機械制造技術課程設計-張力裝置底架加工工藝及銑V型槽夾具設計

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1、 設計說明書 題目：張力裝置底架零件的工藝規(guī)程及銑V型槽的鉆床夾具設計 全套圖紙加扣 3346389411或3012250582 摘 要 本次設計內容涉及了機械制造工藝及機床夾具設計、金屬切削機床、公差配合與測量等多方面的知識。 張力裝置底架加工工藝規(guī)程及銑槽的夾具設計是包括零件加工的工藝設計、工序設計以及專用夾具的設計三部分。在工藝設計中要首先對零件進行分析，了解零件的工藝再設計出毛坯的結構，并選擇好零件的加工基準，設計出零件的工藝路線；接著對零件各個工步的工序進行尺寸計算，關鍵是決定出各個工序的工藝裝備及切

2、削用量；然后進行專用夾具的設計，選擇設計出夾具的各個組成部件，如定位元件、夾緊元件、引導元件、夾具體與機床的連接部件以及其它部件；計算出夾具定位時產生的定位誤差，分析夾具結構的合理性與不足之處，并在以后設計中注意改進。 關鍵詞：工藝、工序、切削用量、夾緊、定位、誤差。 ABSTRCT This design content has involved the machine manufacture craft and the engine bed jig design, the metal-cutting machine tool, the common

3、 difference coordination and the survey and so on the various knowledge. The reduction gear box body components technological process and its the processing hole jig design is includes the components processing the technological design, the working procedure design as well as the unit clamp design

4、 three parts. Must first carry on the analysis in the technological design to the components, understood the components the craft redesigns the semi finished materials the structure, and chooses the good components the processing datum, designs the components the craft route; After that is carrying

5、on the size computation to a components each labor step of working procedure, the key is decides each working procedure the craft equipment and the cutting specifications; Then carries on the unit clamp the design, the choice designs the jig each composition part, like locates the part, clamps the p

6、art, guides the part, to clamp concrete and the engine bed connection part as well as other parts; Position error which calculates the jig locates when produces, analyzes the jig structure the rationality and the deficiency, and will design in later pays attention to the improvement. Keywords: Th

7、e craft, the working procedure, the cutting specifications, clamp, the localization, the error 目 錄 序言…………………………………………………………………1 一. 零件分析 ……………………………………………………2 1.1 零件作用 ………………………………………………2 1.2零件的工藝分析 …………………………………………2 二. 工藝規(guī)程設計…………………………………………………3 2.1確定毛坯的制造形式 ……………………………………4 2.2基面的選擇

8、……………………………………………… 5 2.3制定工藝路線 ……………………………………………5 2.4機械加工余量、工序尺寸及毛坯尺寸的確定 …………6 2.5確定切削用量及基本工時……………………………… 7 三 夾具設計…………………………………………………… 12 3.1問題的提出………………………………………………12 3.2定位基準的選擇…………………………………………14 3.3定位誤差分析……………………………………………16 3.4切削力及夾緊力計算……………………………………18 3.5定向鍵與對刀裝置設計…………………………………22 3.6夾具設

9、計及簡要操作說明………………………………22 總 結………………………………………………………………23 致 謝………………………………………………………………24 參考文獻 …………………………………………………………25 序 言 機械制造業(yè)是制造具有一定形狀位置和尺寸的零件和產品，并把它們裝備成機械裝備的行業(yè)。機械制造業(yè)的產品既可以直接供人們使用，也可以為其它行業(yè)的生產提供裝備，社會上有著各種各樣的機械或機械制造業(yè)的產品。我們的生活離不開制造業(yè)，因此制造業(yè)是國民經濟發(fā)展的重要行業(yè)，是一個國家或地區(qū)發(fā)展的重要基礎及有力支柱。從某中意義上講，機械制造水平的

10、高低是衡量一個國家國民經濟綜合實力和科學技術水平的重要指標。 張力裝置底架的加工工藝規(guī)程及其鉆的夾具設計是在學完了機械制圖、機械制造技術基礎、機械設計、機械工程材料等進行課程設計之后的下一個教學環(huán)節(jié)。正確地解決一個零件在加工中的定位，夾緊以及工藝路線安排，工藝尺寸確定等問題，并設計出專用夾具，保證零件的加工質量。本次設計也要培養(yǎng)自己的自學與創(chuàng)新能力。因此本次設計綜合性和實踐性強、涉及知識面廣。所以在設計中既要注意基本概念、基本理論，又要注意生產實踐的需要，只有將各種理論與生產實踐相結合，才能很好的完成本次設計。 本次設計水平有限，其中難免有缺點錯誤，敬請老師們批評指正。

11、 一、 零件的分析 1.1 零件的作用 張力裝置底架的作用，待查 1.2 零件的工藝分析 張力裝置底架有2個加工面他們相互之間沒有任何位置度要求。 1.寬12的左右端面為基準的加工面，這組加工面主要是90x25端面和Φ10的孔， 2.以Φ10孔為基準的加工面，這組加工面主要是銑9x60°v型槽和鉆2-M8孔。 二. 工藝規(guī)程設計 2.1 確定毛坯的制造形式 零件材料為HT200，考慮到運行時經常需要掛倒檔以倒行或輔助轉向，因此零件在工作過程中經常受到沖擊性載荷，采用這種材料零件的強度也能保證。由于零件成批生產，而且零件的輪廓尺寸不大

12、，選用砂型鑄造，采用機械翻砂造型，鑄造精度為2級，能保證鑄件的尺寸要求，這從提高生產率和保證加工精度上考慮也是應該的。 2.2 基面的選擇 粗基準選擇應當滿足以下要求： （1）粗基準的選擇應以加工表面為粗基準。目的是為了保證加工面與不加工面的相互位置關系精度。如果工件上表面上有好幾個不需加工的表面，則應選擇其中與加工表面的相互位置精度要求較高的表面作為粗基準。以求壁厚均勻、外形對稱、少裝夾等。 （2） 選擇加工余量要求均勻的重要表面作為粗基準。例如：機床床身導軌面是其余量要求均勻的重要表面。因而在加工時選擇導軌面作為粗基準，加工床身的底面，再以底面作為精基準加工導軌面。這樣就能保證

13、均勻地去掉較少的余量，使表層保留而細致的組織，以增加耐磨性。 （3） 應選擇加工余量最小的表面作為粗基準。這樣可以保證該面有足夠的加工余量。 （4） 應盡可能選擇平整、光潔、面積足夠大的表面作為粗基準，以保證定位準確夾緊可靠。有澆口、冒口、飛邊、毛刺的表面不宜選作粗基準，必要時需經初加工。 （5） 粗基準應避免重復使用，因為粗基準的表面大多數是粗糙不規(guī)則的。多次使用難以保證表面間的位置精度。 基準的選擇是工藝規(guī)程設計中的重要工作之一，他對零件的生產是非常重要的。先選取寬12的端面作為定位基準，。 精基準的選擇 精基準的選擇應滿足以下原則： （1）“基準重合”原則 應盡量選擇加工

14、表面的設計基準為定位基準，避免基準不重合引起的誤差。 （2）“基準統(tǒng)一”原則 盡可能在多數工序中采用同一組精基準定位，以保證各表面的位置精度，避免因基準變換產生的誤差，簡化夾具設計與制造。 （3）“自為基準”原則 某些精加工和光整加工工序要求加工余量小而均勻，應選擇該加工表面本身為精基準，該表面與其他表面之間的位置精度由先行工序保證。 （4）“互為基準”原則 當兩個表面相互位置精度及自身尺寸、形狀精度都要求較高時，可采用“互為基準”方法，反復加工。 （5）所選的精基準 應能保證定位準確、夾緊可靠、夾具簡單、操作方便。 以已經加工好的Φ10孔和一端面為定位精基準，加工其它表面及孔

15、。主要考慮精基準重合的問題，當設計基準與工序基準不重合的時候，應該進行尺寸換算，這在以后還要進行專門的計算，在此不再重復 2.3 制定工藝路線 制訂工藝路線的出發(fā)點，應當是使零件的幾何形狀、尺寸精度及位置精度等技術要求能得到合理的保證。在生產綱領已確定為成批生產的條件下，可以考慮采用萬能型機床配以專用夾具，并盡量使工序集中在提高生產率。除此以外，還應當考慮經濟效果，以便使生產成本盡量降下來。 制定以下兩種工藝方案： 方案一 1 鑄造 鑄造 2 時效處理 時效處理 3 銑 銑12mm上端面 4 銑 銑12mm下端面 5 鉆 銑90x25端面 6 銑

16、 鉆2-Φ10孔 7 鏜 銑9x60°v型槽 8 鉆 鉆2-M8孔 9 檢驗 檢驗，入庫 方案二 1 鑄造 鑄造 2 時效處理 時效處理 3 銑 銑12mm上端面 4 銑 銑12mm下端面 5 鉆 鉆2-Φ10孔 6 銑 銑90x25端面 7 鏜 銑9x60°v型槽 8 鉆 鉆2-M8孔 9 檢驗 檢驗，入庫 工藝方案一和方案二的區(qū)別在于方案二把鉆2-Φ10孔放在銑90x25端面的前面，而方案一把銑90x25端面放在鉆2-Φ10孔的前面，這樣我們做鉆孔的時間就可以利用加工好的面作為定位基準，這樣能能更好地保證工件

17、鉆孔時的位置度要求。 具體的加工路線如下 1 鑄造 鑄造 2 時效處理 時效處理 3 銑 銑12mm上端面 4 銑 銑12mm下端面 5 鉆 銑90x25端面 6 銑 鉆2-Φ10孔 7 鏜 銑9x60°v型槽 8 鉆 鉆2-M8孔 9 檢驗 檢驗，入庫 2.4 機械加工余量、工序尺寸及毛坯尺寸的確定 殼體零件材料為HT200 重量為1 生產類型為大批量生產，采用砂型機鑄造毛坯。 1、 不加工表面毛坯尺寸 不加工表面毛坯按照零件圖給定尺寸為自由度公差，由鑄造可直接獲得。 2、 寬12兩端面 由于殼

18、體底面要與其他接觸面接觸，同時又是Φ10孔的中心線的基準。粗糙度要求為6.3，查相關資料知余量留2.5比較合適。 3、孔 毛坯為空心，鑄造出孔。孔的精度要求介于IT7—IT8之間，參照參數文獻，確定工藝尺寸余量為2.5mm 2.5 確定切削用量及基本工時 工序1：鑄造 工序2：退火處理 工序3：銑12mm上端面 1. 選擇刀具 刀具選取不重磨損硬質合金套式面銑刀，刀片采用YG8, ，，，。 2. 決定銑削用量 1） 決定銑削深度 因為加工余量不大，一次加工完成 2） 決定每次進給量及切削速度 根據X51型銑床說明書，其功率為為7.5kw，中等系

19、統(tǒng)剛度。 根據表查出 ，則 按機床標準選?。?600 當＝1600r/min時 按機床標準選取 3） 計算工時 切削工時：，，，則機動工時為 工序4：銑12mm下端面 銑12mm下端面和銑12mm上端面的切削用量和計算工時相同，在此不再累述。 工序5：銑90x25端面 1. 選擇刀具 刀具選取不重磨損硬質合金套式面銑刀，刀片采用YG8, ，，，。 2. 決定銑削用量 4） 決定銑削深度 因為加工余量不大，故可在一次走刀內銑完，則 5） 決定每次進給量及切削速度 根據X51型銑床說明書，其功率為為7.5kw，中等系統(tǒng)剛度。 根

20、據表查出 ，則 按機床標準選?。?000 當＝1000r/min時 按機床標準選取 6） 計算工時 切削工時：l=90 ，，則機動工時為 工序6：鉆2-Φ10孔 確定進給量：根據參考文獻Ⅳ表2-7，當鋼的，時，。由于本零件在加工Φ10孔時屬于低剛度零件，故進給量應乘以系數0.75，則 根據Z525機床說明書，現取 切削速度：根據參考文獻Ⅳ表2-13及表2-14，查得切削速度所以 根據機床說明書，

21、取，故實際切削速度為 切削工時：，，，則機動工時為 工序8：鉆2-M8孔 工步一：鉆M8螺紋底孔， 選用高速鋼錐柄麻花鉆（《工藝》表3.1－6） 由《切削》表2.7和《工藝》表4.2－16查得 （《切削》表2.15） 按機床選取 基本工時： min 工步二：攻螺紋M8mm： 選擇M8mm高速鋼機用絲錐 等于工件螺紋的螺距，即 按機床選取 基本工時： 三、 銑床夾具設計 3.1問題提

22、出 本夾具主要用來工序7：銑960°v型槽，采用張力裝置底架基準B和兩個Φ10H7孔定位。 3.2 定位基準的選擇 擬定加工路線的第一步是選擇定位基準。定位基準的選擇必須合理，否則將直接影響所制定的零件加工工藝規(guī)程和最終加工出的零件質量?；鶞蔬x擇不當往往會增加工序或使工藝路線不合理，或是使夾具設計更加困難甚至達不到零件的加工精度（特別是位置精度）要求。因此我們應該根據零件圖的技術要求，從保證零件的加工精度要求出發(fā)，合理選擇定位基準。此零件圖沒有較高的技術要求，也沒有較高的平行度和對稱度要求，所以我們應考慮如何提高勞動效率，降低勞動強度，提高加工精度。 3.3定位誤差分析 3.3.1移

23、動時基準位移誤差 （式3-1） 式中： ———— A型固定式定位銷孔的最大偏差 ———— A型固定式定位銷孔的最小偏差 ————A型固定式定位銷定位孔與定位銷最小配合間隙 代入（式3-1）得： =0.015+0+0.013 =0.028（mm) 3.3.2轉角誤差 （式3-2） 式中： ———— A型固定式定位銷孔的最大偏差 ———— A型固定式定位

24、銷孔的最小偏差 ———— A型固定式定位銷定位孔與定位銷最小配合間隙 ———— B型固定式定位銷孔的最大偏差 ———— B型固定式定位銷孔的最小偏差 ———— B型固定式定位銷定位孔與定位銷最小配合間隙 其中： 則代入（式3-2）得： 則：≈0.01003° 3.4夾緊力計算 3.4.1銑削力 查《簡明機床夾具設計手冊》表3-3得切削力計算公式： 由工時計算知，，=0.3mm，，， 由《簡明機床夾具設計手冊》表3-3知 即 ≈510×1.86

25、6×0.382×0.024×9.8×8N ≈684N 3.4.2夾緊力 所需夾緊力，查表5得，，安全系數K= 式中為各種因素的安全系數，查表得： K==1.872，當計算K<2.5時，取K=2.5 孔軸部分由M6螺母鎖緊，查參考文獻2，P92，表3-16螺母的夾緊力為2903N ==7257.5N 由上計算得》，因此采用該夾緊機構工作是可靠的。 3.5定向鍵與對刀裝置設計 根據GB2207—80定向鍵結構如圖所示： 圖 1 夾具體槽形與螺釘圖 根據T形槽的寬度 a=18mm 定向鍵的結構尺寸如下： 圖2 定位鍵的規(guī)

26、格及主要尺寸 銑殼體底面，為了防止銑刀銑到工件，故需要限制銑刀的位置，特制對刀塊。 圖3對刀平塞尺 圖4 對刀平塞尺的規(guī)格及主要尺寸 3.6夾具設計及操作簡要說明 如前所述，在設計夾具時，應該注意提高勞動生產率避免干涉。應使夾具結構簡單，便于操作，降低成本。提高夾具性價比。本道工序為銑床夾具選擇是用移動壓板、可調支承釘、螺柱、六角螺母等組成的夾緊機構進行夾緊工件。本工序為銑削余量小，銑削力小，所以一般的手動夾緊就能達到本工序的要求。 總 結 這次設計是大學學

27、習中最重要的一門科目，它要求我們把大學里學到的所有知識系統(tǒng)的組織起來，進行理論聯系實際的總體考慮，需把金屬切削原理及刀具、機床概論、公差與配合、機械加工質量、機床夾具設計、機械制造工藝學等專業(yè)知識有機的結合起來。同時也培養(yǎng)了自己的自學與創(chuàng)新能力。因此本次設計綜合性和實踐性強、涉及知識面廣。所以在設計中既了解了基本概念、基本理論，又注意了生產實踐的需要，將各種理論與生產實踐相結合，來完成本次設計。 這次設計是培養(yǎng)學生綜合運用所學知識,發(fā)現,提出,分析和解決實際問題,鍛煉實踐能力的重要環(huán)節(jié),更是在學完大學所學的所有專業(yè)課及生產實習的一次理論與實踐相結合的綜合訓練。這次設計雖然只有三個月

28、時間，但在這三個月時間中使我對這次課程設計有了很深的體會。 這次畢業(yè)設計使我以前所掌握的關于零件加工方面有了更加系統(tǒng)化和深入合理化的掌握。比如參數的確定、計算、材料的選取、加工方式的選取、刀具選擇、量具選擇等； 也培養(yǎng)了自己綜合運用設計與工藝等方面的知識； 以及自己獨立思考能力和創(chuàng)新能力得到更進一步的鍛煉與提高；再次體會到理論與實踐相結合時，理論與實踐也存在差異。 回顧起此次設計，至今我仍感慨頗多，的確，從選題到完成定稿，從理論到實踐，在整整一學期的日子里，可以說學到了很多很多的的東西，同時鞏固了以前所學過的知識，而且學到了很多在書本上所沒有學到過的知識。通過這次畢業(yè)設計使我懂得了理論與實際

29、相結合是很重要的，只有理論知識是遠遠不夠的，只有把所學的理論知識與實踐相結合起來，從理論中得出結論，才能真正的實用，在生產過程中得到應用。在設計的過程中遇到了許多問題，當然也發(fā)現了自己的不足之處，對以前所學過的知識理解得不夠深刻，掌握得不夠牢固，通過這次畢業(yè)設計，讓自己把以前所學過的知識重新復習了一遍。 這次畢業(yè)設計雖然順利完成了，也解決了許多問題，也碰到了許多問題，老師的辛勤指導下，都迎刃而解。同時，在老師的身上我也學得到很多額外的知識，在此我表示深深的感謝！同時，對給過我?guī)椭乃型瑢W和各位教研室指導老師再次表示忠心的感謝！ 致 謝

30、 這次設計使我收益不小，為我今后的學習和工作打下了堅實和良好的基礎。但是，查閱資料尤其是在查閱切削用量手冊時，數據存在大量的重復和重疊，由于經驗不足，在選取數據上存在一些問題，不過我的指導老師每次都很有耐心地幫我提出寶貴的意見，在我遇到難題時給我指明了方向，最終我很順利的完成了畢業(yè)設計。 這次設計成績的取得，與指導老師的細心指導是分不開的。在此，我衷心感謝我的指導老師，特別是每次都放下她的休息時間，耐心地幫助我解決技術上的一些難題，她嚴肅的科學態(tài)度，嚴謹的治學精神，精益求精的工作作風，深深地感染和激勵著我。從課題的選擇到項目的最終完成，她都始終給予我細心的指導和不懈的支持。多少個日日夜夜，她

31、不僅在學業(yè)上給我以精心指導，同時還在思想、生活上給我以無微不至的關懷，除了敬佩指導老師的專業(yè)水平外，她的治學嚴謹和科學研究的精神也是我永遠學習的榜樣，并將積極影響我今后的學習和工作。在此謹向指導老師致以誠摯的謝意和崇高的敬意。 參 考 文 獻 1. 切削用量簡明手冊,艾興、肖詩綱主編,機械工業(yè)出版社出版，1994年 2.機械制造工藝設計簡明手冊，李益民主編，機械工業(yè)出版社出版，1994年 3.機床夾具設計，哈爾濱工業(yè)大學、上海工業(yè)大學主編，上海科學技術出版社出版，1983年 4.機床夾具設計手冊，東北重型機械學

32、院、洛陽工學院、一汽制造廠職工大學編，上?？茖W技術出版社出版，1990年 5.金屬機械加工工藝人員手冊，上海科學技術出版社，1981年10月 6.機械制造工藝學，郭宗連、秦寶榮主編，中國建材工業(yè)出版社出版，1997年 外文文獻 原文： Basic Machining Operations and Cutting Technology Basic Machining Operations Machine tools have evolved from the early foot-powered lathes of the Egyptians and

33、John Wilkinson's boring mill. They are designed to provide rigid support for both the workpiece and the cutting tool and can precisely control their relative positions and the velocity of the tool with respect to the workpiece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a rat

34、her narrow strip of metal from the surface of a ductile workpiece in the form of a severely deformed chip. The chip is a waste product that is considerably shorter than the workpiece from which it came but with a corresponding increase in thickness of the uncut chip. The geometrical shape of workpie

35、ce depends on the shape of the tool and its path during the machining operation. Most machining operations produce parts of differing geometry. If a rough cylindrical workpiece revolves about a central axis and the tool penetrates beneath its surface and travels parallel to the center of rotation,

36、 a surface of revolution is produced, and the operation is called turning. If a hollow tube is machined on the inside in a similar manner, the operation is called boring. Producing an external conical surface uniformly varying diameter is called taper turning, if the tool point travels in a path of

37、varying radius, a contoured surface like that of a bowling pin can be produced; or, if the piece is short enough and the support is sufficiently rigid, a contoured surface could be produced by feeding a shaped tool normal to the axis of rotation. Short tapered or cylindrical surfaces could also be c

38、ontour formed. Flat or plane surfaces are frequently required. They can be generated by radial turning or facing, in which the tool point moves normal to the axis of rotation. In other cases, it is more convenient to hold the workpiece steady and reciprocate the tool across it in a series of strai

39、ght-line cuts with a crosswise feed increment before each cutting stroke. This operation is called planning and is carried out on a shaper. For larger pieces it is easier to keep the tool stationary and draw the workpiece under it as in planning. The tool is fed at each reciprocation. Contoured surf

40、aces can be produced by using shaped tools. Multiple-edged tools can also be used. Drilling uses a twin-edged fluted tool for holes with depths up to 5 to 10 times the drill diameter. Whether the drill turns or the workpiece rotates, relative motion between the cutting edge and the workpiece is

41、the important factor. In milling operations a rotary cutter with a number of cutting edges engages the workpiece. Which moves slowly with respect to the cutter. Plane or contoured surfaces may be produced, depending on the geometry of the cutter and the type of feed. Horizontal or vertical axes of r

42、otation may be used, and the feed of the workpiece may be in any of the three coordinate directions. Basic Machine Tools Machine tools are used to produce a part of a specified geometrical shape and precise I size by removing metal from a ductile material in the form of chips. The latter are a w

43、aste product and vary from long continuous ribbons of a ductile material such as steel, which are undesirable from a disposal point of view, to easily handled well-broken chips resulting from cast iron. Machine tools perform five basic metal-removal processes: I turning, planning, drilling, milling,

44、 and grinding. All other metal-removal processes are modifications of these five basic processes. For example, boring is internal turning; reaming, tapping, and counter boring modify drilled holes and are related to drilling; bobbing and gear cutting are fundamentally milling operations; hack sawing

45、 and broaching are a form of planning and honing; lapping, super finishing. Polishing and buffing are variants of grinding or abrasive removal operations. Therefore, there are only four types of basic machine tools, which use cutting tools of specific controllable geometry: 1. lathes, 2. planers, 3.

46、 drilling machines, and 4. milling machines. The grinding process forms chips, but the geometry of the abrasive grain is uncontrollable. The amount and rate of material removed by the various machining processes may be I large, as in heavy turning operations, or extremely small, as in lapping or s

47、uper finishing operations where only the high spots of a surface are removed. 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

48、 feeds and speeds usually ranging from 4 to 32 choices in each case. Speed and Feeds in Machining Speeds, feeds, and depth of cut are the three major variables for economical machining. Other variables are the work and tool materials, coolant and geometry of the cutting tool. The rate of metal r

49、emoval and power required for machining depend upon these variables. The depth of cut, feed, and cutting speed are machine settings that must be established in any metal-cutting operation. They all affect the forces, the power, and the rate of metal removal. They can be defined by comparing them t

50、o the needle and record of a phonograph. The cutting speed (V) is represented by the velocity of- the record surface relative to the needle in the tone arm at any instant. Feed is represented by the advance of the needle radially inward per revolution, or is the difference in position between two ad

51、jacent grooves. The depth of cut is the penetration of the needle into the record or the depth of the grooves. Turning on Lathe Centers The basic operations performed on an engine lathe are illustrated. Those operations performed on external surfaces with a single point cutting tool are called t

52、urning. Except for drilling, reaming, and lapping, the operations on internal surfaces are also performed by a single point cutting tool. All machining operations, including turning and boring, can be classified as roughing, finishing, or semi-finishing. The objective of a roughing operation is to

53、 remove the bulk of the material as rapidly and as efficiently as possible, while leaving a small amount of material on the work-piece for the finishing operation. Finishing operations are performed to obtain the final size, shape, and surface finish on the workpiece. Sometimes a semi-finishing oper

54、ation will precede the finishing operation to leave a small predetermined and uniform amount of stock on the work-piece to be removed by the finishing operation. Generally, longer workpieces are turned while supported on one or two lathe centers. Cone shaped holes, called center holes, which fit t

55、he lathe centers are drilled in the ends of the workpiece-usually along the axis of the cylindrical part. The end of the workpiece adjacent to the tailstock is always supported by a tailstock center, while the end near the headstock may be supported by a headstock center or held in a chuck. The head

56、stock end of the workpiece may be held in a four-jaw chuck, or in a type chuck. This method holds the workpiece firmly and transfers the power to the workpiece smoothly; the additional support to the workpiece provided by the chuck lessens the tendency for chatter to occur when cutting. Precise resu

57、lts can be obtained with this method if care is taken to hold the workpiece accurately in the chuck. Very precise results can be obtained by supporting the workpiece between two centers. A lathe dog is clamped to the workpiece; together they are driven by a driver plate mounted on the spindle nose

58、. One end of the Workpiece is mecained;then the workpiece can be turned around in the lathe to machine the other end. The center holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to carry the weight of the workpiece ?and to resist the cutting forces. After the wor

59、kpiece has been removed from the lathe for any reason, the center holes will accurately align the workpiece back in the lathe or in another lathe, or in a cylindrical grinding machine. The workpiece must never be held at the headstock end by both a chuck and a lathe center. While at first thought th

60、is seems like a quick method of aligning the workpiece in the chuck, this must not be done because it is not possible to press evenly with the jaws against the workpiece while it is also supported by the center. The alignment provided by the center will not be maintained and the pressure of the jaws

61、 may damage the center hole, the lathe center, and perhaps even the lathe spindle. Compensating or floating jaw chucks used almost exclusively on high production work provide an exception to the statements made above. These chucks are really work drivers and cannot be used for the same purpose as or

62、dinary three or four-jaw chucks. While very large diameter workpieces are sometimes mounted on two centers, they are preferably held at the headstock end by faceplate jaws to obtain the smooth power transmission; moreover, large lathe dogs that are adequate to transmit the power not generally avai

63、lable, although they can be made as a special. Faceplate jaws are like chuck jaws except that they are mounted on a faceplate, which has less overhang from the spindle bearings than a large chuck would have. Introduction of Machining Machining as a shape-producing method is the most universally

64、used and the most important of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chip form. Most machining is done with equipment that supports both the work piece and cutting tool although in some cases portable equip

65、ment is used with unsupported workpiece. Low setup cost for small Quantities. Machining has two applications in manufacturing. For casting, forging, and press working, each specific shape to be produced, even one part, nearly always has a high tooling cost. The shapes that may he produced by weldi

66、ng depend to a large degree on the shapes of raw material that are available. By making use of generally high cost equipment but without special tooling, it is possible, by machining; to start with nearly any form of raw material, so tong as the exterior dimensions are great enough, and produce any desired shape from any material. Therefore .machining is usually the preferred method for producing one or a few parts, even when the design of the part would logically lead to casting, forging or pre