Forging

Forging is the shaping of a piece of metal by pushing with open or closed dies. It is usually done hot in order to reduce the required force and increase the metal's plasticity.

Open-die forging is usually done by hammering a part between two flat faces. It is used to make parts that are too big to be formed in a closed die or in cases where only a few parts are to be made. The earliest forging machines lifted a large hammer that was then dropped on the workpiece, but now air or steam hammers are used, since they allow greater control over the force and the rate of forming. The part is shaped by moving or turning it between blows.

Closed-die forging is the shaping of hot metal within the walls of two dies that come together to enclose the workpiece on all sides. The process starts with a rod or bar cut to the length needed to fill the die. Since large, complex shapes and large strains are involved, several dies may be used to go from the initial bar to the final shape. With closed dies, parts can be made to close tolerances so that little finish machining is required.

Two closed-die forging operations are given special names. They are upsetting and coining. Coining takes its name from the final stage of forming metal coins, where the desired imprint is formed on a metal disk that is pressed in a closed die. Coining involves small strains and is done cold. Upsetting involves a flow of the metal back upon itself. An example of this process is the pushing of a short length of a rod through a hole, clamping the rod, and then hitting the exposed length with a die to form the head of a nail or bolt.

Vocabulary:

to pull — тянуть

reduction — сокращение

to achieve — достигать

in series — серия, последовательно

beyond — выше, свыше

yield point — точка текучести металла

to retain — сохранять, удерживать

to bend — гнуть

shearing — обрезка, отрезание

edge — край

to grip — схватывать

lower die — нижний штамп

upper die — верхний штамп

forming operation — операция штампования

dimension — измерение, размеры

required — необходимый

increase — увеличение

open-die forging — ковка в открытом штампе (подкладном)

hammering — ковка, колотить

within — внутри, в пределах

to enclose — заключать

rod — прут, стержень

bar — прут, брусок

involved — включенный

tolerance — допуск

upsetting — высадка, выдавливание

blow — удар

coining — чеканка

imprint — отпечаток

clamp — зажим

to hit — ударять

General understanding:

1. How can the reduction of diameter in wire drawing be achieved?

2. What is sheet metal forming and where it can be used?

3. What is close-die forging?

4. What is forging?

5. What are the types of forging?

6. What types of hammers are used now?

7. Where are coining and upsetting used?

8. What process is used in wire production?

9. Describe the process of making the roof of a car.

Exercise 2.3. Find the following word combinations in the text:

1. протягивание металла через фильеру

2. волочение проволоки

3. уменьшение диаметра

4. толщина листа

5. растягивать выше точки текучести

6. сохранить новую форму

7. края отрезаются

8. конечные размеры

9. уменьшить необходимое усилие

10. увеличить пластичность металла

11. воздушные или паровые молоты

12. сила и скорость штампования

13. внутри стенок двух штампов

14. отделочная обработка

15. малые допуски

Exercise 2.4. Translate into English:

1. При волочении проволоки диаметр отверстия волочильной доски каждый раз уменьшается.

2. Штамповка листового металла включает в себя ковку, изгиб и обрезку.

3. Небольшая деформация листа при растяжении помогает сохранить новую форму детали.

4. Изменение формы при штамповке производится путем сжатия между двумя штампами.

5. Края листа при штамповке отрезаются для получения конечных размеров.

6. При проковке деталь должна быть горячей для уменьшения необходимых усилий и увеличения пластичности металла.

7. После ковки в закрытых штампах детали не требуют большой механической обработки.

8. При чеканке деформация металла невелика и отпечаток формируется на поверхности металла.

9. Высадка используется для изготовления головок гвоздей и болтов.

Text C: «METALWORKING AND METAL PROPETIES»

An important feature of hot working is that it provides the improvement of mechanical properties of metals. Hot-working (hot-rolling or hot-forging) eliminates porosity, directionality, and segregation that are usually present in metals. Hot-worked products have better ductility and toughness than the unworked casting. During the forging of a bar, the grains of the metal become greatly elongated in the direction of flow. As a result, the toughness of the metal is greatly improved in this direction and weakened in directions transverse to the flow. Good forging makes the flow lines in the finished part oriented so as to lie in the direction of maximum stress when the part is placed in service.

The ability of a metal to resist thinning and fracture during cold-working operations plays an important role in alloy selection. In operations that involve stretching, the best alloys are those which grow stronger with strain (are strain hardening) — for example, the copper-zinc alloy, brass, used for cartridges and the aluminum-magnesium alloys in beverage cans, which exhibit greater strain hardening.

Fracture of the workpiece during forming can result from inner flaws in the metal. These flaws often consist of nonmetallic inclusions such as oxides or sulfides that are trapped in the metal during refining. Such inclusions can be avoided by proper manufacturing procedures.

The ability of different metals to undergo strain varies. The change of the shape after one forming operation is often limited by the tensile ductility of the metal. Metals such as copper and aluminum are more ductile in such operations than other metals.

Date: 2015-12-13; view: 453; Нарушение авторских прав