Text b Forging

Forging is the process of shaping iron and other malleable metals using localized compressive forces. Forging is often classified according to the temperature at which it is performed: "cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 170 metric tons.

Forging is known to be one of the oldest metalworking processes. Traditionally, forging was performed by a smith using hammer and anvil.

In modern times, industrial forging is done either with presses or with hammers powered by compressed air, electricity, hydraulics or steam. These hammers are very different in size and productivity, their reciprocating weights being from 500 lb (230 kg) or less to the thousands of pounds. Machine-forging operations are frequently accomplished by use of a series of dies being mounted on the same press or hammer. The dies are arranged in sequence so that they form the finished forging in a series of steps.

Forging techniques are useful in the working of metal because the metal can be given the desired form. This process is assumed increasing the physical characteristics of the metal, particularly refining the grain size of the metal. Having been forged the metal becomes stronger and more ductile than cast metal and exhibits greater resistance to fatigue and impact.

In general, six basic types of forging exist: upsetting, or decreasing the length and increasing the diameter of the metal; swaging, decreasing the diameter of the metal; bending; welding, joining two pieces of metal together; punching, the forming of small openings in the metal; and cutting out, the forming of large holes in the metal.

Some metals may be forged cold, however iron and steel are almost always hot forget. Hot forging prevents the work hardening that would result from cold forming, which would increase the difficulty of performing secondary machining operations on the piece.

Production forging is rather expensive process because of the capital machinery and tooling costs. In the case of hot forging, a high temperature furnace will be required to heat ingots or billets. Owing to the massiveness of large forging hammers and presses and the parts they can produce a special building is frequently required to house the operation. In the case of drop forging operations, provisions must be made to absorb the shock and vibration generated by the hammer. Most forging operations will require the use of metal-forming dies, which must be precisely machined and carefully heat treated to correctly shape the workpiece, as well as to withstand the tremendous forces involved.

Задания к тексту B:

I. Найдите в тексте английские эквиваленты следующим русским выражениям:

достаточно дорогой процесс; приводимый в действие сжатым воздухом, электроэнергией, гидравлическими средствами или паром; высокотемпературные печи; точно обработанные; либо прессами, либо молотами; массивность больших ковочных прессов и молотов; один из самых старых процессов металлообработки; капитальные затраты на станки и инструменты; операции машинной ковки; штампы для формовки металла; конечная поковка после ряда операций (шагов).

II. Сформулируйте в нескольких словах содержание каждого абзаца.

III. Напишите резюме к тексту.

IV. Ответьте на вопросы:

1. What is forging?

2. How is Forging often classified?

3. Is forging one of the oldest metalworking processes?

4. How was forging traditionally performed?

5. How is forging performed in modern times?

6. How are machine-forging operations frequently accomplished?

7. Why are forging techniques useful in the working of metal?

8. What basic types of forging exist?

9. What is the difference between hat and cold forging?

10. Why is production forging rather expensive process?

V. Перескажите текст, используя в качестве плана вопросы предыдущего упражнения.