What Is Cold Forging?
Cold forging, cold extrusion, and cold heading are general terms for plastic processing. Cold forging, also called cold volume forming, is a manufacturing process and a processing method. Cold forging is the forming process below the recrystallization temperature of the material, and the forging performed below the recovery temperature.
In production, forging without heating the blank is called cold forging. Cold forging materials are mostly 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 forgings have good surface quality and high dimensional accuracy, which can replace some cutting processes. Cold forging can strengthen the metal and increase the strength of the parts.
It is basically the same as the cold stamping process.
The cold forging process is also composed of three elements: materials, molds, and equipment. However, the material in the stamping process is mainly plate, while the material in the cold forging process is mainly a disc or wire.
Cold forging refers to various volume forming performed below the recrystallization temperature of the metal. From the theory of metal science, the recrystallization temperature of various metal materials is different; T then = (0.3~0.5) T melting.
T melting is shown in the following table:
Minimum Recrystallization Temperature/Celsius
Minimum Recrystallization Temperature/Celsius
Iron (Fe) and copper
From the figures in the table, the minimum recrystallization temperature of ferrous metals and non-metals can be saw. Even at room temperature or normal temperature, the forming process of lead and tin cannot be called cold forging, but hot forging.
However, the forming process of iron, copper, and aluminum at room temperature can be called cold forging.
The shape of cold-forged parts is becoming more and more complex, from the initial stepped shafts, screws, screws, nuts and conduits, etc., to parts with complex shapes.
The typical process of spline shaft is positive extrusion rod part-upsetting middle head part-extrusion spline;
The main process of the spline sleeve is: reverse extrusion of the cup-shaped piece-punching the bottom to make a ring-positive extrusion sleeve.
The cold extrusion technology of cylindrical gears has also been successfully used in production. In addition to ferrous metals, cold extrusion applications of copper alloys, magnesium alloys, and aluminum alloys are becoming more and more extensive.
Scope of application
The current rapid development of the automobile industry, the motorcycle industry, and the machine tool industry provide the driving force for the development of the traditional technology of cold forging.
Cold precision forging is a (near) net forming process. The parts formed by this method have high strength and precision and good surface quality.
At present, the total amount of cold forgings used in an ordinary car abroad is 40~45kg, of which the total amount of tooth-shaped parts is more than 10kg. The weight of a cold-forged gear can reach more than 1kg, and the tooth profile accuracy can reach level 7.
Continuous process innovation has promoted the development of cold extrusion technology. Since the 1980s, domestic and foreign precision forging experts have begun to apply split foraging theory to cold forging forming of spur gears and helical gears.
The main principle of shunt forging is to establish a material shunt cavity or shunt channel in the forming part of the blank or die.
During the forging process, while the material fills the cavity, part of the material flows to the shunt cavity or shunt channel. The application of shunt forging technology enables the small and no-cutting processing of high-precision gears to quickly reach the industrial scale.
For extruded parts with a length-to-diameter ratio of 5, such as piston pins, a cold extrusion can be achieved by adopting a wide range of axial residual material through axial splitting, and the stability of the punch is very good; for flat spur gears forming, the use of radial residual material block can also realize the cold extrusion of the product.
Blocked forging is to form one or two punches one-way or oppositely extruding metal in a closed die to obtain a near-net-shape precision forging without flash.
Foreign countries adopt occluded forging technology to produce these net-shape forgings, which saves most of the cutting processing and greatly reduces the cost.
Cold forging technology has higher forming accuracy than warm forging and hot forging and has its unique advantages in the field of precision farming.
The application of cold forging technology improves the smoothness, dimensional accuracy, and surface strength of the inner chamber, prolongs the life of the barrel, improves the shooting accuracy of the gun correspondingly, and facilitates the processing of the tapered barrel, which can reduce the quality.
The cold forging process was first proposed by Steyr. Later, many countries in the world used Steyr’s cold forging machine tools to process barrels.
The development of cold forging technology is mainly to develop high value-added products and reduce production costs. At the same time, it is constantly infiltrating or replacing it in cutting, powder metallurgy, casting, hot forging, sheet metal forming technology, and other fields. The combination of processes constitutes a composite process.
The hot forging-cold forging compound plastic forming technology is a new precision metal forming process that combines hot forging and cold forging. It makes full use of the respective advantages of hot forging and cold forging:
In the hot state, the metal has good plasticity and low flow stress, so the main deformation process is completed by hot forging; the accuracy of cold forging parts is high, so the important dimensions of the parts are finally formed by the cold forging process.
The hot forging-cold forging composite plastic forming technology appeared in the 1980s and has been more and more widely used since the 1990s. Parts manufactured with this technology have achieved good results in improving accuracy and reducing costs.
Numerical Simulation Technology
Numerical simulation technology is used to check the rationality of process and mold design.
With the rapid development of computer technology and the development of plastic finite element theory in the 1970s, many difficult problems in the plastic forming process can be solved by finite element methods.
In the field of the cold forging forming process, through modeling and determination of appropriate boundary conditions, finite element numerical simulation technology can intuitively obtain the stress, strain, die force, die failure, and possible defects of the forging during the metal flow process.
The acquisition of this important information has important guiding significance for the final determination of reasonable mold structure, mold material selection, heat treatment, and forming process plan.
Effective numerical simulation software is based on the rigid-plastic finite element method. This software includes Deform, Q form, Forge, MSC/Superform, etc. The use of finite element numerical simulation technology can be used to check the rationality of process and mold design.
The pre-forging shunt area-shunt final forging was studied by numerical simulation with the three-dimensional finite element numerical simulation software Deform 3DTM, and the forging load-stroke curve and the stress, strain, and velocity distribution of the entire forming process were obtained and compared with the traditional closed-form The simulation results of the upsetting process were compared.
The analysis shows that the traditional closed upsetting and extrusion forming spur gear has a large forming load, which is not conducive to the filling of the tooth profile.
Adopting the new technology of pre-forging splitting area-splitting final forging can greatly reduce the forming load, significantly improve the filling of the material, and obtain gears with full tooth profile and corners.
The gear cold precision forging forming process was numerically simulated by the three-dimensional large-deformation elastic-plastic finite element method, and the two-step forming mode with closed die forging as pre-forging and closed die forging, hole splitting, and constrained splitting as final forging was performed. Numerical simulation analysis was carried out on the deformation and flow conditions.
Numerical analysis results and process tests show that the diversion in the final forging, especially the restrictive hole diversion, 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 forming process and die design.
The Columbus Bettel Laboratory in the United States has developed a knowledge-based pre-forging geometric dimension design system. Because the shape of the pre-forged part is designed as a spatial geometry, the geometric shape must be manipulated, so the reasoning process cannot be described in the general language.
For the geometric information of the parts, the frame method is used to express, and different slots are used in the frame to define the basic components of the parts and the topological relationship between them. Design rules are expressed by production rules, and use OPS tools to make excuses.
The application of knowledge-based design methods in the design of cold forging forming processes and molds will completely change the traditional plastic forming process by relying on the experience of all designers, repeated modifications during the design process, and low design efficiency.
It uses artificial intelligence, pattern recognition, machine learning, and other technologies to extract appropriate knowledge from the system knowledge base during the design process to guide the cold forging forming process and mold design.
This technology is under further development. The knowledge-based design method has become a characteristic subject in the research of the forging process and mold design intelligent technology.
The cold forging process is a precision plastic forming technology that has unparalleled advantages in cutting processing, such as good mechanical properties, high productivity, and high material utilization.
It is especially suitable for mass production and can be used as a manufacturing method for final products. (Net-shape Forming), has a wide range of applications in the transportation, aerospace, and machine tool industries.
High material requirements; not suitable for small-scale processing; high mold requirements.