As a major metal fabrication, forging is a metal forming technique that uses localized forces of compression. Forgings have undergone major changes that lead to more efficient, faster and more durable processes. Today’s forging is usually done using electric, hydraulic or compressed air driven forging presses or hammer tools.
Hot forging involves heating a workpiece to about 75% of its melting temperature. This reduces the yield stress and energy required to form the metal, effectively increasing the production rate (or strain rate). Hot forging helps make the metal easier to form and less likely to break.
Iron and its alloys are almost always hot forged for two main reasons..
While other materials must be strengthened by the forging process itself, materials such as most titanium and aluminum alloys can be hot forged and then hardened.
Average temperatures for hot forging includes..
In hot forging, the temperature is above the recrystallization point of the metal formed. Because it is a process in which metals are plastically deformed above their recrystallization temperature, these high temperatures are necessary to prevent strain hardening during the deformation.
In this process, the metal is usually heated (above its recrystallization point) after which it is struck into a die - depending on requirements, this die may also be heated. Because the metal is hot, it "moves" easily and manufacturers can make more elaborate shapes than in cold forging.
For superalloys (which have low malleability), processes such as isothermal forging - where deformation takes place in a controlled atmosphere - are used to prevent oxidation.
Isothermal forging, also known as hot die forging, is a hot working process in which the workpiece is maintained at its maximum elevated temperature throughout the forming process.
This temperature is maintained by heating the die - it will be at the temperature of, or slightly below, the elevated temperature of the workpiece. The forces exerted by this die shape the workpiece and, because the die is also at an elevated temperature, cooling of the workpiece between the die-work interface is eliminated. This, in turn, results in an improvement in the flow properties of the metal (workpiece).
It should be noted that isothermal forging can also be performed in vacuum.
Hot forging dies
The dies used in hot forging undergo heavy thermal cycling and mechanical stress. This in turn affects the life of the die, as the die is open to..
Depending on the type of forging operation, the material and the size of the part being formed, to name but a few, forging dies must have the following properties and characteristics..
The Benefits of Hot Forging
Hot forging, which is often used for the types of parts that affect engineering applications, is also a recommended process for deforming metals with a high deformation ratio.
The advantages of hot forging includes..
The Disadvantages of Hot Forging