模具专业英语毕业论文外文文献翻译.doc

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1、外文文献English for Die & MouldLesson 1 Drawing OperationThree bent flanges are shown in Fig. 1-1 , The first one ( Fig. 1-la) is the simple straight bend. The stretch flange and shrink flange ( Fig. 1-lb and c, respectively) involve a plastic flow of metal that does not take place in a straight-bend fl

2、ange. This plastic flow or adjustment of metal is characteristic of all drawing operations. Stresses are involved that exceed the elastic limit of the metal so as to permit the metal to conform to the punch. However, these stresses cannot exceed the ultimate strength without developing cracks. If th

3、e stretch flange ( Fig. 1-lb) is considered to be a section of a circular depression that has been drawn, the metal in arc aa must have been stretched to aa. The action is a thinning one and must be uniform to avoid cracks. In the shrink flange ( Fig. 1-lc) the action is just the opposite, and the m

4、etal in the flange is thickened.Most drawn parts start with a flat plate of metal. As the punch is forced into the metal, severe tensile stresses are induced into the sheet being formed. At the same time the outer edges of the, sheet that have not engaged the punch are in compression and undesirable

5、 wrinkles tend to form. This must be counteracted by a blank holder or pressure plate, which holds the flat plate firmly in place.In a simple drawing operation of relatively thick plates the plate thickness may be sufficient to counteract wrinkling. This may be done in a single-acting press as shown

6、 in Fig. 1-2. Additional draws may be made on the cup-shaped part, each one elongating it and reducing the wall thickness.Most drawing, involving the shaping of thin metal sheets, requires double-acting presses to hold the sheet in place as the drawing progresses. Presses of this type usually have t

7、wo slides, one within the other. One slide controlling the blank-holding rings moves to the sheet ahead of the other to hold it in place. This action is illustrated in Fig. 1-3. The motion of the blank-holding slide is controlled by a toggle or cam mechanism in connection with the crank. Hydraulic p

8、resses are well adapted for drawing because of their relatively slow action, close speed control, and uniform pressure Fig. 1-4 shows a sectional diagram of an inverted drawing die. The punch is stationary and is mounted on the bed of the press. As the die descends, the blank is contacted; then as i

9、ts downward movement continues, the blank-holding ring maintains contact with the blank during drawing. By the use of a die cushion to control the holder the pressures on the blank can be increased and controlled. .The pressure applied to the punch necessary to draw a shell is equal to the product o

10、f the cross-sectional area and the yield strength Ys of the metal. A constant that covers the friction and bending is necessary in this relationship. The pressure P for a cylindrical shell may be expressed by the empirical equationThe amount of clearance between a punch and die for blanking is deter

11、mined by the thickness and kind of stock. For thin material the punch should be a close-sliding fit. For heavier stock the clearance must be larger to create the proper shearing action on the stock arid to prolong the life of the punch.There is a difference of opinion as to the method designating cl

12、earance. Some claim that clearance is the space between the punch and die on one side or one-half difference between the punch and die sizes. Others consider clearance as the total difference between the punch and die sizes For example, if the die is round, clearance equals die diameter minus punch

13、diameter. The advantage of designating clearance as the space on each side is particularly evident in the case of dies with irregular form or shape. Whether clearance is deducted from the diameter of the punch or added to the diameter of the die depends on the work. If a blank has a required size, t

14、he die is made smaller. When holes of a certain size are required, the punch is ground to the required diameter and the die is made larger.Lesson 2 Compound and Progressive DiesCompound dies combine two or more operations at one station as illustrated in Fig. 2-1. Strip stock is fed to the die, two

15、holes are punched, and the piece is blanked on each stroke of the ram. When the operations are not similar, as in the case of a blanking and forming operation, dies of this type are frequently known as combination dies.A progressive die set performs two or more operations simultaneously but at diffe

16、rent stations. A punch-and-die set of this type is shown in Fig. 2-2. As the strip enters the die, the small square hole is punched. The stock is then advanced to the next station, where it is positioned by the pilot as the blanking punch descends to complete the part.This general type of design is

17、simpler than the compound dies, because the respective operations are not crowded together. Regardless of the number of operations to be performed, the finished part is not separated from the until the last operation.In the perforation of metal one or two rows of punches are employed. The metal shee

18、t is moved incrementally through the press each time the punches are withdrawn. The punched holes may he almost any shape. All nonbrittle metals can be perforated.Misalignment of punch and die causes excessive pressures, shearing or chipping of die edges, or actual breaking of the tools. Such action

19、 may occur through shifting even though the setup is originally correct. To prevent these occurrences, proper alignment is ensured by guide rods at two or four corners of the die that fit into holes in the punch holders. These dies are known as pillar dies. This arrangement of having the punch and d

20、ie held in proper alignment facilitates the setting up of the tools. A similar arrangement, known as a subpress die and occasionally used on small work, employs a punch and die mounted in a small frame so that accurate alignment is always maintained. Pressure is applied by a plunger that extends out

21、 of the top of the assembly. Combination and Compound DiesConfusion sometimes arises regarding combination and compound tools largely because the names are similar, but they differ considerably in their design and application. In order to appreciate the function of a combination tool, any newcomer t

22、o press tools must know that this type of equipment is designed to perform two operations on a strip or precut piece of material simultaneously. There are obviously several such combinations and the most well known are: blank and pierce, blank and cup, blank and plunge, and blank, draw and trim.A wa

23、sher-producing tool is a suitable example to use as the operations of blanking the periphery and piercing the central hole are carried out simultaneously. The action differs from a follow-on tool in which the hole is punched and then the strip is fed further through the tool to another punch that re

24、moves the partially-completed blank from the material. In a combination tool both of the cutting stages are carried out without moving the strip. A typical tool for producing washers is shown in Fig 2-3 , and the first significant change from the follow-on tool is the absence of a material guide, an

25、d although a guide can easily be arranged on each side of the die, a strip feeding mechanism outside the tool is usually employed However, this does not affect the design of the tool in which, as shown, the base locates the punch-cum-blanking die A , which has a dual function to perform because the

26、outside diameter serves as the piercing punch for the outside diameter or the washer, while the bore is the die when the centre piece of scrap material is removed. The blanking die is thus carried in the upper member with a central punch and in a recess machined behind this is a headed ejector rod t

27、hat operates four pins used for moving the actual ejector G, Sometimes this ejector is spring-loaded, but a mechanical ejector of the type shown is better for simple components because the part leaves the strip and by using an air blast it is blown from the die surface. With the spring type of eject

28、or the blank is reinserted into the strip and carried along and will require removing by hand. Meanwhile the centre piece of scrap falls away through the bolster.A combination tool is not restricted to pressing circular details of the type depicted here and piercing holes off centre or on a P. C. D.

29、 with a shaped outer profile given to the blank is easily accomplished. One further important factor is that producing a single washer in the manner shown is the most uneconomical way of carrying out the task because of the high material wastage. At least three or preferably five washers can be pres

30、sed simultaneously from the strip in order to reduce wastage to a minimum. This practice is, of course, only feasible for small washers.Lesson 3 Forging Processes and Die DesignForging is one of the most important manufacturing operations. It is a plastic deformation process similar to extrusion but

31、, unlike extrusion, it can he used to manufacture complex 3-D parts. Forging can be classified into three main categories: open-die forging, impression-die forging and closed-die forging.Open-Die ForgingThe process is schematically illustrated in Fig. 3-1. At least one of the workpiece surfaces defo

32、rms freely, and lesser accuracy and dimensional tolerance than impression-die or closed-die forging. However, the tooling is simple, relatively inexpensive and can be designed and manufactured with ease .Impression-Die Forging This forging process is schematically illustrated in Fig. 3-2. It can be

33、used to produce complex 3-D shapes having a greater accuracy than closed-die forging. The specially manufactured dies contain the negative of the forging to be produced. In one form of the process, the shape is obtained by filling: the die cavity formed by the upper and lower dies. Excess material i

34、s allowed to escape into the flash. There may or may not be special provision for flash formation.The die cavity must be filled without defects. Complex shape cannot he filled completely without defects, one operation starting with a rectangular or cylindrical shape. Some preforging steps are necess

35、ary to ensure complete filling of the dies without defect formation. The preforging (preforms) can be produced in other forging operations such as open-die or in the same die with different die cavities, or be other processes such as rolling or roll-forging.The preform may be further shaped to bring

36、 it closer to the final configuration in a blocker die, which ensures proper distribution of material within the die. Excess material is allowed to run out between the dies into a flash. Before forging in the finishing die the excess material may be removed in a trimming die. A thick flash in the fi

37、nishing die means high pressure within the die, which assures proper die filling. Excessive pressure may break dies or reduce their life, and some control on this may be exercised by proper control of the flash land.The geometry of the preform and the forging dies must promote smooth material flow.

38、Therefore, a parting line is chosen with proper consideration of the fibre structure of the finished forming. After the parting line is located the die walls are given sufficient draft to permit removal of the forging from the die cavities. Fillets and corners must be given appropriate radii to ensu

39、re smooth material flow and long die life. Closed-Die ForgingIn closed-die forging the workpiece is completely trapped in the die and no flash is generated. Material utilization is very high, but the control of the workpiece before and after forging is identical and hence control of incoming materia

40、l volume becomes critical. Excess material can create large pressures, which are liable to cause die failure.Lesson 4 Basic Machine Tool ElementsMost machine tools are constructed by using two or more components. These components, although they may have different functions in such machines as a lath

41、e, mill ,or drill press, have common characteristics.Because of the demand for metal removal machines such as lathes, machining centers, milling machines, grinders, and the many others shown throughout this book, there has been continuous development in flexible machining; centers. The mass-produced

42、 and special machine tools are constructed of basic elements.This chapter describes those elements.Important requirements for machine tool structures include rigidity, shape, operator and part accessibility, ease of chip removal, and safety. In terms of machine tool performance, static and dynamic s

43、tiffness is necessary for accuracy and precision. Stability of the machine structure is required to prevent machining chatter. Understanding the basic machine elements is necessary to appreciate the breadth of modern machining methods in the manufacture of products.Structures for Cutting MachinesCas

44、tings, forgings, and hot- or cold-formed shapes usually require machining. The variety of sizes, shapes, and materials calls for diversity in machining.Machine tools differ not only in the number of cutting edges they employ , but also in the way the tool and workpiece are moved in relation to each

45、other. In some machines (vertical machining center, drill presses, boring machines, milling machines shaper, and grinders) the workpiece remains virtually motionless and the tool moves. In other (planers, lathes, and boring mills) the tool is virtually fixed and the workpiece moves. But it should be

46、 pointed out that seldom are these simple elements applied without modification. Study. Fig. 4-1 for the traditional processes used nor machining parts.The single-point tool-shaping machines are the easiest to visualize. The lathe and the boring machine are kinematic inversions employing the single-

47、point tool. In Fig.4-2a the work rotates in the lathe, but the cutting tool is stationary. In the boring machine (Fig. 4-2b) the tool rotates while the work is stationary. Although the lathe tool and the boring machine worktable are not truly stationary, this is overlooked for the moment. To feed a

48、tool carriage past rotating work is usually more acceptable than to feed rotating work with headstock and supports past a stationary tool post. The shaper and planer use single-point cutting tools. Fig. 4-2e and Fig. 4-2d point out that size of the workpiece is a factor in machine structural design.

49、 The smaller workpiece is more efficiently machined on the shaper than on the planer. The general appearance of the machine is changed by reversing the kinematic relationship or work and tool. However, the cutting action principle is identical.With the introduction of the milling cutter by Eli Whitney in the early 300s, the rotating tool was used only as a boring tool. But Whitney gave it a new application. The milling cutter w