Free forging is a metalworking process where metal is deformed freely between an upper and lower die under the application of impact or pressure to achieve the desired shape, size, and mechanical properties. Compared to castings, free forgings eliminate defects such as shrinkage cavities, porosity, and gas pockets, providing superior mechanical properties. Free forging tools and equipment are simple, versatile, and low-cost, making the process especially suitable for single-piece and small-batch production.
Basic Overview of Free Forging
Free forging utilizes hammers or presses (mostly hydraulic presses) to control the shape and size of the forged product. Despite the simplicity and versatility of the equipment, free forging typically involves low precision, large machining allowances, high labor intensity, and low productivity. Therefore, it is primarily used for single-piece or small-batch production. Free forging can be divided into two methods: manual free forging and machine free forging. Manual free forging, due to its low efficiency and high labor intensity, is mainly used for repairs or the production of small, low-batch forged parts. Machine free forging, on the other hand, has become dominant in modern industrial production, especially playing a significant role in heavy machinery manufacturing.
Types of Free Forging Equipment
Free forging equipment is mainly classified into two categories: hammers and hydraulic presses.
Hammers: Hammers are used for metalworking through rapid impact. Common types include air hammers and steam air hammers. Some small factories may also use simple tools like spring hammers and anvil hammers.
Hydraulic Presses: Hydraulic presses use liquid to generate static pressure to deform metal, making them essential for producing large forged parts, especially for heavy-tonnage forgings.
Basic Process Flow of Free Forging
Free forging generally includes a series of interconnected steps that ensure the final product meets dimensional and performance requirements. The common processes in free forging include:
Ingot Blooming: The steel ingot is forged into a bloom, aimed at removing defects like shrinkage cavities and segregation by pressing the edges, rounding corners, and cutting it to the required length.
Lengthening: By repeated compression, the billet's cross-sectional area decreases while its length increases. This is commonly used for producing shafts, rods, and similar items.
Upsetting: The process increases the billet's cross-section while reducing its height, typically used for producing discs, flanges, and similar plate-like forgings, or preparing for subsequent processes such as punching.
Punching: Punching a hole in the billet, either through or blind, is used for producing forgings with holes or preparing for subsequent drilling.
Drilling: Expanding the internal and external diameters of hollow billets, typically used for producing thin-walled forgings.
Core Rod Lengthening: This process reduces the billet's outer diameter while increasing its length, commonly used for producing cylindrical forgings like cylinders and vessels.
Bending and Twisting: Used to bend the billet into a curve or at a certain angle, or twist part of the billet around its axis. This is commonly used for producing hooks, forks, and other bent shape forgings.
Compression: To prevent tensile stress at the center of the steel ingot, compression is used to densify the center, welding internal pores and loose areas together.
Applications of Loose Tooling Forging
Loose tooling forging combines free forging and die forging techniques. By using movable molds for localized die forging, it can achieve more precise forging shapes and sizes. Loose tooling forging is suitable for medium and small-batch production and is characterized by high process flexibility and low costs. Common types of dies include drop dies, closed dies, bending dies, and sleeve dies.
Compared to traditional free forging, die forging not only improves productivity but also reduces material consumption and subsequent machining. Although die forging still faces lower productivity than die forging due to the complexity of the forged shapes, it provides an effective solution for small-batch production.
Application Fields of Free Forging
Free forging is primarily used in the production of heavy machinery and large forgings, holding an important position in the following industries:
Metallurgical Machinery: Free forging is used to produce high-strength, large-sized components for metallurgical equipment, such as large shafts and gears.
Power Machinery: In the production of diesel engines, steam turbines, and similar equipment, free forging is used to manufacture critical parts like crankshafts and rotors.
Mining Machinery: Free forging is used to produce key components for mining equipment, such as drill bits and gears.
Shipbuilding: Used for manufacturing major structural components and parts for ships.
Locomotive Manufacturing: Free forging has wide applications in locomotive and railway equipment manufacturing, mainly for producing wheel sets, bogies, and other parts.
In these industries, free forging serves as a mature processing method, capable of delivering high-quality, reliable forgings that meet the demands of large-scale production and specialized applications.
Challenges in Free Forging
Despite its crucial role in many industries, free forging still faces challenges such as low productivity, low precision, and high labor intensity. With technological advancements, automated equipment and more efficient processing methods are gradually replacing traditional free forging techniques. Nevertheless, free forging remains irreplaceable in some special applications, especially in the production of heavy and large-sized forgings, where it continues to hold significant importance.
Conclusion
Free forging is a long-established and vital metalworking technique used across a wide range of industries, including aerospace, energy, metallurgy, and mechanical manufacturing. While it does face limitations in terms of productivity and precision, it continues to play an irreplaceable role in various fields through a combination of manual and machine forging, along with innovative process improvements. As technology advances, free forging is expected to continue evolving towards higher efficiency and precision, meeting the ever-growing demands of modern industry.
