With the continuous development of China's economy, the use of high-precision forgings is becoming more and more widespread. Therefore, the requirements of forging plants in processing high-precision forgings mainly refer to the requirements for the size, shape, location, and surface accuracy of the forgings. degree.
Compared with ordinary die forgings, the main advantages of precision die forgings are that the machining allowance is small or even zero; the dimensional accuracy is high, that is, the size deviation of precision die forgings is smaller than that of ordinary die forgings, and generally only It is half or even less of the deviation of ordinary die forgings; the surface quality is good, that is, the surface roughness of precision die forgings is low, defects such as surface pits and the residual flash width left after cutting are strictly restricted.
Compared with cutting, the main advantages of precision die forging are: because the shape and size of the forging blank is close to or completely consistent with the finished part, the material utilization rate is high; because of precision plastic forming, the distribution of metal fibers is consistent with the shape of the part and Continuously dense, thus greatly improving the mechanical properties of the part. Therefore, precision die forging is also called less cutting process.
Forging wear is very common, and the causes of this phenomenon can be divided into physical and chemical and mechanical aspects. The wear resistance is almost related to the properties of the forgings, and under different conditions of the wear mechanism, the forging plant has different requirements for the material properties to improve the wear resistance of the forgings. As the friction materials and test conditions are different, they can be expressed by the abrasion index or tested by abrasion testers under specified conditions. Quenching can improve the wear resistance of the surface, and heat treatment and quenching of the forging can improve the wear resistance of the forging. Many forgings fail quickly due to wear. Although material friction, wear and corrosion rarely cause catastrophic damage to metal forgings, the economic losses caused by it are quite amazing.
Overheating is found in the furnace during heat treatment. It can be taken from the superheating temperature to the temperature at which the fire color disappears (approximately 500 ~ 550 ℃), and then reheated to the specified annealing temperature immediately. Forgings that have overheated in the forging factory can be re-normalized or annealed with the correct specifications to refine their grains. Forgings that are not overheated can be normalized once; larger forgings can be normalized twice (Ac3 + 50 ～ 70 ℃). Forgings with severe overheating can use secondary normalizing, secondary Ac3 + 100 ～ 150 ℃; secondary Ac3 + 30 ～ 50 ℃. It is particularly important to prevent overheating, which requires the selection of appropriate heating temperature and heating and holding time, and strict and correct implementation of heating specifications.
The forging plant shall timely repair and control the temperature control instrument and correctly install the thermocouple to avoid the heating temperature being too high. When the heating temperature of the forging is close to the melting temperature of the metal, not only the grains are coarse, but also austenite, the grain boundary is severely oxidized and the low melting point composition is melted, which destroys the interconnections between the grains. So that the forgings are scrapped, this phenomenon is called overburning. During the heating process, the forgings factory sparks out of the steel. When the structure is observed, melting or oxidation occurs along the grain boundaries. At this time, the strength is extremely low and it is no longer available. There is no remedy for overburned parts, and they can only be scrapped.
