Metal working

Metals are important in industry because they can be easily deformed into useful shapes. A lot of metalwork­ing processes have been developed for certain applica­tions. They can be divided into five broad groups:

1. rolling,

2. extrusion,

3. 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, ex­truded, 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

Part II

working hardens metal and makes the part stronger. However, there is a limit to the strain before a cold part cracks.

Rolling

Rolling is the most common metalworking process. More than 90 percent of the aluminum, steel and copper produced is rolled at least once in the course of produc­tion. 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. Aluminium 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) (штамповка выдавливанием), 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 determin­ing the wall thickness. The example of this process is the manufacturing of aluminium beer cans.

Vocabulary:

useful ['ju=sful] — полезный

shape [Jeip] — форма, формировать

rolling — прокатка

extrusion [iks'tru: 33n] — экструзия, выдавливание

Unit 2

drawing [dra: in] — волочение

forging ['fo: d3in] — ковка

sheet [Ji: t] — лист

to subject [, SAbd3'ekt] — подвергать

amount [a'maunt]— количество

condition [ksn'dijbn] — состояние, условие

perform [рэ'гота] — выполнять, проводить

to harden ['ha: dn] — делаться твердым, упрочняться

at least — по крайней мере

common ['кэтзп] — общий

billet ['bilit] — заготовка, болванка

orifice ['onfis] — отверстие

die [dai] — штамп, пуансон, матрица, фильера, во­лочильная доска

cross section — поперечное сечение

window frame [freim] — рама окна

tube [tju: b] — труба

hollow ['holau] — полый

initial [ГшД] — первоначальный, начальный

thick-walled — толстостенный

mandrel ['maendnl] — оправка, сердечник

impact ['impaskt] — удар

loosely — свободно, с зазором

fitting — зд. посадка

ram [raem] — пуансон, плунжер

force [fo: s] — сила

gap [gaep] — промежуток, зазор

to determine [di't3: mm] — устанавливать, опреде­лять

General understanding:

1. Why are metals so important in industry?

2. What are the main metal working processes?

6. Зак. 242