資源目錄里展示的全都有預(yù)覽可以查看的噢，，下載就有,,請放心下載，原稿可自行編輯修改=【QQ：11970985 可咨詢交流】====================喜歡就充值下載吧。。。資源目錄里展示的全都有，，下載后全都有,,請放心下載，原稿可自行編輯修改=【QQ：197216396 可咨詢交流】==================== 專題 高速切削的概念、和應(yīng)用技術(shù) 高速切削理論是1931年4月德國物理學(xué)家Carl.J.Salomon提出的。他指出，在常規(guī)切削速度范圍內(nèi)，切削溫度隨著切削速度的提高而升高，但切削速度提高到一定值后，切削溫度不但不升高反會降低，且該切削速度值與工件材料的種類有關(guān)。對每一種工件材料都存在一個速度范圍，在該速度范圍內(nèi)，由于切削溫度過高，刀具材料無法承受，即切削加工不可能進行，稱該區(qū)為“死谷”。雖然由于實驗條件的限制，當時無法付諸實踐，但這個思想給后人一個非常重要的啟示，即如能越過這個“死谷”，在高速區(qū)工作，有可能用現(xiàn)有刀具材料進行高速切削，切削溫度與常規(guī)切削基本相同，從而可大幅度提高生產(chǎn)效率。 高速切削是個相對的概念，究竟如何定義，目前尚無共識。由于加工方法和工件材料的不同，高速切削的高速范圍也很難給出，一般認為應(yīng)是常規(guī)切削速度的5～10倍。 自從Salomon提出高速切削的概念并于同年申請專利以來，高速切削技術(shù)的發(fā)展經(jīng)歷了高速切削理論的探索、應(yīng)用探索、初步應(yīng)用和較成熟應(yīng)用等四個階段，現(xiàn)已在生產(chǎn)中得到了一定的推廣應(yīng)用。特別是20世紀80年代以來，各工業(yè)發(fā)達國家投入了大量的人力和物力，研究開發(fā)了高速切削設(shè)備及相關(guān)技術(shù)，20世紀90年代以來發(fā)展更迅速。 高速切削技術(shù)是在機床結(jié)構(gòu)及材料、機床設(shè)計、制造技術(shù)、高速主軸系統(tǒng)、快速進給系統(tǒng)、高性能CNC系統(tǒng)、高性能刀夾系統(tǒng)、高性能刀具材料及刀具設(shè)計制造技術(shù)、高效高精度測量測試技術(shù)、高速切削機理、高速切削工藝等諸多相關(guān)硬件和軟件技術(shù)均得到充分發(fā)展基礎(chǔ)之上綜合而成的。因此，高速切削技術(shù)是一個復(fù)雜的系統(tǒng)工程. 高速與超高速切削的特點 隨著高速與超高速機床設(shè)備和刀具等關(guān)鍵技術(shù)領(lǐng)域的突破性進展，高速與超高速切削技術(shù)的工藝和速度范圍也在不斷擴展。如今在實際生產(chǎn)中超高速切削鋁合金的速度范圍為1500m/min～5500m/min，鑄鐵為750m/min～4500m/min，普通鋼為600m/min～800m/min，進給速度高達20 m/min～40m/min。而且超高速切削技術(shù)還在不斷地發(fā)展。在實驗室里，切削鋁合金的速度已達 6000m/min以上，進給系統(tǒng)的加速度可達3g。有人預(yù)言，未來的超高速切削將達到音速或超音速。其特點可歸納如下： (1)可提高生產(chǎn)效率 提高生產(chǎn)效率是機動時間和輔助時間大幅度減少、加工自動化程度提高的必然結(jié)果。據(jù)稱，由于主軸轉(zhuǎn)速和進給的高速化，加工時間減少了50%，機床結(jié)構(gòu)也大大簡化，其零件的數(shù)量減少了25%，而且易于維護。 (2)可獲得較高的加工精度 由于切削力可減少30%以上，工件的加工變形減小，切削熱還來不及傳給工件，因而工件基本保持冷態(tài)，熱變形小，有利于加工精度的提高。特別對大型的框架件、薄板件、薄壁槽形件的高精度高效率加工，超高速銑削則是目前惟一有效的加工方法。 (3)能獲得較好的表面完整性 在保證生產(chǎn)效率的同時，可采用較小的進給量，從而減小了加工表面的粗糙度值；又由于切削力小且變化幅度小，機床的激振頻率遠大于工藝系統(tǒng)的固有頻率，故振動時表面質(zhì)量的影響很??；切削熱傳入工件的比率大幅度減少，加工表面的受熱時間短，切削溫度低，加工表面可保持良好的物理力學(xué)性能。 (4)加工能耗低，節(jié)省制造資源 超高速切削時，單位功率的金屬切除率顯著增大。以洛克希德飛機制造公司的鋁合金超高速銑削為例，主軸轉(zhuǎn)速從4000m/min提高到20000m/min，切削力減小了30%，金屬切除率提高了3倍，單位功率的金屬切除率可達130000mm3/(min·kW)160000mm3/(min·kW)。由于單位功率的金屬切除率高、能耗低、工件的在制時間短，從而提高了能源和設(shè)備的利用率，降低了切削加工在制造系統(tǒng)資源總量中的比例，故超高速切削完全符合可持續(xù)發(fā)展戰(zhàn)略的要求。 高速與超高速切削技術(shù)的應(yīng)用領(lǐng)域 高速切削是當今制造業(yè)中一項快速發(fā)展的新技術(shù)，在工業(yè)發(fā)達國家，高速切削正成為一種新的切削加工理念。 ①高速切削的應(yīng)用領(lǐng)域首先在航空工業(yè)輕合金的加工。飛機制造業(yè)是最早采用高速銑削的行業(yè)。飛機上的零件通常采用“整體制造法”，即在整體上“掏空”加工以形成多筋薄壁構(gòu)件，其金屬切除量相當大，這正是高速切削的用武之地。鋁合金的切削速度已達1500m/min～5500 m/min，最高達7500m/min(美)。 ②模具制造業(yè)也是高速加工應(yīng)用的重要領(lǐng)域。模具型腔加工過去一直為電加工所壟斷，但其加工效率低。而高速加工切削力小，可銑淬硬60HRC的模具鋼，加工表面粗糙度值又很小，淺腔大曲率半徑的模具完全可用高速銑削來代替電加工；對深腔小曲率的，可用高速銑削加工作為粗加工和半精加工，電加工只作為精加工。這樣可使生產(chǎn)效率大大提高，周期縮短。鋼的切削速度可達600m/min～800m/min。 ③汽車工業(yè)是高速切削的又一應(yīng)用領(lǐng)域。汽車發(fā)動機的箱體、氣缸蓋多用組合機加工。國外汽車工業(yè)及上海大眾、上海通用公司，凡技術(shù)變化較快的汽車零件，如：氣缸蓋的氣門數(shù)目及參數(shù)經(jīng)常變化，現(xiàn)一律用高速加工中心來加工。鑄鐵的切削速度可達750m/min～4500m/min。 ④ Ni基高溫合金(Inconel 718)和Ti合金(Ti-6Al-4V)常用來制造發(fā)動機零件，因它們很難加工，一般采用很低的切削速度。如采用高速加工，則可大幅度提高生產(chǎn)效率、減小刀具磨損、提高零件的表面質(zhì)量。 ⑤纖維增強復(fù)合材料切削時對刀具有十分嚴重的刻劃作用，刀具磨損非?？?。用聚晶金剛石PCD刀具進行高速加工，收到滿意效果?？煞乐钩霈F(xiàn)“層間剝離”，效率高、質(zhì)量好。 ⑥干式切削和硬態(tài)切削也是高速切削擴展的領(lǐng)域。 ⑦國內(nèi)的應(yīng)用舉例。國內(nèi)某專業(yè)橡膠模具制造廠，高速銑削在高精度鋁質(zhì)模具型腔加工和輪胎模具型芯加工中取得了很好的效果。所用機床為5軸聯(lián)動高速銑床DIGIT-218，轉(zhuǎn)速為28000r/min，功率為6kW，進給速度υf=10m/min，進給加速度為0.5g。 高精度鋁質(zhì)模具型腔加工是眾多模具制造廠家的一大難題。在傳統(tǒng)銑削加工中，由于鋁熔點低，鋁屑容易粘附在刀具上，雖經(jīng)后續(xù)的鏟刮、拋光工序，型腔也很難達到精度要求，在制時間達60小時。用高速銑削n0粗=18000r/min，ap=2mm，υf=5m/min；n0精＝20000r/min，ap=0.2mm，加工周期僅為6小時，完全達到1500mm長度上的尺寸精度為±0.05mm、Ra0.8μm的要求。 塑料的輪胎型芯加工用傳統(tǒng)方法(手工)需十幾道工序，在制時間20天以上，也很難達到復(fù)雜輪胎花紋的技術(shù)要求。采用高速銑削，n0＝ 18 000r/min，ap=2 mm，υf=10m/min，在制時間僅24小時就完全達到了工藝要求。 高速與超高速切削對機床的新要求 機床是實現(xiàn)高速與超高速切削的首要條件和關(guān)鍵因素。高速與超高速切削對機床提出了很多新要求，歸納如下： (1)主軸要有高轉(zhuǎn)速、大功率和大扭矩 高速與超高速切削不但要求機床主軸轉(zhuǎn)速高，而且要求傳遞的扭矩和功率也要大，并且在高速運轉(zhuǎn)中還要保持良好的動態(tài)特性和熱態(tài)特性。 (2)進給速度也要相應(yīng)提高，以保證刀具每齒進給量基本不變 為了配合主軸10倍于常規(guī)的切削速度，進給速度也必須相應(yīng)提高10倍，由過去的6m/min提高到60m/min～100m/min，以保持刀具的每齒進給量基本不變。 (3)進給系統(tǒng)要有很大的加速度 在切削加工過程中，機床進給系統(tǒng)的工作行程一般只有幾十毫米至幾百毫米。在這樣短的行程中要實現(xiàn)穩(wěn)定的高速與超高速切削，除了進給速度要高外，進給系統(tǒng)必須有很大的加速度，以盡量縮短啟動—變速—停車的過渡過程，以實現(xiàn)平穩(wěn)切削。這是高速與超高速切削對機床結(jié)構(gòu)設(shè)計的新要求，也是機床設(shè)計理論的新發(fā)展。 綜上所述，沿襲數(shù)十年的普通數(shù)控機床的傳動與結(jié)構(gòu)已遠遠不能適應(yīng)要求，必須進行全新設(shè)計。因此，有人稱高速與超高速機床是21世紀的新機床，其主要特征是實現(xiàn)機床主軸和進給的直接驅(qū)動，是機電一體化的新產(chǎn)品。 適用高速與超高速切削的刀具材料 目前適用于高速切削的刀具主要有：涂層刀具、金屬陶瓷刀具、陶瓷刀具、立方氯化硼(CBN)刀具及聚晶金剛石(PCD)刀具等。 1.涂層刀具 涂層在刀具基體上涂復(fù)硬質(zhì)耐磨金屬化合物薄膜以達到提高刀具表面的硬度和耐磨性的目的。常用的刀具基體材料主要有高速鋼、硬質(zhì)合金、金屬陶瓷和陶瓷等。涂層TiN，TiC，Al2O3，TiCN，TiAlN，TiAlCN等；涂層可以是單涂層，也可以是雙涂層或多涂層，甚至是幾種涂層材料復(fù)合而成的復(fù)合涂層。復(fù)合涂層可以是TiC-Al2O3-TiN，TiCN和 TiAlN多元復(fù)合涂層，最新又發(fā)展了TiN/NbN，TiN/CN等多元復(fù)合薄膜。如商品名為“Fire”的孔加工刀具復(fù)合涂層，是用TiN作底層，以保證與基體間的結(jié)合強度；由多層薄涂層構(gòu)成的中間層為緩沖層，以用來吸收斷續(xù)切削產(chǎn)生的振動；頂層是具有良好耐磨性和耐熱性的TiAlN層。還可在“Fire”外層上涂減磨涂層。其中，TiAlN層在高速切削中性能優(yōu)異，最高切削溫度可達800℃。近年開發(fā)出的一些PVD硬涂層材料，有CBN、氮化碳(CN)、Al2O3、氮化物(TiN/NbN，TiN/CN)等，在高溫下具有良好的熱穩(wěn)定性，很適合高速與超高速切削。金剛石膜涂層刀具主要用于有色金屬加工。C-C3N4超硬涂層的硬度有可能超過金剛石。 軟涂層刀具，如 MoS2和 WS2作為涂層材料的高速鋼刀具主要用于高強度鋁合金、鈦合金等的加工。此外，最新開發(fā)的納米涂層材料刀具在高速切削中的應(yīng)用前景也很廣闊。如日本住友公司的納米TiAlN復(fù)合涂層銑刀片，共2000層涂層，每層只有2.5nm厚。 2.金屬陶瓷刀具 金屬陶瓷主要包括高耐磨性能的TiC基硬質(zhì)合金(TiC+Ni或Mo)、高韌性的TiC基硬質(zhì)合金( TiC+TaC+WC)、強韌的TiN基硬質(zhì)合金和高強韌性的TiCN基硬質(zhì)合金(TiCN＋NbC)等。這些合金做成的刀具可在υc=300m/min～500m/min范圍內(nèi)高速精車鋼和鑄鐵。金屬陶瓷可制成鉆頭、銑刀與滾刀。如日本研制的金屬陶瓷滾刀，υc=600m/min，約是硬質(zhì)合金滾刀的10～20倍，加工表面粗糙度值Rmax為2μm，比HSS滾刀(Rmax15μm)和硬質(zhì)合金滾刀(Rmax8μm)小的多，耐磨性優(yōu)于HSS和硬質(zhì)合金，HSS滾刀后刀面磨損量VB＝0.32mm，硬質(zhì)合金滾刀VB＝0.18mm，而金屬陶瓷滾刀VB＝0.08mm。 3.陶瓷刀具 陶瓷刀具可在υc=200m/min～1000m/min范圍內(nèi)切削軟鋼、淬硬鋼和鑄鐵等材料。 4.CBN刀具 CBN刀具是高速精加工或半精加工淬硬鋼、冷硬鑄鐵和高溫合金等的理想對具材料，可以實現(xiàn)“以車代磨”。國外還研制了CBN含量不同的CBN刀具，以充分發(fā)揮CBN刀具的切削性能(見表1)。據(jù)報導(dǎo)，CBN300加工灰鑄鐵的速度可達2000m/min。 表1 不同CBN含量的刀片及用途 CBN含量(%) 用 途 50 連續(xù)切削淬硬鋼(45HRC～65HRC) 65 半斷續(xù)切削淬硬鋼(45HRC～65HRC) 80 Ni-Cr鑄鐵 90 連續(xù)重載切削淬硬鋼(45HRC～65HRC) 80～90 高速切削鑄鐵(45HRC～65HRC)，粗、半精切削淬硬鋼 5.PCD刀具 PCD刀具可實現(xiàn)有色金屬、非金屬耐磨材料的高速加工。據(jù)報導(dǎo)，鑲PCD的鉆頭加工Si-Al則合金的切削速度隊達300m/min～400m/min，PCD與硬質(zhì)合金的復(fù)合片鉆頭加工用Al合金、Mg合金、復(fù)合材料FRP、石墨、粉末冶金坯料，與硬質(zhì)合金刀具相比，刀具壽命提高了65～145倍；采用高強度Al合金刀體的PCD面銑刀加工用合金的速度υc達 3000m/min～4000m/min，有的達到7000m/min。20世紀90年代以后，美、日相繼研制開發(fā)了金剛石薄膜刀具(車銑刀片、麻花鉆、立銑刀、絲錐等)，壽命是硬質(zhì)合合金刀具的10～140倍。 6.性能優(yōu)異的高速鋼和硬質(zhì)合金復(fù)雜刀具 用高性能鈷高速鋼、粉末冶金高速鋼和硬質(zhì)合金制造的齒輪刀具，可用于齒輪的高速切削。 用硬質(zhì)合金粉末和高速鋼粉末配制成的新型粉末冶金材料制成的齒輪滾刀，滾切速度可達150m/min～180m/min。進行對TiAlN涂層處理后，可用于高速干切齒輪。 用細顆粒硬質(zhì)合金制造并涂復(fù)耐磨耐熱及潤滑涂層的麻花鉆加冷卻液加工碳素結(jié)構(gòu)鋼和合金鋼時，切削速度可達200m/min，于切時切削速度也可達150m/min。 用細顆粒硬質(zhì)合金制成的絲錐加工灰鑄鐵時，切削速度可達100m/min。 意大利SU公司研制的硬質(zhì)合金滾刀涂復(fù)TiCN涂層后加工模數(shù)m＝1.5的行星齒輪時，加水基切削液，粗滾速度υc粗=280m/min，精滾υc精＝600m/min。 附錄 (外文翻譯——原文) Fundamentals of Mechanical Design Mechanical design means the design of things and systems of a mechanical nature—machines, products, structures, devices, and instruments. For the most part mechanical design utilizes mathematics, the materials sciences, and the engineering-mechanics sciences. The total design process is of interest to us. How does it begin? Does the engineer simply sit down at his desk with a blank sheet of paper? And, as he jots down some ideas, what happens next? What factors influence or control the decisions which have to be made? Finally, then, how does this design process end? Sometimes, but not always, design begins when an engineer recognizes a need and decides to do something about it. Recognition of the need and phrasing it in so many words often constitute a highly creative act because the need may be only a vague discontent, a feeling of uneasiness, of a sensing that something is not right. The need is usually not evident at all. For example, the need to do something about a food-packaging machine may be indicated by the noise level, by the variations in package weight, and by slight but perceptible variations in the quality of the packaging or wrap. There is a distinct difference between the statement of the need and the identification of the problem. which follows this statement. The problem is more specific. If the need is for cleaner air, the problem might be that of reducing the dust discharge from power-plant stacks, or reducing the quantity of irritants from automotive exhausts. Definition of the problem must include all the specifications for the thing that is to be designed. The specifications are the input and output quantities, the characteristics of the space the thing must occupy and all the limitations on these quantities. We can regard the thing to be designed as something in a black box. In this case we must specify the inputs and outputs of the box together with their characteristics and limitations. The specifications define the cost, the number to be manufactured, the expected life, the range, the operating temperature, and the reliability. There are many implied specifications which result either from the designer's particular environment or from the nature of the problem itself. The manufacturing processes which are available, together with the facilities of a certain plant, constitute restrictions on a designer's freedom, and hence are a part of the implied specifications. A small plant, for instance, may not own cold-working machinery. Knowing this, the designer selects other metal-processing methods which can be performed in the plant. The labor skills available and the competitive situation also constitute implied specifications. After the problem has been defined and a set of written and implied specifications has been obtained, the next step in design is the synthesis of an optimum solution. Now synthesis cannot take place without both analysis and optimization because the system under design must be analyzed to determine whether the performance complies with the specifications. The design is an iterative process in which we proceed through several steps, evaluate the results, and then return to an earlier phase of the procedure. Thus we may synthesize several components of a system, analyze and optimize them, and return to synthesis to see what effect this has on the remaining parts of the system. Both analysis and optimization require that we construct or devise abstract models of the system which will admit some form of mathematical analysis. We call these models mathematical models. In creating them it is our hope that we can find one which will simulate the real physical system very well. Evaluation is a significant phase of the total design process. Evaluation is the final proof of a successful design, which usually involves the testing of a prototype in the laboratory. Here we wish to discover if the design really satisfies the need or needs. Is it reliable? Will it compete successfully with similar products? Is it economical to manufacture and to use? Is it easily maintained and adjusted? Can a profit be made from its sale or use? Communicating the design to others is the final, vital step in the design process. Undoubtedly many great designs, inventions, and creative works have been lost to mankind simply because the originators were unable or unwilling to explain their accomplishments to others. Presentation is a selling job. The engineer, when presenting a new solution to administrative, management, or supervisory persons, is attempting to sell or to prove to them that this solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the solution have been largely wasted. Basically, there are only three means of communication available to us. There are the written, the oral, and the graphical forms. Therefore the successful engineer will be technically competent and versatile in all three forms of communication. A technically competent person who lacks ability in any one of these forms is severely handicapped. If ability in all three forms is lacking, no one will ever know how competent that person is! The competent engineer should not be afraid of the possibility of not succeeding in a presentation. In fact, occasional failure should be expected because failure or criticism seems to accompany every really creative idea. There is a great to be learned from a failure, and the greatest gains are obtained by those willing to risk defeat. In the find analysis, the real failure would lie in deciding not to make the presentation at all. Introduction to Machine Design Machine design is the application of science and technology to devise new or improved products for the purpose of satisfying human needs. It is a vast field of engineering technology which not only concerns itself with the original conception of the product in terms of its size, shape and construction details, but also considers the various factors involved in the manufacture, marketing and use of the product. People who perform the various functions of machine design are typically called designers, or design engineers. Machine design is basically a creative activity. However, in addition to being innovative, a design engineer must also have a solid background in the areas of mechanical drawing, kinematics, dynamics, materials engineering, strength of materials and manufacturing processes. As stated previously, the purpose of machine design is to produce a product which will serve a need for man. Inventions, discoveries and scientific knowledge by themselves do not necessarily benefit people; only if they are incorporated into a designed product will a benefit be derived. It should be recognized, therefore, that a human need must be identified before a particular product is designed. Machine design should be considered to be an opportunity to use innovative talents to envision a design of a product is to be manufactured. It is important to understand the fundamentals of engineering rather than memorize mere facts and equations. There are no facts or equations which alone can be used to provide all the correct decisions to produce a good design. On the other hand, any calculations made must be done with the utmost care and precision. For example, if a decimal point is misplaced, an otherwise acceptable design may not function. Good designs require trying new ideas and being willing to take a certain amount of risk, knowing that is the new idea does not work the existing method can be reinstated. Thus a designer must have patience, since there is no assurance of success for the time and effort expended. Creating a completely new design generally requires that many old and well-established methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques and attitudes. A design engineer should constantly search for ways to improve an existing product and must decide what old, proven concepts should be used and what new, untried ideas should be incorporated. New designs generally have “bugs” or unforeseen problems which must be worked out before the superior characteristics of the new designs can be enjoyed. Thus there is a chance for a superior product, but only at higher risk. It should be emphasized that, if a design does not warrant radical new methods, such methods should not be applied merely for the sake of change. During the beginning stages of design, creativity should be allowed to flourish without a great number of constraints. Even though many impractical ideas may arise, it is usually easy to eliminate them in the early stages of design before firm details are required by manufacturing. In this way, innovative ideas are not inhibited. Quite often, more than one design is developed, up to the point where they can be compared against each other. It is entirely possible that the design which ultimately accepted will use ideas existing in one of the rejected designs that did not show as much overall promise. Psychologists frequently talk about trying to fit people to the machines they operate. It is essentially the responsibility of the design engineer to strive to fit machines to people. This is not an easy task, since there is really no average person for which certain operating dimensions and procedures are optimum. Another important point which should be recognized is that a design engineer must be able to communicate ideas to other people if they are to be incorporated. Initially the designer must communicate a preliminary design to get management approval. This is usually done by verbal discussions in conjunction with drawing layouts and written material. To communicate effectively, the following questions must be answered: (1) Does the design really serve a human need? (2) Will it be competitive with existing products of rival companies? (3) Is it economical to produce? (4) Can it be readily maintained? (5) Will it sell and make a profit? Only time will provide the true answers to the preceding questions, but the product should be designed, manufactured and marketed only with initial affirmative answers. The design engineer also must communicate the finalized design to manufacturing through the use of detail and assembly drawings. Quite often, a problem well occur during the manufacturing cycle. It may be that a change is required in the dimensioning or tolerancing of a part so that it can be more readily produced. This falls in the category of engineering changes which must be approved by the design engineer so that the product function will not be adversely affected. In other cases, a deficiency in the design may appear during assembly or testing just prior to shipping. These realities simply bear out the fact that design is a living process. There is always a better way to do it and the designer should constantly strive towards finding that better way. Machining Turning The engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable 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 today's 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 and accuracy, are now at the designer's fingertips with production speeds 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 experimental part that has been produced on the engine lathe by a skilled operator. In redesigning an experimental part for production, economical tolerances should be used. Turret Lathes Production machining equipment must be evaluated now, more than ever before, in terms of ability to repeat accurately and rapidly. Applying this criterion for establishing the production qualification of a specific method, the turret lathe merits a high rating. In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the optimum tolerances possible on the turret lathe, the designer should strive for a minimum of operations. Automatic Screw Machines Generally, automatic screw machines fall into several categories; single-spindle automatics, multiple-spindle automatics and automatic chucking machines. Originally designed for rapid, automatic production of screws and similar threaded parts, the automatic screw machine has long since exceeded the confines of this narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities play an important part in the economy of the parts machined on the automatic to set up on the turret lathe than on the automatic screw machine. Quantities less than 1000 parts may be more economical to set up on the turret lathe than on the automatic screw machine. The cost of the parts machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantities. Automatic Tracer Lathes Since surface roughness depends greatly upon material turned, tooling ,and fees and speeds employed, minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances. Is some case, tolerances of ±0.05mm are held in continuous production using but one cut. Groove width can be held to ±0.125mm on some parts. Bores and single-point finishes can be held to ±0.0125mm. On high-production runs where maximum output is desirable, a minimum tolerance of ±0.125mm is economical on both diameter and length of turn. Milling With the exceptions of turning and drilling, milling is undoubtedly the most widely used method of removing metal. Well suited and readily adapted to the economical production of any quantity of parts, the almost unlimited versatility of the milling process merits the attention and consideration of designers seriously concerned with the manufacture of their product. As in any other process, parts that have to be milled should be designed with economical tolerances that can be achieved in production milling. If the part is designed with tolerances finer than necessary, additional operations will hav