金属锻造专业英语论文.docxVIP

Forging of Metals Introduction Forging is an important hot-forming process. It is used in producing components of all shapes and sizes, from quite small items to large units weighing several tons. Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force. Hand forging tools comprise variously shaped hammers. The base on which the work is supported during forging is the anvil. For the semimechanized forging of small to medium-sized components, forging hammers powered by various means are employed. The feature common to all of them is that, like the hand forging hammer, they utilize the energy of a falling weight to develop the pressure needed for shaping the metal. Larger components are forged by means of forging presses operated by steam or compressed air or by hydraulic or electric power. Largely automatic forging machines are used for the quantity production of engineering parts. A distinction may be made between open-die forging, usually in the form of hammer forging, and closed-die forging. In hammer forging, the component is shaped by hammer blows aided by relatively simple tools. These may include open dies i.e., dies that do not completely enclose the metal to be shaped. One of the basic operations of hammer forging is the elongation of a piece of metal by stretching with hammer blows, causing it to become thinner and longer. In hand forging the work-piece is usually turned 90°after each blow, in order to forge it thoroughly and prevent its lateral expansion. The opposite of elongation is upsetting, which produces compressive shortening. For example, the diameter of a bar can be increased by heating and hammering axially. More important is closed-die forging, very widely used for mass production in industry, in which the metal is shaped by pressing between a pair of forging dies. The upper die is usually attached to the ram of a forging press or a forging hammer, while the lower die is station