CNC Knowledge: Are cold heading and cold extrusion the same thing? What’s the difference?

Cold heading and cold extrusion are basically deformation processes under the same conditions, but their operation methods are different. Cold pillars forge smaller part deformations and are often used in the fastener industry. Cold extrusion is the extrusion deformation of larger parts and has a wider range of uses.

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What is cold extrusion

Cold extrusion is a processing method in which the metal blank is placed in the cavity of the cold extrusion die, and at room temperature, the fixed punch on the press is applied to the blank to cause a plastic deformation of the metal blank in order to produce parts. Cold press extrusion processing relies on molds to control metal flow and relies on large-scale transfer of metal volume to form parts.

If the blank is extruded without heating, it is called cold extrusion. Cold extrusion is one of the processing processes of chipless and chipless parts, so it is an advanced processing method in plastic processing of gold chips. If the blank is heated to a temperature lower than the recrystallization temperature for extrusion, it is called hot extrusion. Hot extrusion always has the advantage of less chipping.

Cold extrusion technology is an advanced production technology with high precision, high yield, high quality and low consumption. It is mainly used in the large-scale production of small and medium-sized forgings. Compared with hot forging and hot forging processes, it can save 30-50% materials and 40-80% energy. It can also improve the quality of forgings and improve the working environment.

At present, cold extrusion technology has been widely used in fasteners, machinery, instruments, electrical appliances, light industry, aerospace, shipbuilding, military and other industries. other industrial sectors, and has become an indispensable and important processing method in metal-plastic volume forming technology. . With the advancement of science and technology and the continuous improvement of technical requirements of products in automobiles, motorcycles, household appliances and other industries, cold extrusion production technology has gradually become the direction development for the refined production of small and medium-sized forgings.

Cold extrusion is also divided into forward extrusion, reverse extrusion, compound extrusion, radial extrusion, etc.

Advantages of the cold extrusion process

1. Save raw materials

Cold extrusion uses plastic deformation of metal to make parts of the desired shape, which can significantly reduce the cutting process and improve material utilization. The material utilization rate of cold extrusion can generally reach more than 80%.

2. Improve work productivity

Using the cold extrusion process instead of cutting to make parts can increase productivity several times, dozens, or even hundreds of times.

3. Parts can achieve ideal surface roughness and dimensional accuracy

The precision of parts can reach IT7~IT8 level and the surface roughness can reach R0.2~R0.6. This is why parts processed by cold extrusion are generally rarely machined and only need to be finely ground in particularly demanding areas.

4. Improve the mechanical properties of parts

Cold work hardening of the metal after cold extrusion and the formation of a reasonable distribution of fibers inside the part make the strength of the part much higher than the strength of the raw material. In addition, reasonable cold extrusion process can form compressive stress on the surface of the part and improve fatigue resistance. Therefore, some parts that initially require heat treatment and reinforcement may be omitted from the heat treatment process after using the cold extrusion process. Some parts that were originally intended to be made from high-strength steel may be replaced with low-strength steel after cold weather. extrusion process.

5. Can process parts with complex shapes and difficult to machine.

Such as special-shaped sections, complex internal cavities, surface invisible internal teeth and internal grooves, etc.

6. Reduce parts costs

Since the cold extrusion process has the advantages of saving raw materials, improving productivity, reducing the amount of part cutting, and using low-quality materials to replace high-quality materials , the cost of parts is significantly reduced.

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What is a cool head

The cold heading process is one of the few new metal pressure treatment processes without cutting. It is a processing method that uses the plastic deformation of metal under the action of an external force and uses the mold to redistribute and transfer the volume of metal to form the required parts or blanks. The cold heading process is most suitable for the production of standard fasteners such as bolts, screws, nuts, rivets and pins. The equipment commonly used in the cold heading process is a dedicated cold heading machine. If the production volume is not too large, a hand crank press or friction press can be used instead.

Because the cold heading process has high productivity, good product quality, greatly reduces material consumption, reduces production costs and improves working conditions, it is increasingly used in machinery manufacturing , especially in the production of standard fasteners. Among them, the most representative products. produced by multi-station cold heading machines are bolts, screws and nuts.

Advantages of the cold heading process

1. Cold heading is carried out under normal temperature conditions. Cold heading can improve the mechanical properties of metal parts. The tensile strength after cold heading is about 10% higher than that of cutting, and some can even be increased by 20%. In fact, the metal fibers of cold-formed products are not cut, the internal structure of the metal is compacted and the accompanying work hardening phenomenon exists, so that the mechanical properties of the metal are improved.

2. Cold heading process can improve material utilization. Taking cold-formed bolts as an example, the new “dimple” hex head bolt process can achieve a material utilization rate of more than 99%. Except for the loss of the material head and tail, complete processing without cutting is achieved. If cutting is used, the material utilization rate is only 40%. The material utilization rate of cold-formed walnuts can also reach about 80%, while the material utilization rate of cut walnuts is only 54%.

3. Cold heading process can greatly improve productivity. For example, compared with the original cutting process, the productivity of cold-formed nuts is increased by about 25-30 times.

4. Through the use of multi-station cold heading machine, each process can be processed simultaneously on one machine tool, thereby reducing equipment investment, reducing the production space occupied by equipment and reducing the replacement of semi-finished products between each process. Transport, in particular, reduces the labor intensity of workers and improves working conditions.

5. The cold heading process can improve the surface finish of the product and ensure the accuracy of the product. For mass production of bolts, nuts, etc., the precision can be completely guaranteed.

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Are cold heading and cold extrusion the same thing?

Cold drilling and cold extrusion are basically deformation processes under the same conditions, but their operation methods are different. Cold pillars forge smaller part deformations and are often used in the fastener industry. Cold extrusion is the extrusion deformation of larger parts and has a wider range of uses; cold heading is equivalent to a branch of cold extrusion, in the bolt manufacturing process, the formation of the hexagonal head is cold heading, and the shank shrinks. The diameter is cold extrusion (positive extrusion). Uncut (multi-station forming) hex flange bolts include both cold heading and cold extrusion. The forming process of hex nuts only involves cold heading before shaping, and the subsequent hole extrusion process is cold extrusion (forward and reverse extrusion).