Preparations before forging include selection of raw materials, calculation of materials, blanking, heating, calculation of deformation force, selection of equipment and design of die. Before forging, good lubrication method and lubricant shall be selected. Forging materials cover a wide range of surfaces, including various brands of steel and superalloys, and aluminum, magnesium, titanium, copper and other non-ferrous metals into bars and profiles of different sizes, as well as ingots of various specifications; In addition to a large number of materials suitable for domestic resources, there are also foreign materials.
Most forging materials have been included in national standards, and many are new materials developed, tried and promoted. As we all know, product quality is often closely related to the quality of raw materials. Therefore, the forging workers must have the necessary material knowledge and be good at selecting the most appropriate materials according to the process requirements.
Calculating material and blanking is one of the important links to improve material utilization and realize blank refinement. Too much material will not only cause waste, but also aggravate the wear and energy consumption of the mold. If there is no surplus left, it will increase the difficulty of process adjustment and improve the waste rate. In addition, the quality of blanking end face will also affect the process and forging quality.
The purpose of heating is to reduce the forging deformation force and improve the metal plasticity. But heating also brings a series of problems such as oxidation, decarburization, overheating and overheating. Accurate control of initial and final forging temperatures has a great influence on the structure and properties of products. The flame furnace has low heating cost and strong applicability, but the heating time is long, and it is easy to produce oxidation and decarburization. The working conditions need to be constantly improved. Electric induction heating has the advantages of fast 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, correct calculation of deformation force is the basis for selecting equipment and verifying dies. It is also necessary to optimize the technological process and control the microstructure and properties of forgings.
There are four main analysis methods of deformation force. Although the principal stress method is not very strict, it is relatively simple and intuitive, and can calculate the total pressure and stress distribution on the contact surface between the workpiece and the tool. The sliding line method is strict to the plane strain problem, and the stress distribution of local deformation of forgings is relatively intuitive, but its application scope is narrow.
The upper bound method can give overestimated load, and the upper bound element can also predict the change of workpiece shape during deformation. The finite element method can not only give the change of external load and forging shape, but also give the distribution of internal stress and strain. The disadvantage is that the computer takes a lot of time, especially according to the elastic plastic finite element method, the computer capacity is large and the machine time is long. Recently, there has been a trend to use joint methods to analyze problems, such as. The upper bound method is used for rough calculation, and the finite element method is used in key parts.
Reducing friction can not only save energy, but also improve the service life of the die. Lubrication is one of the important measures to reduce friction, because the deformation is relatively uniform, which helps to improve the structure and properties of products. Due to different forging methods and working temperatures, the lubricants used are also different.
Glass lubricant is mainly used for forging of superalloys and titanium alloys. For hot forging of steel, water-based graphite is a widely used lubricant. For cold forging, due to the high pressure, phosphate or oxalate is usually required.