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 therequired force andincrease the metal's plas­ticity.

Open-die forging is usually done byhammering 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 metalwithinthe walls of two dies that come together toenclose the workpiece on all sides. The process starts with arod or bar cut to the length needed to fill the die. Since large, complex shapes and large strains areinvolved, several dies may be used to go from the initial bar to the final shape. With closed dies, parts can be made to closetoler­ances so that little finish machining is required.

Two closed-die forging operations are given special names. They areupsetting andcoining. Coining takes its name from the final stage of forming metal coins, where the desiredimprint 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,clampingthe rod, and thenhitting the exposed length with a die to form the head of anail 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 — ковкав 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 importantfeature of hot working is that itpro­vides theimprovement of mechanicalproperties of met­als . Hot-working (hot-rolling or hot-forging)eliminates porosity, directionality, andsegregation that are usu­ally present in metals. Hot-worked products have better ductility and toughness than the unworkedcasting. Dur­ing the forging of a bar, the grains of the metal become greatlyelongated in the direction of flow. As a result, the toughness of the metal is greatly improved in this direction andweakened in directionstransverse to the flow. Good forging makes the flow lines in thefinishedpart 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 frominner flaws in the metal. These flaws often con­sist of nonmetallicinclusions such as oxides or sulfides that aretrapped in the metal duringrefining. Such in­clusions can beavoided by proper manufacturing pro­cedures.

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