1、 27 附录 A 英文原文 A.1 FORGING Bulk defirnnation of metals refers to various processes, such as forging, rolling, or extruding, where there is a controlled plastic flow or working of metals into useful shapes. The most well known of these processes is forging where deformation is accomplished by means of
2、 pressure, impact blows, or a combination of both. Hammer Forging Hanuner forging consists of striking the hot metal with a large semiautomatic hammer. If no dies are involved, the forging will be dependent mainly on the skill of the operator. If closed or impression dies are used, one blow is struc
3、k for each of several (lie cavities. A- gain, productivity and quality depend to a large degree on the skill of the hanimer operator and the tooling. Press Forging Press forging is characterized by a slow squeezing action. Again, open or closed dies may be used. The open dies are used chiefly for la
4、rge, simple-geometry parts that are later machined to shape. Closed-die forging relies less on operator skill awl more on the design of the preform and forging dies.2 As an example of the versatility of the process, newer developments have made it possible to produce bevel gears with straight or hel
5、ical teeth. Rotation of the die (luring penetration will press bevel gears with spiral teeth. Open-die Forging Open-die forging is distinguished by the fact that the metal is never completely confined as it is shaped by various dies. Most open-die forgings are produced on flat, V, or swaging dies. R
6、ound swaging (lies and V dies are used in pairs or with a flat die. The top (lie is attached to the ram of the press, and the bottom die is attached to the hammer anvil or, in the case of press open-die forging, to the press bed. As the workpiece is hammered or pressed, it is repeatedly manipulated
7、between the dies until hot working forces the metal to the final dimensions, as-shown in Fig. 1. After forging, the part is rough- and finished-machined. As an example of the amount of material allowed 28 for machining, a 6.5 in. diameter shaft would have to be forged to 7.4 in. dianieter. In open-d
8、ie forging of steel, a rule of thumb says that 50 lb of falling weight is required for each square inch of cross section. Impression-die Forging In the simplest example of impression-die forging, two dies are brought together, and the workpiece undergoes plastic deformation until its enlarged sides
9、touch the side walls of the die (Fig. 2). A small amount of material is forced outside the die impression, forming flash that is gradually thinned. The flash cools rapidly and presents increased resistance to deformation, effectively becoming a part of the tool, and helps build up l)ressUre inside t
10、he bulk of the work- piece that aids material flow into unfilled impressions. 29 Closed-die forgings, a special form of impression-die forging, does not depend on the formation of flash to achieve complete filling of the (lie. Thus closed-die forging is considerably more demanding on die design. Sin
11、ce pressing is often completed in one stroke, careful control of the workpieee volume is necessaiy to achieve complete filling without generating extreme pressures in the dies from overfilling. Extrusion Forging As with upsetting, extrusion forging is often accomplished by cold working. Three princi
12、pal types of metal displacement by plastic flow are involved. Backward and forward, tube, and impact extrusion are shown in Fig. 3. The metal is placed in a container and corn- pressed by a ram movement until pressure inside the metal reaches flow-stress levels. The workpiece completely fills the co
13、ntainer, and additional pressure causes it to leave through an orifice and form the extruded product. Extruded products may be either solid or hollow shapes. Tube extrusion is used to produce hollow shapes such as containers and pipes. Reverse-impact extrusion is used for mass production of aluminum
14、 cans. The ram hits a slug of metal in the die at high impact, usually 15 times the yield strength of the metal, which causes it to flow instantaneously up the walls of the die. Other common hollow extrusion products are aerosol cans, lipstick cases, flashlight cases, and vacuum bottles. Secondary operations, such as heading, thread rolling, dimpling, and machining, are often needed to complete the items.
