Introduction of cold forging process~
Cold forging is a general term for cold die forging, cold extrusion, cold heading and other plastic processing. It is the forming process below the recrystallization temperature of the material and the forging process below the recovery temperature. In production, forging without heating blank is called cold forging. Most of the cold forging materials are aluminum and some alloys, copper and some alloys, low carbon steel, medium carbon steel and low alloy structural steel with low deformation resistance and good plasticity at room temperature. Cold forging has good surface quality and high dimensional accuracy, which can replace some cutting processing. Cold forging can strengthen the metal and improve the strength of parts.
Definition of cold forging
Cold forging, also known as cold volume forming, is a manufacturing process and a processing method. It is basically the same as the cold stamping process. The cold forging process is also composed of material, die and equipment. Only the material in stamping is mainly plate, while the material in cold forging is mainly disc or wire.
Japan (JIS) is called cold forging (referred to as cold forging), China (GB) is called cold heading, some screw factories also like to call it heading. Cold forging refers to all kinds of bulk forming below the recrystallization temperature of metal. According to the theory of metal science, the recrystallization temperature of various metal materials is different; T re = (0.3-0.5) t fusion.
(Note: JIS, the abbreviation of Japanese industrial standard, is formulated and deliberated by JIS)
It is known that the minimum recrystallization temperature of ferrous metals and nonmetals. Even at room temperature or at room temperature, the forming of lead and tin can not be called cold forging, but hot forging. But iron, copper, aluminum forming at room temperature can be called cold forging.
Cold Forging Products
Fasteners
Driving technology
other
The shape of cold forging parts tends to be more and more complex, from the initial step shaft, screw, screw, nut and conduit, etc., to the parts with complex shape. The typical process of spline shaft is as follows: extruding the rod - upsetting the middle part - extruding the spline; The main process of spline sleeve is: backward extruding cup-shaped part - punching bottom to make ring-shaped part - forward extruding shaft sleeve. The cold extrusion technology of cylindrical gear is also successfully used in production. In addition to ferrous metals, copper alloy, magnesium alloy and aluminum alloy are widely used in cold extrusion.
Process introduction -- cold forging
Cold precision forging is a (near) net shape forming process. The parts formed by this method have high strength, high precision and good surface quality. At present, the total amount of cold forging used in an ordinary car abroad is 40 ~ 45kg, of which the total amount of gear parts is more than 10kg. The weight of a single gear can reach more than 1kg, and the profile accuracy can reach 7 grades.
Continuous process innovation promotes the development of cold extrusion technology. Since the 1980s, domestic and foreign precision forging experts began to apply the theory of split forging to the cold forging of spur gear and helical gear. The main principle of diffluence forging is to establish a material diffluence cavity or channel in the forming part of the blank or die. During the forging process, when the material fills the cavity, part of the material flows to the shunt cavity or channel. With the application of split flow forging technology, the less cutting and no cutting of high-precision gears has rapidly reached the scale of industrialization. For the extrusion parts with length diameter ratio of 5, such as piston pin, one-step cold extrusion can be realized by widely using the axial residual material block, and the stability of punch is very good; For the flat spur gear forming, the radial residual block can also be used to realize the cold extrusion forming.
Closed die forging is a kind of near net shape precision forging without flash, which is formed by one or two punches extruding metal in one direction or opposite direction in a closed die. If some precision parts of car such as planet and half axle gear, star sleeve, cross bearing are machined by cutting method, not only the material utilization rate is very low (less than 40% on average), but also the production cost is very high. In foreign countries, the closed forging technology is used to produce these net shape forgings, which saves most of the cutting process and greatly reduces the cost.
Development of cold forging technology
The development of cold forging technology is mainly to develop high value-added products and reduce production costs. At the same time, it is also permeating or replacing to cutting, powder metallurgy, casting, hot forging, sheet metal forming and other fields. It can also be combined with these processes to form a composite process. Hot forging cold forging compound plastic forming technology is a new precision metal forming technology which combines hot forging and cold forging. It makes full use of the advantages of hot forging and cold forging: the metal has good plasticity and low flow stress in hot state, so the main deformation process is completed by hot forging; The precision of cold forging is high, so the important dimensions of parts are finally formed by cold forging process. Hot forging cold forging compound plastic forming technology appeared in the 1980s, and has been more and more widely used since the 1990s. The parts manufactured by this technology have achieved good results in improving the accuracy and reducing the cost.
Numerical simulation technology
Effective numerical simulation software is established on the basis of rigid plastic finite element method, such as deform, QFORM, forge, MSC / SuPerform, etc. The finite element numerical simulation technology can be used to test the rationality of process and die design. The three-dimensional finite element numerical simulation software DEFORM 3dtm was used to simulate the pre forging split flow zone split flow final forging. The forging load stroke curve and the distribution of stress, strain and velocity in the whole forming process were obtained, and the results were compared with those of the traditional closed upsetting extrusion process. The analysis shows that the traditional closed upsetting extrusion forming of spur gear has large forming load, which is not conducive to the filling of tooth profile. By adopting the new technology of pre forging split flow zone split flow final forging, the forming load can be greatly reduced, the filling property of material can be improved obviously, and the gear with full tooth shape and corner can be obtained. Three dimensional large deformation elastoplastic finite element method is used to simulate the cold precision forging process of gear. The deformation flow of two-step forming mode with closed die forging as pre forging and closed die forging, hole split and constrained split as final forging is analyzed. The results of numerical analysis and process test show that the diversion, especially the diversion of constraint hole, is very effective in reducing the working load and improving the corner filling capacity.
Intelligent design technology
Intelligent design technology and its application in cold forging process and die design.
A knowledge-based pre forging geometry design system has been developed by Columbus batel laboratory in the United States. Because the shape of pre forging is a spatial geometry, it is necessary to operate its geometry, so the reasoning process can not be simply described by general language. The geometric information of the part is represented by frame method. In the frame, different slots are used to define the basic components of the part and the topological relationship between them. Design rules are expressed by production rules, which are explained by OPS tools. J. C. Choi and C. kim7 developed a knowledge-based integrated process design system for cold forging and hot forging, and established process design rules for cold forging and hot forging respectively.
The application of knowledge-based design method in cold forging process and die design will completely change the traditional state of plastic forming, which depends on the experience of designers, and the design process is repeatedly modified and the design efficiency is not high. It uses artificial intelligence, pattern recognition, machine learning and other technologies to extract appropriate knowledge from the system knowledge base to guide the cold forging process and die design. The technology is under further development. The knowledge-based design method has become a characteristic subject in the research of intelligent forging process and die design.
Analysis of advantages and disadvantages of cold forging
Process advantages
Cold forging technology is a kind of precision plastic forming technology, which has unparalleled advantages of cutting, such as good mechanical properties, high productivity and high material utilization. It is especially suitable for mass production, and can be used as the net shape forming of final products. It has a wide range of applications in transportation, aerospace, machine tool industry and other industries.
Process shortcomings
High material requirements; It is not suitable for small amount of processing; The requirements of mould are high.
The forming precision of cold forging is higher than that of warm forging and hot forging, which has its unique advantages in the field of precision forming. The application of cold forging technology improves the smooth finish, dimensional accuracy and surface strength of the inner bore, prolongs the service life of the barrel, and correspondingly improves the shooting accuracy of the gun. Moreover, it is convenient to process the conical barrel and can reduce the mass. The cold forging process was first proposed by Steyr company, and later many countries in the world used the cold forging machine tool of Steyr company to process gun barrel.
Application scope of cold forging technology
At present, the rapid development of automobile industry, motorcycle industry and machine tool industry provides the driving force for the development of the traditional technology of cold forging. For example, China's total output of motorcycles in 1999 was more than 11.26 million. According to the preliminary estimate in 2000, China's total demand for automobiles will reach 3.3 million by 2005, including 1.3-1.4 million cars. Only the forging demand of the automobile industry is more than 500000-600000 tons. Although it is not too late for cold forging technology to start in China, its development speed is far behind that of developed countries. So far, the weight of cold forging on cars produced in China is less than 20kg, which is half of that of developed countries. It has great development potential. It is an urgent task for China to strengthen the development and popularization of cold forging technology.
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