Forging is manufacturing process where metal is pressed, pounded or squeezed under great pressure into high strength parts known as forgings. The process is normally (but not always) performed hot by preheating the metal to a desired temperature before it is worked. It is important to note that the forging process is entirely different from the casting (or foundry) process, as metal used to make forged parts is never melted and poured (as in the casting process).
Today, the advantages of forged parts assume greater importance as operating temperatures, loads, and stresses increase. Forged parts make possible designs that accommodate the highest loads and stresses. Recent advances in forging technology have greatly increased the range of properties available in forgings.
Economically, forged products are attractive because of their inherent superior reliability, improved tolerance capabilities, and the higher efficiency with which forgings can be machined and further processed by automated methods.
Ecologically, forgings are attractive because they are recyclable. The degree of structural reliability achieved in a forging is unexcelled by any other metalworking process. There are no internal gas pockets or voids that could cause unexpected failure under stress or impact. Often, the forging process assists in improving chemical segregation of the forging stock by moving centreline material to various locations throughout the forging.
To the designer, the structural integrity of forgings means safety factors based on material that will respond predictably to its environment without costly special processing to correct for internal defects.
To the production employee, the structural reliability of forgings means reduced inspection requirements, uniform response to heat treatment, and consistent machinability, all contributing to faster production rates and lower costs.
Designers and materials engineers are recognising the increasing importance of resistance to impact and fatigue as a portion of total component reliability. With the use of proper materials and heat treatments, if required, improved impact strength of forged parts is achievable.
The resulting higher strength-to-weight ratio can be used to reduce section thickness in part designs without jeopardizing performance characteristics of safety. Weight reduction, even in parts produced from less expensive materials, can amount to a considerable cost savings over the life of a product run.
The consistency of material from one forging to the next, and between separate quantities of forgings is extremely high. Forged parts are made through a controlled sequence of production steps rather than random flow of material into the desired shape. Uniformity of composition and structure piece-to-piece, lot-to-lot, assure reproducible response to heat treatment, minimum variation in machinability, and consistent property levels of finished parts.
Dimensional characteristics are remarkably stable. Successive forgings are produced from the same die impression, and because die impressions exert control over all contours of the forged part, the possibility of transfer distortion is eliminated.
The forging process can create parts that are stronger than those manufactured by any other metalworking process. This is why forgings are almost always used where reliability and human safety are critical. But you'll rarely see forgings, as they are normally component parts contained inside assembled items such a airplanes, automobiles, tractors, ships, oil drilling equipment, engines, missiles and all kinds of capital equipment, to name a few.
Forgings are produced economically in an extremely broad range of sizes. With the increased use of special punching, piercing, shearing, trimming, and coining operations, there have been substantial increases in the range of economical forging shapes and the feasibility of improved precision. However, parts with small holes, internal passages, re-entrant pockets, and severe draft limitations usually require more elaborate forging tooling and more complex processing, and are therefore usually more economical in larger sizes.
Forgings are failure-safe and reliable components due to their favourable material properties, the high repeatability of the process during their production, as well as the good testing possibilities. They are implemented anywhere where reliability and service life at high power density or high stresses play an important role.
The main applications are as follows: