【正文】 denly closed. Excitation forces caused, say by changes in flow of fluids or outofbalance rotating or reciprocating parts, can often be reduced by attention to design and manufacturing details. Atypical machine has many moving parts, each of which is a potential source of vibration or shockexcitation. Designers face the problem of promising between an acceptable amount of vibration and noise, and costs involved in reducing excitation. The mechanical vibrations dealt with are either excited by steady harmonic forces ( i. e. obeying sine and cosine laws in cases of forced vibrations ) or, after an initial disturbance, by no external force apart from gravitational force called weight ( i. e. in cases of natural or free vibrations). Harmonic vibrations are said to be “simple” if there is only one frequency as represented diagrammatically by a sine or cosine wave of displacement against time. Vibration of a body or material is periodic change in position or displacement from a static equilibrium position. Associated with vibration are the interrelated physical quantities of acceleration, velocity and displacemente. g. an unbalanced force causes acceleration (a = F/m ) in a system which, by resisting, induces vibration as a response. We shall see that vibratory or oscillatory motion may be classified broadly as (a) transient。 2. it provedes relative motion between the workpiece and the cutting tools。液體中的振動總是縱向的，而且由于液體的可壓縮性低，這種振動還會產(chǎn)生很大的力。與振動有關(guān)的物理量是相互關(guān)聯(lián)的加速度，速度和位移。能量的消耗有多種方式，磨擦和隨后將所產(chǎn)生的熱傳到周圍，聲波和噪聲，以及通過機架與基礎的應力波等到。每個單位時間內(nèi)的循環(huán)數(shù)目被稱為頻率。這個激勵或干擾通常是時間的函數(shù)。但是，電學上，收音機和電視機的接收器則被設計成在共振頻率時工作。一種能夠提供黏性阻尼的裝置被稱為“ 阻尼器”。機器表面的幾何形狀取決于刀具的形狀 以及加工操作過程中刀具的路徑。它們可以通過徑向車削或端面車削來完成，其中刀具尖端沿垂直于旋轉(zhuǎn)軸的方向運動。在銑削作業(yè)中，有許多切削刃的旋轉(zhuǎn)銑刀與工件相接合，這種工件相對銑刀運動緩慢。因此，僅有 4 種使用專用可控幾何形狀的刀具的基本機床： ?？梢酝ㄟ^把它們與留聲機的唱針和唱片相比較給出其定義。有時，在精加工工序前進行 半精加工作業(yè)以便在工件上留下少的、預定期和均勻量的原材料供精加工去除。一個車床夾頭夾在工件上；然后由安裝在主軸前端的撥盤一起帶動。這些卡盤是自動偏心夾緊卡盤不能起到普通三爪或四爪卡盤同樣的作用。 型心孔和鉆的孔有時相對于車床的旋轉(zhuǎn)是偏心的。大的肩部使用前導裝置定位的鏜孔工具進行刮削，使用橫向滑板進給刀具。這允許在孔的“后側(cè)”進行鏜削切削，在車床前面，從操作者的位置易于看到孔。這臺車床有一個偏心夾型的主軸前端，允許在任意一方向旋轉(zhuǎn)時進行切削。內(nèi)槽是用與外部開槽工具相擬的工具切削?？椎闹睆娇梢杂脙?nèi)卡尺和外千分卡尺測量。由頂尖獲得的對正不能維持而且爪的壓力可能損壞頂尖孔、車床頂尖甚至車床主軸。如果仔細地將工件精確固定在卡盤上，用這種方法將可以獲得精密的結(jié)果。粗加工工序的目的是盡可能迅速且高效地去除大量的材料，在工件上只留下少量的材料給精加工工序。 切割深度、進給和切削速率是在任何金屬切削作業(yè)中必須都建立的機器設置。其它所有金屬切削工藝都是這 5 種基本工藝的變形。鉆削使用兩刃刀具，孔深可達鉆頭直徑的 5～ 10 倍。短的錐面或柱面也可以仿形切削?；旧现v，在金屬切削中一個磨尖的楔形工具以緊湊螺紋形的切屑形式從有韌性工件表面去除一條很窄的金屬。 能量耗散以某種方式與系統(tǒng)的部件或元件之間的相對運動有關(guān)，它是由于某種類型的磨擦引起的。當外力的頻率與系統(tǒng)的固有頻率相同或相近時就會產(chǎn)生共振。也就是說，自由振動是在彈性系統(tǒng)固有彈性恢復力的作用下產(chǎn)生的，而固有頻率則是系統(tǒng)的一個特性。 穩(wěn)態(tài)機械振動是系統(tǒng)在一定時間范圍內(nèi)的重復運動，該時間范圍 被稱為周期。 穩(wěn)態(tài)振動 通常和機器的連續(xù)運轉(zhuǎn)在關(guān)，而且盡管這種振動是周期性的，但不一定是 諧振或正弦振動。如果僅用一個頻率的正弦或余弦波圖形就可表示位移與時間的關(guān)系，諧振就被認為是“簡單的”。 moreover, large lathe dogs that are adequate to transmit the power not generally available, although they can be maed as a special. Faceplate jaws are like chuck jaws except that thet are mounted on a faceplate, which has less overhang from the spindle bearings than a large chuck would have. Boring The boring operation is generally performed in two steps。 hack sawong and broaching are a form of planing and honing。 (b) continuing or steadystate。 3. it provides a range of 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 removal 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 metalcutting operation. They all affect the forces, the power, and the rate of metal removal. They can be defined by paring them to the needle and record of a phonograph. The cutting speed 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 the needle radially inward per revolution, or is the difference in position between two adjacent grooves. Turning on Lathe Centers The basic operations performed on an engine lathe are illustrated in Fig. Those operations performed on extemal surfaces with a single point cutting tool are called turning. Except for drilling, reaming, and tapping, the operations on intermal surfaces are also performed by a single point cutting tool. All machining operations, including turning and boring, can be classified as roughing, finishing, or semifinishing. The objective of a roughing ooperation is to remove the bulk of the material sa repidly and as efficiently as possible, while leaving a small amount of material on the workpiece for the finishing operation. Finishing operations are performed to btain the final size, shape, and surface finish on the work