銑削機械加工外文翻譯、中英文翻譯、機械類外文文獻翻譯

外文原文： MILLING Milling is a basic machining process in which the surface is generated by the progressive formation and removal of chips of material from the workpiece as it is fed to a rotating cutter in a direction perpendicular to the axis of the cutter. In some cases the workpiece is stationary and the cutter is fed to the work. In most instances a multiple-tooth cutter is used so that the metal removal rate is high, and frequently the desired surface is obtained in a single pass of the work. The tool used in milling is known as a milling cutter. It usually consists of a cylindrical body which rotates on its axis and contains equally spaced peripheral teeth that intermittently engage and cut the workpiece. 1 In some cases the teeth extend part way across one or both Ends of the cylinder. Because the milling principle provides rapid metal removal and can produce good surface finish, it is particularly well-suited for mass-production work, and excellent milling machines have been developed for this purpose. However, very accurate and versatile milling Machines of a general-purpose nature also have been developed that are widely used in jobshop and tool and die work. A shop that is equipped with a milling machine and an engine lathe can machine almost any type of product of suitable size. Types of Milling Operations. Milling operations can be classified into two broad categories, each of which has several variations: 1. In peripheral milling a surface is generated by teeth located in the periphery of the cutter body； the surface is parallel with the axis of rotation of the cutter. Both flat and formed surfaces can be produced by this method. The cross section of the resulting surface corresponds to the axial contour of the cutter. This procedure often is called slab milling. 2. In face milling the generated flat surface is at right angles to the cutter axis and is the combined result of the actions of the portions of the teeth located on both the periphery and the face of the cutter. 2 The major portion of the cutting is done by the peripheral portions of the teeth with the face portions providing a finishing action. The basic concepts of peripheral and face milling are illustrated in Fig. 16-1. Peripheral milling operations usually are performed on machines having horizontal spindles, whereas face milling is done on both horizontal- and vertical-spindle machines. Surface Generation in Mimng. Surfaces can be generated in milling by two distinctly different methods depicted in Fig. 16-2. Note that in up milling the cutter rotates againsi the direction of feed the workpiece, whereas in down milling the rotation is in the same direction as the feed. As shown in Fig. 16-2, the method of chip formation is quite different in the two cases. In up milling the c hip is very thin at the beginning, where the tooth first contacts the work, and increases in thickness, becoming a maximum where the tooth leaves the work. The cutter tends topush the work along and lift it upward from Tool-work relationshios in peripheral and face milling the table. This action tends to eliminate any effect of looseness in the feed screw and nut of the milling machine table and results in a smooth cut. However, the action also tends to loosen the work from the clamping device so that greater clamping forcers must be employed. In addition, the smoothness of the generated surface depends greatly on the sharpness of the cutting edges. In down milling, maximum chip thickness cecum close to the point at which the tooth contacts the work. Because the relative motion tends to pull the workpiece into the cutter, all possibility of looseness in the table feed screw must be eliminated if down milling is to be used. It should never be attempted on machines that are not designed for this type of milling. Inasmush as the material yields in approximately a tangential direction at the end of the tooth engagement, there is much less tendency for the machined surface to show tooth marks than when up milling is used. Another considerable advantage of down milling is that the cutting force tends to hold the work against the machine table, permitting lower clamping force to be employed. 3 This is particularly advantageous when milling thin workpiece or when taking heavy cuts. Sometimes a disadvantage of down milling is that the cutter teeth strike against the surface of the work at the beginning of each chip. When the workpiece has a hard surface, such as castings do, this may cause the teeth to dull rapidly. Milling Cutters. Milling cutters can be classified several ways. One method is to group them into two broad classes, based on tooth relief, as follows: 1.Profile-cutters have relief provided on each tooth by grinding a small land back of the cutting edge. The cutting edge may be straight or curved. 2.In form or cam-reheved cutters the cross section of each tooth is an eccentric curve behind the cutting edge, thus providing relief. All sections of the eccentric relief, parallel with the cutting edge, must have the same contour as the cutting edge. Cutters of this type are sharpened by grinding only the face of the teeth, with the contour of the cutting edge thus remaining unchanged. Another useful method of classification is according to the method of mounting the cutter. Arbor cutters are those that have a center hole so they can be mounted on an arbor. Shank cutters have either tapered or straight integral shank. Those with tapered shanks can be mounted directly in the milling machine spindle, whereas straight-shank cutters are held in a chuck. Facing cutters usually are bolted to the end of a stub arbor. The common types of milling cutters, classified by this system are as follows: Types of Milling Cutters. Hain milling cutters are cylindrical or disk-shaped, having straight or helical teeth on the periphery. They are used for milling flat surfaces. This type of operation is called plai n or slab milling. Each tooth in a helical cutter engages the work gradually, and usually more than one tooth cuts at a given time. This reduces shock and chattering tendencies and promotes a smoother surface. Consequently, this type of cutter usually is preferred over one with straight teeth. Side milling cutters are similar to plain milling cutters except that the teeth extend radially part way across one or both ends of the cylinder toward the :center. The teeth may be either straight or helical. Frequently these cutters are relatively narrow, being disklike in shape. Two or more side milling cutters often are spaced on an arbor to make simultaneous, parallel cuts, in an operation called straddle milling. Interlocking slotting cutters consist of two cutters similar to side mills, but made to operate as a unit for milling slots. The two cutters are adjusted to the desired width by inserting shims between them. Staggered-tooth milling cutters are narrow cylindrical cutters having staggered teeth, and with alternate teeth having opposite helix angles. They are ground to cut only on the periphery, but each tooth also has chip clearance ground on the protruding side. These cutters have a free cutting action that makes them particnlarly effective in milling deep slots. Metal-slitting saws are thin, plain milling cutters, usually from 1/32 to 3/16 inch thick, which have their sides slightly dished to provide clearance and prevent binding. They usually have more teeth per inch of diameter than ordinary plain milling cutters and are used for milling deep, narrow slots and for cutting-off operations. 譯文： 銑 削 銑削是機械加工的一個基礎方法。在這一加工過程中，當工件沿垂直于旋轉刀具軸線方向進給時，在工件上形成并去除切屑從而逐漸地銑出表面。有時候，工件是固定的，而刀具處于進給狀 態(tài)。在大多數情況下，使用多齒刀具，金屬切削量大，只需一次銑削就可以獲得所期望的表面。在銑削加工中使用的刀具稱做銑刀。它通常是一個繞其軸線旋轉并且周邊帶有同間距齒的圓柱體，銑刀齒間歇性接觸并切削工件。在某些情況下，銑刀上的刀齒會高出圓柱體的一端或兩端。 由于銑削切削金屬速度很快，并且能產生良好的表面光潔度，故特別適合大規(guī)模生產加工。為了實現這一目的，已經制造出了質量一流的銑床。然而在機修車間和工具模具加工中也已經廣泛地使用了非常精確的多功能通用的銑床。車間里擁有一臺銑床和一臺普通車床就能加工出具有適合尺寸的各 種產品。 銑削操作類型：銑削操作可以分成兩大種類，每一類又有多種類型。 1圓周銑削 在圓周銑削中，使用的銑刀刀齒固定在刀體的圓周面上，工件銑削表面與旋轉刀具軸線平行，從而加工表面。使用這種方法可以加工出平面和成型表面，加工中表面橫截面與刀具的軸向外輪廓相一致。這種加工過程常被稱為平面銑削。 2端面銑削 銑削平面與刀具的軸線垂直，被加工平面是刀具位于周邊和端面的齒綜合作用形成的。刀具周邊齒完成銑削的主要任務，而端面齒用于精銑。 圓周銑削和端面銑削的基本概念，圓周銑削通常使用臥式銑床，而端銑削則既可在臥式銑 床又可以在立式銑床上進行。 銑削面的形成：銑削時可以采用兩種完全不同的方法。應注意，在逆銑時，銑刀旋轉方向與工件進給方向相反，而在順銑時銑刀旋轉與工件進給方向相同。在逆銑過程中，當銑刀齒剛切人工件時，切屑是非常薄的，然后漸漸增厚，在刀齒離開工件的地方，切屑最厚。在兩種銑削方法中，切屑的形成是不同的，逆銑過程中，刀具有推動工什丌使工件從工作臺上提升的趨勢，這種作用有助于消除銑床工作臺進給螺桿和螺母間的間隙，從而形成平穩(wěn)的切削。然而，這種作用也有造成工件與夾緊裝置之間的松動的趨勢，這時應施加更大的夾緊力。此外， 銑削表面的平整度主要取決于切削刃的鋒利程度。 順銑時，最大切屑厚度產生于靠近刀具與工件接觸點處。由于相對運動趨于把工件拉向銑刀，如果采用順銑法，要消除工作臺進給螺桿可能產生的松動。因此，對于不能用于順銑的銑床，不要采用順銑方法。因為在銑刀結束切削時，處于切線方向的被切材料發(fā)生屈服，所以與逆銑相比，順銑的被加工表面沒有什么切痕。順銑的另一個優(yōu)勢是切削力趨于將工件壓緊在工作臺上，因此對工件的夾緊力可以小于逆銑。這一優(yōu)勢可以用于銑削較薄的工件或進行強力切削。順銑的弱點是銑刀齒剛一切削每片鐵屑時，刀齒會撞擊工件的 表面。如果工件表面堅硬，像鑄件，就