Forging has a long history in China, which has been continued by the way of manual workshop production. Probably at the beginning of the 20th century. It gradually appeared in the railway, military, shipbuilding and other industries in the way of mechanical industrialization. The main sign of this transformation is the use of machines with strong forging ability.
Fig. 1 Forging
Forging is widely used in automobile manufacturing. With the progress of science and technology, the requirements for workpiece accuracy are constantly improved, and precision forging technology, which has the advantages of high efficiency, low cost, low energy consumption and high quality, is more and more widely used. According to the different deformation temperatures during metal plastic forming, precision cold forging can be divided into cold forging forming, temperature forming, sub hot forging forming, hot precision forging forming, etc. The automobile parts produced include: automobile clutch engagement ring, input shaft parts of automobile transmission, bearing ring, sliding sleeve series of automobile constant velocity universal joint, automobile differential gear, automobile front axle, etc.
Fig. 2 Common Automobile Forgings
1、 Definition and classification of forging
1. Definition of forging
Forging is a processing method that uses forging machinery to exert pressure on metal blank to make it produce plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes. Forging (forging and stamping) is one of the two major components.
Forging can eliminate as cast porosity and other defects produced in the smelting process of metal, optimize the microstructure. At the same time, due to the preservation of complete metal streamline, the mechanical properties of forgings are generally superior to castings of the same material. For important parts with high load and severe working conditions in related machinery, forgings are mostly used, except for simple rolled plates, profiles or weldments.
2. Classification of forging
According to different production tools, forging technology can be divided into free forging, module forging, roller ring forging and special forging.
Free forging: refers to the processing method of forging which uses simple universal tools or directly exerts external force on the blank between the upper and lower anvils of forging equipment to deform the blank and obtain the required geometric shape and internal quality.
Die forging: refers to the forging obtained by the compression deformation of the metal blank in the forging die chamber with a certain shape. 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, and also represent the level of forging technology.
Grinding ring: It refers to the ring parts with different diameters produced by special equipment grinding ring machine, and also used to produce wheel shaped parts such as car hubs and train wheels.
Special forging: including roll forging, cross wedge rolling, radial forging, liquid die forging and other forging methods, which are more suitable for the production of parts with special shapes. For example, roll forging can be used as an effective pre forming process to greatly reduce the subsequent forming pressure; Cross wedge rolling can produce steel ball, transmission shaft and other parts; Radial forging can produce large gun barrel, step shaft and other forgings.
According to forging temperature, forging technology can be divided into hot forging, warm forging and cold forging.
The initial recrystallization temperature of steel is about 727 ℃, but 800 ℃ is generally used as the dividing line, and hot forging is used above 800 ℃; It is called warm forging or semi hot forging at 300~800 ℃, and cold forging at room temperature. Forgings used in most industries are hot forging. Warm forging and cold forging are mainly used for forging parts such as automobiles and general machinery. Warm forging and cold forging can effectively save materials.
According to the motion mode of forging die, forging can be divided into rotary forging, rotary forging, roll forging, cross wedge rolling, ring rolling and cross rolling.
3. Forging materials
Forging materials are mainly carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, copper, titanium and their alloys, iron base superalloys, nickel base superalloys, and cobalt base superalloys. Deformed alloys are also forged or rolled. However, due to their relatively narrow plastic zones, these alloys are relatively difficult to forge. There are strict requirements for the heating temperature, opening and final forging temperatures of different materials.
The original state of materials includes bar stock, ingot, metal powder and liquid metal. The ratio of cross sectional area of metal before deformation to that after deformation is called forging ratio.
The correct selection of forging ratio, reasonable heating temperature and holding time, reasonable initial and final forging temperature, reasonable deformation amount and deformation speed have a great relationship to improve product quality and reduce cost.
2、 Common forging methods and their advantages and disadvantages
1. Free forging
Free forging refers to the processing method of forging which uses simple universal tools or directly exerts external force on the blank between the upper and lower anvils of forging equipment to deform the blank and obtain the required geometric shape and internal quality. Forgings produced by free forging method are called free forgings.
Fig. 3 Free forging
Free forging is mainly used to produce forgings with small batch. Forging hammer, hydraulic press and other forging equipment are used to shape the blank and obtain qualified forgings. The basic processes of free forging include upsetting, elongation, punching, cutting, bending, twisting, staggering and forging. Free forging adopts hot forging.
Free forging process
It includes basic process, auxiliary process and finishing process.
The basic processes of free forging include upsetting, elongation, punching, bending, cutting, torsion, stagger and forging, while the most commonly used processes in actual production are upsetting, elongation and punching.
Auxiliary process: pre deformation process, such as pressing jaw, pressing ingot edge, shoulder cutting, etc.
Finishing process: the process to reduce the surface defects of forgings, such as removing the uneven surface of forgings and shaping.
