【正文】 original NC systems were vastly different from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development. A major problem was the fragility of the punched paper tape medium. It was mon for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was produced on a machine tool, the paper tape carrying the programmed instructions had to be rerun through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use. This led to the development of a special magic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magic dots. The plastic tape was much stronger than the paper taps, which solved the problem of frequent tearing and breakage. However, it still left two other problems. The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make even the most minor adjustments in a program of instructions, it was necessary to interrupt machining operations and make a new tape .It was also still necessary to run the tape through the reader as many times as there were parts to be produced. Fortunately, puter technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape. The development of a concept known as direct numerical control (DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control .machine tools are tied, via a data transmission link, to a host puter. Programs for operating the machine tools are stored in the host puter and fed to the machine tool as needed via the data transmission linkage. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend on a host puter. When the lost puter goes down, the machine tools also experience downtime. This problem led to the development of puter numerical control. The development of the microprocessor allowed for the development of programmable logic controllers (PLCs) and microputers. These two technologies allowed for the development of puter numerical control (CNC).With CNC, each machine tool has a PLC or a microputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. It also allows programs to be developed offline and downloaded at the individual machine tool. CNC solved the problems associated with downtime of the host puter, but it introduced another known as data management. The same program might be loaded on ten different microputers with no munication among them. This problem is in the process of being solved by local area works that connect microputers for better data management. Cutting Tool Geometry Shape of cutting tools, particularly the angles, and tool material are very important factors. Angles determine greatly not only tool life but finish quality as well. General principles upon which cutting tool angles are based do not depend on the particular tool, Basically, the same considerations hold true whether a lathe tool, a milling cutter, a drill, or even a grinding wheel are being designed. Since, however the lathe tool, depicted in Fig. , might be easiest to visualize, its geometry is discussed. Tool features have been identified by many names. The technical literature is full of confusing terminology. Thus in the attempt to cleat up existing disanized conceptions and nomenclature, this American Society of Mechanical Engineers published ASA Standard B5221950. What follows is based on it. A singlepoint tool is a cutting tool having one face and one continuous cutting edge, Tool angles identified in Fig. are as follows: Tool angle 1, on front view, is the backrank angle. It is the angle between the tool face and a line parallel to the tool base of the shank in a longitudinal plane perpendicular to the tool base. When this angle is downward from front to rear of the cutting edge, the rake is positive。 數(shù)控中，測量系統(tǒng)這一術(shù)語指的是機床的兩種測量系統(tǒng)是絕對測量系統(tǒng)和增量測量系統(tǒng)。增量測量系統(tǒng)有一個移動的坐標系統(tǒng)。這種系統(tǒng)的一個缺點是，如果產(chǎn)生的任何錯誤沒有被發(fā)現(xiàn)與校正，則錯誤會在整個過程中反復存在。點位控制系統(tǒng)常用于需確定孔位的轉(zhuǎn) 床和需進行直線銑銷加工的簡單銑床上。這些機床用于加工兩維或三維空間中各種不同大小的弧行、圓角、圓及斜角。 步進電機伺服機構(gòu)用于不太貴重的數(shù)控設備上。液壓伺服馬達使壓力液體流過齒輪或拄塞，從而使周轉(zhuǎn)動。 使用開環(huán)系統(tǒng) 的數(shù)控機床，沒有反饋信號來確保機床的坐標做是否運動了所需的距離。反饋裝置真實地將工作臺已運動的量與輸入信號進行比較。因為，它們除了完成常規(guī)的車削工作之外 ，還可以完成某些銑削、鉆削工作。在數(shù)控技術(shù)出現(xiàn)之前，所有的機床都是由人工操縱和控制的。 數(shù)字控制意味著采用預先錄制的，存儲的符號指令，控制機床和其他制造系統(tǒng)。數(shù)字控制的機器比人工控制的機器的精度更高、生產(chǎn)的零件的一致性更好、生產(chǎn)的速度更快、而且長期的工藝裝備成本更低。 與許多先進技術(shù)一樣，數(shù)控誕生于麻省理工學院的實驗室中。構(gòu)成臺階的每個線段越短，曲線就越光滑。 APT 語言的研究和發(fā)展是在數(shù)控技術(shù)進一步發(fā)展過程中的一大進步。所有這些共同構(gòu)成了機床數(shù)字控制方面的巨大的進步。在機床上每加工一個零件，都需要將載有編程指令的紙帶放入閱讀機中重新運行一次。 這就導致了一種專門的塑料磁帶的研制。 其中最重要的一個問題是，對輸入帶中的指令進行修改是非常困難的，或者是根本不可能的。幸運的是，計算機技術(shù)的實際應用很快解決了數(shù)控技術(shù)中與穿孔紙帶和塑料帶有關(guān)的問題。當需要時，通過數(shù)據(jù)傳輸線路提供給每臺機床。這個問題促使了計算機數(shù)字控制技術(shù)的產(chǎn)生。這可以使得程序被輸入和存儲在每臺機器內(nèi)部。這個問題正在解決之中，它是通過采用局部區(qū)域網(wǎng)絡將各個微機連接起來，以利于更好地進行數(shù)據(jù)管理。車刀、銑刀、轉(zhuǎn)頭甚至最砂輪的設計，所要考慮的因素基本相同。 單尖刀具是指只有一 個前刀面和一條連續(xù)切削刃的刀具。 角度 2 為側(cè)前角，它是刀具前刀面在垂直于刀具基面的