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A the Text: «METALWORKING PROCESSES»
Metals are by important in the industry for They Because the BE CAN Easily Into Useful deformed shapes. A lot of metalworking processes have been developed for certain applica¬tions. The BE DIVIDED CAN for They Into a five Broad The groups:
1. rolling,
2. extrusion,
3. drawing Explosional drawing,
4. forging,
5. sheet-metal forming.
During the first four processes metal is subjected to large amounts of strain (deformation). But if deformation goes at a high temperature , the metal will recrystallize - that is, new strain-free grains will grow instead of deformed grains. For this reason metals are usually rolled, ex¬truded, drawn, or forged above their recrystallization temperature. This is called hot working. Under these conditions there is no limit to the compressive plastic strain to which the metal can be subjected.
Other processes are performed below the recrystallization temperature . These are called cold working. Cold working hardens metal and makes the part stronger. However, there is a limit to the strain before a cold part cracks.
The Rolling
the Rolling is the metalworking process are most common all. More than 90 percent of the aluminum, steel and copper produced is rolled at least once in the course of produc¬tion. The most common rolled product is sheet. Rolling can be done either hot or cold . If the rolling is finished cold, the surface will be smoother and the product stronger.
Extrusion
Extrusion is pushing the billet to flow through the orifice of a die. Products may have either a simple or a complex cross section. Aluminum window frames are the examples of complex extrusions.
Tubes or other hollow parts can also be extruded. The initial piece is a thick-walled tube, and the extruded part is shaped between a die on the outside of the tube and a mandrel held on the inside.
In impact extrusion (also called back- extrusion) ( extruding), the workpiece is placed in the bottom of a hole and a loosely fitting ram is pushed against it. The ram forces the metal to flow back around it, with the gap between the ram and the die determin¬ing the wall thickness. The example of this process is the manufacturing of aluminum beer cans
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