Plastic deformation is an important concept in material mechanics, which describes the irreversible deformation of a material that exceeds the elastic limit. For
forgings, plastic deformation is an indispensable part of the forming process, because it directly affects the final shape and performance of the forgings. Metal materials such as steel, aluminum alloy, etc. are widely used in the manufacture of various forgings because of their good plasticity. However, understanding and applying the basic laws of plastic deformation is of vital significance for ensuring the quality of forgings and optimizing the production process. In the forging design, excessive plastic deformation should be avoided to ensure the structural integrity and service life of the
forging.
Plastic deformation is a kind of deformation that cannot be restored by itself. Engineering materials and components will be permanently deformed after the load exceeds the elastic deformation range, that is, after the load is removed, there will be unrecoverable deformation, or residual deformation, which is plastic deformation. Not all engineering materials are capable of plastic deformation. Metals, plastics, etc., have different degrees of plastic deformation ability, so it can be called plastic materials. Brittle materials such as glass, ceramics and graphite have no plastic deformation ability. The design inch of engineering components generally does not allow obvious plastic deformation, otherwise the components will not be able to maintain the original shape or even fracture.
Forging under the action of external force, only when the maximum internal shear stress reaches the critical value, it is possible to produce plastic deformation. The size of the critical shear stress depends on the type of forging (composition, organization) and deformation conditions (deformation temperature, deformation degree, etc.), so the law of shear stress is a very important basic law of plastic deformation. In the forging process, controlling the size of the shear stress is the key to ensure that the forging reaches the ideal shape and performance.
Forgings remain unchanged in volume during plastic deformation. Although in the actual forging production, the porosity and cracks in the blank such as ingot are compacted after forging, the density of the blank increases and the volume decreases slightly. After cold deformation, the forging becomes more loose and the volume increases slightly. But these small changes are negligible. The law of constant volume is one of the important bases for calculating forging blank size, process size and mold design, and is especially important in the forging forming process, because it ensures the uniform distribution of materials and the exact size of the final product.
When the forging produces plastic deformation, each particle inside it always moves in the direction of the least resistance, which is called the law of least resistance. According to the law of minimum resistance, the flow direction of each particle of metal deformation can be determined in many complex cases in forging production, so as to control the flow path of forging blank deformation, so as to facilitate the forging and forming of forging blank, and achieve the purpose of reducing energy consumption and improving productivity. During forging, by following this law, engineers can optimize the deformation path of the forgings, thereby obtaining the ideal structure and performance.
The plastic deformation of metal is accompanied by elastic deformation. Moreover, the plastic deformation of the metal outside the elastic limit still has elastic deformation. In order for plastic deformation to occur, the shear stress must reach a certain value. Because the metal has a polycrystalline structure, a smooth deformation and stress relationship curve is obtained. Under the action of external force, the size of the deformation of the forging is not equal to the size when the external force is cancelled. Therefore, the size of the forging and the size of the die is not completely consistent. However, due to good plasticity and small elastic deformation, the springback phenomenon of metal in hot deformation is negligible. This is especially important in the production of forgings, as springback can affect the dimensional accuracy of the final product.
To sum up, plastic deformation plays an important role in the manufacturing and forming of forgings. Understanding the law of shear stress, the law of constant volume, the law of minimum resistance and the law of elastic deformation can not only help to optimize the forming process of forging, but also effectively control the energy consumption in the production process and improve production efficiency. By applying these basic laws properly, engineers can ensure that forgings meet their expectations in terms of load bearing capacity and service life, thereby laying a solid foundation for sustainable industrial production.
