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長春工業(yè)大學本科畢業(yè)設計論文
Shapers, Drilling and Milling Machines
A shapers utilizes a single-point tool on a tool holder mounted on the end of the ram. Cutting is generally done on the forward stroke. The tool is lifted slightly by the clapper box to prevent excessive drag across the work, which is fed under the tool during the return stroke in preparation for the next cut. The column houses the operating mechanisms of the shaper and also serves as a mounting unit for the work-supporting table. The table can be moved in two directions mutually perpendicular to the ram. The tool slide is used to control the depth of cut and is manually fed. It can be rotated through 90 deg, on either side of its normal vertical position, which allows feeding the tool at an angle to the surface of the table.
Two types of driving mechanisms for shapers are a modified Whitworth quick-return mechanism and a hydraulic drive. For the Whitworth mechanism, the motor drives the bull gear, which drives a crank arm with an adjustable crank pin to control the length of stroke. As the bull gear rotates, the rocker arm is forced to reciprocate, imparting this motion to the shaper ram.
The motor on a hydraulic shaper is used only to drive the hydraulic pump. The remainder of the shaper motions are controlled by the direction of the flow of the hydraulic oil. The cutting stroke of the mechanically driven shaper uses 220 deg. Of rotation of the bull gear, while the return stroke uses 140 deg. This gives a cutting stroke to return stroke ratio of 1.6 to 1. The velocity diagram for a hydraulic shaper shows that for most of the tool during cutting stroke is never constant, while the velocity diagram for a hydraulic shaper shows that for most of the cutting stroke the cutting speed is constant. The hydraulic shaper has an added advantage of infinitely variable cutting speeds. The principal disadvantage of this type of machine is the lack of a definite limit at the end of the ram stroke, which may allow a few thousandths of an inch variation in stroke length.
A duplicating device that makes possible the reproduction of contours from a sheet-metal template is available. The sheet metal template is used in conjunction with hydraulic control.
Upright drilling machines or drill presses are available in a variety of sizes and types, and are equipped with a sufficient range of apindle speeds and automatic feeds to fit the neds of most industries. Speed ranges on a typical machine are from 76 to 2025 rpm., with drill feed from 0.002 to 0.020 in.per revolution of the spindle.
Radial drilling machines are used to drill workpieces that are too large or cumbersome to conveniently move. The spindle with the speed and feed changing mechanism is mounted on the radial arm; by combining the movement of the radial arm around column and the movement of the spindle assembly along the arm, it is possible to align the spindle and the drill to any position within reach of the machine. For work that is too large to conveniently support on the base, the spindle assembly can be swung out over the floor and the workpiece set on the beside the machine.
Plain radial drilling machines provide only for vertical movement of the spindle; universal machines allow the spindle to swivel about an axis normal to the radial arm and the radial arm to rotate about a horizontal axis, thus permitting drilling at any angle.
A multispindle drilling machine has one or more heads that drive the spindles through universal joints and telescoping splined shafts. All spindles are usually driven by the same motor and fed simultaneously to drill the desired number of holes. In most machines each spindle is held in an adjustable plate so that it can be moved relative to the others. The area covered by adjacent spindles overlap so that the machine can be set to drill holes at any location within its range.
The milling operation involves metal removal with a rotating cutter. It includes removal of metal from the surface of a workspiece, enlarging holes, and form cutting, such as threads and gear teeth.
Within an knee and column type of milling machine the column is the main supporting member for the other components, and includes the base containing the drive motor, the spindle, and the cutters. The cutter is mounted on an arbor held in the spindle, and supported on its outer extremity by a bearing in the overarm. The knee is held on the column in dovetail slots, the saddle is fastened to the knee in dovetail slots, and the table is attached to the saddle. Thus, the build-up the knee and column machine provides three motions relative to the cutter. A four motion may be provided by swiveling the table around a vertical axis provided on the saddle.
Fixed-bed milling machines are designed to provide more rigidity than the knee and column type. The table is mounted directly on the machine base, which provides the rigidity necessary for absorbing heavy cutting load, and allows only longitudinal motion to the table. Vertical motion is obtained by moving the entire cutting head.
Tracer milling is characterized by coordinated or synchronized movements of either the paths of the cutter and tracing elements, or the paths of the workpiece and model. In a typical tracer mill the tracing finger follow the shape of the master pattern, and the cutter heads duplicate the tracer motion.
The following are general design considerations for milling:
1. Wherever possible, the part should be designed so that a maximum number of surfaces can be milled from one setting.
2. Design for the use of multiple cutters to mill several surfaces simultaneously.
3. The largest flat surface will be milled first, so that all dimensions are best referred to such surface.
4. Square inside corners are not possible, since the cutter rotates.
Grinding Machines and Special Metal-removal Process
Random point-cutting tools include abrasives in the shape of a wheel, bonded to a belt, a stick, or simply suspended in liquid. The grinding process is of extreme importance in production work for several reasons.
1.It is most common method for cutting hardened tool steel or other heat-treated steel. Parts are first machined in the un-heat-treated condition, and then ground to the desired dimensions and surface finish.
2.It can provide surface finish to 0.5μm without extreme cost.
3.The grinding operation can assure accurate dimensions in a relatively short time, since machines are built to provide motions in increments of ten-thousandths of an inch, instead of thousandths as is common in other machines.
4.Extremely small and thin parts can be finished by this method, since light pressure is used and the tendency for the part to deflect away from the cutter is minimized.
On a cylindrical grinding machine the grinding wheel rotates between 5500 and 6500 rpm., while the work rotates between 60 and 125 rpm... The depth of cut is controlled by moving the wheel head, which includes both the wheel and its drive motor. Coolants are provided to reduce heat distortion and to remove chips and abrasive dust.
Material removal from ductile materials can be accomplished by using a tool which is harder than the workpiece. However during Word War Ⅱ the widespread use of materials which were as hard or harder than cutting tools created a demand for new material-removal methods. Since then a number of processes have been developed which, although relatively slow and costly, can effectively remove excess material in a precise and repeatable fashion. There are two types of processes. The first type is based on electrical phenomena and is used primarily for hard materials; the second depends upon chemical dissolution.
Chemical milling is controlled etching process using strong alkaline or acid etchants. Aluminum, titanium, magnesium, and steel are the principal metals processed by this method. The area to remain untouched by the etchant are masked with a protective coating. For example, the entire part may be dipped in the masking material and the mask removed from those areas to be etched, or a chemically resistant prescribed time, after which the part is rinsed in cold water, the masking removed, the part inspected, and thoroughly cleaned.
There are certain disadvantages to consider. Metal will erode equally in all directions, so that walls of the etched section will have a radius equal to the depth of etch. A second disadvantage is that a better finish is obtained on surfaces parallel to the direction of rolling of a sheet than on surface perpendicular to the direction of rolling. This can be compared to the surface obtained when working wood parallel to, or across the grain. A third disadvantage, not unique with this process, is the warpage that will occur in thin, previously stressed sections etched on just one side.
Chemical milling, however, has many advantages over conventional metal-removal methods. There is no warpage of heavy sections such as forgings or extrusions when the etchant is applied simultaneously to all sides for reduction of section thickness. In conventional milling only one side can be worked at a time, and frequent turning of a part is necessary to prevent warpage. Chemical milling can be applied to parts of irregular shape where conventional milling may be very difficult. Light-weight construction can be obtained with chemical milling by the elimination of welding, riveting, and stiffeners; parts can be contoured to distribute the load in the most suitable manner. As an example of the potential savings of this process, as compared to machine milling, one company reports that the cost of removing aluminum by chem.-milling is $0.27 per pound as compared to $1.00 per pound by conventional milling. The rate of metal removal for chem.-milling is 0.001in. for aluminum.
Electric-discharge machining is a process in which an electrical potential is impressed between the workpiece and the tool, and the current, emanating from a point source on the workpoiece, flows to the tool in the form of a spark. The forces that accomplish the metal removal are within the workpiece proper and, as a result, it is not necessary to construct the unit to withstand the heavy pressures and loads prevalent with conventional machining methods.
The frequency of the electrical discharge ranges from 20,00 cps (cycles per second) for rough machining, to 50,000 cps for finishing such items as hardened tools and dies. The current may vary from 50 amp, during rough machining, to as low as 0.5 amp, during finishing. The process is currently applied to the machining of single-point tools, form tools, milling cutters, broaches, and die cavities. It is also applicable to the removal of broken drills, taps, and studs without damaging the workpiece in which the broken tool is imbedded. Other uses are the machining of oil holes in a hardened part, and the machining of small safety-wire holes in the heads of special alloy bolts, such as titanium.
The ultrasonic machining process is applied to both conducting and non-conducting material, and relies entirely upon abrasive action for metal removal. The workpiece is submerged in slurry of finely fivided abrasive particles in a vehicle such as water. The tool is coupled to an oscillator and vibrates at frequencies between 15,000 and 30,000 cps. The vibrating tool cavitates the liquid, and the force drives the abrasive into the surface of the workpiece to remove metal chips which are carried away by the liquid. The acceleration given the abrasive grains is as much as 100,000 times the acceleration of gravity, providing a smooth and rapid cutting force.
Introduction of Machining
Machining as a shape-producing method is the most universally used and the most important of all manufacturing processes. Machining is a shape-producing process in which a power-driven device causes material to be removed in chip form. Most machining is done with equipment that supports both the work piece and cutting tool although in some cases portable equipment is used with unsupported workpiece.
Low setup cost for small quantities. Machining has tow applications in manufacturing. For casting, forging, and pressworking, each specific shape to be p5roduced, even one part, nearly always has a high tooling cost. The shapes that may be produced, even one part, nearly always has a high tooling cost. The shapes that may be produced by welding depend to a large degree on the shapes of raw material that are available. By making use of generally high cost equipment but without special tooling, it is possible, bu machining, to start with nearly any form of any material, so long as the exterior dimensions are great enough, and produce any desired shape from any material. Therefore, machining is usually the preferred method for producing one or a few parts, even when the design of the part would logically lead to casting, forging or pressworking if a high quantity were to be produced.
Close accuracies, good finishes. The second application for machining is based on the high accuracies and surface finishes possible. Many of the parts machined in low quantities would be produced with lower but acceptable tolerances if produced in high quantities by some other process. On the other hand, many pars are given shapes by some high quantity deformation process and machined only on selected surfaces where high accuracies are needed. Internal threads, for example, are seldom produced by any means other than machining and small holes in pressworked parts may be machined following the pressworking operations.
牛頭刨床、鉆床和銑削
刨床是刀具特有者利用單點刀具將其安裝在滑頭的末梢。一般在做切削時都會向前沖程.刀具被擺動刀架稍微舉起，以避免（刀具）劃過工件時產(chǎn)生嚴重的拖刮。它通過刀具在返回沖程期間運轉(zhuǎn)并為下次的切割做準備。立柱被裝有刨床的操作機械系統(tǒng)以及作為一個固定的單元為輔助點提供服務，工作臺移動的兩個方向是與滑塊相互垂直的。刀具的滑行是用來控制切削的深度以及手動式地運轉(zhuǎn)。它能在它的正常垂直方向的每一邊上旋轉(zhuǎn)90度。它允許在工作臺表面的某個角落來運動刀具。
刨床的兩種驅(qū)動系統(tǒng)是一個改善的whitworth快速返回機械系統(tǒng)和一個液壓驅(qū)動器。對于whitworth機械系統(tǒng)來講，是發(fā)動機驅(qū)動大型的齒輪，它能通過控制可調(diào)整的曲柄驅(qū)動曲柄轉(zhuǎn)臂來控制沖程的長度。對于大型的齒輪轉(zhuǎn)動。搖動式的曲柄轉(zhuǎn)臂被迫沿直線往復移動。增強了刨床滑枕的動向。
液壓刨床發(fā)動機只用來驅(qū)動液壓泵。刨床動向的提醒物被水硬油的流量方向所控制。機械驅(qū)動刨床的切削行程用了大齒輪轉(zhuǎn)動的220度，返回行程用了140度，這就使切削行程與返回行程之速比為1.6:1速度圖顯示了切削行程的大部分切削速度是連續(xù)不斷的。液壓刨床是無窮變化的切削速度限制的缺乏，它可以允許在行程長度中有一些少量的變化。
可能產(chǎn)生與薄形鋼板樣板外型復制品的完全相同的裝置是可利用的。薄型鋼板的樣板用來連接液壓控制器。
直式鉆床或鉆孔式印刷機可用于各種尺寸和種類，它能安裝軸速度的足夠范圍和自動運轉(zhuǎn)以適應大多工業(yè)的要求。一個典型機器的速度范圍是70至2025rmp，以及鉆孔的運轉(zhuǎn)速度是0.002到0.020英尺。
旋轉(zhuǎn)鉆床用來鉆那些太大或太笨重的而不能夠移動的工件。通過將轉(zhuǎn)臂繞立柱的轉(zhuǎn)動和主軸組件沿轉(zhuǎn)臂的移動組合，可使主軸鉆頭對準機床可達范圍內(nèi)的任何位置，由于運轉(zhuǎn)太大而不方便建立在此基礎上，主軸能夠在垂直的地上方搖擺以及工件能固定在機器旁邊的地上。
普通的旋臂鉆床只提供軸的垂直運動和徑向轉(zhuǎn)臂，通過平行軸來運轉(zhuǎn)。因此允許鉆頭處于任何一個角度。
一個多軸通過萬能連接和可伸縮的花鍵軸來驅(qū)動的鉆床有一個或多個頭。通常所有的軸都是通過相同的發(fā)動機來驅(qū)動和同時運轉(zhuǎn)，目的是鉆出理想中洞的數(shù)量。很多鉆床的每個軸容納在一個可調(diào)整的盤里，以便與其他相關的部件移動。相鄰的軸重疊部分的覆蓋區(qū)域目的促使機器能夠在它的范圍的任何地方開始鉆孔。
銑床操作與轉(zhuǎn)動的切削金屬和移動相關。它包括了一個工件的表面金屬移動，洞的擴大和成型切削，比如線和齒輪。
銑銷機床的升降臺式柱是其他部件的主要支持部分。包括了容量驅(qū)動機的基礎，心軸切割工具。切割工具固定在容納在主軸的刀桿上能過一個懸臂的軸承支撐在它的外部的末端。升降臺通過燕尾槽滑動支撐立柱和立柱機器，提供一——三種與切割工具相關的意向。另一種意向可能是工作臺由提供的滑板圍繞著軸旋轉(zhuǎn)而得到的。
固定的銑銷機床的設計目的是比升降臺或立柱提供更大的剛度。工作臺直接固定在機窗的根部，它能為強大切割負荷提供強度的需要。而且允許對工作臺徑度的方向。垂直運動是通過移動整個切割工具才能達到。
仿型銑床的特點是刀具和跟蹤元件的軌道運動的協(xié)調(diào)或同步，或者是工件或模型的軌跡運動的協(xié)調(diào)或同步典型的仿型銑床的仿型號像是遵照模型的形式，而且切割機頭部分與仿行部分相同。
下面是銑削的總體的設計目錄：
1. 如果可能的話，零件將被設計以便在一個工位上最大的平面能被銑削。
2. 對選擇性的切割工具的設計目的是同時銑削幾個平面。
3. 應當首先銑最大的平面，這樣所有的尺寸都能很好的參照這個表面。
4. 因為切割工具的轉(zhuǎn)動，仿形里的各個角落是不可能的。
刺耳的機器和特殊的金屬移動程序
隨機點切削刀具包括構成輪子形狀的，或粘結到帶子或棍子上或直接懸浮在液體中的研磨材料。因為幾個原因研磨進程在工件的生產(chǎn)中很重要。
1. 對切削硬化的刀具鋼材料或其他的熱處理鋼材來講它是最普通的方法。零件在沒有熱處理條件下第一次機器切割，然后得到理想的尺度和表面光潔度。
2. 它能在沒有極限范疇時提供表面光潔度達0.5微米。
3. 研磨操作在相對較短的時間內(nèi)能確保精確的尺度，因為機器在作為其它機器的一般精度構造時提供的動態(tài)是每英尺增加了百分之一的精度，而不是千分之一。
4. 尤其是小而細的零件能用這個方法完成，由于輕壓力被使用和零件的柔韌性所折射出的切削值是最小的。
研磨輪子在圓柱形的研磨機器上在5500和6500rmp之間轉(zhuǎn)動，當工件在60和125rmp之間轉(zhuǎn)動時，切削的深度運動由木頭控制，它包括了輪子和它的驅(qū)動發(fā)動機。冷卻液用來降低熱扭曲和移動切削以及研磨材料時的灰塵。
有韌性的材料的運動通過那些材質(zhì)硬的刀具來完成，但是在二戰(zhàn)期間材料的廣泛傳播使用，它比新材料運動方法的切削刀具的要求更高。因為大量的過程被改進，盡管相當慢且花費高，它能用精確接受的方式來移動過量的材料，這里有兩種進程模式：第一種類型是建立在電子現(xiàn)象的基礎上，它用于基本的原材料；第二種取決于化學溶解。
化學物質(zhì)的銑削用于控制那些用了很濃的堿性或酸性的腐蝕劑腐蝕進程。鋁、鈦、鎂和鋼是通過這種方式的主要原料進程?；瘜W銑削開始于一個零件的傳統(tǒng)的光潔，包括脫脂、脫酸和烘干，這個領域用以維持不與那些籠罩在制服外面的腐蝕劑接觸?？梢詫⒄麄€零件侵入遮蓋材料，然后將遮蓋層從將要被侵蝕的區(qū)域去除；也可以使用抗化學侵蝕的粘接帶遮蓋要保護的區(qū)域，遮蓋之后要侵蝕一般指定的時間，然后要將零件在冷水中清洗，將遮蓋層去除，檢查零件，并徹底全面的清洗。
還應該考慮到的缺點：第一缺點是金屬在各個方面都是平等的侵蝕，以至于侵蝕的外部半徑和侵蝕的深度相等；第二個缺點是在平行于鋼板的方向上所得光潔度要比垂直于木紋的方向上工作所得的表面相比較；第三個缺點不是過程的唯一，而是發(fā)生在細的只腐蝕一邊的壓力段上的翹曲。
而化學銑削在傳統(tǒng)的金屬移動方發(fā)中有很多的優(yōu)點。這在很多部件沒有翹曲例如當腐蝕被用來降低縱切面厚度的各個面上時的鍛造和擠壓，傳統(tǒng)的銑削里一次只用一面來運轉(zhuǎn)，而且零件的頻繁轉(zhuǎn)變是阻止翹曲所必要的?；瘜W銑削能用于不規(guī)則的部件，而那是傳統(tǒng)銑削很難做到的。輕易的建筑物可通過焊接的清除，鉚接和加強筋與銑削而獲得零件可以被定形通過以適當?shù)姆绞椒峙湄摵珊蜐撛诘墓?jié)省過程的例子一樣，與機器切割銑床相比。一個文件報道了有關化學銑削移動鋁的成本，是0.27美元每英鎊，而傳統(tǒng)銑削則是1.00美元每英鎊。所以銑削鋁金屬移動的比率是0.001英尺每分鐘。
電子排放機器是一個電壓作用于工件和刀具之間的過程，電流從金屬工件的源頭流出，以火花的形式流向刀具。完成金屬移動的力量是金屬工件本身。結果，對一般的傳統(tǒng)機械手段而言，沒有必要建設一個單元來抵制重壓和重負荷。由于排放器的范圍大約從2000cps至5000cps用來精加工如此硬的刀具和模具。電流在粗加工期間是不斷變化的。從50amp低到精加工期間的0.5amp，這個過程應用了機械的單點刀具，成形刀具，銑削切割刀具，拉刀以及模具渦凹。它也能移動壞了的鉆頭，而絲錐和螺栓不損壞嵌入的工件。其他的使用方法是一個硬部件的油洞，小安全電線洞的機械是由大量特殊合金制造的，如鈦。
超聲機械程序用于導體和半導體，而且完全依靠于金屬移動的研磨行為，工件淹沒在液下分數(shù)的研磨微粒如水。刀具連接著震蕩器以及在15000至3000cps之間頻繁的震動，震動的刀具抽空液體，沖力研磨材料進入工件的表面用來移動金屬切削。它們能隨著液體流動。研磨的紋密加速度是重力的100000倍，以提供一個光滑而快速的切削沖力。
關于機械加工
作為一種成形方式的機械加工是廣泛使用的也是所有機械制造進程中的最重要的部分。機械加工是通過切削形式使驅(qū)動裝置引起材料運動產(chǎn)生形狀的過程。盡管在某些場合，工作支持情況下，使用移動式裝備實現(xiàn)加工，但是大多數(shù)的機械加工還是通過既支撐工件有支撐刀具的裝備來完成。
小批量生產(chǎn)低費用，機械加工在制造方面有兩種用途：對澆筑，鍛造，壓力加工，即將生產(chǎn)的每個具體形狀，甚至一個零件而言，幾乎是一個高標準的刀具鑄型。這些通過焊接可能產(chǎn)生的形狀在很大程度上取決可利用的原材料的形狀。一般說來，通過利用高價設備而又無需特種加工條件下，幾乎可以從任何種類原材料開始，借助機械加工把原材料加工成任意要求的結構形狀，只要外部尺寸夠大，那都是可能的。因此，機械加工是常用來生產(chǎn)少量零件，甚至在大量生產(chǎn)以及當零件的設計在邏輯上導致澆鑄、鍛造，壓力加工的時候所推薦的方法。
嚴密的精度，合適的平面粗糙度，對機械加工的第二個應用是建立在可行性的高精度和高表面粗糙度之上。很多用機械切割的少量部件會產(chǎn)生較小且能夠接受的偏差是否能夠通過其他的工藝流程生產(chǎn)大量的部件。另一方面，很多部件通過一些大量的變形過程和由機械切割所需要的高精度選擇平面有了他們的一般形狀，例如：內(nèi)部的螺紋很少能通過其他的方式生產(chǎn)，除了機械加工和壓力加工部件的小洞可能被機器切割成的壓力加工過的操作。
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