撥叉七的加工工藝及其夾具設(shè)計【含10張cad圖紙+文檔全套資料】

喜歡就充值下載吧。。資源目錄里展示的文件全都有，，請放心下載，，有疑問咨詢QQ:414951605或者1304139763 ======================== 喜歡就充值下載吧。。資源目錄里展示的文件全都有，，請放心下載，，有疑問咨詢QQ:414951605或者1304139763 ======================== 理工科類 本科生畢業(yè)設(shè)計（論文）開題報告 論文(設(shè)計)題目 撥叉的加工工藝及其夾具 設(shè)計 作者所在系別 機電工程學(xué)院 作者所在專業(yè) 機械設(shè)計制造及其自動化 作者所在班級 B13113 作 者 姓 名 王瀟 作 者 學(xué) 號 20134011337 指導(dǎo)教師姓名 趙忠澤 指導(dǎo)教師職稱 副教授 完 成 時 間 2017 年 3 月 北華航天工業(yè)學(xué)院教務(wù)處制 說 明 1．根據(jù)學(xué)校《畢業(yè)設(shè)計(論文)工作暫行規(guī)定》，學(xué)生必須撰寫《畢業(yè)設(shè)計（論文）開題報告》。開題報告作為畢業(yè)設(shè)計（論文）答辯委員會對學(xué)生答辯資格審查的依據(jù)材料之一。 2．開題報告應(yīng)在指導(dǎo)教師指導(dǎo)下，由學(xué)生在畢業(yè)設(shè)計（論文）工作前期內(nèi)完成，經(jīng)指導(dǎo)教師簽署意見及所在專業(yè)教研室論證審查后生效。開題報告不合格者需重做。 3．畢業(yè)設(shè)計開題報告各項內(nèi)容要實事求是，逐條認(rèn)真填寫。其中的文字表達(dá)要明確、嚴(yán)謹(jǐn)，語言通順，外來語要同時用原文和中文表達(dá)。第一次出現(xiàn)縮寫詞，須注出全稱。 4．開題報告中除最后一頁外均由學(xué)生填寫，填寫各欄目時可根據(jù)內(nèi)容另加附頁。 5．閱讀的主要參考文獻(xiàn)應(yīng)在10篇以上（土建類專業(yè)文獻(xiàn)篇數(shù)可酌減），其中外文資料應(yīng)占一定比例。本學(xué)科的基礎(chǔ)和專業(yè)課教材一般不應(yīng)列為參考資料。 6．參考文獻(xiàn)的書寫應(yīng)遵循畢業(yè)設(shè)計（論文）撰寫規(guī)范要求。 7．開題報告應(yīng)與文獻(xiàn)綜述、一篇外文譯文和外文原文復(fù)印件同時提交，文獻(xiàn)綜述的撰寫格式按畢業(yè)設(shè)計（論文）撰寫規(guī)范的要求，字?jǐn)?shù)在2000字左右。 畢業(yè)設(shè)計(論文)開題報告 學(xué)生姓名 王瀟 專 業(yè) 機制 班 級 B13113 指導(dǎo)教師姓名 趙忠澤 職 稱 副教授 工作單位 機電工程學(xué)院 課題來源 課題性質(zhì) 課題名稱 撥叉的加工工藝及其夾具設(shè)計 本設(shè)計的科學(xué)依據(jù) （科學(xué)意義和應(yīng)用前景，國內(nèi)外研究概況，目前技術(shù)現(xiàn)狀、水平和發(fā)展趨勢等） 意義：提高零部件制造的可行性和經(jīng)濟性。研究其工藝性能以便能方便地生產(chǎn)出來，使零部件的缺陷少、成本低，同時使其達(dá)到環(huán)保、高效、節(jié)能、使用壽命長、工作可靠的目的，即所設(shè)計的零部件應(yīng)具有較好的結(jié)構(gòu)工藝性和良好的使用性。 前景：高度發(fā)達(dá)的制造業(yè)和先進(jìn)的制造技術(shù)，已成為衡量一個國家實力和科技水平的重要標(biāo)志之一，成為一個國家在競爭激烈的國際市場上獲勝的關(guān)鍵因素。 國內(nèi)外研究概況：國內(nèi)把自動化生產(chǎn)的重點轉(zhuǎn)移到中、小批量生產(chǎn)領(lǐng)域中，這就要求加速數(shù)控機床的發(fā)展速度，以滿足市場要求。當(dāng)前數(shù)控設(shè)備正在采用最新技術(shù)成就，向著高速化，高精度化，智能化，多功能化及高可靠性的方向發(fā)展。利用NC編程技術(shù)，特別是CNC編程中的自動編程技術(shù)可以快速應(yīng)對市場的變化，提高產(chǎn)品的競爭力。 國外自動編程軟件技術(shù)被廣泛應(yīng)用于機械、電子、航空等領(lǐng)域，因其出色的表現(xiàn)，在制造業(yè)領(lǐng)域有著極其廣闊的前景，將其應(yīng)用于撥叉類零件機械加工工藝規(guī)程及優(yōu)化設(shè)計，正是當(dāng)今制造行業(yè)所需要的。 設(shè)計內(nèi)容和預(yù)期成果 （具體設(shè)計內(nèi)容和重點解決的技術(shù)問題、預(yù)期成果和提供的形式） 主要內(nèi)容： 1.設(shè)計撥叉類零件的加工工藝及關(guān)鍵工序的夾具。 重點解決的技術(shù)問題： 1. 設(shè)計撥叉類零件的加工工藝； 2. 設(shè)計撥叉類零件的加工工藝的過程中相關(guān)的工序所需要的專門夾具的設(shè)計。 預(yù)期成果和提供的形式： 1.提交撥叉零件的工藝過程卡與工序卡，提交相關(guān)工藝參數(shù)的設(shè)計計算資料。 2. 提交關(guān)鍵工序的夾具設(shè)計資料及夾具裝配圖、零件工作圖。 3. 在原理上不出現(xiàn)錯誤，能夠出現(xiàn)操作上的可行性與可靠性。 擬采取設(shè)計方法和技術(shù)支持 （設(shè)計方案、技術(shù)要求、實驗方法和步驟、可能遇到的問題和解決辦法等） 設(shè)計方案及技術(shù)要求： 1. 根據(jù)設(shè)計內(nèi)容查閱相關(guān)期刊資料。 2. 利用網(wǎng)絡(luò)查找相關(guān)資料進(jìn)行修改。 3. 對實際生產(chǎn)中撥叉零件的應(yīng)用進(jìn)行統(tǒng)計總結(jié)。 實驗方法和步驟： 1.利用CAD對撥叉零件進(jìn)行二維平面設(shè)計，畫出整體零件圖； 2.確定加工工藝，繪制零件的機械制造工藝規(guī)程和機械加工工藝卡片； 3.設(shè)計關(guān)鍵工序的夾具，繪制夾具裝配圖和主要零件工作圖。 可能遇到的問題和解決辦法： 工件本身剛性差，定位夾緊時容易引起工件的變形，就可以采用適當(dāng)?shù)妮o助支撐增加工件的剛性。 實現(xiàn)本項目預(yù)期目標(biāo)和已具備的條件 （包括過去學(xué)習(xí)、研究工作基礎(chǔ)，現(xiàn)有主要儀器設(shè)備、設(shè)計環(huán)境及協(xié)作條件等） 預(yù)期目標(biāo)： 1. 能熟練運用機械制造工藝學(xué)的基本理論和夾具設(shè)計原理的知識，正確地解決一個零件在加工中的定位，夾緊以及合理制定工藝流程等問題的方法。 2. 通過對零件所有工序的機械制造工藝規(guī)程的制定和夾具設(shè)計，學(xué)會工藝裝備設(shè)計的一般方法。 3. 設(shè)計過程重理論聯(lián)系實際，并學(xué)會使用手冊、查詢相關(guān)資料等，增強自己的解決工程實際問題的能力。 已具備的條件： 1． 通過大學(xué)期間的學(xué)習(xí)，對機械制造方面的知識有了一定的儲備，學(xué)習(xí)過《機械制造工藝學(xué)》等課程。多次的課程設(shè)計也讓我們有了一定設(shè)計經(jīng)驗。 2.掌握CAD等二維設(shè)計軟件的使用方法。 3.在圖書館和網(wǎng)上查閱相關(guān)資料。 各環(huán)節(jié)擬定階段性工作進(jìn)度 (以周為單位) 1.第一周至第四周：查閱資料，完成開題報告、文獻(xiàn)綜述、外文文獻(xiàn)翻譯。開題報告的審閱。 2.第五周：總結(jié)前期工作，分析撥叉的作用并繪制零件圖。 3.第六周：確定加工工藝?yán)L制零件圖。 4.第七周：繪制毛坯圖。 5.第八周：繪制零件的機械制造工藝規(guī)程和機械加工工藝卡片。 6.第九周至第十周：設(shè)計關(guān)鍵工序的夾具，繪制夾具裝配圖和主要零件工作圖。 7.第十一周至第十二周：繪制夾具體和主要零件工作圖。 8.第十三周至十五周：整理最后資料，完成畢業(yè)設(shè)計論文。準(zhǔn)備答辯。 開 題 報 告 審 定 紀(jì) 要 時 間 地點 主持人 參 會 教 師 姓 名 職 務(wù)（職 稱） 姓 名 職 務(wù)（職 稱） 論 證 情 況 摘 要 記錄人： 指 導(dǎo) 教 師 意 見 指導(dǎo)教師簽名： 年 月 日 教 研 室 意 見 教研室主任簽名： 年 月 日 5 本科生畢業(yè)設(shè)計 (論文) 外 文 翻 譯 原 文 標(biāo) 題 ?Gear manufacturing methods 譯 文 標(biāo) 題 齒輪的加工方法 作者所在系別 機械工程學(xué)院 作者所在專業(yè) 機械設(shè)計制造及其自動化 作者所在班級 B13113 作 者 姓 名 王瀟 作 者 學(xué) 號 200134011337 指導(dǎo)教師姓名 趙忠澤 指導(dǎo)教師職稱 副教授 完 成 時 間 2017 年 3 月 北華航天工業(yè)學(xué)院教務(wù)處制 譯文標(biāo)題 齒輪的加工方法 原文標(biāo)題 Gear manufacturing methods 作 者 Zhang Baozhu 譯 名 張寶珠 國 籍 中國 原文出處 百度文庫 譯文： 齒輪的加工方法 加工齒輪輪齒有兩種基本的方法：產(chǎn)生過程和形成過程。當(dāng)一個輪齒產(chǎn)生時，工件和切削或磨削工具，是不斷嚙合在一起的，輪齒的形式是由刀具決定的。換句話說，工件和刀具是共軛的。滾齒機，成型切割機，剃齒機，磨床都使用這個原理。 當(dāng)一個輪齒形成時，該刀具是呈正被加工出來的空間的形狀的。一些磨床使用此原理，與一個指示裝置配套在一起使輪齒一個挨一個形成。刀就是同時加工所有輪齒形成刀具的例子。 成型 成型本質(zhì)上是與平面圖類似的，但采用了圓形的切削刀具替代了齒條，由此產(chǎn)生的往復(fù)慣性的減少，允許更高的行程速度：現(xiàn)代的成型切割汽車齒輪可以以每分鐘2000切割行程運行。切削刀具的形狀大致是與漸開線齒輪相同的，但輪齒的頂端是圓形的。 切削刀具和工件之間的發(fā)電驅(qū)動器之間不涉及機架或連接螺釘 ，因為只有圓周運動在涉及的范圍內(nèi)。切割機每走一個行程，工具和工件通常在切線方向移動0.5毫米。在返回的行程中，刀具必須被縮進(jìn)約1毫米留有間隙，否則就會產(chǎn)生摩擦，馬上發(fā)生故障。這類型機床的速度被限制，保證大約50千克重的切割機和軸承可移動1毫米的距離。加速度所涉及的扭矩可增加5000N的力，但必須保持高的精度。 成型機的優(yōu)點是生產(chǎn)效率相對較高，可能在齒頂上切出直角。不幸的是，對于斜齒輪，螺旋導(dǎo)向器需要在直線運動中施加旋轉(zhuǎn)運動，這種螺旋導(dǎo)向器不容易生產(chǎn)，也不便宜。所以該方法只適合在斜齒輪上的長距離，因為對每個不同的螺旋角就要生產(chǎn)特殊的刀具和導(dǎo)向器。成型機的一個很大的優(yōu)點，是它可以生產(chǎn)環(huán)形齒輪，例如那些需要大型epicyclie周轉(zhuǎn)圓的驅(qū)動器。 非常高的精確度是十分重要的，而成型切割機的不準(zhǔn)確性也是相當(dāng)要緊的。因為它們可能轉(zhuǎn)移到削減齒輪。很明顯側(cè)面的錯誤將轉(zhuǎn)移，但比起離心機或破碎機給予的特點， “掉落的輪齒” ，是相當(dāng)不明顯的。對于掉齒有幾個原因，但它發(fā)生最頻繁的是，當(dāng)工件的直徑大約是刀具直徑的一半，1.5倍或2.5倍時。如果刀具開始在高點，在最后完成漸開線齒輪期間結(jié)束在低點，在刀具上峰與峰的偏心誤差發(fā)生在最后的漸開線切割齒輪的第一個和最后一個齒輪之間。當(dāng)?shù)毒叩睦鄯e螺距誤差可能剛好超過25微米時，切割輪齒時就會有一個突然的這個數(shù)量的螺距誤差。在機床上切割的下一個齒輪可能在鄰近的節(jié)圓上是好的，如果在切割機上最后的切割碰巧發(fā)生在一個有利的位置。 各種嘗試已經(jīng)作出，防止這種效應(yīng)，特別是通過連續(xù)旋轉(zhuǎn)，沒有任何進(jìn)一步的刀料，但如果成型機是不是很堅固，刀具不是很尖銳，然后沒有進(jìn)一步的切割發(fā)生，誤差將不會被消除。 滾齒 滾齒是最常用的金屬切削方法，使用機架產(chǎn)生的原理，但避免了由在旋轉(zhuǎn)切削機上增加許多齒條引起的緩慢的往復(fù)運動。齒條在軸線方向上替換為切口蝸桿。 齒條不能為整個輪齒的工作長度產(chǎn)生正確的漸開線形狀，因為他們在圓弧軌跡上移動，所以滾刀緩慢地沿輪齒走刀，在軸向或法向或傾斜的滾齒機螺旋線方向上。 金屬去除率高，因為螺旋銑刀或工件沒有做往復(fù)運動的需要，所以40m/min的切割速度可用于傳統(tǒng)的滾刀,切割速度高達(dá)150m/min的用于硬質(zhì)合金滾刀。通常一個直徑為100毫米的滾刀轉(zhuǎn)速達(dá)到100rpm ，所以20個齒的工件以每分鐘5轉(zhuǎn)的速度旋轉(zhuǎn)。工件的每個旋轉(zhuǎn)運動將對應(yīng)于0.75毫米的進(jìn)給量，所以滾刀會提前通過工件約每分鐘4毫米。對于汽車生產(chǎn)，近似多頭開始的滾刀，可用于每轉(zhuǎn)3毫米的粗糙進(jìn)給量，以便在切割機上達(dá)到100rpm的速度，一個兩頭開始的滾刀和20個齒的齒輪可提供每分鐘30毫米的進(jìn)給速率。 粗糙進(jìn)給速率的缺點是在工件上會留下明顯的標(biāo)志，尤其是在齒根，每轉(zhuǎn)在進(jìn)給速率的空間顯示一種圖案。齒側(cè)標(biāo)記的表面波紋比齒跟要少，當(dāng)有一個隨后的整理操作時，如剃齒或磨削，這一點就不重要了。當(dāng)沒有進(jìn)一步的操作時，每轉(zhuǎn)的進(jìn)給量必須加以限制，保證粗糙度在一個界限以下，通常這決定于潤滑條件。齒根上波紋的高度指定乘以每轉(zhuǎn)的進(jìn)給量，然后除以滾刀直徑的4倍。1毫米的進(jìn)給量和100毫米的直徑可產(chǎn)生2.5微米高的波紋。對齒側(cè)波紋大約跟cos70一樣大，即約0.85微米。 滾齒機的精度對齒距和螺旋線來說，通常很高，假設(shè)機床維持不變，漸開線單單決定于滾刀齒廓的精度。漸開線的形式隨著滾刀的切入產(chǎn)生，在滾刀上留有裂痕時，漸開線是不真實的。但是，如果說有14條切線產(chǎn)生在曲率半徑約20毫米的齒側(cè)，從真實的漸開線分離，僅僅大約0.5微米。滾刀的制造和安裝誤差可以超過10微米。使用兩頭開始的滾刀或斜滾齒機可增加誤差水平，因為滾刀的齒距誤差的轉(zhuǎn)移到切割齒輪上。 拉削 ? 拉削不被用于斜齒輪，但對內(nèi)齒直齒輪時十分有用的。聯(lián)系全局來看，拉削的最重要的用途是用任何其他的方法都不容易加工的內(nèi)花鍵。跟所有的拉削方法一樣，這種方法對批量生產(chǎn)是經(jīng)濟的，因為安裝成本較高。 拉削技術(shù)對內(nèi)齒斜齒輪主要的應(yīng)用是由Gleasons在其G-TRAC機床上。這臺機器的運作，增加滾齒切割機的有效半徑至無限遠(yuǎn)，使刀具的每一個齒都能在一條直線上轉(zhuǎn)動，而不是對在一個半徑上。這使得切割行為延長超過齒輪的整個端面寬度，替代了傳統(tǒng)的滾刀每轉(zhuǎn)0.75毫米的進(jìn)給量。由此產(chǎn)生的過程中提供了非常高的生產(chǎn)率，更適合于美國，美國的產(chǎn)量在整個歐洲來說，相對較低，盡管初始成本高，但非常具有競爭力。 拉削提供了較高的精確度和良好的表面光潔度，但象所有切削過程一樣，僅限于 “軟”材料，必須隨后進(jìn)行表面淬火或熱處理，使其變形。 剃齒 剃齒切割機看起來像一個在齒根有著額外間隙的齒輪，齒側(cè)有槽，提供切削邊緣。它是運行在網(wǎng)格與粗糙齒輪軸交叉處，以便與做剩余運動的輪齒的相對速度有理論聯(lián)系點。該剃齒刀的輪齒相對靈活的彎曲，所以當(dāng)它們在兩個齒輪的輪齒間兩兩接觸時，只有有效地運作。齒輪和刀具橫向在工作面以高轉(zhuǎn)速運轉(zhuǎn)時，大約100毫米的材料被去除。周期時間可以少于半分鐘，機床并不昂貴，但刀具是精密的，很難制造。在剃齒機邊緣容易對齒廓作出調(diào)整，然后凸緣能被利用。剃齒可以使用刀具在凸肩處完成，向下到某一深度，無軸向運動。這種方法速度快，但需要更復(fù)雜的刀具設(shè)計。 磨削 磨削是非常重要的，因為它是硬化正在加工的齒輪的主要途徑。當(dāng)要求高精度時，熱處理不足以使其變形，那么，磨削是很必要的。 磨削的最簡單的方法往往被稱為orcutt方法。車輪的輪廓使用單點鉆石精確的裝飾使其變形，被模板切割控制到所需要的真實形狀。一個縮放儀6:1的比例是常用的。車輪的輪廓然后沿齒輪作軸向往復(fù)運動，齒輪旋轉(zhuǎn)允許受螺旋角的影響。當(dāng)一個齒形已經(jīng)完成，通常包括100微米的金屬去除，齒輪被指引到下一個齒的空間。這種方法可清楚查看，但一貫有著高的精度要求。安裝尺寸過長，因為如果模數(shù)，齒數(shù)，螺旋角或齒廓校正線改變時，需要不同的裝飾模板。 最快的磨削方法跟滾齒機使用相同的原理，但取代了憑借磨削輪增加切口和減輕的蝸桿，磨削輪是機架上的一節(jié)。由于高的表面速度的需求，砂輪的直徑被增大，使直徑為0.5米的砂輪可以超過2000 rpm的速度運轉(zhuǎn)，給予必要的1000米/分鐘的速度。只有單頭蝸桿可在砂輪上切削，但齒輪轉(zhuǎn)速很高，通常情況下 為100rpm。因此很難設(shè)計驅(qū)動系統(tǒng)提供精度和剛度。該過程的精度是在合理的高水平，雖然在磨削期間有砂輪和工件的轉(zhuǎn)向變化的一種傾向。所以砂輪的形式可能需要補償機床撓度的影響。磨削輪上一代蝸桿的形狀是一個緩慢的進(jìn)程，因為裝飾的鉆石或滾子，不僅要形成機架上的輪廓，而且當(dāng)砂輪旋轉(zhuǎn)時必須做軸向運動。一旦砂輪已經(jīng)形成，齒輪必須被快速的磨削，直到要求再做調(diào)整。這就是用小齒輪創(chuàng)造高生產(chǎn)率的最流行的方法，通常被稱為reishauer方法。 大型齒輪通常由Maag方法產(chǎn)生，與其方法中的規(guī)劃相似，但使用大直徑的磨削輪，形成側(cè)面的理論嚙合齒條。非常大的直徑的齒輪不能被輕易移動，所以齒輪基本上是平穩(wěn)的，而磨削輪的活動部分在螺旋線方向上作往復(fù)運動。磨削輪只在斜齒輪的端面上有一小部分是接觸的，所以，當(dāng)在一年內(nèi)制造這個齒數(shù)的幾個齒輪時，這并不重要。與形成磨削相同，磨削后，一對側(cè)面的齒輪被指引到下一對。 類似的方法用于中等大小的齒輪，這種齒輪有固定的輪子，而粗糙的齒輪是走過了車輪下。齒輪相應(yīng)的旋轉(zhuǎn)運動由輪上的皮帶控制，這條皮帶從一圓柱體的節(jié)圓直徑上散開，使齒輪相對齒條的運動是正確的。 另一種方法，尼羅河的做法，采用了車輪，它被形成提供了理論上的嚙合機架，而不是象Maag方法一樣用兩個杯輪子。這種做法最適合在小齒輪上中等精度的工作，速度介于reishauer方法和Maag方法之間。 所有磨削加工與切削加工相比，是緩慢和昂貴的，因此只用于精度要求至關(guān)重要的條件下。一個粗略的經(jīng)驗法則是，磨削會增加齒輪的切削成本，這是10個因素之一，但輪齒的成本，往往只占變速箱總費用的一小部分。令人驚訝地是，可獲得的精度不是非常取決于齒輪的大小，齒輪的直徑是5米或50米，可獲得的節(jié)圓漸開線和螺旋線的精度是預(yù)想的5微米或更好，比起任何其他因素，更取決于操作工和檢查員的技術(shù)和耐心。 它往往是假定磨削將去除在粗的階段產(chǎn)生的所有誤差。不幸的是，磨床是較靈活的，所以砂輪有一個按照以往誤差的趨勢。誤差將因此減少，但并沒有完全消除，除非很多切削方法被使用。任何時候磨削過程給出的都一致的結(jié)果，這是可在粗切的階段檢測精度是可取的。唯一的例外是磨削的形成過程，將不跟隨漸開線誤差，但仍允許螺旋線和節(jié)圓誤差。 原文： Gear manufacturing methods There are two basic methods of manufacturing gear teeth: the generating process and the forming process. when a gear tooth is generated, the workpiece and the cutting or grinding tool are in continuous mesh and the tooth form is generated by the tool. In other words, the work and the tool are conjugated to each other. hobbing :machines, shaper cutters, shaving machines, and grinders use this principle. When a gear tooth is formed, the tool is in the shape of the space that is being machined out. Some grinding machines use this principle with an indexing mechianism which allows the gear teeth to be formed tooth by tooth. Broaches are examples of form tools that machine all the gear teeth simultaneously. shaping Shaping is inherently similar to planning but uses a circular cuttrer instead of rack and the resulting reduction in the reciprocating inertia allows much higher stroking speeds: modern shapers cutting car gears can run at 2,000 cutting strokes per minmute. The shape of the cutter is roughly the same as an involute gear but the tips of the teeth are rounded. The generating drive between cutter and workpiece does not involve a rack or leadscrew since only circular motion in involved. The tool and workpiece move tangential typically 0.5 mm for each stroke of the cutter. On the return stroke the cutter must be retracted about 1 mm to give clearance otherwise tool rub occurs on the backstroke and failure is rapid. The speed on this type of machine is limited by the rate at which some 50kg of cutter and bearings can be moved a distance of 1 mm. the accelerations involved tequire forces of the order of 5000N yet high accuracy must be maintained. The advantages of shaping are that production rates are relatively high and that it is possible to cut right up to a shoulder. Unfortunately, for helical gears, a helical guide is required to impose a rotational motion on the stroking motion; such helical guides cannot be produced easily or cheaply so the method is only suitable for long runs with helical gears since special cutters and guides must be manufactured for each different helix angle. A great advantage of shaping is its ability to annular gears such as those required for large epicyclie drives. When very high accuracy is of importance the inaccuracies in the shaping cutter matter since they may transfer to the cut gear. It is obvious that profile errors will transfer but it is less obvious than an eccentrically mounted or ground cutter will give a characteristic “dropped tooth”. There are several causes for “dropped tooth” but it occurs most commonly when the diameter of the workpiece is about half, one and half, two and a half, etc, times the cutter diameter. If the cutter starts on a high point and finishes on a low point during the final finishing revolution of the gear the peak to peak eccentricity errors in the cutter occurs between the last and the first tooth of the final revolution of the cut gear; as the cumulative pitch error of the cutter may well be over 25 microns there is a sudden pitch error of this amount on the cut gear. The next gear cut on the machine may however be very good on adjacent pitch if the final cut happened to start in a favorable position on the cutter. Various attempts have been made to prevent this effect, in particular by continuing rotation without any further cutter infeed but if the shaping machine is not very rigid and the cutter very sharp then no further cutting will occur and the error will not be removed. hobbing hobbing, the most used metal cutting method, uses the rack generating principle but avoids slow reciprocation by mounting many “racks ” on a rotating cutter. The “racks” are displaced axially to form a gashed worm. The “racks” do not generate the correct involute shape for the whole length of the teeth since they are moving on a circular path and so the hob is fed slowly along the teeth either axially in normal or in the direction of the helix in “oblique” hobbing. Metal removal rates are high since no reciprocation of hob or workpiece is required and so cutting speeds of 40 m/min can be used for conventional hobs and up to 150m/min for carbide hobs. Typically with a 100mm diameter hob the rotation speed will be 100rpm and so a twenty tooth workpiece will rotate at 5 rpm. Each revolution of the workpiece will correspond to 0.75mm feed so the hob will advance through the workpiece at about 4mm per minute. For car production roughing multiple start hobs can be used with coarse feeds of 3mm per revolution so that 100 rpm on the cutter, a two-start hob and a 20 tooth gear will give a feed rate of 30mm/minute. The disadvantage of a coarse feed rate is that a clear marking is left on the workpiece, particularly in the root, showing a pattern at a spacing of the feed rate per revolution. This surface undulation is less marked on the flanks than in the root and is not important when there is a subsequent finishing operation such as shaving or grinding. When there are no further operations the feed per revolution must be restricted to keep the undulations below a limit which is usually dictated by lubrication conditions. The height of the undulations in the root of the gear is given by squaring the feed per revolution and dividing by four times the diameter of the hob; 1 mm feed and 100mm diameter gives 2.5 micron high undulations in the root. On the gear flank the undulation is roughly cos70 as large, i.e., about 0.85 micron. Accuracy of hobbing is normally high for pitch and for helix, provided machines are maintained; involute is dependent solely on the accuracy of the hob profile. As the involute form is generated by as many cuts as there are gashes on the hob the involute is not exact, but if there are, say, 14 tangents generating a flank of 20 mm radius curvature about 4 mm high the divergence from a true involute is only about half a micron; hob manufacturing and mounting errors can be above 10 microns. Use of twostart hobs or oblique hobbing gives increased error levels since hob errors of pitching transfer to the cut gear. broaching Broaching is not used for helical gears but is useful for internal spur gears; the principal use of broaching in this context is for internal splines which cannot easily be made by any other method. As with all broaching the method is only economic for large quantities since setup costs are high. The major application of broaching techniques to helical external gears is that used by Gleasons in their G-TRAC machine .this machine operates by increasing the effective radius of a hobbing cutter to infinity so that each tooth of the cutter is traveling in a straight line instead of on a radius. This allows the cutting action to extend over the whole facewidth of a gear instead of the typical 0.75 mm feed per revolution of hobbing. The resulting process gives a very high production rate , more suitable for U.S.A. production volumes than for the relatively low European volumes and so, despite a high initial cost ,is very competitive. Broaching give high accuracy and good surface finish but like all cutting processes is limited to “soft” materials which must be subsequently casehardened or heat treated, giving distortion. Shaving A shaving cutting cutter looks like a gear which has extra clearance at the root and whose tooth flanks have been grooved to give cutting edges. It is run in mesh with the rough gear with crossed axes so that there is in theory point contact with a relative velocity along the teeth giving scraping action. The shaving cutter teeth are relatively flexible in bending and so will only operate effectively when they are in double contact between two gear teeth. The gear and cutter operate at high rotational speeds with traversing of the workface and about 100 mm micron of material is removed. Cycle times can be less than half a minute and the machines are not expensive but cutters are delicate and difficult to manufacture. It is easy to make adjustments of profile at the shaving stage and crowning can be applied. Shaving can be carried out near a shoulder by using a cutter which is plunged in to depth without axial movement; this method is fast but requires more complex cutter design. grinding Grinding is extremely important because it is the main way hardened gear are machined. When high accuracy is required it is not sufficient to pre-correct for heat treatment distortion and grinding is then necessary. The simplest approach to grinding, often termed the Orcutt method. The wheel profile is dressed accurately to shape using single point diamonds which are controlled by templates cut to the exact shape required; 6:1 scaling with a pantograph is often used. The profile wheel is then reciprocated axially along the gear which rotates to allow for helix angle effects; when one tooth shape has been finished, involving typically 100 micron metal removal the gear is indexed to the next tooth space. This method is fairly show but gives high accuracy consistently. Setting up is lengthy because different dressing templates are needed if module, number of teeth, helix angle, or profile correction are changed. The fastest grinding method uses the same principle as hobbing but replaces a gashed and relieved worm by a grinding wheel which is a rack in section. Since high surface speeds are needed the wheel diameter is increased so that wheels of 0.5 m diameter can run at over 2000 rpm to give the necessary 1000 m/min. only single start worms are cut on the wheel but gear rotation speeds are high,100 rpm typically, so it is difficult to design the drive system to give accuracy and rigidity. Accuracy of the process is reasonably high although there is a tendency for wheel and workpiece to deflect variably during grinding so the wheel form may require compensation for machine deflection effects. Generation of a worm shape on the grinding wheel is a slow process since a dressing diamond or roller must not only form the rack profile but has to move axially as the wheel rotates. Once the wheel has been trued, gears can be ground rapidly until redressing is required. This is the most popular method for high production rates with small gear and is usually called the Reishauer method. Large gears are usually generated by the Maag method which is similar to planning in its approach but uses cup grinding wheels of large diameter to form the flanks of the theoretical mating rack. Gears of very large diameter cannot easily be moved so the gear is essentially stationary while the grinding wheel carriage reciprocates in the direction of the helix. The wheel is only in contact over a small part of the facewidth in helical gears so this is not important when only a few gears of this size are made in a year. As with form grinding, after grinding a pair of flanks the gear is indexed to the next pair. A similar method used for medium size gears has stationary wheels, while the rough gear is traversed under the wheels. Corresponding rotational movement of the gear is controlled by steel bands unwrapping from a cylinder of pitch circle diameter so that the motion of gear relative to “rack” is correct. Another method, the Nile approach, uses a wheel which is formed to give the “theoretical mating rack” instead of using two cup wheels as in the Maag method. This approach is best suited to medium precision work on smaller gears and is intermediate in speed between the Reishauer and Maag methods. All grinding processes are slow and costly compared with cutting processed and so are only used when accuracy is essential. A rough rule of thumb is that grinding will increase gear cutting costs by a factor of 10 but the cost of the teeth is often only a small part of the total cost of a gearbox. The accuracies attainable are surprisingly not very dependent on size of gear ; whether a gear is 5 m or 50 m diameter the pitch involute and helix accuracies attainable are of the order of 5 microns or better and more dependent on the skill and patience of the operator and inspectors than on any other factors. It is often assumed that grinding will remove all error generated at the roughing stage. Unfortunately, grinding machines are relatively flexible and so the grinding wheel has a tendency to follow previous errors. The errors will thus be reduced but not completely eliminated unless very many cuts are used; whenever a grinding process is giving in consistent results it is advisable to check the accuracies at the rough-cut stage. The only exception is the form grinding process which will not follow involute errors though it will still allow helix and pitch errors. 8 指 導(dǎo) 教 師 評 語 外文翻譯成績： 指導(dǎo)教師簽字： 年 月 日 9