Cold extrusion technology is a high-precision, high-efficiency, high-quality and low-consumption advanced production technology, which is mostly used in the large-scale production of small and medium forgings. Compared with the normal-scale forging process, it can save 30% ~ 50% of material, 40% ~ 80% of energy, and can improve the quality of forgings and improve the working environment. After World War II, cold extrusion technology has been widely developed and applied in the automobile, motorcycle, household appliances and other industries in foreign industrialized countries. The emergence of new extrusion materials, new steel grades and large-tonnage presses has further expanded Its development space. In the 1980s, Japan claimed that 30%-40% of the parts produced by forging processes in its car production were produced by cold forging processes. In recent years, new cars produced in recent years used an average of 42kg of cold forging parts per car. In the production of cars in the United States and other countries, an average of 40kg cold forging parts are used per car. With the advancement of science and technology and the continuous improvement of product technical requirements in industries such as automobiles, motorcycles, and household appliances, cold forging production technology has gradually become the development direction of refined production of small and medium forgings.

1.1 Advantages of cold extrusion

(1) Save raw materials. Cold extrusion processing is the use of metal plastic deformation to make parts of the required shape, which can greatly reduce the cutting process and increase the utilization rate of materials. The utilization rate of cold extrusion materials can generally reach more than 80%.

(2) Improve labor productivity. Using cold extrusion technology to replace cutting to manufacture mechanical parts can increase productivity several times, tens of times, or even hundreds of times.

(3) Parts can obtain ideal surface roughness and dimensional accuracy. The precision of cold extrusion parts can reach I17~IT8, and the surface roughness can reach R.0.2~1.6. Therefore, the parts processed by cold extrusion are generally seldom processed again, and only need to be fine-grinded where the requirements are particularly high.

(4) Improve the mechanical properties of parts. The cold working and hardening of the metal after cold extrusion and the formation of a reasonable fiber streamline distribution inside the parts make the strength of the parts much higher than the strength of the raw materials. In addition, a reasonable cold extrusion process can form compressive stress on the surface of the part and increase the fatigue strength. Therefore, some parts that originally need heat treatment strengthened can be omitted after the cold extrusion process; some parts originally need to be made of higher strength steel, and can be replaced by lower strength steel after the cold extrusion process.

(5) It can process parts with complex shapes and difficult to cut. Such as special-shaped cross-sections, complex internal cavities, internal teeth and internal grooves that are invisible on the surface.

(6) Reduce the cost of parts. Because the cold extrusion process has the advantages of saving raw materials, improving productivity, reducing the amount of machining of parts, and using poor materials to substitute high-quality materials, the cost of parts is greatly reduced.

1.2 Disadvantages of cold extrusion

(1) High requirements for molds. During cold extrusion, the blank is subjected to three-way compressive stress in the die, which significantly increases the deformation resistance, which makes the stress on the die far greater than that of a general stamping die. When cold extruding steel, the stress on the die often reaches 2000MPa~2500MPa. In addition to high strength, the die must also have sufficient impact toughness and wear resistance. In addition, the strong plastic deformation of the metal blank in the mold will increase the mold temperature to about 250°C ~ 300°C. Therefore, the mold material must have a certain tempering stability. Due to the above situation, the life of cold extrusion dies is much lower than that of stamping dies. To further promote the cold extrusion process, it is necessary to try to improve the life of the mold from the aspects of mold design, mold material and mold manufacturing process.

(2) A large-tonnage press is required. Due to the large deformation resistance of the blank during cold extrusion, hundreds of tons or even thousands of tons of presses are required.

(3) Due to the high cost of cold extrusion molds, it is generally only suitable for mass-produced parts.

(4) The blank needs to be surface treated before extrusion. This not only increases the number of processes, requires a larger production area, but also makes it difficult to automate production.

(5) Not suitable for processing high-strength materials.

(6) The plasticity and impact toughness of cold extrusion parts are poor, and the residual stress of the parts is large, which will cause the deformation of the parts and the reduction of corrosion resistance (stress corrosion).