Forging industry is an important part of the national economy. Forging is indispensable in all fields of production. Large parts such as airplanes, automobiles, ships, power generation equipment, petrochemical equipment and small parts such as clocks and watches are all produced and processed by means of forging, which covers a wide range.
The preparation before forging includes raw material selection, material calculation, blanking, heating, deformation force calculation, equipment selection and die design.
Lubrication method and lubricant should be selected before forging. Forging materials cover a wide range of areas, including various grades of steel and high temperature alloys, as well as non-ferrous metals such as aluminum, magnesium, titanium, copper, etc. They are processed into bars and profiles of different sizes at one time, and ingots of various specifications. In addition to a large number of domestic materials suitable for China's resources, they also have materials from abroad. Most of the forged materials have been listed in the national standards, and many of them are new materials for development, trial use and promotion. As we all know, the quality of products is often closely related to the quality of raw materials. Therefore, forgers must have the necessary knowledge of materials and be good at selecting the most suitable materials according to the technological requirements.
Material calculation and blanking is one of the important links to improve material utilization rate and realize blank refinement. Excessive material not only causes waste, but also aggravates the wear and energy consumption of the mould chamber. If there is not a little surplus, it will increase the difficulty of process adjustment and the waste rate. In addition, the quality of blanking end also affects the process and forging quality.
The purpose of heating is to reduce forging deformation force and improve metal plasticity. But heating also brings a series of problems, such as oxidation, decarbonization, overheating and overheating. Accurate control of initial forging and final forging temperature has a great influence on the structure and properties of products.
Flame furnace heating has the advantages of low cost and strong applicability, but the heating time is long, easy to produce oxidation and decarbonization, and the working conditions need to be constantly improved. Inductance heating has the advantages of rapid heating and less oxidation, but it has poor adaptability to product shape, size and material changes.
Forging is produced under the action of external force. Therefore, the correct calculation of deformation force is the basis for selecting equipment and checking dies. Stress and strain analysis of the inner part of the deformed body is also indispensable for optimizing the process and controlling the structure and properties of forgings.
There are four main methods to analyze the deformation force. Although the principal stress method is not very rigorous, it is relatively simple and intuitive. It can calculate the total pressure and the stress distribution on the contact surface between workpiece and tool. The slip line method is rigorous for plane strain problems and intuitive for solving stress distribution of local deformation of high parts, but its application scope is narrow. The upper bound method can give an overestimated load, and the upper bound element can also predict the shape change of the workpiece when it is deformed. Finite element method can not only give the change of external load and workpiece shape, but also the distribution of internal stress and strain. The disadvantage is that there are more computer time, especially when solving by elastic-plastic finite element method, the computer capacity is larger and the machine time is longer. Recently, there is a tendency to use joint methods to analyze problems, for example. The upper bound method is used for rough calculation and the finite element method is used for fine calculation in key parts.
Reducing friction can not only save energy, but also improve the life of the die. As the deformation is more uniform, it helps to improve the structure and properties of products, and one of the important measures to reduce friction is to use lubrication. Because of the different forging methods and working temperature, the lubricants used are also different. Glass lubricants are mostly used in forging of superalloys and titanium alloys. For hot forging of steel, water-based graphite is a widely used lubricant. For cold forging, because of high pressure, phosphate or oxalate treatment is needed before forging.