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徐州工程學(xué)院畢業(yè)設(shè)計(jì)(論文) 附錄 附錄1 Basic Machining Operations and Machine Tools Basic Machining Operations Machine tools have evolved from the early foot-powered lathes of the Egyptians and John Wilkinson’s boring mill. They are designed to provide rigid support for both the workpiece and the cutting tool and can precisely control their relative positions and the velocity of the tool with respect to the workpiece. Basically, in metal cutting, a sharpened wedge-shaped tool removes a rather narrow strip of metal from the surface of a ductile workpiece in the form of a severely deformed chip. The chip is a waste product that is comsiderably shorter than the workpiece from which it came but woth a corresponding increase in thickness of the uncut chip. The geometrical shape of the machine surface depedns on the shape of the tool and its path during the machinig operation. Most machining operations produce parts of differing geometry. If a rough cylindrical workpiece revolves about a central axis and the tool penetrates beneath its surface and travels parallel to the center of rotation, a surface of revolution is producedand the operation is called turning. If a hollow tube is machined on the inside in a similar manner, the operation is called boring. Producing an external conical surface of uniformly varying diameter is called taper turning. If the tool point travels in a path of varying radius,a contoured surface like that of a bowling pin a can be produced; or, if the piece is short enough and the support is sufficiently rigid, a contoured surface could be produced by feeding a shaped tool normal to the axis of rotation. Short tapered or cylindrical surfaces could also be contour formed. Flat or plane surfaces are frequently required. The can be generated by adial turning or facing, in which the tool point moves normal to the axis of rotation. In other cases, it is more convenient to hold the workpiece steady and reciprocate the tool across it in a series of straight-line cuts with a crosswise feed increment before each cutting stroke. This operation is called planing and is carried out on a shaper. For larger pieces it is easier to keep the tool stationary and draw the workpiece under it as in planing. The tool is fed at each reciprocation. Contoured surfaces can be produced by using shaped tools. Multiple-edged tools can also be used. Drilling uses a twin-edged fluted tool for holes with depths up to 5 10times the drill diameter. Whether the dril turns or the workpiece rotates, relative motion between the cutting edge and the workpiece is the important factor. In milling operations a rotary cutter with a number of cutting edges engages the workpiecem which moves slowly with respect to the cutter. Plane or contoured surfaces may be produced, depending on the geometry of the cutter and the type of feed. Horizontal or vertical axes of rotation ma be used, and the feed of the workpiece may be in any of the three coordinate directions. Basic Machine Tools Machine tools are used to produce a part of a specified geometrical shape and precise size by removing metal from a ductile materila in the form of chips. The latter are a waste product and vary from long continuous ribbons of a ductile material such as steel, which are undesirable from a disposal point of view, to easily handled well-broken chips resulting from cast iron. Machine tools perform five basic metal-removal processes: turning, planing, drilling, milling, and frinding. All other metal-removal processes are modifications of these five basic processes. For example, boring is internal turning;reaming,tapping, and counterboring modify drilled holes and are related to drilling; hobbing and gear cutting are fundamentally milling operations; hack sawong and broaching are a form of planing and honing; lapping, superfinishing, polishing, and buffing are avariants of grinding or abrasive removal operations. Therefore, there are only four types of basic machine tools, which use cutting tools of specific controllable feometry: 1.lathes, 2.planers, 3.drilling machines, and 4.milling machines. The frinding process forms chips, but the geometry of the barasive grain is uncontrollable. The amount and rate of material removed by the various machining processes may be large, as in heavy truning operations, or extremely small, as in lapping or superfinishing operations where only the high spots of a surface are removed. A machine tool performs three major functions: 1.it rigidly supports the workpiece or its holder and the cutting tool; 2. it provedes relative motion between the workpiece and the cutting tools; 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 metal-cutting operation. They all affect the forces, the power, and the rate of metal removal. They can be defined by comparing 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 semi-finishing. 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 work-piece for the finishing operation. Finishing operations are performed to btain the final size, shape, and surface finish on the workpiece. Sometimes a semi-finishing operation will precede the finishing operation to leave a small predetermined and uniform amount of stoxd on the work-piece to be removed by the finishing operation. Generally, longer workpieces are turned while supported on one or two lathe centers. Cone shaped holes, called center holes, which fit the lathe centers are drilled in the ends of the workpiece-usually along the axis of the cylindrical part. The end of the workpiece adjacent to the tailstock is always supported by a tailstock center, while the end near the headstock may be supported by a headstock cener or held in a chuck. The headstock end of the workpiece may be held in a four-jar chuck, or in a collet type chuck. This method holds the workpiece firmly and transfers the power to the workpiece smoothly; the additional support to the workpiece priovided by the chuck lessens the tendency for chatter to occur when cutting. Precise results can be obtained with this method if care is taken to hold the workpiece accurately in the chuck. Very precise results can be obtained by supporting the workpiece between two centers. A lathe dog is clamped to the workpiece; together they are driven by a driver p;ate mounted on the spindle nose. One end of the workpiece is machined; then the workpiece can be turned around in the lathe to machine the other end. The center holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to carry the weight of the workpiece and to resist the xutting forces. After the workpiece has been removed from the lathe for any reason, the center holes will accurately align the workpiece back in the lathe or in another lathe,or in a cylindrical grinding machine. The workpiece must never be held at the headstock end by both a chuck and a lathe center. While at first thought this seems like a quick method of aligning the workpiece in the chuck, this must not be done because it is not possible to press evenly with the jaws against the workpiece while it is also supported by the center. The alignment provided by the center will not be maintained and the pressure of the jaws may damage the center hole, the lathe center,and prehaps even the lathe spindle. Compensatng or floating jaw chucks used almost exclusively on high production work provice an exception to the statements made above. These chucks are really work drivers and cannot be used for the same purpose as ordinary three or four=jaw chucks. While very large diameter workpieces are sometimes mounted on two centers, they are preferably held at the headstock end by faceplate jaes to obtain the smooth power transmission; 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; namely, rough boring and finish boring. The objective of the rough-boring operation is to remove the excess metal rapidly and efficiently, and the objective of the finish-boring operation is to obtain the desired size, surface finish, and location of the hole. The size of the hole is obtained by using the trial-cut procedure. The diameter of the hole can be measured with inside calipers and outside micrometer calipers. Basic Measuring Insteruments, or inside micrometer calipers can be used to measure the diameter directly. Cored holes and drilled holes are sometimes eccentric wwith respect to the rotation of the lathe. When the boring tool enters the work, the boring bar will take a deeper cut on one side of the hole than on the other, and will deflect more when taking this deeper cut,with the result that the bored hole will not be concentric with the rotation of the work. This effect is corrected by taking several cuts through the hole using a shallow depth of cut. Each succeeding shallow cut causes the resulting hole to be more concentric than it was with the previous cut. Before the final, finish cut is taken, the hole should be concentric with the rotation of the work in order to make certain that the finished hole will be accurately located. Shoulders, grooves, contours, tapers, and threads are bored inside of holes. Internal grooves are cut using a tool that is similar to an external grooving tool. The procedure for boring internal shoulders is very similar to the procedure for turning shoulders.large shoulders are faced with the boring tool positioned with the nose leading, and using the cross slide to feed the tool. Internal contours can be machined using a tracing attachment on a lathe. The tracing attachment is mounted on the cross slide and the stylus follows the outline of the master profile plate. This causes the cutting tool to move in a path corresponding to the profile of the master profile plate. Thus, the profile on the master profile plate is reproduced inside the bore. The master profile plate is accurately mounted on a special slide which can be precisely adjusted in two dirctions, in two directionsm, in order to align the cutting tool in the correct relationship to the work. This lathe has a cam-lick type of spindle nose which permits it to take a cut when rotating in either direction. Normal turning cuts are taken with the spindle rotating counterclockwise. Thie boring cut is taken with the spindle revolving in a clockwise direction, or “backwards”. This permits the boring cut to be taken on the “back side” of the bore which is easier to see from the operator’sposition in front of the lathe. This should not be done on lathes having a threaded spindle nose because the cutting force will tend to unscrew the chuck. 附錄2 基本的加工工序和機(jī)床 基本的加工工序 機(jī)床是從早期的埃及人的腳踏動(dòng)力車床和約翰·威爾金森的鏜床發(fā)展而來。它們用于為工件和刀具兩者提供剛性支承并且可以精確控制它們的相對(duì)位置和相對(duì)速度?；旧现v，在金屬切削中一個(gè)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。切屑是廢棄的產(chǎn)品，與其工件相比相當(dāng)短但是比未切屑的部分有相對(duì)的增加。機(jī)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。 大多數(shù)加工工序生產(chǎn)出不同幾何形狀的部件。如果一個(gè)粗糙的柱形工件繞中心軸旋轉(zhuǎn)而且刀具穿破工件表面并沿與旋轉(zhuǎn)中心平行的方向前進(jìn)，就會(huì)產(chǎn)生一個(gè)旋轉(zhuǎn)面，這道工序叫車削。如果以類似的方式加工一根空心管的內(nèi)部，則這道工序就叫鏜削。制造一個(gè)直徑均勻變化的錐形外表面叫做錐體車削。如果刀具尖端以一條半徑可變的路徑前進(jìn)，就可以制造出像保齡球桿那種仿形表面；如果工件足夠短而且支承具有足夠的剛性，仿形表面可以通過進(jìn)給一個(gè)垂直于旋轉(zhuǎn)軸的仿形工具來制造。短的錐面或柱面也可以仿形切削。 常常需要的是平坦的或平的表面。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(yùn)動(dòng)。在其他情況下，更方便的是固定工件不動(dòng)，以一系列直線式切削的方式往復(fù)運(yùn)動(dòng)刀具橫過工件，在每次切削行程前具有一定橫向進(jìn)給量。這種龍門刨削，和牛頭刨削是在刨床上進(jìn)行的。大一些的工作很容易保持刀具固定不動(dòng)，而像龍門刨削那樣在其下面拉動(dòng)工件，在每次往復(fù)時(shí)進(jìn)給刀具。仿形面可以通過使用仿形刀具來制造。 也可以使用多刃刀具。鉆削使用兩刃刀具，孔深可達(dá)鉆頭直徑的5～10倍。不管是鉆頭轉(zhuǎn)動(dòng)還是工件旋轉(zhuǎn)，切削刃與工件之間的相對(duì)運(yùn)動(dòng)是一個(gè)重要因數(shù)。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(duì)銑刀運(yùn)動(dòng)緩慢。根據(jù)銑刀的幾何形狀和進(jìn)給的方式，可以加工出平面和仿形面?？梢允褂盟交虼怪毙D(zhuǎn)軸，工件可以沿三個(gè)坐標(biāo)方向中的任意一個(gè)進(jìn)給。 基本的機(jī)床 機(jī)床用于以切屑的形式從韌性材料上去除金屬來加工特殊幾何形狀和精密尺寸的部件。切屑是廢品，其變化形狀從像鋼這樣的韌性材料的長(zhǎng)的連續(xù)帶狀屑到鑄鐵形成的易于處理、徹底斷掉的切屑，從處理的觀點(diǎn)來講，不想要長(zhǎng)的連續(xù)帶狀屑。機(jī)床完成5種基本的金屬切削工藝：車削、刨削、鉆削、銑削和磨削。其它所有金屬切削工藝都是這5種基本工藝的變形。例如：鏜削是內(nèi)部的車削；鉸削、錐體車削和平底锪孔則修改鉆孔，與鉆削有關(guān)；滾齒與切齒是基本銑削作業(yè)；弓鋸削和拉削是刨削和珩磨的一種形式；而研磨、超精加工、拋光和磨光則是磨削和研磨切屑作業(yè)的各種變化形式。因此，僅有4種使用專用可控幾何形狀的刀具的基本機(jī)床：1.車床2.刨床3.鉆床4.銑床。磨削工藝形成碎屑，但是磨粒的幾何形狀不可控制。 不同的加工工藝切屑的材料的量和速度可能大，如大型車削作業(yè)；或者極小，如研磨或超精加工作業(yè)，只有表面高出的點(diǎn)被去除。 機(jī)床完成3種主要功能：1.剛性支承工件或工件夾具以及切削刀具；2.提供工件與切削刀具之間的相對(duì)運(yùn)動(dòng)；3.提供了一定范圍的速度和進(jìn)給，通常每種情況有4～32種選擇。 加工中的速度和進(jìn)給 切割速度、進(jìn)給和深度是經(jīng)濟(jì)加工的3個(gè)主要變量，其它變量還有工件和工具的材料、冷卻劑以及切削刀具的幾何形狀。金屬切削的速率和加工所需的功率就取決于這些變量。 切割深度、進(jìn)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(jī)器設(shè)置。它們都影響切削力、功率和對(duì)金屬切削的速率?？梢酝ㄟ^把它們與留聲機(jī)的唱針和唱片相比較給出其定義。切削速度由任意時(shí)刻唱片表面相對(duì)于拾音器支臂內(nèi)部的速度來表示；進(jìn)給由唱針每圈徑向向內(nèi)的前進(jìn)量或者由兩個(gè)相鄰槽的位置差來表示。切削的深度是唱針進(jìn)入唱片的量或者是槽的深度。 切削 在普通車床上完成的基本車削工序，那些在外表面上用單刃刀具完成的工序叫車削。除鉆削、鉸削和錐體車削外，在內(nèi)表面的作業(yè)也由單刃刀具完成。 包括車削和鏜削在內(nèi)的所有加工工序都可以分為粗加工、精加工和半精加工。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。精加工工序用以獲得工件最終的大小、形狀和表面光潔度。有時(shí)，在精加工工序前進(jìn)行半精加工作業(yè)以便在工件上留下少的、預(yù)定期和均勻量的原材料供精加工去除。 通常，較長(zhǎng)的工件是在一個(gè)或兩個(gè)車床頂尖的支承下進(jìn)行車削的。用于安裝車床頂尖的錐形孔叫作頂尖孔，它是在工件的端部鉆出的—通常沿著柱形部件的軸心。與尾架鄰近的工件端部總是由尾架頂尖支承，而挨著主軸箱的一端則由主軸箱頂尖支承或裝在卡盤內(nèi)。工件的主軸箱一端可以裝在一個(gè)四爪卡盤內(nèi)。這種方法牢固地夾持工件并且把功率平穩(wěn)地傳送到工件；由卡盤提供的額外支承減少了車削作業(yè)時(shí)發(fā)生震動(dòng)的傾向。如果仔細(xì)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。 通過將工件支承在兩個(gè)頂尖之間可以獲得非常精密的結(jié)果。一個(gè)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(dòng)。先加工工件的一端，然后可以在車床上將工件轉(zhuǎn)過來加工另一端。工件上的頂尖孔是用作精確定位面以及承受工件重量和抵抗車削力的軸承面。在工件由于任何原因被從車床上拆下后，頂尖孔可以精確地將工件裝回車床或另一臺(tái)車床，或都裝在一臺(tái)外圓磨床上。工件永遠(yuǎn)也不要同時(shí)通過卡盤和車床頂尖安裝在主軸箱端。雖然乍一想這似乎是一種在卡盤中對(duì)正工件的快捷辦法，但是一定不能這么做，因?yàn)楫?dāng)工件同時(shí)同頂尖支承時(shí)不可能將工件均勻地壓在爪上。由頂尖獲得的對(duì)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。幾乎被獨(dú)自用在大量生產(chǎn)工件上的補(bǔ)償或浮動(dòng)爪式卡盤是上述的一個(gè)例外。這些卡盤是自動(dòng)偏心夾緊卡盤不能起到普通三爪或四爪卡盤同樣的作用。 直徑非常大的工件雖然有時(shí)安裝在兩個(gè)頂尖上，但是最好用花盤爪把它們固定在主軸箱端以獲得流暢的動(dòng)力傳輸；此外，可以把它們制造成專用部件，但是一般沒有提供足夠大的車床夾頭來傳輸動(dòng)力。除了是安裝在花盤上以外，花盤爪像卡盤爪，其主軸軸承上的外伸要比大卡盤上的也要少一些。 鏜削 鏜削工序一般分兩步完成，即粗鏜和精鏜。粗鏜工序的目的是快速，高效地去除多余的金屬；而精鏜工序的目的是獲得所需的尺寸、表面光潔度和孔的位置?？椎某叽缤ㄟ^使用試切割程序而獲得?？椎闹睆娇梢杂脙?nèi)卡尺和外千分卡尺測(cè)量。測(cè)量?jī)x表或內(nèi)千分卡尺可用于直接測(cè)量直徑。 型心孔和鉆的孔有時(shí)相對(duì)于車床的旋轉(zhuǎn)是偏心的。當(dāng)鏜孔工具進(jìn)入工件時(shí)，鏜桿在孔的一邊的切口比另一邊深，當(dāng)采用這一深切口時(shí)就會(huì)更偏斜了，結(jié)果鏜的孔不與工件旋轉(zhuǎn)同心。這一影響通過利用淺切口在整個(gè)孔加工中進(jìn)行幾次線切口來糾正。因?yàn)槊總€(gè)淺切口使形成的孔比使用先前切口形成的孔更加同心。在完工前，進(jìn)行精加工，孔應(yīng)該與工件的旋轉(zhuǎn)同心以確保完工孔會(huì)精確定位。 肩、溝槽、輪廓、錐度和螺紋也應(yīng)該在孔內(nèi)鏜出。內(nèi)槽是用與外部開槽工具相擬的工具切削。鏜削內(nèi)槽的步驟非常類似于肩部的步驟。大的肩部使用前導(dǎo)裝置定位的鏜孔工具進(jìn)行刮削，使用橫向滑板進(jìn)給刀具。內(nèi)部輪廓使用車床上的描摹附件加工。仿形板附件安裝在橫向滑板上，靠模指跟隨標(biāo)準(zhǔn)剖面樣板的輪廓線運(yùn)動(dòng)。這使刀具對(duì)應(yīng)于標(biāo)準(zhǔn)剖面樣板的輪廓線的路徑進(jìn)行移動(dòng)。這樣標(biāo)準(zhǔn)剖面樣板的輪廓就在孔內(nèi)得到復(fù)制。標(biāo)準(zhǔn)剖面樣板精確安裝在一個(gè)專用的滑板上，滑板可以在兩個(gè)方向上進(jìn)行精確調(diào)整以使刀具與工件以正確的關(guān)系對(duì)正。這臺(tái)車床有一個(gè)偏心夾型的主軸前端，允許在任意一方向旋轉(zhuǎn)時(shí)進(jìn)行切削。正常的車削世削是在主軸逆時(shí)針轉(zhuǎn)動(dòng)時(shí)進(jìn)行的；鏜削切削是在主軸順時(shí)針方向或“向后”轉(zhuǎn)動(dòng)時(shí)進(jìn)行的。這允許在孔的“后側(cè)”進(jìn)行鏜削切削，在車床前面，從操作者的位置易于看到 孔。在具有螺紋主軸前端的車床上不應(yīng)這么做，因?yàn)榍邢髁?huì)旋松卡盤。 8