外文翻譯---先進的加工工藝

1、<p>　　畢業(yè)設(shè)計(論文)外文資料翻譯</p><p>　　設(shè)計題目: 貽貝殼破碎、磨粉綜合加工機械設(shè)計 </p><p>　　譯文題目: 先進的加工工藝 </p><p>　　院系名稱： 機電工程學院 專業(yè)班級： 機制F0805 </p&g

2、t;<p>　　學生姓名： 李礦峰 學 號： 200849050927 </p><p>　　指導教師： 翟雪琴 教師職稱： </p><p>　　附 件： 1.外文資料翻譯譯文；2.外文原文。 </p><p><b>　　先進的加工工藝&

3、lt;/b></p><p>　　隨著先進科技的硬件變得復雜化，把原料加工成為有用產(chǎn)品的理想的、新的加工手段得到了普遍應(yīng)用。這已經(jīng)成為近幾年機床加工的發(fā)展趨勢。先進的機床控制方法和完全不同的材料成形方法還迫使機械設(shè)計人員進行前幾年還完全沒有進行的方向（研究）。</p><p>　　其他科技如電子技術(shù)和計算機技術(shù)的并行發(fā)展，使機床設(shè)計者有辦法讓機床具有超過絕大多數(shù)經(jīng)驗豐富的機械師（在普

4、通機床上）所具有的加工能力。</p><p>　　在這個部分我們來看數(shù)控機床切削使用的工具。CNC控制器能被用來驅(qū)動和控制多種機床和機構(gòu)。舉幾個例子，如刳刨機進行木料加工；激光、離子弧、火焰切削、噴水切削鋼板；在制造和裝配中機器人的控制等。本書的這個部分僅是一般介紹而不能作為專業(yè)機床的設(shè)計手冊。由于計算機能力和容量的巨大增長，機床的控制技術(shù)很頻繁地發(fā)生著變化。在機床控制發(fā)展中的精彩部分是在每個先進技術(shù)上的使用變得

5、很容易了。</p><p><b>　　NC的優(yōu)勢</b></p><p>　　人工操作機床可能有和CNC機床一樣的物理特性，例如馬力和尺寸，其金屬切削原理也是一樣的。CNC最大的好處是通過計算機控制機床刀具的運動，CNC控制的機床可能簡單得像2刀鉆床或復雜得像5刀的加工中心（如圖O-1）。兩軸的加工機床，其特點是低轉(zhuǎn)速、高馬力軸有高進給率，高轉(zhuǎn)速軸允許高效的高速切削

6、刀具如鉆石和小直徑的刀具的使用（如圖O-2）。它的切削刀具是標準的刀具如磨床的刀具、鉆子、鉆探工具或車刀，這些刀具依賴于所使用的機床型號。切削速度和進給量要像在其他操作機床中一樣是正確的。</p><p>　　CNC機床的最大優(yōu)勢來自無錯的和快速的可能運動的控制。數(shù)控機床不會在一次加工完成后停下來計劃下一次的運動，它不會疲勞，它是不中斷的機床，機床只有在它切削的時候才有生產(chǎn)性。</p><p&

7、gt;　　當切削過程被適當?shù)倪M給量和切削速度控制時，時間的節(jié)約可以通過快速的進給率來完成?？焖龠M給從60發(fā)展到200到400到現(xiàn)在已接近每分1000英寸了。這樣高的進給率對在機床工作區(qū)的任何人構(gòu)成了安全威脅在CNC機床之前，復雜形狀的加工是極困難的。CNC使這些形狀的加工制造在經(jīng)濟上是可行的。零件的設(shè)計變化通過改變控制機床的程序而相對容易實現(xiàn)。</p><p>　　CNC機床不需要額外的時間和特別的預(yù)防就可生產(chǎn)高

8、精度的嚴格公差的零件。CNC使機床不需要復雜的夾具，這使零件很快被加工從而節(jié)約了時間。一旦程序準備好并加工零件，每個零件都將花與第一個一樣的時間。這個一致性允許很精確地控制加工成本。數(shù)控機床的另一個優(yōu)勢是大量存貨的減少，零件可以在需要時再被加工。在傳統(tǒng)制造中，為了增加效率，通常一大批零件被同時加工。有了CNC即使一件也能夠被經(jīng)濟地加工。在很多情況下，一個CNC機床完成了要建立幾臺相同傳統(tǒng)機床才能做的操作。</p><

9、p><b>　　CAM和CNC</b></p><p>　　CAM系統(tǒng)改變了CNC程序員的工作，即從手工編制CNC代碼到CNC機床的輸出最大值。自從手工CNC機床被一大批廠家生產(chǎn)以來，許多不同的CNC控制單元就被使用了。各個不同的廠家的控制單元使用各個不相同的程序與代碼。許多CNC代碼語句可被不同的控制器識別。但其間還有眾多的區(qū)別。為了在有著不同控制器（如FAWC、OKUMA、或DYN

10、APATH）生產(chǎn)一個可互換的零件，將需要完全不同的CNC代碼。每個制造商在不斷地提高和更新其CNC控制。這些改進通常包括附加的代碼語句在已有代碼如何工作上的變化。CAM系統(tǒng)允許CNC程序員在高效的加工過程的建立上濃縮、精選、而不重新學習已改變的代碼格式。一個CNC程序員看著一個零件的圖紙，并且設(shè)計必要的機床操作來制造這個零件（如圖O-3）。這個設(shè)計包括以下每個因素，從可能使用的CNC機床的選擇，到機床的使用選擇，再到加工時的零件裝夾的選

11、擇。CNC程序員必須對這個即將寫入程序的CNC機床的能力和局限有一個完全的了解。機床主參數(shù)如馬力主軸馬力、最大轉(zhuǎn)速、工作臺的重量、工具的尺寸限制、加工變化能力等只是值得考慮的影響程序的因素中的一些。對程序員要求的另一個最重要領(lǐng)域是制</p><p>　　為加工中心使用的軟件是ENGERSOLL CUTTING TOOL公司的ACTUAL CHIP THICKNESS。程序被用來計算磨床每次進的給量，特別是在微量的

12、光潔度加工中。ENGERSOLL的“精密分析”軟件作為機床剛度和機床力的功能來。在這一點上我們觀察一些廣泛的設(shè)計人員應(yīng)掌握的規(guī)格。現(xiàn)在我們測試CAM系統(tǒng)怎樣工作。點控公司（POINT CPNTROLL COMPANY）的SMARTCAM 系統(tǒng)使用接下來的手段：首先設(shè)計人員使用一個金屬零件模型去加工。這包括的加工方式是------車或磨。接著這個零件圖被研究來做成機床加工工序，粗加工或精加工、鉆、沖、磨等操作。被使用的裝夾夾具是虎鉗，抓盤

13、還是卡盤？這些考慮之后，計算機輸出就可開始了。首先還是工藝卡的建立。這個工藝卡由各種記錄（例如：英制或公制，機床類型、零件卡、切削材料類型、安裝記錄、和所需要機床的描述</p><p>　　其第二個編程的步驟是零件的制造。這描述了一個所設(shè)計機床操作的生動模型。從已準備好的JOBPLAN中選好機床后，切削加工的參數(shù)就被編入。對鉆床而言，一旦孔的位置坐標和深度被給出，一個孔就給出現(xiàn)在那點。如果其位置是錯的，其撤消命令

14、選擇這一記錄，并允許你給這個工序新的值。當端面磨時，切削運動通常被定義為弧。當一條直線被編入程序， TOOLPATH就會生動的顯示，其錯誤也可立即被糾正。</p><p>　　在程序運行的任意時刻，命令SHOWPATH會顯示當前的刀具軌跡，也會顯示刀具在實際加工時的使用順序。當?shù)毒哌\動順序需要改變時，可用一個按鍵來實現(xiàn)它。</p><p>　　有時，CAM的程序順序和實際加工的順序是各不相

15、同的。某部件的孔的加工就是一個例子。首先，在CAM中編譯已加工孔的外部輪廓，再把外部輪廓當成粗基準來加工內(nèi)孔。根據(jù)輸入切削的寬和深以及完成切削需切去的材料，計算機產(chǎn)生粗切削的加工程序。程序員嘗試各種粗基準，以便選出最有效的切削加工方法。由于用不同的顏色代表不同的刀具，所以觀察不同刀具的軌跡是很容易的。一個CAM系統(tǒng)可讓程序員從不同的角度觀察圖形，比如說從頂部、正面、側(cè)面或立體圖。俯視中正確的刀具軌跡，在正視圖中，切削的深度是不正確的，其

16、變化顯而易見。</p><p>　　當?shù)毒呗窂郊捌漤樞蚨ê煤?，機床的代碼應(yīng)被做好。這和詳細指明加工這個部件的CNC機床一樣容易。運行時，指定機床的代碼發(fā)生器相當于四個不同的鍵。JOBPLAN文件運行時，表示刀具信息，GRAPHICS文件表示刀具路徑和切削順序。也用MACHINE DEFINE文件表示CNC代碼命令。這個文件可提供最大的進給速度、轉(zhuǎn)速、加工時間等等。當代碼發(fā)生器完成時，加工的計劃時間就確定了。這個時

17、間是根據(jù)進給速度，運行的距離，兩點間在最大進給時間速度下無切削運動的時間，換刀時間等等確定的。這個計劃加工時間可通過改變安裝后達到更智能的移動速度或創(chuàng)造一種更有效的刀具軌跡來調(diào)整。所需的總時間的確定可用來估計生產(chǎn)費用。若不只一個CNC機床可以來加工這工件，制作代碼和比較在加工總時間可以表示一個機床是否比另一個機床該更有效，</p><p><b>　　CAM/CAD</b></p>

18、;<p>　　另一個確立刀具路徑的方法是借助計算機輔助繪圖。大多數(shù)的機械繪圖使用電腦存儲了零件平面圖形及其注釋。格式化的CAM通過它的CAM CONNECTION，可以讀一個CAD文件和轉(zhuǎn)移它的圖形到它的輪廓基準中去。這圖形可表示零件的外形輪廓、孔等等。程序員仍需準備一個工藝卡，含有所用需要的刀具。但相對于用一排排程序來表示外形，現(xiàn)在刀具只用現(xiàn)有的輪廓來表示即可。另外，使用SHOWPATH功能可以顯示每個刀具的路徑和他們的

19、順序。CAD/CAM相互影響的方向的不斷探索和發(fā)展將會改變他們的工作方式。一些CAD和CAM程序，如果在相同的計算機上下載，可同時使用一些按鍵、圖紙和程序，使其能相互匹配。</p><p>　　機床周圍應(yīng)該保持清潔，并且無導致絆倒或打滑的障礙物。機床表面不應(yīng)該被用作工作臺。用正確的方法提升重的工作部件，或固定重的切削刀具。啟動機床之前，確定工作裝置和工件是否安全的固定了 。換刀時，保護工件不受傷害，同時保護你的手

20、不被鋒利的尖角弄傷。使用鋒利的切削刀具時，檢查切削刀具是否正確和安全的安裝。</p><p>　　直到你理解它們的功能和動作方可操作這臺機床。</p><p>　　數(shù)控機床刀具早期的發(fā)展</p><p>　　今天在機器化大生產(chǎn)領(lǐng)域中千形百態(tài)，結(jié)構(gòu)復雜的刀具，起源于一些主要的工業(yè)國，開始很簡陋。這個領(lǐng)域中，最早的一些研究和發(fā)展完成于美國，并記載了UK關(guān)于數(shù)控發(fā)展方面的

21、貢獻。第二次世界大戰(zhàn)后的一個主要問題是，商業(yè)和軍隊迅速發(fā)展，在勞動力密集的加工中，現(xiàn)代工業(yè)界所需的自動化與精確度不可獲得。問題是怎么樣來克服來自常規(guī)的加工方法和手工制作的不足。通常認為，關(guān)于數(shù)控的研究是1949年美國政府的授權(quán)。結(jié)論就是致使美國空軍與Parsons公司簽約，讓他們找到一種靈活的、有力的制造系統(tǒng)，它能擴大生產(chǎn)。麻省理工大學開始進入研究，而Parsons公司使之發(fā)展起來。在1949—1951期間，他們聯(lián)合發(fā)明了一種可適合多種

22、刀具的第一個數(shù)控系統(tǒng)。辛辛那提機床刀具公司把他們的一個28英寸的“Hydro—Tel”軍用機床改裝為三軸自動機床，改變了它們的外部輪廓。在控制桌面位置，典型的機床是三軸連續(xù)曲線的機床刀具，它能產(chǎn)生一個所需要的形狀或曲線，可能的話，通過一個連續(xù)的滑移實現(xiàn)。</p><p>　　與美國機床刀具控制發(fā)展的同時，UK中的ALIFRED Herber產(chǎn)生了第一臺NC機床。1956年更可靠的曲線路徑控制系統(tǒng)開始使用。幾年后，

23、在USA與歐洲開始了更深遠的研究。早期數(shù)控的發(fā)展主要為了航空業(yè)，它需要切削加工復雜的幾何形狀，如機件部件與渦輪機葉片。在航空所需要的復雜的控制系統(tǒng)發(fā)展的同時，點與點控制器發(fā)展起來，更廣泛的用于加工當中。較簡單的點與點機床比復雜的連續(xù)路徑的同類產(chǎn)品便宜一些，并在用于需要精確定位的加工中。作為一個鉆操作的機床刀具的點至點移動例子，典型的運動是快速經(jīng)過在鉆主軸下的工件，鉆空后，迅速的滑移的運動可能過每軸以連續(xù)且獨立的方式獲得。分開的控制可由每

24、軸完成，在早期的點到點機床中，選取路徑不很重要，但它必須避免在獲得多需要精度中所產(chǎn)生的沖擊。所以，趨勢下一點的方向必須是相同的。最早的這些點到點機床長循環(huán)的球形螺絲釘，這就意味著那些運動必須很緩慢，移動中遇到的沖擊不可避免，關(guān)于這個問題下章有更詳細的敘述。</p><p>　　早期的NC機床，主要的在磨床基礎(chǔ)發(fā)展起來的，控制的概念主要用于形成，打孔，磨削以及后來的大量的另外的機床刀具。19世紀50年代以來，流件滑

25、動在高精度的機床中常被結(jié)合使用，它在某種程度上克服了常規(guī)滑軌相關(guān)的問題，然而平均輸出導軌的不精確度對刀具要求更高并增加了它的控制特性。</p><p>　　加工中心的概念是早期工作的結(jié)果，它允許機床在一個安裝上對工件進行多種加工，而不需要把工件轉(zhuǎn)移到另外的刀具下。一個加工中心不同于一個磨床，相互要在于它能利用轉(zhuǎn)移裝置和分離器自動的把切削刀具從刀具庫中轉(zhuǎn)移到主軸上。用這種方式，自動換刀特性使這加工中心高效的加工多種

26、部件，用新刀具代替舊刀具或預(yù)選刀具，使得現(xiàn)今的加工過程循環(huán)操作。</p><p>　　在19世紀60年代中時，一個UK公司，Molins介紹他們獨特的“系統(tǒng)24”意思是一天能加工24小時。它可被認為是系列但作用刀具通過計算機上控制的運輸系統(tǒng)連接起來的復合機床。這個運輸裝置讓工件放在托盤上送至所需的機床刀具下。這是早期情形，是值得欽佩的。靈活制作系統(tǒng)方面嘗試都失敗了，它的主要短處是僅僅小部分的零件種類可隨時加工，而

27、更少的工件需要完成于它相同的操作。事實上它的利用水平很低，機床刀具昂貴會導致加工頻繁時的“頸瓶”現(xiàn)象，于是進一步限制了整個操作。</p><p>　　13世紀70年代初中葉，是機床刀具控制器變革時期，這個時期，CNC成為了一個現(xiàn)實。新的控制器的產(chǎn)生便使公司可通過改變程序改變了一個工件外形。微型技術(shù)的發(fā)展，可成功的加工一批或一個2全件。當兩個相關(guān)的因素存在后，在一個生產(chǎn)環(huán)境中，讓CNC實現(xiàn)靈活且輕松的編程的夢想變成

28、為現(xiàn)實。這些現(xiàn)實是：</p><p>　　集成電路的發(fā)展，它減少了電路的尺寸，使得維護便利且有利于設(shè)計的標準化。</p><p>　　計算機的體積減小，從而它的生產(chǎn)費用也極大的降低。價格便宜，性能穩(wěn)定等多種優(yōu)點使得今天的CNC安裝在機床刀具上。隨著它的不斷發(fā)展成熟，使在高級的CNC系統(tǒng)上可安上人工智能。這些年來，刀具制作者已經(jīng)制作了多種多樣的刀具可用在CNC系統(tǒng)上，其中的一部分在第3冊中將

29、被討論。</p><p>　　由資金耗費項目上的考慮，就CNC機床刀具而言，為了明確新計劃是否必要或證明在短期內(nèi)實現(xiàn)資金回收，一個公司必須進行可行性分析。這些想法及重要的決定將會成為考慮CNC系統(tǒng)經(jīng)濟性調(diào)整問題的主題。</p><p><b>　　英文原文</b></p><p>　　ADVANCED MACHINING PROCESSES

30、 </p><p>　　As the hardware of an advanced technology becomes more complex, new and visionary approaches to the processing of materials into useful products come into common use. This h

31、as been the trend in machining processes in recent years.. Advanced methods of machine control as well as completely different methods of shaping materials have permitted the mechanical designer to proceed in directions

32、that would have been totally impossible only a few years ago.</p><p>　　Parallel development in other technologies such as electronics and computers have made available to the machine tool designer methods an

33、d processes that can permit a machine tool to far exceed the capabilities of the most experienced machinist.</p><p>　　In this section we will look at CNC machining using chip-making cutting tools. CNC contro

34、llers are used to drive and control a great variety of machines and mechanisms, Some examples would be routers in wood working; lasers, plasma-arc, flame cutting, and waterjets for cutting of steel plate; and controlling

35、 of robots in manufacturing and assembly. This section is only an overview and cannot take the place of a programming manual for a specific machine tool. Because of the tremendous growth in n</p><p>　　Advant

36、ages of Numerical Control</p><p>　　A manually operated machine tool may have the same physical characteristics as a CNC machine, such as size and horsepower. The principles of metal removal are the same. The

37、 big gain comes from the computer controlling the machining axes movements. CNC-controlled machine tools can be as simple as a 2-axis drilling machining center (Figure O-1). With a dual spindle machining center, the low

38、RPM, high horsepower spindle gives high metal removal rates. The high RPM spindle allows the efficient use o</p><p>　　Since the chip-making process is controlled by the proper feeds and speeds, time savings

39、can be achieved by faster rapid feed rates. Rapid feeds have increased from 60 to 200 to 400 and are now often approaching 1000 inches per minute (IPM). These high feed rates can pose a safety hazard to anyone within the

40、 working envelope of the machine tool.</p><p>　　Complex contoured shapes were extremely difficult to product prior to CNC machining .CNC has made the machining of these shapes economically feasible. Design c

41、hanges on a part are relatively easy to make by changing the program that directs the machine tool.</p><p>　　A CNC machine produces parts with high dimensional accuracy and close tolerances without taking ex

42、tra time or special precautions, CNC machines generally need less complex work-holding fixtures, which saves time by getting the parts machined sooner. Once a program is ready and production parts, each part will take ex

43、actly the same amount of time as the previous one. This repeatability allows for a very precise control of production costs. Another advantage of CNC machining is the elimination of </p><p>　　With modern CNC

44、 machine tools a trained machinist can program and product even a single part economically .CNC machine tools are used in small and large machining facilities and range in size from tabletop models to huge machining cent

45、ers. In a facility with many CNC tools, programming is usually done by CNC programmers away from the CNC tools. The machine control unit (MCU) on the machine is then used mostly for small program changes or corrections.

46、Manufacturing with CNC tools usually requires</p><p>　　CNC controls are generally divided into two basic categories. One uses a ward address format with coded inputs such as G and M codes. The other users a

47、conversational input; conversational input is also called user-friendly or prompted input. Later in this section examples of each of these programming formats in machining applications will be describes.</p><p

48、>　　CAM and CNC</p><p>　　CAM systems have changed the job of the CNC programmer from one manually producing CNC code to one maximizing the output of CNC machines. Since CNC machine tools are made by a grea

49、t number of manufacturers, many different CNC control units are in use. Control units from different manufacturers use a variety of program formats and codes. Many CNC code words are identical for different controllers,

50、but a great number vary from one to another.</p><p>　　To produce an identical part on CNC machine tools with different controllers such as one by FANCU, OKUMA or DYNAPATH, would require completely different

51、CNC codes. Each manufacturer is constantly improving and updating its CNC controllers. These improvements often include additional code words plus changes in how the existing code works.</p><p>　　A CAM syste

52、m allows the CNC programmer to concentrate on the creation of an efficient machining process, rather than relearning changed code formats. A CNC programmer looks at the print of a part and then plans the sequence of mach

53、ining operations necessary to make it (Figure O-3). This plan includes everything, from the selection of possible CNC machine tools, to which tooling to use, to how the part is held while machining takes place. The CNC p

54、rogrammer has to have a thoroughunderstanding of </p><p>　　Another area of major importance to the programmer is the knowledge of machining processes. An example would be the selection of the surface finish

55、requirement specified in the part print. The sequence of machining processes is critical to obtain acceptable results. Cutting tool limitations have to be considered and this requires knowledge of cutting tool materials,

56、 tool types, and application recommendations.</p><p>　　A good programmer will spend a considerable amount of time in researching the rapidly growing volume of new and improved tools and tool materials. Often

57、 the tool that was on the cutting edge of technology just two years ago is now obsolete. Information on new tools can come from catalogs or tool manufacturers' tooling engineers. Help in tool selection or optimum too

58、l working conditions can also be obtained from tool manufacturer software. Examples would be Kennametal's "TOOLPRO", software design</p><p>　　Software for a machining center application would b

59、e Ingersoll Tool Company's "Actual Chip Thickness", a program used to calculate the chip thickness in relation to feed-per-tooth for a milling cutter, especially during a shallow finishing cut. Ingersoll

60、9;s "Rigidity Analysis" software ealculates tool deflection for end mills as a function of tool stiffness and tool force.</p><p>　　To this point we looked at some general qualifications that a prog

61、rammer should possess. Now we examine how a CAM system works. Point Control Company's SmartCam system uses the following approach. First, the programmer makes a mental model of the part to be machined. This includes

62、the kind of machining to be performed-turning or milling. Then the part print is studied to develop a machining sequence, roughing and finishing cuts, drilling, tapping, and boring operations. What work-holding device &l

63、t;/p><p>　　This line of information describes the tool by number, type, and size and includes the appropriate cutting speed and feed rate. After all the selected tools are entered, the file is saved.</p>

64、<p>　　The second programming step is the making of the part. This represents a graphic modeling of the projected machining operation. After selecting a tool from the prepared JOBPLAN, parameters for the cutting ope

65、ration are entered. For a drill, once thecoordinate location of the hole and the depth are given, a circle appears on that spot. If the location is incorrect, the UNDO command erases this entry and allows you to give new

66、 values for this operation. When an end mill is being used, cutting move</p><p>　　At any time during programming, the command SHOWPATH will show the actual toolpath for each of the programmed tools. The tool

67、s will be displayed in the sequence in which they will be used during actual machining. If the sequence of a tool movement needs to be changed, a few keystrokes will to that.</p><p>　　Sometimes in CAM the pr

68、ogramming sequence is different from the actual machining order. An example would be the machining of a pocket in a part. With CAM, the finished pocket outline is programmed first, then this outline is used to define the

69、 roughing cuts to machine the pocket. The roughing cuts are computer generated from inputs such as depth and width of cut and how much material to leave for the finish cut. Different roughing patterns can be tried out to

70、 allow the programmer to select the m</p><p>　　A CAM system lets the programmer view the graphics model from varying angles, such as a top, front, side, or isometric view. A toolpath that looks correct from

71、a top view, may show from a front view that the depth of the cutting tool is incorrect. Changes can easily be made and seen immediately.</p><p>　　When the toolpath and the sequence of operations are satisfac

72、tory, machine ready code has to be made. This is as easy as specifying the CNC machine that is to be used to machine the part. The code generator for that specific CNC machine during processing accesses four different fi

73、les. The JOBPLAN file for the tool information and the GRAPHICE file for the toolpath and cutting sequence. It also uses the MACHINE DEFINE file which defines the CNC code words for that specific machine. This file also&

74、lt;/p><p><b>　　CAD/CAM</b></p><p>　　Another method of creating toolpath is with the use of a Computer-aided Drafting (CAD) file. Most machine drawings are created using computers with t

75、he description and part geometry stored in the computer database. SmartCAM, though its CAM CONNECTION, will read a CAD file and transfer its geometry represents the part profile, holes, and so on. The programmer still ne

76、eds to prepare a JOBPLAN with all the necessary tools, but instead of programming a profile line by line, now only a tool has to be</p><p>　　The work area around the machine needs to be kept clean and clear

77、of obstructions to prevent slipping or tripping. Machine surfaces should not be used as worktables. Use proper lifting methods to handle heavy workpieces, fixtures, or heavy cutting tools. Make measurements only when the

78、 spindle has come to a complete standstill. Chips should never be handled with bare hands.</p><p>　　Before starting the machine make sure that the work-holding device and the workpiece are securely fastened.

79、 When changing cutting tools, protect the workpiece being machined from damage, and protect your hands from sharp cutting edges. Use only sharp cutting tools. Check that cutting tools are installed correctly and securely

80、.</p><p>　　Do not operate any machine controls unless you understand their function and what they will do.</p><p>　　The Early Development Of Numerically Controlled Machine Tools</p><p

81、>　　The highly sophisticated CNC machine tools of today, in the vast and diverse range found throughout the field of manufacturing processing, started from very humble beginnings in a number of the major industrialized

82、 countries. Some of the earliest research and development work in this field was completed in USA and a mention will be made of the UK's contribution to this numerical control development.</p><p>　　A maj

83、or problem occurred just after the Second World War, in that progress in all areas of military and commercial development had been so rapid that the levels of automation and accuracy required by the modern industrialized

84、 world could not be attained from the lab our intensive machines in use at that time. The question was how to overcome the disadvantages of conventional plant and current manning levels. It is generally acknowledged that

85、 the earliest work into numerical control was the study</p><p>　　At about the same times as these American advances in machine tool control were taking Place, Alfred Herbert Limited in the United Kingdom had

86、 their first Mutinous path control system which became available in 1956.Over the next few years in both the USA and Europe, further development work occurred. These early numerical control developments were principally

87、for the aerospace industry, where it was necessary to cut complex geometric shapes such as airframe components and turbine blades. In para</p><p>　　The earliest examples of these cheaper point-to-point machi

88、nes usually did not use recalculating ball screws; this meant that the motions would be sluggish, and sideways would inevitably suffer from backlash, but more will be said about this topic later in the chapter.</p>

89、<p>　　The early NC machines were, in the main, based upon a modified milling machine with this concept of control being utilized on turning, punching, grinding and a whole host of other machine tools later. Toward

90、s the end of the 1950s,hydrostatic sideways were often incorporated for machine tools of highly precision, which to sonic extent overcame the section problem associated with conventional sideway response, whiles averagin

91、g-out sideway inaccuracy brought about a much increased preasion in the m</p><p>　　In the mid 1960s,a UK company, Molins, introduced their unique "System 24" which was meant represent the ability o

92、f a system to machine for 24 hours per day. It could be thought of as a "machining complex" which allowed a series of NC single purpose machine tools to be linked by a computerized conveyor system. This conveyo

93、r allowed the work pieces to be palletized and then directed to as machine tool as necessary. This was an early, but admirable, attempt at a form of Flexible manufacturing Syst</p><p>　　The early to mid-1970

94、s was a time of revolutionary in the area of machine tool controller development, when the term computerized numerical control (CNC) became a reality. This new breed of controllers gave a company the ability to change wo

95、rk piece geometries, together with programs, easily with the minimum of development and lead time, allowing it to be economically viable to machine small batches, or even one-off successfully. The dream of allowing a com

96、puterized numerical controller the flex</p><p>　　The multipie benefits of cheaper electorics with greater reliability have result in the CNC fitted to the machine tools today, with the power and sophisticati

97、on progtessing considerably in the last few years, allowing an almost artificial intelligence(AI) to the latest systems. Over the years, the machine tools builders have produced a large diversity in the range of applicat

98、ions of CNC and just some of those development will be reviewed in Volume Ⅲ。</p><p>　　With any capital cost item, such as a CNC machine tool, it is necessary for a company to undergo a feasibility study in o

99、rder to ascertain whether the purchase of new plant is necessary and can be justified over a relatively short pay-back period. These thoughts and other circial decisions will be the subject of the next section which is c