Hot Forging Guide

What is Hot Forging?

Hot forging is a metal shaping process consisting of several stages such as heating, hammering, upsetting, pressing, and more. The workpiece is heated to about three-quarters of its melting point to reach high formability. As the workpiece softens, the hot press machine forges it into a particular shape. The process is called hot forging because it is performed under high temperatures; as opposed to cold forging, which is performed under room (ambient) temperature.

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. Read on and we will break down the exact process for you.
 

Process Explained

During a hot forging process, the temperature is above the recrystallization point of the resulting metal. Being a process in which metals are plastically deformed above their recrystallization temperature, a high temperature is required to avoid work 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 process. This temperature is maintained by heating the die. It will be at a temperature slightly lower than the elevated temperature of the workpiece. The forces exerted by this die form the workpiece. Since the die also has an elevated temperature, cooling off the workpiece between the molds is eliminated. This in turn results in improved flow characteristics and mechanical properties of the workpiece.
 

Advantages

One of the advantages of hot forging is the process produces the most diverse shapes compared to the cold-forged or warm forged products. And since dies are not very expensive to produce, it is very well suited to small batches and shaped parts. Other processes 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 using the hot forging press. 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, which further preserves the quality of the hot-forged parts.
 

Applications

The hot forging method is mainly used to manufacture parts for vehicles 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 and 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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