Forging is a processing method that uses forging machinery to pressure the metal blanks, which obtains certain mechanical properties, certain shape and size of forgings by the plastic deformation of the metal blanks. It is also one of the two major components of forging (forging and stamping). Forging can eliminate defects like loose as cast condition that produced in the smelting process of metal and optimize the microstructure. At the same time, the mechanical properties of forgings are generally better than the same material castings because of the preservation of a complete metal flow line. Most of the important parts with high load and severe working conditions in the related machinery use forgings except some simple shape parts can use rolling plate, profiles or welding parts.
The starting recrystallization temperature of steel is about 727 ℃. However, 800℃ is widely used as the dividing line: the hot forging is higher than 800 ℃; the forging between 300 to 800℃ is called warm forging or semi hot forging; and the forging at room temperature is called cold forging. Forgings that used in most industries are hot forging while warm forging and cold forging are mainly used for forging of parts such as automobiles and general machinery. Warm forging and cold forging can be effective.
As mentioned above, forging can be divided into hot forging, warm forging and cold forging according to the forging temperature.
According to the forming mechanism, forging can be divided into free forging, die forging, ring rolling and special forging.
1. Free forging refers to the processing methods that use simple, general tools, or directly exert forces to the blank between the upper and lower anvil iron in the forging equipment in order to obtain the required geometrical shape and internal quality of forgings from the deformation of the billet. Forgings produced by free forging method are known as the free forging parts. Free forgings are mainly a small batch production of forgings, which use forged equipment like forging hammers, hydraulic presses and so on to have forming processing on the billet and obtain qualified forgings. The basic working procedure of free forging includes upsetting, pulling, punching, cutting, bending, torsion, dislocation shifting and forging. Hot forging is adopted in free forging.
2. Die forging. Die forging is divided into open die forging and closed die forging. Metal blanks are compressed and deformed in a certain shape of the forging die to obtain forgings. Die forging is generally used in producing small weight and large batch of parts. Die forging can be divided into hot forging, warm forging and cold forging. Warm forging and cold forging are the future development direction of die forging, which also represent the level of forging technology. Forge services
play an essential role in the future development of forging.
According to the material, die forging can also be divided into ferrous metal die forging, non-ferrous metal die forging and powder products forming. As the name suggests, the material is individually ferrous metals like carbon and steel, non-ferrous metal like copper and aluminum, and powder metallurgy materials.
Extrusion should be attributed to die forging, which can be divided into heavy metal extrusion and light metal extrusion.
Closed die forging and closed upsetting are two kinds of advanced technology of die forging. The utilization rate of material is high because there is no burr. The finishing of complex forgings may be accomplished with only a process or several processes. Because there is no burr, the force area of forgings and the required load reduce. However, it should be noted that the blank can not be completely restricted. So, we should strictly control the volume of the billet, the relative position of the forging die and the measurement of forgings, and strive to reduce the wear of forging die.
3. Ring rolling . Ring rolling refers to the ring-shaped parts with different diameters that is produced through a dedicated equipment mill, and it is also used to the production of wheel parts such as automobile wheels and train wheels.
4. Special forging. Special forging includes forging methods like roll forging, cross wedge rolling, radial forging and liquid die forging. These methods are suitable for the production of some certain special shape parts. For example, roll forging can be used as an effective preforming process, which significantly reduces the subsequent forming pressure; cross wedge rolling can produce parts like steel ball and shaft; and radial forging can produce forgeable piece like large barrel and step shaft.
Compared with castings, the microstructure and mechanical properties of metal can be improved after forging. After the hot working forging process, the casting organization deforms, and the original coarse dendrite and columnar grains turn into the equiaxed recrystallization with thinner grains and uniform size because of the deformation and recrystallization of the metal. It can compact and weld the original segregation, porosity, porosity and slag of the steel ingot. In this way, the organization becomes closer. It can also improve the plasticity and mechanical properties of the metal.
The mechanical properties of castings are lower than those of the same material forgeable pieces. In addition, the forging process can guarantee the continuity of the metal fibrous tissue and make the fibrous tissue of the forgings consistent with the shape of the forgings. The complete flow line of metal can guarantee the parts have good mechanical properties and long service life. The forgeable pieces which are produced by processes like precision die forging, cold extrusion and warm extrusion, can not be compared with castings.
Forgings are objects in which metals are pressured to shape required shapes or suitable compression forces through plastic deformation. This power is typically achieved by using a hammer or pressure. The forging process builds a refined particle structure and improves the physical properties of the metal. In the actual use of parts, a correct design can make the particle flow in the direction of the main pressure. Castings are the metal forming objects obtained by various casting methods. It is the object with a certain shape, size and performance, which is obtained by pouring, pressing, inhaling or other casting methods to inject the smelted liquid metal into a prepared mold and after cooling through sand removal, cleaning and reprocessing.