Hot forging is a metal shaping process consisting of several stages such as hammering, upsetting, pressing, and so on, where the workpiece is heated to about three-quarters of its melting point, machine a ductile metal component known as a billet or workpiece, to a particular shape. At the beginning of this procedure, you have a cast ingot that is heated to the desired shape and scale at a plastic deformation temperature and then forged into a die. The cast coarse grain structure is broken down during this forging process and substituted with a finer grain, which is done by grinding the ingot. Usually, the product is subjected to extra heat treatment after hot welding.
During hot forging processes, the temperature is above the recrystallization point of the resulting metal. Being a process in which metals are plastically deformed above their recrystallization temperature, these high temperatures are required to avoid hardening during deformation. This process usually involves heating the metal, after which it is pushed into a die - depending on the requirements, this die can also be heated. Because the metal is hot, it 'moves' easily and allows manufacturers to create more elaborate shapes than cold forging.
In the case of special alloys, processes such as isothermal forging,where deformation takes place in a controlled atmosphere,are used to avoid oxidation. Isothermal forging, also known as hot forging, is a hot working process in which the workpiece is kept at a maximum elevated temperature throughout the forming process. This temperature is maintained by heating the die - it will be a temperature or slightly lower than the elevated temperature of the workpiece. The forces exerted by this dying form the workpiece, and since the die also has an elevated temperature, cooling of the workpiece between the mold interface is eliminated. This in turn results in improved flow characteristics of the workpiece.
The hot forging process produces the most diverse shapes compared to other forging processes, and since dies are not very expensive to produce, it is very well suited to small batches and shaped parts. Other processes (hot and cold forging) are intended for high-volume production, for example, automotive parts, and fasteners, with simpler geometries, for which extremely complex dies can be designed and cushioned on a large number of parts produced.
Hot forging provides good ductility and the ability to produce custom parts. You also get excellent surface quality and high deformation rates. The reduced yield point and thus less energy required for hot forging should also not be underestimated. Finally, the chemical heterogeneity of the castings is reduced due to the increased diffusion.
Steel forging is mainly used for forging in the automotive industry. Formable aluminum alloys are increasing in number due to increasing demands for lightweight structures; the use of magnesium is rare. In the volume segment, elements are forged mainly in small and medium series in the closed die forging process. This enables the use of most high-strength, high-performance auto parts.
Recrystallization accompanying high temperatures and increased deformability allows for precise matching of the very fine-grained microstructure. Combinations of strength and durability can be defined more than any other forming process, qualifying hot forging as the manufacturing process in all cases where high operational loads place special demands on the component. Generally, such items are referred to as "Safety-Critical Parts". As a result, the automotive and aerospace sectors are the most important buyer markets for hot forgings.
In the aerospace sector, in addition to steel forgings, special high-strength and temperature-resistant materials such as nickel and titanium alloys are used, as well as lightweight construction materials such as forged aluminum and magnesium alloys. Hot forging is not limited to automotive and aerospace applications. There are other important application areas such as construction, mechanical engineering, agriculture, steel structures, and more.
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