附录A 英文原文
A.1 FORGING
sichenBulk defirnnation of metals refers to various process, such as forging, rolling, or extruding, where there is a controlled plastic flow or working of metals into uful shapes. The most well known of the process is forging where deformation is accomplished by means of pressure, impact blows, or a combination of both.
Hammer Forging
Hanuner forging consists of striking the hot metal with a large miautomatic hammer. If no dies are involved, the forging will be dependent mainly on the skill of the operator. If clod or impression dies are ud, one blow is struck for each of veral (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 clod dies may be ud. The open dies are ud chiefly for large, simple-geometry parts that are later machined to shape. Clod-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 helical teeth. Rotation of the die (luring penetration will press bevel gears with spiral teeth.
英语词典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. Round swaging (lies and V dies are ud 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 ca of press open-die forging, to the press bed.
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As the workpiece is hammered or presd, it is repeatedly manipulated 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 for machining, a 6.5 in. diameter shaft would have to be forged to 7.4 in. dianieter.
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In open-die forging of steel, a rule of thumb says that 50 lb of falling weight is required for each square inch of cross ction.
Impression-die Forging王子用英语怎么说
In the simplest example of impression-die forging, two dies are brought together, and the workpiece undergoes plastic deformation until its enlarged sides 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 prents incread resistance to deformation, effectively becoming a part of the tool, and helps build up l)ressUre inside the bulk of the work- piece that aids material flow into unfilled impressions.
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Clod-die forgings, a special form of impression-die forging, does not depend on the for
mation of flash to achieve complete filling of the (lie. Thus clod-die forging is considerably more demanding on die design. Since 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 Forgingjunglegym
As with uptting, extrusion forging is often accomplished by cold working. Three principal 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- presd by a ram movement until pressure inside the metal reaches flow-stress levels. The workpiece completely fills the container, and additional pressure caus it to leave through an orifice and form the extruded product.
Extruded products may be either solid or hollow shapes. Tube extrusion is ud to produce hollow shapes such as containers and pipes. Rever-impact extrusion is ud for mass production of aluminum cans. The ram hits a slug of metal in the die at high impact, usually 15 times the yield strength of the metal, which caus it to flow instantaneously up the walls of the die. Other common hollow extrusion products are aerosol cans, lipstick cas, flashlight cas, and vacuum bottles. Secondary operations,
such as heading, thread rolling, dimpling, and machining, are often needed to complete the items.
Generally steel impacts are limited to 2.5 times the punch diameter. Hydraulic press are ud for loads of over 2000 tons becau they have a greater variation in stroke length, speed, and other economic advantages. Tolerances vary with materials arid design, hut production runs calling for 0.002- to 0.005-in, tolerance are regularly made.
Roll Forging
Roll forging in its simplest form consists of a heated billet passing between a pair of rolls that deform it along its length (Fig. 8-4). Compared to conventional rolling process, the rolls are relatively small in diameter and rve as an arbor into which the forging tools are cured. The active surface of the tool occupies only a portion (usually half) of the roll circumference to accommodate the full cross ction of the stock.
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shenghuodabaozhaThe reduction of the cross ction obtainable in one pass is limited by the tendency of the material to spread and form an undesirable flash that may be forged into the surface as a defect in the subquent operations. The workpiece is int roduced repeatedly with rota- tion between pass.
Ring Rolling
Ring rolling offers a homogeneous circumferential grain flow, ea of fabrication and machining, and versatility of material size . Manu- facture of a rolled ring starts with a sheared blank, which is forged to a pancake, punched, and pierced.
There is no limit to the size of the rolled rings, ranging from roller-bearing sleeves to Fig. 4 Roll forging rings 25 ft in diameter with face heights of 80 in. Various profiles may be rolled by suitably shaping the driven, idling rolls.
CAD/CAM in Forging
CAD/CAM is being increasingly applied to frging. Using the three-dimensional description of a machined part, which may have been computer designed, it is possible to generate the geometry of the associated forging. Thus the forging ctions can be obtained from a common (laiR ba. Using well-known techniques, forging loads and stress can be obtained and flash dimensions can be lected for each ction where metal flow is approximated as ro dimensional (plane strain or axisymmetric ). In some rel
atively simple ction geomethes, computer simulation can be conducted to evaluate initial guess on preform ctions. Once the preform geometry has been developed to the designer¡¯s satisfaction, this geometric data ba can utilized to write NC part programs to obtain the NC tapes or disks for machining.
