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Process for forging forgings

Jan 24, 2019

Forgings are indispensable in every production field. Large parts such as airplanes, automobiles, ships, power generation equipment, petrochemical equipment, and small components such as watches and clocks are manufactured by forging. It covers a wide range.

       Preparation before forging includes raw material selection, material calculation, blanking, heating, calculation of deformation force, selection of equipment, design of molds.

       Lubrication methods and lubricants must be selected before forging. Forging materials cover a wide range of surfaces, including steels and high-temperature alloys of various grades, as well as non-ferrous metals such as aluminum, magnesium, titanium, and copper; both have been processed into rods and profiles of different sizes, and various types. Specifications of ingots; in addition to a large number of domestic materials suitable for China's resources, there are materials from abroad. Most of the forged materials have been included in national standards, and many are new materials developed, tested and promoted. As we all know, the quality of products is often closely related to the quality of raw materials. Therefore, for forging workers, it is necessary to have the necessary material knowledge, and be good at selecting the most suitable materials according to the process requirements.

       Calculating and unloading is one of the important links to improve material utilization and achieve blank refinement. Excessive materials not only cause waste, but also exacerbate mold wear and energy consumption. If the blank is not left blank, it will increase the difficulty of process adjustment and increase the scrap rate. In addition, the quality of the blanking end face also has an impact on the quality of the process and forgings.

       The purpose of heating is to reduce the forging deformation force and to improve the metal plasticity. But heating also brings a series of problems, such as oxidation, decarburization, overheating and overburning. Accurate control of the initial forging and final forging temperatures has a major impact on product organization and performance.

       The furnace heating has the advantages of low cost and strong applicability, but the heating time is long, the oxidation and decarburization are easy to occur, and the working conditions also need to be continuously improved. Electric induction heating has the advantages of rapid heating and less oxidation, but has poor adaptability to changes in product shape and material.

       Forging shape is generated under the action of external force. Therefore, correct calculation of deformation force is the basis for selecting equipment and performing mold calibration. Stress and strain analysis inside the deformed body is also indispensable for optimizing the process and controlling the microstructure of the forging.

       There are four main methods for analyzing the deformation force. Although the principal stress method is not very strict, it is relatively simple and intuitive, and the total pressure and the stress distribution on the contact surface between the workpiece and the tool can be calculated. The slip line method is strict for the plane strain problem, and the stress distribution for the high part local deformation is relatively straightforward, but the scope of application is narrow. The upper limit method can give an overestimated load, and the upper limit element can also predict the shape change of the workpiece during deformation. The finite element method can not only give the external load and the shape change of the workpiece, but also give the internal stress and strain distribution. The disadvantage is that the computer has more machine time, especially when it is solved by elastoplastic finite element, it needs a large computer capacity. The machine is longer. There has been a recent trend to analyze problems using a joint approach, for example. The upper limit method is used for rough calculation, and the key parts are calculated by finite element.

       Reducing friction not only saves energy but also increases mold life. One of the important measures to reduce the friction of the product due to the uniform deformation is to use lubrication. Due to the different ways of forging forgings and the difference in operating temperature, the lubricant used is also different. Glass lubricants are mostly used in high temperature alloys and titanium alloy forging. For hot forging of steel, water-based graphite is a widely used lubricant. For cold forging, due to the high pressure, it is often necessary to carry out phosphate or oxalate treatment before forging.