Forging is a method that uses forging machines to apply pressure to metal billets to produce plastic deformation to obtain forgings with certain materials, certain shapes and sizes, is one of two the importance of forging (forging and stamping). By forging can eliminate defects such as cast looseness created by the metal in the melting process, optimize the microstructure, while the strength of forgings is generally better than castings of the same fabric due to the preservation of all metal flow lines. Other machinery in the high load, working conditions of the main parts, in addition to the simple shape of the rolled plate, profile or welded parts, many forgings.
The initial recrystallization temperature of steel is about 727 ° C, but 800 ° C is usually used as a dividing line, above 800 ° C is hot forging; between 300 and 800 °C is called hot forging or semi-hot forging, forging at room temperature is called cold forging. 
Forgings used in most industries are hot forging, hot forging and cold forging are only used in the forged of parts for vehicles and general machinery
As mentioned above, according to the forging temperature, it can be divided into hot forging, hot forging and cold forging.
According to the production process, forging can be divided into free forging, die forging, lap ring and special forging. 
Three Gorges boat load nut column empty
Three Gorges boat lift olive column empty
1, Free forging. Regarding the use of simple tools, or in the forging tools of the upper and lower metal directly on the application to the external force, so that the billet deformation and obtain the desired geometry and side in quality of process forgings. . The forgings produced by the free forging method are called free forgings. Free forging is used only to produce forgings in small batches, using forging hammers, hydraulic presses and other forging equipment to produce the billets and obtain the necessary forgings. The basic process of forging includes fretting, drawing, punching, cutting, bending, twisting, misalignment and forging. The free forging takes place in hot forging mode. 
2. Divine forging. Die forging is also divided into open forging and closed forging. Iron billet in a certain quality of the forging die chamber high deformation and obtain forgings, die forging is mainly used for the production of heavy weight, a large set of parts.
Die forging can be divided into hot forging, hot forging and cold forging. Hot forging and cold forging are the future development of die forging, but also represent the level of forging technology.
According to the details of the material, forging can be divided into ferrous metal forging, non-ferrous metal forging and powder production. As the name implies, the materials are ferrous metals such as carbon steel, non-ferrous metals such as copper and aluminum and powder metallurgy materials respectively.
Extrusion should be classified as die forging, which can be divided into heavy metal extrusion and light metal extrusion.
Closed forging and closed stress are the two best methods of forging, which have a higher use of material due to the absence of flying edges. It is possible to complete the forging process in one process or several processes. Since there is no plane, the strength of the forging is reduced and the required capacity is reduced. However, care should be taken not to make the billet too limited, the volume of the billet should be strictly controlled, the relative position of the doll should be controlled and the forging should be measured, and should be done to reduce the action. carried on the doll.
3. Ring plating. Ring lapping refers to the production of rings of different diameters by using special equipment ring lapping machines, which are also used to produce wheels such as car and train tires. 
4, special forging. Special forging includes roll forging, wedge cross-rolling, radial forging, liquid die forging and other forging methods , which are more suitable for the production of certain special-shaped parts. 
For example, roll forging can be used as an effective pre-forming process to significantly reduce the subsequent forming pressure; wedge cross-rolling can produce parts such as steel balls and drive shafts; and radial forging can produce large barrels, step shafts, and other forgings. 
China’s first 400MN (40,000 tons) heavy aviation die forging hydraulic press
China’s first 400MN (40,000 tons) heavy-duty aerospace die forging hydraulic press
According to the movement of the forging die, forging can be divided into pendulum rolling, pendulum swivel forging, roll forging, wedge cross-rolling, ring rolling and inclined rolling. Pendulum rolling, pendulum swivel forging and ring rolling can also be processed by fine forging. In order to improve the utilization of material, roll forging and cross rolling can be used as the pre-processing of slender materials. Like free forging, rotary forging is also partial forming, which has the advantage of being formed with less forging force compared to the forging size. In this forging method, including free forging, the material expands from near the die surface to the free surface during processing, therefore, it is difficult to guarantee the accuracy. Therefore, the direction of the forging die movement and the rotary forging process are controlled by computer, so that products with complex shapes and high accuracy can be obtained with lower forging forces, for example, the production of forgings such as turbine blades with many varieties and large sizes.
Forging equipment die movement and degrees of freedom are inconsistent, according to the lower dead center deformation restriction characteristics, forging equipment can be divided into the following four forms.
1、Limiting forging force form: hydraulic press with direct drive of slider by hydraulic pressure.
2、Quasi-stroke limiting mode: hydraulic presses that drive crank linkage mechanism.
3、Stroke limiting mode: mechanical press with crank, linkage and wedge mechanism driving the ram.
Heavy-duty aerospace die-forging hydraulic press for hot test
Heavy-duty aero-die forging hydraulic press for hot test
4、Energy limiting method: screw and friction presses using screw mechanism.
In order to obtain high accuracy care should be taken to prevent overload at the lower dead center, control the speed and die position. Because these will have an impact on forging tolerances, shape accuracy and dolly life. In addition, in order to maintain accuracy, attention should be paid to measures such as adjusting the slide guide clearance, ensuring stiffness, adjusting the lower dead point and utilizing a subsidized drive.
Forging materials are only carbon and alloy steels of various compositions, followed by aluminum, magnesium, copper, titanium, etc. and their alloys. The first state of the product is bar, ingot, metal powder and liquid metal. The ratio of the cross-sectional area of the metal before deformation to the cross-sectional area after deformation is called the forging ratio. The correct selection of forging ratio, appropriate temperature and holding time, appropriate initial forging temperature and final forging temperature, appropriate deformation and deformation speed are very important to improve product quality and reduce cost.
Generally, small and medium forgings are made from round or square bars as billets. The organization code and the property of the bar are good and good, the shape and size are correct, the quality of the place is good, and it is easy to prepare large items. As long as the heat and deformation conditions are properly controlled, forgings with excellent performance can be forged without forging large deformation.
Ingots are used only for large forgings. An ingot is a cast organization, with a large columnar crystal and loose space. Therefore, through large plastic deformation, the cracks must be broken into fine grains and sparsely compacted to obtain good metal organization and mechanical properties.
The powder metallurgy preform billets are pressed and sintered, and powder forgings can be made in the hot state by die forging without flying edges. Powder forging is close to the speed of die casting, with good quality and high precision, which can reduce the subsequent cutting process. Powder forgings have a uniform organization, no separation, and can be used to produce small glasses and other accessories. However, the cost of the powder is more than the cost of general equipment, and the application in production is somewhat limited.
By applying static pressure to the liquid metal poured into the casting chamber and making it solidify, crystallize, flow, deform plastically and form under pressure, the die forged part of the desired shape and products can be obtained. Liquid metal die forging is a die and die forging production process, especially suitable for complex thin-walled parts that are difficult to produce by general die forging.
Forging materials other than traditional materials, such as various carbon steel and metal alloy, followed by aluminum, magnesium, copper, titanium and other alloys, metal-based high-temperature alloys, nickel-based high-temperature alloys, cobalt. -such as high-temperature alloys of the deformation of the alloy can also be used forging or rolling to finish, but the alloys because of its plastic area is narrow, so the forging will be more difficult, the heat of different materials, open forging gold. and the final forged gold All have very strict rules.