Cold precision forging is a (near) net-shape forming process. The parts formed by this method have high strength and precision, and good surface quality. At present, the total amount of cold forging parts used in an ordinary foreign car is 40~45kg, of which the total amount of gear parts is more than 10kg. The weight of a single cold-forged gear can reach more than 1kg, and the tooth shape accuracy can reach level 7.
The main principle of split-flow forging is to establish a split-flow cavity or split-flow channel for the material in the forming part of the blank or die. During the forging process, while the material fills the cavity, part of the material flows to the split-flow cavity or split-flow channel. The application of split-flow forging technology has enabled the low-cut and no-cutting processing of high-precision gears to quickly reach industrial scale. For extrusion parts with a length-to-diameter ratio of 5, such as piston pins, the use of axial excess material blocks can achieve one-time cold extrusion forming through axial splitting, and the stability of the punch is very good; for the forming of flat spur gears, the use of radial excess material blocks can also achieve cold extrusion forming of the product.
Closed forging is to form metal in a closed die by one or two punches in one direction or opposite directions to obtain near-net-shape precision forgings without flash. If some precision car parts such as planetary and half-shaft gears, star sleeves, cross bearings, etc. are processed by cutting, not only the material utilization rate is very low (less than 40% on average), but also it takes a lot of time and the production cost is extremely high. Foreign countries use closed forging technology to produce these net-shape forgings, eliminating most of the cutting processing and greatly reducing the cost.
The forming accuracy of cold forging technology is higher than that of warm forging and hot forging, and it has its unique advantages in the field of precision forming. The use of cold forging technology improves the inner bore finish, dimensional accuracy, and surface strength, prolongs the life of the barrel, and improves the shooting accuracy of the gun accordingly. It is also easy to process tapered barrels and can reduce the mass. The cold forging process was first proposed by Steyr, and later many countries in the world used Steyr's cold forging machine tools to process gun barrels.