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Author: Site Editor Publish Time: 2025-02-13 Origin: Site
Cold heading is a forging method that uses a die to upset and shape metal bars at room temperature. It is usually used to make the heads of screws, bolts, rivets, etc. It can reduce or replace cutting processing. The forging material can be copper, aluminum, carbon steel, alloy steel, stainless steel and titanium alloy. Cold heading is mostly carried out on a dedicated cold heading machine, which is convenient for continuous, multi-station and automated production. On the cold heading machine, the processes of cutting, upsetting, accumulation, forming, chamfering, thread rolling, reducing diameter and trimming can be completed in sequence.
Cold heading is a processing technology for plastic deformation of metal at room temperature, which is widely used in the production of fasteners (such as bolts, nuts, screws, etc.). This process uses a multi-station cold heading machine to stamp and shape metal billets, and has the following significant advantages:
High production efficiency: The production speed of the cold heading process is much higher than that of traditional cutting processing, and the efficiency can be increased by dozens of times.
High material utilization rate: Through cold heading, the material utilization rate can reach 85% - 95%, which is significantly higher than the 25% - 35% of cutting.
Excellent mechanical properties: The metal fibers are not cut during the cold heading process, and the product strength is higher.
Good surface quality: Cold heading can make the surface finish of the product reach V5 or even V6 level.
The raw materials for cold heading need to have high plasticity and low hardness, and the surface hardness is usually required to be 75 - 85HRB. The surface quality requirements of the material are extremely high, and defects such as scratches, pockmarks, and rust are not allowed. Dimensional accuracy also needs to be strictly controlled to ensure the accuracy of the blank volume.
Cold heading equipment needs to be precisely set according to product requirements, including adjusting parameters, installing suitable molds, and cleaning and lubrication. Mold design needs to consider product structure, dimensional accuracy and surface finish.
(III) Cold heading process
During the cold heading process, the metal blank undergoes plastic deformation under the action of the die to form the desired shape. The parameters must be strictly controlled during processing to ensure the accuracy of the product size and shape.
(IV) Subsequent processing
After cold heading, the fasteners may need to be heat treated, such as quenching and tempering, to improve strength and hardness. In addition, cleaning, rust removal and surface treatment are required to remove dirt and oxides generated during the processing and improve the surface hardness and corrosion resistance of the product.
(1) According to the theory of metal plastic deformation, a certain pressure is applied to the metal blank at room temperature to cause it to plastically deform in the die cavity and form it into the specified shape and size.
(2) High-quality metal materials with good plastic deformation must be selected, and their chemical composition and mechanical properties must meet strict standards.
(3) There are many models and series of cold heading bolt and nut forming machines, with reliable performance, high efficiency and stable quality.
(4) The workpiece forming forging force is large, and the configuration of power equipment is expensive.
(5) The workpiece has good surface quality and high dimensional accuracy. Due to the cold hardening during the upsetting process, the deformation should not be too large.
(6) The cold upsetting process is applicable to workpieces of large batches and various specifications.
The mold is a key factor affecting the accuracy of cold upsetting products. High-precision molds can ensure the accuracy of product size and shape. The mold design needs to be optimized according to product requirements to meet the requirements of dimensional accuracy and surface finish.
During the cold upsetting process, process parameters such as forming temperature, speed and pressure need to be strictly controlled. Reasonable process parameters can ensure uniform deformation of the metal, avoid defects, and thus improve product accuracy.
The use of automated cold upsetting equipment can improve the consistency and stability of production. Automated equipment can accurately control every link in the processing process, reduce human errors, and thus improve product accuracy.
Strict quality inspection is an important link to ensure product accuracy. Through dimensional measurement, appearance inspection and performance testing, problems in the production process can be discovered and corrected in a timely manner to ensure that the products meet the standard requirements.
V. Reasons affecting cold heading accuracy
(1) Chemical composition of raw materials: Pure metals have better plasticity than alloys. Impurity elements usually cause brittleness and reduce plasticity. Various alloys have different effects on plasticity.
(2) Metallographic structure of raw materials: The properties, shapes, sizes, quantities and distribution states of multiphase structures are different, and the degree of influence on plasticity is also different. Defects such as grains and segregation, inclusions, bubbles, and looseness will reduce the plasticity of metals.
(3) Process deformation temperature: Plasticity increases with increasing temperature, but this increase is not a simple linear increase.
(4) Metal strain rate: The increase in strain rate has both a side that reduces the plasticity of metals and a side that increases the plasticity of metals. The combined effect of these two factors ultimately determines the change in metal plasticity.
(5) Deformation mechanical conditions: Compression strain is conducive to the development of plasticity, while tensile strain is not conducive to plasticity. The plastic processing method with three-dimensional compression principal stress diagram and two-dimensional compression and one-dimensional tensile principal strain diagram is extremely conducive to the development of metal plasticity.
(6) Other problem factors: Under the condition of discontinuous deformation, the plasticity of metal can also be improved, especially when low-plasticity metal is thermally deformed.
(1) The connection between the crankshaft and the body and the impact connecting rod is made of high-wear-resistant alloy copper bearings, which has large bearing capacity, long service life and low maintenance cost.
(2) The body is made of ductile iron with alloy addition, which has high tensile strength and good wear resistance.
(3) It adopts a two-stage gear transmission system with high transmission efficiency and large transmission torque.
(4) It is equipped with pneumatic clutch brake to reduce motor power consumption.
(5) The cutting system uses a guide plate to drive the cutting rod. The guide plate reciprocates and the cutting force is transmitted linearly. The force is large and stable and the dynamic balance is good.
(6) The multi-station cold heading machine uses an open and closed clamp to transfer the workpiece, and the clamp system can be flipped or translated, which is conducive to the arrangement of the forming process.
(7) It is equipped with a variable frequency speed regulation device, which can adjust the speed infinitely within a certain range.
(8) It is equipped with a fault detector and a safety protection device, which automatically stops the machine when the equipment fails, providing great protection for the equipment and the mold.
(9) The feed box is equipped with a thrust device to improve the feeding accuracy.
(10) The oil circuit design of the lubrication system is simple and efficient, and it can effectively protect the punch and the workpiece on the basis of ensuring circulation filtration.
(1) The raw materials must be spheroidized and annealed, and the metallographic structure of the material is spherical pearlite.
(2) In order to minimize the cracking tendency of the material and increase the service life of the mold, the cold-drawn material is also required to have the lowest hardness possible to improve the plasticity.
(3) The dimensional accuracy of the raw materials should generally be determined according to the specific requirements of the product and the process conditions. Generally speaking, the multi-station cold heading machine has lower requirements for the dimensional accuracy of the reduction and strong reduction.
(4) The surface quality of the raw material requires a lubricating film with a dull dark color, and the surface must not have defects such as scratches, folds, cracks, burrs, rust, oxide scale, pits and pits.
(5) The total thickness of the decarburized layer in the radial direction of the raw material is required to not exceed 1% of the raw material diameter.
(6) In order to ensure the cutting quality during cold forming, the raw material is required to have a hard surface and a soft core.
(7) The raw material should be subjected to cold heading test. Due to cold hardening, the deformation resistance increases. The lower the sensitivity of the material to cold hardening, the better.
(1) It has excellent extreme pressure lubrication performance, high temperature resistance, extreme pressure wear resistance, rust resistance and high temperature oxidation resistance and stability. It improves the accuracy and finish of the workpiece, can prevent mold sintering, meets the multi-station forming processing of standard and non-standard parts, and is fully competent for cold heading stainless steel workpiece processing.
(2) It can reduce the oil smoke and "drifting fog" to a very low level, meeting the strict requirements of multi-die punching machines with strong shrink molds for processing nuts.
(3) It has good processing performance for products with relatively large deformation, such as hollow, high-strength bolts, sleeves, stainless steel hollow, semi-hollow rivets, etc.
(4) It can effectively protect the punch (punch needle) and mold, extend the service life, and reduce the overall cost.
(5) It has good heat dissipation effect, avoiding excessive local temperature of the workpiece and mold during cold forming.
(6) It has good high temperature resistance and is not easy to produce oil sludge. Low odor and low smoke protect the operating environment.
(7) It has a certain degree of rust resistance and can meet the rust prevention requirements between processing steps in the processing process.
(8) It can meet the demanding cold heading stainless steel forming processing and large deformation carbon steel forming processing.
The above are the key points to improve the precision of fastener manufacturing process. Strictly following the rules and regulations can improve efficiency and avoid accidents.
