【正文】 pacities and limitations of the CNC machine tools that a program is to be made for. Machine specifications such as horsepower, maximum spindle speeds, workpiece weight and size limitations, and tool changer capacity are just some of the considerations that affect programming. Another area of major importance to the programmer is the knowledge of machining processes. An example would be the selection of the surface finish 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, tool types, and application remendations. 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 the tool that was on the cutting edge of technology just two years ago is now obsolete. Information on new tools can e from catalogs or tool manufacturers39。 it is capable of uninterrupted machining error free, hour after hour. A machine tool is productive only while it is making chips. Since the chipmaking process is controlled by the proper feeds and speeds, time savings 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 working envelope of the machine tool. Complex contoured shapes were extremely difficult to product prior to CNC machining .CNC has made the machining of these shapes economically feasible. Design changes on a part are relatively easy to make by changing the program that directs the machine tool. A CNC machine produces parts with high dimensional accuracy and close tolerances without taking extra time or special precautions, CNC machines generally need less plex workholding fixtures, which saves time by getting the parts machined sooner. Once a program is ready and production parts, each part will take exactly 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 elimi nation of large inventories。 and controlling 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 numbers and capability of puters ,changes in machine controls are rapidly and constantly taking place. The exciting part of this evolution in machine controls is that programming beeseasier with each new advanced in this technology. Advantages of Numerical Control 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 big gain es from the puter controlling the machining axes movements. CNCcontrolled machine tools can be as simple as a 2axis drilling machining center (Figure O1). With a dual spindle machining center, the low RPM, high horsepower spindle gives high metal removal rates. The high RPM spindle allows the efficient use of high cutting speed tools such as diamonds and small diameter cutters (Figure O2). The cutting tools that remove materials are standard tools such as milling cutters, drills, boring tools, or lathe tools depending on the type of machine used. Cutting speeds and feeds need to be correct as in any other machining operation. The greatest advantage in CNC machining es from the unerring and rapid positioning movements possible. A CNC machine does dot stop at the end of a cut to plan its next move。 英文原文 ADVANCED MACHINING PROCESSES As the hardware of an advanced technology bees more plex, new and visionary approaches to the processing of materials into useful products e into mon use. This has been the trend in machining processes in recent years.. Advanced methods of machine control as well as pletely different methods of shaping materials have permitted the mechanical designer to proceed in directions that would have been totally impossible only a few years ago. Parallel development in other technologies such as electronics and puters have made available to the machine tool designer methods and processes that can permit a machine tool to far exceed the capabilities of the most experienced machinist. In this section we will look at CNC machining using chipmaking cutting tools. CNC controllers are used to drive and control a great variety of machines and mechanisms, Some examples would be routers in wood working。 由資金耗費(fèi)項(xiàng)目上的考慮，就 CNC 機(jī)床刀具而言，為了明確新計(jì)劃是否必要或證明在短期內(nèi)實(shí)現(xiàn)資金回收，一個公司必須進(jìn)行可行性分析。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。 計(jì)算機(jī)的體積減小，從而它的生產(chǎn)費(fèi)用也極大的降低。當(dāng)兩個相關(guān)的因素存在后，在一個生產(chǎn)環(huán)境中，讓 CNC 實(shí)現(xiàn)靈活且 輕松的編程的夢想變成為現(xiàn)實(shí)。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。事實(shí)上它的利用水平很低，機(jī)床刀具昂貴會導(dǎo)致加工頻繁時的“頸瓶”現(xiàn)象，于是進(jìn)一步限制了整個操作。這是早期情形，是值得欽佩的。它可被認(rèn)為是系列但作用刀具通過計(jì)算機(jī)上控制的運(yùn)輸系統(tǒng)連接起來的復(fù)合機(jī)床。用這種方式，自動換刀特性使這加工中心高效的加工多種部件，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。 加工中心 的概念是早期工作的結(jié)果，它允許機(jī)床在一個安裝上對工件進(jìn)行多種加工，而不需要把工件轉(zhuǎn)移到另外的刀具下。 早期的 NC 機(jī)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(jī)床刀具。所以，趨勢下一點(diǎn)的方向必須是相同的。作為一個鉆操作的機(jī)床刀具的點(diǎn)至點(diǎn)移動例子，典型的運(yùn)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(yùn)動可能過每軸以連續(xù)且獨(dú)立的方式獲得。在航空所需要的復(fù)雜的控制系統(tǒng)發(fā)展的同時，點(diǎn)與點(diǎn)控制器發(fā)展起來，更廣泛的用于加工當(dāng)中。幾年后，在 USA 與歐洲開始了更深遠(yuǎn)的研究。 與美國機(jī)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(jī)床。辛辛那提機(jī)床刀具公司把他們的一個 28 英寸的“ Hydro— Tel”軍用機(jī)床改裝為三軸自動機(jī)床，改變了它們的外部輪廓。麻省理工大學(xué)開始進(jìn)入研究，而 Parsons 公司使之發(fā)展起來。通常認(rèn)為，關(guān)于數(shù)控的研究是 1949 年美國政府的授權(quán)。第二次世界大戰(zhàn)后的一個主要問題是，商業(yè)和軍隊(duì)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。 數(shù)控機(jī)床刀具早期的發(fā)展 今天在機(jī)器化大生產(chǎn)領(lǐng)域中千形百態(tài)，結(jié)構(gòu)復(fù)雜的刀具，起源于一些主要的工業(yè)國，開始很簡陋。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。啟動機(jī)床之前，確定工作裝置和工件是否安全的固定了 。機(jī)床表面不應(yīng)該被用作工作臺。一些 CAD 和 CAM 程序，如果在相同的計(jì)算機(jī)上下載，可同時使用一些按鍵、圖紙和程序，使其能相互匹配。另外，使用SHOWPATH 功能可以顯示每個刀具的路徑和他們的順序。程序員仍需準(zhǔn)備一個工藝卡，含有所用需要的刀具