The temperature of forging determines its classification as hot, warm, or cold. The intended product characteristics and production cost optimization, taking into consideration batch size, determine hot forging, the oldest manufacturing process. The choice between hot forging and other processes is not determined by quality. Forging enhances the grain structure of the used materials, mostly metals, and alloys, hence enhancing the mechanical characteristics of the component and increasing its strength. Advanced hammers and presses are used to manipulate the material into a desired form.
What is the process of hot forging?
The hot forging manufacturing process is conducted at temperatures that do not compromise the metallurgical properties of the specific alloy. For steel, this temperature may reach up to 1250°C, for Al-Alloys it ranges from 300 to 460°C, for titanium alloys it ranges from 750 to 1040°C, and for Cu-Alloys it ranges from 700 to 800°C.
Manufacturing using the process of hot forging
Recrystallization and deformation occur concurrently, hence preventing strain hardening. To provide optimal outcomes, it is essential to keep the forging temperature consistently above a specified minimum, which varies depending on the alloy being used. This condition also prevents the potential for lack of forgeability, which may result in the formation of fractures due to a significant reduction in ductility at lower temperatures. The forging sequence is thereafter constrained in duration to adhere to these temperature restrictions.
If the forging process is not done when the lower limit is reached, it is necessary to reheat if feasible, or otherwise, the component should be regarded as forged and completed using alternative methods. The temperature range necessary for the hot forging process is crucial, as it ensures that all toolings are heated to minimize any temperature loss of the component during the forging stage. This has resulted in the development of a very precise and specialized procedure for closed die forging known as "isothermal forging".
During isothermal forging carried out by the steel forging manufacturers, the tools, specifically the dies, are maintained at the necessary forging temperature. However, the application of this principle varies significantly depending on the material type and the specific forging temperature. The material grade used for the dies must successfully retain the high mechanical characteristics necessary to deform the component material at the forging temperature.
Some examples of isothermal forging implemented on various materials:
● Aluminum forging necessitates the use of die grades that can withstand the essential mechanical qualities since aluminum has a rapid cooling rate and a relatively low forging temperature.
● Copper and titanium alloys may achieve the desired result provided a high-quality (and costly) grade is used for the dies
● Steel alloys have significant challenges in withstanding the forging stress at a temperature of 1250 °C, with only a limited number of materials, such as pure molybdenum, being able to endure such conditions.
Thus, isothermal forging is atypical for titanium alloys and highly restricted to steel and nickel-based alloys, namely those used for manufacturing the most challenging turbine disks in jet engines. Some forging manufacturers in India offer a top-notch isothermal forging technique specifically designed for aluminum alloys.
To mitigate gas contamination, such as the presence of O2, H2, or even N2, that may occur during the hot forging process, it is feasible to safeguard the component by using glass coating or implementing a controlled environment, namely an inert gas, inside the heating furnace, induction heater, and even the press laboratory.
The process of hot forging involves subjecting a forged metal ingot or a cast metal piece to compression in specialized dies. This compression results in the breakdown of the grain structure and the creation of smaller grains, which enhances the material's yield strength and ductility. Due to the high temperature of the metal, it undergoes deformation more readily, enabling steel forging manufacturers to fabricate intricate geometries that are not achievable with cold forging.
Plastic deformation of the metal above its recrystallization temperature enables it to maintain its distorted shape throughout the cooling process. Following the shaping process, it is crucial to cool the hot forged pieces properly, since too rapid cooling might lead to deformation.
Advantages of Hot Forging
The hot forging technique yields a wide range of forms, surpassing other forging methods. Additionally, the production of dies for this process is quite inexpensive, making it highly suitable for short production runs and intricate components. Other manufacturing methods, such as hot and cold forging, are specifically intended for high-volume production in industries like automobile and fastener manufacturing. These methods are suitable for components with simpler shapes, allowing for the construction of highly intricate dies that may be cost-effective when used to make a large number of parts.
Some salient advantages include the following:
● Excellent malleability
● The capability to produce tailor-made components
● Exceptional surface quality
● High ratios of formability
● The yield strength is reduced, resulting in a decrease in the amount of energy used
● Enhanced dispersion results in less chemical heterogeneity.
Some of the best materials for hot forging
The forging manufacturers in India and around the globe can use hot forging to fabricate a broad spectrum of parts, making use of even the most ferrous and non-ferrous metal alloys as:
● Molybdenum alloys
● Nickel/cobalt alloys
● Structural steels
● Stainless steels
● Titanium alloys
● Aluminum and magnesium wrought alloys
● Free-cutting steels
The majority of steel alloys are typically hot forged due to the increasing difficulty of deformation as work hardening progresses on hard materials. Moreover, it is much more economically advantageous to use hot forging techniques on metals like steel, followed by a heat treatment process.
Concluding Remarks
Hot-forged products are often used in the automotive, agricultural, aerospace, and construction industries where strength and endurance are essential. Caparo as one of the leading steel forging manufacturers in India has expertise in a wide range of forging methods and offers comprehensive component development services for hot, warm, and cold forging processes. The company’s research & development team has extensive metallurgical expertise to precisely modify all necessary parameters, ensuring its clients get a faultless design and execution of the complete process.