Cold forging refers to the process of applying cold forging to products or specific product components by shaping products to meet specific specification requirements at room temperature. According to incomplete statistics, the history of forging development in foreign countries is nearly 5000 years, and that in China has been nearly thousands of years from steel smelting to manufacturing. Today, more and more diversified cold extrusion technologies are applied.
In the previous chapter, we have introduced the Differences between Cold Forging and Cold Extrusion. First, they have different names, but also different processes. Because of different processes and materials, the application fields are different;
The rapid development of the current automobile industry has provided the driving force for the development of cold forging technology. According to incomplete statistics, the weight of cold and warm precision forgings in each car is 45~50 kg. The half shaft on the rear axle driven car, the cross shaft in the universal joint, straight bevel gear, spline, hub nut, automobile alternator claw pole, front drive car constant velocity universal joint parts, synchronizer gear ring, etc. are typical automobile cold forgings. Figure 1-1 shows the precision forging parts newly put into production for Japanese cars every five years from 1960 to 1995, which are summarized by Professor Hideki Kudo of Japan. In 1965, each car of precision forging was only about 6kg, and by 1995, it had increased to 45kg. Since the 1960s, small axisymmetric products (such as hub bolts) have been mainly produced, while large forgings (such as steam pump rotors) have been produced since the 1970s. In the 1980s, CVJ parts were important products. Since 1990, precision gears have become the main target products.
The modern cold forging technology began at the end of the 18th century, but it was not until the 1930s when the Germans invented the surface lubrication method of forming phosphate film on the workpiece surface that the cold forging technology gradually became practical. In 1967, the International Cold Forging Group (ICFG) was established and the first plenary meeting was held in London, England, in 1968. ICFG holds a plenary meeting every year and publishes a large number of industrial technical documents or standards, which plays an important role in promoting international academic exchanges and production of cold forging technology. At present, ICFG mainly works in the following areas:
(1) Tool life and tool quality of die manufacturers: mainly study die materials, surface treatment, friction, fatigue, etc. related to die life and die quality.
(2) Process simulation: mainly studies the application of numerical simulation software, the reliability of input data, the development of commercial software, the limitations of existing models, etc.
(3) Properties of cold forged products: mainly study the residual stress, work hardening, dimensional accuracy, deformation, metallographic structure, machining performance, lightweight design, etc. of cold forged parts.
(4) Incremental bulk forming: mainly studies numerical modeling, material testing, physical simulation, die wear, innovative applications, etc. related to incremental bulk forming.
The cold forging technology in China started in the late 1950s, and the first ferrous metal cold extrusion part (shuttle core sleeve) was successfully developed in 1962 at Shanghai Jiaotong University. 1965-1975 was the first climax of industrial application of cold forging technology in China, which was mainly used in bicycles, sewing machines, trucks and electronic industries. Special mechanical cold forging presses from abroad were introduced, and 1600~3000 kN mechanical cold forging presses, 6300 kN hydraulic extruders, 2500 kN two-way automatic extruders, etc. were developed. At the same time, in terms of theoretical innovation, the allowable deformation degree theory of ferrous metal cold extrusion is proposed, which lays a foundation for the development of cold forging technology in China. Figures 1-2 to 1-4 show some ferrous metals (materials include pure iron, carbon steel, low alloy steel, stainless steel, high-speed steel and heat-resistant steel), copper and brass cold extrusions, aluminum and aluminum alloy cold extrusions completed in China from the 1960s to the 1970s.
As some products did not reach the economic batch size, the cold forging technology in China failed to develop continuously in the late 1970s and turned to a low ebb. Since the 1990s, with the rapid growth of the production of cars and motorcycles in China, the cold forging market has been expanded, and technologies such as multi station forming, warm (hot) cold composite forming, closed forging, back pressure forging, diffluent forging and numerical simulation of cold and warm forging have been applied. However, there is still a big gap between the cold forging technology in China and that in developed countries. Strengthening the development and promotion of cold forging technology is an urgent task.
High speed forging technology is especially suitable for mass production of parts due to its high production efficiency. High speed cold forging machine has been widely used in foreign precision forging enterprises. For example, the Coldmatic series cold heading forging machines of Switzerland HATEBUR Company adopt multi station horizontal forging, and automatic feeding of manipulator clamps and high-speed shearing blanking system are used between stations to ensure the surface quality and accuracy of blanks The independently adjustable manipulator can well clamp workpieces of any shape and length and transfer them to the next station at the right time. On the Coldmatic AKP 4-6S equipment, precision blanking can be realized and the forming of small gear parts shown in Fig. 1-14 can be completed through 6 stations: ① precision blanking; ② It is unnecessary to extrude the small diameter part without reshaping the material section; ③ Positive extrusion of keyway part; ④ End upsetting; ⑤ Reverse extrusion forming of small teeth (no need to turn over parts); ⑥ Reduce the shoulder diameter at the die side; ⑦ Finish the small teeth after Z. The production efficiency of this part can reach 160 pieces/minute.