What is cold forging?

The 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.

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What Is Cold Forging?

The 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 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:
Metal Minimum Recrystalliz
ation Temperature/Cel
Metal Minimum Recrystalliz
ation Temperature/Cel

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sius sius
Iron (Fe) and copper 360~450 Tin（Sn） 0
Copper（Cu） 200~270 Lead（Pb） 0
Aluminum（Al） 100~150 Tungsten（W） 1200


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.
Technical introduction
Craft
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.

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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.
skills requirement
Cold forging technology has higher forming accuracy than warm forging and hot forging and has
its unique advantages in the field of precision forming.
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.
Technological development
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

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flow process.
The acquisition of these 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, Qform, 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 of relying on
the experience of all designers, repeated modifications during the design process, and low design
efficiency.

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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.
Process advantages
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 transportation, aerospace, and machine tool industries.
Process disadvantages
High material requirements not suitable for small-scale processing; high mold requirements.