材料的性能和機(jī)床與材料之間的相互作用。
還有另外一些工程師——材料工程師,他們致力于研制新型和更好的材料,他們也應(yīng)該關(guān)心這些材料的加工方法和加工對(duì)這些材料性能的影響。
盡管工程師們所起的作用可能有很大的差別,但是,大部分工程師們都必須考慮材料與制造工藝之間的相互關(guān)系。低成本制造并不是自動(dòng)產(chǎn)生的.在產(chǎn)品設(shè)計(jì),材料選擇,加工工藝裝備選擇和設(shè)計(jì)之間都有著非常密切的相互依賴關(guān)系。這些步驟中的每一個(gè)都必須在開(kāi)始制造前仔細(xì)地加以考慮,規(guī)劃和協(xié)調(diào)。這種從產(chǎn)品設(shè)計(jì)到實(shí)際生產(chǎn)的準(zhǔn)備工作,特別是對(duì)于復(fù)雜產(chǎn)品,可能需要數(shù)月甚至數(shù)年的時(shí)間,并且可能花費(fèi)很多錢(qián)。典型的例子有,對(duì)于一種全新的汽車,從設(shè)計(jì)到投產(chǎn)所需要的時(shí)間大約為2年,而一種現(xiàn)代化飛機(jī)則可能需要4年。
隨著計(jì)算機(jī)和由計(jì)算機(jī)產(chǎn)生的紙帶與由計(jì)算機(jī)本身控制的機(jī)器的出現(xiàn),我們進(jìn)入了一個(gè)生產(chǎn)計(jì)劃的新時(shí)代。采用計(jì)算機(jī)將產(chǎn)品的設(shè)計(jì)功能與制造功能集成,被稱為CAD/CAM(計(jì)算機(jī)輔助設(shè)計(jì)/計(jì)算機(jī)輔助制造).這種設(shè)計(jì)被用來(lái)制定加工工藝規(guī)程和提供加工過(guò)程本身的編程信息?？梢愿鶕?jù)供設(shè)計(jì)由于制造用的中心數(shù)據(jù)庫(kù)內(nèi)的信息繪制零件圖,需要時(shí)可以生成加工這些零件時(shí)所使用的程序。此外,對(duì)加工后的零件的計(jì)算機(jī)輔助試驗(yàn)與檢測(cè)也得到了廣泛的應(yīng)用。隨著計(jì)算機(jī)價(jià)格的降低和性能的提高,這種趨勢(shì)將毫無(wú)疑問(wèn)地得到不斷加速的發(fā)展。
車床主要是為了進(jìn)行車外圓、車端面和鏜孔等項(xiàng)工作而設(shè)計(jì)的機(jī)床。車削很少在其他種類的機(jī)床上進(jìn)行，而且任何一種其他機(jī)床都不能像車床那樣方便地進(jìn)行車削加工。由于車床還可以用來(lái)鉆孔和鉸孔，車床的多功能性可以使工件在一次安裝中完成幾種加工。因此，在生產(chǎn)中使用的各種車床比任何其他種類的機(jī)床都多。
車床的基本部件有：床身、主軸箱組件、尾座組件、溜板組件、絲杠和光杠。
床身是車床的基礎(chǔ)件。它能常是由經(jīng)過(guò)充分正火或時(shí)效處理的灰鑄鐵或者球墨鐵制成。它是一個(gè)堅(jiān)固的剛性框架，所有其他基本部件都安裝在床身上。通常在床身上有內(nèi)外兩組平行的導(dǎo)軌。有些制造廠對(duì)全部四條導(dǎo)軌都采用導(dǎo)軌尖朝上的三角形導(dǎo)軌（即山形導(dǎo)軌），而有的制造廠則在一組中或者兩組中都采用一個(gè)三角形導(dǎo)軌和一個(gè)矩形導(dǎo)軌。導(dǎo)軌要經(jīng)過(guò)精密加工以保證其直線度精度。為了抵抗磨損和擦傷，大多數(shù)現(xiàn)代機(jī)床的導(dǎo)軌是經(jīng)過(guò)表面淬硬的，但是在操作時(shí)還應(yīng)該小心，以避免損傷導(dǎo)軌。導(dǎo)軌上的任何誤差，常常意味著整個(gè)機(jī)床的精度遭到破壞。
主軸箱安裝在內(nèi)側(cè)導(dǎo)軌的固定位置上，一般在床身的左端。它提供動(dòng)力，并可使工件在各種速度下回轉(zhuǎn)。它基本上由一個(gè)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(guò)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8~12種轉(zhuǎn)速，一般按等比級(jí)數(shù)排列。而且在現(xiàn)代機(jī)床上只需扳動(dòng)2~4個(gè)手柄，就能得到全部轉(zhuǎn)速。一種正在不斷增長(zhǎng)的趨勢(shì)是通過(guò)電氣的或者機(jī)械的裝置進(jìn)行無(wú)級(jí)變速。
由于機(jī)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，通常安裝在預(yù)緊后的重型圓錐滾子軸承或球軸承中。主軸中有一個(gè)貫穿全長(zhǎng)的通孔，長(zhǎng)棒料可以通過(guò)該孔送料。主軸孔的大小是車床的一個(gè)重要尺寸，因此當(dāng)工件必須通過(guò)主軸孔供料時(shí)，它確定了能夠加工的棒料毛坯的最大尺寸。
尾座組件主要由三部分組成。底板與床身的內(nèi)側(cè)導(dǎo)軌配合，并可以在導(dǎo)軌上作縱向移動(dòng)。底板上有一個(gè)可以使整個(gè)尾座組件夾緊在任意位置上的裝置。尾座體安裝在底板上，可以沿某種類型的鍵槽在底板上橫向移動(dòng)，使尾座能與主軸箱中的主軸對(duì)正。尾座的第三個(gè)組成部分是尾座套筒。它是一個(gè)直徑通常大約在51~76mm（2~3英寸）之間的鋼制空心圓柱體。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。
車床的規(guī)格用兩個(gè)尺寸表示。第一個(gè)稱為車床的床面上最大加工直徑。這是在車床上能夠旋轉(zhuǎn)的工件的最大直徑。它大約是兩頂尖連線與導(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。車床床面上最大加工直徑表示在車床上能夠車削的最大工件直徑，而兩頂尖之間的最大距離則表示在兩個(gè)頂尖之間能夠安裝的工件的最大長(zhǎng)度。
普通車床是生產(chǎn)中最經(jīng)常使用的車床種類。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：車床床面上最大加工直徑為305~610mm（12~24英寸）；但是，床面上最大加工直徑達(dá)到1270mm（50英寸）和兩頂尖之間距離達(dá)到3658mm的車床也并不少見(jiàn)。這些車床大部分都有切屑盤(pán)和一個(gè)安裝在內(nèi)部的冷卻液循環(huán)系統(tǒng)。小型的普通車床—車床床面最大加工直徑一般不超過(guò)330mm（13英寸）--被設(shè)計(jì)成臺(tái)式車床，其床身安裝在工作臺(tái)或柜子上。
雖然普通車床有很多用途，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。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)操作普通車床，這種工人的工資高而且很難雇到。然而，操作工人的大部分時(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熟練工人，六角車床、螺紋加工車床和其他類型的半自動(dòng)和自動(dòng)車床已經(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。
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)被稱為閱讀機(jī)的界面裝置，用來(lái)接受和解譯出編程指令。
發(fā)展數(shù)控技術(shù)是為了克服人類操作者的局限性，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)期的工藝裝備成本更低。數(shù)控技術(shù)的發(fā)展導(dǎo)致了制造工藝中其他幾項(xiàng)新發(fā)明的產(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)很多類的零件，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)廠家承擔(dān)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)控誕生于麻省理工學(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)行直線切割。
然而，曲線軌跡成為機(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。構(gòu)成臺(tái)階的每一個(gè)線段越短，曲線就越光滑。臺(tái)階中的每一個(gè)線段都必須經(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)專門(mén)適用于數(shù)控的編程語(yǔ)言，使用類似于英語(yǔ)的語(yǔ)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)言的研究和發(fā)展是在數(shù)控技術(shù)進(jìn)一步發(fā)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)是有很大差別的。在那時(shí)的機(jī)床中，只有硬線邏輯電路。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)題變得很嚴(yán)重。如果需要制造100個(gè)某種零件，則應(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嚴(yán)配的車間環(huán)境和這種重復(fù)使用。
這就導(dǎo)致了一種專門(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)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。
微處理器的發(fā)展為可編程邏輯控制器和微型計(jì)算機(jī)的發(fā)展做好了準(zhǔn)備。這兩種技術(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。
普通車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)床主要用在規(guī)模較小的工廠中，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)車間中，普通車床已經(jīng)被種類繁多的自動(dòng)車床所取代，諸如自動(dòng)仿形車床，六角車床和自動(dòng)螺絲車床?，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表面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。
普通車床的加偏差主要信賴于操作者的技術(shù)熟練程度。設(shè)計(jì)工程師應(yīng)該認(rèn)真地確定由熟練工人在普通車床上加工的試驗(yàn)件的公差。在把試驗(yàn)伯重新設(shè)計(jì)為生產(chǎn)零件時(shí)，應(yīng)該選用經(jīng)濟(jì)的公差。
六角車床 對(duì)生產(chǎn)加工設(shè)備來(lái)說(shuō)，目前比過(guò)去更注重評(píng)價(jià)其是否具有精確的和快速的重復(fù)加工能力。應(yīng)用這個(gè)標(biāo)準(zhǔn)來(lái)評(píng)價(jià)具體的加工方法，六角車床可以獲得較高的質(zhì)量評(píng)定。
在為小批量的零件（100~200件）設(shè)計(jì)加工方法時(shí)，采用六角車床是最經(jīng)濟(jì)的。為了在六角車床上獲得盡可能小的公差值，設(shè)計(jì)人員應(yīng)該盡量將加工工序的數(shù)目減至最少。
自動(dòng)螺絲車床 自動(dòng)螺絲車床通被分為以下幾種類型：?jiǎn)屋S自動(dòng)、多軸自動(dòng)和自動(dòng)夾緊車床。自動(dòng)螺絲車床最初是被用來(lái)對(duì)螺釘和類似的帶有螺紋的零件進(jìn)行自動(dòng)化和快速加工的。但是，這種車床的用途早就超過(guò)了這個(gè)狹窄的范圍。現(xiàn)在，它在許多種類的精密零件的大批量生產(chǎn)中起著重要的作用。工件的數(shù)量對(duì)采用自動(dòng)螺絲車床所加工的零件的經(jīng)濟(jì)性有較大的影響。如果工件的數(shù)量少于1000件，在六角車床上進(jìn)行加工比在自動(dòng)螺絲車床上加工要經(jīng)濟(jì)得多。如果計(jì)算出最小經(jīng)濟(jì)批量，并且針對(duì)工件批量正確地選擇機(jī)床，就會(huì)降低零件的加工成本。
自動(dòng)仿形車床 因?yàn)榱慵谋砻娲植诙仍诤艽蟪潭壬先Q于工件材料、刀具、進(jìn)給量和切削速度，采用自動(dòng)仿形車床加工所得到的最小公差一定是最經(jīng)濟(jì)的公差。
在某些情況下，在連續(xù)生產(chǎn)過(guò)程中，只進(jìn)行一次切削加工時(shí)的公差可以達(dá)到0.05mm。對(duì)于某些零件，槽寬的公差可以達(dá)到0.125mm。鏜孔和休用單刃刀具進(jìn)行精加工時(shí)，公差可達(dá)到0.0125mm。在希望獲得最大主量的大批量生產(chǎn)中，進(jìn)行直徑和長(zhǎng)度的車削時(shí)的最小公差值為0.125mm是經(jīng)濟(jì)的。
19
Mechanical Engineering in the Information Age
In the early 1980s, engineers thought that massive research would be needed to speed up product development. As it turns out, less research is actually needed because shortened product development cycles encourage engineers to use available technology for use in a new product is risky and prone to failure. Taking short steps is a safer and usually more successfully approach to product development.
Shorter product development cycles are also beneficial in an engineering world in which both capital and labor are global. People who can design and manufacture various products can be found anywhere in the world, but containing a new idea is hard. Geographic distance is no longer a barrier to others finding out about your development six months into the process. If you’ve got a short development cycle, the situation is not catastrophic —as long as you maintain you lead. But if you’re in the midst of a six year development process and a competitor gets wind of your worker, the project could be in more serious trouble.
The idea that engineers need to creat a new design to solve every problem is quickly becoming obsolete. The first step in the modern design process is to browse the Internet or other information systems to see if someone else has already a new transmission, or a heat exchanger that is close to what you need. Through these information system, you may discover that someone already has manufacturing drawings, numerical control tapes ,and everything else required to manufature your product. Engineers can then focus their professional competence on unsolved problems.
In talckling such problems, the availability of wokstations and access to the information hignway dramatically enhance the capability of the engineering team and its productivity. These information age tools can give the team access to massive databases of material properties, standards, technologies, and successful designs. Such protested designs can be downloaded for direct use or quickly modified to meet specific needs. Remote manufacturing, in which productions are sent out over a network, is also possible. You could end up with a virtual company where you don’t have to see any hardware. When the product is completed you can direct the manufaturer to drop-ship it to your customer. Periodic visits to the customer can be made to ensure that the product you designed working according to the specification. Although all of the developments won’t apply equally to every company, the potential is there.
Custom design used to be left to small company. Big companies sneered at it—they hated the idea of dealing with niche markets small-valum custom solutions. “Here is my product,” one of the big companies would say:“This is the best we can make it —you ought like it. If you don’t, there’s smaller company down the street that will work on your problem.”
Today, nearly every market is a niche market, because customers are selective. If you ignore the potential for tailoring your product to specific customers’ needs, you will lose the major part of your market share. Since these niche markets are transient, your company needs to be in a positiong to respond to them quickly.
The emgergence of niche markets and design on demand has altered the way engineers conduct research. Today, research is commonly directed toward sovling particular problems. Although this situstion is probably temporary, much uncommitted technology, developed at government expense or written off by major corporationgs, is available today at very low cost. Following modest modificationgs, such technology can ofen be used directly in product development, which allows many organizations to avoid the expense of an extensive research effort. Once the technology is free of major obstacles, the research effort can focus on overcoming the barriers to commercializationg rather than on pursuing new and interesting, but undefined, alternatives.
When view in this prospective, engineering research must focus primarily on removing the barriers to rapid commercilizationg of known technologies. Much of this effort must address quality and reliability concerns, which are foremost in the minds of today’s consumers. Clearly, a reputationg for poor quality is synonymous with bad business. Everything possible—including thorough inspection at the end of the manufacturing line and automatic replacement of defective products—must be dong to assure that the customer receives a properly functionging product.
Research has to focus on the cost benefit of fators such as reliability. As reliability increases, manufanturing costs and the final costs of the system will decrease. Having 30%junk at the end of a production line not only costs a forturn but also creats an opportunity for a competitor to take your idea and sell it to your customers.
Central to the process of improving reliability and lowing costs is the intensive and widespread use of design software, which allows engineers to speed up every stage of the design process. Shortening each stage, however ,may not sufficiently reduce the time required for the entire process. Therefore, attention must also be devoted to concurrent engineering software with shared databases can be accessed by all members of the design team.
As we move more fully into the Information Age, success will require that the engineer possess some unique knowledge of and experience in both the development and the management of technology. Success will require broad knowledge and skills as well as expertise in some key technologies and disciplines; it also require a keen awareness of the social and economic factors at work in the marketplace. Increasingly, in the future, routin problems will not justify heavry engineering expenditures, and engineers will be expected to work cooperatively in solving more challenging , more demanding problems in substantially less time. We have begun a new phase in the practice of engineering. It offers great promise and excitement as more and more problem-solving capability is placed in the hands of the computerized and wired engineer. To assure success, the capability of our tools and the unquenched thirst for better products and systems must be matched by the joy of creation that marks all great engineering endeavors. mechanical engineering is a great profession, and it will become even greater as we make the most of the opportunities offered by the Information Age.
Many engineers have as their function the designing of products that are to be brought into reality through the processing or fabrication of materials. In this capacity they are a key fator in the material selection-manufaturing procedure. A design engineer, better than any other person, should know what he or she wants a design to accomplish. He knows what assumptions he has made about service loads and requirements, what service environment the product must withstand, and what appearance he wants the final product to have. In order to meet these requirements he must select and specify the material（s）to be used. In most cases, in order to utilize the material and to enable the product to have the desired form, he knows that certain manufacturing processes will have to be employed. In many instances, the selection of a specific material may dictate what processing must be used. At the same time, when certain processes are to be used, the design may have to be modified in order for the process to be utilized effectively and economically. Certainly dimensional tolerances can dictate the processing. In any case, in the sequence of converting the design into reality, such decisions must be made by someone. In most distances they can be made most effectively at the design stage, by the designer if he has a reasonably adequate knowledge concerning materials and manufacturing processes. Otherwise, decisions may be made that will detragt from the effetiveness of the product, or the product may be needlessly costly. It is thus apparent that design engineers are a vital fator in the manufacturing process, and it is indeed the company if they design for producibility—that is, for effient production.
Manufacturing engineers select and coordinate specific processes and equipment to be used, or supervise and manage their use. Some design special tooling that is used so that standard machines can be utilized in producing special products. These engineers must have a broad knowledge of machine and process capabilities and of materials, so that desired operations can be done effectively and efficiently without overloading or damaging machines and without adversely affecting the materials being processed. These manufacturing engineers also play an important role in manufacturing.
A relatively small group of engineers design the machines and equipment used in manufacturing. They obviously are design engineers and, relative to their products, they have the same concerns of the interrelationship of design, materials, and manufacturing processes. However, they have an even greater concern regarding the properties of the materials that their machines are going to process and the interreaction of the materials and the machines.
Still another group of engineers—the materials engineers—devote their major efforts toward developing new and better materials. They, too, must be concerned with how these materials can be processed and with the effects the processing will have on the properties of the materials.
Although their roles may be quite different, it is apparent that a large proportion of engineers must concern themselves with the interrelationship between materials and manufacturing processes.
Low-cost manufature does not just happen. There is a close and interdependent relationship between the design of a product, selection of materials, selection of processes and equipment, and tooling selection and design. Each of these steps must be carefully considered, planned, and coordinated before manufacturing starts. This lead time, particularly for complicated products, may take months, even years, and the expenditure of large amount of money may be involved. Typically, the lead time for a completely new model of an automobile is about 2 years, for a modern aircraft it may be 4 years.
With the advent of computers and machines that can be controlled by either tapes made by computers or by the computers themselves, we are entering a new era of production planning. The integration of the design function and the manufacturing function through the computer is called CAD/CAM（computer aided design/computer aided manufacturing）. The design is used to determine the manufacturing process planning and the programming information for the manufacturing processes themselves. Detailed drawing can also be made from the central data base used for the design and manufature, and programs can be generated to make the parts as needed. In addition, extensive computer aidedtesting and inspection（CATI）of the manufactured parts is taking place. There is no doubt that this trend will continue at ever-accelerating rates as computers become chesper and smarter.
Lathes 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 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 are 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, 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 precisi
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