In the field of mechanical manufacturing, forgings are the core components of many mechanical devices, and their quality and performance directly affect the operating efficiency and reliability of the entire equipment. Cold extrusion technology, as an advanced metalworking process, is gradually changing the traditional production methods of forgings. This article will focus on cold extrusion forgings, exploring their technical principles, advantages, applications, and challenges in depth to help readers gain a comprehensive understanding of the application prospects of this technology in the forging industry.
Cold extrusion forgings refer to forgings produced through the cold extrusion process, whose shapes and dimensions are close to or meet the requirements of the finished products. Cold extrusion technology has evolved from traditional metal plastic working. It utilizes the plastic deformation capability of metals at room temperature, forcing metal blanks to pass through the die cavity under high pressure and a certain speed to obtain forgings with the desired shape and dimensions.
During the cold extrusion process, the metal material undergoes plastic deformation under triaxial unequal compressive stress. This deformation method makes the metal grain structure more compact, and the metal flow lines are not interrupted, forming continuous metal flow lines along the contour of the extruded part. This optimization of the microstructure not only enhances the strength of the forgings but also makes it possible to replace high-strength steel with low-strength steel, thereby reducing raw material costs.
Cold extrusion technology demonstrates many significant advantages in the forging field, which have made it highly favored in modern manufacturing. It has become a key technology for improving production efficiency, reducing costs, and enhancing product quality.
One of the greatest advantages of cold extrusion forgings is the high material utilization rate. Traditional cutting processes generate a large amount of metal waste chips, while cold extrusion technology achieves metal forming through plastic deformation, avoiding such waste. For example, one ton of metal material can produce forgings equivalent to two tons, or even three to five tons, produced by traditional processing methods after cold extrusion processing. This not only saves raw materials but also reduces the cost of waste disposal in the production process.
The production efficiency of cold extrusion forgings is far higher than that of traditional processing methods. Taking the production of automotive engine piston pins as an example, the production rate has increased by 3.2 times compared with turning processing after adopting cold extrusion technology. Moreover, the emergence of cold extrusion automatic machines has further improved production efficiency. One cold extrusion automatic machine can produce as much as 100 horizontal lathes or 10 four-axis automatic lathes. This highly efficient production method is particularly suitable for mass production, significantly shortening the production cycle and enhancing the market competitiveness of enterprises.
Cold extrusion technology can process forgings with complex shapes, small sizes, and high precision requirements. For example, thin-walled irregular parts and cylindrical parts with reinforcing ribs, which are complex in shape, would not only have low production efficiency and high material consumption but also be extremely difficult to process if using traditional cutting methods. However, cold extrusion technology can easily complete the processing of these complex shapes, greatly improving production efficiency and product quality.
The performance of cold extrusion forgings has been significantly enhanced. During the cold extrusion process, the metal material is under triaxial compressive stress, and the deformed metal grain structure becomes more compact. The metal flow lines are not interrupted and form a continuous distribution. This optimization of the microstructure greatly increases the strength of the forgings. At the same time, the work hardening characteristics of metal material during cold deformation are utilized to further enhance the performance of the forgings. For example, in the past, China used low-alloy structural steel 20Cr to produce automotive engine piston pins by cutting processing. After switching to cold extrusion production, the mechanical properties of the piston pin forgings were improved, allowing the use of low-carbon steel 20 as the material and reducing raw material costs.
The surface quality of cold extrusion forgings is very good. During the cold extrusion process, the surface of the metal material is smoothed by the smooth surface of the die under high pressure, resulting in a very small surface roughness value and a significant increase in surface strength. The surface roughness value Ra of cold extruded parts is generally at least above 0.63-1.25μm. This means that some parts of the forgings processed by cold extrusion can have minimal or even no machining allowance to meet the technical requirements of the product drawings, reducing subsequent machining processes and lowering production costs.
The dimensional accuracy of cold extrusion forgings generally reaches precision grades IT8-IT9, and the dimensional tolerance range of some parts can be controlled within 0.015mm. This enables the cold extrusion process to achieve ideal surface roughness and dimensional accuracy of the parts. Some forgings can be used directly after cold extrusion without further cutting processing, thus opening up a broad path for replacing forging, casting, and cutting processing of some forgings with the cold extrusion method.
The production cost of cold extrusion forgings is relatively low. Since cold extrusion can greatly save raw materials and metal cutting machining time, it inevitably reduces the manufacturing cost of forgings. For example, there are three methods for producing automotive piston pins: cold extrusion, cutting processing of round steel, and cutting processing of seamless steel pipes. The cost of cold extrusion forming piston pins is the lowest, reducing costs by 45% compared with cutting processing of round steel and by 29% compared with processing using seamless steel pipes as raw materials.
Cold extrusion forgings are widely used in the automotive industry. Statistics show that the weight of cold extruded parts in each car has reached 80kg, and it is expected to continue to increase in the future. The production of key components such as automotive engine piston pins and car bases has already adopted cold extrusion technology. In addition, cold extrusion forgings are also widely used in mechanical manufacturing, aerospace, electronics, and other fields. For example, Chengda Forgings produces various automotive forgings and mechanical accessory forgings using cold extrusion technology, improving product quality and performance while reducing production costs.
Despite the many advantages of cold extrusion forgings, there are also some challenges in practical applications.
During cold extrusion, the blank is subjected to triaxial compressive stress in the die, significantly increasing the deformation resistance, and the stress on the die is much greater than that on ordinary stamping dies. For example, when processing a low-carbon steel cup-shaped part with a diameter of 38mm, a wall thickness of 5.6mm, and a height of 100mm using the cold extrusion method, the maximum deformation force can reach 132t, and the unit pressure on the cold extrusion punch is above 2300MPa. This means that the die not only needs to have high strength but also sufficient impact toughness and wear resistance. Moreover, the intense plastic deformation of the metal blank in the die can raise the die temperature to around 250℃-300℃, so the die material needs to have certain tempering stability. Due to the above situations, the life of cold extrusion dies is much lower than that of stamping dies.
Due to the high deformation resistance of the blank during cold extrusion, presses with hundreds of tons or even thousands of tons are required. This not only increases equipment investment but also puts higher demands on the load-bearing capacity of the workshop.
The manufacturing cost of cold extrusion dies is high and is generally only suitable for mass-produced parts. The minimum batch size suitable for it is 50,000-100,000 pieces. For small-batch production, the economic advantages of cold extrusion technology are not obvious.
The blanks need to be surface treated before extrusion, which not only increases the number of processes but also occupies a large production area and is difficult to automate production.
Cold extrusion technology is not suitable for processing high-strength materials. High-strength materials have high deformation resistance, which requires higher demands on dies and equipment, making the processing difficulty greater. Moreover, the plasticity and impact toughness of the parts after processing are reduced, the residual stress is large, which can easily cause part deformation and reduced corrosion resistance.
As an advanced metalworking process, cold extrusion technology has a broad application prospect in the forging industry. It not only improves production efficiency, saves raw materials, and reduces production costs but also significantly enhances the performance and surface quality of forgings. However, cold extrusion technology also faces some challenges in application, such as short die life, high equipment investment, high die cost, high surface treatment requirements for blanks, and unsuitability for high-strength material processing. Despite these challenges, with the continuous progress and innovation of technology, these problems are expected to be solved. In the future, cold extrusion technology will be applied in more fields, bringing more development opportunities to the mechanical manufacturing industry.
